A Split Luciferase Complementation Assay for the Quantification of β-Arrestin2 Recruitment to Dopamine D(2)-Like Receptors

Investigations on functional selectivity of GPCR ligands have become increasingly important to identify compounds with a potentially more beneficial side effect profile. In order to discriminate between individual signaling pathways, the determination of β-arrestin2 recruitment, in addition to G-protein activation, is of great value. In this study, we established a sensitive split luciferase-based assay with the ability to quantify β-arrestin2 recruitment to D(2long) and D(3) receptors and measure time-resolved β-arrestin2 recruitment to the D(2long) receptor after agonist stimulation. We were able to characterize several standard (inverse) agonists as well as antagonists at the D(2long)R and D(3)R subtypes, whereas for the D(4.4)R, no β-arrestin2 recruitment was detected, confirming previous reports. Extensive radioligand binding studies and comparisons with the respective wild-type receptors confirm that the attachment of the Emerald luciferase fragment to the receptors does not affect the integrity of the receptor proteins. Studies on the involvement of GRK2/3 and PKC on the β-arrestin recruitment to the D(2long)R and D(3)R, as well as at the D(1)R using different kinase inhibitors, showed that the assay could also contribute to the elucidation of signaling mechanisms. Its broad applicability, which provides concentration-dependent and kinetic information on receptor/β-arrestin2 interactions, renders this homogeneous assay a valuable method for the identification of biased agonists.