We have also sequenced exon 2 of the recently identified candidate tumour suppressor gene, p16, in six individuals and found no evidence for germline mutations in this region of the p16 gene in our families with inherited malignant melanoma.
Recent progress of positional cloning technique further revealed that p16 gene which is an inhibitor of cycline-dependent kinase is the gene for some of familial malignant melanoma/dysplastic nervus syndrome and sporadic melanoma.
The reported data suggest the existence of several tumor suppressor genes at 9p that are involved in the predisposition to and/or progression of CMM and exclude p16 from involvement in the early development of some melanoma tumors.
Some bladder primary tumors and some bladder and melanoma tumor cell lines contain mutations in both P16 and P53 at frequencies that suggest that p53 and p16 function in different pathways, each of which is important in suppressing malignant transformation.
Taken together with a predominance of UV-induced mutations in the CDKN2/ p16 gene demonstrated in melanoma cell lines, our data support a role of sunlight exposure in the etiology of malignant melanoma.
The lack of complete concordance between p15 and p16 expression implies that the genes are not functionally redundant and that loss of either gene may be important in the pathogenesis of MM.
The first of these genes to be cloned is the cell cycle regulatory protein inhibitor--the p16 gene-- and a second gene locus for melanoma predisposition has been linked to the chromosome 1p36 band region.
Germline mutations in CDKN2 on chromosome 9p21, which codes for the cyclin D kinase inhibitor p16, and more rarely, mutations in the gene coding for CDK4, the protein to which p16 binds, underlie susceptibility in some melanoma families.
MeWo cells, which alone expressed intrinsic wild-type p16 among six melanoma cell lines examined, showed higher radiosensitivity in comparison with the other five melanoma cells.
In an example presented regarding a planned study of the p16 gene and its role in melanoma, a conventional case-control study may require up to 70 times as many subjects to achieve equivalent precision to the study of second primaries.
The aim of this study was to investigate the involvement of CDKN2A and elucidate the mechanisms of p16 inactivation in a panel of 60 cell lines derived from sporadic melanomas.
The p16/CDKN2(MTS1) gene encoding for the p16 inhibitor of cyclin D/CDK4 complexes is frequently mutated and deleted in a large fraction of melanoma cell lines, and p16 germline mutations have also been observed in familial melanomas.
These results suggest that (1) the homozygous deletions of p16/p15 genes and the replication errors may occur in rather early stages of melanoma tumorigenesis, while the p16/p15 gene mutation may occur in later stages, and (2) the p16 and p15 gene mutations in sporadic malignant melanomas might not be induced by the defect in mismatch repair, implying that p16 as well as p15 gene alterations may play an important role in the pathogenesis of sporadic malignant melanomas.
In summary, our results show frequent involvement of the p16 gene in familial melanoma and confirm the role of the CDK4 gene as a melanoma-predisposing gene.
Therefore, these data suggest that deletion of p16 may play an important role in the development of dysplastic nevus as an early event and that the changes may represent an early event in the development of malignant melanoma.
Thus the addition of activating ras mutations to a melanoma cell line already deficient in p16 leads to enhanced proliferation, survival and migration in vitro and to enhanced subcutaneous tumour formation in vivo.