Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transformation of cells in culture by polyomavirus is mediated by one of its early gene products, middle-sized tumor antigen (MTAg). This protein forms multiple complexes with cellular enzymes such as tyrosine kinases (pp60c-src), a phosphatidylinositol 3-kinase, and phosphatase 2A. Association with MTAg leads to the activation of pp60c-src through interference with phosphorylation at Tyr-527, a site negatively regulating src kinase activity. MTAg abrogates mitosis-specific activation of pp60c-src, resulting in constitutive high kinase activity of the enzyme throughout all phases of the cell cycle. Here we report that MTAg is transiently modified during mitosis, resulting in an increase in its apparent molecular size on SDS/acrylamide gels. Similarly, MTAg isolated from interphase cells and phosphorylated by the cell cycle-regulated serine/threonine kinase p34cdc2 in vitro has increased molecular mass. The large molecular mass form of the protein can be converted to the authentic 56-kDa form upon dephosphorylation by potato acid phosphatase. Two putative phosphorylation sites for a cdc2-like kinase were identified as Thr-160 and -291, respectively. Conversion of Thr-160 to Ala resulted in a transformation-defective mutant protein that was still capable of associating with pp60c-src, phosphatidylinositol 3-kinase, and phosphatase 2A, while the corresponding mutant in position 291 was wild type with respect to all parameters measured so far. These data suggest that phosphorylation by p34cdc2 or a related cell cycle-regulated kinase modulates the interaction of MTAg with cellular targets that are crucial for cell transformation.
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PMID:Mitosis-specific phosphorylation of polyomavirus middle-sized tumor antigen and its role during cell transformation. 769 Jan 42

In an attempt to define the basis for sphingolipid regulation of cell proliferation, we studied the effects of glucosylceramide (GlcCer) synthase inhibition by threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) on NIH 3T3 cells overexpressing insulin-like growth factor-1 (IGF-1) receptor. PDMP treatment resulted in a time-dependent decrease in GlcCer levels and an increase in cellular ceramide levels. PDMP abolished serum and IGF-1-stimulated cell proliferation, as measured by a reduction in [3H]thymidine incorporation, protein, and DNA levels. However it did not affect IGF-1-mediated early signaling events, including receptor tyrosine kinase, MAP kinase, and phosphatidylinositol 3-kinase activities. Two-color flow cytometry with propidium iodide and 5-bromo-2'-deoxyuridine monophosphate labeling revealed an arrest of the cell cycle at G1/S and G2/M transitions in an asynchronous population of cells. These changes were time dependent, with maximal effects seen by 12-24 h. Removal of PDMP from the cell medium resulted in reversal of the cell cycle changes, with cells re-entering the S phase. The cell cycle arrest at the G1/S and G2/M transitions was confirmed in cells synchronized by pretreatment with nocodazole, aphidicolin, or hydroxyurea, and released from blockade in the presence of PDMP. A decrease in the activities of two cyclin-dependent kinases, p34cdc2 kinase and cdk2 kinase, was observed with PDMP treatment. When cell ceramide levels were increased by N-acetylsphingosine, comparable changes in the cell cycle distribution were seen. However, sphingomyelinase treatment was without effect. Therefore, it appears that ceramide mediates in part the inhibitory effect of GlcCer synthase inhibition on IGF-1-induced cell proliferation in 3T3 cells. The rapid production of decreased cyclin-dependent kinase activities by PDMP suggests that one of the crucial sites of action of the inhibitor lies in this area.
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PMID:Cell cycle arrest induced by an inhibitor of glucosylceramide synthase. Correlation with cyclin-dependent kinases. 785 61

