G PROTEINS G Proteins Impede Maturation

Abstract:

Steroid hormones can influence cellular events by two very different mechanisms: interaction with ligand-activated transcription factors to regulate gene expression or interaction with cell-surface proteins to regulate nongenomic signaling pathways. Lutz et al. studied progesterone-induced maturation of Xenopus oocytes, which have high and low affinity-binding sites for progesterone at the plasma membrane. Injection of a variety of RNAs and chemicals to influence G protein subunit activity suggested that constitutively active free Gß subunits act as inhibitors of oocyte maturation. Treatments that depleted free Gß enhanced progesterone-stimulated oocyte maturation and promoted tyrosine phosphorylation of extracellular signal-regulated kinase 1 (ERK1) and treatments that increased free Gß levels inhibited progesterone-stimulated maturation and decreased ERK1 phosphorylation. The authors propose that progesterone acts via an unknown mechanism (possibly by antagonizing a constitutively active G protein-linked receptor) to sequester these inhibitory Gß subunits and promote maturation.

Lutz, L.B., Kim, B., Jahani, D., and Hammes, S.R. (2000) G protein ß subunits inhibit nongenomic progesterone-induced signaling and maturation of Xenopus laevis oocytes. J. Biol. Chem. 275: 41512-41520. [Abstract] [Full Text]