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

UCN-01 (7-hydroxyl-staurosporine) was originally isolated as a Ca2+- and phospholipid-dependent protein kinase C selective inhibitor and now is being developed as an anticancer agent. Results from our and other laboratories have suggested that UCN-01 induces preferential G1-phase accumulation in several human tumor cell lines tested. To elucidate this mechanism, we examined the effects of UCN-01 on several cell cycle-regulatory proteins critical for G1-S-phase transition in p53-mutated human epidermoid carcinoma A431 cells. After 24 h exposure at around 50% growth-inhibitory concentrations (IC50s), 260 and 520 nM, UCN-01 induced the accumulation of pRb (the dephosphorylated retinoblastoma protein form). The protein expression of cyclin A but not cyclin E was markedly reduced and that of cyclin D1 was partially reduced under the same condition. UCN-01 also showed the concentration-dependent inhibitions of the activity of cyclin-dependent kinase 2 (CDK2) using histone H1 and pRb as substrates in vitro (IC50, 530 and 640 nM, respectively). In addition, CDK2 activities of the cells pretreated with UCN-01 for 24 h at 260 and 520 nM were markedly inhibited, giving IC50s of far less than 260 nM. When the same cell lysates were analyzed by Western blotting for CDK2, the lower band (e.g., active and phosphorylated CDK2) was remarkably reduced, in accordance with the reduced activity. Furthermore, UCN-01 induced the expression of the CDK inhibitor p21 protein and its complex formation with CDK2 after 24 h exposure at 260 and 520 nM, whereas the expression level was very low or undetectable in untreated or DNA-damaged cells. The increase of p21 mRNA levels was also induced under the same condition. UCN-01 further increased luciferase activities in A431 cells transiently transfected with p21 promoter-luciferase reporter plasmid after 24 h exposure at 260 and 520 nM. UCN-01 also increased the expression of the CDK inhibitor p27 protein after 24 h exposure at 260 and 520 nM. These results suggest that G1-phase accumulation induced by UCN-01 is associated with dephosphorylation of Rb and CDK2 proteins as well as induction of CDK inhibitors p21 and p27.
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PMID:G1 phase accumulation induced by UCN-01 is associated with dephosphorylation of Rb and CDK2 proteins as well as induction of CDK inhibitor p21/Cip1/WAF1/Sdi1 in p53-mutated human epidermoid carcinoma A431 cells. 910 51

A large fraction of non-Hodgkin's lymphomas (NHLs) accumulate a wild-type form of the p53 tumor suppressor protein at the nuclear level. In normal cells, p53 induction is associated with a temporary cell growth arrest at the G1-S boundary of the cell cycle. This activity of p53 as a G1 checkpoint molecule is strictly dependent on its ability to induce the transcription of the inhibitor of the cyclin dependent kinase, p21. To verify the functionality of the wild-type p53 protein accumulated in NHL cells, 70 cases were comparatively analyzed for p53 and p21 expression and status of the respective genes. Overexpression of the wt p53 protein was associated with the accumulation of p21, indicating that p53 is functional with respect to p21 induction in these tumors. The coaccumulation of p53 with Ki-67 antigen indicates that wt p53-positive cells and p21-positive cells, as well, are actively proliferative elements, supporting the notion that p53-induced, p21-mediated growth arrest is somehow overridden in NHL cells. No p21 mutation or particular allele variant was shown to correlate with p21 protein accumulation, thus excluding a role for p21 structural abnormalities. Taken together, our data suggest the existence in NHL of a peculiar mechanism of functional inactivation of the p53 G1 checkpoint pathway occurring downstream of the CDK inhibitor p21.
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PMID:Human non-Hodgkin's lymphomas overexpress a wild-type form of p53 which is a functional transcriptional activator of the cyclin-dependent kinase inhibitor p21. 911 98

