Decreased expression of the p16/MTS1 gene without mutation is frequent in human urinary bladder carcinomas

The p16 (CDKN2,MTS1) gene is located at 9p21 and its product, p16, inhibits the cyclin D/CDK4 complex, Loss of heterozygosity on chromosome 9p is very common in human bladder carcinomas and has been found in all stages of lesions, suggesting that it occurs early in bladder tumor progression, Several studies have revealed frequent homozygous deletion of the p16 gene in cell lines, and that such deletions are also common in some types of cancers, In addition, point mutations in the p16 gene have been identified in several types of neoplasia, In the present examination of urinary bladder tumors, no p16 gene mutations were detected, but nine cases out of 23 (39%) showed decreased mRNA expression, revealed by the reverse transcriptase polymerase chain reaction, There were no histological differences apparent between those cases with normal and those with decreased p16 expression, These results indicate that while p16 gene mutations may be rare, changes in the level of the p16 transcripts could play a role in human bladder carcinoma development.