NanoLuc-Based Methods to Measure β-Arrestin2 Recruitment to G Protein-Coupled Receptors

Cytosolic β-arrestins are key regulators of G protein-coupled receptors (GPCRs) by sterically uncoupling G protein activation, facilitating receptor internalization, and/or acting as G protein-independent signaling scaffolds. The current awareness that GPCR ligands may display bias toward G protein signaling or β-arrestin recruitment makes β-arrestin recruitment assays important additions to the drug discovery toolbox. This chapter describes two NanoLuc-based methods to monitor β-arrestin2 recruitment to the human histamine H₁ receptor by measuring bioluminescence resonance energy transfer and enzyme-fragment complementation in real-time on living cells with reasonable high throughput. In addition to the detection of agonism, both assay formats can be used to qualitatively evaluate the binding kinetics of antihistamines on the human histamine H₁ receptor.

Synergetic Roles of Formyl Peptide Receptor 1 Oligomerization in Ligand-Induced Signal Transduction

G protein-coupled receptors (GPCRs) transduce extracellular signals into cells by interacting with G proteins and arrestins. Emerging evidence suggests that GPCRs on the plasma membrane are in a dynamic equilibrium among monomers, dimers, and larger oligomers. Nevertheless, the role of the oligomer formation in the GPCR signal transduction remains unclear. Using multicolor single-molecule live-cell imaging, we show a dynamic interconversion between small and large oligomer states of a chemoattractant GPCR, Formyl Peptide Receptor 1 (FPR1), and its binding affinity with G protein. Full agonist stimulation increased a fraction of large FPR1 oligomers, which allowed for prolonged FPR1-G protein interaction. The G protein interaction with FPR1 was most stabilized at the full agonist-bound large FPR1 oligomers. Based on these results, we propose that G protein-mediated signal transduction may be regulated synergistically by the ligand-binding and FPR1 oligomerization. Cooperative signal control induced by receptor oligomerization is anticipated as a target for drug discovery.

Live Cell Bioluminescence Imaging in Temporal Reaction of G Protein-Coupled Receptor for High-Throughput Screening and Analysis

G protein-coupled receptors (GPCRs) are notable targets of basic therapeutics. Many screening methods have been established to identify novel agents for GPCR signaling in a high-throughput manner. However, information related to the temporal reaction of GPCR with specific ligands remains poor. We recently developed a bioluminescence method for the quantitative detection of the interaction between GPCR and β-arrestin using split luciferase complementation. To monitor time-course variation of the interactions, a new imaging system contributes to the accurate evaluation of drugs for GPCRs in a high-throughput manner.