PARENT SESSION

(M775) GONADOTROPIN-RELEASING HORMONES (GnRH) I AND II INDUCED GROWTH INHIBITION OF OVARIAN CANCER CELLS VIA THE GnRH-I RECEPTOR (GnRHR) AND PROTEIN KINASE C PATHWAY.

Kim, Ki-Yon ¹, Choi, Kyung-Chul¹, Park, Se-Hyung¹, Park, Dong-Wook¹, An, Beum-Soo¹, Auersperg, Nelly ¹, Leung, Peter C. K.¹, ¹ University of British Columbia, Vancouver, BC, Canada

ABSTRACT- It has been reported that a second form of gonadotropin-releasing hormone (GnRH-II) may exert a stronger anti-proliferative effect than a classical form of GnRH-I in ovarian cancer cells. In this study, the mechanism of GnRH-II, specifically, the potential involvement of GnRH receptor (GnRHR), protein kinase C (PKC) stimulation and epidermal growth factor (EGF) receptor was investigated in the regulation of proliferation in ovarian cancer cells. Immunocytochemistry using streptavidin/biotin immunoperoxidase was carried out to demonstrate the expression of GnRHR protein in SKOV-3 and OVCAR-3 cells. To determine whether GnRH-I or II activates extracellular-regulated kinases (ERK1/2), immunoblot analysis was performed in SKOV-3 and OVCAR-3 cells. The cells were pretreated with specific antagonists/inhibitors of GnRH-I (Antide), PKC (GF109203X), or EGF receptor (AG1478). To knockdown GnRHR gene expression, short-interfering RNA (siRNA) was transfected into the cells. The expression levels of GnRHR mRNA and protein in the transfected cells were significantly knock-down, in part, and confirmed by real-time PCR and Western blot analysis, respectively. Thymidine incorporation assay was performed to investigate the effect of GnRH-II in the regulation of cell proliferation. The pretreatment with Antide, GF109203X, or AG1478 reversed the GnRH-I or II (10^-7 M)-induced ERK1/2 activation. An anti-proliferative effect of GnRH-II was blocked by Antide and GF109203X, whereas AG1478 failed to block the anti-proliferative effect of GnRH-I or II. In addition, the transfection of the cells with siRNA for GnRHR reversed the anti-proliferative effect of GnRH-II. Taken together, these results indicate that the type I GnRHR is essential for both GnRH-I and II-induced anti-proliferation of ovarian cancer cells. In addition, a PKC pathway, but not EGF receptor, may be involved in GnRH-II-induced inhibition of cell proliferation through ERK1/2 in these cells. [This work was supported by the Canadian Institutes of Health Research]

KEY WORDS: GnRH, GnRH receptor, ovarian cancer, MAPK