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)

The cell cycle is governed by a family of cyclin-dependent kinases (Cdks). Cdk2 forms a functional complex with cyclin E and plays a pivotal role in the regulation of G1/S transition. Cdk2 activity is negatively regulated by interactions with inhibitors. p27Kip1, one of the most potent inhibitors of Cdk2, was recently identified as a powerful negative prognostic marker in non-small cell lung cancer as well as in colorectal and breast cancer. In the present study, the expression of p27 and Ki-67 antigen in nonneoplastic and cancerous lung tissues was determined by immunohistochemistry. After establishing that the antibody-measured p27 labeling index was a good reflection of the level of p27 expression measured by Western blotting, we show that p27 labeling index is decreased in cancerous lung tissues, compared with nonneoplastic lung tissues, and exhibits a significant inverse relation to the proliferation marker Ki-67 antigen, detected with monoclonal antibody MIB-1. Consistent with these data, all cancerous lung tissues showed enhanced degradation activity of p27 compared with nonneoplastic lung tissues and, in addition, increased levels of the phosphorylated form of Cdk2, as determined with Western blot analysis. The H1 histone kinase activity associated with Cdk2 was also increased in non-small cell lung cancers. Statistical analysis showed that proliferative activity as measured by MIB-1 labeling index was highly correlated with Cdk2 activity (r = 0.767, P < 0.0015). These results suggest that p27 and Cdk2 may play an important role in the proliferation of non-small cell cancer.
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PMID:Role of p27Kip1 and cyclin-dependent kinase 2 in the proliferation of non-small cell lung cancer. 970 10

Loss-of-function mutations of p16(INK4a) have been identified in a large number of human tumors. An established biochemical function of p16 is its ability to specifically inhibit cyclin D-dependent kinases in vitro, and this inhibition is believed to be the cause of the p16-mediated G1 cell cycle arrest after reintroduction of p16 into p16-deficient tumor cells. However, a mutant of Cdk4, Cdk4(N158), designed to specifically inhibit cyclin D-dependent kinases through dominant negative interference, was unable to arrest the cell cycle of the same cells (S. van den Heuvel and E. Harlow, Science 262:2050-2054, 1993). In this study, we determined functional differences between p16 and Cdk4(N158). We show that p16 and Cdk4(N158) inhibit the kinase activity of cellular cyclin D1 complexes through different mechanisms. p16 dissociated cyclin D1-Cdk4 complexes with the release of bound p27(KIP1), while Cdk4(N158) formed complexes with cyclin D1 and p27. In cells induced to overexpress p16, a higher portion of cellular p27 formed complexes with cyclin E-Cdk2, and Cdk2-associated kinase activities were correspondingly inhibited. Cells engineered to express moderately elevated levels of cyclin E became resistant to p16-mediated growth suppression. These results demonstrate that inhibition of cyclin D-dependent kinase activity may not be sufficient to cause G1 arrest in actively proliferating tumor cells. Inhibition of cyclin E-dependent kinases is required in p16-mediated growth suppression.
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PMID:Requirement of cyclin E-Cdk2 inhibition in p16(INK4a)-mediated growth suppression. 971 Jun 13

