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  • Title: Regulation of G-protein signaling by RKTG via sequestration of the G betagamma subunit to the Golgi apparatus.
    Author: Jiang Y, Xie X, Zhang Y, Luo X, Wang X, Fan F, Zheng D, Wang Z, Chen Y.
    Journal: Mol Cell Biol; 2010 Jan; 30(1):78-90. PubMed ID: 19884349.
    Abstract:
    Upon ligand binding, G-protein-coupled receptors (GPCRs) impart the signal to heterotrimeric G proteins composed of alpha, beta, and gamma subunits, leading to dissociation of the G alpha subunit from the G betagamma subunit. While the G alpha subunit is imperative for downstream signaling, the G betagamma subunit, in its own right, mediates a variety of cellular responses such as GPCR desensitization via recruiting GRK to the plasma membrane and AKT stimulation. Here we report a mode of spatial regulation of the G betagamma subunit through alteration in subcellular compartmentation. RKTG (Raf kinase trapping to Golgi apparatus) is a newly characterized membrane protein specifically localized at the Golgi apparatus. The N terminus of RKTG interacts with G beta and tethers G betagamma to the Golgi apparatus. Overexpression of RKTG impedes the interaction of G betagamma with GRK2, abrogates the ligand-induced change of subcellular distribution of GRK2, reduces isoproterenol-stimulated phosphorylation of the beta2-adrenergic receptor (beta 2AR), and alters beta 2AR desensitization. In addition, RKTG inhibits G betagamma- and ligand-mediated AKT phosphorylation that is enhanced in cells with downregulation of RKTG. Silencing of RKTG also alters GRK2 internalization and compromises ligand-induced G beta translocation to the Golgi apparatus. Taken together, our results reveal that RKTG can modulate GPCR signaling through sequestering G betagamma to the Golgi apparatus and thereby attenuating the functions of G betagamma.
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