Promoter hypermethylation: A common cause of reduced p16(INK4a) expressionin uveal melanoma

Tumors often display unrestricted cell cycling attributable to a dysfunctio nal G(1)-S checkpoint. One of the mechanisms leading to such a defect is th e inactivation of the cyclin-dependent kinase inhibitor p16(INK4a) Although inactivation of p16(INK4a) is observed in a wide range of tumors, includin g cutaneous melanoma, genetic alteration of p16(INK4a) is reportedly uncomm on in uveal melanoma, Here we show that the p16(INK4a) promoter is hypermet hylated in 6 of 12 uveal melanoma cell lines and in 7 of 22 primary uveal m elanomas analyzed. Five of seven patients with a methylated primary tumor d ied of metastatic disease compared with 2 of 15 patients with a nonmethylat ed primary tumor. We also show that all uveal melanoma cell lines with a hy permethylated p16(INK4a) promoter have lost p16(INK4a) expression but have maintained the expression of p14(ARF). Treatment of uveal melanoma cell lin es with 5-aza-2 ' -deoxycytidine results in demethylation of p16(INK4a) and in reexpression of p16(INK4a) mRNA, which is maintained upon withdrawal of the 5-aza-2 ' -deoxycytidine. In conclusion, p16(INK4a) promoter methylati on appears to be a common event in uveal melanoma and is accompanied by the loss of p16(INK4a) expression.