RT Journal Article SR Electronic T1 Isoform-Specific Biased Agonism of Histamine H3 Receptor Agonists JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 87 OP 99 DO 10.1124/mol.116.106153 VO 91 IS 2 A1 Darren M. Riddy A1 Anna E. Cook A1 Natalie A. Diepenhorst A1 Sanja Bosnyak A1 Ryan Brady A1 Clotilde Mannoury la Cour A1 Elisabeth Mocaer A1 Roger J. Summers A1 William N. Charman A1 Patrick M. Sexton A1 Arthur Christopoulos A1 Christopher J. Langmead YR 2017 UL http://molpharm.aspetjournals.org/content/91/2/87.abstract AB The human histamine H3 receptor (hH3R) is subject to extensive gene splicing that gives rise to a large number of functional and nonfunctional isoforms. Despite the general acceptance that G protein–coupled receptors can adopt different ligand-induced conformations that give rise to biased signaling, this has not been studied for the H3R; further, it is unknown whether splice variants of the same receptor engender the same or differential biased signaling. Herein, we profiled the pharmacology of histamine receptor agonists at the two most abundant hH3R splice variants (hH3R445 and hH3R365) across seven signaling endpoints. Both isoforms engender biased signaling, notably for 4-[3-(benzyloxy)propyl]-1H-imidazole (proxyfan) [e.g., strong bias toward phosphorylation of glycogen synthase kinase 3β (GSK3β) via the full-length receptor] and its congener 3-(1H-imidazol-4-yl)propyl-(4-iodophenyl)-methyl ether (iodoproxyfan), which are strongly consistent with the former’s designation as a “protean” agonist. The 80 amino acid IL3 deleted isoform hH3R365 is more permissive in its signaling than hH3R445: 2-(1H-imidazol-5-yl)ethyl imidothiocarbamate (imetit), proxyfan, and iodoproxyfan were all markedly biased away from calcium signaling, and principal component analysis of the full data set revealed divergent profiles for all five agonists. However, most interesting was the identification of differential biased signaling between the two isoforms. Strikingly, hH3R365 was completely unable to stimulate GSK3β phosphorylation, an endpoint robustly activated by the full-length receptor. To the best of our knowledge, this is the first quantitative example of differential biased signaling via isoforms of the same G protein–coupled receptor that are simultaneously expressed in vivo and gives rise to the possibility of selective pharmacological targeting of individual receptor splice variants.