Extracellular signal-regulated protein kinase, but not c-JunN-terminal kinase, is activated by type II gonadotropin-releasing hormone involved in the inhibition of ovarian cancer cell proliferation

Although a novel second form of GnRH (GnRH-II) has been reported to have an antiproliferative effect on gynecologic cancer cells, its biological mechanism remains to be elucidated. We have previously demonstrated that GnRH-II activates p38 MAPK. There is accumulating evidence that activation of MAPKs by GnRH-I and -II is important for cell proliferation, differentiation, and apoptosis. In the present study, we further investigated the involvement of GnRH-II in the inhibition of cell proliferation and activation of ERK1/2 and c-Jun N-terminal protein kinase/stress-activated protein kinase (JNK/SAPK) in ovarian cancer cells, OVCAR-3. The [H-3] thymidine incorporation and 3-(4,5-dimethylthiazol-2-yl)2,5- diphenyltetrazolium bromide (MTT) assays revealed that treatment with GnRH-II suppresses cell proliferation of ovarian cancer cells. Western blot analysis demonstrated that ERK1/2 was activated by GnRH-II ( 100 nM). Moreover, PD98059 ( 10 mu M), an inhibitor of a MAPK/ERK kinase, reversed the activation of ERK1/2 induced by GnRH-II. The activation of ERK1/2 by GnRH-II subsequently phosphorylated Elk-1 as a downstream pathway, which was blocked by PD98059. On the other hand, it is not likely that GnRH-II activates the JNK/SAPK pathway. Taken together, these results indicate that the ERK1/2 pathway is involved in the effect of GnRH-II on antiproliferation and may be an important target for ovarian cancer therapy.