Abrogation of apoptosis induced by DNA-damaging agents in human bladder-cancer cell lines with p21/WAF1/CIP1 and/or p53 gene alterations

The P53-inducible cyclin-dependent kinase inhibitor, p21/WAF1/CIP1 (P21), plays a pivotal role in the G(1) arrest or apoptosis of cells exposed to genotoxic stimuli. To determine whether p21 is a putative tumor-suppressor gene, p21 status was investigated in 4 human bladder-cancer cell lines of known p53 status. A p21-gene mutation, one base-pair insertion at codon 20 resulting in a chain-termination change at codon 35, was observed in one cell line, HT1376, suggesting structural or functional alteration of the p21 protein. When exposed to DNA-damaging agents, cisplatin or mitomycin C, apoptosis was induced in RT4 with the wild-type (wt) p53/wt p21, whereas T24 with the p53 non-sense mutation/wt p21 was resistant. Of the other 2 cell lines with the p53 mis-sense mutation, apoptosis was induced in SCaBER with the wt p21, but HT1376 with the p21 frame-shift mutation was fairly resistant. These findings suggest that not only p53 alteration, but also P21 alteration, is important to prevent apoptosis induced by DNA-damaging agents. When exposed to these agents, p53 and p21 expression was increased in RT4, and not induced in T24. p53 was not induced, but PZ I expression was increased in SCaBER, whereas p53 expression was increased but PZ I expression was absent in HT1376. Thus, p21 expression itself may have an important role in the induction of apoptosis by DNA-damaging agents. (C) 1996 Wiley-Liss, Inc.