?-Arrestin Recruitment and Biased Agonism at Free Fatty Acid Receptor 1.

ABSTRACT: FFAR1/GPR40 is a seven-transmembrane domain receptor (7TMR) expressed in pancreatic ? cells and activated by FFAs. Pharmacological activation of GPR40 is a strategy under consideration to increase insulin secretion in type 2 diabetes. GPR40 is known to signal predominantly via the heterotrimeric G proteins Gq/11. However, 7TMRs can also activate functionally distinct G protein-independent signaling via ?-arrestins. Further, G protein- and ?-arrestin-based signaling can be differentially modulated by different ligands, thus eliciting ligand-specific responses ("biased agonism"). Whether GPR40 engages ?-arrestin-dependent mechanisms and is subject to biased agonism is unknown. Using bioluminescence resonance energy transfer-based biosensors for real-time monitoring of cell signaling in living cells, we detected a ligand-induced GPR40-?-arrestin interaction, with the synthetic GPR40 agonist TAK-875 being more effective than palmitate or oleate in recruiting ?-arrestins 1 and 2. Conversely, TAK-875 acted as a partial agonist of Gq/11-dependent GPR40 signaling relative to both FFAs. Pharmacological blockade of Gq activity decreased FFA-induced insulin secretion. In contrast, knockdown or genetic ablation of ?-arrestin 2 in an insulin-secreting cell line and mouse pancreatic islets, respectively, uniquely attenuated the insulinotropic activity of TAK-875, thus providing functional validation of the biosensor data. Collectively, these data reveal that in addition to coupling to Gq/11, GPR40 is functionally linked to a ?-arrestin 2-mediated insulinotropic signaling axis. These observations expose previously unrecognized complexity for GPR40 signal transduction and may guide the development of biased agonists showing improved clinical profile in type 2 diabetes.

SUBMITTER: Mancini AD 

PROVIDER: S-EPMC4543669 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature