Granulosa cell lines as models of ovarian carcinogenesis

Abstract

Cell lines derived from rat ovarian granulosa cells were established as an epithelial model system for studies of in vitro transformation. A series of experiments focused on analysis of an unusual nuclear distribution of the oncogene products T-antigen and p53 in an SV40- transformed cell line, DC3. Antibodies to T-antigen and p53 were used in conjunction with morphological and biochemical approaches to explain the nature of these antigens in DC3 cells as compared to COS-1, an established SV40-transformed cell line. Approaches included indirect immunofluorescence, double immunolabelling, cell cycle analysis, confocal microscopy, immunogold electron microscopy, nuclear fractionation, Western blot analysis, and DNA transfection of SV40 genes into both primary granulosa and DC3 cells. The results suggested that the unusual distribution of T-antigen and p53 in DC3 cells appears to be characteristic of interphase and is probably not due to gross structural alterations in either protein. A second series of experiments focused on developing a series of cell lines representative of progressive steps in the multistep process of malignant transformation. Primary granulosa cells and a spontaneously immortalized cell line, SIGC, represented the normal state and an intermediate step in transformation, respectively. Several morphological and functional properties of SIGC were evaluated with respect to those of normal granulosa cells. Cell lines further in the transformation pathway were generated by transfecting SIGC with pSV3neo and from tumor explants of transfected cells from a nude mouse. A dye transfer technique showed that progressive stages of transformation were correlated with a progressive loss of gap junction mediated cell-cell communication. The results of this study suggest that the in vitro transformation model system consisting of several cell lines derived from ovarian granulosa cells may be useful for studies of the fundamental nature of transformation in cell types other than those of fibroblast origin. These studies include using DC3 cells for investigation of novel functions of T-antigen, and SIGC cells for transfection or infection with other oncogenes in order to investigate the impact of their expression on cell-cell communication and other growth properties in an epithelial model system.