Regulation of G-protein signaling by RKTG via sequestration of the G betagamma subunit to the Golgi apparatus

Mol Cell Biol. 2010 Jan;30(1):78-90. doi: 10.1128/MCB.01038-09.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Chlorocebus aethiops
  • G-Protein-Coupled Receptor Kinases / metabolism
  • GTP-Binding Protein beta Subunits / metabolism*
  • GTP-Binding Protein gamma Subunits / metabolism*
  • Gene Silencing
  • Golgi Apparatus / metabolism*
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / physiology*
  • Ligands
  • Membrane Proteins / genetics
  • Membrane Proteins / physiology*
  • Mice
  • Phosphorylation
  • Protein Transport
  • Proto-Oncogene Proteins c-akt / metabolism
  • Receptors, Adrenergic, beta-2 / metabolism
  • Saccharomyces cerevisiae / genetics
  • Signal Transduction
  • Two-Hybrid System Techniques

Substances

  • GTP-Binding Protein beta Subunits
  • GTP-Binding Protein gamma Subunits
  • Intracellular Signaling Peptides and Proteins
  • Ligands
  • Membrane Proteins
  • PAQR3 protein, human
  • Receptors, Adrenergic, beta-2
  • Proto-Oncogene Proteins c-akt
  • G-Protein-Coupled Receptor Kinases