MUTATIONS AND DEFECTIVE EXPRESSION OF THE WAF1 P21 TUMOR-SUPPRESSOR GENE IN MALIGNANT MELANOMAS

The WAF1 gene, located on chromosome 6p, encodes a M(r) 21 000 protein (p21) that can arrest cell growth by associating with and inhibiting cyclin-dependent kinase complexes that are necessary for cells to exit G(r). Transcriptional activation of WAF1 can be accomplished by incre asing levels of p53 protein induced by various cellular stresses, incl uding DNA damage. Metastatic melanomas are paradoxical in that most ov erexpress wild-type p53 protein, yet cell growth is not inhibited. Thu s, it is possible that lack of growth suppression in melanomas is due, in part, to mutations in the WAF1 gene. Therefore, we examined the en tire coding region of the WAF1 gene in 24 metastatic melanoma cell lin es and three normal melanocyte lines by single-strand conformation pol ymorphism (SSCP) analysis and direct DNA sequencing. We similarly exam ined the DNA from lymphoblastoid cell lines, derived from nine individ uals belonging to seven melanoma-prone families, in which haplotypes o f markers on 6p cosegregate with melanoma for germline mutations in th e WAF1 gene. Results indicate that (i) mutation of the WAF1 gene is an infrequent event in individuals with sporadic melanoma or predisposed to familial melanoma and (ii) the uncontrolled growth of melanoma cel ls is not due to mutation of the WAF1 gene. However, expression studie s found a wide variation in the level of p21 protein in melanoma cells , suggesting that aberrant regulation of p21 may play a role in melano ma development. Moreover, there was no predictable relationship betwee n p21 expression and p53 expression, indicating that other, p53-indepe ndent, pathways may be important for the regulation of p21 in melanoma cells.