Methylation silencing and mutations of the p14ARF and p16INK4a genes in colon cancer

The INK4a-ARF locus encodes two tumor suppressor proteins involved in cell-cycle regulation, p16(INK4a) and p14(ARF), whose functions are inactivated in many human cancers. The aim of this study was to evaluate p14(ARF) and p16(INK4a) gene inactivation and its association with some clinocopathological parameters in colon cancer. The mutational and methylation status of the p14(ARF) and p16(INK4a) genes was analyzed in 60 primary colon carcinomas and 8 colon cancer cell lines. We have identified the first two reported mutations affecting exon 1 beta of p14(ARF) in the HCT116 cell line and in one of the primary colon carcinomas, Both mutations occur within the N-terminal region of p14(ARF), documented as important for nucleolar localization and interaction with Mdm2. Tumor-specific methylation of the p14(ARF) and p16(INK4a) genes was found in 33% and 32% of primary colon carcinomas, respectively. Methylation of the p14(ARF) was inversely correlated with p53 overexpression (p = 0.02). p14(ARF) and p16(INK4a) gene methylation was significantly more frequent in right-sided than in left-sided tumors (p = 0.02). Methylation of the p14(ARF) gene occurred more frequently in well-differentiated adenocarcinomas (p = 0.005), whereas the p16(INK4a) gene was more often methylated in poorly differentiated adenocarcinomas (p = 0.002). The present results underline the role of p14(ARF) and p16(INK4a) gene inactivation in the development of colon carcinoma. They suggest that the methylation profile of specific genes, in particular p14(ARF) and p16(INK4a), might be related to biologically distinct subsets of colon carcinomas and possibly to different tumorigenic pathways.