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)

p107 is a retinoblastoma protein-related phosphoprotein that, when overproduced, displays a growth inhibitory function. It interacts with and modulates the activity of the transcription factor, E2F-4. In addition, p107 physically associates with cyclin E-CDK2 and cyclin A-CDK2 complexes in late G1 and at G1/S, respectively, an indication that cyclin-dependent kinase complexes may regulate, contribute to, and/or benefit from p107 function during the cell cycle. Our results show that p107 phosphorylation begins in mid G1 and proceeds through late G1 and S and that cyclin D-associated kinase(s) contributes to this process. In addition, E2F-4 binds selectively to hypophosphorylated p107, and G1 cyclin-dependent p107 phosphorylation leads to the dissociation of p107-E2F-4 complexes as well as inactivation of p107 G1 blocking function.
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PMID:Regulation of the retinoblastoma protein-related protein p107 by G1 cyclin-associated kinases. 864 55

Cells which are highly proliferative typically lack expression of differentiated, lineage-specific characteristics. Id2, a member of the helix-loop-helix (HLH) protein family known to inhibit cell differentiation, binds to the retinoblastoma protein (pRb) and abolishes its growth-suppressing activity. We found that Id2 but not Id1 or Id3 was able to bind in vitro not only pRb but also the related proteins p107 and p130. Also, an association between Id2 and p107 or p130 was observed in vivo in transiently transfected Saos-2 cells. In agreement with these results, expression of Id1 or Id3 did not affect the block of cell cycle progression mediated by pRb. Conversely, expression of Id2 specifically reversed the cell cycle arrest induced by each of the three members of the pRb family. Furthermore, the growth-suppressive activities of cyclin-dependent kinase inhibitors p16 and p21 were efficiently antagonized by high levels of Id2 but not by Id1 Id3. Consistent with the role of p16 as a selective inhibitor of pRb and pRb-related protein kinase activity, p16-imposed cell cycle arrest was completely abolished by Id2. Only a partial reversal of p21-induced growth suppression was observed, which correlated with the presence of a functional pRb. We also documented decreased levels of cyclin D1 protein and mRNA and the loss of cyclin D1-cdk4 complexes in cells constitutively expressing Id2. These data provide evidence for important Id2-mediated alterations in cell cycle components normally involved in the regulatory events of cell cycle progression, and they highlight a specific role for Id2 as an antagonist of multiple tumor suppressor proteins.
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PMID:Id2 specifically alters regulation of the cell cycle by tumor suppressor proteins. 864 64

The protein kinase inhibitor staurosporine has been shown to induce G1 phase arrest in normal cells but not in most transformed cells. Staurosporine did not induce G1 phase arrest in the bladder carcinoma cell line 5637 that lacks a functional retinoblastoma protein (pRB-). However, when infected with a pRB-expressing retrovirus [Goodrich, D. W., Chen, Y., Scully, P. & Lee, W.-H. (1992) Cancer Res. 52, 1968-1973], these cells, now pRB+, were arrested by staurosporine in G1 phase. This arrest was accompanied by the accumulation of hypophosphorylated pRB. In both the pRB+ and pRB- cells, cyclin D1-associated kinase activities were reduced on staurosporine treatment. In contrast, cyclin-dependent kinase (CDK) 2 and cyclin E/CDK2 activities were inhibited only in pRB+ cells. Staurosporine treatment did not cause reductions in the protein levels of CDK4, cyclin D1, CDK2, or cyclin E. The CDK inhibitor proteins p21(Waf1/Cip1) and p27 (Kip1) levels increased in staurosporine-treated cells. Immunoprecipitation of CDK2, cyclin E, and p2l from staurosporine-treated pRB+ cells revealed a 2.5- to 3-fold higher ratio of p2l bound to CDK2 compared with staurosporine-treated pRB- cells. In pRB+ cells, p2l was preferentially associated with Thrl6O phosphorylated active CDK2. In pRB- cells, however, p2l was bound preferentially to the unphosphorylated, inactive form of CDK2 even though the phosphorylated form was abundant. This is the first evidence suggesting that G1 arrest by 4 nM staurosporine is dependent on a functional pRB protein. Cell cycle arrest at the pRB- dependent checkpoint may prevent activation of cyclin E/CDK2 by stabilizing its interaction with inhibitor proteins p2l and p27.
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PMID:G1 arrest and down-regulation of cyclin E/cyclin-dependent kinase 2 by the protein kinase inhibitor staurosporine are dependent on the retinoblastoma protein in the bladder carcinoma cell line 5637. 865 Jan 98

