title: Internalization and down-regulation of mu opioid receptors by endomorphins and morphine in SH-SY5Y human neuroblastoma cells.
abstract: The human neuroblastoma cell line, SH-SY5Y, was used to examine the effects of morphine and the endogenous opioid peptides, endomorphin-1 (EM-1) and endomorphin-2 (EM-2), on mu opioid receptor (MOR) internalization and down-regulation. Treatment for 24 h with EM-1, EM-2 or morphine at 100 nM, 1 microM and 10 microM resulted in a dose-dependent down-regulation of mu receptors. Exposure of cells to 10 microM EM-1 for 2.5, 5 and 24 h resulted in a time-dependent down-regulation of mu receptors. Down-regulation of mu receptors by morphine and EM-1 was blocked by treatment with hypertonic sucrose, consistent with an endocytosis-dependent mechanism. Sensitive cell-surface binding studies with a radiolabeled mu antagonist revealed that morphine was able to induce internalization of mu receptors naturally expressed in SH-SY5Y cells. EM-1 produced a more rapid internalization of mu receptors than morphine, but hypertonic sucrose blocked the internalization induced by each of these agonists. This study demonstrates that, like morphine, the endomorphins down-regulate mu opioid receptors in a dose- and time-dependent manner. This study also demonstrates that morphine, as well as EM-1, can induce rapid, endocytosis-dependent internalization of mu opioid receptors in SH-SY5Y cells. These results may help elucidate the ability of mu agonists to regulate the number and responsiveness of their receptors.
authors.affiliation: Neuroscience Program, Tulane University School of Medicine, New Orleans, LA 70112, USA.
authors.forename: Kristen A
authors.initials: KA
authors.lastname: Horner
authors.forename: James E
authors.initials: JE
authors.lastname: Zadina
mesh_terms: D000701:Analgesics, Opioid / Q000493:pharmacokinetics / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004347:Drug Interactions; D004705:Endocytosis / Q000187:drug effects; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000493:pharmacokinetics; D006801:Humans; D007038:Hypotonic Solutions / Q000494:pharmacology; D009020:Morphine / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000493:pharmacokinetics; D009447:Neuroblastoma; D009842:Oligopeptides / Q000494:pharmacology*; D010455:Peptides / Q000493:pharmacokinetics; D011869:Radioligand Assay / Q000379:methods; D017450:Receptors, Opioid, mu / Q000187:drug effects / Q000378:metabolism*; D013395:Sucrose / Q000494:pharmacology; D013997:Time Factors; D014316:Tritium / Q000493:pharmacokinetics
chemical_list: D000701:Analgesics, Opioid; D007038:Hypotonic Solutions; D009292:Narcotic Antagonists; D009842:Oligopeptides; D010455:Peptides; D017450:Receptors, Opioid, mu; C105293:endomorphin 1; D014316:Tritium; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; C105294:endomorphin 2; D013395:Sucrose; C009862:connective tissue-activating peptide; D009020:Morphine