The preceding paper (Cha, H. H., Cram, E. J., Wang, E. C., Huang, A. J., Kasler, H. G., and Firestone, G. L. (1998) J. Biol. Chem. 273, 0000-0000(478563) defined a glucocorticoid responsive region within teh promoter of the p21 CDK inhibitor gene that contains a putative DNA-binding site for the transcription factor CCAAT/ enhancer binding protein-alpha (C/EBP alpha). Wild type rat BDS1 hepatoma cells as well as as4 hepatoma cells, which express antisense sequences to C/EBP alpha and ablate its protein production, were utilized to investigate the role of this transcription factor in the glucocorticoid regulation of p21 gene expression. The stimulation of p21 protein levels and promoter activity, as well as inhibition of CDK2-mediated retinoblastoma protein phosphorylation, by the synthetic glucocorticoid, dexamethasone, required the expression of C/EBP alpha. Overexpression of C/EBP alpha in as4 cells rescued the dexamethasone responsiveness of the p21 promoter. Site-directed mutagenesis of the p21 promoter revealed that dexamethasone stimulation of p21 promoter activity required the C/EBP consensus DNA-binding site. Furthermore, in glucocorticoid receptor-defective EDR1 hepatoma cells, dexamethasone failed to stimulate C/EBP alpha and p21 protein expression and promoter activities. Our results have established a functional link between the glucocorticoid receptor signaling pathway that mediates a G1 cell cycle arrest of rat hepatoma cells and the transcriptional control of p21 by a cascade that requires the steroid induction of C/EBP alpha gene expression.
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PMID:Role of the CCAAT/enhancer binding protein-alpha transcription factor in the glucocorticoid stimulation of p21waf1/cip1 gene promoter activity in growth-arrested rat hepatoma cells. 944 37

The nuclear transcription factor, CCAAT/enhancer binding protein alpha (C/EBPalpha) is expressed at high levels in the liver and inhibits growth in cultured cells. We have tested the correlation between C/EBPalpha levels, cell cycle proteins and hepatocyte proliferation in old and young animals as an in vivo model system in which the proliferative response to partial hepatectomy (PH) has been shown to be reduced and delayed in old animals. Here we present evidence that the expression of C/EBPalpha in old rats (24 months) differs from its expression in young animals (6-10 months) during liver regeneration. Induction of proliferating cell nuclear antigen (PCNA), a marker of DNA synthesis, occurs at 24 h after PH in young rats but is delayed and reduced in old animals. Induction of the mitotic-specific protein, cdc2 p34, is 3-4-fold less in regenerating liver of old rats than in the liver of young animals, confirming the reduced proliferative response in old animals. In young rats, the normal regenerative response involves a reduction of 3-4-fold in the levels of C/EBPalpha protein at 3-24 h. In old animals, C/EBPalpha is not reduced within 24 h after PH, but a decrease of C/EBPalpha protein levels can be detected at 72 h after PH. Induction of C/EBPbeta, another member of the C/EBP family, is delayed in old animals. Changes in the expression of C/EBP proteins are accompanied by alteration of the CDK inhibitor, p21, which is also decreased in young rats after PH, but in old animals remains unchanged. High levels of p21 protein in older animals correlate with the lack of cdk2 activation. We suggest that the failure to reduce the amount of C/EBPalpha and p21 is a critical event in the dysregulation of hepatocyte proliferation in old animals following PH.
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PMID:Regenerating livers of old rats contain high levels of C/EBPalpha that correlate with altered expression of cell cycle associated proteins. 962 32

Activation of the p53-mediated DNA damage response induces either G1 cell cycle arrest or apoptosis. The G1 cell cycle arrest is in part caused by the p53-dependent transcriptional activation of the CDK inhibitor, p21(Cip1/Waf1). We report here that human p21 protein is rapidly induced but selectively cleaved during the apoptotic response to gamma-irradiation. Such an event occurred early, well before the morphological appearance of apoptosis. Ectopical expression of p53 in tumor cells alone could induce p21 expression, followed by p21 cleavage and apoptosis. The cleavage of p21 could be reproduced in extracts prepared from irradiated cells or by recombinant caspase-3, suggesting that a caspase-like activity is responsible for this cleavage. p21 binds independently to both CDK2 and proliferation cell nuclear antigen (PCNA). Our studies indicated that p21 cleavage by the caspase-like activity specifically abolished its interaction with PCNA, suggesting that p21 cleavage may interfere with normal PCNA-dependent repair. Our data suggest that p21 may serve as a critical checkpoint regulator for both cell cycle arrest and apoptosis during the p53-mediated DNA damage response. Manipulation of the checkpoint regulators involved in cell cycle arrest and apoptosis may thus provide a novel strategy to cancer therapy.
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PMID:Cleavage of CDK inhibitor p21(Cip1/Waf1) by caspases is an early event during DNA damage-induced apoptosis. 966 8

