Involvement of CaM kinase II in gonadotropin-releasing hormone-induced activation of MAP kinase in cultured hypothalamic neurons

Gonadotropin-releasing hormone (GnRH) is secreted from hypothalamic GnRH neurons. There is accumulating evidence that GnRH neurons have GnRH receptors and that the autocrine action of GnRH activates MAP kinase. In this study, we found that KN93, an inhibitor of Ca2+/calmodulin-dependent protein kinases (CaM kinases), inhibited the GnRH-induced activation of MAP kinase in immortalized GnRH neurons (GT1-7 cells). Immunoblot analysis indicated that the CaM kinase IIδ2 isoform (CaM kinase IIδ2) and synapsin I were expressed in GT1-7 cells. GnRH treatment rapidly increased phosphorylation of synapsin I at serine 603, a specific phosphorylation site for CaM kinase II, suggesting that GnRH treatment rapidly activated CaM kinase IIδ2. In addition, when we stably overexpressed CaM kinase IIδ2 in GT1-7 cells, the activation of MAP kinase was strongly enhanced. These results suggest that CaM kinase IIδ2 was involved in the GnRH-induced activation of MAP kinase in GT1-7 cells.