Involvement of Gq/11 in both integrin signal-dependent and -independent pathways regulating endothelin-induced neural progenitor proliferation

We have previously shown that endothelin-B receptor stimulation increases neural progenitor proliferation, partly in Gi and extracellular matrix molecule-dependent manner. In the present study, we investigated whether Gq/11 is also involved in this response and how Gi and Gq/11 might regulate the extracellular signal-regulated kinase (ERK) pathway and integrin signaling. Endothelin-induced ERK phosphorylation was independent of integrin ligands, and an inhibitor of Gq/11, YM-254890, as well as pertussis toxin, partially inhibited endothelin-stimulated phosphorylation of Raf-1 and ERK. Endothelin-stimulated protein kinase C (PKC) was partially inhibited by both YM-254890 and pertussis toxin, while only pertussis toxin attenuated endothelin-induced Ras activation. In contrast, endothelin increased tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin in an integrin ligand-dependent manner. Both YM-254890 and pertussis toxin partially inhibited endothelin-stimulated phosphorylation of these proteins. A PKC inhibitor and down-regulation of PKC prevented endothelin-induced phosphorylation of paxillin and ERK. In addition, endothelin-induced proliferation and DNA synthesis were partially inhibited by YM-254890 and pertussis toxin. Taken together, the results indicate that endothelin activates PKC via Gq/11 and Gi, and consequently stimulates the ERK cascade in cooperation with Ras signaling stimulated by Gi. PKC appears to increase tyrosine phosphorylation of paxillin to enhance integrin signaling, which further increases DNA synthesis and proliferation.