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)

Apoptosis of SK-HEP-1 human hepatoma cells induced by treatment with ginsenoside Rh2 (G-Rh2) is associated with rapid and selective activation of cyclin A-associated cyclin-dependent kinase 2 (Cdk2). Here, we show that in apoptotic cells, the Cdk inhibitory protein p21(WAF1/CIP1), which is associated with the cyclin A-Cdk2 complex, undergoes selective proteolytic cleavage. In contrast, another Cdk inhibitory protein, p27(KIP1), which is associated with cyclin A-Cdk2 and cyclin E-Cdk2 complexes, remained unaltered during apoptosis. Ectopic overexpression of p21(WAF1/CIP1) suppressed apoptosis as well as cyclin A-Cdk2 activity induced by treatment of SK-HEP-1 cells with G-Rh2. The suppressive effects of p21(WAF1/CIP1) were much higher in the cells transfected with p21D112N, an expression vector that encodes a p21(WAF1/CIP1) mutant resistant to caspase 3 cleavage. Overexpression of cyclin A in SK-HEP-1 cells dramatically up-regulated cyclin A-Cdk2 activity and accordingly enhances apoptosis induced by treatment with G-Rh2. These up-regulating effects were blocked by coexpression of a dominant negative allele of cdk2. Furthermore, olomoucine, a specific inhibitor of Cdks, also blocked G-Rh2-induced apoptosis. These data suggest that the induction of apoptosis in human hepatoma cells treated with G-Rh2 occurs by a mechanism that involves the activation of cyclin A-Cdk2 by caspase 3-mediated cleavage of p21(WAF1/CIP1).
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PMID:Caspase 3-mediated cleavage of p21WAF1/CIP1 associated with the cyclin A-cyclin-dependent kinase 2 complex is a prerequisite for apoptosis in SK-HEP-1 cells. 1088 82

Several clinical trials have demonstrated the effectiveness of combination therapy with 5-fluorouracil (5-FU) and IFN-alpha in colon cancer, hepatocellular carcinoma (HCC), and other malignancies. In our preliminary clinical studies, we have observed outstanding effects with this combination therapy in patients with advanced HCC. However, the underlying mechanism by which IFN-alpha modulates the effects of 5-FU is unknown. We, therefore, conducted a mechanistic study using two HCC cell lines, PLC/PRF/5 and HuH7. IFN-alpha significantly enhanced the growth inhibitory effect of 5-FU in PLC/PRF/5 cells but not in HuH7 cells, and the isobolographic analysis indicated that this effect was synergistic. Flow cytometric analysis showed a delay in the progression of G0-G1 to S phase in PLC/PRF/5, and a sustained, induction of the cyclin-dependent kinase inhibitor p27-Kip1 and down-regulation of cyclin D1 was observed. Moreover, increased expression of p27Kip1 was associated with reduced CDK-2-associated kinase activity. Another difference in the two cell types was that PLC/PRF/5 expressed abundant IFN receptors, but HuH7 did not. Apoptosis assays were not helpful in explaining the mechanism. Our results suggest that the synergistic effects of 5-FU and IFN-alpha may in part be attributable to alterations in cell cycle progression via up-regulation of p27Kip1.
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PMID:Augmentation of antitumor activity of 5-fluorouracil by interferon alpha is associated with up-regulation of p27Kip1 in human hepatocellular carcinoma cells. 1091 38

The cyclin-dependent kinase (Cdk)-associated protein phosphatase (KAP) is a human dual specificity protein phosphatase that dephosphorylates Cdk2 on threonine 160 in a cyclin-dependent manner. To investigate whether mutations of this enzyme occur in hepatocellular carcinoma (HCC), KAP mRNA was analyzed by reverse transcription-PCR (RT-PCR), followed by cloning and sequencing. Eight of 14 biopsy tissues obtained from advanced HCC, 6 of 13 surgically removed HCC tissues, and 2 of the adjacent noncancerous tissues contained aberrant KAP transcripts. Using the yeast two-hybrid system, five of seven representative KAP mutants were shown to be defective in interacting with Cdk2. These data suggest a possible role of KAP mutations in multiple-step hepatocarcinogenesis.
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PMID:Aberrant transcripts of the cyclin-dependent kinase-associated protein phosphatase in hepatocellular carcinoma. 1098 70

