title: Turnover of mu-opioid receptors in neuroblastoma cells.
abstract: This study investigated the turnover of mu-opioid receptors (MOR) in neuroblastoma (N2A) cells under basal and agonist-stimulated opioid receptor down-regulation. Cells were labeled with [35S]methionine for 24 h and MOR degradation was quantified by immunoprecipitation using monoclonal anti (MOR) antibody followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiography. Treatment of N2A cells with the selective mu-opioid ligand (DAMGO) increased the rate of MOR degradation. The radiolabeled immunoprecipitable receptor was lost from the cells with a half-life (t(1/2)) of 12 and 7 h in the absence and presence of DAMGO, respectively. On the other hand, the protein synthesis inhibitor cycloheximide (10 microg/ml) produced a decrease in the rate of receptor degradation, t(1/2)=22 h indicated that the rate of MOR turnover was attenuated almost 2-fold following the inhibition of protein synthesis. Furthermore, when N2A cells were exposed to a combination of DAMGO and cycloheximide, the t(1/2) was 9.7 h. These data provided the first evidence that MOR is down-regulated during agonist stimulation and that the turnover rate of MOR is sum of both accelerated receptor degradation and decreased receptor biosynthesis.
authors.affiliation: Department of Pharmacology, Faculty of Pharmacy, University of Alexandria, Egypt. afify001@hotmail.com
authors.forename: Elham A
authors.initials: EA
authors.lastname: Afify
mesh_terms: D000701:Analgesics, Opioid / Q000378:metabolism; D000818:Animals; D003513:Cycloheximide / Q000378:metabolism; D015536:Down-Regulation / Q000502:physiology*; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000378:metabolism; D008715:Methionine / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D009447:Neuroblastoma; D009474:Neurons / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism*; D013462:Sulfur Radioisotopes / Q000737:chemistry / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000701:Analgesics, Opioid; D011500:Protein Synthesis Inhibitors; D017450:Receptors, Opioid, mu; D013462:Sulfur Radioisotopes; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D003513:Cycloheximide; D008715:Methionine