Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:PRAS40 is an insulin-regulated inhibitor of the mTORC1 protein kinase. 1738 66

FSH-mediated regulation of mammalian target of rapamycin (mTOR) signaling in proliferating granulosa cells and the effect of dihydrotestosterone (DHT) on this pathway were examined. Inhibiting mTOR activation using rapamycin significantly reduced the FSH-mediated increase in cyclin D2 mRNA expression, suggesting that mTOR plays a role in the FSH-mediated increase in granulosa cell proliferation. FSH treatment of granulosa cells showed a 2-fold increase in phosphorylation of p70S6 kinase (p70S6K), the downstream target of mTOR. The increase in p70S6K phosphorylation by FSH treatment was abolished by prior exposure to DHT, suggesting that DHT inhibits FSH-mediated activation of mTOR signaling in cultured granulosa cells. The effect of FSH and DHT treatment on tuberin (TSC2), the upstream regulator of mTOR, was then examined. FSH treatment increased TSC2 phosphorylation, and pretreatment with DHT for 24 h reduced this stimulation. These results indicate that reduced p70S6K phosphorylation observed in DHT-treated cells might be the result of reduced TSC2 phosphorylation. Because Akt is the upstream activator of TSC2 phosphorylation, the effect of Akt inhibition was examined to test whether FSH-mediated TSC2 phosphorylation proceeds through an Akt-dependent pathway. Our results show that inhibiting Akt phosphorylation did not block FSH-stimulated TSC2 phosphorylation, whereas ERK inhibition reduced FSH-mediated stimulation. These results demonstrate the involvement of ERK rather than Akt in FSH-mediated TSC2 phosphorylation in granulosa cells. Based on these observations, we conclude that in granulosa cells, FSH uses a protein kinase A-/ERK-dependent pathway to stimulate TSC2 phosphorylation and mTOR signaling, and DHT treatment significantly reduces this response.
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PMID:Follicle-stimulating hormone increases tuberin phosphorylation and mammalian target of rapamycin signaling through an extracellular signal-regulated kinase-dependent pathway in rat granulosa cells. 1751 Feb 44

TOR (Target of Rapamycin) is a highly conserved protein kinase and a central controller of cell growth. TOR is found in two functionally and structurally distinct multiprotein complexes termed TOR complex 1 (TORC1) and TOR complex 2 (TORC2). In the present study, we developed a two-dimensional liquid chromatography tandem mass spectrometry (2D LC-MS/MS) based proteomic strategy to identify new mammalian TOR (mTOR) binding proteins. We report the identification of Proline-rich Akt substrate (PRAS40) and the hypothetical protein Q6MZQ0/FLJ14213/CAE45978 as new mTOR binding proteins. PRAS40 binds mTORC1 via Raptor, and is an mTOR phosphorylation substrate. PRAS40 inhibits mTORC1 autophosphorylation and mTORC1 kinase activity toward eIF-4E binding protein (4E-BP) and PRAS40 itself. HeLa cells in which PRAS40 was knocked down were protected against induction of apoptosis by TNFalpha and cycloheximide. Rapamycin failed to mimic the pro-apoptotic effect of PRAS40, suggesting that PRAS40 mediates apoptosis independently of its inhibitory effect on mTORC1. Q6MZQ0 is structurally similar to proline rich protein 5 (PRR5) and was therefore named PRR5-Like (PRR5L). PRR5L binds specifically to mTORC2, via Rictor and/or SIN1. Unlike other mTORC2 members, PRR5L is not required for mTORC2 integrity or kinase activity, but dissociates from mTORC2 upon knock down of tuberous sclerosis complex 1 (TSC1) and TSC2. Hyperactivation of mTOR by TSC1/2 knock down enhanced apoptosis whereas PRR5L knock down reduced apoptosis. PRR5L knock down reduced apoptosis also in mTORC2 deficient cells. The above suggests that mTORC2-dissociated PRR5L may promote apoptosis when mTOR is hyperactive. Thus, PRAS40 and PRR5L are novel mTOR-associated proteins that control the balance between cell growth and cell death.
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PMID:PRAS40 and PRR5-like protein are new mTOR interactors that regulate apoptosis. 1803 Mar 48

