title: Translational repression of mouse mu opioid receptor expression via leaky scanning.
abstract: Mu opioid receptor (MOR) expression is under temporal and spatial controls, but expression levels of the MOR gene are relatively low in vivo. In addition to transcriptional regulations, upstream AUGs (uAUGs) and open reading frames (uORFs) profoundly affect the translation of the primary ORF and thus the protein levels in several genes. The 5'-untranslated region (UTR) of mouse MOR mRNA contains three uORFs preceding the MOR main initiation codon. In MOR-fused EGFP or MOR promoter/luciferase reporter constructs, mutating each uAUG individually or in combinations increased MOR transient heterologous expression in neuroblastoma NMB and HEK293 cells significantly. Translation of such constructs increased up to 3-fold without altering the mRNA levels if either the third uAUG or both the second and third AUGs were mutated. Additionally, these uAUG-mediated translational inhibitions were independent of their peptide as confirmed by internal mutation analyses in each uORF. Translational studies indicated that protein syntheses were initiated at these uAUG initiation sites, with the third uAUG initiating the highest translation level. These results support the hypothesis that uORFs in mouse MOR mRNA act as negative regulators through a ribosome leaky scanning mechanism. Such leaky scanning resulted in the suppression of mouse MOR under normal conditions.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA. songx047@umn.edu
authors.forename: Kyu Young
authors.initials: KY
authors.lastname: Song
authors.forename: Cheol Kyu
authors.initials: CK
authors.lastname: Hwang
authors.forename: Chun Sung
authors.initials: CS
authors.lastname: Kim
authors.forename: Hack Sun
authors.initials: HS
authors.lastname: Choi
authors.forename: Ping-Yee
authors.initials: PY
authors.lastname: Law
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Wei
authors.forename: Horace H
authors.initials: HH
authors.lastname: Loh
mesh_terms: D020121:5' Untranslated Regions / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018387:Codon, Initiator; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D014176:Protein Biosynthesis; D017450:Receptors, Opioid, mu / Q000096:biosynthesis / Q000235:genetics*; D012270:Ribosomes / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D018387:Codon, Initiator; C404943:Oprm protein, mouse; D017450:Receptors, Opioid, mu