Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cyclin-dependent protein kinase 5 (Cdk5) depends on the association with neuronal Cdk5 activator (Nck5a) for kinase activity. A variety of cellular proteins have been shown to undergo high affinity association with Nck5a, including three novel proteins, C42, C48, and C53 found by a yeast two-hybrid screen (Ching, Y. P., Qi, Z., and Wang, J. H. (2000) Gene 242, 285-294). The three proteins show competitive binding to Nck5a suggesting that they bind at a common site. The binding site has been mapped to a region of 26 amino acid residues (residues 145 to 170) at the N-terminal boundary of the kinase activation domain of Nck5a. This region of Nck5a contains an amphipathic alpha-helix whose hydrophobic face is involved in Cdk5 activation (Chin, K. T., Ohki, S, Tang, D., Cheng, H. C., Wang, J. H. , and Zhang, M. (1999) J. Biol. Chem. 274, 7120-7127). Several lines of evidence suggest that Nck5a interacts with the binding proteins at the hydrophilic face of the amphipathic alpha-helix. First, the Nck5a-(145-170) peptide can bind Cdk5 and Nck5a-binding proteins simultaneously. Second, the association of Nck5a-(145-170) to C48 can be markedly reduced by high ionic strength whereas the interaction between Nck5a and Cdk5 is not affected. Third, substitution of Glu(157) by glutamine in Nck5a-(145-170) abolishes the peptide's ability to bind to the three Nck5a-binding proteins without diminishing its Cdk5 binding activity.
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PMID:Identification of a common protein association region in the neuronal Cdk5 activator. 1091 92

Differentiation in the developing Drosophila eye requires synchronization of cells in the G(1) phase of the cell cycle. The roughex gene product plays a key role in this synchronization by negatively regulating cyclin A protein levels in G(1). We show here that coexpressed Roughex and cyclin A physically interact in vivo. Roughex is a nuclear protein, while cyclin A was previously shown to be exclusively cytoplasmic during interphase in the embryo. In contrast, we demonstrate that in interphase cells in the eye imaginal disk cyclin A is present in both the nucleus and the cytoplasm. In the presence of ectopic Roughex, cyclin A becomes strictly nuclear and is later degraded. Nuclear targeting of both Roughex and cyclin A under these conditions is dependent on a C-terminal nuclear localization signal in Roughex. Disruption of this signal results in cytoplasmic localization of both Roughex and cyclin A, confirming a physical interaction between these molecules. Cyclin A interacts with both Cdc2 and Cdc2c, the Drosophila Cdk2 homolog, and Roughex inhibits the histone H1 kinase activities of both cyclin A-Cdc2 and cyclin A-Cdc2c complexes in whole-cell extracts. Two-hybrid experiments suggested that the inhibition of kinase activity by Roughex results from competition with the cyclin-dependent kinase subunit for binding to cyclin A. These findings suggest that Roughex can influence the intracellular distribution of cyclin A and define Roughex as a distinct and specialized cell cycle inhibitor for cyclin A-dependent kinase activity.
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PMID:Roughex mediates G(1) arrest through a physical association with cyclin A. 1102 91

Progression through the eukaryotic cell cycle is regulated by phosphorylation, which is catalyzed by cyclin-dependent kinases. Cyclin-dependent kinases are regulated through several mechanisms, including negative regulation by p21 (variously called CAP20, Cip1, Sdi1, and WAF1). It has been proposed that multiple p21 molecules are required to inhibit cyclin-dependent kinases, such that p21 acts as a sensitive buffer of cyclin-dependent kinase activity or as an assembly factor for the complexes formed by the cyclins and cyclin-dependent kinases. Using purified, full-length proteins of known concentration (determined by absorbance) and cyclin A-Cdk2 of known activity (calibrated with staurosporine), we find that a 1:1 molar ratio of p21 to cyclin A-Cdk2 is able to inhibit Cdk2 activity both in the binary cyclin A-Cdk2 complex and in the presence of proliferating cell nuclear antigen (PCNA). Our results indicate that the mechanism of p21 inhibition of cyclin A-Cdk2 does not involve multiple molecules of bound p21.
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PMID:Stoichiometry of cyclin A-cyclin-dependent kinase 2 inhibition by p21Cip1/Waf1. 1107 34