Activation of the multicomponent interleukin-2 receptor (IL-2R) complex leads to a rapid increase in tyrosine phosphorylation of a number of cellular proteins including the IL-2R beta and IL-2R gamma chains of the IL-2R and the RAF-1 serine threonine kinase. In addition, phosphatidylinositol 3-kinase (PI-3K) protein and activity can be immunoprecipitated with anti-phosphotyrosine and anti-IL-2R beta antibodies from IL-2-activated but not resting T lymphocytes. We have demonstrated that the SH2 (SRC homology 2) domains of the 85 kDa subunit of PI-3K are sufficient to mediate binding of the PI-3K complex to tyrosine phosphorylated, but not non-phosphorylated IL-2R beta, suggesting that tyrosine phosphorylation is an integral component of the activation of PI-3K by the IL-2R. Since none of the members of the IL-2R complex contains an intrinsic tyrosine kinase domain, IL-2-induced tyrosine phosphorylation must be the consequence of activation of intracellular tyrosine kinases. SRC family members including lck, lyn and fyn have been demonstrated to associate with IL-2R beta through binding of the kinase domain to the acidic domain of IL-2R beta. However, we have demonstrated that the serine rich (SD) region of the cytosolic domain of IL-2R beta is also required for association of a tyrosine kinase with the IL-2R complex and that IL-2 can induce proliferation and tyrosine phosphorylation in cell lines which lack the known SRC family kinases expressed by T lymphocytes. Thus members of other kinase families besides SRC may also be involved in mediating IL-2 signal transduction. Biochemical studies and studies of cells expressing mutant IL-2 receptors indicate that IL-2-induced tyrosine kinase activation initiates a complex signaling cascade. The cascade includes SRC family kinase members such as lck, fyn, and lyn, activation of Raf-1 and PI-3K, and ras, and increased expression of the fos, fra-1, and jun protooncogenes. In addition, ligation of the IL-2R leads to rapid increases in myc expression and more delayed increases in the expression of the cdc2 and cdk2 kinases and the cyclins through a tyrosine phosphorylation independent pathway. Whether other biochemical processes initiated by IL-2R ligation, including activation of the MAP2, p70S6 and p90RSK serine threonine kinases, activation of NF-kappa B, and increased expression of Raf-1, Pim-1, bcl-2, IL-2R alpha and IL-2R beta, are consequences of the IL-2-induced tyrosine kinase cascade remains to be determined.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Transmembrane signaling by the interleukin-2 receptor: progress and conundrums. 826 Jun 51

The gene mutated in the human genetic disorder ataxia-telangiectasia (A-T) has been described recently (Savitsky et al., 1995a) and the complete coding sequence of this gene, ATM, has been reported (Savitsky et al., 1995b). The derived amino acid sequence demonstrates significant homologies to several proteins containing a phosphatidylinositol 3-kinase (PI3-kinase) domain, including the yeast TOR proteins and the human protein FRAP. Since the TOR and FRAP proteins are targets for the immunosuppressive drug rapamycin, we have investigated the effects of this compound on A-T cells. We report here that 3 A-T cell lines are more resistant than control cells to rapamycin's growth inhibiting effects but were more sensitive to the PI3-kinase inhibitor wortmannin. As expected rapamycin (1 nM) inhibited the rate of exit of control cells from G1 phase but failed to perturb the progression of A-T cells. This difference in cell cycle progress after rapamycin treatment is reflected in ribosomal S6 protein kinase (p70S6k) by both a downward mobility shift on SDS-PAGE and inhibition of activity. Furthermore, the G1 phase cyclin-dependent kinase, cyclin E-cdk2, was rapidly inhibited in control cells post-treatment, whereas in A-T cells it took considerably longer to observe inhibition. There was no evidence that a GST-FKBP12 fusion protein specifically precipitated the ATM protein in the presence of rapamycin in either cell type. These results demonstrate that the ATM protein is not a direct target for rapamycin but its functional loss renders cells more resistant to this compound.
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PMID:Rapamycin resistance in ataxia-telangiectasia. 880 86

Platelet-derived growth factor (PDGF) and serum, but not epidermal growth factor (EGF), stimulated sphingosine kinase activity in Swiss 3T3 fibroblasts and increased intracellular concentrations of sphingosine 1-phosphate (SPP), a sphingolipid second messenger (Olivera, A., and Spiegel, S. (1993) Nature 365, 557-560). We report herein that DL-threo-dihydrosphingosine (DHS), a competitive inhibitor of sphingosine kinase that prevents PDGF-induced SPP formation, specifically inhibited the activation of two cyclin-dependent kinases (p34(cdc2) kinase and Cdk2 kinase) induced by PDGF, but not by EGF. SPP reversed the inhibitory effects of DHS on PDGF-stimulated cyclin-dependent kinases and DNA synthesis, demonstrating that the DHS effects were mediated via inhibition of sphingosine kinase. DHS also markedly reduced PDGF-stimulated but not EGF-stimulated mitogen-activated protein kinase activity and DNA binding activity of activator protein-1. Examination of the early signaling events of PDGF action revealed that DHS did not affect PDGF-induced autophosphorylation of the growth factor receptor or phosphorylation of the SH2/SH3 adaptor protein Shc and its association with Grb2. This sphingosine kinase inhibitor did not abrogate activation of phosphatidylinositol 3-kinase by PDGF. In agreement, treatment with SPP had no effect on these responses but did, however, potently stimulate phosphorylation of Crk, another SH2/SH3 adaptor protein. Moreover, DHS inhibited PDGF-stimulated, but not EGF-stimulated, Crk phosphorylation. Thus, regulation of sphingosine kinase activity defines divergence in signal transduction pathways of PDGF and EGF receptors leading to mitogen-activated protein kinase activation.
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PMID:Divergence in signal transduction pathways of platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptors. Involvement of sphingosine 1-phosphate in PDGF but not EGF signaling. 909 30

