Activation of Phospholipase A2 by the Nociceptin Receptor Expressed in Chinese Hamster Ovary Cells

To gain insight into the molecular mechanism for nociceptin function, functional coupling of the nociceptin receptor expressed in Chinese hamster ovary (CHO) cells with phospholipase A 2 (PLA 2 ) was examined. In the presence of A23187, a calcium ionophore, activation of the nociceptin receptor induced time- and dose-dependent release of arachidonate, which was abolished by pretreatment of the cells with pertussis toxin (PTX). Immunoblot analysis using anti-Ca 2+ -dependent cytosolic PLA 2 (cPLA 2 ) monoclonal antibody demonstrates that activation of the nociceptin receptor induces a time- and dose-dependent electrophoretic mobility shift of cPLA 2 , suggesting that phosphorylation of cPLA 2 is induced by the nociceptin receptor. Pretreatment of the cells with PD98059, a specific mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 inhibitor, or staurosporine, a potent inhibitor of serine/threonine protein kinases and tyrosine protein kinases, partially inhibited the nociceptin-induced cPLA 2 phosphorylation and arachidonate release. These results indicate that the nociceptin receptor expressed in CHO cells couples with cPLA 2 through the action of PTX-sensitive G proteins and suggest that cPLA 2 is activated by phosphorylation induced by the nociceptin receptor via mechanisms partially dependent on p44 and p42 mitogen-activated protein kinases.