T-Cell Receptor/CD28-Mediated Activation of Human T Lymphocytes Induces Expression of Functional -Opioid Receptors

ABSTRACT Opiates function as immunomodulators, partly by their effects on T cells. Opioids act via -, ␦-, and -opioid receptors, among which the -type is of particular interest, because morphine-like opioids preferentially bind to it. Here we report that -opioid receptor mRNA was induced after CD3/28-mediated activation of primary human T lymphocytes and Jurkat T cells, neither of which expresses the gene constitutively. Moreover, a reporter gene construct containing 2624 base pairs of the -opioid receptor promoter was transactivated by CD3/28 stimulation. Transcriptional induction of the -opioid receptor gene was mediated by activator protein-1 (AP-1), nuclear factor-B, and nuclear factor of activated T cells (NFAT). NFAT was found to bind to three sequences of the -opioid receptor promoter, located at nucleotides Ϫ1064, Ϫ785, and Ϫ486. Although the Ϫ486 element is in close proximity to a putative AP-1 site, there was no evidence for a combined AP-1/NFAT site. Furthermore, we demonstrated that the induction of interleukin-2 mRNA and protein in activated T cells was inhibited by morphine in cells, in which -opioid receptors had been induced by CD3/28 monoclonal antibodies (mAbs), and that this effect was blocked by the -opioid receptor-specific antagonist D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH 2 . CD3/28 mAb-induced interleukin-2 transcription was also inhibited by the opioids fentanyl and loperamide. This indicates that the induced -opioid receptor mRNA is translated into functional receptor protein. Furthermore, a -opioid receptor-enhanced green fluorescent protein-fusion protein was localized in membranes of Jurkat cells and internalized in response to [D-Ala 2 ,NMe-Phe 4 ,Gly 5 -ol]-enkephalin but not morphine. In conclusion, these data emphasize the role of opioids in the modulation of T lymphocyte signaling