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J. Biol. Chem. 275 (52): 41512-41520

© 2000 by The American Society for Biochemistry and Molecular Biology, Inc.

G Protein β{gamma} Subunits Inhibit Nongenomic Progesterone-induced Signaling and Maturation in Xenopus laevis Oocytes


Lindsey B. Lutz, Bonnie Kim, David Jahani, , and Stephen R. Hammes{ddagger}

From the Department of Internal Medicine, University of Texas Southwestern Medical School, Dallas, Texas 75390-8857

ABSTRACT Back to Top

Abstract: Progesterone-induced maturation ofXenopus oocytes is a well known example of nongenomic signaling by steroids; however, little is known about the early signaling events involved in this process. Previous work has suggested that G proteins and G protein-coupled receptors may be involved in progesterone-mediated oocyte maturation as well as in other nongenomic steroid-induced signaling events. To investigate the role of G proteins in nongenomic signaling by progesterone, the effects of modulating Gα and Gβ{gamma} levels in Xenopus oocytes on progesterone-induced signaling and maturation were examined. Our results demonstrate that Gβ{gamma} subunits, rather than Gα, are the principal mediators of progesterone action in this system. We show that overexpression of Gβ{gamma} inhibits both progesterone-induced maturation and activation of the MAPK pathway, whereas sequestration of endogenous Gβ{gamma} subunits enhances progesterone-mediated signaling and maturation. These data are consistent with a model whereby endogenous free Xenopus{gamma} subunits constitutively inhibit oocyte maturation. Progesterone may induce maturation by antagonizing this inhibition and therefore allowing cell cycle progression to occur. These studies offer new insight into the early signaling events mediated by progesterone and may be useful in characterizing and identifying the membrane progesterone receptor in oocytes.

Received for publication July 27, 2000. Revision received September 12, 2000.

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