ANALYSIS OF THE P16 TUMOR-SUPPRESSOR GENE IN EARLY-STAGE PROSTATE-CANCER

To identify whether alterations of the p16 tumor suppressor gene are a common event in localized prostate cancer, we examined the frequency of p16 gene mutations in 30 primary tumors. Only two tumors demonstrat ed altered single-strand conformation polymorphism patterns for exon 2 of p16. In both cases, sequencing revealed a missense at codon 148, a G-->A transition that resulted in the replacement of the alanine by t hreonine. Polymerase chain reaction-single-strand conformation polymor phism analysis of matched blood samples revealed the same abnormal ban d shifts as the tumor samples, suggesting that these base changes are polymorphic. In addition, transcriptional inactivation by means of CpG island methylation has also been reported as a possible means of p16 gene inactivation. To address this point, we determined the pattern of DNA methylation at the SmaI site for 21 of 30 samples for which DNA w as available. Only one sample had an altered methylation pattern at th e SmaI site downstream of exon 1 of the p16 gene, which is outside the CpG island and is not normally associated with transcriptional inacti vation. However, two samples did have deletions proximal to or within the p16 gene. These results indicate that mutations in p16 may not be a dominant pathway for p16 loss of function or that inactivation of p1 6 by DNA methylation may not be necessary for the transformation and p rogression of prostate cancer. (C) 1998 Wiley-Liss, Inc.