Correlation between p21(waf1) and p16(INK4a) expression in hepatocellular carcinoma

CDKN2A promoter methylation and hepatocellular carcinoma risk: A meta-analysis

AIM

Lots of studies have explored cyclin-dependent kinase inhibitor 2A (CDKN2A) promoter methylation in hepatocellular carcinoma (HCC), but the established results were controversial. Hence, we conducted the meta-analysis to comprehensively investigate the association between CDKN2A promoter methylation and HCC risk.

METHODS

A comprehensive search was implemented through searching PubMed, Web of Science and Embase. Associations of CDKN2A promoter methylation with HCC risk, clinicopathological features, and CDKN2A expression were assessed by the pooled odds ratios (ORs) with corresponding 95% confidence intervals (CIs). Subgroup analyses and meta-regression were served for exploring the potential sources of heterogeneity.

RESULTS

A total of 59 articles including 3067 cases and 2951 controls were incorporated in this meta-analysis. Overall, we observed a high CDKN2A promoter methylation rate (58.18%) in HCC and a significant association between the methylation and HCC risk (OR, 7.07; 95% CI, 5.67-8.80). Furthermore, CDKN2A promoter methylation was robustly associated with decreased mRNA (OR, 13.89; 95% CI, 5.44-35.45) and protein (OR, 48.19; 95% CI, 5.56-417.29). In addition, we found the methylation was related with HBV infection (OR, 3.31; 95% CI, 1.47-7.47), HCV infection (OR, 2.76; 95% CI, 1.80-4.23), cirrhosis status (OR, 1.57; 95% CI, 1.01-2.44) and older age (OR, 1.83; 95% CI, 1.14-2.94).

CONCLUSIONS

Our results indicated that CDKN2A promoter methylation was associated with an enhancive HCC risk and played a crucial role in the process of HCC with a potential value to being a triage marker for HCC.

p16(INK4A) positively regulates p21(WAF1) expression by suppressing AUF1-dependent mRNA decay

Background

p16^INK4a and p21^WAF1 are two independent cyclin-dependent kinase inhibitors encoded by the CDKN2A and CDKN1A genes, respectively. p16^INK4a and p21^WAF1 are similarly involved in various anti-cancer processes, including the regulation of the critical G1 to S phase transition of the cell cycle, senescence and apoptosis. Therefore, we sought to elucidate the molecular mechanisms underlying the link between these two important tumor suppressor proteins.

Methodology/Principal Findings

We have shown here that the p16^INK4a protein positively controls the expression of p21^WAF1 in both human and mouse cells. p16^INK4a stabilizes the CDKN1A mRNA through negative regulation of the mRNA decay-promoting AUF1 protein. Immunoprecipitation of AUF1-associated RNAs followed by quantitative RT-PCR indicated that endogenous AUF1 binds to the CDKN1A mRNA in a p16^INK4A-dependent manner. Furthermore, while AUF1 down-regulation increased the expression level of the CDKN1A mRNA, the concurrent knockdown of AUF1 and CDKN2A, using specific silencing RNAs, restored the normal expression of the gene. Moreover, we used EGFP reporter fused to the CDKN2A AU-rich element (ARE) to demonstrate that p16^INK4A regulation of the CDKN1A mRNA is AUF1- and ARE-dependent. Furthermore, ectopic expression of p16^INK4A in p16^INK4A-deficient breast epithelial MCF-10A cells significantly increased the level of p21^WAF1, with no effect on cell proliferation. In addition, we have shown direct correlation between p16^INK4a and p21^WAF1 levels in various cancer cell lines.

Conclusion/Significance

These findings show that p16^INK4a stabilizes the CDKN1A mRNA in an AUF1-dependent manner, and further confirm the presence of a direct link between the 2 important cancer-related pathways, pRB/p16^INK4A and p14^ARF/p53/p21^WAF1.

Vitamin K2 inhibits the proliferation of HepG2 cells by up-regulating the transcription of p21 gene

AIM

Vitamin K2 has been reported to inhibit the growth of human hepatocellular carcinoma (HCC) in vitro and suppress hepatocarcinogenesis in vivo. However, its inhibitory mechanism has not yet been clarified.

METHODS

Different concentrations of vitamin K2 (30, 10, 1, 0.1 and 0.01 muM) were added to the HCC cell line HepG2 to assess effects on cell growth. The effect of vitamin K2 on cell cycle progression was determined by flow-cytometric analysis. The expression of cell cycle regulatory proteins p21 and p27 was then examined by Western blot. Whether vitamin K2 regulates the gene expression through action on the p21 promoter region was investigated by luciferase assay.