There are two points (brake-points) through which the cell must pass before it can enter cell division. Progress through each brake-point requires the presence of an active cyclin-dependent kinase (Cdk). There are specific cyclins to activate the Cdk's at different parts of the cell cycle. Activation of the cyclin-Cdk complex is tightly regulated by the phosphorylation state of the Cdk. Exogenous growth stimulators (hormones, growth factors, and cytokines) all work through an intracellular kinase cascade that drives the production and activation of early nuclear proteins that, in turn, induce transcription of the genes for cyclins, Cdk's, and other cell cycle regulators. Retinoblastoma protein regulates cell division by inactivating specific growth-promoting proteins. Therefore, mutation of the Rb gene can lead to uncontrolled cell division and thus promotion of transformed cells. p53 protein will prevent replication of cells with damaged DNA. Hence, transformed cells can only readily progress to tumors if the p53 gene is mutated in a manner that inactivates the protein product. Members of the bcl-2 family act, in homodimers and heterodimers, to shunt cells either into cell division or into apoptosis. Understanding the mechanisms by which the balance of cell cycle: apoptosis can be manipulated will lead to new ways of controlling abnormal cellular growth. Most aspects of cellular function reflect changes in phosphorylation of critical serine, threonine, and tyrosine residues on the relevant regulatory proteins. The kinases the phosphatases involved are themselves under tight control.
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PMID:The cell cycle and regulation of cancer cell growth. 865 73

Ceramide mediates the effects of extracellular agents on cellular growth, differentiation and apoptosis. In this study, we explored the mechanisms by which ceramide induces its cellular effects. In Molt-4 cells, phorbol 12-myristate 13-acetate (PMA) induced retinoblastoma gene product (Rb) phosphorylation, and ceramide inhibited this effect, suggesting an inhibitory effect of ceramide on the protein kinase C (PKC) pathway, the primary target of PMA. Molt-4 cells contained primarily PKCalpha and betaII isoforms of PKC. To determine the effects of ceramide on PKC, we developed an immunoprecipitation assay for PKCalpha activity. Exposure of Molt-4 cells to C6-ceramide resulted in a concentration and time-dependent inhibition of immunoprecipitated protein kinase Calpha (PKCalpha). Initial inhibition was observed as early as 4.5 h after treatment of cells with C6-ceramide, and the activity was completely lost by 13 h. Inhibition of PKCalpha activity was seen at concentrations of ceramide as low as 5 microM with maximal effects occurring at a concentration of 15 microM. Both C2 and C6-ceramide were inhibitory, but C2 and C6 dihydroceramides were not. Ceramide did not directly inhibit PKCalpha in vitro or modulate the levels of PKCalpha protein, suggesting that ceramide acted indirectly. Moreover, ceramide did not inhibit PMA-induced translocation of PKCalpha. Taken together, these results suggested that ceramide caused inactivation of PKCalpha. Since PKC requires phosphorylation for activity, we determined the effects of ceramide on phosphorylation of PKCalpha. C6-ceramide inhibited basal and PMA-induced phosphorylation of PKCalpha. In addition, okadaic acid, a potent phosphatase inhibitor, slightly stimulated PKC activity and blocked the effects of ceramide on PKCalpha inhibition. These results demonstrate that ceramide causes inhibition/inactivation of PKCalpha and suggest these effects of ceramide may be mediated by a protein phosphatase.
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PMID:Ceramide inactivates cellular protein kinase Calpha. 866 81

