title: Ric-8 proteins are molecular chaperones that direct nascent G protein α subunit membrane association.
abstract: Ric-8A (resistance to inhibitors of cholinesterase 8A) and Ric-8B are guanine nucleotide exchange factors that enhance different heterotrimeric guanine nucleotide-binding protein (G protein) signaling pathways by unknown mechanisms. Because transgenic disruption of Ric-8A or Ric-8B in mice caused early embryonic lethality, we derived viable Ric-8A- or Ric-8B-deleted embryonic stem (ES) cell lines from blastocysts of these mice. We observed pleiotropic G protein signaling defects in Ric-8A(-/-) ES cells, which resulted from reduced steady-state amounts of Gα(i), Gα(q), and Gα(13) proteins to <5% of those of wild-type cells. The amounts of Gα(s) and total Gβ protein were partially reduced in Ric-8A(-/-) cells compared to those in wild-type cells, and only the amount of Gα(s) was reduced substantially in Ric-8B(-/-) cells. The abundances of mRNAs encoding the G protein α subunits were largely unchanged by loss of Ric-8A or Ric-8B. The plasma membrane residence of G proteins persisted in the absence of Ric-8 but was markedly reduced compared to that in wild-type cells. Endogenous Gα(i) and Gα(q) were efficiently translated in Ric-8A(-/-) cells but integrated into endomembranes poorly; however, the reduced amounts of G protein α subunits that reached the membrane still bound to nascent Gβγ. Finally, Gα(i), Gα(q), and Gβ(1) proteins exhibited accelerated rates of degradation in Ric-8A(-/-) cells compared to those in wild-type cells. Together, these data suggest that Ric-8 proteins are molecular chaperones required for the initial association of nascent Gα subunits with cellular membranes.
authors: Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY 14642, USA.
authors: Meital
authors: M
authors: Gabay
authors: Mary E
authors: ME
authors: Pinter
authors: Forrest A
authors: FA
authors: Wright
authors: PuiYee
authors: P
authors: Chan
authors: Andrew J
authors: AJ
authors: Murphy
authors: David M
authors: DM
authors: Valenzuela
authors: George D
authors: GD
authors: Yancopoulos
authors: Gregory G
authors: GG
authors: Tall
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits / Q000096:biosynthesis*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008817:Mice, Mutant Strains; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*
chemical_list: D044385:GTP-Binding Protein alpha Subunits; D020662:Guanine Nucleotide Exchange Factors; D018832:Molecular Chaperones; C561938:Ric8A protein, human; C485884:Ric8a protein, mouse; C559967:Ric8b protein, mouse; D019205:GTP-Binding Protein alpha Subunits, Gs; C549039:RIC8B protein, human