BRD-K4477 australia br Experimental Procedures br Acknowledg
Acknowledgments This work was supported by NIH/National Human Genome Research Institute (NHGRI)R00 HG006922 and NIH/NHGRIR01 HG008974 (to J.G.), the Huntsman Cancer Institute, and the Women’s Cancers Disease-Oriented Team at the Huntsman Cancer Institute. Research reported in this publication utilized the High-Throughput Genomics Shared Resource at the University of Utah and was supported by NIH/National Cancer Institute award P30 CA042014. A.C.R. was supported by BRD-K4477 australia supplement R00 HG006922S1. We thank Ed Grow for providing reagents and we thank K.-T. Varley as well as Gertz and Varley laboratory members for their helpful comments on the study and the manuscript.
Introduction Together with their cognate ligands, members of the seven transmembrane G protein-coupled receptors (GPCRs) family are key component of numerous pivotal (patho)physiological processes such as neurotransmission, vision, cellular proliferation, development, pain, vascular homeostasis, muscle contraction or hormone secretion . In addition, this group of receptors constitutes undoubtedly a productive source of drug targets . The literature describing the targets for registered medicines proposes a proportion ranging from ∼20 to more than 50% of drugs producing their therapeutic actions through the modulation of a GPCR , , . The discrepancies in these numbers are probably a consequence of the varying definitions of the “target” (direct or indirect, individual receptors or families,…) or drugs (several non-overlapping databases for registered drugs exist). Recently, Sriram & Insel have tackled this issue by analyzing three public databases and carefully curated the receptors list. They concluded that 134 GPCRs were currently mediating the therapeutic effect of ∼25%–∼33% of registered drugs . Another recent extensive analysis by Hauser et al. suggested that ∼34% of the FDA-approved drugs targeted 108 unique receptors . These numbers place the GPCR family at the first place of protein families targeted by approved drugs. However, only a small portion (100–140) of the ∼360 non olfactory GPCRs is currently exploited and the family is globally underused with regard to its potential in drug discovery. Regarding GPCR-dependent propagation of the signal, a general paradigm has long been established. It proposes that these membrane receptors have the ability to adopt several conformations characterized by different affinities toward extracellular ligands and intracellular signaling partners . In the presence of an activating ligand, a population with restricted conformations will be enriched by stabilization . These restricted sets of conformations will promote the binding of receptor-specific G proteins. The various families of G proteins have the ability to activate distinct signaling pathways. For instance, Gs and Gi/o regulate intracellular levels of cyclic AMP through positive and negative modulation of adenylate cyclase, whereas Gq induces a rapid release of Ca2+ from intracellular stores after phospholipase C activation. The extinction of GPCR signaling is processed by desensitization, where the uncoupling of the receptor from its G protein occurs generally by specific GPCR kinase (GRK)-mediated phosphorylation of the intracellular C-terminal tail of the receptor . Activation and phosphorylation enhance the affinity of the receptor for the cytosolic adaptor protein arrestin that promotes receptor internalization through clathrin-coated pits . It is noteworthy that arrestins have been proposed to initiate a cellular signaling independent of G protein activation , . However, this concept has been challenged recently with cells genetically depleted for arrestins or G proteins , . In addition, intracellular signaling from the endosomal compartment has been evidenced for GPCR, which seems to be driven by receptor-G protein-arrestin super-complexes , .