PHOSPHOLIPASE C-DELTA-1 AND OXYTOCIN RECEPTOR SIGNALING - EVIDENCE OFITS ROLE AS AN EFFECTOR

Although the oxytocin receptor modulates intracellular Ca2+ ion levels in myometrium, the identities of signal molecules have not been clear ly clarified. Our previous studies on oxytocin receptor signalling dem onstrated that 80 kDa G(h) alpha is a signal mediator [Baek, Kwon, Lee , Kim, Muralidhar and Im (1996) Biochem. J. 315, 739-744]. To elucidat e the effector in the oxytocin receptor signalling pathway, we evaluat ed the oxytocin-mediated activation of phospholipase C (PLC) by using solubilized membranes from human myometrium and a three-component prep aration containing the oxytocin receptor-G(h) alpha-PLC-delta 1 comple x. PLC-delta 1 activity in the three-component preparation, as well as PLC activity in solubilized membranes, was increased by oxytocin in t he presence of Ca2+ and activated G(h) alpha (GTP-bound G(h) alpha). F urthermore the stimulated PLC-delta 1 activity resulting from activati on of G(h) alpha via the oxytocin receptor was significantly attenuate d by the selective oxytocin antagonist desGlyNH(2)d(CH2)5[Tyr(Me)(2),T hr(4)] ornithine vasotocin or GDP. Consistent with these observations, co-immunoprecipitation and co-immunoadsorption of PLC-delta 1 in the three-component preparation by anti-G(h7)alpha antibody resulted in th e PLC-delta 1 being tightly coupled to activated G(h) alpha on stimula tion of the oxytocin receptor. These results indicate that PLC-delta 1 is the effector for G(h) alpha-mediated oxytocin receptor signalling.