RESULTS

Vitamin K2 inhibited the growth of HepG2 cells dose-dependently, and its inhibitory rate reached approximately 50% at the dose of 30 muM after 96 h treatment. After treatment with vitamin K2, the proportion of cells in G0-G1 phase increased, and in S phase decreased. Apoptotic cells were not detected. The expression of cell cycle regulatory protein p21 was induced by vitamin K2 treatment, but p27 was not. By the luciferase assay, vitamin K2 significantly activated the promoter of p21. Knock-down of p21 by siRNA reversed the growth inhibition of HepG2 cells by vitamin K2.

CONCLUSIONS

The findings suggest that vitamin K2 suppresses the proliferation of HCC cells by blocking the cell cycle G1/S progression through the transcriptional induction of p21.

DDX3, a DEAD box RNA helicase with tumor growth-suppressive property and transcriptional regulation activity of the p21waf1/cip1 promoter, is a candidate tumor suppressor

DDX3 is a DEAD box RNA helicase with diverse biological functions. Using colony formation assay, our results revealed that DDX3 inhibited the colony formation ability of various tumor cells, and this inhibition might be due to a reduced growth rate caused by DDX3. Additionally, we identified p21(waf1/cip1), a cyclin-dependent kinase inhibitor, as a target gene of DDX3, and the up-regulation of p21(waf1/cip1) expression accounted for the colony-suppressing activity of DDX3. Moreover, DDX3 exerted its transactivation function on p21(waf1/cip1) promoter through an ATPase-dependent but helicase-independent mechanism, and the four Sp1 sites located within the -123 to -63 region, relative to the transcription start site of p21(waf1/cip1) promoter, were essential for the response to DDX3. Furthermore, DDX3 interacted and cooperated with Sp1 to up-regulate the promoter activity of p21(waf1/cip1). To determine the relevance of DDX3 in clinical cancers, the expression profile of DDX3 in various tumors was also examined. A declined expression of DDX3 mRNA and protein was found in approximately 58% to 73% of hepatoma specimens, which led to the reduction of p21(waf1/cip1) expression in a manner independent of p53 status. Additionally, an alteration of subcellular localization from nuclei to cytoplasm was also observed in >70% of cutaneous squamous cell carcinoma samples. Because DDX3 exhibits tumor suppressor functions, such as a growth-suppressive property and transcriptional activation of the p21(waf1/cip1) promoter, and is inactivated through down-regulation of gene expression or alteration of subcellular localization in tumor cells, all these features together suggest that DDX3 might be a candidate tumor suppressor.

DDX3, a DEAD box RNA helicase, is deregulated in hepatitis virus-associated hepatocellular carcinoma and is involved in cell growth control

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer deaths worldwide and is highly correlated with hepatitis virus infection. Our previous report shows that a DEAD box RNA helicase, DDX3, is targeted and regulated by hepatitis C virus (HCV) core protein, which implicates the involvement of DDX3 in HCV-related HCC development. In this study, the potential role of DDX3 in hepatocarcinogenesis is investigated by examining its expression in surgically excised human HCC specimens. Here we report the differential deregulation of DDX3 expression in hepatitis virus-associated HCC. A significant downregulation of DDX3 expression is found in HCCs from hepatitis B virus (HBV)-positive patients, but not from HCV-positive ones, compared to the corresponding nontumor tissues. The expression of DDX3 is differentially regulated by the gender and, moreover, there is a tendency that the downregulation of DDX3 expression in HCCs is more frequent in males than in females. Genetic knockdown of DDX3 with small interfering RNAs (siRNA) in a nontransformed mouse fibroblast cell line, NIH-3T3, results in a premature entry to S phase and an enhancement of cell growth. This enhanced cell cycle progression is linked to the upregulation of cyclin D1 and the downregulation of p21(WAF1) in the DDX3 knockdown cells. In addition, constitutive reduction of DDX3 expression increases the resistance of NIH-3T3 cells to serum depletion-induced apoptosis and enhances the ras-induced anchorage-independent growth, indicating the involvement of DDX3 in cell growth control. These findings together with the previous study suggest that the deregulation of DDX3, a DEAD box RNA helicase with cell growth-regulatory functions, is involved in HBV- and HCV-associated pathogenesis.