title: Dopamine receptor-interacting protein 78 acts as a molecular chaperone for Ggamma subunits before assembly with Gbeta.
abstract: Heterotrimeric G proteins play a central role in intracellular communication mediated by extracellular signals, and both Galpha and Gbetagamma subunits regulate effectors downstream of activated receptors. The particular constituents of the G protein heterotrimer affect both specificity and efficiency of signal transduction. However, little is known about mechanistic aspects of G protein assembly in the cell that would certainly contribute to formation of heterotrimers of specific composition. It was recently shown that phosducin-like protein (PhLP) modulated both Gbetagamma expression and subsequent signaling by chaperoning nascent Gbeta and facilitating heterodimer formation with Ggamma subunits (Lukov, G. L., Hu, T., McLaughlin, J. N., Hamm, H. E., and Willardson, B. M. (2005) EMBO J. 24, 1965-1975; Humrich, J., Bermel, C., Bunemann, M., Harmark, L., Frost, R., Quitterer, U., and Lohse, M. J. (2005) J. Biol. Chem. 280, 20042-20050). Here we demonstrate using a variety of techniques that DRiP78, an endoplasmic reticulum resident protein known to regulate the trafficking of several seven transmembrane receptors, interacts specifically with the Ggamma subunit but not Gbeta or Galpha subunits. Furthermore, we demonstrate that DRiP78 and the Gbeta subunit can compete for the Ggamma subunit. DRiP78 also protects Ggamma from degradation until a stable partner such as Gbeta is provided. Furthermore, DRiP78 interaction may represent a mechanism for assembly of specific Gbetagamma heterodimers, as selectivity was observed among Ggamma isoforms for interaction with DRiP78 depending on the presence of particular Gbeta subunits. Interestingly, we could detect an interaction between DRiP78 and PhLP, suggesting a role of DRiP78 in the assembly of Gbetagamma by linking Ggamma to PhLP.Gbeta complexes. Our results, therefore, suggest a role of DRiP78 as a chaperone in the assembly of Gbetagamma subunits of the G protein.
authors.affiliation: Department of Pharmacology and Therapeutics, McGill University, Montréal, Québec, H3G 1Y6, Canada.
authors.forename: Denis J
authors.initials: DJ
authors.lastname: Dupré
authors.forename: Mélanie
authors.initials: M
authors.lastname: Robitaille
authors.forename: Maxime
authors.initials: M
authors.lastname: Richer
authors.forename: Nathalie
authors.initials: N
authors.lastname: Ethier
authors.forename: Aida M
authors.initials: AM
authors.lastname: Mamarbachi
authors.forename: Terence E
authors.initials: TE
authors.lastname: Hébert
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D005326:Fetal Proteins; D044385:GTP-Binding Protein alpha Subunits / Q000096:biosynthesis / Q000235:genetics; D044387:GTP-Binding Protein beta Subunits / Q000096:biosynthesis* / Q000235:genetics; D044388:GTP-Binding Protein gamma Subunits / Q000096:biosynthesis* / Q000235:genetics; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000096:biosynthesis* / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D021381:Protein Transport / Q000502:physiology
chemical_list: D002352:Carrier Proteins; C476535:DNAJC14 protein, human; D005326:Fetal Proteins; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D008565:Membrane Proteins; D018832:Molecular Chaperones; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; C098789:PDCL protein, human