The activation of the AMP-activated protein kinase (AMPK) and inhibition of the mammalian target of rapamycin complex 1 (mTORC1) is hypothesized to underlie the fact that muscle growth following resistance exercise is decreased by concurrent endurance exercise. To directly test this hypothesis, the capacity for muscle growth was determined in mice lacking the primary upstream kinase for AMPK in skeletal muscle, LKB1. Following either 1 or 4 weeks of overload, there was no difference in muscle growth between the wild type (wt) and LKB1(-/-) mice (1 week: wt, 38.8 +/- 7.75%; LKB1(-/-), 27.8 +/- 12.98%; 4 week: wt, 75.8 +/- 15.2%; LKB1(-/-), 85.0 +/- 22.6%). In spite of the fact that the LKB1 had been knocked out in skeletal muscle, the phosphorylation and activity of the alpha1 isoform of AMPK were markedly increased in both the wt and the LKB1(-/-) mice. To identify the upstream kinase(s) responsible, we studied potential upstream kinases other than LKB1. The activity of both Ca(2+)-calmodulin-dependent protein kinase kinase alpha (CaMKKalpha) (5.05 +/- 0.86-fold) and CaMKKbeta (10.1 +/- 2.59-fold) increased in the overloaded muscles, and this correlated with their increased expression. Phosphorylation of TAK-1 also increased 10-fold following overload in both the wt and LKB1 mice. Even though the alpha1 isoform of AMPK was activated by overload, there were no increases in expression of mitochondrial proteins or GLUT4, indicating that the alpha1 isoform is not involved in these metabolic adaptations. The phosphorylation of TSC2, an upstream regulator of the TORC1 pathway, at the AMPK site (Ser1345) was increased in response to overload, and this was not affected by LKB1 deficiency. Taken together, these data suggest that the alpha1 isoform of AMPK is preferentially activated in skeletal muscle following overload in the absence of metabolic adaptations, suggesting that this isoform might be important in the regulation of growth but not metabolism.
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PMID:Normal hypertrophy accompanied by phosphoryation and activation of AMP-activated protein kinase alpha1 following overload in LKB1 knockout mice. 1820 1

The mammalian target of rapamycin (mTOR) is a protein kinase that forms two functionally distinct complexes important for nutrient and growth factor signaling. Both complexes phosphorylate a hydrophobic motif on downstream protein kinases, which contributes to the activation of these kinases. mTOR complex 1 (mTORC1) phosphorylates S6K1, while mTORC2 phosphorylates Akt. The TSC1-TSC2 complex is a critical negative regulator of mTORC1. However, how mTORC2 is regulated and whether the TSC1-TSC2 complex is involved are unknown. We find that mTORC2 isolated from a variety of cells lacking a functional TSC1-TSC2 complex is impaired in its kinase activity toward Akt. Importantly, the defect in mTORC2 activity in these cells can be separated from effects on mTORC1 signaling and known feedback mechanisms affecting insulin receptor substrate-1 and phosphatidylinositol 3-kinase. Our data also suggest that the TSC1-TSC2 complex positively regulates mTORC2 in a manner independent of its GTPase-activating protein activity toward Rheb. Finally, we find that the TSC1-TSC2 complex can physically associate with mTORC2 but not mTORC1. These data demonstrate that the TSC1-TSC2 complex inhibits mTORC1 and activates mTORC2, which through different mechanisms promotes Akt activation.
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PMID:The TSC1-TSC2 complex is required for proper activation of mTOR complex 2. 1841 1

The bipartite transcription factor beta-catenin/TCF (cat/TCF) has been recognized as the major effector of the Wnt signaling pathway for more than a decade, and its over-activation has been associated with malignancy such as colon and breast cancer. Extensive examination in different cell lineages has shown that the activity of cat/TCF can be stimulated by mechanisms other than via the Wnt glycoproteins, including the stimulation of beta-cat nuclear translocation and enhanced binding of cat/TCF to the Wnt target gene promoters by insulin and insulin-like growth factor-1 (IGF-1). In addition, the heterotrimeric G proteins of the G(12) subfamily can interact with the cytoplasmic domain of cadherins, resulting in the release of the transcriptional activator beta-cat. Furthermore, certain peptide hormones may stimulate cat/TCF-mediated gene transcription via activation of their corresponding G-protein coupled receptors. Recently, the serine/threonine kinase GSK-3 has been recognized to coordinate with AMP activated protein kinase (AMPK) in phosphorylation and activation of TSC2, the major component of the tumor suppressor complex TSC1/2. Thus, Wnt activation can stimulate protein translation via GSK-3 and TSC1/2 inactivation, followed by mTOR activation. Finally, beta-cat also functions as a pivotal molecule in defense against oxidative stress via serving as a partner of forkhead box O (FOXO) transcription factors. Thus, FOXO proteins, which mainly mediate aging and stress signaling, and TCF factors, which mainly mediate developmental and proliferation signaling, compete for a limited pool of free beta-cat. Insulin and growth factors, on the other hand, control the balance between TCF- and FOXO-mediated gene transcription via phosphorylation and nuclear exclusion of FOXO proteins. These observations provide new insight to understand how Wnt, insulin/growth factors, and FOXOs are involved in versatile physiological events and the development and progression of various human diseases.
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PMID:Wnt and beyond Wnt: multiple mechanisms control the transcriptional property of beta-catenin. 1855 64

The signalling components upstream and downstream of the protein kinase mammalian target of rapamycin (mTOR) are frequently altered in a wide variety of human diseases. Upstream of mTOR key signalling molecules are the small GTPase Ras, the lipid kinase PI3K, the Akt kinase, and the GTPase Rheb, which are known to be deregulated in many human cancers. Mutations in the mTOR pathway component genes TSC1, TSC2, LKB1, PTEN, VHL, NF1 and PKD1 trigger the development of the syndromes tuberous sclerosis, Peutz-Jeghers syndrome, Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Lhermitte-Duclos disease, Proteus syndrome, von Hippel-Lindau disease, Neurofibromatosis type 1, and Polycystic kidney disease, respectively. In addition, the tuberous sclerosis proteins have been implicated in the development of several sporadic tumors and in the control of the cyclin-dependent kinase inhibitor p27, known to be of relevance for several cancers. Recently, it has been recognized that mTOR is regulated by TNF-alpha and Wnt, both of which have been shown to play critical roles in the development of many human neoplasias. In addition to all these human diseases, the role of mTOR in Alzheimer's disease, cardiac hypertrophy, obesity and type 2 diabetes is discussed.
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PMID:The mTOR pathway and its role in human genetic diseases. 1859 80

