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

Pancreatic carcinoma is one of the leading causes of cancer mortality worldwide,although the molecular mechanisms of this disease are poorly understood. The aimof this study was to examine the expression of cyclin-dependent kinase inhibitors(CDKIs) and the epigenetic modifications in the promoters of these genes. We alsoevaluated the correlation between the methylation status of CDKI genes and smokinghabit in clinical pancreatic carcinoma specimens. Western blotting and real-timePCR were performed to assess CDKI expression. Methylation-specific PCR was carriedout to examine the methylation status of the promoters of CDKI genes. In thisstudy, 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 p15INK4bgenes, 60% (3 of 5) of the p16INK4a genes and 60% of the p21cip1 genes, whichmarkedly correlated with their decreased mRNA expression. No hypermethylationwas detected in the p27kip1 gene promoter in 5 pancreatic carcinoma patients withmarkedly decreased expression of p27kip1 mRNA, suggesting an alternative mechanismof p27kip in these patients. In this study, patients with a smoking habit displayedmethylation of 2 CDKI genes in their pancreatic carcinoma specimens. We concludedthat epigenetic modification via hypermethylation represents a critical mechanismfor the inactivation of CDKI genes in pancreatic carcinoma.