Multiplexed cell-based assays to profile GPCR activities and cellular signalling

Abstract

G protein-coupled receptors (GPCRs) are the largest class of cell surface receptors that are implicated in the physiological regulation of many biological processes. They mediate signals through complex networks of G protein-dependent and independent signalling pathways. The high diversity of GPCRs and their physiological functions make them to primary targets for therapeutic drugs. The property of drugs to potentially modulate multiple targets, termed polypharmacology, is widely seen as undesired source for adverse side effects. However, polypharmacology may also explain the clinical efficacy of some drug classes, such as antipsychotic drugs used for the treatment of psychiatric diseases. In this thesis, a GPCR profiling system is introduced comprising two aspects of multiplexed GPCR assays monitoring multiple selected events both at the level of receptor activation and downstream cellular signalling. Firstly, the multiplexed GPCR activity assay combines split TEV and EXTassay technologies and enables simultaneous measurements of receptor activities for multiple GPCR-ligand combinations within one experiment. In proof-of-principle experiments, the specificity of endogenous agonists as well as the polypharmacological effects of described antipsychotics on GPCR activities was demonstrated. Secondly, the multiplexed GPCR signalling assay allows monitoring multiple cellular downstream signalling events following to GPCR activation. Both profiling approaches use molecular barcodes as reporters that are invariably linked to either a single GPCR activity or cellular signalling event, thus enabling a precise and simultaneous measurement of individual events in a global profiling setup. The assay was successfully applied to different GPCRs, their correlation to G protein-coupled signalling and downstream signalling activities. In summary, the multiplexed assays presented constitute a flexible and scalable approach, which enables simultaneous profiling of receptor activities and downstream signalling, and offer a thorough analysis of compound actions in living cells.