The present study was designed to determine the spatial correlation among extent of DNA synthetic activity, expressions of G(1)/S phase cyclins, cyclin-dependent kinases (CDKs) and CIP/KIP family of CDK inhibitors (CKIs), and activities of G(1)/S phase CDKs in glomeruli and outer medullae of kidneys during the active regeneration period after ischemic injury. DNA synthetic activity was measured using [(3)H]-thymidine autoradiogram in the kidney sections. Cyclin, CDK, and CKI proteins were determined by Western blot analysis. CDK activities were determined by phosphorylation amount using specific substrate. The protein levels of cyclins (D1, D3, E, A) and activities of CDK4 and CDK2 were increased concomitant with the induction of DNA synthetic activity in outer medullae, but not in glomeruli, in adult kidneys during DNA synthetic period after ischemic injury. The p27(KIP1) protein, but not the p21(CIP1) protein, increased equally in total kidney, glomeruli, and outer medullae after ischemic injury. These results indicate that renal tubules have an active cyclin/CDK system, while glomeruli, do not have a cyclin/CDK system during active regeneration of kidneys after ischemic injury.
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PMID:Differential changes of CDK activities in glomeruli and tubules during the active DNA synthetic period after ischemic injury. 1109 88

Cyclin-dependent kinases have been implicated in the inactivation of retinoblastoma (Rb) protein and cell cycle progression. Recent studies have demonstrated that the lipid molecule ceramide is able to induce Rb hypophosphorylation leading to growth arrest and cellular senescence. In this study, we examined the underlying mechanisms of Rb hypophosphorylation and cell cycle progression utilizing the antiproliferative molecule ceramide. C6-Ceramide induced a G0/G1 arrest of the cell cycle in WI38 human diploid fibroblasts. Employing immunoprecipitation kinase assays, we found that ceramide specifically inhibited cyclin-dependent kinase CDK2, with a mild effect on CDC2 and significantly less effect on CDK4. The effect of ceramide was specific such that C6-dihydroceramide was not effective. Ceramide did not directly inhibit CDK2 in vitro but caused activation of p21, a major class of CDK-inhibitory proteins, and led to a greater association of p21 to CDK2. Using purified protein phosphatases, we showed that ceramide activated both protein phosphatase 1 and protein phosphatase 2A activities specific for CDK2 in vitro. Further, calyculin A and okadaic acid, both potent protein phosphatase inhibitors, together almost completely reversed the effects of ceramide on CDK2 inhibition. Taken together, these results demonstrate a dual mechanism by which ceramide inhibits the cell cycle. Ceramide causes an increase in p21 association with CDK2 and through activation of protein phosphatases selectively regulates CDK2. These events may lead to activation of Rb protein and subsequent cell cycle arrest.
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PMID:Regulation of cyclin-dependent kinase 2 activity by ceramide. 1111 37