We have investigated the effect of the endogenous genotoxin malondialdehyde (MDA) on cell cycle kinetics and the expression and biochemical activity of several cell cycle regulatory proteins. MDA treatment of two human cell lines (RKO and H1299) resulted in a 3- to 6-fold elevation in the levels of the major detectable MDA-DNA adduct, M1G-dR. The increase in M1G-dR was accompanied by irreversible cell cycle arrest, elevation in p53 and p21 protein levels, and inhibition of cyclin E- and cyclin B-associated kinase activities. The decrease in cyclin E- and cyclin B-dependent kinase activities was caused by increased p21 and decreased cdc2 levels, respectively. Comparable levels of p21 induction were observed in RKO (wild-type p53) and H1299 (p53-null) cells. Thus, MDA was able to engage cell cycle checkpoint function in human cell lines when used at concentrations that produce M1G-dR levels of the same magnitude found in human tissues.
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PMID:Induction of cell cycle arrest by the endogenous product of lipid peroxidation, malondialdehyde. 968 89

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) inhibits 17beta-estradiol (E2) mammary tumor growth in rodents and in MCF-7 human breast cancer cells; however, the cell cycle genes/proteins which are inhibited have not been determined. Initial studies showed that treatment of MCF-7 cells with 10 nM E2 significantly increased cyclin D1 (protein and mRNA), cdk2- and cdk4-dependent kinase activities, and hyperphosphorylation of retinoblastoma (RB) protein. In contrast to results of recent studies (M. D. Planas-Silva and R. A. Weinberg, 1997, Mol. Cell. Biol. 17, 4059-4069), E2 induced dissociation of both cdk2 and cdk4 proteins from the p21 protein complex and significantly increased cdk7-dependent kinase activity. Treatment of MCF-7 cells with E2 also induced cdc25A phosphatase protein, which was accompanied by increased cdk2 and cdk4 proteins containing unphosphorylated tyrosine residues. Although TCDD alone has minimal effects on cell cycle proteins/enzymes, several E2-induced responses were significantly inhibited in MCF-7 cells cotreated with E2 plus TCDD. For example, TCDD significantly inhibited E2-induced hyperphosphorylation of RB, cyclin D1 protein, and cdk2-, cdk4-, and cdk7-dependent kinase activities. Inhibition of E2-induced cdk4-dependent kinase activity by TCDD may be related to the parallel decrease of E2-induced cyclin D1 protein, and inhibition of induced cdk2- and cdk4-dependent kinase activities may be due to significantly increased p21 levels in cells cotreated with TCDD plus E2. These results demonstrate that the antiestrogenic activity of TCDD is due to downregulation of several E2-induced cell cycle proteins/activities and this illustrates the complex cross talk between the aryl hydrocarbon and the E2 receptor signaling pathways.
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PMID:Aryl hydrocarbon receptor-mediated antiestrogenicity in MCF-7 cells: modulation of hormone-induced cell cycle enzymes. 970 14

