title: Isolating and characterizing three alternatively spliced mu opioid receptor variants: mMOR-1A, mMOR-1O, and mMOR-1P.
abstract: Extensive alternative pre-mRNA splicing of the mu opioid receptor gene, OPRM1, has demonstrated an array of splice variants in mice, rats and humans. Three classes of splice variants have been identified: full-length seven transmembrane (TM) domain variants with C-terminal splicing, truncated 6TM variants and single TM variants. The current studies isolates and characterizes an additional three full-length C-terminal splice variants generated from the mouse OPRM1 gene: mMOR-1A, mMOR-1O, and mMOR-1P. Using RT-qPCR, we demonstrated differential expression of these variants' mRNAs among selected brain regions, supporting region-specific alternative splicing. When expressed in Chinese Hamster Ovary cells, all the variants displayed high mu binding affinity and selectivity with subtle differences in the affinities toward some agonists. [³⁵S]γGTP binding assays revealed marked differences in agonist-induced G protein activation in both potency and efficacy among the variants. Together with the previous studies of mu agonist-induced phosphorylation and internalization in several carboxyl terminal splice variants, the current studies further suggest the existence of biased signaling of various agonists within each individual variant and/or among different variants.
authors.affiliation: Molecular Pharmacology and Chemistry Program, Memorial Sloan-Kettering Cancer Center, New York, New York, 10065.
authors.forename: Jin
authors.initials: J
authors.lastname: Xu
authors.forename: Mingming
authors.initials: M
authors.lastname: Xu
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Bolan
authors.forename: Annie-Kim
authors.initials: AK
authors.lastname: Gilbert
authors.forename: Gavril W
authors.initials: GW
authors.lastname: Pasternak
authors.forename: Ying-Xian
authors.initials: YX
authors.lastname: Pan
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006160:Guanosine Triphosphate / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: C404943:Oprm protein, mouse; D020033:Protein Isoforms; D017450:Receptors, Opioid, mu; D006160:Guanosine Triphosphate
keywords: G-protein coupled receptor; GPCR; OPRM1; alternative splicing; biased agonism; biased signaling; morphine; opioid peptide