Phospholipase C-delta 1 and oxytocin receptor signalling: evidence of its role as an effector

Abstract

Although the oxytocin receptor modulates intracellular Ca2+ ion levels in myometrium, the identities of signal molecules have not been clearly clarified. Our previous studies on oxytocin receptor signalling demonstrated that 80 kDa G(h) alpha is a signal mediator [Baek, Kwon, Lee, Kim, Muralidhar and Im (1996) Biochem. J. 315, 739-744]. To elucidate the effector in the oxytocin receptor signalling pathway, we evaluated the oxytocin-mediated activation of phospholipase C (PLC) by using solubilized membranes from human myometrium and a three-component preparation containing the oxytocin receptor-G(h) alpha-PLC-delta 1 complex. PLC-delta 1 activity in the three-component preparation, as well as PLC activity in solubilized membranes, was increased by oxytocin in the presence of Ca2+ and activated G(h) alpha (GTP-bound G(h) alpha). Furthermore the stimulated PLC-delta 1 activity resulting from activation of G(h) alpha via the oxytocin receptor was significantly attenuated by the selective oxytocin antagonist desGlyNH(2)d(CH2)5[Tyr(Me)(2),Thr(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 the PLC-delta 1 being tightly coupled to activated G(h) alpha on stimulation of the oxytocin receptor. These results indicate that PLC-delta 1 is the effector for G(h) alpha-mediated oxytocin receptor signalling.