Priming GPCR signaling through the synergistic effect of two G proteins.
Although individual G-protein-coupled receptors (GPCRs) are known to activate one or more G proteins, the GPCR-G-protein interaction is viewed as a bimolecular event involving the formation of a ternary ligand-GPCR-G-protein complex. Here, we present evidence that individual GPCR-G-protein interactions can reinforce each other to enhance signaling through canonical downstream second messengers, a phenomenon we term "GPCR priming." Specifically, we find that the presence of noncognate Gq protein enhances cAMP stimulated by two Gs-coupled receptors, β2-adrenergic receptor (β2-AR) and D1dopamine receptor (D1-R). Reciprocally, Gs enhances IP1through vasopressin receptor (V1A-R) but not α1 adrenergic receptor (α1-AR), suggesting that GPCR priming is a receptor-specific phenomenon. The C terminus of either the Gαs or Gαq subunit is sufficient to enhance Gα subunit activation and cAMP levels. Interaction of Gαs or Gαq C termini with the GPCR increases signaling potency, suggesting an altered GPCR conformation as the underlying basis for GPCR priming. We propose three parallel mechanisms involving (i) sequential G-protein interactions at the cognate site, (ii) G-protein interactions at distinct allosteric and cognate sites on the GPCR, and (iii) asymmetric GPCR dimers. GPCR priming suggests another layer of regulation in the classic GPCR ternary-complex model, with broad implications for the multiplicity inherent in signaling networks.
Department of Genetics, Cell Biology, and Development, University of Minnesota, Twin Cities, Minneapolis, MN 55455.
Tejas M
TM
Gupte
Department of Genetics, Cell Biology, and Development, University of Minnesota, Twin Cities, Minneapolis, MN 55455.
Rabia U
RU
Malik
Department of Genetics, Cell Biology, and Development, University of Minnesota, Twin Cities, Minneapolis, MN 55455.
Ruth F
RF
Sommese
Department of Genetics, Cell Biology, and Development, University of Minnesota, Twin Cities, Minneapolis, MN 55455.
Michael
M
Ritt
Department of Genetics, Cell Biology, and Development, University of Minnesota, Twin Cities, Minneapolis, MN 55455 sivaraj@umn.edu.
Sivaraj
S
Sivaramakrishnan
D000495:Allosteric Site; D000818:Animals; D001665:Binding Sites; D000242:Cyclic AMP / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D011485:Protein Binding; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry / Q000378:metabolism*; D015290:Second Messenger Systems; D061987:Sf9 Cells
D043562:Receptors, G-Protein-Coupled; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs
ER/K linker; G protein; GPCR; GPCR priming; cell signaling