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INS MTOR (1 - 50 of 84)
PMID: 11784721
Insulin regulation of insulin-like growth factor-binding protein-1 gene expression is dependent on the mammalian target of rapamycin, but independent of ribosomal S6 kinase activity.
... the mammalian target of rapamycin (mTOR) and ... subsequent activation of ... by insulin, ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 11784721

Insulin regulation of insulin-like growth factor-binding protein-1 gene expression is dependent on the mammalian target of rapamycin, but independent of ribosomal S6 kinase activity.
Source

The Journal of biological chemistry (3/22/2002)

Abstract

Insulin regulation of insulin-like growth factor-binding protein-1 gene expression is dependent on the mammalian target of rapamycin, but independent of ribosomal S6 kinase activity. Insulin inhibits the expression of the hepatic insulin-like growth factor-binding protein-1 (IGFBP-1) and glucose-6-phosphatase (G6Pase) genes. The signaling pathway that mediates these events requires the activation of phosphatidylinositol 3-kinase, whereas transfection studies have suggested an involvement of Akt (protein kinase B) and FKHR, a transcription factor regulated by Akt. We now demonstrate that insulin repression of endogenous IGFBP-1 gene transcription was blocked by rapamycin or by amino acid starvation. Rapamycin inhibited the mammalian target of rapamycin (mTOR) and the subsequent activation of p70/p85 S6 protein kinase-1 (S6K1) by insulin, whereas amino acid depletion prevented insulin induction of these signaling molecules. Importantly, we demonstrate that insulin regulation of the thymine-rich insulin response element of the IGFBP-1 promoter was also inhibited by rapamycin. However, sustained activation of S6K1 did not repress this promoter. In addition, rapamycin did not affect insulin regulation of G6Pase expression or Akt activation. We propose that these observations indicate that an mTOR-dependent, but S6K-independent mechanism regulates the suppression of IGFBP-1 (but not G6Pase) gene expression by insulin. Therefore, although the insulin-responsive sequence of the G6Pase gene promoter is related to that of the IGFBP-1 promoter, the signaling pathways that mediate suppression of these genes are distinct.

PMID: 12393186
Multiple signalling pathways mediate insulin-stimulated gene expression in 3T3-L1 adipocytes.
... by insulin requires both the FRAP/mTOR and ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 12393186

Multiple signalling pathways mediate insulin-stimulated gene expression in 3T3-L1 adipocytes.
Source

Biochimica et biophysica acta (10/11/2002)

Abstract

Multiple signalling pathways mediate insulin-stimulated gene expression in 3T3-L1 adipocytes. In differentiated 3T3-L1 adipocytes, insulin stimulated the expression of the mRNA for the genes encoding Fra-1 (> 100-fold), which is a component of the AP-1 transcriptional complex, beta-actin (6.0-fold) and hexokinase II (2.4-fold). We have examined the signalling pathways involved in these effects of insulin. Rapamycin, which binds to FRAP/mTOR and completely suppressed the activation of p70S6 kinase by insulin, almost completely blocked the induction of the hexokinase II gene, and caused an approximately 50% inhibition of the induction of the Fra-1 gene. PD98059, which completely blocks MAP kinase activation by insulin, inhibited insulin-induced Fra-1 and beta-actin gene expression by approximately 70% and 40%, respectively. These findings suggest that a FRAP/mTOR-dependent pathway is responsible for the induction of hexokinase II expression, and that MAP kinase is required, at least in part, for the stimulation of beta-actin gene expression. However, the induction of Fra-1 gene expression by insulin requires both the FRAP/mTOR and MAP kinase pathways.

PMID: 14560959
Modulation of the protein kinase activity of mTOR.
... of mTOR, ... is stimulated by insulin in ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 14560959

Modulation of the protein kinase activity of mTOR.
Source

Current topics in microbiology and immunology (2004)

Abstract

Modulation of the protein kinase activity of mTOR. mTOR is a founding member of a family of protein kinases having catalytic domains homologous to those in phosphatidylinositol 3-OH kinase. mTOR participates in the control by insulin of the phosphorylation of lipin, which is required for adipocyte differentiation, and the two translational regulators, p70S6K and PHAS-I. The phosphorylation of mTOR, itself, is stimulated by insulin in Ser2448, a site that is also phosphorylated by protein kinase B (PKB) in vitro and in response to activation of PKB activity in vivo. Ser2448 is located in a short stretch of amino acids not found in the two TOR proteins in yeast. A mutant mTOR lacking this stretch exhibited increased activity, and binding of the antibody, mTAb-1, to this region markedly increased mTOR activity. In contrast, rapamycin-FKBP12 inhibited mTOR activity towards both PHAS-I and p70S6K, although this complex inhibited the phosphorylation of some sites more than that of others. Mutating Ser2035 to Ile in the FKBP12-rapamycin binding domain rendered mTOR resistant to inhibition by rapamycin. Unexpectedly, this mutation markedly decreased the ability of mTOR to phosphorylate certain sites in both PHAS-I and p70S6K. The results support the hypotheses that rapamycin disrupts substrate recognition instead of directly inhibiting phosphotransferase activity and that mTOR activity in cells is controlled by the phosphorylation of an inhibitory regulatory domain containing the mTAb-1 epitope.

PMID: 14660591
Insulin promotes rat retinal neuronal cell survival in a p70S6K-dependent manner.
Insulin treatment induced p70S6K, mTOR, ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 14660591

Insulin promotes rat retinal neuronal cell survival in a p70S6K-dependent manner.
Source

The Journal of biological chemistry (3/5/2004)

Abstract

Insulin promotes rat retinal neuronal cell survival in a p70S6K-dependent manner. The purpose of this study was to examine the role of the ribosomal protein S6 protein kinase (p70S6K), a protein synthesis regulator, in promoting retinal neuronal cell survival. Differentiated R28 rat retinal neuronal cells were used as an experimental model. Cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% newborn calf serum, and during the period of experimentation were exposed either to the absence or presence of 10 nm insulin. Insulin treatment induced p70S6K, mTOR, and Akt phosphorylation, effects that were completely prevented by the PI3K inhibitor, LY294002. Insulin-induced phosphorylation of p70S6K and mTOR was prevented by the mTOR inhibitor, rapamycin. Apoptosis, induced by serum deprivation and evaluated by Hoechst staining, was inhibited by insulin treatment in R28 cells, but not in L6 muscle cells. This effect of insulin was also largely prevented by rapamycin. Inhibition of p70S6K activity by exogenous expression of a dominant negative mutant of p70S6K prevented insulin-induced cell survival, whereas, overexpression of wild type p70S6K or expression of a rapamycin resistant form of the kinase enhanced the effect of insulin on survival. Enhanced cell survival under the latter condition was accompanied by increased p70S6K activity and phosphorylation. Rapamycin did not inhibit insulin induced p70S6K phosphorylation and activity in cells transfected with the rapamycin-resistant mutant. Together, these results suggest that p70S6K plays a key role in insulin stimulated retinal neuronal cell survival.

Insulin-induced phosphorylation ... and mTOR was ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 14660591

Insulin promotes rat retinal neuronal cell survival in a p70S6K-dependent manner.
Source

The Journal of biological chemistry (3/5/2004)

Abstract

Insulin promotes rat retinal neuronal cell survival in a p70S6K-dependent manner. The purpose of this study was to examine the role of the ribosomal protein S6 protein kinase (p70S6K), a protein synthesis regulator, in promoting retinal neuronal cell survival. Differentiated R28 rat retinal neuronal cells were used as an experimental model. Cells were maintained in Dulbecco's modified Eagle's medium supplemented with 10% newborn calf serum, and during the period of experimentation were exposed either to the absence or presence of 10 nm insulin. Insulin treatment induced p70S6K, mTOR, and Akt phosphorylation, effects that were completely prevented by the PI3K inhibitor, LY294002. Insulin-induced phosphorylation of p70S6K and mTOR was prevented by the mTOR inhibitor, rapamycin. Apoptosis, induced by serum deprivation and evaluated by Hoechst staining, was inhibited by insulin treatment in R28 cells, but not in L6 muscle cells. This effect of insulin was also largely prevented by rapamycin. Inhibition of p70S6K activity by exogenous expression of a dominant negative mutant of p70S6K prevented insulin-induced cell survival, whereas, overexpression of wild type p70S6K or expression of a rapamycin resistant form of the kinase enhanced the effect of insulin on survival. Enhanced cell survival under the latter condition was accompanied by increased p70S6K activity and phosphorylation. Rapamycin did not inhibit insulin induced p70S6K phosphorylation and activity in cells transfected with the rapamycin-resistant mutant. Together, these results suggest that p70S6K plays a key role in insulin stimulated retinal neuronal cell survival.

PMID: 14684180
mTOR-mediated regulation of translation factors by amino acids.
Insulin decreases ... effect requires mTOR signalling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 14684180

mTOR-mediated regulation of translation factors by amino acids.
Source

Biochemical and biophysical research communications (1/9/2004)

Abstract

mTOR-mediated regulation of translation factors by amino acids. The mammalian-target-of-rapamycin (mTOR) is a multidomain protein that is important in regulating several components of the translational machinery. mTOR signalling is stimulated by hormones (e.g., insulin) and by amino acids. Our recent data suggest that TOR signalling responds to intracellular amino acids rather than to external amino acid levels. The translational repressor eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) is regulated through mTOR and undergoes phosphorylation at multiple sites, which affects its function. It contains two regulatory motifs: the C-terminal TOS motif interacts with the mTOR-binding partner, raptor, and mediates phosphorylation of specific sites in 4E-BP1. However, the N-terminal RAIP motif affects a larger range of mTOR-regulated sites. Since this motif does not bind raptor, mTOR must signal to 4E-BP1 via additional mechanisms that are independent of raptor. The kinase that phosphorylates and inhibits elongation factor 2 (eEF2 kinase) is inactivated by insulin via mTOR. Insulin decreases the ability of eEF2 kinase to bind calmodulin, its essential activator, and this effect requires mTOR signalling and a novel phosphorylation site in eEF2 kinase, Ser78. Ser78 is not phosphorylated by known components of the mTOR pathway implying the existence of novel mTOR-regulated kinases that control eEF2 kinase.

PMID: 15319361
Impaired anabolic response of muscle protein synthesis is associated with S6K1 dysregulation in elderly humans.
... mTOR, ... similarly increased by insulin and ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 15319361

Impaired anabolic response of muscle protein synthesis is associated with S6K1 dysregulation in elderly humans.
Source

FASEB journal : official publication of the Federation of American Societies for Experimental Biology (October 2004)

Abstract

Impaired anabolic response of muscle protein synthesis is associated with S6K1 dysregulation in elderly humans. Age-related loss of muscle protein may involve a decreased response to anabolic factors of muscle protein synthesis through dysregulation of translation factors. To verify this hypothesis, we simultaneously investigated muscle protein synthesis and expression of some factors implicated in insulin signal transduction during hyperinsulinemia and hyperaminoacidemia in 6 young (25+/-1 year; mean+/-sem) and 8 elderly subjects (72+/-2 year). Incorporation of L- [1-13C] leucine in muscle proteins (fractional synthesis rate, FSR) was measured in vastus lateralis, before and during a euglycemic hyperinsulinemic hyperaminoacidemic clamp, together with Western blot analysis of protein kinase B (PKB), mTOR, 4E-BP1, and S6K1 phosphorylation. In basal state, muscle protein FSR was reduced in elderly in comparison with young subjects (0.061+/-0.004% per hour) vs 0.082+/-0.010% per hour, elderly vs. young, P < 0.05). During clamp, muscle protein FSR was stimulated in young (0.119+/-0.006% per hour; P < 0.05), but this response was significantly lower in elderly subjects (0.084+/-0.005% per hour, P < 0.05 vs young subjects). Phosphorylation of PKB, mTOR, and 4E-BP1 were similarly increased by insulin and amino acid in both groups, except for S6K1 phosphorylation, which was not stimulated in elderly subjects. In conclusion, 1) response of muscle protein synthesis to insulin and amino acid is impaired in elderly humans; 2) a defect in S6K1 pathway activation may be responsible for this alteration. This modification is a mechanistic basis of sarcopenia development during aging.

