CDKN2A and CDK4 mutation analysis in Italian melanoma-prone families: functional characterization of a novel CDKN2A germ line mutation.

Physical interaction between CDKN2A/p16 and CDK4 proteins regulates the cell cycle progression through the G1 phase and dysfunction of these proteins by gene mutation is implicated in genetic predisposition to melanoma. We analysed 15 Italian melanoma families for germ line mutations in the coding region of the CDKN2A gene and exon 2 of the CDK4 gene. One novel disease-associated mutation (P48T), 3 known pathological mutations (R24P, G101W and N71S) and 2 common polymorphisms (A148T and Nt500 G>C) were identified in the CDKN2A gene. In a family harbouring the R24P mutation, an intronic variant (IVS1, +37 G>C) of uncertain significance was detected in a non-carrier melanoma case. The overall incidence of CDKN2A mutations was 33.3%, but this percentage was higher in families with 3 or more melanoma cases (50%) than in those with only 2 affected relatives (25%). Noteworthy, functional analysis established that the novel mutated protein, while being impaired in cell growth and inhibition assays, retains some in vitro binding to CDK4/6. No variant in the p16-binding region of CDK4 was identified in our families. Our results, obtained in a heterogeneous group of families, support the view that inactivating mutations of CDKN2A contribute to melanoma susceptibility more than activating mutations of CDK4 and that other genetic factors must be responsible for melanoma clustering in a high proportion of families. In addition, they indicate the need for a combination of functional assays to determine the pathogenetic nature of new CDKN2A mutations.