PT  - JOURNAL ARTICLE
AU  - Zhigang Lu
AU  - Jin Xu
AU  - Mingming Xu
AU  - Gavril W. Pasternak
AU  - Ying-Xian Pan
TI  - Morphine Regulates Expression of <em>μ</em>-Opioid Receptor MOR-1A, an Intron-Retention Carboxyl Terminal Splice Variant of the <em>μ</em>-Opioid Receptor (<em>OPRM1</em>) Gene via miR-103/miR-107
AID  - 10.1124/mol.113.089292
DP  - 2014 Feb 01
TA  - Molecular Pharmacology
PG  - 368--380
VI  - 85
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/85/2/368.short
4100  - http://molpharm.aspetjournals.org/content/85/2/368.full
SO  - Mol Pharmacol2014 Feb 01; 85
AB  - 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 that 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 and Northern blot analyses, we 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 human embryonic kidney 293 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.