Role of Dynamin, Src, and Ras in the Protein Kinase C-mediated Activation of ERK by Gonadotropin-releasing Hormone

G-protein-coupled receptors are a large group of integral membranal receptors, which in response to ligand binding initiate diverse downstream signaling. Here we studied the gonadotropin-releasing hormone (GnRH) receptor, which uses Gq for its downstream signaling. We show that extracellular signal-regulated kinase (ERK) activation is fully dependent on protein kinase C (PKC), but only partially dependent on Src, dynamin, and Ras. Receptor tyrosine kinases, FAK, Gβγ, and β-arrestin, which were implicated in some G-protein-coupled receptor signaling to MAPK cascades, do not play a role in the GnRH to ERK pathway. Our results suggest that the activation of ERK by GnRH involves two distinct signaling pathways, which converge at the level of Raf-1. The main pathway involves a direct activation of Raf-1 by PKC, and this step is partially dependent on a second pathway consisting of Ras activation, which occurs in a dynamin-dependent manner, downstream of Src.