Terminal differentiation of many cell lineages involves an exit from the mitotic cycle and entry into, and maintenance of, a permanent state of G1 arrest. We found that during terminal differentiation of mouse 3T3-L1 preadipocytes, the level of cyclin-dependent kinase 4 (CDK4) remained constant, but the subunit composition of the CDK4 complex underwent a dynamic rearrangement. As 3T3-L1 cells differentiated, the levels of cyclin D1 and cyclin D1-CDK4 complexes declined to negligible levels. Meanwhile, cyclins D2 and D3 levels and their associations with CDK4 increased transiently and persistently, respectively, with cyclin D3 becoming the predominant cyclin partner of CDK4 in mature adipocytes. At least five CDK inhibitors are expressed during the differentiation program of 3T3-L1 cells. Both p15INK4b and p16INK4a continuously declined to undetectable levels immediately after differentiation induction. p21 was transiently expressed during the exit of 3T3-L1 cells from mitotic clonal expansion and then decreased to undetectable levels in mature adipocytes. The level of p27KiP1 and p27-CDK4 complexes remain high during differentiation and in mature adipocytes. Distinctly, there is a remarkable induction of p18INK4c mRNA and protein that was not seen in the closely related nondifferentiating 3T3-C2 cell line, suggesting that p18 induction in 3T3-L1 cells is related to cell differentiation, not cell cycle arrest. The pRb kinase activity of cyclin D3 and CDK4 was not detected in quiescent 3T3-L1 cells and was then induced as the cells entered the mitotic clonal expansion phase. Unexpectedly, cyclin D3 and CDK4 pRb kinase activity remained high after 3T3-L1 cells completed their mitotic division and was still readily detectable in mature adipocytes. Our study reveals an active regulation, rather than passive inhibition, of CDK4 activity during adipocyte differentiation. Two central features of this complex regulation are switching of activating cyclin D subunits and concurrent binding by the p18 and p27 CDK inhibitors.
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PMID:Regulation of cyclin-dependent kinase 4 during adipogenesis involves switching of cyclin D subunits and concurrent binding of p18INK4c and p27Kip1. 971 77

An important question in the cell cycle field is how cyclin-dependent kinases (cdks) target their substrates. We have studied the role of a conserved hydrophobic patch on the surface of cyclin A in substrate recognition by cyclin A-cdk2. This hydrophobic patch is approximately 35A away from the active site of cdk2 and contains the MRAIL sequence conserved among a number of mammalian cyclins. In the x-ray structure of cyclin A-cdk2-p27, this hydrophobic patch contacts the RNLFG sequence in p27 that is common to a number of substrates and inhibitors of mammalian cdks. We find that mutation of this hydrophobic patch on cyclin A eliminates binding to proteins containing RXL motifs without affecting binding to cdk2. This docking site is critical for cyclin A-cdk2 phosphorylation of substrates containing RXL motifs, but not for phosphorylation of histone H1. Impaired substrate binding by the cyclin is the cause of the defect in RXL substrate phosphorylation, because phosphorylation can be rescued by restoring a cyclin A-substrate interaction in a heterologous manner. In addition, the conserved hydrophobic patch is important for cyclin A function in cells, contributing to cyclin A's ability to drive cells out of the G1 phase of the cell cycle. Thus, we define a mechanism by which cyclins can recruit substrates to cdks, and our results support the notion that a high local concentration of substrate provided by a protein-protein interaction distant from the active site is critical for phosphorylation by cdks.
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PMID:Substrate recruitment to cyclin-dependent kinase 2 by a multipurpose docking site on cyclin A. 972 24

Oligodendrocyte differentiation is a complex process believed to be controlled by an intrinsic mechanism associated with cell-cycle arrest. Recently, the cell-cycle inhibitor protein p27 Kip1 has been proposed as a key element in causing growth arrest of oligodendrocyte precursor cells. To investigate the effects of p27 upon oligodendrocyte cell development, we have introduced the p27 cDNA in oligodendrocyte progenitor cells using an adenovirus vector. Progenitor cells normally express low levels of p27. After adenoviral infection and p27 overexpression, progenitor cells were able to undergo cell-cycle arrest, even in the presence of strong mitogens. The effects of p27 were shown to be directly upon cyclin-dependent kinase-2 (CDK2), the protein kinase complex responsible for G1/S transition, as immunodepletion of oligodendrocyte extracts of p27 protein resulted in the activation of CDK2 activity. However, cells that became growth arrested owing to infection with p27 adenovirus did not display conventional oligodendrocyte differentiation markers, such as O4 or O1. Taken together, these data provide mechanistic evidence indicating that p27 is primarily involved in oligodendroglial progenitor proliferation by inhibiting CDK2 activity and inducing oligodendrocyte cell-cycle arrest.
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PMID:Ectopic expression of p27Kip1 in oligodendrocyte progenitor cells results in cell-cycle growth arrest. 973 77

