MECHANISMS OF REGULATION OF WAF1 CIP1 GENE-EXPRESSION IN HUMAN BREAST-CARCINOMA - ROLE OF P53-DEPENDENT AND INDEPENDENT SIGNAL-TRANSDUCTIONPATHWAYS

WAF1/Cip1 was recently identified as the wild-type p53 target that app ears to mediate the tumor suppressing effects of p53. We investigated the mechanisms of regulation of WAF1/Cip1 gene expression in human bre ast carcinoma (HBC) cells. Our results demonstrate that the HBC cells harboring wild-type p53 express 26-33-fold higher WAF1/Cip1 mRNA level s than the cells harboring mutant p53. The DNA damaging agent etoposid e induced p53 accumulation only in cells harboring wild-type p53 yet i t induced WAF1/Cip1 gene expression in cells carrying wild-type or mut ant p53, suggesting the involvement of p53-dependent and independent s ignaling pathways in the regulation of WAF1/Cip1 gene expression. Seru m starvation-induced growth arrest although not altering the endogenou s p53 levels or its ability to transactivate the reporter gene, induce d WAF1/Cip1 gene expression in cells carrying wild-type as well as mut ant p53. These results further implicated the involvement of p53-indep endent signal transduction pathways in WAF1/Cip1 gene regulation. Our data also suggest that WAF1/Cip1 gene expression is tightly associated with cell cycle progression in cells containing either wild-type or m utant p53. WAF1/Cip1 expression was transiently induced in response to serum treatment and declined as the cells passed through the S-phase of the cell cycle. We thus provide evidence that the mechanisms of WAF 1/Cip1 gene regulation involve p53-dependent and independent signaling pathways in HBC.