PMID: 15479767
Amino acids and leucine allow insulin activation of the PKB/mTOR pathway in normal adipocytes treated with wortmannin and in adipocytes from db/db mice.
... mTOR is regulated by insulin via ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 15479767

Amino acids and leucine allow insulin activation of the PKB/mTOR pathway in normal adipocytes treated with wortmannin and in adipocytes from db/db mice.
Source

FASEB journal : official publication of the Federation of American Societies for Experimental Biology (December 2004)

Abstract

Amino acids and leucine allow insulin activation of the PKB/mTOR pathway in normal adipocytes treated with wortmannin and in adipocytes from db/db mice. Amino acids are nutrients responsible for mammalian target of rapamycin (mTOR) regulation in mammalian cells. The mTOR protein is mainly known for its role in regulating cell growth, notably via protein synthesis. In addition to amino acids, mTOR is regulated by insulin via a phosphatidylinositol 3-kinase (PI 3-kinase) -dependent pathway. mTOR mediates crosstalk between amino acids and insulin signaling. We show that in freshly isolated rat adipocytes, insulin stimulates the phosphorylation of mTOR on serine 2448, a protein kinase B (PKB) consensus phosphorylation site. This site is also phosphorylated by amino acids, which in contrast to insulin do not activate PKB. Moreover, insulin and amino acids have an additive effect on mTOR phosphorylation, indicating that they act via two independent pathways. Importantly, amino acids, notably leucine, permit insulin to stimulate PKB when PI 3-kinase is inhibited. They also rescue glucose transport and the mTOR pathway. Further, leucine alone can improve insulin activation of PKB in db/db mice. Our results define the importance of amino acids in insulin signaling and reveal leucine as a key amino acid in disease situations associated with insulin-resistance in adipocytes.

PMID: 15576463
Activation of the mammalian target of rapamycin pathway acutely inhibits insulin signaling to Akt and glucose transport in 3T3-L1 and human adipocytes.
Activation of mTOR/S6K1 by insulin was ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 15576463

Activation of the mammalian target of rapamycin pathway acutely inhibits insulin signaling to Akt and glucose transport in 3T3-L1 and human adipocytes.
Source

Endocrinology (March 2005)

Abstract

Activation of the mammalian target of rapamycin pathway acutely inhibits insulin signaling to Akt and glucose transport in 3T3-L1 and human adipocytes. The mammalian target of rapamycin (mTOR) pathway has recently emerged as a chronic modulator of insulin-mediated glucose metabolism. In this study, we evaluated the involvement of this pathway in the acute regulation of insulin action in both 3T3-L1 and human adipocytes. Insulin rapidly (t (1/2) = 5 min) stimulated the mTOR pathway, as reflected by a 10-fold stimulation of 70-kDa ribosomal S6 kinase 1 (S6K1) activity in 3T3-L1 adipocytes. Inhibition of mTOR/S6K1 by rapamycin increased insulin-stimulated glucose transport by as much as 45% in 3T3-L1 adipocytes. Activation of mTOR/S6K1 by insulin was associated with a rapamycin-sensitive increase in Ser636/639 phosphorylation of insulin receptor substrate (IRS)-1 but, surprisingly, did not result in impaired IRS-1-associated phosphatidylinositol (PI) 3-kinase activity. However, insulin-induced activation of Akt was increased by rapamycin. Insulin also activated S6K1 and increased phosphorylation of IRS-1 on Ser636/639 in human adipocytes. As in murine cells, rapamycin treatment of human adipocytes inhibited S6K1, blunted Ser636/639 phosphorylation of IRS-1, leading to increased Akt activation and glucose uptake by insulin. Further studies in 3T3-L1 adipocytes revealed that rapamycin prevented the relocalization of IRS-1 from the low-density membranes to the cytosol in response to insulin. Furthermore, inhibition of mTOR markedly potentiated the ability of insulin to increase PI 3,4,5-triphosphate levels concomitantly with an increased phosphorylation of Akt at the plasma membrane, low-density membranes, and cytosol. However, neither GLUT4 nor GLUT1 translocation induced by insulin were increased by rapamycin treatment. Taken together, these results indicate that the mTOR pathway is an important modulator of the signals involved in the acute regulation of insulin-stimulated glucose transport in 3T3-L1 and human adipocytes.

PMID: 15604215
Increased activation of the mammalian target of rapamycin pathway in liver and skeletal muscle of obese rats: possible involvement in obesity-linked insulin resistance.
... that mTOR and S6K1 activation by insulin was ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 15604215

Increased activation of the mammalian target of rapamycin pathway in liver and skeletal muscle of obese rats: possible involvement in obesity-linked insulin resistance.
Source

Endocrinology (March 2005)

Abstract

Increased activation of the mammalian target of rapamycin pathway in liver and skeletal muscle of obese rats: possible involvement in obesity-linked insulin resistance. The mammalian target of rapamycin (mTOR) pathway integrates insulin and nutrient signaling in numerous cell types. Recent studies also suggest that this pathway negatively modulates insulin signaling to phosphatidylinositol 3-kinase/Akt in adipose and muscle cells. However, it is still unclear whether activation of the mTOR pathway is increased in obesity and if it could be involved in the promotion of insulin resistance. In this paper we show that basal (fasting state) activation of mTOR and its downstream target S6K1 is markedly elevated in liver and skeletal muscle of obese rats fed a high fat diet compared with chow-fed, lean controls. Time-course studies also revealed that mTOR and S6K1 activation by insulin was accelerated in tissues of obese rats, in association with increased inhibitory phosphorylation of insulin receptor substrate-1 (IRS-1) on Ser636/Ser639 and impaired Akt activation. The relationship between mTOR/S6K1 overactivation and impaired insulin signaling to Akt was also examined in hepatic cells in vitro. Insulin caused a time-dependent activation of mTOR and S6K1 in HepG2 cells. This was associated with increased IRS-1 phosphorylation on Ser636/Ser639. Inhibition of mTOR/S6K1 by rapamycin blunted insulin-induced Ser636/Ser639 phosphorylation of IRS-1, leading to a rapid (approximately 5 min) and persistent increase in IRS-1-associated phosphatidylinositol 3-kinase activity and Akt phosphorylation. These results show that activation of the mTOR pathway is increased in liver and muscle of high fat-fed obese rats. In vitro studies with rapamycin suggest that mTOR/S6K1 overactivation contributes to elevated serine phosphorylation of IRS-1, leading to impaired insulin signaling to Akt in liver and muscle of this dietary model of obesity.

Insulin caused a ... of mTOR and ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 15604215

Increased activation of the mammalian target of rapamycin pathway in liver and skeletal muscle of obese rats: possible involvement in obesity-linked insulin resistance.
Source

Endocrinology (March 2005)

Abstract

Increased activation of the mammalian target of rapamycin pathway in liver and skeletal muscle of obese rats: possible involvement in obesity-linked insulin resistance. The mammalian target of rapamycin (mTOR) pathway integrates insulin and nutrient signaling in numerous cell types. Recent studies also suggest that this pathway negatively modulates insulin signaling to phosphatidylinositol 3-kinase/Akt in adipose and muscle cells. However, it is still unclear whether activation of the mTOR pathway is increased in obesity and if it could be involved in the promotion of insulin resistance. In this paper we show that basal (fasting state) activation of mTOR and its downstream target S6K1 is markedly elevated in liver and skeletal muscle of obese rats fed a high fat diet compared with chow-fed, lean controls. Time-course studies also revealed that mTOR and S6K1 activation by insulin was accelerated in tissues of obese rats, in association with increased inhibitory phosphorylation of insulin receptor substrate-1 (IRS-1) on Ser636/Ser639 and impaired Akt activation. The relationship between mTOR/S6K1 overactivation and impaired insulin signaling to Akt was also examined in hepatic cells in vitro. Insulin caused a time-dependent activation of mTOR and S6K1 in HepG2 cells. This was associated with increased IRS-1 phosphorylation on Ser636/Ser639. Inhibition of mTOR/S6K1 by rapamycin blunted insulin-induced Ser636/Ser639 phosphorylation of IRS-1, leading to a rapid (approximately 5 min) and persistent increase in IRS-1-associated phosphatidylinositol 3-kinase activity and Akt phosphorylation. These results show that activation of the mTOR pathway is increased in liver and muscle of high fat-fed obese rats. In vitro studies with rapamycin suggest that mTOR/S6K1 overactivation contributes to elevated serine phosphorylation of IRS-1, leading to impaired insulin signaling to Akt in liver and muscle of this dietary model of obesity.

PMID: 15755733
Insulin stimulates postsynaptic density-95 protein translation via the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin signaling pathway.
... insulin rapidly induced the ... and mTOR, ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 15755733

Insulin stimulates postsynaptic density-95 protein translation via the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin signaling pathway.
Source

The Journal of biological chemistry (5/6/2005)

Abstract

Insulin stimulates postsynaptic density-95 protein translation via the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin signaling pathway. Insulin receptors are highly enriched at neuronal synapses, but whose function remains unclear. Here we present evidence that brief incubations of rat hippocampal slices with insulin resulted in an increased protein expression of dendritic scaffolding protein postsynaptic density-95 (PSD-95) in area CA1. This insulin-induced increase in the PSD-95 protein expression was inhibited by the tyrosine kinase inhibitor, AG1024, phosphatidylinositol 3-kinase (PI3K) inhibitors, LY294002 and wortmannin, translational inhibitors, anisomycin and rapamycin, but not by LY303511 (an inactive analogue of LY294002), and transcriptional inhibitor, actinomycin D, suggesting that insulin regulates the translation of PSD-95 by activating the receptor tyrosine kinase-PI3K-mammalian target of rapamycin (mTOR) signaling pathway. A similar insulin-induced increase in the PSD-95 protein expression was detected after stimulation of the synaptic fractions isolated from the hippocampal neurons. Furthermore, insulin treatment did not affect the PSD-95 mRNA levels. In agreement, insulin rapidly induced the phosphorylation of 3-phosphoinositide-dependent protein kinase-1 (PDK1), protein kinase B (Akt), and mTOR, effects that were prevented by the AG1024 and LY294002. We also show that insulin stimulated the phosphorylation of 4E-binding protein 1 (4E-BP1) and p70S6 kinase (p70S6K) in a mTOR-dependent manner. Finally, we demonstrate the constitutive expression of PSD-95 mRNA in the synaptic fractions isolated from hippocampal neurons. Taken together, these findings suggest that activation of the PI3K-Akt-mTOR signaling pathway is essential for the insulin-induced up-regulation of local PSD-95 protein synthesis in neuronal dendrites and indicate a new molecular mechanism that may contribute to the modulation of synaptic function by insulin in hippocampal area CA1.