The suspension of keratinocytes containing episomal forms of the human papillomavirus (HPV)-31 genome in semisolid medium results in the induction of viral late functions. In this study, the suspension in semisolid medium was used to analyze how HPV deregulates the process of cell cycle exit during differentiation. In cells that contain the entire HPV-31 genome, induction of late protein synthesis was found to be linked with the expression of cyclin A. Consistent with analyses in organotypic rafts, the expression of the high-risk E7 oncoprotein alone was sufficient to retain cyclin A expression during suspension-induced differentiation. The cyclin-dependent kinase inhibitors (CKIs) p27 and p57 were found to be up-regulated in normal keratinocytes, as well as in the lines that express the HPV oncoproteins. The up-regulation of these CKIs is coincident with the inhibition of cyclin/cdk activity in normal keratinocytes. Cells expressing E7 were found to retain significant cdk2-associated kinase activity, although it was partially inhibited, coincident with CKI induction. When the phosphorylation state of Rb was examined during differentiation, cells expressing E7 retained phosphorylated forms of Rb, whereas Rb in normal keratinocytes was hypophosphorylated. As previously reported, E7-expressing cells were found to contain less Rb protein than normal keratinocytes. Interestingly, the Rb levels decreased during normal keratinocyte differentiation, and this differentiation-dependent reduction in Rb levels was enhanced by EG and E7 expression. This study identified proteins that may be critical for cell cycle regulation during normal epithelial differentiation and demonstrated that HPV oncoproteins alter their activities.
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PMID:Human papillomavirus oncoproteins alter differentiation-dependent cell cycle exit on suspension in semisolid medium. 977 Apr 16

We show here that the adenovirus E1A oncoprotein prevents growth arrest by the CDK2 inhibitor p27(Kip1) (p27) in rodent fibroblasts. However, E1A neither binds p27 nor prevents inhibition of CDK2 complexes in vivo. In contrast, the amount of free p27 available to inhibit cyclin E/CDK2 is increased in E1A-expressing cells, owing to reduced expression of cyclins D1 and D3. Moreover, E1A allows cell proliferation in the presence of supraphysiological p27 levels, while c-Myc, known to induce a cellular p27-inhibitory activity, is only effective against physiological p27 concentrations. E1A also bypasses G1 arrest by roscovitine, a chemical inhibitor of CDK2. Altogether, these findings imply that E1A can act downstream of p27 and CDK2. Retinoblastoma (pRb)-family proteins are known CDK substrates; as expected, association of E1A with these proteins (but not with p300/CBP) is required for E1A to prevent growth arrest by either p27 or the CDK4/6 inhibitor p16(INK4a). Bypassing CDK2 inhibition requires an additional function of E1A: the mutant E1A Delta26-35 does not overcome p27-induced arrest, while it binds pRb-family proteins, prevents p16-induced arrest, and alleviates pRb-mediated repression of E2F-1 transcriptional activity (although E1A Delta26-35 fails to restore expression of E2F-regulated genes in p27-arrested cells). We propose that besides the pRb family, E1A targets specific effector(s) of CDK2 in G1-S control.
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PMID:A novel function of adenovirus E1A is required to overcome growth arrest by the CDK2 inhibitor p27(Kip1). 977 42

