G protein-coupled receptors (GPCRs) are one of the largest families of transmembrane receptors and a major target of current therapeutic drugs. At the signaling level, it has become clear that ligands acting on the same receptor can activate multiple and sometime opposing signaling cascades;a process defined as functional selectivity or biased agonism. One of the main effectors of functional selectivity are beta-arrestins, multifunction proteins recruited to activated receptors. However, how receptor activation translates into beta-arrestin signaling is not clearly defined. Our preliminary work combining state-of-the-art live cell imaging with molecular and biochemical techniques identifies ligand-specific dwell times, the time receptors are clustered into individual endocytic pits before endocytosis, as a mechanism by which receptors can control beta-arrestin mediated signaling. Our hypothesis suggests that ligands induce specific phosphorylations at the receptor level, eliciting specific endocytic dwell times during which beta-arrestins remain recruited and engaged in signaling. We propose to define a mechanism by which the Cannabinoid 1 Receptor (CB1R), one of the most abundant receptors in the CNS and target of cannabis, controls beta-arrestin signaling during endocytic dwell times.
Our aims are: 1) Characterize ligand-specific dwell times of the CB1R to test our hypothesis that ligands can elicit specific dwell times that ar independent of their endocytic efficacy. 2) Define the mechanisms underlying ligand-specific dwell times of the CB1R. We will test the hypothesis that dwell times are controlled by ligand-specific phosphorylation profiles ("bar-codes") of the receptor. Alternative mechanisms will be also investigated. 3) Determine if beta-arrestin signaling is the physiological target of ligand specific dwell times in heterologous systems and native tissue. Finally, we will test different manipulations to control arrestin signaling by altering CB1R dwell times.
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