Abstract
μ-Opioid receptors mediate such opioid effects as analgesia, euphoria, and immunomodulation. Gene expression of μ-opioid receptors can be modulated by various substances, including cytokines, hormones, and drugs. Some of these stimuli (e.g., IL-1β and cocaine) have been shown to activate members of the AP-1 transcription factor family. In addition, transcription of the μ-opioid receptor gene is induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, which in turn is an activator of AP-1 transcription factors. This indicates that signaling pathways involving protein kinase C and activator protein 1 (AP-1) transcription factors are important for the specific expression pattern of the μ-opioid receptor gene. In this report, we show that TPA activates AP-1 as well as the transcription factor nuclear factor κB (NFκB) in the μ-opioid receptor expressing neuroblastoma cell line SH SY5Y. In transfection experiments performed in these cells, both factorstrans-activate expression of reporter gene constructs containing the human μ-opioid receptor gene promoter. By excluding the effects of TPA on NFκB with the specific NFκB inhibitor sulfasalazine, AP-1 regulatory elements were localized. Two AP-1 elements, which differ in one nucleotide each from the classic AP-1 binding site, were delineated to positions −2388 and −1434 of the promoter. Independent of their orientation, these elements conferred TPA responsiveness on the heterologous thymidine kinase promoter. AP-1 binding to these elements was confirmed using electrophoretic mobility shift and immunoshift assays.
- The American Society for Pharmacology and Experimental Therapeutics
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