TRANSFORMING GROWTH-FACTOR-BETA-1 CAN INDUCE CIP1 WAF1 EXPRESSION INDEPENDENT OF THE P53 PATHWAY IN OVARIAN-CANCER CELLS/

Transforming growth factor beta (TGF beta) is an important regulator o f cellular proliferation. In normal ovarian epithelial cells, TGF beta acts to inhibit growth. However, in ovarian cancer cell lines, this e ffect is usually lost. Although the regulatory pathway of TGF beta rem ains unclear, TGF beta-treated cells arrest late in G(1). This inhibit ion appears to involve blocking of the cyclin-dependent kinase phospho rylation of the retinoblastoma protein. Recently, a general inhibitor of cyclin-dependent kinases, CIP1/WAF1/p21, was identified. Expression of CIP1 is positively regulated by binding of wild-type p53 to a cons ensus response element upstream of the CIP1 gene. Overexpression of th e CIP1 protein causes growth suppression, analogous to TGF beta and wi ldtype p53. We have examined the induction of CIP1 by TGF beta 1 in ov arian cancer cell lines that have been previously characterized for th eir proliferative response to TGF beta 1. OVCA420, a cell line that is dramatically growth inhibited by TGF beta 1, significantly induced CI P1 expression in response to TGF beta 1. CIP1 induction was accompanie d by a decrease in cdk2 kinase activity and cdk2 protein levels. In th ree other cell lines that respond weakly to TGF beta 1, CIP1 expressio n was not induced. To determine if TGF beta 1 induction occurs via p53 , regulation of p53 RNA and protein was examined. No differences in p5 3 transcription, steady-state protein level, de novo synthesis, phosph orylation, or subcellular accumulation were noted. Furthermore, TGF be ta 1 could not induce transcription from a consensus p53 DNA binding s ite in the TGF beta 1-responsive cell line. Our results suggest that C IP1 expression is an important mediator of TGF beta growth suppression . However, it appears that TGF beta induces CIP1 independent of the p5 3 pathway.