PMID: 16396989
Differential mitogenic signaling in insulin receptor-deficient fetal pancreatic beta-cells.
... mammalian target of rapamycin (mTOR), ... in response to insulin.   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 16396989

Differential mitogenic signaling in insulin receptor-deficient fetal pancreatic beta-cells.
Source

Endocrinology (April 2006)

Abstract

Differential mitogenic signaling in insulin receptor-deficient fetal pancreatic beta-cells. Insulin receptor (IR) may play an essential role in the development of beta-cell mass in the mouse pancreas. To further define the function of this signaling system in beta-cell development, we generated IR-deficient beta-cell lines. Fetal pancreata were dissected from mice harboring a floxed allele of the insulin receptor (IRLoxP) and used to isolate islets. These islets were infected with a retrovirus to express simian virus 40 large T antigen, a strategy for establishing beta-cell lines (beta-IRLoxP). Subsequently, these cells were infected with adenovirus encoding cre recombinase to delete insulin receptor (beta-IR (-/-)). beta-Cells expressed insulin and Pdx-1 mRNA in response to glucose. In beta-IRLoxP beta-cells, p44/p42 MAPK and phosphatidylinositol 3 kinase pathways, mammalian target of rapamycin (mTOR), and p70S (6) K phosphorylation and beta-cell proliferation were stimulated in response to insulin. Wortmannin or PD98059 had no effect on insulin-mediated mTOR/p70S (6) K signaling and the corresponding mitogenic response. However, the presence of both inhibitors totally impaired these signaling pathways and mitogenesis in response to insulin. Rapamycin completely blocked insulin-activated mTOR/p70S (6) K signaling and mitogenesis. Interestingly, in beta-IR (-/-) beta-cells, glucose failed to stimulate phosphatidylinositol 3 kinase activity but induced p44/p42 MAPKs and mTOR/p70S (6) K phosphorylation and beta-cell mitogenesis. PD98059, but not wortmannin, inhibited glucose-induced mTOR/p70S (6) K signaling and mitogenesis in those cells. Finally, rapamycin blocked glucose-mediated mitogenesis of beta-IR (-/-) cells. In conclusion, independently of glucose, insulin can mediate mitogenesis in fetal pancreatic beta-cell lines. However, in the absence of the insulin receptor, glucose induces beta-cell mitogenesis.

PMID: 16798736
Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1.
Activation of mammalian target of rapamycin (mTOR) by insulin is ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 16798736

Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1.
Source

The Journal of biological chemistry (8/25/2006)

Abstract

Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1. Insulin stimulates protein synthesis by promoting phosphorylation of the eIF4E-binding protein, 4EBP1. This effect is rapamycin-sensitive and mediated by mammalian target of rapamycin (mTOR) complex 1 (mTORC1), a signaling complex containing mTOR, raptor, and mLST8. Here we demonstrate that insulin produces a stable increase in the kinase activity of mTORC1 in 3T3-L1 adipocytes. The response was associated with a marked increase in 4EBP1 binding to raptor in mTORC1, and it was abolished by disrupting the TOR signaling motif in 4EBP1. The stimulatory effects of insulin on both 4EBP1 kinase activity and binding occurred rapidly and at physiological concentrations of insulin, and both effects required an intact mTORC1. Results of experiments involving size exclusion chromatography and coimmunoprecipitation of epitope-tagged subunits provide evidence that the major insulin-responsive form is dimeric mTORC1, a structure containing two heterotrimers of mTOR, raptor, and mLST8.

... that insulin produces ... stable increase in ... of mTORC1 in ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 16798736

Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1.
Source

The Journal of biological chemistry (8/25/2006)

Abstract

Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1. Insulin stimulates protein synthesis by promoting phosphorylation of the eIF4E-binding protein, 4EBP1. This effect is rapamycin-sensitive and mediated by mammalian target of rapamycin (mTOR) complex 1 (mTORC1), a signaling complex containing mTOR, raptor, and mLST8. Here we demonstrate that insulin produces a stable increase in the kinase activity of mTORC1 in 3T3-L1 adipocytes. The response was associated with a marked increase in 4EBP1 binding to raptor in mTORC1, and it was abolished by disrupting the TOR signaling motif in 4EBP1. The stimulatory effects of insulin on both 4EBP1 kinase activity and binding occurred rapidly and at physiological concentrations of insulin, and both effects required an intact mTORC1. Results of experiments involving size exclusion chromatography and coimmunoprecipitation of epitope-tagged subunits provide evidence that the major insulin-responsive form is dimeric mTORC1, a structure containing two heterotrimers of mTOR, raptor, and mLST8.

... of insulin on ... effects required an intact mTORC1.   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 16798736

Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1.
Source

The Journal of biological chemistry (8/25/2006)

Abstract

Activation of mammalian target of rapamycin (mTOR) by insulin is associated with stimulation of 4EBP1 binding to dimeric mTOR complex 1. Insulin stimulates protein synthesis by promoting phosphorylation of the eIF4E-binding protein, 4EBP1. This effect is rapamycin-sensitive and mediated by mammalian target of rapamycin (mTOR) complex 1 (mTORC1), a signaling complex containing mTOR, raptor, and mLST8. Here we demonstrate that insulin produces a stable increase in the kinase activity of mTORC1 in 3T3-L1 adipocytes. The response was associated with a marked increase in 4EBP1 binding to raptor in mTORC1, and it was abolished by disrupting the TOR signaling motif in 4EBP1. The stimulatory effects of insulin on both 4EBP1 kinase activity and binding occurred rapidly and at physiological concentrations of insulin, and both effects required an intact mTORC1. Results of experiments involving size exclusion chromatography and coimmunoprecipitation of epitope-tagged subunits provide evidence that the major insulin-responsive form is dimeric mTORC1, a structure containing two heterotrimers of mTOR, raptor, and mLST8.

PMID: 16887816
Effect of TRB3 on insulin and nutrient-stimulated hepatic p70 S6 kinase activity.
... inhibited insulin-stimulated S6K1 ... by mammalian target of rapamycin, ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 16887816

Effect of TRB3 on insulin and nutrient-stimulated hepatic p70 S6 kinase activity.
Source

The Journal of biological chemistry (10/6/2006)

Abstract

Effect of TRB3 on insulin and nutrient-stimulated hepatic p70 S6 kinase activity. Insulin and nutrients activate hepatic p70 S6 kinase (S6K1) to regulate protein synthesis. Paradoxically, activation of S6K1 also leads to the development of insulin resistance. In this study, we investigated the effect of TRB3, which acts as an endogenous inhibitor of Akt, on S6K1 activity in vitro and in vivo. In cultured cells, overexpression of TRB3 completely inhibited insulin-stimulated S6K1 activation by mammalian target of rapamycin, whereas knockdown of endogenous TRB3 increased both basal and insulin-stimulated activity. In C57BL/6 mice, adenoviral overexpression of TRB3 inhibited insulin-stimulated activation of hepatic S6K1. In contrast, overexpression of TRB3 did not inhibit nutrient-stimulated S6K1 activity. We also investigated the effect of starvation, feeding, or insulin treatment on TRB3 levels and S6K1 activity in the liver of C57BL/6 and db/db mice. Both insulin and feeding activate S6K1 in db/db mice, but only insulin activates in the C57BL/6 strain. TRB3 levels were 3.5-fold higher in db/db mice than C57BL/6 mice and were unresponsive to feeding or insulin, whereas both treatments reduced TRB3 in C57BL/6 mice. Akt was activated by insulin alone in the C57BL/6 strain and but not in db/db mice. Both insulin and feeding activated mammalian target of rapamycin similarly in these mice; however, feeding was unable to activate the downstream target S6K1 in C57BL/6 mice. These results suggest that the nutrient excess in the hyperphagic, hyperinsulinemic db/db mouse primes the hepatocyte to respond to nutrients resulting in elevated S6K1 activity. The combination of elevated TRB3 and constitutive S6K1 activity results in decreased insulin signaling via the IRS-1/phosphatidylinositol 3-kinase/Akt pathway.

Both insulin and feeding activated mammalian target of rapamycin similarly ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 16887816

Effect of TRB3 on insulin and nutrient-stimulated hepatic p70 S6 kinase activity.
Source

The Journal of biological chemistry (10/6/2006)

Abstract

Effect of TRB3 on insulin and nutrient-stimulated hepatic p70 S6 kinase activity. Insulin and nutrients activate hepatic p70 S6 kinase (S6K1) to regulate protein synthesis. Paradoxically, activation of S6K1 also leads to the development of insulin resistance. In this study, we investigated the effect of TRB3, which acts as an endogenous inhibitor of Akt, on S6K1 activity in vitro and in vivo. In cultured cells, overexpression of TRB3 completely inhibited insulin-stimulated S6K1 activation by mammalian target of rapamycin, whereas knockdown of endogenous TRB3 increased both basal and insulin-stimulated activity. In C57BL/6 mice, adenoviral overexpression of TRB3 inhibited insulin-stimulated activation of hepatic S6K1. In contrast, overexpression of TRB3 did not inhibit nutrient-stimulated S6K1 activity. We also investigated the effect of starvation, feeding, or insulin treatment on TRB3 levels and S6K1 activity in the liver of C57BL/6 and db/db mice. Both insulin and feeding activate S6K1 in db/db mice, but only insulin activates in the C57BL/6 strain. TRB3 levels were 3.5-fold higher in db/db mice than C57BL/6 mice and were unresponsive to feeding or insulin, whereas both treatments reduced TRB3 in C57BL/6 mice. Akt was activated by insulin alone in the C57BL/6 strain and but not in db/db mice. Both insulin and feeding activated mammalian target of rapamycin similarly in these mice; however, feeding was unable to activate the downstream target S6K1 in C57BL/6 mice. These results suggest that the nutrient excess in the hyperphagic, hyperinsulinemic db/db mouse primes the hepatocyte to respond to nutrients resulting in elevated S6K1 activity. The combination of elevated TRB3 and constitutive S6K1 activity results in decreased insulin signaling via the IRS-1/phosphatidylinositol 3-kinase/Akt pathway.

PMID: 16952420
Effects of rapamycin on cell proliferation and phosphorylation of mTOR and p70(S6K) in HepG2 and HepG2 cells overexpressing constitutively active Akt/PKB.
Insulin increased the ... phosphorylated mTOR and ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 16952420

Effects of rapamycin on cell proliferation and phosphorylation of mTOR and p70(S6K) in HepG2 and HepG2 cells overexpressing constitutively active Akt/PKB.
Source

Biochimica et biophysica acta (January 2007)

Abstract

Effects of rapamycin on cell proliferation and phosphorylation of mTOR and p70 (S6K) in HepG2 and HepG2 cells overexpressing constitutively active Akt/PKB. Mammalian target of rapamycin (mTOR) is a serine-threonine kinase that plays an important role in the regulation of cell proliferation and protein synthesis through the activation of its downstream target ribosomal p70 S6 kinase (p70 (S6K)). The levels of p-mTOR are regulated by the protein kinase B (Akt/PKB). Therefore, the effects of insulin and rapamycin (an inhibitor of mTOR) on the phosphorylation of mTOR (Ser 2448) and p70 (S6K) (Thr 389) as well as on cell proliferation in parental HepG2 cells and HepG2 cells overexpressing constitutively active Akt/PKB (HepG2-CA-Akt/PKB) were studied. Insulin increased the levels of phosphorylated mTOR and p70 (S6K) in both the cell lines. Rapamycin treatment partially decreased the phosphorylation of mTOR but completely abolished the phosphorylation of p70 (S6K) in the absence as well as presence of insulin in both cell lines. The effect of insulin and rapamycin on the cell proliferation in both cell lines was further studied. In the presence of serum, parental HepG2 cells and HepG2-CA-Akt/PKB showed an increase in cell proliferation until 120 and 168 h respectively. Rapamycin inhibited cell proliferation under all experimental conditions more evident under serum deprived conditions. Parental HepG2 cells showed decline in the cell proliferation after 48 h and the presence of insulin prolonged cell survival until 120 h and this effect were also inhibited by rapamycin under serum deprived conditions. On the contrary, HepG2-CA-Akt/PKB cells continued proliferation until 192 h. The effects of insulin on cell proliferation were more pronounced in parental HepG2 cells as compared to HepG2-CA-Akt/PKB cells. Long term effects of rapamcyin significantly decreased the levels of p-mTOR (Ser 2448) both in the presence and absence of insulin in these cells. A positive correlation between the levels of p-mTOR (Ser2448) and cell proliferation was observed (99% confidence interval, r (2) =0.525, p < 0.0001). These results suggest that rapamycin causes a decline in the cell growth through the inhibition of mTOR.

