PROTOONCOGENE PRODUCT, C-MOS KINASE, IS INVOLVED IN UP-REGULATING NA+H+ ANTIPORTER IN XENOPUS OOCYTES/

Progesterone-stimulated Xenopus laevis oocytes undergo an increase in their intracellular pH from 7.3 to 7.7 because of the activation of Na +/H+ antiporters in their plasma membrane. Activation of Na+/H+ exchan gers (NHE) in other cell systems appears to be regulated by phosphoryl ation of the NHE protein. In the current study we demonstrated that cy toplasm taken from steroid-stimulated oocytes rapidly induced an incre ase in intracellular pH when microinjected into full-grown stage VI re cipient oocytes. The protein within the cytoplasm that appears to be r esponsible for this activity is c-mos kinase. Microinjected pure mos(x e) kinase protein rapidly activated the Na+/H+ exchangers in full-grow n recipient oocytes. Furthermore, injected mos(xe) protein rapidly act ivated the Na+/H+ exchangers in smaller progesterone-insensitive stage IV oocytes. Therefore, it appears that the protooncogene product, p39 c-mos kinase, which is normally synthesized in full-grown stage VI oo cytes in response to progesterone stimulation, is involved in the upre gulation of the Na+/H+ antiporters during oocyte meiotic maturation.