Frequent alteration of CDKN2 (p16(INK4A)/MTS1) expression in human primary prostate carcinomas.

CDKN2 (p16(INK4A)/MTS1) is found to be mutated in a variety of human tumor types. To explore the involvement of CDKN2 in prostate carcinogenesis, alterations of CDKN2 were examined in 116 human prostate tissues and cell lines and xenografts. Markedly reduced expression of CDKN2 mRNA was found in 43% (26 of 60) of untreated primary carcinomas, whereas no alteration was observed in 10 benign prostatic hyperplasias. In 17 matched sets from individual patients, 41% of cancerous tissues in contrast to 6% of noncancerous tissues expressed low levels of CDKN2 mRNA, supporting the role of CDKN2 as a tumor suppressor in prostate cancer. Alteration of CDKN2 was observed in each prostate tumor cell line, including one with a missense mutation, and in one of three xenograft tumor tissues derived from primary carcinomas. Two cell lines (PC-3 and TSU-Pr1) expressed only CDKN2 E1beta transcripts, indicating that the expression of CDKN2 E1alpha and E1beta are under separate control in the prostate. A high level of CDKN2 expression was related to abnormal RB1 in one primary tumor and in the DU145 cell line, which expressed the mutated CDKN2 allele. Analysis of genomic DNA indicated that altered CDKN2 expression in primary carcinomas of the prostate was more frequently due to down-regulation of transcription (five of seven) than deletion of the gene (two of seven). Additionally, CDKN2 mRNA was induced in nonexpressor cell lines by treatment with 5-aza-2'-deoxycytidine. This study demonstrates that alteration of CDKN2 is one of the most frequent genetic abnormalities in prostate cancer and may contribute to prostate carcinogenesis.