Regulation of MAP kinase by calcium-sensing receptor in bovine parathyroidand CaR-transfected HEK293 cells

Regulation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pa thway by the extracellular calcium (Ca-o(2+))-sensing receptor (CaR) was in vestigated in bovine parathyroid and CaR-transfected human embryonic kidney (HEKCaR) cells. Elevating Ca-o(2+) or adding the selective CaR activator N PS R-467 elicited rapid, dose-dependent phosphorylation of ERK1/2. These ph osphorylations were attenuated by pretreatment with pertussis toxin (PTX) o r by treatment with the phosphotyrosine kinase (PTK) inhibitors genistein a nd herbimycin, the phosphatidylinositol-specific phospholipase C (PI-PLC) i nhibitor U-73122, or the protein kinase C (PKC) inhibitor GF109203X and wer e enhanced by the PKC activator phorbol 12-myristate 13-acetate. Combined t reatment with PTX and inhibitors of both PKC and PTK nearly abolished high Ca-o(2+)-evoked ERK1/2 activation in HEKCaR cells, demonstrating CaR-mediat ed coupling via both G(q) and G(i). High Ca-o(2+) increased serine phosphor ylation of the 85-kDa cytosolic phospholipase A(2) (cPLA(2)) in both parath yroid and HEKCaR cells. The selective mitogen-activated protein kinase (MAP K) inhibitor PD98059 abolished high-Ca-o(2+)-induced ERK1/2 activation and reduced cPLA(2) phosphorylation in both cell types, documenting MAPK's role in cPLA(2) activation. Thus our data suggest that the CaR activates MAPK t hrough PKC, presumably through G(q/11)-mediated activation of PI-PLC, as we ll as through G(i)- and PTK-dependent pathway(s) in bovine parathyroid and HEKCaR cells and indicate the importance of MAPK in cPLA(2) activation.