Previous reports have indicated that DNA-damaging treatments including certain anticancer therapeutics cause death of postmitotic nerve cells both in vitro and in vivo. Accordingly, it has become important to understand the signaling events that control this process. We recently hypothesized that certain cell cycle molecules may play an important role in neuronal death signaling evoked by DNA damage. Consequently, we examined whether cyclin-dependent kinase inhibitors (CKIs) and dominant-negative (DN) cyclin-dependent kinases (CDK) protect sympathetic and cortical neurons against DNA-damaging conditions. We show that Sindbis virus-induced expression of CKIs p16(ink4), p21(waf/cip1), and p27(kip1), as well as DN-Cdk4 and 6, but not DN-Cdk2 or 3, protect sympathetic neurons against UV irradiation- and AraC-induced death. We also demonstrate that the CKIs p16 and p27 as well as DN-Cdk4 and 6 but not DN-Cdk2 or 3 protect cortical neurons from the DNA damaging agent camptothecin. Finally, in consonance with our hypothesis and these results, cyclin D1-associated kinase activity is rapidly and highly elevated in cortical neurons upon camptothecin treatment. These results suggest that postmitotic neurons may utilize Cdk4 and 6, signals that normally control proliferation, to mediate death signaling resulting from DNA-damaging conditions.
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PMID:Cyclin-dependent kinases participate in death of neurons evoked by DNA-damaging agents. 978 55

Genistein, the principal isoflavonoid in soybeans, is reported to inhibit cell cycle progression, but the molecular basis for this event is unknown. Here we show that genistein inhibits DNA synthesis and suppresses cyclin E-associated cyclin-dependent kinase-2 (CDK2) activity when quiescent BALB/c 3T3 fibroblasts are stimulated with serum. In these cells, a CDK2 inhibitor, p21(Cip1/WAF1), is markedly increased by genistein, but another CDK2 inhibitor, p27(Kip1), is not increased. In exponentially growing BALB/c 3T3 cells, genistein inhibits proliferation of the cells in a dose-dependent manner. Flow cytometric analysis and measurement of DNA synthesis indicate that genistein blocks the G1 to S phase transition of these cells, which is concomitant with G2-M arrest. In mouse B16-F1 melanoma cells, genistein also blocks the transition of G1 to S phase without arresting at G2-M at low doses. In both cell lines, genistein suppresses cyclin E/CDK2 activity and induces p21(Cip1/WAF1) expression. These results suggest that genistein affects the restriction point control of the cell cycle by inducing p21(Cip1/WAF1) expression in mouse fibroblast and melanoma cells.
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PMID:Genistein induces p21(Cip1/WAF1) expression and blocks the G1 to S phase transition in mouse fibroblast and melanoma cells. 979 Sep 49

We studied spheroid (multicellular aggregate) formation by hepatocytes and the expression of liver-specific functions such as albumin secretion when hepatocytes were cultured with various extracellular matrices. Hepatocytes cultured on Primaria(R) and poly-D-lysine coated dishes, and in the presence of a polymer, Eudragit, formed spheroids, and they also exhibited higher liver-specific functions and poor growth compared to monolayer cultures. The results indicated that the cell morphological change and cell-cell interaction caused by the spheroid formation were key factors promoting the expression of the liver-specific functions. To elucidate the mechanism underlying the poor growth in spheroids, we examined the HGF signaling pathway. Phosphorylation and down-regulation of the HGF receptor (c-Met proto-oncogene product) were observed for the cells from both monolayer and spheroid cultures, but Ras activation was partly blocked in spheroids. Furthermore, we found that CDK inhibitors, p21 and p27, were highly expressed in spheroids. These results suggested that the reduced Ras signaling and high expression of the CDK inhibitors might cause the lower growth in spheroids. We then examined the relationship between liver-enriched transcription factors (C/EBPalpha and beta) and liver-specific functions. The results revealed that the high expression of C/EBPalpha was maintained during cultures when hepatocytes formed spheroids. Antisense oligonucleotides of C/EBPalpha repressed albumin secretion and the expression of p21, suggesting that the transcription factor, C/EBPalpha, may play a crucial role in the growth and differentiation of hepatocytes in spheroids.
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PMID:Differentiation and proliferation of primary rat hepatocytes cultured as spheroids. 979 21


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