Regulation of μ-Opioid Receptor Gene Transcription by Interleukin-4 and Influence of an Allelic Variation within a STAT6 Transcription Factor Binding Site

Abstract

Morphine and the endogenous opioid peptide ␤-endorphin exert neuromodulatory as well as immunomodulatory effects, which are transduced by -opioid receptors. In this report we show that stimulation with interleukin-4 induces -opioid receptor transcripts in human primary blood cells (T cells and polymorphonuclear leukocytes), immune cell lines (Raji, U-937, and HMEC-1), and dendritic cells. In nonstimulated immune cells this gene is silent. In addition, receptor transcription is up-regulated by interleukin-4 in cultures of primary rat neurons. Transient transfection experiments in Raji and SH SY5Y neuronal cells with human and rat reporter gene constructs linked the interleukin-4 effect directly to cis-active receptor promoter elements located at nucleotide ؊997 on the human gene and nucleotide ؊727 on the rat gene. The interleukin-4 response elements function orientation independently. They bind STAT6 transcription factors as shown by electrophoretic mobility shift assays. In the human gene, a single nucleotide polymorphism within the interleukin-4 response element reduces the trans-activating potential of this element by 50%, which may affect the phenotype of persons carrying this variation. These findings provide a molecular basis for understanding bidirectional interactions between the opioid system and the immune system.Opioids are classically associated with phenomena such as analgesia, respiratory depression, and addiction. The effects of opioids are mediated by at least three different opioid receptors, termed , ␦, and , which belong to the G-protein-coupled membrane receptor family (1, 2). During the last years, evidence has accumulated showing that exogenous opiates like morphine and endogenous opioid peptides derived from the precursors proopiomelanocortin, proenkephalin, and prodynorphin have multiple immunomodulatory properties in addition to their classical functions as neuromodulators. It was stated that the endogenous opioid peptides would now be considered members of the cytokine family if they had been first discovered by immunologists (3). Elucidation of a broad bidirectional communication between the opioid system and the immune system strengthens this concept. Thus, morphine, the prototypical exogenous ligand for the receptor, is an immunosuppressive drug and is responsible for increased susceptibility of opioid addicts to infections (4 -8). Studies with -opioid receptor knockout mice emphasized the role of this receptor in immunosuppression (9). After chronic morphine treatment, these mice developed none of the symptoms characteristic of wild type mice, namely lymphoid organ atrophy, diminished CD4 ϩ / CD8 ϩ cell ratio and strongly reduced natural killer cell activity. In contrast, cytokines modulate the expression of opioid peptide genes and opioid receptor genes. For example, studies with IL-6 1 knockout mice revealed decreased levels of receptors in the brain compared with wild type animals, suggesting a positive regulation of this receptor by IL-6 in vivo (10). In vitro, up-regulation of ...

The opioid antagonist, β-funaltrexamine, inhibits chemokine expression in human astroglial cells

“…We recently determined that expression of the human muopioid receptor (hMOR) mRNA is up-regulated in A172 cells following TNFα exposure (unpublished data). TNFα also induces MOR expression in various cell types including peripheral immune effector cells, microvascular endothelial cells and SH SY5Y neuroblastoma cells (Borner et al, 2004;Kraus et al, 2003). Further characterization of opioid receptor expression in A172 cells is currently being investigated in our laboratory.…”

Clinical response to morphine in cancer patients and genetic variation in candidate genes

“…Importantly, the binding site for the transcription factor stat6 has been reported to contain an SNP that alters IL-4 upregulation of the m-opioid receptor. 20 This nucleotide was not polymorphic in our Caucasian population.…”

“…18,19 Functional studies have highlighted the role of stat6, which causes an increase in m-opioid receptor gene expression. 20 Genetic variation in the gene encoding the m-opioid receptor has been shown to alter the binding affinities of different opioids. [21][22][23][24] Different opioids may therefore cause differential activation and desensitisation of the m-opioid receptor.…”

IL-4, JAK-STAT signaling, and pain

“…IL-4 links the immune system to the opioid system by inducing mu-and delta-opioid receptors (MOR, DOR) 64,65 and pro-opiomelanocortin (POMC) 66 transcription. Opioid receptor gene expression in T cells thereby was STAT6-dependent while POMC gene expression in lymphocytes was mediated via JAK-STAT activation and involved STAT3 but not STAT6.…”