ACTIVATION OF PHOSPHOLIPASE A(2) BY THE NOCICEPTIN RECEPTOR EXPRESSEDIN CHINESE-HAMSTER OVARY CELLS

To gain insight into the molecular mechanism for nociceptin function, functional coupling of the nociceptin receptor expressed in Chinese ha mster ovary (CHO) cells with phospholipase A, (PLA,) was examined. In the presence of A23187, a calcium ionophore, activation of the nocicep tin 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-Ca2+-dependent cytosolic PLA(2) (cPLA(2)) monoclonal antibody demonstrates that activation of the noc iceptin receptor induces a time- and dose-dependent electrophoretic mo bility shift of cPLA(2), suggesting that phosphorylation of cPLA(2) is induced by the nociceptin receptor. Pretreatment of the cells with PD 98059, a specific mitogen-activated protein kinase/extracellular signa l-regulated kinase kinase 1 inhibitor, or staurosporine, a potent inhi bitor of serine/threonine protein kinases and tyrosine protein kinases , partially inhibited the nociceptin-induced cPLA(2) phosphorylation a nd arachidonate release. These results indicate that the nociceptin re ceptor expressed in CHO cells couples with cPLA(2) through the action of PTX-sensitive G proteins and suggest that cPLA(2) is activated by p hosphorylation induced by the nociceptin receptor via mechanisms parti ally dependent on p44 and p42 mitogen-activated protein kinases.