Positive Transcriptional Regulation of the Human μ Opioid Receptor Gene by Poly(ADP-ribose) Polymerase-1 and Increase of Its DNA Binding Affinity Based on Polymorphism of G [sup-172] → T.

μ opoid receptor (MOR) agonists such as morphine are applied widely in clinical practice as pain therapy. The effects of morphine through MOR, such as analgesia and development of tolerance and dependence, are influenced by individual specificity. Recently, we analyzed single nucleotide polymorphisms on the human MOR gene to investigate the factors that contribute to individual specificity. In process of single nucleotide polymorphisms analysis, we found that specific nuclear proteins bound to G[sup-172] →T region in exon 1 in MOR gene, and its affinity to DNA was increased by base substitution from G[sup-172] to T-[sup-172]. The isolated proteins was identified by mass spectrometry and was confirmed by Western blotting to be poly (ADP-ribose) polymerase-1 (PARP-1). The overexpressed PARP-1 bound to G[sup-172] → T and enhanced the transcription of reporter vectors containing G[sup-172] and T[sup-172]. Furthermore, PARP-1 inhibitor (benzamide) decreased PARP-1 binding to G[sup-172] → T without affecting mRNA or protein expression level of PARP-1 and down-regulated the subsequent MOR gene expression in SH-SY5Y cells. Moreover, we found that tumor necrosis factor-α enhanced MOR gene expression as well as increased PARP-1 binding to the G[sup-172] → T region and G[sup-172] → T-dependent transcrition in SH-SY5Y cells. These effects were also inhibited by benzamide. In this study, our data suggest that PARP-1 positively regulates MOR gene transcription via G[sup-172] → T, which might influenced individual specificity in therapeutic opioid effects. [ABSTRACT FROM AUTHOR]