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 D1 dopamine receptor (D1 -R). Reciprocally, Gs enhances IP1 through 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.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Apr 4 2017|
Bibliographical noteFunding Information:
We thank Dr. Lincoln R. Potter and Potter Laboratory members for assistance with radioligand experiments and Dr. Sean Conner for access to a gamma counter. Work was done using Typhoon Gel Imager (GE Healthcare) at the University of Minnesota-University Imaging Centers (uic.umn.edu). Research was funded by American Heart Association Scientist Development Grant 13SDG14270009 and NIH Grants 1DP2 CA186752-01 and 1-R01-GM-105646-01-A1 (to S.S.). T.M.G. is a National Centre for Biological Sciences-inStem Career Development Fellow. R.F.S. is a Life Sciences Research Foundation postdoctoral fellow.
- Cell signaling
- Er/k linker
- G protein
- Gpcr priming