WAF1/p21 regulates proliferation, but does not mediate p53-dependent apoptosis in urothelial carcinoma cell lines

The WAF1/p21 gene product is an inhibitor of cyclin-dependent kinases which can be induced by the tumor suppressor p53 and mediate some of its effects, or function in p53-independent pathways of cell cycle regulation. Although a potential tumor suppressor gene, WAF1/p21 is expressed in bladder cancer. To elucidate the function of p21 in tumor cells we have investigated in urothelial carcinoma cell lines: i) WAF1/p21 mRNA and protein expression, ii) the biological effects of p21 overexpression or down-regulation and (iii) whether p21 can be induced by p53. WAF1/p21 mRNA levels examined in four cell lines were comparable to bladder mucosa. One cell line, HT1376, failed to express p21 protein due to a frame shift mutation. Overexpression of WAF1/p21 cDNA inhibited clone formation in three cell lines, whereas transfection with antisense WAF1 increased clone sizes and numbers. WAF1 sense clones showed diminished cell proliferation compared to the parental cell line. Apoptosis-induced wild-type p53 was not inhibited by overexpression of antisense WAF1/p21. In a cell clone derived from line VMCub1 by stable transfection with wild-type p53 under the control of a metallothionein promotor, p21 was induced along with p53 upon activation of the promoter with zinc chloride. This induction was accompanied by a decrease in cell proliferation but by little apoptosis. These data suggest that p21 inhibits proliferation in a p53-dependent or independent manner but does not mediate p53-induced apoptosis in urothelial carcinoma cells.