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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activation of the extra cellular signal regulated kinase (ERK) pathway is involved in both proliferation and growth arrest of cells depending on intensity and duration of stimuli. In this study, we have elucidated differential regulation of the zinc-stimulated p21(CiP/WAF1) and cyclin D1 activation by inhibition of phosphoinositide 3-kinase (PI3K). In HT-29 colorectal cancer cells, the ERK activities were increased by zinc, which was accompanied by the induction of p21(Cip/WAF1) and cyclin D1. However, in the HT-29 cells pre-treated with PI3K inhibitor, LY294002, zinc induced further the p21(CiP/WAF) induction whereas abrogated cyclin D1 induction. In addition, the induction of p21(Cip/WAF1) expression completely inhibited the incorporation of bromodeoxyuridine (BrdU) into the nucleus, indicating that p21(CiP/WAF1) is an important indicator for ERK-dependent growth arrest. These studies suggest presence of an inter-related regulatory mechanism of cell proliferation by ERK and PI3K pathways.
Exp Mol Med 2002 Mar 31
PMID:Differential modulation of zinc-stimulated p21(Cip/WAF1) and cyclin D1 induction by inhibition of PI3 kinase in HT-29 colorectal cancer cells. 1198 75

Endocytosis is required for efficient mitogen-activated protein kinase (MAPK) activation by activated growth factor receptors. We examined if H-Ras and K-Ras proteins, which are distributed across different plasma membrane microdomains, have equal access to the endocytic compartment and whether this access is necessary for downstream signaling. Inhibition of endocytosis by dominant interfering dynamin-K44A blocked H-Ras but not K-Ras-mediated PC12 cell differentiation and selectively inhibited H-Ras- but not K-Ras-mediated Raf-1 activation in BHK cells. H-Ras- but not K-Ras-mediated Raf-1 activation was also selectively dependent on phosphoinositide 3-kinase activity. Stimulation of endocytosis and endocytic recycling by wild-type Rab5 potentiated H-Ras-mediated Raf-1 activation. In contrast, Rab5-Q79L, which stimulates endocytosis but not endocytic recycling, redistributed activated H-Ras from the plasma membrane into enlarged endosomes and inhibited H-Ras-mediated Raf-1 activation. Rab5-Q79L expression did not cause the accumulation of wild-type H-Ras in enlarged endosomes. Expression of wild-type Rab5 or Rab5-Q79L increased the specific activity of K-Ras-activated Raf-1 but did not result in any redistribution of K-Ras from the plasma membrane to endosomes. These results show that H-Ras but not K-Ras signaling though the Raf/MEK/MAPK cascade requires endocytosis and endocytic recycling. The data also suggest a mechanism for returning Raf-1 to the cytosol after plasma membrane recruitment.
Mol Cell Biol 2002 Jul
PMID:H-Ras signaling and K-Ras signaling are differentially dependent on endocytosis. 1207 41

The tumor suppressor PTEN possesses lipid and protein phosphatase activities. It has been well established that the lipid phosphatase activity is essential for its tumor-suppressive function via the phosphoinositide 3-kinase (PI3K) and Akt pathways. The precise role of the protein phosphatase activity is still unclear. In the current study, we demonstrate that overexpression of wild-type PTEN in the MCF-7 breast cancer line results in phosphatase activity-dependent decreases in the phosphorylation of ETS-2, which is a transcription factor whose DNA-binding ability is controlled by phosphorylation. Exposure of MCF-7 cells to insulin, insulin-like growth factor 1 (IGF-1) or epidermal growth factor (EGF) can lead to the phosphorylation of ETS-2, Akt and ERK1/2. The MEK inhibitor PD590089 abrogates insulin-stimulated phosphorylation of ETS-2. In contrast, the PI3K inhibitor LY492002 has no effect on insulin-stimulated phosphorylation of ETS-2, despite the fact that it diminishes insulin-stimulated phosphorylation of Akt. Interestingly, overexpression of PTEN in MCF-7 leads to blockade of insulin-stimulated, but not EGF-stimulated, phosphorylation of ERK, accompanied by dramatic decreases in ETS-2 phosphorylation. We further show that the relationship of PTEN and ETS-2 has functional significance by demonstrating that PTEN abrogates activation of the uPA Ras-responsive enhancer, a target of ETS-2 action, in a phosphatase-dependent manner, irrespective of the presence or absence of insulin. Our observations, therefore, suggest that PTEN blocks insulin-stimulated ETS-2 phosphorylation through inhibition of the ERK members of the MAP kinase family independently of PI3K, and that the PTEN effect on the phosphorylation status of ETS-2 may be mediated through PTEN's protein phosphatase activity.
Hum Mol Genet 2002 Jul 15
PMID:PTEN blocks insulin-mediated ETS-2 phosphorylation through MAP kinase, independently of the phosphoinositide 3-kinase pathway. 1209 11