The tumor suppressor p53 is activated upon genotoxic and oxidative stress and in turn inhibits cell proliferation and growth through induction of specific target genes. Cell growth is positively regulated by mTOR, whose activity is inhibited by the TSC1:TSC2 complex. Although genotoxic stress has been suggested to inhibit mTOR via p53-mediated activation of mTOR inhibitors, the precise mechanism of this link was unknown. We now demonstrate that the products of two p53 target genes, Sestrin1 and Sestrin2, activate the AMP-responsive protein kinase (AMPK) and target it to phosphorylate TSC2 and stimulate its GAP activity, thereby inhibiting mTOR. Correspondingly, Sestrin2-deficient mice fail to inhibit mTOR signaling upon genotoxic challenge. Sestrin1 and Sestrin2 therefore provide an important link between genotoxic stress, p53 and the mTOR signaling pathway.
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PMID:p53 target genes sestrin1 and sestrin2 connect genotoxic stress and mTOR signaling. 1869 68

Death-associated protein kinase (DAPK) is a multidomain enzyme that plays a central role in autophagic and apoptotic signaling, although the protein-protein interactions regulating DAPK functions are not well defined. Peptide aptamer libraries were used to identify the tumor suppressor protein tuberin (TSC2) as a novel DAPK death domain-binding protein, and we evaluated whether DAPK is a positive or negative effector of the TSC2-regulated mammalian target of rapamycin (mTORC1) signaling pathway. Binding studies using death domain miniproteins in vitro and deletion analysis in vivo determined that the death domain of DAPK is the major site for the interaction with TSC2. Recombinant DAPK phosphorylates TSC2 in vitro, and DAPK kinase activity is stimulated by growth factor signaling. Transfection of DAPK promotes phosphorylation of TSC2 in vivo, whereas short interfering RNA-mediated attenuation of DAPK reduces growth factor-stimulated phosphorylation of TSC2. DAPK-dependent phosphorylation leads to TSC1-TSC2 complex dissociation, and consequently manipulation of DAPK by transfection or short interfering RNA demonstrated that DAPK is a positive regulator of mTORC1 in response to growth factor activation. Epistatic studies suggest that DAPK functions downstream from the RAS-MEK-ERK and phosphatidylinositol 3-kinase-AKT growth factor signaling pathways. DAPK(+/-) mouse embryo fibroblasts have attenuated mTORC1 signaling compared with DAPK+/+ counterparts, and overexpression of DAPK in DAPK(+/-) MEFs stimulates mTORC1 activity. These data uncover a novel interaction between DAPK and TSC2 proteins that has revealed a positive link between growth factor stimulation of DAPK and mTORC1 signaling that may ultimately affect autophagy, cell survival, or apoptosis.
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PMID:Peptide combinatorial libraries identify TSC2 as a death-associated protein kinase (DAPK) death domain-binding protein and reveal a stimulatory role for DAPK in mTORC1 signaling. 1897 95

The AMP-activated serine/threonine protein kinase (AMPK) is a sensor of cellular energy status found in all eukaryotes that is activated under conditions of low intracellular ATP following stresses such as nutrient deprivation or hypoxia. In the past 5 years, work from a large number of laboratories has revealed that one of the major downstream signalling pathways regulated by AMPK is the mammalian target-of-rapamycin [mammalian target of rapamycin (mTOR) pathway]. Interestingly, like AMPK, the mTOR serine/threonine kinase plays key roles not only in growth control and cell proliferation but also in metabolism. Recent work has revealed that across eukaryotes mTOR orthologues are found in two biochemically distinct complexes and only one of those complexes (mTORC1 in mammals) is acutely sensitive to rapamycin and regulated by nutrients and AMPK. Many details of the molecular mechanism by which AMPK inhibits mTORC1 signalling have also been decoded in the past 5 years. AMPK directly phosphorylates at least two proteins to induce rapid suppression of mTORC1 activity, the TSC2 tumour suppressor and the critical mTORC1 binding subunit raptor. Here we explore the molecular connections between AMPK and mTOR signalling pathways and examine the physiological processes in which AMPK regulation of mTOR is critical for growth or metabolic control. The functional conservation of AMPK and TOR in all eukaryotes, and the sequence conservation around the AMPK phosphorylation sites in raptor across all eukaryotes examined suggest that this represents a fundamental cell growth module connecting nutrient status to the cell growth machinery. These findings have broad implications for the control of cell growth by nutrients in a number of cellular and organismal contexts.
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PMID:LKB1 and AMP-activated protein kinase control of mTOR signalling and growth. 1924 54


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