Regulation of mu-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 P-endorphin exert neuromodulator y as well as immunomodulatory effects, which are transduced by mu -opioid r eceptors. In this report we show that stimulation with interleukin-4 induce s Ik-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, mu receptor transcription is up-regulated by interleukin-4 in cu ltures of primary rat neurons. Transient transfection experiments in Raji a nd SH SY5Y neuronal cells with human and rat reporter gene constructs linke d the interleukin-4 effect directly to cis-active mu receptor promoter elem ents located at nucleotide -997 on the human gene and nucleotide -727 on th e rat gene. The interleukin-4 response elements function orientation indepe ndently. 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 pote ntial of this element by 50%, which may affect the phenotype of persons car rying this variation. These findings provide a molecular basis for understa nding bidirectional interactions between the opioid system and the immune s ystem.