The S/T-protein kinases activated by phosphoinositide 3-kinase (PI3K) regulate a myriad of cellular processes. Here, we show that an approach using a combination of biochemistry and bioinformatics can identify substrates of these kinases. This approach identifies the tuberous sclerosis complex-2 gene product, tuberin, as a potential target of Akt/PKB. We demonstrate that, upon activation of PI3K, tuberin is phosphorylated on consensus recognition sites for PI3K-dependent S/T kinases. Moreover, Akt/PKB can phosphorylate tuberin in vitro and in vivo. We also show that S939 and T1462 of tuberin are PI3K-regulated phosphorylation sites and that T1462 is constitutively phosphorylated in PTEN(-/-) tumor-derived cell lines. Finally, we find that a tuberin mutant lacking the major PI3K-dependent phosphorylation sites can block the activation of S6K1, suggesting a means by which the PI3K-Akt pathway regulates S6K1 activity.
Mol Cell 2002 Jul
PMID:Identification of the tuberous sclerosis complex-2 tumor suppressor gene product tuberin as a target of the phosphoinositide 3-kinase/akt pathway. 1215 Sep 15

The protein kinase B (PKB)/Akt family of serine kinases is rapidly activated following agonist-induced stimulation of phosphoinositide 3-kinase (PI3K). To probe the molecular events important for the activation process, we employed two distinct models of posttranslational inducible activation and membrane recruitment. PKB induction requires phosphorylation of two critical residues, threonine 308 in the activation loop and serine 473 near the carboxyl terminus. Membrane localization of PKB was found to be a primary determinant of serine 473 phosphorylation. PI3K activity was equally important for promoting phosphorylation of serine 473, but this was separable from membrane localization. PDK1 phosphorylation of threonine 308 was primarily dependent upon prior serine 473 phosphorylation and, to a lesser extent, localization to the plasma membrane. Mutation of serine 473 to alanine or aspartic acid modulated the degree of threonine 308 phosphorylation in both models, while a point mutation in the substrate-binding region of PDK1 (L155E) rendered PDK1 incapable of phosphorylating PKB. Together, these results suggest a mechanism in which 3' phosphoinositide lipid-dependent translocation of PKB to the plasma membrane promotes serine 473 phosphorylation, which is, in turn, necessary for PDK1-mediated phosphorylation of threonine 308 and, consequentially, full PKB activation.
Mol Cell Biol 2002 Sep
PMID:Multiple phosphoinositide 3-kinase-dependent steps in activation of protein kinase B. 1216 17

