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

Morphine and the endogenous opioid peptide β-endorphin exert neuromodulatory as well as immunomodulatory effects, which are transduced by μ-opioid receptors. In this report we show that stimulation with interleukin-4 induces μ-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, μ 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 μ 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.