PMID: 17351147
Aerobic exercise overcomes the age-related insulin resistance of muscle protein metabolism by improving endothelial function and Akt/mammalian target of rapamycin signaling.
Insulin improved ... and increased mTOR/S6 kinase ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17351147

Aerobic exercise overcomes the age-related insulin resistance of muscle protein metabolism by improving endothelial function and Akt/mammalian target of rapamycin signaling.
Source

Diabetes (June 2007)

Abstract

Aerobic exercise overcomes the age-related insulin resistance of muscle protein metabolism by improving endothelial function and Akt/mammalian target of rapamycin signaling. Muscle protein metabolism is resistant to insulin's anabolic effect in healthy older subjects. This is associated with reduced insulin vasodilation. We hypothesized that aerobic exercise restores muscle protein anabolism in response to insulin by improving vasodilation in older subjects. We measured blood flow, endothelin-1, Akt/mammalian target of rapamycin (mTOR) signaling, and muscle protein kinetics in response to physiological local hyperinsulinemia in two groups of older subjects following a bout of aerobic exercise (EX group: aged 70 +/- 2 years; 45-min treadmill walk, 70% heart rate max) or rest (CTRL group: aged 68 +/- 1 years). Baseline endothelin-1 was lower and blood flow tended to be higher in the EX group, but protein kinetics was not different between groups. Insulin decreased endothelin-1 (P < 0.05) in both groups, but endothelin-1 remained higher in the CTRL group (P < 0.05) and blood flow increased only in the EX group (EX group: 3.8 +/- 0.7 to 5.3 +/- 0.8; CTRL group: 2.5 +/- 0.2 to 2.6 +/- 0.2 ml x min (-1) x 100 ml leg (-1)). Insulin improved Akt phosphorylation in the EX group and increased mTOR/S6 kinase 1 phosphorylation and muscle protein synthesis (EX group: 49 +/- 11 to 89 +/- 23; CTRL group: 58 +/- 8 to 57 +/- 12 nmol x min (-1) x 100 ml leg (-1)) in the EX group only (P < 0.05). Because breakdown did not change, net muscle protein balance became positive only in the EX group (P < 0.05). In conclusion, a bout of aerobic exercise restores the anabolic response of muscle proteins to insulin by improving endothelial function and Akt/mTOR signaling in older subjects.

PMID: 17386266
PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase.
Insulin stimulates ... which prevents its ... of mTORC1 in ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 17386266

PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase.
Source

Molecular cell (3/23/2007)

Abstract

PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase. The heterotrimeric mTORC1 protein kinase nucleates a signaling network that promotes cell growth in response to insulin and becomes constitutively active in cells missing the TSC1 or TSC2 tumor suppressors. Insulin stimulates the phosphorylation of S6K1, an mTORC1 substrate, but it is not known how mTORC1 kinase activity is regulated. We identify PRAS40 as a raptor-interacting protein that binds to mTORC1 in insulin-deprived cells and whose in vitro interaction with mTORC1 is disrupted by high salt concentrations. PRAS40 inhibits cell growth, S6K1 phosphorylation, and rheb-induced activation of the mTORC1 pathway, and in vitro it prevents the great increase in mTORC1 kinase activity induced by rheb1-GTP. Insulin stimulates Akt/PKB-mediated phosphorylation of PRAS40, which prevents its inhibition of mTORC1 in cells and in vitro. We propose that the relative strengths of the rheb- and PRAS40-mediated inputs to mTORC1 set overall pathway activity and that insulin activates mTORC1 through the coordinated regulation of both.

PMID: 17430894
Role of the transcription factor ATF4 in the anabolic actions of insulin and the anti-anabolic actions of glucocorticoids.
Insulin-mediated ... ATF4 required the mammalian target of rapamycin complex ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17430894

Role of the transcription factor ATF4 in the anabolic actions of insulin and the anti-anabolic actions of glucocorticoids.
Source

The Journal of biological chemistry (6/8/2007)

Abstract

Role of the transcription factor ATF4 in the anabolic actions of insulin and the anti-anabolic actions of glucocorticoids. In most mammalian cells, insulin and glucocorticoids promote anabolism and catabolism, respectively. Whereas the opposing effects of insulin and glucocorticoids on catabolic gene expression have been explained at the molecular level, comparatively little is known about how these hormones alter anabolic gene expression. These studies identify ATF4 as an anabolic transcription factor that is repressed by glucocorticoids and induced by insulin. Insulin-mediated induction of ATF4 required the mammalian target of rapamycin complex 1, was required for the activation of a genetic program for the cellular uptake of essential amino acids and the synthesis of nonessential amino acids and aminoacyl-tRNAs, and was coupled to the repression of Foxo-dependent genes needed for protein and lipid catabolism. These results suggest that ATF4 plays a central role in hormonal regulation of amino acid and protein anabolism by coupling amino acid uptake and synthesis, as well as the generation of charged tRNAs, to mammalian target of rapamycin complex 1-mediated mRNA translation.

PMID: 17478528
Nutrient signalling in the regulation of human muscle protein synthesis.
... and insulin stimulate mTOR signalling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17478528

Nutrient signalling in the regulation of human muscle protein synthesis.
Source

The Journal of physiology (7/15/2007)

Abstract

Nutrient signalling in the regulation of human muscle protein synthesis. The mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) are important nutrient- and energy-sensing and signalling proteins in skeletal muscle. AMPK activation decreases muscle protein synthesis by inhibiting mTOR signalling to regulatory proteins associated with translation initiation and elongation. On the other hand, essential amino acids (leucine in particular) and insulin stimulate mTOR signalling and protein synthesis. We hypothesized that anabolic nutrients would be sensed by both AMPK and mTOR, resulting in an acute and potent stimulation of human skeletal muscle protein synthesis via enhanced translation initiation and elongation. We measured muscle protein synthesis and mTOR-associated upstream and downstream signalling proteins in young male subjects (n=14) using stable isotopic and immunoblotting techniques. Following a first muscle biopsy, subjects in the ` Nutrition' group ingested a leucine-enriched essential amino acid-carbohydrate mixture (EAC). Subjects in the Control group did not consume nutrients. A second biopsy was obtained 1 h later. Ingestion of EAC significantly increased muscle protein synthesis, modestly reduced AMPK phosphorylation, and increased Akt/PKB (protein kinase B) and mTOR phosphorylation (P < 0.05). mTOR signalling to its downstream effectors (S6 kinase 1 (S6K1) and 4E-binding protein 1 (4E-BP1) phosphorylation status) was also increased (P < 0.05). In addition, eukaryotic elongation factor 2 (eEF2) phosphorylation was significantly reduced (P < 0.05). Protein synthesis and cell signalling (phosphorylation status) was unchanged in the control group (P > 0.05). We conclude that anabolic nutrients alter the phosphorylation status of both AMPK- and mTOR-associated signalling proteins in human muscle, in association with an increase in protein synthesis not only via enhanced translation initiation but also through signalling promoting translation elongation.

PMID: 17510057
PRAS40 regulates mTORC1 kinase activity by functioning as a direct inhibitor of substrate binding.
In response to insulin and... mTORC1, ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 17510057

PRAS40 regulates mTORC1 kinase activity by functioning as a direct inhibitor of substrate binding.
Source

The Journal of biological chemistry (7/6/2007)

Abstract

PRAS40 regulates mTORC1 kinase activity by functioning as a direct inhibitor of substrate binding. Mammalian target of rapamycin (mTOR) functions in two distinct signaling complexes, mTORC1 and mTORC2. In response to insulin and nutrients, mTORC1, consisting of mTOR, raptor (regulatory-associated protein of mTOR), and mLST8, is activated and phosphorylates eukaryotic initiation factor 4E-binding protein (4EBP) and p70 S6 kinase to promote protein synthesis and cell size. Previously we found that activation of mTOR kinase in response to insulin was associated with increased 4EBP1 binding to raptor. Here we identify prolinerich Akt substrate 40 (PRAS40) as a binding partner for mTORC1. A putative TOR signaling motif, FVMDE, is identified in PRAS40 and shown to be required for interaction with raptor. Insulin stimulation markedly decreases the level of PRAS40 bound by mTORC1. Recombinant PRAS40 inhibits mTORC1 kinase activity in vivo and in vitro, and this inhibition depends on PRAS40 association with raptor. Furthermore, decreasing PRAS40 expression by short hairpin RNA enhances 4E-BP1 binding to raptor, and recombinant PRAS40 competes with 4E-BP1 binding to raptor. We, therefore, propose that PRAS40 regulates mTORC1 kinase activity by functioning as a direct inhibitor of substrate binding.

PMID: 17553476
Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart.
... for insulin-dependent mTOR signalling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17553476

Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart.
Source

Cardiovascular research (10/1/2007)

Abstract

Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart. [OBJECTIVE] Insulin regulates both glucose uptake and postnatal cardiac growth. The anabolic effects of insulin are mediated by the mammalian target of rapamycin (mTOR), an evolutionarily conserved kinase which is also a convergence point between nutrient sensing and cell growth. We postulated that mTOR signalling in the heart requires the metabolism of glucose. [METHODS] We interrogated the insulin-mediated mTOR signalling pathway in response to different metabolic interventions regulating substrate metabolism in the isolated working rat heart and in isolated cardiomyocytes. [RESULTS] Although insulin enhanced Akt activity, phosphorylation of mTOR and its downstream targets (p70S6K and 4EBP1) required the addition of glucose. Glucose-dependent p70S6K phosphorylation was independent of the hexosamine biosynthetic pathway, the AMP kinase pathway, and the pentose phosphate pathway. However, inhibition of glycolysis downstream of hexokinase markedly enhanced p70S6K phosphorylation. Furthermore, 2-deoxyglucose activated p70S6K suggesting that phosphorylation of glucose is required for carbohydrate-mediated mTOR signalling in the heart. Lastly, we also found enhanced p70S6K phosphorylation in the hearts of diabetic rats. [CONCLUSION] Phosphorylation of glucose is necessary for insulin-dependent mTOR activity in the heart, suggesting a link between intermediary metabolism and cardiac growth.

