Ligand-specific endocytic dwell times control functional selectivity of the cannabinoid receptor 1

G protein-coupled receptors (GPCRs) are the major transducers of external stimuli and key therapeutic targets in many pathological conditions. When activated by different ligands, one receptor can elicit multiple signalling cascades that are mediated by G proteins or b-arrestin, a process defined as functional selectivity or ligand bias. However, the dynamic mechanisms underlying beta-arrestin signalling remain unknown. Here by studying the cannabinoid receptor 1 (CB1R), we identify ligand-specific endocytic dwell times, that is, the time during which receptors are clustered into clathrin pits together with beta-arrestins before endocytosis, as the mechanism controlling beta-arrestin signalling. Agonists inducing short endocytic dwell times produce little or no beta-arrestin signalling, whereas those eliciting prolonged dwell times induce robust signalling. Remarkably, extending CB1R dwell times by preventing endocytosis substantially increased beta-arrestin signalling. These studies reveal how receptor activation translates into beta-arrestin signalling and identify a mechanism to control this pathway.