Ovarian Carcinoma Cell Cultures Are Resistant to TGF-β1-Mediated Growth Inhibition Despite Expression of Functional Receptors

Abstract

Objective. The purpose of this study was to determine the response of ovarian carcinoma cells to TGF-β1 and to examine components of the TGF-β signaling pathway.Methods. Twenty-three primary ovarian cancer cell (CSOC) cultures established from solid ovarian carcinomas were treated with TGF-β1 and assayed for growth response by MTT assay. Expression of TGF-β receptor I (TβR-I) and receptor II (TβR-II), essential for effective signaling, was determined by Western analysis of CSOC cultures. TGF-β1 ligand-induced phosphorylation of TβR-I was determined by immunoprecipitation of TβR-I followed by a protein kinase assay to assess TβR-I phosphorylation, an essential first step in TGF-β signal transduction. Gelatin zymography performed on 5 CSOC cultures incubated with TGF-β1 was used to determine TGF-β's effect on matrix metalloproteinase production. Normal ovarian surface epithelial cells were used for comparison.Results. Eighteen of twenty-three (78%) CSOC cultures demonstrated no significant growth inhibition in response to TGF-β1 treatment. All cell cultures expressed TβR-I and TβR-II and exhibited TβR-I phosphorylation following TGF-β1 treatment. CSOC cultures produced significantly higher levels of matrix metalloproteinase-2 (MMP-2) than normal ovarian surface epithelial cells; however, the level of MMP-2 expression was not regulated by TGF-β1.Conclusion. These results indicate that TGF-β1 resistance and higher levels of MMP-2 production may be inherent properties of the ovarian cancer phenotype. The initial steps in the TGF-β signaling pathway, receptor expression, ligand binding, and TβR-I phosphorylation, appear to be functional in primary ovarian cancer cell cultures. Therefore, the mechanism of growth resistance is downstream of TβR-I phosphorylation.