Curcumin (CCM), a major yellow pigment of turmeric obtained from powdered rhizomes of the plant Curcuma longa Linn, is commonly used as coloring agent in foods, drugs and cosmetics. In this study we report that gavage administration of 200 mg/kg or 600 mg/kg CCM effectively suppressed diethylnitrosamine (DEN)-induced liver inflammation and hyperplasia in rats, as evidenced by histopathological examination. Immunoblotting analysis showed that CCM strongly inhibited DEN-mediated the increased expression of oncogenic p21(ras) and p53 proteins in liver tissues of rats. In cell-cycle-related proteins, CCM selectively reduced the expression of proliferating cell nuclear antigen (PCNA), cyclin E and p34(cdc2), but not Cdk2 or cyclin D1. Moreover, CCM also inhibited the DEN-induced increase of transcriptional factor NF-kappa B. However, CCM failed to affect DEN-induced c-Jun and c-Fos expression. It has become widely recognized that the development of human hepatocellular carcinoma (HCC) is predominantly due to the chronic inflammation by virus, bacteria or chemical. Our results suggest a potential role for CCM in the prevention of HCC.
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PMID:Inhibition by curcumin of diethylnitrosamine-induced hepatic hyperplasia, inflammation, cellular gene products and cell-cycle-related proteins in rats. 1103 36

The p27 cyclin-dependent kinase inhibitor is a negative regulator of cell-cycle progression. In many human epithelial malignancies, decreased expression of p27 correlates with high grade, early recurrence, and poor prognosis. To evaluate the prognostic significance of p27 in hepatocellular carcinoma (HCC), we studied 54 HCCs along with corresponding nontumoral tissue. Immunohistochemistry (IHC) and Western blot (WB) analysis before and after immunoprecipitation with Cdk2 were performed on paraffin-embedded tissues and protein homogenates, respectively, to compare localization and expression of the p27 protein and to determine the total and active (Cdk2-bound) fractions of p27. Correlations were analyzed between IHC-assessed levels of p27, survival, and major clinical and pathological variables. IHC revealed no p27 expression in the majority of hepatocytes from normal and cirrhotic liver, whereas 14 HCCs (26%) were high p27 expressers (>50% positive cells), 26 (48%) low expressers (<50% positive cells), and 14 (26%) negative. High IHC signals of p27 correlated with Cdk2-bound p27 as assessed by immunoprecipitation-WB; by contrast, WB alone displayed similar levels of p27 protein in all normal and tumoral samples. High IHC p27 expression correlated with prolonged survival (P = 0.027), whereas the presence of cirrhosis was associated with poor outcome (P = 0.029). We conclude that with respect to their nonneoplastic counterparts, a subset of HCCs acquire significant p27 expression and that high expression of p27 is a favorable independent prognostic parameter for HCC.
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PMID:Acquired expression of p27 is a favorable prognostic indicator in patients with hepatocellular carcinoma. 1105 Dec 45

The inactivation of the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor p16INK4A may be caused by gene deletion, mutation or promoter hypermethylation. We have previously reported that p16INK4A in hepatocellular carcinoma (HCC) tissues and cell lines is inactivated predominantly by promoter hypermethylation rather than genomic aberrations. In the present experiments, we have studied the effects of the demethylating agent, 5-aza-2'-deoxycytidine (5-AZA/decitabine), on the expression of aberrant p16INK4A RNA transcripts and the CDK-retinoblastoma gene pathway in HCC cell lines with p16INK4A promoter hypermethylation. The expression of aberrant p16INK4A RNA transcripts was down-regulated and p16INK4A protein was strongly re-expressed in the HCC cell lines, SNU 354, 398, 423 and 475 after 5-AZA/decitabine treatment for 5 days. The re-expressed p16INK4A was functional, because it bound to and inhibited CDK4 kinase activity, and increased the concentrations of the hypophosphorylated form of retinoblastoma protein (pRB) in cells with a wild type RB gene. Moreover, treatment with the demethylating agent led not only to G1 cell cycle arrest, but also to the increased expression of the senescence-associated marker beta-galactosidase. This up-regulation of p16INK4A mRNA and protein correlated with demethylation of the p16INK4A promoter, and with the down-regulation or disappearance of aberrant p16INK4A transcripts. These results suggest that the aberrant p16INK4A RNA transcript can be transcribed from the methylated p16INK4A gene, and endogenous reactivation of functional p16INK4A mRNA by a demethylating agent can restore the pRB pathway in HCC, and foster the terminal differentiation of the malignant cells. Therefore, demethylating agents, such as 5-AZA/decitabine, may have potential in the treatment of HCC.
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PMID:5-Aza-2'-deoxycytidine leads to down-regulation of aberrant p16INK4A RNA transcripts and restores the functional retinoblastoma protein pathway in hepatocellular carcinoma cell lines. 1109 88

