The use of biosensors to study GPCR function: Applications for high-content screening

Plasma membrane-associated G protein-coupled receptors (GPCRs) initiate the transmission of multiple intracellular signals leading to a myriad of physiological and pathophysiological effects. The downstream signaling events associated with occupation of the GPCR and activation of the G-protein include the generation of numerous second messenger molecules to provide the necessary signal amplification within the appropriate intracellular compartment to transmit a specific signal from the cell surface to the cell interior. The complex process of signal transmission also requires a series of highly orchestrated events which includes the translocation of cellular proteins to discreet intracellular destinations. A better understanding of these events has made it possible to design assays to examine multiple endpoints within whole cells. In this review we describe recent advances in assay biology and instrumentation useful for broadening our understanding of the molecular events associated with GPCR activation. This review will focus on novel cell-based approaches using fluorescent biosensors, such as fluorescent dyes and fluorescent protein tags, to generate information-rich data from multiple cellular targets-a process that has been referred to as high-content screening. High-content screening applications will be discussed as they pertain to specific signal transduction cascades initiated upon GPCR activation and examples of specific biosensors will be provided.