TY - JOUR T1 - Morphine Regulates Expression of MOR-1A, an Intron-retention Carboxyl Terminal Splice Variant of the μ Opioid Receptor (OPRM1) Gene Via miR-103/miR-107 JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.113.089292 SP - mol.113.089292 AU - Zhigang Lu AU - Jin Xu AU - Mingming Xu AU - Gavril W Pasternak AU - Ying-Xian Pan Y1 - 2013/01/01 UR - http://molpharm.aspetjournals.org/content/early/2013/12/03/mol.113.089292.abstract N2 - The μ opioid receptor (MOR-1) gene, OPRM1, undergoes extensive alternative splicing, generating an array of splice variants. Of these variants, MOR-1A, an intron-retention carboxyl terminal splice variant identical to MOR-1 except for the terminal intracellular tail encoded by exon 3b, is quite abundant and conserved from rodent to humans. Increasing evidence indicates that miroRNAs (miRNAs) regulate MOR-1 expression and μ agonists such as morphine modulate miRNA expression. However, little is known about miRNA regulation of the OPRM1 splice variants. Using 3' rapid amplification cDNA end (RACE) and Northern blot analyses, the present study identified the complete 3' untranslated region (3'-UTR) for both mouse and human MOR-1A and their conserved polyadenylation site, and defined the role the 3'-UTR in mRNA stability using a luciferase reporter assay. Computer models predicted a conserved miR 103/107 targeting site in the 3'-UTR of both mouse and human MOR-1A. The functional relevance of miR-103/107 in regulating expression of MOR-1A protein through the consensus miR-103/107 binding sites in the 3'- UTR was established by using mutagenesis and a miR-107 inhibitor in transfected HEK293 cells and Be(2)C cells that endogenously express human MOR-1A. Chronic morphine treatment significantly upregulated miR-103 and miR-107 levels, leading to downregulation of polyribosome-associated MOR-1A in both Be(2)C cells and the striatum of a morphine tolerant mouse, providing a new perspective on understanding the roles of miRNAs and OPRM1 splice variants in modulating the complex actions of morphine in animals and humans. ER -