Reduced levels of p15INK4b, p16INK4a, p21cip1 and p27kip1 in pancreatic carcinoma

Abstract

Pancreatic carcinoma is one of the leading causes of cancer mortality worldwide, although the molecular mechanisms of this disease are poorly understood. The aim of this study was to examine the expression of cyclin-dependent kinase inhibitors (CDKIs) and the epigenetic modifications in the promoters of these genes. We also evaluated the correlation between the methylation status of CDKI genes and smoking habit in clinical pancreatic carcinoma specimens. Western blotting and real-time PCR were performed to assess CDKI expression. Methylation-specific PCR was carried out to examine the methylation status of the promoters of CDKI genes. In this study, we revealed that reduced levels of the CDKI proteins, p15INK4b, p16INK4a, p21cip1 and p27kip1, are a prominent feature of pancreatic carcinoma patients. The DNA hypermethylation of the promoter was observed in 40% (2 of 5) of the p15INK4b genes, 60% (3 of 5) of the p16INK4a genes and 60% of the p21cip1 genes, which markedly correlated with their decreased mRNA expression. No hypermethylation was detected in the p27kip1 gene promoter in 5 pancreatic carcinoma patients with markedly decreased expression of p27kip1 mRNA, suggesting an alternative mechanism of p27kip in these patients. In this study, patients with a smoking habit displayed methylation of 2 CDKI genes in their pancreatic carcinoma specimens. We concluded that epigenetic modification via hypermethylation represents a critical mechanism for the inactivation of CDKI genes in pancreatic carcinoma.