CypHer 5: A Generic Approach for Measuring the Activation and Trafficking of G Protein-Coupled Receptors in Live Cells

Abstract

GPCRs are one of the most popular classes of therapeutic drug targets. It is therefore important to design specific assay formats to readily identify ligands at these receptors. CypHer 5 technology utilizes the general ability of GPCRs to be internalized into the endosomal pathway of a cell in response to agonist ligands. The CypHer 5 dye is fluorescent in acidic environments, but nonfluorescent at neutral pH. When CypHer 5 is bound to a receptor on the extracellular surface of the cell, it is essentially nonfluorescent. On internalization into a cell, it displays a significant increase in fluorescence. Here we demonstrate the detection of agonist activation of two GPCRs in stably transfected live cells using CypHer 5 technology. The G_q-coupled TRHR-1 and the G_s-coupled β₂-adrenoceptor were both N-terminally tagged with VSV-G. Following addition of CypHer 5-labeled anti-VSV-G antibodies to HEK 293 cells stably expressing the β₂-adrenoceptor or CHO-K1 cells stably expressing the TRHR-1, the cells were treated with agonists and then imaged on Amersham Biosciences' IN Cell Analyzer 3000. Data were quantified using a granularity analysis module. Concentration-response curves were obtained with signal-to-background ratios of 7:1 for both receptors. An EC₅₀ of 0.52 nM was observed on TRH stimulation of the TRHR-1, and an EC₅₀ of 30 nM was obtained on isoprenaline stimulation of the β₂-adrenoceptor. These results demonstrated that the CypHer technology was capable of measuring high-potency agonist responses. The β₂-adrenoceptor antagonist, alprenolol, competed for isoprenaline with an IC₅₀ of 30 nM, indicating that a high-potency antagonist inhibition curve could also be observed using CypHer. CypHer 5 provides a generic tool to measure GPCR activation in a live cell, homogeneous assay format, and may be equally suitable for detecting activation of other classes of cell surface receptors.