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

Saikosaponin a, a purified ingredient of Chinese herb with known antitumor activity, can inhibit cell growth and DNA synthesis of hepatoma cell line HepG2. Both mRNA and protein of the CDK inhibitor p-16(INK4a) and p-15(INK4b) in HepG2 were greatly induced by saikosaponin a while that of p-21(CIP), p-27(KIP) and other cell cycle related genes were not. In addition, reduced phosphorylation of RB protein is observed in saikosaponin a-treated HepG2. Staurosporin, one of the PKC inhibitors, significantly prevented the saikosaponin a induced growth inhibition suggesting PKC pathway be involved. On the other hand, the phorbol ester tumor promoter TPA (12-O-Tetredecanolyphorbol 13-acetate) also inhibited HepG2 growth and specifically induced p-16(INK4a) and p-15(INK4b) mRNA expression. The results suggest that both saikosaponin a and TPA-induced HepG2 growth inhibition are associated with p-15(INK4a) and p-16(INK4b) gene expression and might be mediated by PKC signaling pathway.
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PMID:Involvement of p-15(INK4b) and p-16(INK4a) gene expression in saikosaponin a and TPA-induced growth inhibition of HepG2 cells. 1144 23

The X-gene product of hepatitis B virus (HBx) has been implicated in hepatitis B virus (HBV)-mediated hepatocellular carcinoma through its ability to induce liver cancer in some transgenic mice and to transactivate a variety of viral and cellular promoters. In this study, we demonstrated that the level of p21(waf1) RNA was decreased in the HBx-expressing cells and this effect was due to the transcriptional repression of the p21(waf1) gene by HBx via a p53-independent pathway. As the Sp1 binding sites of the p21(waf1) promoter were sufficient to confer HBx responsiveness to a previously non-responsive promoter, we suggested that HBx represses the transcription of p21(waf1) by downregulating the activity of Sp1. Because the tumor repressor p21(waf1) protein is a universal inhibitor of cyclin-CDK complexes and DNA replication that induces cell cycle arrest at the G1-S checkpoint, the repression of p21(waf1) by HBx might play an important role in a HBV-mediated pathogenesis.
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PMID:Transcriptional repression of p21(waf1) promoter by hepatitis B virus X protein via a p53-independent pathway. 1157 65

p21(WAF1/CIP1) is a universal cyclin-dependent kinase inhibitor. To investigate the role of p21(WAF1/CIP1) in proliferation of human liver cancer cells, we examined the expression of p53, p21(WAF1/CIP1), cdk2 and cdk4 expression in two human liver cancer cell lines (HepG2 and PLC/PRF/5 cells). The effects of p21(WAF1/CIP1) on [(3)H]thymidine incorporation and cdks were also examined in these cells. HepG2 cells expressed all these proteins with lower level of cdk4. PLC/PRF/5 cells expressed the other proteins except p21(WAF1/CIP1). Transfection of p21(WAF1/CIP1) gene inhibited [(3)H]thymidine incorporation of both cells with different extent. Although the transfection of p21(WAF1/CIP1) did not affect cdk2 and cdk4 expression, it did reduce cdk2 kinase activity by 20%. These results suggest that: (a) p21(WAF1/CIP1) involved in DNA synthesis of human liver cancer cells; (b) p21(WAF1/CIP1) could be a target gene for the treatment of human hepatocellular carcinoma.
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PMID:A cyclin-dependent kinase inhibitor (p21(WAF1/CIP1)) affects thymidine incorporation in human liver cancer cells. 1187 May 47


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