... of insulin are mediated by the mammalian target of rapamycin (mTOR), ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17553476

Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart.
Source

Cardiovascular research (10/1/2007)

Abstract

Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart. [OBJECTIVE] Insulin regulates both glucose uptake and postnatal cardiac growth. The anabolic effects of insulin are mediated by the mammalian target of rapamycin (mTOR), an evolutionarily conserved kinase which is also a convergence point between nutrient sensing and cell growth. We postulated that mTOR signalling in the heart requires the metabolism of glucose. [METHODS] We interrogated the insulin-mediated mTOR signalling pathway in response to different metabolic interventions regulating substrate metabolism in the isolated working rat heart and in isolated cardiomyocytes. [RESULTS] Although insulin enhanced Akt activity, phosphorylation of mTOR and its downstream targets (p70S6K and 4EBP1) required the addition of glucose. Glucose-dependent p70S6K phosphorylation was independent of the hexosamine biosynthetic pathway, the AMP kinase pathway, and the pentose phosphate pathway. However, inhibition of glycolysis downstream of hexokinase markedly enhanced p70S6K phosphorylation. Furthermore, 2-deoxyglucose activated p70S6K suggesting that phosphorylation of glucose is required for carbohydrate-mediated mTOR signalling in the heart. Lastly, we also found enhanced p70S6K phosphorylation in the hearts of diabetic rats. [CONCLUSION] Phosphorylation of glucose is necessary for insulin-dependent mTOR activity in the heart, suggesting a link between intermediary metabolism and cardiac growth.

... for insulin-dependent mTOR activity ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17553476

Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart.
Source

Cardiovascular research (10/1/2007)

Abstract

Glucose phosphorylation is required for insulin-dependent mTOR signalling in the heart. [OBJECTIVE] Insulin regulates both glucose uptake and postnatal cardiac growth. The anabolic effects of insulin are mediated by the mammalian target of rapamycin (mTOR), an evolutionarily conserved kinase which is also a convergence point between nutrient sensing and cell growth. We postulated that mTOR signalling in the heart requires the metabolism of glucose. [METHODS] We interrogated the insulin-mediated mTOR signalling pathway in response to different metabolic interventions regulating substrate metabolism in the isolated working rat heart and in isolated cardiomyocytes. [RESULTS] Although insulin enhanced Akt activity, phosphorylation of mTOR and its downstream targets (p70S6K and 4EBP1) required the addition of glucose. Glucose-dependent p70S6K phosphorylation was independent of the hexosamine biosynthetic pathway, the AMP kinase pathway, and the pentose phosphate pathway. However, inhibition of glycolysis downstream of hexokinase markedly enhanced p70S6K phosphorylation. Furthermore, 2-deoxyglucose activated p70S6K suggesting that phosphorylation of glucose is required for carbohydrate-mediated mTOR signalling in the heart. Lastly, we also found enhanced p70S6K phosphorylation in the hearts of diabetic rats. [CONCLUSION] Phosphorylation of glucose is necessary for insulin-dependent mTOR activity in the heart, suggesting a link between intermediary metabolism and cardiac growth.

PMID: 17804721
Activation of insulin-like growth factor signaling induces apoptotic cell death under prolonged hypoxia by enhancing endoplasmic reticulum stress response.
... and insulin enhanced ... was suppressed by ... and mTOR activity ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17804721

Activation of insulin-like growth factor signaling induces apoptotic cell death under prolonged hypoxia by enhancing endoplasmic reticulum stress response.
Source

Cancer research (9/1/2007)

Abstract

Activation of insulin-like growth factor signaling induces apoptotic cell death under prolonged hypoxia by enhancing endoplasmic reticulum stress response. Malignant cells in solid tumors survive under prolonged hypoxia and can be a source of resistance to current cancer therapies. Mammalian target of rapamycin (mTOR), one of the downstream molecules of the insulin-like growth factor (IGF) pathway, is a key regulator of translation, integrating multiple environmental and nutritional cues. The activity of mTOR is known to be suppressed under hypoxic conditions in cancer cells, whereas the contribution of this suppression to cell survival has not yet been clarified. We show that stimulating IGF signaling provoked caspase-dependent apoptosis under low oxygen tension in two cancer cell lines, COLO 320 and AsPC-1. In concurrence with increased levels of BAD phosphorylation, cell death was not accompanied by cytochrome c release from mitochondria. The cells were rescued from apoptosis when phosphatidylinositol 3-kinase (PI3K) or mTOR activity was inhibited, suggesting that these signals are critical in the observed cell death. IGFs and insulin enhanced the endoplasmic reticulum (ER) stress response as monitored by induction of the CCAAT/enhancer binding protein homologous protein (CHOP) proteins and the X box protein-1 splicing under hypoxic conditions, and this response was suppressed by inhibiting PI3K and mTOR activity. IGF-induced cell death under hypoxic conditions was prevented by treatment with cycloheximide, suggesting that de novo protein synthesis is required. Indeed, suppression of CHOP protein levels with small hairpin RNA reduced cell death. Taken together, the data suggest that stimulating IGF signaling under hypoxic conditions provokes apoptosis by enhancing the ER stress response.

PMID: 17878222
Activation by insulin and amino acids of signaling components leading to translation initiation in skeletal muscle of neonatal pigs is developmentally regulated.
   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 17878222

Activation by insulin and amino acids of signaling components leading to translation initiation in skeletal muscle of neonatal pigs is developmentally regulated.
Source

American journal of physiology. Endocrinology and metabolism (December 2007)

Abstract

Activation by insulin and amino acids of signaling components leading to translation initiation in skeletal muscle of neonatal pigs is developmentally regulated. Insulin and amino acids act independently to stimulate protein synthesis in skeletal muscle of neonatal pigs, and the responses decrease with development. The purpose of this study was to compare the separate effects of fed levels of INS and AA on the activation of signaling components leading to translation initiation and how these responses change with development. Overnight-fasted 6- (n = 4/group) and 26-day-old (n = 6/ group) pigs were studied during 1) euinsulinemic-euglycemiceuaminoacidemic conditions (controls), 2) euinsulinemic-euglycemichyperaminoacidemic clamps (AA), and 3) hyperinsulinemic-euglycemic-euaminoacidemic clamps (INS). INS, but not AA, increased the phosphorylation of protein kinase B (PKB) and tuberous sclerosis 2 (TSC2). Both INS and AA increased protein synthesis and the phosphorylation of mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase-1, and eukaryotic initiation factor protein 1 (4E-BP1), and these responses were higher in 6-day-old compared with 26-day-old pigs. Both INS and AA decreased the binding of 4E-BP1 to eIF4E and increased eIF4E binding to eIF4G; these effects were greater in 6-day-old than in 26-day-old pigs. Neither INS nor AA altered the composition of mTORC1 (raptor, mTOR, and GbetaL) or mTORC2 (rictor, mTOR, and GbetaL) complexes. Furthermore, neither INS, AA, nor age had any effect on the abundance of Rheb and the phosphorylation of AMP-activated protein kinase and eukaryotic elongation factor 2. Our results suggest that the activation by insulin and amino acids of signaling components leading to translation initiation is developmentally regulated and parallels the developmental decline in protein synthesis in skeletal muscle of neonatal pigs.

PMID: 18093179
Insulin and IGF-1 enhance the expression of the neuronal monocarboxylate transporter MCT2 by translational activation via stimulation of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin pathway.
... that insulin and IGF-1 induced p44- ... and mTOR phosphorylation ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 18093179

Insulin and IGF-1 enhance the expression of the neuronal monocarboxylate transporter MCT2 by translational activation via stimulation of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin pathway.
Source

The European journal of neuroscience (January 2008)

Abstract

Insulin and IGF-1 enhance the expression of the neuronal monocarboxylate transporter MCT2 by translational activation via stimulation of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin pathway. MCT2 is the main neuronal monocarboxylate transporter essential for facilitating lactate and ketone body utilization as energy substrates. Our study reveals that treatment of cultured cortical neurons with insulin and IGF-1 led to a striking enhancement of MCT2 immunoreactivity in a time- and concentration-dependent manner. Surprisingly, neither insulin nor IGF-1 affected MCT2 mRNA expression, suggesting that regulation of MCT2 protein expression occurs at the translational rather than the transcriptional level. Investigation of the putative signalling pathways leading to translation activation revealed that insulin and IGF-1 induced p44- and p42 MAPK, Akt and mTOR phosphorylation. S6 ribosomal protein, a component of the translational machinery, was also strongly activated by insulin and IGF-1. Phosphorylation of p44- and p42 MAPK was blocked by the MEK inhibitor PD98058, while Akt phosphorylation was abolished by the PI3K inhibitor LY294002. Phosphorylation of mTOR and S6 was blocked by the mTOR inhibitor rapamycin. In parallel, it was observed that LY294002 and rapamycin almost completely blocked the effects of insulin and IGF-1 on MCT2 protein expression, whereas PD98059 and SB202190 (a p38K inhibitor) had no effect on insulin-induced MCT2 expression and only a slight effect on IGF-1-induced MCT2 expression. At the subcellular level, a significant increase in MCT2 protein expression within an intracellular pool was observed while no change at the cell surface was apparent. As insulin and IGF-1 are involved in synaptic plasticity, their effect on MCT2 protein expression via an activation of the PI3K-Akt-mTOR-S6K pathway might contribute to the preparation of neurons for enhanced use of nonglucose energy substrates following altered synaptic efficacy.

PMID: 18490760
Differential involvement of IkappaB kinases alpha and beta in cytokine- and insulin-induced mammalian target of rapamycin activation determined by Akt.
... and insulin-induced mammalian target of rapamycin activation determined ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 18490760

Differential involvement of IkappaB kinases alpha and beta in cytokine- and insulin-induced mammalian target of rapamycin activation determined by Akt.
Source

Journal of immunology (Baltimore, Md. : 1950; 6/1/2008)

Abstract

Differential involvement of IkappaB kinases alpha and beta in cytokine- and insulin-induced mammalian target of rapamycin activation determined by Akt. The mammalian target of rapamycin (mTOR) is a mediator of cell growth, survival, and energy metabolism at least partly through its ability to regulate mRNA translation. mTOR is activated downstream of growth factors such as insulin, cytokines such as TNF, and Akt-dependent signaling associated with oncoprotein expression. mTOR is negatively controlled by the tuberous sclerosis complex 1/2 (TSC1/2), and activation of Akt induces phosphorylation of TSC2, which blocks the repressive TSC1/2 activity. Previously, we showed that activation of mTOR in PTEN-deficient cancer cells involves IkappaB kinase (IKK) alpha, a catalytic subunit of the IKK complex that controls NF-kappaB activation. Recently, a distinct IKK subunit, IKKbeta, was shown to phosphorylate TSC1 to promote mTOR activation in an Akt-independent manner in certain cells stimulated with TNF and in some cancer cells. In this study, we have explored the involvement of both IKKalpha and IKKbeta in insulin- and TNF-induced mTOR activation. Insulin activation of mTOR requires Akt in a manner that involves IKKalpha, preferentially to IKKbeta, and TSC2 phosphorylation. TNF, in most cells examined, activates Akt to use IKKalpha to control mTOR activation. In MCF7 cells, TNF does not activate Akt and requires IKKbeta to activate mTOR. The results show that Akt-dependent signaling, induced by cytokines or insulin, alters the IKK subunit-dependent control of mTOR.