We have investigated the effect of the flavonoid derivative LY 294002, a potent and selective phosphatidylinositol 3-kinase inhibitor, on cell cycle progression in human choroidal melanoma cells. We demonstrate that LY 294002 induces a specific G1 block in asynchronously growing cells leading to an almost complete inhibition of cell proliferation after three days of treatment. When melanoma cells are released from a nocodazole-induced G2/M block, LY 294002 is shown to delay and greatly restrain the G1/S transition. The inhibitor is able to exert its action as long as it is added during the G1 progression and before the cells enter in S phase. We report that the LY 294002-induced G1 arrest is closely correlated to inhibition of CDK4 and CDK2 activities leading to the impairment of pRb phosphorylation which normally occurs during G1 progression. While the inhibition of CDK4 may be attributed at least in part to the decline in CDK4 protein level, CDK2 activity reduction is rather due to the up-regulation of the CDK inhibitor p27Kip1 and to its increased association to CDK2.
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PMID:G1 phase arrest by the phosphatidylinositol 3-kinase inhibitor LY 294002 is correlated to up-regulation of p27Kip1 and inhibition of G1 CDKs in choroidal melanoma cells. 949 22

Using a new inducible form of phosphatidylinositol 3-kinase (PI 3-kinase) we have found that PI 3-kinase activation has the following effects on cell growth and proliferation. (i) Activation of PI 3-kinase was sufficient to promote entry into S phase of the cell cycle within several hours. This was shown by activation of cyclin-dependent kinase 4 (Cdk4) and Cdk2 and by the induction of DNA synthesis. (ii) PI 3-kinase activation alone was not, however, sufficient to provide for progression through the entire cell cycle. Instead, prolonged activation of PI 3-kinase in the absence of serum stimulation resulted in apoptosis. It is possible that the cells undergo apoptosis because the PI 3-kinase-induced entry into the cell cycle is abnormal. For example, we found that the cyclin E-Cdk2 complex, which normally disappears after entry into S phase of the cell cycle, fails to be downregulated following induction by PI 3-kinase. (iii) Finally, we found that prolonged activation of PI 3-kinase in the presence of serum resulted in cellular changes that resemble those associated with oncogenic transformation. The cells reached high densities, were irregular and refractile in appearance, and formed colonies in soft agar. In contrast, neither PI 3-kinase nor serum stimulation alone could induce these changes. Our results suggest that activation of PI 3-kinase promotes anchorage-independent cell growth and entry into the cell cycle but does not abrogate the growth factor requirement for cell proliferation.
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PMID:Activation of phosphatidylinositol 3-kinase is sufficient for cell cycle entry and promotes cellular changes characteristic of oncogenic transformation. 974 87

Proliferation of vascular smooth muscle cells contributes to initimal hyperplasia during atherogenesis, but the factors regulating their proliferation are not well known. In the present study we report that sublytic C5b-9 assembly induced proliferation of differentiated human aortic smooth muscle cells (ASMC) in culture. Cell cycle re-entry occurred through activation of cdk4, cdk2 kinase and the reduction of p21 cell cycle inhibitor. We also investigated if C5b-9 cell cycle induction is mediated through activation of mitogen activated protein kinase (MAPK) pathways. Extracellular signal regulated kinase (ERK) 1 activity was significantly increased, while c-jun NH2-terminal kinase (JNK) 1 and p38 MAPK activity were only transiently increased. Pretreatment with wortmannin inhibits ERK1 activation by C5b-9, suggesting the involvement of phosphatidylinositol 3-kinase (PI 3-kinase). Both PI 3-kinase and p70 S6 kinase were activated by C5b-9 but not by C5b6. C5b-9 induced DNA synthesis was abolished by pretreatment with inhibitors of ERK1 and PI 3-kinase, but not by p38 MAPK. These data indicated that ERK1 and PI 3-kinase play a major role in C5b-9 induced ASMC proliferation.
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PMID:Sublytic C5b-9 induces proliferation of human aortic smooth muscle cells: role of mitogen activated protein kinase and phosphatidylinositol 3-kinase. 992 May 5

