Ubiquitination of the heterotrimeric G protein α subunits Gαi2 and Gαq is prevented by the guanine nucleotide exchange factor Ric-8A

Biochem Biophys Res Commun. 2013 Jun 7;435(3):414-9. doi: 10.1016/j.bbrc.2013.04.103. Epub 2013 May 9.

Abstract

The cytosolic protein Ric-8A acts as a guanine nucleotide exchange factor for Gα subunits of the Gi, Gq, and G12/13 classes of heterotrimeric G protein in vitro, and is also known to increase the amounts of these Gα proteins in vivo. The mechanism whereby Ric-8 regulates Gα content, however, has not been fully understood. Here we show that Ric-8 Astabilizes Gαi2 and Gαq by preventing their ubiquitination. Ric-8A interacts with and stabilizes Gαi2, Gαq, Gα12, but not Gαs, when expressed in COS-7 cells. The protein levels of Gαi2 and Gαq appear to be controlled via the ubiquitin-proteasome degradation pathway, because these Gα subunits undergo polyubiquitination and are stabilized with the proteasome inhibitor MG132. The ubiquitination of Gαi2 and Gαq is suppressed by expression of Ric-8A. The suppression likely requires Ric-8A interaction with these Gα proteins; the C-terminal truncation of Gαq and Gαi2 completely abrogates their interaction with Ric-8A, their stabilization by Ric-8A, and Ric-8A-mediated inhibition of Gα ubiquitination.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • COS Cells
  • Chlorocebus aethiops
  • GTP-Binding Protein alpha Subunit, Gi2 / antagonists & inhibitors*
  • GTP-Binding Protein alpha Subunit, Gi2 / chemistry*
  • GTP-Binding Protein alpha Subunit, Gi2 / metabolism
  • GTP-Binding Protein alpha Subunits, Gq-G11 / antagonists & inhibitors*
  • GTP-Binding Protein alpha Subunits, Gq-G11 / chemistry*
  • GTP-Binding Protein alpha Subunits, Gq-G11 / metabolism
  • Guanine Nucleotide Exchange Factors / genetics
  • Guanine Nucleotide Exchange Factors / physiology*
  • Humans
  • Protein Stability
  • Ubiquitination

Substances

  • Guanine Nucleotide Exchange Factors
  • Ric8A protein, human
  • GTP-Binding Protein alpha Subunit, Gi2
  • GTP-Binding Protein alpha Subunits, Gq-G11