Morphine modulates the expression of mu-opioid receptor exon 5-associated full-length C-terminal splice variants by upregulating miR-378a-3p

• Published in: The FASEB journal Vol. 34; no. 3; p. 4540
• Main Authors: Lu, Zhigang, Xu, Jin, Wang, Qian, Pan, Ying-Xian
• Format: Journal Article
• Language: English
• Published: United States 01.03.2020
• Subjects: 3' Untranslated Regions - genetics; Animals; Binding Sites - genetics; Brain Stem - drug effects; Brain Stem - metabolism; Cell Line; Exons - genetics; HEK293 Cells; Humans; Mice; Mice, Inbred C57BL; MicroRNAs - genetics; MicroRNAs - metabolism; Morphine - therapeutic use; Plasmids - genetics; Receptors, Opioid, mu - genetics; Receptors, Opioid, mu - metabolism; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; RNA, Messenger - metabolism; microRNA; OPRM1; splicing; opioid; morphine
• DOI: 10.1096/fj.201901879RR

The mu-opioid receptor gene, OPRM1, undergoes extensive alternative splicing, creating an array of splice variants that are conserved from rodent to human. Both mouse and human OPRM1 have five exon 5-associated seven transmembrane full-length carboxyl terminal variants, MOR-1B1, MOR-1B2, MOR-1B3, MOR-1B4, and MOR-1B5, all of which are derived from alternative 3' splicing from exon 3 to alternative sites within exon 5. The functional relevance of these exon 5-associated MOR-1Bs has been demonstrated in mu agonist-induced G protein coupling, adenylyl cyclase activity, receptor internalization and desensitization, and post-endocytic sorting, as well as region-specific expression at the mRNA level. In the present study, we mapped a polyadenylation site for both mouse and human MOR-1Bs that defines the 3'-untranslated regions (3'-UTR) of MOR-1Bs and stabilizes mMOR-1Bs mRNAs. We identified a conserved miR378a-3p sequence in the 3'-UTR of both mouse and human MOR-1B transcripts through which miR-378a-3p can regulate the expression of MOR-1Bs at the mRNA level. Chronic morphine treatment significantly increased the miR-378-3p level in Be(2)C cells and the brainstem of the morphine tolerant mice, contributing to the decreased expression of the mouse and human MOR-1B3 and MOR-1B4. Our study provides new insights into the role of miRNAs and Oprm1 splice variants in morphine tolerance.