NO EVIDENCE EXISTS FOR METHYLATION INACTIVATION OF THE P16 TUMOR-SUPPRESSOR GENE IN OVARIAN CARCINOGENESIS

The p16(ink4)/CDKN2/MTS1 tumor suppressor gene encodes a cyclin-depend ent kinase inhibitor which plays an important role in regulation of th e G1/S phase cell cycle checkpoint. Loss of heterozygosity (LOH) at th e p16 locus, 9p21, has been documented in a wide variety of tumors inc luding ovarian carcinoma. However, inactivating mutations of the remai ning allele and homozygous deletions are relatively infrequent events in primary tumors, even in cases where expression of p16 at the mRNA a nd protein level is clearly absent. These findings initially cast doub t on the role of p16 as a tumor suppressor gene in vivo. Recently, an alternative mechanism of p16 inactivation involving methylation of the CpG island in the 5' region of the gene has been demonstrated in a nu mber of malignancies and cell lines. In this study we have analyzed th e methylation status of four CpG dinucleotides in a panel of 23 ovaria n tumors using a multiplex PCR approach to correlate our findings with the LOH data in this region. Using the microsatellite markers D9S171 and D9S1679 LOH was demonstrated in 4/22 (18%) informative cases. All 23 tumors showed no evidence of methylation at the p16 locus including the 4 tumors demonstrating LOH at 9p21. These results suggest that me thylation inactivation of the p16 gene does not play an important role in ovarian carcinogenesis. (C) 1998 Academic Press.