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 i ts effects, or function in p53-independent pathways of cell cycle regu lation. Although a potential tumor suppressor gene, WAF1/p21 is expres sed 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 overexp ression 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 d ue to a frame shift mutation. Overexpression of WAF1/p21 cDNA inhibite d clone formation in three cell lines, whereas transfection with antis ense WAF1 increased clone sizes and numbers. WAF1 sense clones showed diminished cell proliferation compared to the parental cell line. Apop tosis-induced wild-type p53 was not inhibited by overexpression of ant isense WAF1/p21. In a cell clone derived from line VMCub1 by stable tr ansfection with wild-type p53 under the control of a metallothionein p romotor, p21 was induced along with p53 upon activation of the promote r with zinc chloride. This induction was accompanied by a decrease in cell proliferation but by little apoptosis. These data suggest that p2 1 inhibits proliferation in a p53-dependent or independent manner but does not mediate p53-induced apoptosis in urothelial carcinoma cells.