Expression and action of kit ligand/stem cell factor in normal human and bovine ovarian surface epithelium and ovarian cancer

Greater than 95% of ovarian cancers originate from the epithelial cells on the surface of the ovary termed ovarian surface epithelium (OSE). A normal aspect of OSE function is repeated proliferation after ovulation, and this is postulated to be involved in part in the onset of ovarian cancer. The hypothesis tested is that locally produced growth factors have an important role in controlling OSE proliferation. The current study investigates the potential role of the growth factor kit ligand (KL)/stem cell growth factor and its receptor c-kif in normal OSE biology and ovarian cancer. Human tumors from borderline, stage I, and stage III cases of ovarian cancer were found to express KL and c-kif protein in the epithelial cell component by ICC analysis. The stromal cell component of human ovarian tumors contained little immunostaining. Bovine ovarian physiology and endocrinology are similar to the human such that cow ovaries were used as a model system to investigate normal OSE functions. KL and c-kit proteins were detected in the OSE from both normal human and bovine ovaries. Adjacent ovarian stromal tissue contained less intense but positive KL and c-kif immunostaining. To extend the ICC results, RNA was collected from normal bovine OSE and ovarian stromal cells to examine KL gene expression. KL transcripts were detected in cultured OSE and stromal cells by Northern blot analysis. KL gene expression was found to be high in freshly isolated OSE but low in freshly isolated stroma using a quantitative polymerase chain reaction procedure. Levels of KL gene expression in cultured OSE and stroma increased to high levels. Observations indicate that normal OSE expresses high levels of KL in vivo and in vitro. The actions of KL on the growth of both normal OSE cells and ovarian cancer cells was investigated. KL was found to stimulate the growth of normal OSE cells in a similar manner to epidermal growth factor. Observations demonstrate the production and action of KL by normal OSE cells and ovarian cancer cells. Coexpression of KL and c-kit by normal OSE suggests that KL can act as an autocrine factor for OSE. The local production and action of KL on OSE provides insight into normal OSE biology, and a factor that may be involved in the onset and progression of ovarian cancer.