title: Ubiquitination of the heterotrimeric G protein α subunits Gαi2 and Gαq is prevented by the guanine nucleotide exchange factor Ric-8A.
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.
authors.affiliation: Department of Biochemistry, Kyushu University, Graduate School of Medical Sciences, 3-1-1 Maidashi, Fukuoka 812-8582, Japan.
authors.forename: Kanako
authors.initials: K
authors.lastname: Chishiki
authors.forename: Sachiko
authors.initials: S
authors.lastname: Kamakura
authors.forename: Satoru
authors.initials: S
authors.lastname: Yuzawa
authors.forename: Junya
authors.initials: J
authors.lastname: Hayase
authors.forename: Hideki
authors.initials: H
authors.lastname: Sumimoto
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000502:physiology*; D006801:Humans; D055550:Protein Stability; D054875:Ubiquitination
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C561938:Ric8A protein, human; D051960:GTP-Binding Protein alpha Subunit, Gi2; D043802:GTP-Binding Protein alpha Subunits, Gq-G11