PMID: 18765678
Amino acid regulation of TOR complex 1.
Insulin, ... stressors regulate mTORC1 by ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 18765678

Amino acid regulation of TOR complex 1.
Source

American journal of physiology. Endocrinology and metabolism (April 2009)

Abstract

Amino acid regulation of TOR complex 1. TOR complex 1 (TORC1), an oligomer of the mTOR (mammalian target of rapamycin) protein kinase, its substrate binding subunit raptor, and the polypeptide Lst8/GbetaL, controls cell growth in all eukaryotes in response to nutrient availability and in metazoans to insulin and growth factors, energy status, and stress conditions. This review focuses on the biochemical mechanisms that regulate mTORC1 kinase activity, with special emphasis on mTORC1 regulation by amino acids. The dominant positive regulator of mTORC1 is the GTP-charged form of the ras-like GTPase Rheb. Insulin, growth factors, and a variety of cellular stressors regulate mTORC1 by controlling Rheb GTP charging through modulating the activity of the tuberous sclerosis complex, the Rheb GTPase activating protein. In contrast, amino acids, especially leucine, regulate mTORC1 by controlling the ability of Rheb-GTP to activate mTORC1. Rheb binds directly to mTOR, an interaction that appears to be essential for mTORC1 activation. In addition, Rheb-GTP stimulates phospholipase D1 to generate phosphatidic acid, a positive effector of mTORC1 activation, and binds to the mTOR inhibitor FKBP38, to displace it from mTOR. The contribution of Rheb's regulation of PL-D1 and FKBP38 to mTORC1 activation, relative to Rheb's direct binding to mTOR, remains to be fully defined. The rag GTPases, functioning as obligatory heterodimers, are also required for amino acid regulation of mTORC1. As with amino acid deficiency, however, the inhibitory effect of rag depletion on mTORC1 can be overcome by Rheb overexpression, whereas Rheb depletion obviates rag's ability to activate mTORC1. The rag heterodimer interacts directly with mTORC1 and may direct mTORC1 to the Rheb-containing vesicular compartment in response to amino acid sufficiency, enabling Rheb-GTP activation of mTORC1. The type III phosphatidylinositol kinase also participates in amino acid-dependent mTORC1 activation, although the site of action of its product, 3'OH-phosphatidylinositol, in this process is unclear.

PMID: 19000755
Sphingosine-1-phosphate induced mTOR-activation is mediated by the E3-ubiquitin ligase PAM.
... and insulin-induced mTOR activation ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19000755

Sphingosine-1-phosphate induced mTOR-activation is mediated by the E3-ubiquitin ligase PAM.
Source

Cellular signalling (February 2009)

Abstract

Sphingosine-1-phosphate induced mTOR-activation is mediated by the E3-ubiquitin ligase PAM. The signaling pathways that are regulated by sphingosine-1-phosphate (S1P) and mammalian target of rapamycin (mTOR) modulate cell growth, mitogenesis and apoptosis in various cell types and are of major interest for the development of new cancer therapeutics. Previous reports show that S1P can cross-activate the mTOR pathway although the mechanisms that connect both pathways are still unknown. We found that S1P-treatment activates mTOR in several cancer cell lines and primary cells. The activation was independent of ERK, Akt and PI3-kinase, but instead was mediated by the E3 ubiquitin ligase Protein Associated with Myc (PAM). Increased intracellular PAM concentrations facilitated S1P- and insulin-induced mTOR activation as well as p70S6K and 4EBP1 phosphorylation while genetic deletion of PAM decreased S1P- and insulin-induced mTOR activation. PAM activated by facilitating the GDP/GTP-exchange of Rheb which is an activator of mTOR. In conclusion we show that PAM is a novel regulator of the mTOR pathway and that PAM may directly activate Rheb as a guanosine exchange factor (GEF).

PMID: 19169352
Effect of testosterone on insulin stimulated IRS1 Ser phosphorylation in primary rat myotubes--a potential model for PCOS-related insulin resistance.
... increased insulin-induced mTOR-Ser ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19169352

Effect of testosterone on insulin stimulated IRS1 Ser phosphorylation in primary rat myotubes--a potential model for PCOS-related insulin resistance.
Source

PloS one (2009)

Abstract

Effect of testosterone on insulin stimulated IRS1 Ser phosphorylation in primary rat myotubes -- a potential model for PCOS-related insulin resistance. [BACKGROUND] Polycystic ovary syndrome (PCOS) is characterized by a hyperandrogenic state and frequently develops skeletal muscle insulin resistance. We determined whether testosterone adversely affects insulin action by increasing serine phosphorylation of IRS-1 (636/639) in differentiated rat skeletal muscle myotubes. The phosphorylation of Akt, mTOR, and S6K, downstream targets of the PI3-kinase-IRS-1 complex were also studied. [METHODS] Primary differentiated rat skeletal muscle myotubes were subjected to insulin for 30 min after 16-hour pre-exposure to either low (20 ng/ml) or high (200 ng/ml) doses of testosterone. Protein phosphorylation of IRS-1 Ser (636/639), Akt Ser (473), mTOR-Ser (2448), and S6K-Thr (389) were measured by Western blot with signal intensity measured by immunofluorescence. [RESULTS] Cells exposed to 100 nM of insulin had increased IRS-1 Ser (636/639) and Akt Ser (473) phosphorylation. Cells pre-exposed to low-dose testosterone had significantly increased insulin-induced mTOR-Ser (2448) and S6K-Thr (389) phosphorylation (p < 0.05), and further increased insulin-induced IRS-1 Ser (636/639) phosphorylation (p = 0.042) compared to control cells. High-dose testosterone pre-exposure attenuated the insulin-induced mTOR-Ser (2448) and S6K-Thr (389) phosphorylation. [CONCLUSIONS] The data demonstrated an interaction between testosterone and insulin on phosphorylation of intracellular signaling proteins, and suggests a link between a hyperandrogenic, hyperinsulinemic environment and the development of insulin resistance involving serine phosphorylation of IRS-1 Ser (636/639). These results may guide further investigations of potential mechanisms of PCOS-related insulin resistance.

... the insulin-induced mTOR-Ser ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19169352

Effect of testosterone on insulin stimulated IRS1 Ser phosphorylation in primary rat myotubes--a potential model for PCOS-related insulin resistance.
Source

PloS one (2009)

Abstract

Effect of testosterone on insulin stimulated IRS1 Ser phosphorylation in primary rat myotubes -- a potential model for PCOS-related insulin resistance. [BACKGROUND] Polycystic ovary syndrome (PCOS) is characterized by a hyperandrogenic state and frequently develops skeletal muscle insulin resistance. We determined whether testosterone adversely affects insulin action by increasing serine phosphorylation of IRS-1 (636/639) in differentiated rat skeletal muscle myotubes. The phosphorylation of Akt, mTOR, and S6K, downstream targets of the PI3-kinase-IRS-1 complex were also studied. [METHODS] Primary differentiated rat skeletal muscle myotubes were subjected to insulin for 30 min after 16-hour pre-exposure to either low (20 ng/ml) or high (200 ng/ml) doses of testosterone. Protein phosphorylation of IRS-1 Ser (636/639), Akt Ser (473), mTOR-Ser (2448), and S6K-Thr (389) were measured by Western blot with signal intensity measured by immunofluorescence. [RESULTS] Cells exposed to 100 nM of insulin had increased IRS-1 Ser (636/639) and Akt Ser (473) phosphorylation. Cells pre-exposed to low-dose testosterone had significantly increased insulin-induced mTOR-Ser (2448) and S6K-Thr (389) phosphorylation (p < 0.05), and further increased insulin-induced IRS-1 Ser (636/639) phosphorylation (p = 0.042) compared to control cells. High-dose testosterone pre-exposure attenuated the insulin-induced mTOR-Ser (2448) and S6K-Thr (389) phosphorylation. [CONCLUSIONS] The data demonstrated an interaction between testosterone and insulin on phosphorylation of intracellular signaling proteins, and suggests a link between a hyperandrogenic, hyperinsulinemic environment and the development of insulin resistance involving serine phosphorylation of IRS-1 Ser (636/639). These results may guide further investigations of potential mechanisms of PCOS-related insulin resistance.

PMID: 19281842
Hydrogen peroxide impairs insulin-stimulated assembly of mTORC1.
... on insulin-stimulated mTORC1 activity ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 19281842

Hydrogen peroxide impairs insulin-stimulated assembly of mTORC1.
Source

Free radical biology & medicine (6/1/2009)

Abstract

Hydrogen peroxide impairs insulin-stimulated assembly of mTORC1. Oxidants are well recognized for their capacity to reduce the phosphorylation of the mammalian target of rapamycin (mTOR) substrates, eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and p70 S6 kinase 1 (S6K1), thereby hindering mRNA translation at the level of initiation. mTOR functions to regulate mRNA translation by forming the signaling complex mTORC1 (mTOR, raptor, GbetaL). Insulin signaling to mTORC1 is dependent upon phosphorylation of Akt/PKB and the inhibition of the tuberous sclerosis complex (TSC1/2), thereby enhancing the phosphorylation of 4E-BP1 and S6K1. In this study we report the effect of H (2) O (2) on insulin-stimulated mTORC1 activity and assembly using A549 and bovine aortic smooth muscle cells. We show that insulin stimulated the phosphorylation of TSC2 leading to a reduction in raptor-mTOR binding and in the quantity of proline-rich Akt substrate 40 (PRAS40) precipitating with mTOR. Insulin also increased 4E-BP1 coprecipitating with mTOR and the phosphorylation of the mTORC1 substrates 4E-BP1 and S6K1. H (2) O (2), on the other hand, opposed the effects of insulin by increasing raptor-mTOR binding and the ratio of PRAS40/raptor derived from the mTOR immunoprecipitates in both cell types. These effects occurred in conjunction with a reduction in 4E-BP1 phosphorylation and the 4E-BP1/raptor ratio. siRNA-mediated knockdown of PRAS40 in A549 cells partially reversed the effect of H (2) O (2) on 4E-BP1 phosphorylation but not on S6K1. These findings are consistent with PRAS40 functioning as a negative regulator of insulin-stimulated mTORC1 activity during oxidant stress.

... of insulin-stimulated mTORC1 activity ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 19281842

Hydrogen peroxide impairs insulin-stimulated assembly of mTORC1.
Source

Free radical biology & medicine (6/1/2009)

Abstract

Hydrogen peroxide impairs insulin-stimulated assembly of mTORC1. Oxidants are well recognized for their capacity to reduce the phosphorylation of the mammalian target of rapamycin (mTOR) substrates, eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) and p70 S6 kinase 1 (S6K1), thereby hindering mRNA translation at the level of initiation. mTOR functions to regulate mRNA translation by forming the signaling complex mTORC1 (mTOR, raptor, GbetaL). Insulin signaling to mTORC1 is dependent upon phosphorylation of Akt/PKB and the inhibition of the tuberous sclerosis complex (TSC1/2), thereby enhancing the phosphorylation of 4E-BP1 and S6K1. In this study we report the effect of H (2) O (2) on insulin-stimulated mTORC1 activity and assembly using A549 and bovine aortic smooth muscle cells. We show that insulin stimulated the phosphorylation of TSC2 leading to a reduction in raptor-mTOR binding and in the quantity of proline-rich Akt substrate 40 (PRAS40) precipitating with mTOR. Insulin also increased 4E-BP1 coprecipitating with mTOR and the phosphorylation of the mTORC1 substrates 4E-BP1 and S6K1. H (2) O (2), on the other hand, opposed the effects of insulin by increasing raptor-mTOR binding and the ratio of PRAS40/raptor derived from the mTOR immunoprecipitates in both cell types. These effects occurred in conjunction with a reduction in 4E-BP1 phosphorylation and the 4E-BP1/raptor ratio. siRNA-mediated knockdown of PRAS40 in A549 cells partially reversed the effect of H (2) O (2) on 4E-BP1 phosphorylation but not on S6K1. These findings are consistent with PRAS40 functioning as a negative regulator of insulin-stimulated mTORC1 activity during oxidant stress.