Anchorage-independent growth is a hallmark of transformed cells, but little is known of the molecular mechanisms that underlie this phenomenon. We describe here studies of cell cycle control of anchorage-independent growth induced by the ras oncogene, with the use of a somatic cell mutant fibroblast line (ER-1-2) that is specifically defective in oncogene-mediated, anchorage-independent growth. Control, nontransformed PKC3-F4 cells and ER-1-2 cells cannot proliferate in semisolid medium. Three important cell cycle events are dependent on adhesion of these cells to a substratum: phosphorylation of the retinoblastoma protein, pRB; cyclin E-dependent kinase activity; and cyclin A expression. PKC3-F4 cells that express ras (PKC3-F4/ras cells) proliferate in nonadherent cultures, and each of these three events occurs in the absence of adhesion in PKC3-F4/ras cells. Thus, ras can override the adhesion requirement of cellular functions that are necessary for cell cycle progression. ER-1-2 cells that express ras (ER-1-2/ras cells) possess hyperphosphorylated forms of pRB and cyclin E-dependent kinase activity in the absence of adhesion but remain adhesion dependent for expression of cyclin A. The adhesion dependence of pRB phosphorylation and cyclin E-dependent kinase activity is therefore dissociable from the adhesion dependence of cyclin A expression. Furthermore, ectopic expression of cyclin A is sufficient to rescue anchorage-independent growth of ER-1-2/ras cells but does not induce anchorage-independent growth of PKC3-F4 or ER-1-2 cells. However, like pRB phosphorylation and cyclin E-dependent kinase activity, the kinase activity associated with ectopically expressed cyclin A is dependent on cell adhesion, and this dependence is overcome by ras. Thus, the induction of anchorage-independent growth by ras may involve multiple signals that lead to both expression of cyclin A and activation of G1 cyclin-dependent kinase activities in the absence of cell adhesion.
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PMID:Ras induces anchorage-independent growth by subverting multiple adhesion-regulated cell cycle events. 866 52

The biological effects of c-kit ligand (stem-cell factor: SCF) on an immortalized human megakaryocytic cell line (CMK) was evaluated using methods including the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, surface marker analysis, DNA cell-cycle analysis and immunoblotting. SCF stimulated the growth of CMK cells. Incubation with SCF resulted in increased expression of IIb/IIIa platelet-related glycoprotein (gpIIb, IIIa), indicating enhanced differentiation of CMK cells. Treatment of CMK cells with SCF resulted in a decrease in the subpopulation in the G1 phase, with a reciprocal increase in those in the S phase and the G2 + M phase. Moreover, SCF significantly increased cellular expression of cyclin A, a regulatory subunit of cyclin-dependent protein kinase (CDK), and the ratio of phosphorylated/dephosphorylated retinoblastoma gene product (RB protein). These results suggest that SCF stimulates the growth and differentiation of megakaryocytic cells possibly through mechanisms related to the activation of cell-cycle-dependent serine/threonine kinase and inactivation of the nuclear tumor-suppressor gene product.
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PMID:Stem-cell factor regulates the expression of cyclin A and retinoblastoma gene product in the growth and differentiation pathway of human megakaryocytic cells. 869 43

