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  2. Nonconventional glucagon and GLP-1 receptor agonist and antagonist interplay at the GLP-1 receptor revealed in high-throughput FRET assays for cAMP

Nonconventional glucagon and GLP-1 receptor agonist and antagonist interplay at the GLP-1 receptor revealed in high-throughput FRET assays for cAMP

  • J Biol Chem. 2019 Mar 8;294(10):3514-3531. doi: 10.1074/jbc.RA118.005682.
Oleg G Chepurny 1 Minos-Timotheos Matsoukas 2 George Liapakis 3 Colin A Leech 4 Brandon T Milliken 5 Robert P Doyle 6 5 George G Holz 7 8
Affiliations

Affiliations

  • 1 From the Departments of Medicine.
  • 2 the Department of Pharmacy, University of Patras, 26500 Patras, Greece.
  • 3 the Department of Pharmacology, School of Medicine, University of Crete, 71003 Heraklion, Crete, Greece, and.
  • 4 Surgery, and.
  • 5 the Department of Chemistry, Syracuse University, Syracuse, New York 13244.
  • 6 From the Departments of Medicine, rpdoyle@syr.edu.
  • 7 From the Departments of Medicine, holzg@upstate.edu.
  • 8 Pharmacology, State University of New York (SUNY), Upstate Medical University, Syracuse, New York 13210.
Abstract

G protein-coupled receptors (GPCRs) for glucagon (GluR) and glucagon-like peptide-1 (GLP-1R) are normally considered to be highly selective for glucagon and GLP-1, respectively. However, glucagon secreted from pancreatic α-cells may accumulate at high concentrations to exert promiscuous effects at the β-cell GLP-1R, as may occur in the volume-restricted microenvironment of the islets of Langerhans. Furthermore, systemic administration of GluR or GLP-1R agonists and antagonists at high doses may lead to off-target effects at other receptors. Here, we used molecular modeling to evaluate data derived from FRET assays that detect cAMP as a read-out for GluR and GLP-1R activation. This analysis established that glucagon is a nonconventional GLP-1R agonist, an effect inhibited by the GLP-1R orthosteric antagonist exendin(9-39) (Ex(9-39)). The GluR allosteric inhibitors LY2409021 and MK 0893 antagonized glucagon and GLP-1 action at the GLP-1R, whereas des-His1-[Glu9]glucagon antagonized glucagon action at the GluR, while having minimal inhibitory action versus glucagon or GLP-1 at the GLP-1R. When testing Ex(9-39) in combination with des-His1-[Glu9]glucagon in INS-1 832/13 cells, we validated a dual agonist action of glucagon at the GluR and GLP-1R. Hybrid peptide GGP817 containing glucagon fused to a fragment of peptide YY (PYY) acted as a triagonist at the GluR, GLP-1R, and neuropeptide Y2 receptor (NPY2R). Collectively, these findings provide a new triagonist strategy with which to target the GluR, GLP-1R, and NPY2R. They also provide an impetus to reevaluate prior studies in which GluR and GLP-1R agonists and antagonists were assumed not to exert promiscuous actions at other GPCRs.

Keywords

G protein-coupled receptor (GPCR); GLP-1; fluorescence resonance energy transfer (FRET); glucagon; high-throughput microplate assay; pharmacology; type 2 diabetes.

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