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 cel l cycle progression through the G1 phase and dysfunction of these proteins by gene mutation is implicated in genetic predisposition to melanoma. We an alysed 15 Italian melanoma families for germ line mutations in the coding r egion of the CDKN2A gene and exon 2 of the CDK4 gene. One novel disease-ass ociated mutation (P48T), 3 known pathological mutations (R24P. G101W and N7 1S) and 2 common polymorphisms (A148T and Nt500 G >C) were identified in th e CDKN2A gene. In a family harbouring the R24P mutation, an intronic varian t (IVS1, +37 G >C) of uncertain significance was detected in a noncarrier m elanoma 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 anal ysis established that the novel mutated protein, while being impaired in ce ll growth and inhibition assays, retains some in vitro binding to CDK4/6. N o variant in the p16-binding region of CDK4 was identified in our families. Our results, obtained in a heterogeneous group of families, support the vi ew that inactivating mutations of CDKN2A contribute to melanoma susceptibil ity more than activating mutations of CDK4 and that other genetic factors m ust be responsible for melanoma clustering in a high proportion of families . In addition, they indicate the need for a combination of functional assay s to determine the pathogenetic nature of new CDKN2A mutations. (C) 2001 Ca ncer Research Campaign.