Transforming growth factor-beta regulates Kit ligand expression in rat ovarian surface epithelial cells

In preparation for ovulation, paracrine communication between the preovulat ory follicle and overlying theca/ stromal cells and ovarian surface epithel ium (OSE) must take place to facilitate the degradative and apoptotic event s associated with ovulation. Kit tyrosine kinase receptors and their ligand , kit ligand (KL) are expressed within ovarian follicles. and ligand-induce d receptor activation appears to account for some of the cell-cell interact ions important for oocyte development. We investigated the expression of Ki t receptors and KL in OSE cells and the possibility that modulation of thei r expression could affect OSE cell activity.. KL mRNA and protein,were dete cted in the OSE cell layer of rat ovaries, and primary cultures of rat OSE as well as the immortalized rat OSE cell line, ROSE 199, expressed KL, but not Kit receptors, Both primary and immortalized OSE cells preferentially e xpressed KL-1, rather than KL-2. transcripts, suggesting that these cells p roduce predominantly the soluble form of KL. Activation of the cAMP signall ing pathway using dibutyryl cAMP decreased proliferation of ROSE 199 cells and elicited a threefold increase in KL expression. TGF-P similarly inhibit ed ROSE 199 cell proliferation but strongly inhibited dibutyryl cAMP-induce d KL expression, indicating that changes in KL expression were not directly associated with OSE cell proliferation. The expression of mostly soluble K L in the surface epithelium suggests that this cytokine may be acting in a paracrine fashion, perhaps interacting with nearby Kit receptor-bearing the ca cells.