Characterization of cultured human ovarian surface epithelial cells: phenotypic plasticity and premalignant changes

The ovarian surface epithelium (OSE) is a modified mesothelium that gives rise to most human ovarian carcinomas. In culture, OSE cells tend to assume atypical morphologies that make it difficult to accurately identify normal OSE cells and to recognize pathologic changes. The present study was undertaken to improve the accuracy of OSE identification and to distinguish phenotypic variations of normal OSE cells from early (pre)neoplastic changes.

The expression of epithelial and stromal markers was compared between OSE cultures in low passage, three simian virus 40-immortalized OSE lines (IOSE lines) and two ovarian carcinoma lines, using immunofluorescence microscopy, immunocytochemistry, and Western blots, with fibroblasts and vascular endothelial cells as controls.

Whereas keratin remained a convenient and specific epithelial marker for normal OSE, it was not expressed by all cells, and it diminished with passages in culture. E-cadherin and desmoplakins were absent in cultured OSE, mucin was detected in few cells, and microvilli diminished within one to two passages. Laminin and collagen IV were uniformly expressed and stable with time but were also found in endothelial cells. In contrast to endothelial cells, OSE lacked Factor VIII and did not bind Ulex Europaeus Lectin. The three IOSE lines were more stable than OSE morphologically, and keratin was expressed consistently in 100%, 90%, and 0% of the cells, respectively. All IOSE cells produced laminin and collagen IV but lacked E-cadherin. Microvilli persisted in 50% of the cells in one IOSE line and were lacking in the others. The antibody to breast/ovarian carcinoma, 2G3, reacted with few OSE cells but with significantly more IOSE cells. All fibroblast markers tested (vimentin, collagen types I and III, and prolyl-4-hydroxylase) were expressed in OSE and IOSE cultures, concurrently with the epithelial markers. There was no consistent relationship between any of the markers and cell morphology.

Cultured OSE is more accurately identified if the demonstration of keratin is supplemented by 2G3, laminin, or the lack of endothelial markers. The modulation to a fibroblast-like morphology by OSE cells may reflect the expression of their dual epithelio-mesenchymal phenotype rather than epithelio-mesenchymal conversion. Possible indicators of early neoplastic change in immortalized OSE cells include reduced morphologic plasticity and increased 2G3 binding.