We recently demonstrated that endothelin-1 (ET-1) activates two types of Ca(2+)-permeable nonselective cation channel (designated NSCC-1 and NSCC-2) and a store-operated Ca(2+) channel (SOCC) in Chinese hamster ovary cells expressing endothelin(A) receptor (CHO-ET(A)R). In addition, these channels can be discriminated using Ca(2+) channel blockers (R,S)-(3,4-dihydro-6,7-dimethoxy-isochinolin-1-yl)-2-phenyl-N,N-di[2-(2,3,4-trimethoxyphenyl)ethyl]acetamid mesylate (LOE 908) and 1-(beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl)-1H-imidazole (SK&F 96365). LOE 908 is a blocker of NSCC-1 and NSCC-2, whereas SK&F 96365 is a blocker of SOCC and NSCC-2. In this study, we investigated the effects of phosphoinositide 3-kinase (PI3K) on the ET-1-induced activation of these channels and mitogenesis in CHO-ET(A)R using wortmannin and 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY 294002), inhibitors of phosphoinositide 3-kinase (PI3K). ET-1-induced Ca(2+) influx was partially inhibited in CHO-ET(A)R pretreated with wortmannin or LY 294002. In contrast, addition of wortmannin or LY 294002 after stimulation with ET-1 did not suppress Ca(2+) influx. The Ca(2+) channels activated by ET-1 in wortmannin or LY 294002-treated CHO-ET(A)R were sensitive to LOE 908 and resistant to SK&F 96365. Wortmannin also partially inhibited ET-1-induced mitogenesis. LOE 908, but not SK&F 96365, abolished the wortmannin-resistant part of mitogenesis. The IC(50) values (~30 nM) of wortmannin for the ET-1-induced Ca(2+) influx and mitogenesis were similar to those for the ET-1-induced PI3K activation. In conclusion, NSCC-2 and SOCC are stimulated by ET-1 via PI3K-dependent cascade, whereas NSCC-1 is stimulated via PI3K-independent cascade. Moreover, PI3K seems to be required for the activation of the Ca(2+) entry, but not for its maintenance. In addition, PI3K is involved in the ET-1-induced mitogenesis that depends on the extracellular Ca(2+) influx through SOCC and NSCC-2.
Mol Pharmacol 2002 Sep
PMID:Effects of phosphoinositide 3-kinase on the endothelin-1-induced activation of voltage-independent Ca(2+) channels and mitogenesis in Chinese hamster ovary cells stably expressing endothelin(a) receptor. 1218 54

In the present study, we identified novel negative cross-talk between the angiotensin II subtype 2 (AT2) receptor and insulin receptor signaling in the regulation of phosphoinositide 3-kinase (PI3K), Akt, and apoptosis in rat pheochromocytoma cell line, PC12W cells, which exclusively express AT2 receptor. We demonstrated that insulin-mediated insulin receptor substrate (IRS)-2-associated PI3K activity was inhibited by AT2 receptor stimulation, whereas IRS-1-associated PI3K activity was not significantly influenced. AT2 receptor stimulation did not change insulin-induced tyrosine phosphorylation of IRS-2 or its association with the p85alpha subunit of PI3K, but led to a significant reduction of insulin-induced p85alpha phosphorylation. AT2 receptor stimulation increased the association of a protein tyrosine phosphatase, SHP-1, with IRS-2. Moreover, we demonstrated that AT2 receptor stimulation inhibited insulin-induced Akt phosphorylation and that insulin-mediated antiapoptotic effect was also blocked by AT2 receptor activation. Overexpression of a catalytically inactive dominant negative SHP-1 markedly attenuated the AT2 receptor- mediated inhibition of IRS-2-associated PI3K activity, Akt phosphorylation, and antiapoptotic effect induced by insulin. Taken together, these results indicate that AT2 receptor-mediated activation of SHP-1 and the consequent inhibition IRS-2-associated PI3K activity contributed at least partly to the inhibition of Akt phosphorylation, thereby inducing apoptosis.
Mol Endocrinol 2002 Sep
PMID:Angiotensin II subtype 2 receptor activation inhibits insulin-induced phosphoinositide 3-kinase and Akt and induces apoptosis in PC12W cells. 1219 47

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor containing an inducibly expressed HIF-1alpha subunit and a constititutively expressed HIF-1beta subunit. Under hypoxic conditions, the HIF-1alpha subunit accumulates due to a decrease in the rate of proteolytic degradation, and the resulting HIF-1alpha-HIF-1beta heterodimers undergo posttranslational modifications that promote transactivation. Recent studies suggest that amplified signaling through phosphoinositide 3-kinase, and its downstream target, mTOR, enhances HIF-1-dependent gene expression in certain cell types. In the present study, we have explored further the linkage between mTOR and HIF-1 in PC-3 prostate cancer cells treated with hypoxia or the hypoxia mimetic agent, CoCl(2). Pretreatment of PC-3 cells with the mTOR inhibitor, rapamycin, inhibited both the accumulation of HIF-1alpha and HIF-1-dependent transcription induced by hypoxia or CoCl(2). Transfection of these cells with wild-type mTOR enhanced HIF-1 activation by hypoxia or CoCl(2), while expression of a rapamycin-resistant mTOR mutant rendered both HIF-1alpha stabilization and HIF-1 transactivating function refractory to inhibition by rapamycin. Studies with GAL4-HIF-1alpha fusion proteins pinpointed the oxygen-dependent degradation domain as a critical target for the rapamycin-sensitive, mTOR-dependent signaling pathway leading to HIF-1alpha stabilization by CoCl(2). These studies position mTOR as an upstream activator of HIF-1 function in cancer cells and suggest that the antitumor activity of rapamycin is mediated, in part, through the inhibition of cellular responses to hypoxic stress.
Mol Cell Biol 2002 Oct
PMID:Regulation of hypoxia-inducible factor 1alpha expression and function by the mammalian target of rapamycin. 1224 81

