Sci. STKE, 24 January 2006
G PROTEINS Independent of GPCRs and Nucleotide Exchange
Sato et al. used a strain of yeast lacking the pheromone receptor to functionally screen mammalian cDNA libraries and identify nonreceptor proteins that activate heterotrimeric guanine nucleotide-binding protein (G protein) signaling. They identified a previously uncharacterized protein that they called activator of G protein signaling (AGS) 8, which was derived from cardiac tissue in a rat model of transient myocardial ischemia. Expression of AGS8 mRNA was increased in ischemic ventricles but not in other models of cardiac dysfunction. The effects of hypoxia were specific: Whereas expression of AGS8 mRNA increased in response to hypoxia in cultured ventricular myocytes, it was unaffected in aortic smooth muscle cells, aortic endothelial cells, and cardiac fibroblasts. AGS8 was functionally active in yeast strains that expressed various Gα subunits, including a mutant Gαi2 believed to remain bound to GDP (rather than exchanging GTP for GDP), but required the presence of Gβ and downstream components of the mitogen-activated protein kinase signaling pathway (the kinase Ste20 and the scaffolding protein Ste5). Moreover, an in vitro binding assay indicated that AGS8 interacted with Gβ but not with Gαi1/2, Gαi3, Gαo, or Gαs. In COS-7 cells, coexpression of AGS8 with Gβ and the Gβ effector PLC-β2 did not inhibit Gβ-stimulated inositol phosphate production; rather, it reversed inhibition of Gβ-stimulated inositol phosphate production by Gα13. A similar reversal by AGS8 of inhibitory effects of Gα on Gβ function was apparent in yeast. Thus, AGS8 appears to be a regulator of G protein signaling that is induced in ischemic heart to act through a mechanism involving interaction with Gβ.
M. Sato, M. J. Cismowski, E. Toyota, A. V. Smrcka, P. A. Lucchesi, W. M. Chilian, S. M. Lanier, Identification of a receptor-independent activator of G protein signaling (AGS8) in ischemic heart and its interaction with Gβ. Proc. Natl. Acad. Sci. U.S.A. 103, 797-802 (2006). [Abstract] [Full Text]
Citation: Independent of GPCRs and Nucleotide Exchange. Sci. STKE 2006, tw35 (2006).
Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882