Normal cell proliferation is closely regulated by proteins called cyclins. One of these, cyclin D1, in combination with its corresponding cyclin-dependent kinase (cdk), is essential for G(1)/S phase transition. Cyclin/cdk complexes are generally inhibited by cyclin-dependent kinase inhibitors(ckis), some of which are induced by wild-type p53. The aims of this study were: to investigate levels of cyclin D1 expression in transitional cell carcinoma (TCC) of the bladder; to correlate these results with data concerning the expression of p53, waf1, pRb and Ki67; and to determine whether cyclin D1 expression could predict clinical outcome. Paraffin-sections from 150 newly diagnosed bladder tumours (Ta/T1 = 97; T2-T4 = 53) were stained for cyclin D1 using immunohistochemistry and a cyclin D1 index assigned. These results were correlated with data relating to the expression of p53 and waf1 by the same tumours. A representative subset of 54 tumours (Ta/T1 = 28; T2-T4 = 26) was also stained for Ki67 and 55 were stained for pRb. The clinical course of each patient was recorded and multivariate analyses of risk factors for tumour recurrence, stage progression and overall survival were performed. Positive staining for cyclin D1 was found in 83% of tumours. The staining pattern varied between tumours with nuclear, cytoplasmic or a combination of the two evident in different tumours. 89% of Ta/T1 and 74% of T2-T4 tumours showed nuclear staining with or without cytoplasmic staining. The median value for cyclin D1 staining was significantly higher in Ta/T1 tumours (41%) compared with T2-T4 tumours (8%, P< 0.005) with 26% of muscle-invasive tumours demonstrating absent staining. In addition, the median value for cyclin D1 staining was significantly higher in G1/G2 tumours (43%) compared with G3 tumours (14%, P< 0.005). There was a significant positive correlation between expression of cyclin D1 and waf1 expression (P< 0.0001) as well as pRb expression but not between cyclin D1 expression and expression of p53. Ki67 expression was significantly associated with increasing tumour stage (P< 0.005) and histological grade (P< 0.05) but did not correlate with cyclin D1 expression. A cyclin D1 index > or = 8% was associated with significantly better survival in those patients with muscle-invasive disease (T2-T4). In addition, there was a significantly higher progression rate for those patients with Ta/T1 disease whose tumours demonstrated cytoplasmic cyclin D1 staining. These results indicate that cyclin D1 expression is significantly higher in low-stage, well differentiated bladder tumours and strongly correlates with waf1 expression. In a multivariate analysis, cyclin D1 expression is an independent prognostic indicator of survival in those patients with muscle-invasive disease.
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PMID:Cyclin D1 expression in transitional cell carcinoma of the bladder: correlation with p53, waf1, pRb and Ki67. 1116 87

The potential antiproliferative effects of interferon-alpha (IFN-alpha) in the treatment of hepatocellular carcinoma (HCC) are controversial, and the growth inhibitory mechanisms remain poorly understood. Therefore, the current study was designed to delineate the molecular mechanisms responsible for direct antiproliferative actions of IFN-alpha in HCC cells. IFN-alpha receptor expression and signal transduction were examined by RT-PCR, immunoprecipitation, Western analysis, and transient transactivation assays. Effects of IFN-alpha on cell growth and cell-cycle distribution were evaluated based on cell numbers and flow cytometry. Composition and activity of cyclin-dependent kinase complexes were determined by immunoblotting and histone-H1-kinase assays. Expression of IFN-alpha receptors was found in all 3 HCC cell lines. IFN-alpha binding initiated phosphorylation of Jak1 and Tyk2 kinases leading to Stat1/Stat2 activation, nuclear translocation, and transactivation of an ISRE-luciferase reporter gene construct. IFN-alpha treatment resulted in a time- and dose-dependent reduction of proliferation. Cell cycle analysis of G1-synchronized, IFN-alpha-treated HCC cells revealed a substantial delay in S-phase progression but no alteration of G1/S-phase transition or evidence of apoptotic cell death. Reflecting the time course of S-phase accumulation, cell cycle-dependent induction of Cyclin A and Cyclin B was impaired, resulting in reduced activity of Cdk2 and Cdc2 kinases. Furthermore, Cdc25C was selectively down-regulated. IFN-alpha treatment inhibits growth of HCC cells by specifically delaying S-phase progression, most likely because of inhibition of Cyclin A induction, resulting in decreased activity of the associated Cdk2 and Cdc2 kinases.
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PMID:Interferon-alpha delays S-phase progression in human hepatocellular carcinoma cells via inhibition of specific cyclin-dependent kinases. 1117 36

