The role of transcription factors Sp1 and YY1 in proximal promoter region in initiation of transcription of the mu opioid receptor gene in human lymphocytes.

Although previous studies have shown that the mechanism of the lymphocyte mu opioid receptor (MOR) gene expression was distinctly different from that in the central nervous system, and is involved in several disparate aspects of the immune response, its precise molecular mechanism is still undefined. In this study, we analyzed the proximal promoter region of the MOR gene in lymphocytes to identify the influences of potential trans-acting factors in activating the initiation of the expression of the MOR gene in lymphocytes. The electrophoretic mobility shift assay showed that two transcription factors, Sp1 and YY1, were able to bind the promoter region. Using sequence overlapping probes and mutation assays, we determined that the CCC sequence of Sp1 and the GGC sequence of YY1 binding elements were core sequences, and replacement of these sequences lead to substantial loss of promoter activity. Stimulation with morphine was capable of up-regulating the intracellular level of Sp1 and YY1 proteins. Chromatin immunoprecipitation assays showed that the blockage of naloxone is achieved through down-regulation of transcription factor YY1. Furthermore, coimmunoprecipitation and transfection assays confirmed that the functional interaction of Sp1 and YY1 transcription factors was a crucial step in the initiation of expression of the MOR in lymphocytes. Thus, we conclude that the cooperative interaction of Sp1 and YY1 transcription factors is the critical event triggering the initiation of transcription of the MOR gene in lymphocytes, and this finding will be helpful to understand the pharmacological effect of morphine on lymphocytes.