Transcriptional Regulation of μ Opioid Receptor Gene by cAMP Pathway

Abstract

The utility of morphine for the treatment of chronic pain is hindered by the development of tolerance. Fentanyl has been shown to be a potent analgesic with a lower propensity to produce tolerance and physical dependence in the clinical setting. Previous finding has shown that fentanyl induces opioid receptor gene expression in PC-12 cells (Brain Res 859:217-223, 2000). In this report, we aim to identify the molecular mechanism of -opioid receptor (MOR) gene regulation by fentanyl. We demonstrated that the 4.7-kilobase MOR promoter could be induced by fentanyl in PC-12 cells, and we defined a partial cAMP response element (CRE) located at Ϫ106/Ϫ111 in 5Ј-untranslated region of the MOR gene. In electrophoretic mobility shift assay, cAMP response elementbinding protein (CREB) was found in the protein-DNA complex formed on the CRE box. CREB was phosphorylated after forskolin induction, and both CREB and CREB-binding protein (CBP) binding to the endogenous MOR promoter was increased by forskolin in chromatin immunoprecipitation assay. The functional role of CREB in the induction of MOR gene was further elucidated by an experiment in which a dominant-negative mutant CREB, CREB-S133A, abolished the forskolin-mediated MOR induction. Moreover, we found that this CRE box is conserved in mouse, rat, and human MOR gene, implying physiological relevance in different species. Collectively, this study demonstrated that fentanyl-triggered MOR gene induction was mediated by the sequential activation of CREB and the binding of CREB and CBP to MOR promoter, thus provides direct evidence for lower propensity of fentanyl to produce tolerance.

Reduced nicotine reward in obesity: cross-comparison in human and mouse

“…Activation of the Jak-Stat pathway (Friedman and Halaas 1998) as well as the cAMP pathway (Zhao et al 2002) are associated with leptin signaling in the hypothalamus. The promotor region of the MOR gene contains potential cytokine response elements (Roy et al 1992) as well as cAMP response elements (Lee and Lee 2003), suggesting that these pathways could regulate MOR expression following leptin receptor activation. Downregulation of leptin receptor mRNA in the VTA following a high fat diet may result in reductions of cytokine and or cAMP-mediated mu-opiate receptor gene expression, although further studies are necessary to elucidate this mechanism of regulation.…”

Transcriptional Regulation of Mouse μ Opioid Receptor Gene: Sp3 Isoforms (M1, M2) Function as Repressors in Neuronal Cells to Regulate the μ Opioid Receptor Gene

“…Previously, several papers indicated that the region of Ϫ250 to ϩ1 bp in the mouse MOR proximal promoter is important for regulation of mouse MOR (Ikeda et al, 2001;Lee and Lee, 2003). The molecular mechanisms responsible for MOR reg-ulation in this region are not well known, and therefore this study focuses on this regulatory region.…”

A Major Species of Mouse μ-opioid Receptor mRNA and Its Promoter-Dependent Functional Polyadenylation Signal

“…For example, our lab has identified multiple regulatory elements in the MOR promoter region, such as Sp1 (Ko et al, 1998), single-stranded DNA-binding site (Ko and Loh, 2001), Sox (Hwang et al, 2003), PU.1 , neuronrestrictive silencer factor , and Sp3 isoforms (Choi et al, 2005). Regulatory sequences in the 5Ј-UTR have also been defined by other labs, including STAT6 (Kraus et al, 2001), cAMP response element-binding protein (Lee and Lee, 2003), and neurorestrictive suppressor element (Andria and Simon, 2001). However, studies of its 3Ј-UTR have been very limited.…”