Cross-talk between p38MAPK and Giα in regulating cPLA2 activity by ET-1 in pulmonary smooth muscle cells

Endothelin-1 (ET-1) is known as the most potent vasoconstrictor yet described. Infusion of ET-1 into isolated rabbit lung has been shown to cause pulmonary vasoconstriction with the involvement of arachidonic acid metabolites. Given the potency of arachidonic acid metabolites, the activity of phospholipase A2 must be tightly regulated. Herein, we determined the mechanisms by which ET-1 stimulates cPLA2 activity during ET-1 stimulation of bovine pulmonary artery smooth muscle cells. We demonstrated that (i) treatment of bovine pulmonary artery smooth muscle cells with ET-1 stimulates cPLA2 activity in the cell membrane; (ii) ET-1 caused increase in O2·− production occurs via NADPH oxidase-dependent mechanism; (iii) ET-1-stimulated NADPH oxidase activity is markedly prevented upon pretreatment with PKC-ζ inhibitor, indicating that PKC-ζ plays a prominent role in this scenario; (iv) ET-1-induced NADPH oxidase-derived O2·− stimulates an aprotinin sensitive protease activity due to prominent increase in [Ca2+]i; (v) the aprotinin sensitive protease plays a pivotal role in activating PKC-α, which in turn phosphorylates p38MAPK and subsequently Giα leading to the activation of cPLA2. Taken together, we suggest that cross-talk between p38MAPK and Giα with the involvement of PKC-ζ, NADPH oxidase-derived O2·−, [Ca2+]i, aprotinin-sensitive protease and PKC-α play a pivotal role for full activation of cPLA2 during ET-1 stimulation of pulmonary artery smooth muscle cells.