PMID: 19346248
Mammalian target of rapamycin complex 1 (mTORC1) activity is associated with phosphorylation of raptor by mTOR.
... of mTORC1 activity in response to insulin signaling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 19346248

Mammalian target of rapamycin complex 1 (mTORC1) activity is associated with phosphorylation of raptor by mTOR.
Source

The Journal of biological chemistry (5/29/2009)

Abstract

Mammalian target of rapamycin complex 1 (mTORC1) activity is associated with phosphorylation of raptor by mTOR. mTORC1 contains multiple proteins and plays a central role in cell growth and metabolism. Raptor (regulatory-associated protein of mammalian target of rapamycin (mTOR)), a constitutively binding protein of mTORC1, is essential for mTORC1 activity and critical for the regulation of mTORC1 activity in response to insulin signaling and nutrient and energy sufficiency. Herein we demonstrate that mTOR phosphorylates raptor in vitro and in vivo. The phosphorylated residues were identified by using phosphopeptide mapping and mutagenesis. The phosphorylation of raptor is stimulated by insulin and inhibited by rapamycin. Importantly, the site-directed mutation of raptor at one phosphorylation site, Ser (863), reduced mTORC1 activity both in vitro and in vivo. Moreover, the Ser (863) mutant prevented small GTP-binding protein Rheb from enhancing the phosphorylation of S6 kinase (S6K) in cells. Therefore, our findings indicate that mTOR-mediated raptor phosphorylation plays an important role on activation of mTORC1.

PMID: 19487463
Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth.
... that insulin-phosphatidylinositol 3-kinase signaling promotes mTOR S1261 ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19487463

Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth.
Source

Molecular and cellular biology (August 2009)

Abstract

Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth. The mammalian target of rapamycin (mTOR) complex 1 (mTORC1) functions as a rapamycin-sensitive environmental sensor that promotes cellular biosynthetic processes in response to growth factors and nutrients. While diverse physiological stimuli modulate mTORC1 signaling, the direct biochemical mechanisms underlying mTORC1 regulation remain poorly defined. Indeed, while three mTOR phosphorylation sites have been reported, a functional role for site-specific mTOR phosphorylation has not been demonstrated. Here we identify a new site of mTOR phosphorylation (S1261) by tandem mass spectrometry and demonstrate that insulin-phosphatidylinositol 3-kinase signaling promotes mTOR S1261 phosphorylation in both mTORC1 and mTORC2. Here we focus on mTORC1 and show that TSC/Rheb signaling promotes mTOR S1261 phosphorylation in an amino acid-dependent, rapamycin-insensitive, and autophosphorylation-independent manner. Our data reveal a functional role for mTOR S1261 phosphorylation in mTORC1 action, as S1261 phosphorylation promotes mTORC1-mediated substrate phosphorylation (e.g., p70 ribosomal protein S6 kinase 1 [S6K1] and eukaryotic initiation factor 4E binding protein 1) and cell growth to increased cell size. Moreover, Rheb-driven mTOR S2481 autophosphorylation and S6K1 phosphorylation require S1261 phosphorylation. These data provide the first evidence that site-specific mTOR phosphorylation regulates mTORC1 function and suggest a model whereby insulin-stimulated mTOR S1261 phosphorylation promotes mTORC1 autokinase activity, substrate phosphorylation, and cell growth.

... whereby insulin-stimulated mTOR S1261 ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19487463

Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth.
Source

Molecular and cellular biology (August 2009)

Abstract

Site-specific mTOR phosphorylation promotes mTORC1-mediated signaling and cell growth. The mammalian target of rapamycin (mTOR) complex 1 (mTORC1) functions as a rapamycin-sensitive environmental sensor that promotes cellular biosynthetic processes in response to growth factors and nutrients. While diverse physiological stimuli modulate mTORC1 signaling, the direct biochemical mechanisms underlying mTORC1 regulation remain poorly defined. Indeed, while three mTOR phosphorylation sites have been reported, a functional role for site-specific mTOR phosphorylation has not been demonstrated. Here we identify a new site of mTOR phosphorylation (S1261) by tandem mass spectrometry and demonstrate that insulin-phosphatidylinositol 3-kinase signaling promotes mTOR S1261 phosphorylation in both mTORC1 and mTORC2. Here we focus on mTORC1 and show that TSC/Rheb signaling promotes mTOR S1261 phosphorylation in an amino acid-dependent, rapamycin-insensitive, and autophosphorylation-independent manner. Our data reveal a functional role for mTOR S1261 phosphorylation in mTORC1 action, as S1261 phosphorylation promotes mTORC1-mediated substrate phosphorylation (e.g., p70 ribosomal protein S6 kinase 1 [S6K1] and eukaryotic initiation factor 4E binding protein 1) and cell growth to increased cell size. Moreover, Rheb-driven mTOR S2481 autophosphorylation and S6K1 phosphorylation require S1261 phosphorylation. These data provide the first evidence that site-specific mTOR phosphorylation regulates mTORC1 function and suggest a model whereby insulin-stimulated mTOR S1261 phosphorylation promotes mTORC1 autokinase activity, substrate phosphorylation, and cell growth.

PMID: 19497867
mTOR complex 2 in adipose tissue negatively controls whole-body growth.
mTORC2, ... is activated by insulin/IGF1 and ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC2   (MAPKAP1   MLST8   RICTOR   MTOR )

PMID: 19497867

mTOR complex 2 in adipose tissue negatively controls whole-body growth.
Source

Proceedings of the National Academy of Sciences of the United States of America (6/16/2009)

Abstract

mTOR complex 2 in adipose tissue negatively controls whole-body growth. Mammalian target of rapamycin (mTOR), a highly conserved protein kinase that controls cell growth and metabolism in response to nutrients and growth factors, is found in 2 structurally and functionally distinct multiprotein complexes termed mTOR complex 1 (mTORC1) and mTORC2. mTORC2, which consists of rictor, mSIN1, mLST8, and mTOR, is activated by insulin/IGF1 and phosphorylates Ser-473 in the hydrophobic motif of Akt/PKB. Though the role of mTOR in single cells is relatively well characterized, the role of mTOR signaling in specific tissues and how this may contribute to overall body growth is poorly understood. To examine the role of mTORC2 in an individual tissue, we generated adipose-specific rictor knockout mice (rictor (ad-/-)). Rictor (ad-/-) mice are increased in body size due to an increase in size of nonadipose organs, including heart, kidney, spleen, and bone. Furthermore, rictor (ad-/-) mice have a disproportionately enlarged pancreas and are hyperinsulinemic, but glucose tolerant, and display elevated levels of insulin-like growth factor 1 (IGF1) and IGF1 binding protein 3 (IGFBP3). These effects are observed in mice on either a high-fat or a normal diet, but are generally more pronounced in mice on a high-fat diet. Our findings suggest that adipose tissue, in particular mTORC2 in adipose tissue, plays an unexpectedly central role in controlling whole-body growth.

PMID: 19509187
Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver.
... repress insulin-induced mammalian target of rapamycin complex ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19509187

Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver.
Source

American journal of physiology. Endocrinology and metabolism (August 2009)

Abstract

Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver. The opposing actions of insulin and glucagon on hepatic carbohydrate metabolism are well documented. In contrast, relatively little is known about how the two hormones interact to regulate hepatic protein metabolism. Previously, we reported that glucagon in the absence of insulin represses signaling through the mammalian target of rapamycin complex 1 (mTORC1). In the present study, we sought to determine whether or not the action of one hormone would dominate over the other in the regulation of mTORC1 signaling. Livers were perfused in situ with medium containing either no added hormones (control), 10 nM insulin, 100 nM glucagon, or a combination of the hormones. Compared with control livers, insulin stimulated Akt phosphorylation and mTORC1 signaling, as assessed by increased phosphorylation of the mTORC1 targets eIF4E-binding protein (4E-BP) 1 and ribosomal protein S6 kinase (S6K) 1, and promoted assembly of the eIF4G x eIF4E complex. Glucagon alone had no effect on mTORC1 signaling but stimulated the activity of protein kinase A (PKA). In the presence of a combination of insulin and glucagon, Akt and TSC2 phosphorylation and PKA activity were all increased compared with controls. However, mTORC1 signaling was repressed compared with livers perfused with medium containing insulin alone, and this effect was associated with reduced assembly of the mTORC1 x eIF3 complex. Overall, the results suggest that glucagon acts in a dominant manner to repress insulin-induced mTORC1 signaling, which is in contrast to previous studies showing a dominant action of insulin in the control of hepatic gluconeogenesis.

... insulin stimulated Akt ... and mTORC1 signaling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 19509187

Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver.
Source

American journal of physiology. Endocrinology and metabolism (August 2009)

Abstract

Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver. The opposing actions of insulin and glucagon on hepatic carbohydrate metabolism are well documented. In contrast, relatively little is known about how the two hormones interact to regulate hepatic protein metabolism. Previously, we reported that glucagon in the absence of insulin represses signaling through the mammalian target of rapamycin complex 1 (mTORC1). In the present study, we sought to determine whether or not the action of one hormone would dominate over the other in the regulation of mTORC1 signaling. Livers were perfused in situ with medium containing either no added hormones (control), 10 nM insulin, 100 nM glucagon, or a combination of the hormones. Compared with control livers, insulin stimulated Akt phosphorylation and mTORC1 signaling, as assessed by increased phosphorylation of the mTORC1 targets eIF4E-binding protein (4E-BP) 1 and ribosomal protein S6 kinase (S6K)1, and promoted assembly of the eIF4G x eIF4E complex. Glucagon alone had no effect on mTORC1 signaling but stimulated the activity of protein kinase A (PKA). In the presence of a combination of insulin and glucagon, Akt and TSC2 phosphorylation and PKA activity were all increased compared with controls. However, mTORC1 signaling was repressed compared with livers perfused with medium containing insulin alone, and this effect was associated with reduced assembly of the mTORC1 x eIF3 complex. Overall, the results suggest that glucagon acts in a dominant manner to repress insulin-induced mTORC1 signaling, which is in contrast to previous studies showing a dominant action of insulin in the control of hepatic gluconeogenesis.

... repress insulin-induced mTORC1 signaling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 19509187

Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver.
Source

American journal of physiology. Endocrinology and metabolism (August 2009)

Abstract

Glucagon acts in a dominant manner to repress insulin-induced mammalian target of rapamycin complex 1 signaling in perfused rat liver. The opposing actions of insulin and glucagon on hepatic carbohydrate metabolism are well documented. In contrast, relatively little is known about how the two hormones interact to regulate hepatic protein metabolism. Previously, we reported that glucagon in the absence of insulin represses signaling through the mammalian target of rapamycin complex 1 (mTORC1). In the present study, we sought to determine whether or not the action of one hormone would dominate over the other in the regulation of mTORC1 signaling. Livers were perfused in situ with medium containing either no added hormones (control), 10 nM insulin, 100 nM glucagon, or a combination of the hormones. Compared with control livers, insulin stimulated Akt phosphorylation and mTORC1 signaling, as assessed by increased phosphorylation of the mTORC1 targets eIF4E-binding protein (4E-BP) 1 and ribosomal protein S6 kinase (S6K) 1, and promoted assembly of the eIF4G x eIF4E complex. Glucagon alone had no effect on mTORC1 signaling but stimulated the activity of protein kinase A (PKA). In the presence of a combination of insulin and glucagon, Akt and TSC2 phosphorylation and PKA activity were all increased compared with controls. However, mTORC1 signaling was repressed compared with livers perfused with medium containing insulin alone, and this effect was associated with reduced assembly of the mTORC1 x eIF3 complex. Overall, the results suggest that glucagon acts in a dominant manner to repress insulin-induced mTORC1 signaling, which is in contrast to previous studies showing a dominant action of insulin in the control of hepatic gluconeogenesis.