Although it is well established that endothelin-1 (ET-1) has not only vasoconstrictive effects but also mitogenic effects, which seem to be implicated in vascular remodeling, little is known about the molecular mechanisms by which ET-1 induces cell-cycle progression. In this study, we examined the effects of ET-1 on the cell-cycle regulatory machinery, including cyclins, cyclin-dependent kinase (cdk), and cdk inhibitors in NIH3T3 cells. ET-1 increased cyclin D1 protein (5.1+/-1.9-fold increase, 8 hours after stimulation, P<0.05), cdk4 kinase activity (2.8+/-0. 5-fold increase, 12 hours after stimulation, P<0.01), and cdk2 kinase activity (2.1+/-0.4-fold increase, 16 hours after stimulation, P<0.05) in a time- and dose-dependent manner. ET-1-induced increase in cyclin D1 protein, and cdk4 kinase activity was not significantly inhibited by an inhibitor of the mitogen-activated protein kinase kinase 1/2, PD98059, nor by the protein kinase C inhibitor calphostin C, whereas ET-1-induced upregulation of cyclin D1 protein and cdk4 kinase activity was significantly inhibited by the phosphatidylinositol 3-kinase inhibitor LY294002. In contrast, ET-1-induced activation of cdk2 kinase was significantly inhibited by PD98059, calphostin C, and LY294002. ET-1 increased 3H-thymidine uptake in a time-dependent fashion (0 hours, 4216+/-264 cpm per well; 8 hours, 5025+/-197 cpm per well; 16 hours, 9239+/-79 cpm per well, P<0.001 versus 0 hours). ET-1-induced increase in 3H-thymidine uptake was significantly inhibited by PD98059, calphostin C, and LY294002. These results suggest that ET-1-induced cell-cycle progression is, at least in part, mediated by the extracellular signal-regulated kinase, protein kinase C, and phosphatidylinositol 3-kinase and that those pathways may be involved in the progression of the cell cycle at distinct points.
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PMID:Molecular mechanisms of endothelin-1-induced cell-cycle progression: involvement of extracellular signal-regulated kinase, protein kinase C, and phosphatidylinositol 3-kinase at distinct points. 1008 82

Deregulation of cell cycle checkpoints is an almost universal abnormality in human cancers and is most often due to loss-of-function mutations of tumor suppressor genes such as Rb, p53, or p16(INK4a). In this study, we demonstrate that BCR/ABL inhibits the expression of a key cell cycle inhibitor, p27(Kip1), by signaling through a pathway involving phosphatidylinositol 3-kinase (PI3K). p27(Kip1) is a widely expressed inhibitor of cdk2, an essential cell cycle kinase regulating entry into S phase. We demonstrate that the decrease of p27(Kip1) is directly due to BCR/ABL in hematopoietic cells by two different approaches. First, induction of BCR/ABL by a tetracycline-regulated promoter is associated with a reversible down-regulation of p27(Kip1). Second, inhibition of BCR/ABL kinase activity with the Abl tyrosine kinase inhibitor STI571 rapidly increases p27(Kip1) levels. The PI3K inhibitor LY-294002 blocks the ability of BCR/ABL to induce p27(Kip1) down-regulation and inhibits BCR/ABL-induced entry into S phase. The serine/threonine kinase AKT/protein kinase B is a known downstream target of PI3K. Transient expression of an activated mutant of AKT was found to decrease expression of p27(Kip1), even when PI3K was inhibited by LY-294002. The mechanism of p27(Kip1) regulation is primarily related to protein stability, since inhibition of proteasome activity increased p27(Kip1) levels in BCR/ABL-transformed cells, whereas very little change in p27 transcription was found. Overall, these data are consistent with a model in which BCR/ABL suppresses p27(Kip1) protein levels through PI3K/AKT, leading to accelerated entry into S phase. This activity is likely to explain in part previous studies showing that activation of PI3K was required for optimum transformation of hematopoietic cells by BCR/ABL in vitro and in vivo.
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PMID:BCR/ABL regulates expression of the cyclin-dependent kinase inhibitor p27Kip1 through the phosphatidylinositol 3-Kinase/AKT pathway. 1101 Sep 72


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