Immortalisation of human ovarian surface epithelium with telomerase and temperature-sensitive SV40 large T antigen

Epithelial ovarian cancer is the most common form of gynaecological malignancy. This lethal disease is thought to arise in ovarian surface epithelial (OSE) cells. The biology of these cells is not well understood, due to the limited amount of tissue that can be obtained from a single biopsy and their limited life span in culture. To overcome these problems, we have conditionally immortalised OSE cells with the catalytic subunit of telomerase (hTERT) and a temperature-sensitive form of SV40 Large T antigen (tsT). We have maintained these cells (designated OSE-C2) in culture for more than 100 population doublings after introduction of the immortalising genes. Early passage OSE-C2 cells have a near-tetraploid karyotype and exhibit a dual mesenchymal-epithelial phenotype, with consistent expression of vimentin and variable expression of cytokeratins and type III collagen, and absence of E cadherin expression. OSE-C2 cells proliferate steadily at the permissive temperature of 33 degrees C, but fail to increase in number at the nonpermissive temperature of 39 degrees C. Serum-deprived OSE-C2 cells are stimulated to grow at 33 degrees C by EGF, whereas they are growth inhibited at 33 degrees C by TGFbeta in the presence or the absence of serum. When temperature shifted to the nonpermissive temperature, OSE-C2 cells modulate to a more mesenchymal phenotype, and a proportion of the cells undergo senescence and/or apoptosis. Moreover, at the nonpermissive temperature, the levels of p53 and SV40 Large T antigen diminish, whilst the level of p21 increases, whereas the level of p16 and telomerase activity is unchanged. This experimental system shows that expression of telomerase alone only allows limited proliferative potential of OSE cells; expression of tsT is necessary to maintain these cells in culture for longer periods, perhaps by its ability to inactivate components of the p53/Rb pathway. OSE-C2 cells may be useful in studying the physiology and differentiation of human OSE cells and provide insight into the poorly understood earliest stages of epithelial ovarian cancer.