The rat ovarian surface epithelium in vitro
Creators: name: Adams, Anne Theresa
Publisher: name: University of British Columbia
Year: 2010

description: The ovarian surface epithelium, a very small portion of the total mass of the ovary, is generally thought to be the site of origin of over 85% of ovarian cancers. Such cancers are classified with the "Common Epithelial Tumours" of the ovary. In most industrialized countries, malignancies of the ovary rank fourth in cancer deaths in women; over 70% of these neoplasms have spread beyond the ovary when first diagnosed. Experimental approaches to the study of carcinogenesis in this tissue have been limited by the lack of pure populations of ovarian surface epithelial cells. Studies done on rodents in vivo suggest that both chemicals and C-type RNA viruses can induce ovarian cancers similar to those which are said to arise from the surface epithelium. However, the cell of origin cannot be proven in such studies. The purpose of this project was to develop a model for ovarian cancers of surface epithelial origin based on-carcinogenesis in vitro. To this end a method was devised to culture the rat ovarian surface epithelium in pure form. These cultured cells, whose identity has been confirmed by morphological, histochemical and ultrastructural means, are polygonal with clear cytoplasm, have well-defined borders, and grow in confluent monolayers. Their morphology is quite distinct from those of other ovarian cells in vitro. Cultured rat ovarian surface epithelial cells are histochemically positive for 17β-hydroxysteroid dehydrogenase, and negative for Δ5-3β-hydroxysteroid dehydrogenase, the same as in frozen sections of whole rat ovary. Ultrastructurally, cultured surface epithelial cells have basal laminae, microvilli, apical intercellular junctions, large nuclei, abundant rough endoplasmic reticulum, Golgi complexes, perinuclear bundles of microfilaments, and numerous vesicles. Although the ovarian suface epithelium is suspected of being an estrogen target tissue, there is no previous report of estrogen receptors in these cells. In this study cultured rat ovarian surface epithelial cells have been shown by autoradiographic means to exhibit estrogen receptor-like activity. Translocation of tritiated estradiol from cytoplasm to nucleus, and estrogen-specific binding have been demonstrated. Estradiol was shown to be mitogenic for cultured ovarian surface epithelial cells. From these results, the surface epithelial .cells of the ovary should be considered an estrogen target tissue. Kirsten murine sarcoma virus was used to produce three transformed cell lines from pure, first passage cultures of these cells. These three lines retained 170-hydroxysteroid dehydrogenase activity and showed slight Δ5-3β-hydroxysteroid dehydrogenase activity. Tumours resulting when these cells were injected into immunosuppressed female rats were highly malignant and resembled histologically human endometrioid stromal sarcomas of the ovary. This neoplasm is classed with the "Common Epithelial Tumours" of the ovary, but is generally not considered a derivative of the surface epithelium. In light of this study, perhaps this tumour should: be considered, to be of surface epithelial origin. A continuous cell line arising from pure cultures of rat ovarian surface epithelial cells produced structures in vitro resembling those found in ovarian serous papillary cystadenomas of borderline malignancy. This tumour is classed as a common epithelial ovarian tumour. Hence, in this study the rat ovarian surface epithelium has been cultured in pure form, has been characterized for a number of properties by several investigative techniques, and has been shown to be susceptible to transformation by an oncogenic virus; This work supports the theory that the "Common Epithelial Tumours" of the ovary are, in fact, derived from the surface epithelium. The availability of cultured ovarian surface epithelial cells should allow investigation into factors which make this tissue so susceptible to malignant transformation. From such cultures could come markers suitable for use in tests to detect ovarian cancers at an early stage. The culture of pure rat ovarian surface epithelium, as described herein, could readily be used to study chemical, physical and viral carcinogenesis in this tissue to produce experimental models of cancers arising in the ovarian surface epithelium.