All eukaryotes use feedback controls to order and coordinate cell cycle events. In Schizosaccharomyces pombe, several classes of checkpoint genes serve to ensure that DNA replication is complete and free of error before the onset of mitosis. Wild-type cells normally arrest upon inhibition of DNA synthesis or in response to DNA damage, although the exact mechanisms controlling this arrest are unclear. Genetic evidence in fission yeast suggests that the dependence of mitosis upon completion of DNA replication is linked to the regulation of the p34cdc2 cyclin-dependent kinase. It has been hypothesized that inhibition of DNA synthesis triggers down-regulation of p34cdc2 kinase activity, although this has never been shown biochemically. We analyzed the activity of p34cdc2 in wild-type and checkpoint-defective cells treated with a DNA synthesis inhibitor. Using standard in vitro assays we demonstrate that p34cdc2 kinase activity is maintained in wild-type cells arrested at the replication checkpoint. We also used a novel in vivo assay for p34cdc2 kinase activity, in which we expressed a fragment of the human retinoblastoma tumor suppressor protein in fission yeast. Phosphorylation of this fragment of the human retinoblastoma tumor suppressor protein is dependent on p34cdc2 kinase activity, and this activity is also maintained in cells arrested at the replication checkpoint. These data suggest that the mechanism for cell-cycle arrest in response to incomplete DNA synthesis is not dependent on the attenuation of p34cdc2 activity.
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PMID:p34cdc2 kinase activity is maintained upon activation of the replication checkpoint in Schizosaccharomyces pombe. 871 Aug 61

Considerable progress has been made toward elucidating the pathway of induction of terminal differentiation of transformed cells by hybrid polar compounds such as hexamethylene bisacetamide (HMBA). HMBA alters factors controlling G1-to-S phase transition, leading to G1 arrest and inhibition of DNA synthesis. Among the inducer-mediated changes, suppression of cyclin-dependent kinase cdk4, which may be required for phosphorylation of the retinoblastoma protein pRB and perhaps p107, is critical in the pathway of terminal differentiation. HMBA induces an increase in the level of p21 which inhibits cyclin-dependent kinase activity and, in turn, may cause cells to arrest in G1. p107 complexes with transcription factor E2F, which may alter E2F-dependent gene transcription. the relationship of the inducer-mediated changes in cyclins, cdks, cyclin-cdk inhibitors and transcription factors to the expression of differentiation-specific genes has not yet been established. The hybrid polar compounds are potent inducers of differentiation of a wide variety of transformed cells. HMBA has been shown to induce differentiation of neoplastic cells in patients. A second generation of hybrid polar compounds have been synthesized which are up to 1000 fold more potent than HMBA on a molar basis as inducers of murine erythroleukemia (MEL) cells and other transformed cells in vitro. The potential of these compounds as clinically useful inducers of differentiation of cancer cells is under study.
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PMID:Cell cycle regulatory proteins are targets for induced differentiation of transformed cells: Molecular and clinical studies employing hybrid polar compounds. 871 72

Inactivation of the cyclin-dependent kinase inhibitor p16INK4a (CDKN2/MTS1) is documented in a wide variety of cancer cell lines and tumors. We have shown that loss of p16INK4a protein expression is a common event in early stage non-small cell lung cancer (NSCLC), correlates with a significantly worse survival, and is more common in higher stage disease. One hundred NSCLC tumors from patients undergoing definitive thoracotomies at a single institution were examined for p16INK4a and retinoblastoma protein (pRB) expression. Abnormal pRB staining was identified in 15% of the tumors, whereas 51% possessed aberrant p16INK4a protein expression. Tumors with aberrant expression of p16INK4a by immunohistochemistry were associated with a significantly worse survival (P=0.04). Additionally, the inverse correlation of pRB and p16INK4a expression previously noted in lung cancer cell lines and tumors was confirmed in this large cohort of patients, with 65% of the tumors demonstrating inverse expression of pRB and p16INK4a (p=0.00019). A statistically significant increase in aberrant p16INK4a expression, as well as inverse expression of p16INK4a and pRB, was seen with increasing pathological stage of disease. These findings establish the prognostic significance (of the absence of p16INK4, in resected NSCLC and confirm the critical importance of disrupting the pathway of cyclin-dependent kinase-mediated phosphorylation of pRB in the molecular oncogenesis and progression of NSCLC.
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PMID:Rb and p16INK4a expression in resected non-small cell lung tumors. 875 4


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