A green-fluorescent-protein-based assay for the characterization of G-protein-coupled receptors.

A simple and sensitive system to monitor activation and pharmacology of G-protein-coupled receptors in mammalian cells is described. It is based on cAMP-responsible-element-regulated expression of green fluorescent protein (GFP). Cotransfection with appropriate G-protein-coupled receptors and subsequent activation with agonists induces expression of GFP in a dose-dependent manner. This system is suited for the analysis of most G-protein-coupled receptors, including those that are coupled to Gs, Gi, and Gq. It can replace reporter systems for G-protein-coupled receptors currently in use. Time-consuming and labor-intensive analysis is avoided because it is a noninvasive system, which allows multiple reprobing without disturbing the cells. In addition, adaptation to high-throughput approaches is possible. Together with human embryonic kidney cells, it is a zero-background expression system, making it ideally suited to the pharmacological characterization of cloned receptors, to expression cloning experiments, and to the identification of the natural ligand of orphan G-protein-coupled receptors.