Cyclin D family members are cellular protooncogenes, and their viral homologues in the Kaposi's sarcoma-associated herpesvirus (KSHV, human herpesvirus type 8 [HHV-8]) and the closely related Herpesvirus saimiri have been implicated as putative cofactors of viral transformation and pathogenesis. KSHV is regularly found in Kaposi's sarcoma and in the primary effusion B cell lymphoma and Castleman's disease associated with immunosuppression and AIDS. H. saimiri strain C488 transforms human and marmoset T cells in vitro and causes polyclonal T cell lymphoma in New World monkeys. The viral cyclins stimulate cell cycle progression of quiescent fibroblasts, and they form active cyclin-dependent kinase (CDK)6 complexes of broad substrate specificity that can resist and downregulate cellular CDK inhibitors. This study shows that the viral cyclin of H. saimiri strain C488 is not required for viral replication, T cell transformation, and pathogenicity in New World primates.
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PMID:Independence of herpesvirus-induced T cell lymphoma from viral cyclin D homologue. 1123 94

Eukaryotic cell division is regulated by cyclins, cyclin-dependent kinases (CDK), and cyclin-dependent kinase inhibitors (CKI). Genes encoding these proteins are mutated or deleted in many types of cancer. For example, 20%-30% of B-lineage acute lymphoblastic leukemias (ALL) have deletions in the CKI known as INK4a. The contribution of INK4a deletions to the progression of B-lineage ALL is uncertain, partially due to a paucity of data on expression in normal B-cell precursors. We therefore conducted a comparative analysis of normal and leukemic human B-cell development for the expression of cyclins, CDK, and CKI. Specific stages of human B-cell development from normal bone marrow were purified by fluorescence-activated cell sorting. The sorted populations and B-lineage ALL cell lines (BLIN-1, 2, 3, 4) were examined for expression of cyclins, CDK, and CKI by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting.RT-PCR analysis showed that cyclin D2, cyclin D3, CDK4, and CDK6 were ubiquitously expressed in normal B-cell development and in the BLIN ALL cell lines. The p19(INK4d) CKI was the most commonly expressed member of the INK4 family, whereas p16(INK4a) was more weakly and variably expressed. Expression of the p57(KIP2) CKI varied as a function of the stage of B-cell development. Analysis of normal B-cell precursors by Western blotting indicated that CDK4, CDK6, p19(INK4d), and p57(KIP2) were expressed, whereas p16(INK4a) was not detected. Cyclin D/CDK expression in normal and leukemic human B-cell precursors is similar to expression of these proteins in human and murine mature B cells. In contrast, the ubiquitous expression of p19(INK4d) has not been previously described in human or murine B-lineage cells. Our results suggest that loss of INK4a may only minimally contribute to tumor cell progression in B-lineage ALL, since expression of INK4d could provide a compensatory function as a cyclin-dependent kinase inhibitor.
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PMID:Novel expression of cyclin-dependent kinase inhibitors in human B-cell precursors. 1130 Nov 89

DNA damage produces delayed mitosis (G2/M delay) in proliferating cells, and shortening the delay sensitizes human malignant glioma and medulloblastoma cells to cytotoxic chemotherapy. Although activation of the cyclin-dependent kinase CDC2 mediates G2/M transition in all tumor cells studied to date, regulation of CDC2 varies between tumor types. Persistent hyperphosphorylation of kinase and reduced cyclin expression have been implicated as mediators of treatment-induced G2 delay in different tumor models. To evaluate regulation of G2/M transition in human brain tumors, we studied the expression and/or activity of CDC2 kinase and cyclins A and B1 in U-251 MG and DAOY medulloblastoma cells after their treatment with camptothecin (CPT). Synchronized cells were treated during S phase, then harvested at predetermined intervals for evaluation of cell cycle kinetics, kinase activity mRNA, and protein expression. CPT produced G2 delay associated with decreased CDC2 kinase activity and cyclin B1 expression. Kinase activity was associated with CDC2 bound to cyclin B1, not cyclin A, in both cell lines. Cyclin A mRNA and protein expression were reduced after CPT treatment; however, decreased protein expression was short lived and moderate in the glioma and primitive neuroectodermal tumor/medulloblastoma cells, respectively. We conclude that G2 delay is a common response of brain tumor cells to chemotherapy with topoisomerase I inhibitors and that a mechanism of this delay may be reduced expression of cyclin B1.
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PMID:Decreased cyclin B1 expression contributes to G2 delay in human brain tumor cells after treatment with camptothecin. 1130 12


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