Germline mutations in genes encoding several components of the retinoblastoma pathway have been linked with inherited predisposition to melanoma. Most commonly, such mutations involve CDKN2A, a cyclindependant kinase inhibitor of two kinases, CDK4 and CDK6, which phosphorylate the retinoblastoma protein (pRB) and thereby promote passage through the G 1 /S cell-cycle restriction point. Less frequently, germline mutations in the CDK4 gene have also been linked with an increased risk of melanoma. Despite the sequence and functional homology between CDK4 and CDK6, the role of germline mutations in CDK6 in melanoma predisposition is unknown. We detected no CDK6 mutations within the p16 (CDKN2A) binding domain in index cases from 60 melanoma-prone kindreds that lacked germline mutations in the coding regions of either CDKN2A or within the entire CDK4 coding region. We conclude that germline mutations in CDK6 do not make a signi®cant contribution to melanoma predisposition. Oncogene (2000) 19, 1849 ± 1852.
Keywords: familial melanoma; CDK6Between 8 and 12% of melanoma cases arise in families with a genetic predisposition to the disease (Tucker and Goldstein, 1995). In a subset of these kindreds, germline coding mutations of the CDKN2A gene (on human chromosome 9p21) co-segregate with cases of melanoma (Hussussian et al., 1994;Walker et al., 1995;Dracopoli and Fountain, 1996;FitzGerald et al., 1996; NL and DH, unpublished). The CDKN2A gene product ± designated p16 ± is a cyclin-dependent kinase (CDK) inhibitor (CDKI). p16 plays a key regulatory role in the retinoblastoma (Rb) pathway at the G 1 /S cell-cycle restriction point by inhibiting the phosphorylation of Rb via CDK4/6 (Kato et al., 1993;Weinberg, 1995;Ruas and Peters, 1998). The genetic basis for melanoma in families and individuals that lack coding mutations of CDKN2A is not well understood at this time. Possible explanations include non-coding mutations of CDKN2A; alterations in other genes located at 9p21; and mutations of other major or minor melanoma predisposition genes located elsewhere in the human genome.Genetic alterations of two other members of the Rb pathway in addition to CDKN2A have been linked with an increased risk of melanoma. Individuals harbouring germline mutations in the Rb gene and who have retinoblastoma as children show an increased risk of melanoma as adults (Draper et al., 1986;Traboulsi et al., 1988;Eng et al., 1993;Bataille et al., 1995). In addition, three melanoma prone families have been reported to possess germline mutations in the CDK4 gene that cosegregate with the disease. Two of these families possess a cysteine rather than the wild-type arginine at amino acid 24 (R24C; Zuo et al., 1996). More recently, an additional mutation at position 24 (R24H) was identi®ed in a single French kindred (Sou®r et al., 1998). Moreover, the R24C (and presumably the R24H) mutant protein has a reduced a nity for p16, resulting in relaxation of control at the G1/S restriction point. CDK6 shows considerable amino acid homology with CDK4 ( Figure...