We have examined the effect of neutralizing TGF-beta antibodies on cisplatin-mediated cytotoxicity against MDA-231 human breast tumor cell spheroids. These tridimensional in vitro systems have been shown to recapitulate the drug sensitivity pattern of tumor cells in vivo. MDA-231 tumor cell spheroids exhibit higher protein levels of the cyclin-dependent kinase (Cdk) inhibitors p21 and p27 and >10-fold lower Cdk2 activity compared to adherent cell monolayers, as well as pRb hypophosphorylation, a predominant G1 population, and a cisplatin 1-h IC50 of approximately 100 microM. Treatment of MDA-231 cells in monolayer with cisplatin for 1 h, subsequently grown as spheroids, increased steady-state TGF-beta1 mRNA levels, secretion of active TGF-beta, cellular Cdk2 activity, pRb phosphorylation, and p21 protein levels, while downregulating p27. Accumulation of cells in G2M and progression into S were noted 48 h after treatment with 100 microM cisplatin. We tested whether drug-induced upregulation of TGF-beta1 and p21, perhaps by preventing cell cycle progression, were protective mechanisms against drug-mediated toxicity by using neutralizing anti-TGF-beta antibodies. Anti-TGF-beta antibodies diminished the induction of p21, enhanced the activation of Cdk2, and facilitated progression into S and G2M following cisplatin treatment. This resulted in a >twofold enhancement of drug-induced DNA fragmentation and a shift in the cisplatin 1-h IC50 from 100 to <10 microM. These data suggest that tumor cell TGF-beta1 may protect from DNA damage and that postchemotherapy administration of TGF-beta inhibitors may facilitate progression beyond G1/S, potentially increasing the efficacy of cytotoxic chemotherapy.
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PMID:Blockade of tumor cell transforming growth factor-betas enhances cell cycle progression and sensitizes human breast carcinoma cells to cytotoxic chemotherapy. 985 76

This study provides the first report that the same cytokine (interleukin-1 (IL-1)) can induce opposite effects on cyclin-dependent kinases (Cdks) and Cdk inhibitors (Cdkis) in the G1 phase even in the same type of cancer cells (papillary thyroid carcinoma cells). Cell cycle analysis revealed an increase in NIM1 cells and a decrease in NPA cells in the S and G2+M phases after treatment with IL-1alpha. The addition of IL-1alpha to NIM1 cells reduced the expression of p16 and p21 protein and induced the expression of Cdk2 and Cdk4 protein, which leads to the phosphorylation of retinoblastoma protein. The addition of IL-1alpha to NPA cells induced the expression of p27 protein and reduced the expression of Cdk2 protein, which leads to induction of p107 protein expression. It is of interest that p21 protein expression was not observed in NPA cells. These results suggest that several Cdks and Cdkis play a regulatory role in the G1 cell cycle progression and arrest induced by IL-1alpha in thyroid carcinoma cell lines.
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PMID:Interleukin-1alpha regulates G1 cell cycle progression and arrest in thyroid carcinoma cell lines NIM1 and NPA. 985 78

During a normal cell cycle, entry into S phase is dependent on completion of mitosis and subsequent activation of cyclin-dependent kinases (Cdks) in G1. These events are monitored by checkpoint pathways. Recent studies and data presented herein show that after treatment with microtubule inhibitors (MTIs), cells deficient in the Cdk inhibitor p21(Waf1/Cip1) enter S phase with a >/=4N DNA content, a process known as endoreduplication, which results in polyploidy. To determine how p21 prevents MTI-induced endoreduplication, the G1/S and G2/M checkpoint pathways were examined in two isogenic cell systems: HCT116 p21(+/+) and p21(-/-) cells and H1299 cells containing an inducible p21 expression vector (HIp21). Both HCT116 p21(-/-) cells and noninduced HIp21 cells endoreduplicated after MTI treatment. Analysis of G1-phase Cdk activities demonstrated that the induction of p21 inhibited endoreduplication through direct cyclin E/Cdk2 regulation. The kinetics of p21 inhibition of cyclin E/Cdk2 activity and binding to proliferating-cell nuclear antigen in HCT116 p21(+/+) cells paralleled the onset of endoreduplication in HCT116 p21(-/-) cells. In contrast, loss of p21 did not lead to deregulated cyclin D1-dependent kinase activities, nor did p21 directly regulate cyclin B1/Cdc2 activity. Furthermore, we show that MTI-induced endoreduplication in p53-deficient HIp21 cells was due to levels of p21 protein below a threshold required for negative regulation of cyclin E/Cdk2, since ectopic expression of p21 restored cyclin E/Cdk2 regulation and prevented endoreduplication. Based on these findings, we propose that p21 plays an integral role in the checkpoint pathways that restrain normal cells from entering S phase after aberrant mitotic exit due to defects in microtubule dynamics.
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PMID:p21(Waf1/Cip1) inhibition of cyclin E/Cdk2 activity prevents endoreduplication after mitotic spindle disruption. 985 45


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