| Abstract: |
Homozygous deletions of 9p21, including the cyclin-dependent kinase inhibitor genes pl6INK4 and pl5INK4, have been reported frequently in melanoma (as well as other tumor) cell lines. Germline mutations within the pl6lNK4 gene have also been described in a proportion of familial melanoma kindreds, suggesting that pl6lNK4 is the 9p21 “melanoma” gene. We have previously concluded that deletion of this chromosomal region can occur early (before metastasis) and in vivo in sporadic melanoma due to the identification of identical hemizygous losses on 9p21 in six autologous melanoma cell lines established from an individual patient (DX). These related cell lines have now been used to evaluate the timing of deletion/mutation of the pl6iNK4 and pl5lNK4B genes during tumor progression in melanoma. Surprisingly, homozygous deletions of a ⩽200-kb region surrounding p/5INK4B, but not pl6INK4, were detected in all six cell lines. Furthermore, single strand conformation polymorphism and sequencing analysis of the remaining pidINK4 allele in each case revealed only one intragenic mutation (in DX-6), whereas Western analysis provided evidence that pl6INK4 protein was expressed in all six instances. These findings, taken together with those generated on other unrelated melanoma tumors and cell lines, suggest that hemizygous loss (or haplo-insufficiency) of the pl6INk4 gene may be enough to place a melanocyte on a tumor pathway, and/or that the pl6lNK4 gene is not the sole 9p21 locus targeted in sporadic melanoma. © 1995, American Association for Cancer Research. All rights reserved. |