PMID: 19593385
Insulin stimulates adipogenesis through the Akt-TSC2-mTORC1 pathway.
... block insulin-stimulated mTORC1 signaling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 19593385

Insulin stimulates adipogenesis through the Akt-TSC2-mTORC1 pathway.
Source

PloS one (2009)

Abstract

Insulin stimulates adipogenesis through the Akt-TSC2-mTORC1 pathway. [BACKGROUND] The signaling pathways imposing hormonal control over adipocyte differentiation are poorly understood. While insulin and Akt signaling have been found previously to be essential for adipogenesis, the relative importance of their many downstream branches have not been defined. One direct substrate that is inhibited by Akt-mediated phosphorylation is the tuberous sclerosis complex 2 (TSC2) protein, which associates with TSC1 and acts as a critical negative regulator of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1). Loss of function of the TSC1-TSC2 complex results in constitutive mTORC1 signaling and, through mTORC1-dependent feedback mechanisms and loss of mTORC2 activity, leads to a concomitant block of Akt signaling to its other downstream targets. [METHODOLOGY/PRINCIPAL FINDINGS] We find that, despite severe insulin resistance and the absence of Akt signaling, TSC2-deficient mouse embryo fibroblasts and 3T3-L1 pre-adipocytes display enhanced adipocyte differentiation that is dependent on the elevated mTORC1 activity in these cells. Activation of mTORC1 causes a robust increase in the mRNA and protein expression of peroxisome proliferator-activated receptor gamma (PPARgamma), which is the master transcriptional regulator of adipocyte differentiation. In examining the requirements for different Akt-mediated phosphorylation sites on TSC2, we find that only TSC2 mutants lacking all five previously identified Akt sites fully block insulin-stimulated mTORC1 signaling in reconstituted Tsc2 null cells, and this mutant also inhibits adipogenesis. Finally, renal angiomyolipomas from patients with tuberous sclerosis complex contain both adipose and smooth muscle-like components with activated mTORC1 signaling and elevated PPARgamma expression. [CONCLUSIONS/SIGNIFICANCE] This study demonstrates that activation of mTORC1 signaling is a critical step in adipocyte differentiation and identifies TSC2 as a primary target of Akt driving this process. Therefore, the TSC1-TSC2 complex regulates the differentiation of mesenchymal cell lineages, at least in part, through its control of mTORC1 activity and PPARgamma expression.

PMID: 19738034
mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat.
... or insulin can stimulate p-mTOR, ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19738034

mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat.
Source

American journal of physiology. Endocrinology and metabolism (December 2009)

Abstract

mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat. Three transduction pathways are involved in amino acid (AA) sensing in liver: mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), and general control nondepressible kinase 2 (GCN2). However, no study has investigated the involvement of these signaling pathways in hepatic AA sensing. To address the question of liver AA sensing and signaling in response to a high-protein (HP) dietary supply, we investigated the changes in the phosphorylation state of hepatic mTOR (p-mTOR), AMPKalpha (p-AMPKalpha), and GCN2 (p-GCN2) by Western blotting. In rats fed a HP diet for 14 days, the hepatic p-AMPKalpha and p-GCN2 were lower (P < 0.001), and those of both the p-mTOR and eukaryotic initiation factor 4E-binding protein-1 phosphorylation (p-4E-BP1) were higher (P < 0.01) compared with rats receiving a normal protein (NP) diet. In hepatocytes in primary culture, high AA concentration decreased AMPKalpha phosphorylation whether insulin was present or not (P < 0.01). Either AAs or insulin can stimulate p-mTOR, but this is not sufficient for 4E-BP1 phosphorylation that requires both (P < 0.01). As expected, branched-chain AAs (BCAA) or leucine stimulated the phosphorylation of mTOR, but both insulin and BCAA or leucine are required for 4E-BP1 phosphorylation. GCN2 phosphorylation was reduced by both AAs and insulin (P < 0.01), suggesting for the first time that the translation inhibitor GCN2 senses not only the AA deficiency but also the AA increase in the liver. The present findings demonstrate that AAs and insulin exert a coordinated action on translation and involved mTOR, AMPK, and GCN2 transduction pathways.

... of mTOR, ... both insulin and ... are required for ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 19738034

mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat.
Source

American journal of physiology. Endocrinology and metabolism (December 2009)

Abstract

mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat. Three transduction pathways are involved in amino acid (AA) sensing in liver: mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), and general control nondepressible kinase 2 (GCN2). However, no study has investigated the involvement of these signaling pathways in hepatic AA sensing. To address the question of liver AA sensing and signaling in response to a high-protein (HP) dietary supply, we investigated the changes in the phosphorylation state of hepatic mTOR (p-mTOR), AMPKalpha (p-AMPKalpha), and GCN2 (p-GCN2) by Western blotting. In rats fed a HP diet for 14 days, the hepatic p-AMPKalpha and p-GCN2 were lower (P < 0.001), and those of both the p-mTOR and eukaryotic initiation factor 4E-binding protein-1 phosphorylation (p-4E-BP1) were higher (P < 0.01) compared with rats receiving a normal protein (NP) diet. In hepatocytes in primary culture, high AA concentration decreased AMPKalpha phosphorylation whether insulin was present or not (P < 0.01). Either AAs or insulin can stimulate p-mTOR, but this is not sufficient for 4E-BP1 phosphorylation that requires both (P < 0.01). As expected, branched-chain AAs (BCAA) or leucine stimulated the phosphorylation of mTOR, but both insulin and BCAA or leucine are required for 4E-BP1 phosphorylation. GCN2 phosphorylation was reduced by both AAs and insulin (P < 0.01), suggesting for the first time that the translation inhibitor GCN2 senses not only the AA deficiency but also the AA increase in the liver. The present findings demonstrate that AAs and insulin exert a coordinated action on translation and involved mTOR, AMPK, and GCN2 transduction pathways.

PMID: 20051528
Activation of the cardiac mTOR/p70(S6K) pathway by leucine requires PDK1 and correlates with PRAS40 phosphorylation.
... the insulin-induced and ... of mTOR/p70 ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 20051528

Activation of the cardiac mTOR/p70(S6K) pathway by leucine requires PDK1 and correlates with PRAS40 phosphorylation.
Source

American journal of physiology. Endocrinology and metabolism (April 2010)

Abstract

Activation of the cardiac mTOR/p70 (S6K) pathway by leucine requires PDK1 and correlates with PRAS40 phosphorylation. Like insulin, leucine stimulates the mammalian target of rapamycin (mTOR) /p70 ribosomal S6 kinase (p70 (S6K)) axis in various organs. Insulin proceeds via the canonical association of phosphatidylinositol 3-kinase (PI3K), phosphoinositide-dependent protein kinase-1 (PDK1), and protein kinase B (PKB/Akt). The signaling involved in leucine effect, although known to implicate a PI3K mechanism independent of PKB/Akt, is more poorly understood. In this study, we investigated whether PDK1 could also participate in the events leading to mTOR/p70 (S6K) activation in response to leucine in the heart. In wild-type hearts, both leucine and insulin increased p70 (S6K) activity whereas, in contrast to insulin, leucine was unable to activate PKB/Akt. The changes in p70 (S6K) activity induced by insulin and leucine correlated with changes in phosphorylation of Thr (389), the mTOR phosphorylation site on p70 (S6K), and of Ser (2448) on mTOR, both related to mTOR activity. Leucine also triggered phosphorylation of the proline-rich Akt/PKB substrate of 40 kDa (PRAS40), a new pivotal mTOR regulator. In PDK1 knockout hearts, leucine, similarly to insulin, failed to induce the phosphorylation of mTOR and p70 (S6K), leading to the absence of p70 (S6K) activation. The loss of leucine effect in absence of PDK1 correlated with the lack of PRAS40 phosphorylation. Moreover, the introduction in PDK1 of the L155E mutation, which is known to preserve the insulin-induced and PKB/Akt-dependent phosphorylation of mTOR/p70 (S6K), suppressed all leucine effects, including phosphorylation of mTOR, PRAS40, and p70 (S6K). We conclude that the leucine-induced stimulation of the cardiac PRAS40/mTOR/p70 (S6K) pathway requires PDK1 in a way that differs from that of insulin.

PMID: 20053679
The late endosome is essential for mTORC1 signaling.
... and insulin-stimulated mTORC1 signaling ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

Theme:  mTORC1   (MLST8   RPTOR   MTOR )

PMID: 20053679

The late endosome is essential for mTORC1 signaling.
Source

Molecular biology of the cell (3/1/2010)

Abstract

The late endosome is essential for mTORC1 signaling. The multisubunit mTORC1 complex integrates signals from growth factors and nutrients to regulate protein synthesis, cell growth, and autophagy. To examine how endocytic trafficking might be involved in nutrient regulation of mTORC1, we perturbed specific endocytic trafficking pathways and measured mTORC1 activity using S6K1 as a readout. When early/late endosomal conversion was blocked by either overexpression of constitutively active Rab5 (Rab5CA) or knockdown of the Rab7 GEF hVps39, insulin- and amino acid-stimulated mTORC1/S6K1 activation were inhibited, and mTOR localized to hybrid early/late endosomes. Inhibition of other stages of endocytic trafficking had no effect on mTORC1. Overexpression of Rheb, which activates mTOR independently of mTOR localization, rescued mTORC1 signaling in cells expressing Rab5CA, whereas hyperactivation of endogenous Rheb in TSC2-/- MEFs did not. These data suggest that integrity of late endosomes is essential for amino acid- and insulin-stimulated mTORC1 signaling and that blocking the early/late endosomal conversion prevents mTOR from interacting with Rheb in the late endosomal compartment.

PMID: 20167101
AMPK exerts dual regulatory effects on the PI3K pathway.
... whereas insulin-stimulated activation of mTOR was ...   (details)

INS MTOR

Type:  positive regulation
Is this interaction correct?
Yes
No

Comments

PMID: 20167101

AMPK exerts dual regulatory effects on the PI3K pathway.
Source

Journal of molecular signaling (2010)

Abstract

AMPK exerts dual regulatory effects on the PI3K pathway. [BACKGROUND] AMP-activated protein kinase (AMPK) is a fuel-sensing enzyme that is activated when cells experience energy deficiency and conversely suppressed in surfeit of energy supply. AMPK activation improves insulin sensitivity via multiple mechanisms, among which AMPK suppresses mTOR/S6K-mediated negative feedback regulation of insulin signaling. [RESULTS] In the present study we further investigated the mechanism of AMPK-regulated insulin signaling. Our results showed that 5-aminoimidazole-4-carboxamide-1 ribonucleoside (AICAR) greatly enhanced the ability of insulin to stimulate the insulin receptor substrate-1 (IRS1) -associated PI3K activity in differentiated 3T3-F442a adipocytes, leading to increased Akt phosphorylation at S473, whereas insulin-stimulated activation of mTOR was diminished. In 3T3-F442a preadipocytes, these effects were attenuated by expression of a dominant negative mutant of AMPK alpha1 subunit. The enhancing effect of ACIAR on Akt phosphorylation was also observed when the cells were treated with EGF, suggesting that it is regulated at a step beyond IR/IRS1. Indeed, when the cells were chronically treated with AICAR in the absence of insulin, Akt phosphorylation was progressively increased. This event was associated with an increase in levels of phosphatidylinositol -3,4,5-trisphosphate (PIP3) and blocked by Wortmannin. We then expressed the dominant negative mutant of PTEN (C124S) and found that the inhibition of endogenous PTEN per se did not affect phosphorylation of Akt at basal levels or upon treatment with AICAR or insulin. Thus, this result suggests that AMPK activation of Akt is not mediated by regulating phosphatase and tensin homologue (PTEN). [CONCLUSION] Our present study demonstrates that AMPK exerts dual effects on the PI3K pathway, stimulating PI3K/Akt and inhibiting mTOR/S6K.