Ghrelin inhibits ovarian epithelial carcinoma cell proliferation in vitro

The only orexigenic peptide, ghrelin, which is primarily produced by the gastrointestinal tract, has been implicated in malignant cell proliferation and invasion. Ghrelin is a natural ligand of the growth hormone secretagogue receptor 1a (GHSR1a). However, the role of ghrelin in ovarian epithelial carcinoma remains unknown since the expression of GHSR1a in ovary is not confirmed. The aim of the present study was to assess expression of ghrelin and its receptor in human ovarian epithelial carcinoma and to examine the effect of ghrelin on carcinoma cell proliferation. Frozen sections of ovarian samples and the human ovarian epithelial carcinoma cell line, HO-8910, were used to characterize the expression of ghrelin/GHSR1a axis and the effect of ghrelin on proliferation. We found that ghrelin and GHSR1a are expressed in ovarian epithelial carcinoma in vivo and in vitro. Ghrelin inhibits the proliferation and growth of HO-8910 cells by G1 phase arrest, and this inhibition may be abolished by the ghrelin receptor antagonist D-Lys-3-GH-releasing peptide-6 and ghrelin neutralizing antibody. Ghrelin enhances HO-8910 cell apoptosis and autophagy. The activation of mammalian target of rapamycin (mTOR) signaling pathway blocks the effects of ghrelin-induced autophagy and apoptosis, therefore reverses the inhibition of HO-8910 cell proliferation induced by ghrelin. In conclusion, the present study demonstrates that ghrelin inhibits the proliferation of human HO-8910 ovarian epithelial carcinoma cells by inducing apoptosis and autophagy via the mTOR signaling pathway. This study provides a novel regulatory signaling pathway of ghrelin-regulated ovarian epithelial carcinoma growth and may contribute to ovarian cancer prevention and therapy.