Abnormalities in the CDKN2 (p16^INK4/MTS-1) gene in human melanoma cells: Relevance to tumor growth and metastasis

The inhibitor of cyclin-dependent kinase 4, CDKN2 (also known as p16^INK4 or MTS-1, multiple tumor suppressor gene 1), has been mapped to 9p21. The gene has been shown to be deleted or mutated in high frequency in human melanoma cell lines and familial melanoma patients, suggesting that it could be a melanoma suppressor gene. How these observations are related to tumorigenicity and metastasis of human melanoma is not clear however. To test the role of CDKN2 in human melanoma metastasis, 14 human melanoma cell lines with different metastatic abilities in nude mice were analysed for possible abnormalities in the CDKN2 gene. Homozygous deletions that resulted in a lack of gene expression were found in six of 14 cell lines tested. SSCP-direct sequencing revealed point mutations in three other cell lines. One cell line displayed CC to TT transitions which constitute a hallmark of ultraviolet-induced DNA damage. Overall, abnormalities in the CDKN2 gene were found in nine of 14 (64%) cell lines tested. Homozygous deletion and lack of gene expression were found in several low tumorigenic and nonmetastatic melanoma lines, whereas other metastatic cells did not exhibit abnormalities in the CDKN2 gene. These data suggest that the absence of normal CDKN2 does not confer growth advantage to melanoma cells in vivo and that the production of metastasis by human melanoma cells can occur in the absence of CDKN2 gene abnormalities.