title: Regulation of mammalian MOR-1 gene expression after chronic treatment             with morphine.
abstract: Morphine is an effective analgesic that acts by binding to the µ-opioid receptor (MOR) coded in the human by the OPRM1 gene. In the present study, we investigated the regulation of µ-opioid receptor (MOR-1) mRNA levels in all-trans-retinoic acid-differentiated SH-SY5Y human neuroblastoma cells under in vitro conditions with 10 µM morphine treatment for 24 h. In addition, we measured the MOR-1 levels in recombinant Chinese hamster ovary (CHO) cells, transfected with human µ-opioid receptor gene (hMOR) with 10 µM morphine treatment for 24 h. The isolated mRNA from these cells was subjected to real-time quantitative RT-PCR analysis to determine the regulation of µ-opioid receptor gene expression. It was observed that morphine treatment did not alter MOR-1 levels in undifferentiated SH-SY5Y cells compared to undifferentiated control cells. However, the MOR-1 levels in all-trans-retinoic acid-differentiated cells were significantly higher compared to the undifferentiated cells. Morphine treatment in differentiated SH-SY5Y cells caused significant downregulation of MOR-1 expression compared to the control cells. In the morphine-treated CHO cells, the hMOR-1 mRNA levels remained the same as the untreated control. Finally, pretreatment of SH-SY5Y cells with 10 µM naloxone, the antagonist of µ-opioid receptor, for 1 h significantly blocked the downregulation of MOR-1 mRNA levels with morphine treatment. These findings suggest that regulation of MOR-1 gene expression is cell-type specific after chronic morphine treatment and provide some evidence in the understanding of morphine tolerance.
authors.affiliation: College of Pharmacy and Pharmaceutical Sciences, Florida A__AMB__M                     University, Tallahassee, FL 32307, USA.
authors.forename: Rose V
authors.initials: RV
authors.lastname: Prenus
authors.forename: Ebens
authors.initials: E
authors.lastname: Luscar
authors.forename: Zhi-Ping
authors.initials: ZP
authors.lastname: Zhu
authors.forename: Ramesh B
authors.initials: RB
authors.lastname: Badisa
authors.forename: Carl B
authors.initials: CB
authors.lastname: Goodman
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D016466:CHO Cells; D045744:Cell Line, Tumor; D006224:Cricetinae; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D009020:Morphine / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; C485764:OPRM1 protein, human; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D009270:Naloxone; D009020:Morphine