uAUG-mediated translational initiations are responsible for human mu opioid receptor gene expression.
Mu opioid receptor (MOR) is the main site of interaction for major clinical analgesics, particularly morphine. MOR expression is regulated at the transcriptional and post-transcriptional levels. However, the protein expression of the MOR gene is relatively low and the translational control of MOR gene has not been well studied. The 5'-untranslated region (UTR) of the human MOR (OPRM1) mRNA contains four upstream AUG codons (uAUG) preceding the main translation initiation site. We mutated the four uAUGs individually and in combination. Mutations of the third uAUG, containing the same open reading frame, had the strongest inhibitory effect. The inhibitory effect caused by the third in-frame uAUG was confirmed by in vitro translation and receptor-binding assays. Toeprinting results showed that OPRM1 ribosomes initiated efficiently at the first uAUG, and subsequently re-initiated at the in-frame #3 uAUG and the physiological AUG site. This re-initiation resulted in negative expression of OPRM1 under normal conditions. These results indicate that re-initiation in MOR gene expression could play an important role in OPRM1 regulation.
Department of Pharmacology, University of Minnesota Medical School, Minneapolis, MN 55455, USA. songx047@umn.edu
Kyu Young
KY
Song
Chun Sung
CS
Kim
Cheol Kyu
CK
Hwang
Hack Sun
HS
Choi
Ping-Yee
PY
Law
Li-Na
LN
Wei
Horace H
HH
Loh
D020121:5' Untranslated Regions / Q000235:genetics; D000595:Amino Acid Sequence; D001483:Base Sequence; D045744:Cell Line, Tumor; D018387:Codon, Initiator / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics*; D017450:Receptors, Opioid, mu / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism
D020121:5' Untranslated Regions; D018387:Codon, Initiator; D017450:Receptors, Opioid, mu