No abstract

The growth-inhibitory protein p21WAF1/CIP1 is a potent inhibitor of various cyclin-dependent kinases, the expression of which is regulated at the transcriptional level by p53-dependent and -independent mechanisms. We examined p21WAF1/CIP1 mRNA and protein expression in 5 human ovarian-adenocarcinoma cell lines, 1 primary culture of normal surface epithelium and 17 human ovarian-tumor specimens. In culture cells, the p21WAF1/CIP1 protein was expressed in normal ovarian epithelial cells and at a high level in the adenocarcinoma 2008 and IGROV-1 cell lines. p21 WAF1/CIP1 expression was undetectable at the mRNA and protein levels in the NIH-OVCAR-3 and SKOV-3 ovarian-adenocarcinoma cell lines which are respectively mutated and deleted in the p53 gene. Heterogeneous expression of p21WAF1/CIP1 observed in ovarian-cancer cell lines in culture was also found in vivo on tumor specimens. p21WAF1/CIP1 expression is undetectable in 25% of the ovarian biopsies examined. Since it has been found that the p53 gene is mutated in 79% of ovarian cancer, the absence of p21WAF1/CIP1 expression in 25% of these ovarian cancer could not be correlated with p53 mutation. The proliferation index of the 17 tumors showed great variation from one tumor to another. However, no significant correlation was found between p21WAF1/CIP1 expression and the proliferation rate of the tumors.

In the human breast carcinoma cell line (MCF-7), exogenous TGF-beta 1 induces a dose-dependent inhibition of cell proliferation. In a MCF-7 cell subline [MCF-7(-)], which has an undetectable level of type II TGF-beta receptor, exogenous TGF-beta 1 does not inhibit cell proliferation but is still able to induce its own message. In both cell lines, TGF-beta 1 stimulates expression of c-jun, whereas a rapid, transient and marked increase in c-fos mRNA is only observed in the MCF-7 cells sensitive to the growth inhibitory effect of TGF-beta 1. Depletion of protein kinase C abolishes the c-fos but not the c-jun response to TGF-beta 1. Our results suggest that growth inhibition and autoinduction by TGF-beta 1 are mediated by different signalling pathways. In addition, a PKC-dependent increase in c-fos expression seems to be associated with the growth inhibitory effect of TGF-beta 1.

The antiproliferative effects of TGF-/31 were investigated in a human breast adenocarcinoma cell line (MCF-7). We report that TGF-I~I inhibits proliferation through cell cycle arrest in G~. A MCF-7 cell subline (MCF-7(-)), in which the type II TGF-I~ receptor is not detected, was shown to be resistant to TGF-J~I growth inhibitory effect. Cdk2 kinase activity was inhibited in the MCF-7 sensitive cell subline in parallel with the inhibition of cell cycle progression. In both sensitive and resistant cell lines, TGF-I~I treatment did not affect cdk2, cdk4, cyclin E and cyclin D1 mRNA and protein levels. However, in the MCF-7 sensitive cell subline, a time-dependent increase in cells positive for p21 wArltclpl nuclear localization was observed after TGF-g31 treatment. These findings suggest that TGF-131 inhibition of MCF-7 cell proliferation is achieved through a type II receptordependent down-regulation of Cdk2 kinase activity without modification of Cdk and cyclin expression, but correlated with an increase in p21WAFvcmn nuclear accumulation.