Differential gene expression activity among species-specific polypyrimidine/polypurine motifs in mu opioid receptor gene promoters

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

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.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

The polypyrimidine/polypurine motif in the mouse mu opioid receptor gene promoter is a supercoiling-regulatory element

The mu opioid receptor (MOR) is the principle molecular target of opioid analgesics. The polypyrimidine/polypurine (PPy/u) motif enhances the activity of the MOR gene promoter by adopting a non-B DNA conformation. Here, we report that the PPy/u motif regulates the processivity of torsional stress, which is important for endogenous MOR gene expression. Analysis by topoisomerase assays, S1 nuclease digests, and atomic force microscopy showed that, unlike homologous PPy/u motifs, the position- and orientation-induced structural strains to the mouse PPy/u element affect its ability to perturb the relaxation activity of topoisomerase, resulting in polypurine strand-nicked and catenated DNA conformations. Raman spectrum microscopy confirmed that mouse PPy/u containing-plasmid DNA molecules under the different structural strains have a different configuration of ring bases as well as altered Hoogsteen hydrogen bonds. The mouse MOR PPy/u motif drives reporter gene expression fortyfold more effectively in the sense orientation than in the antisense orientation. Furthermore, mouse neuronal cells activate MOR gene expression in response to the perturbations of topology by topoisomerase inhibitors, whereas human cells do not. These results suggest that, interestingly among homologous PPy/u motifs, the mouse MOR PPy/u motif dynamically responds to torsional stress and consequently regulates MOR gene expression in vivo.