Methylation profile of promoter region of p16 gene in colorectal cancer patients of Kashmir valley

Colorectal cancer (CRC) commonly known as bowel cancer is the third most common cause of cancer-related deaths in the western world and has been reported to show geographical variation in its incidence. Cancer development and progression is a complex process dictated by changes in expression and regulation of various genes which include tumor suppressor genes, DNA repair genes, translation regulatory genes and others. The aim of this case control study was to analyze the promoter hypermethylation at CpG islands of p16 gene in CRC patients among the Kashmiri population and co- relate it with expression pattern of p16. Genomic DNA was isolated from surgically resected tumor and adjacent normal samples and was modified using bisulphite modification kit. Methylation-specific polymerase chain reaction (PCR) was setup for the analysis of the promoter hypermethylation of p16 gene. The epigenetic analysis revealed that unlike other high risk regions, Kashmiri population has a different promoter hypermethylation profile of p16 gene as 66 percent of the cases showed p16 promoter hypermethylation in comparison to 20 percent of the normal cases which also showed promoter hypermethylation of p16 gene. The association of promoter hypermethylation with colorectal cancer was found to be significant (P=0.0006). Occurrence of p16 promoter hypermethylation was found to be unequally distributed in males and females with more frequency in males than in females but the difference was not statistically significant(P =0.7635). Similarly, frequency of p16 promoter hypermethylation was found to be certainly higher in Stage III/IV (83.33 percent) compared to Stage I/II (56.25 percent) but the difference was not statistically significant (P =0.0673). Also, the degree of p16 promoter hypermethylation increased with the increasing severity of the lesion but the difference was not again statistically significant (P =0.6145). Promoter hypermethylation correlated with the decrease in expression of the p16 gene in CRC patients leading to the diseased phenotype. These results suggest that p16 aberrant promoter hypermethylation in Kashmiri population contributes to the process of carcinogenesis in CRC and may be developed into a valuable tool for CRC diagnosis at early stages.