Myosin VI and β-arrestin synergistically regulate GIPR internalization and signaling

Glucose-dependent insulinotropic peptide receptor (GIPR) stimulates insulin release and regulates metabolic homeostasis. GIPR function is shaped by spatiotemporal trafficking of this G protein-coupled receptor (GPCR). While GPCR endocytosis is traditionally associated with β-arrestin, GIPR internalization is only modestly dependent on this pathway. In this study, we demonstrate that GIPR engages a cytoskeletal motor, myosin VI to drive receptor endocytosis. GIPR engages the adaptor-motor complex through a PDZ-binding motif (PBM) at its C-ail. Interestingly, β-arrestin binding to phosphorylated residues upstream of the PBM enhance myosin VI recruitment and activation. GIPR internalization is dependent on both receptor phosphorylation and the PBM site to recruit β-arrestin and myosin VI, respectively. Synergistic engagement of β-arrestin and myosin VI results in desensitization of GIP-stimulated cAMP signaling while activating pERK1/2 from endosomal compartments. Blocking myosin VI activity enhances insulin release in pancreatic beta cells, demonstrating a novel role for this pathway in regulating the physiological effects of GIPR. Our findings highlight the direct convergence of two independent trafficking pathways at the level of the receptor C-tail, with implications for the nuanced regulation of individual GPCRs through the differential engagement of β-arrestin and myosin VI.

GIPR has emerged as a frontline drug target in type 2 diabetes and obesity. Cellular effects of GIPR are regulated by receptor internalization and desensitization through mechanisms that are unclear. Here, we identify a novel GIPR trafficking pathway through the engagement of a cytoskeletal motor, myosin VI. Myosin VI and β-arrestin synergistically regulate GIPR endocytosis, signaling and insulin response in pancreatic beta cells. Our study highlights the convergence of two parallel trafficking mechanisms in GPCR function with potential implications in targeting metabolic disorders.