Analysis of p21(WAF1/CIP1) in primary bladder tumors

The p21(WAF1/CIP1) gene is regulated by p53 and encodes a cyclin- dependent kinase (Cdk)-inhibitor involved in senescence and cell quiescence. The role of p21 as a negative regulator of cell proliferation suggests that it may function as a tumor suppressor gene. However, only a few mutations of the p21(WAF1/CIP1) gene have been reported to date. In order to assess potential p21(WAF1/CIP1) gene alterations in human bladder cancer, we have examined this gene and its encoded product in a well-characterized cohort of 27 primary bladder tumors. Mobility shifts by single-strand conformation polymorphism in the p21(WAF1/CIP1) gene were identified in 2 cases. Sequencing analyses revealed that one of these cases had point mutations in the 3' untranslated region, while the other case had a frame shift mutation at positions 322 (C to A) and a deletion of 8 nucleotides (323→331; CCG→ACG, codon 81 Arg→Thr) that produced a stop signal at codon 83 (Gly→Stop). This tumor had a p21-negative phenotype by immunohistochemistry, but did not lose any allele. We further characterized these cases by the study of TP53 mutations using single-strand conformation polymorphism (PCR- SSCP) and sequencing, as well as immunohistochemical assays. Seven mobility shifts were identified and seven cases showed p53 nuclear accumulation. The two cases displaying mutated p21(WAF1/CIP1) had wild-type TP53. It is concluded that p21(WAF1/CIP1) gene aberrations are infrequent in bladder carcinoma but may be occasionally identified in primary bladder tumors.