Differential regulation of mouse and human Mu opioid receptor gene depends on the single stranded DNA structure of its promoter and α-complex protein 1

Abstract

Abstract. The Mu opioid receptor (MOR) mediates various functions of opioid-induced analgesia, euphoria and respiratory depression, and is a major target of opioid analgesics. Understanding of MOR gene expression among species is important for understanding its analgesic function in humans. In the current study, the polypyrimidine/polypurine (PPy/u) region, a key element of MOR gene expression, was compared in humans and mice. The mouse PPy/u element is highly homologous to its human element (84%), and the mouse MOR (mMOR) reporter drives luciferase activity 35-fold more effectively than the human MOR (hMOR) reporter. The structural study of reporter plasmids using S1 nuclease indicates that the mouse PPy/u element has a particular conformational structure, namely a single-stranded DNA (ssDNA) region that promotes strong promoter activity. DNA electrophoretic mobility shift assays demonstrated that the recombinant α-complex protein 1 (α-CP1) is capable of binding to a single-stranded mouse PPy/u sequence. Furthermore, plasmid-expressing α-CP1 activated the expression of a luciferase reporter when cotransfected with a single-stranded (p336/306) construct. In addition, the α-CP1 gene induced the mMOR gene in mouse neuronal cells and did not induce the human neuronal MOR gene. The current study demonstrates that α-CP1 functions as a transcriptional activator in the mMOR gene, but does not function in the hMOR gene due to species-specific structural differences. The differences in human and mouse MOR gene expression are based on α-CP1 and the ssDNA structure of the MOR promoter. The MOR gene is species-specifically regulated, as the PPy/u element adopts a unique species-specific conformation and α-CP1 recruitment.

Evidence for Endogenous Opioid Dependence Related to Latent Sensitization in a Rat Model of Chronic Inflammatory Pain

“…Although this seems not to considerably affect the amino acid sequences of their MOR proteins (which show 97% homology) [33], interspecies differences have been found to occur in the overall organization of rat and mouse MOR genes, particularly involving the identity and location of several transcription initiation sites within the DNA sequence [34]. These rat-mouse MOR genomic differences, and potentially others not yet explored [35], can likely lead to species specificity in regulating MOR gene expression and responsiveness to endogenous transcriptional regulatory factors. In this respect, it is interesting to note that peripheral inflammation has been proven to induce changes in the expression of the MOR gene in rodents [36].…”