INCREASED LEVEL OF P21 IN HUMAN OVARIAN-TUMORS IS ASSOCIATED WITH INCREASED EXPRESSION OF CDK2, CYCLIN-A AND PCNA

dependent kinase inhibitor p21 in various ovarian-cancer cell lines as well as in ovarian-tumor biopsies. This increase in p21 expression re lative to that observed in normal ovarian epithelial cells is unrelate d to proliferation index. In the present study, we found that p21 is f unctional, since the protein extracted from IGROVI cells is still able to inhibit cdk2-kinase activity. We then investigated how IGROVI cell s overcome the growth-inhibitory function of p21. Immunofluorescence a ssays and subcellular fractionation showed that p21 is located in cyto plasm and nucleus both in normal and in tumoral cells. Compared with n ormal ovarian epithelial cells in culture, the increase in level of p2 1 in IGROVI cells was found to be associated with increased expression of cdk2, cyclin-A and PCNA proteins. In IGROVI cells, p21 is associat ed with inactive cdk2/cyclin-A complex, indicating that it acts as an inhibitory factor rather than an assembly factor. Over-expression of c dk2 and of cyclin A observed in IGROVI cells allows them to escape to p21-inhibitory activity. The fact that cells from ovarian-tumor biopsi es exhibited a concomitant increase in p21 and in its partners cdk2 an d PCNA suggest that ovarian-tumor cells can tolerate high levels of fu nctional p21 via over-expression of other cell-cycle-regulatory protei ns. (C) 1998 Wiley-Liss, Inc.