v-Crk, an oncogene product of avian sarcoma virus CT10, efficiently transforms chicken embryo fibroblasts (CEF). We have recently reported that constitutive activation of the phosphoinositide 3-kinase (PI3K)/AKT pathway plays a critical role in the v-Crk-induced transformation of CEF. In the present study we investigated the molecular mechanism by which v-Crk activates the PI3K/AKT pathway. First, we found that v-Crk promotes the association of the p85 regulatory subunit of PI3K with focal adhesion kinase (FAK) by inducing the phosphorylation of the Y397 residue in FAK. This FAK phosphorylation needs activation of the Src family tyrosine kinase(s) for which the v-Crk SH2 domain is responsible. v-Crk was unable to activate the PI3K/AKT pathway in FAK-null cells, indicating the functional importance of FAK. In addition, we found that H-Ras is also required for the activation of the PI3K/AKT pathway. The v-Crk-induced activation of AKT was greatly enhanced by the overexpression of H-Ras or its guanine nucleotide exchange factor mSOS, which binds to the v-Crk SH3 domain, whereas a dominant-negative mutant of H-Ras almost completely suppressed this activation. Furthermore, we showed that v-Crk stimulates the interaction of H-Ras with the Ras binding domain in the PI3K p110 catalytic subunit. Our data indicated that the v-Crk-induced activation of PI3K/AKT pathway was cooperatively achieved by two distinct interactions. One is the interaction of p85 with tyrosine-phosphorylated FAK promoted by the v-Crk SH2 domain, and another is the interaction of p110 with H-Ras dictated by the v-Crk SH3 domain.
Mol Cell Biol 2002 Oct
PMID:v-Crk activates the phosphoinositide 3-kinase/AKT pathway by utilizing focal adhesion kinase and H-Ras. 1224 82

Mitogen-activated protein (MAP) kinase and phosphoinositide 3-kinase (PI3K) pathways are necessary for cell cycle progression into S phase; however the importance of these pathways after the restriction point is poorly understood. In this study, we examined the regulation and function of extracellular signal-regulated kinase (ERK) and PI3K during G(2)/M in synchronized HeLa and NIH 3T3 cells. Phosphorylation and activation of both the MAP kinase kinase/ERK and PI3K/Akt pathways occur in late S and persist until the end of mitosis. Signaling was rapidly reversed by cell-permeable inhibitors, indicating that both pathways are continuously activated and rapidly cycle between active and inactive states during G(2)/M. The serum-dependent behavior of PI3K/Akt versus ERK pathway activation indicates that their mechanisms of regulation differ during G(2)/M. Effects of cell-permeable inhibitors and dominant-negative mutants show that both pathways are needed for mitotic progression. However, inhibiting the PI3K pathway interferes with cdc2 activation, cyclin B1 expression, and mitotic entry, whereas inhibiting the ERK pathway interferes with mitotic entry but has little effect on cdc2 activation and cyclin B1 and retards progression from metaphase to anaphase. Thus, our study provides novel evidence that ERK and PI3K pathways both promote cell cycle progression during G(2)/M but have different regulatory mechanisms and function at distinct times.
Mol Cell Biol 2002 Oct
PMID:Distinct cell cycle timing requirements for extracellular signal-regulated kinase and phosphoinositide 3-kinase signaling pathways in somatic cell mitosis. 1224 99


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