title: Effects of cycloheximide and tunicamycin on opiate receptor activities in neuroblastoma X glioma NG108-15 hybrid cells.
abstract: The molecular mechanism of opiate receptor down-regulation and desensitization was investigated by studying the effects of cycloheximide and tunicamycin on opiate receptor activities in neuroblastoma X glioma NG108-15 hybrid cells. Cycloheximide inhibited [35S]methionine and [3H]-glucosamine incorporation by hybrid cells, while tunicamycin inhibited [3H]glucosamine incorporation only. Exposing hybrid cells to these two agents did not alter the viability of the cell. Treatment of NG108-15 cells with cycloheximide or tunicamycin produced a decrease in [3H]diprenorphine binding dependent on both time and concentrations of inhibitors, with no measurable modification in the ability of etorphine to regulate intracellular cyclic AMP production. Cycloheximide attenuated [3H]-diprenorphine binding by decreasing both the number of sites, Bmax, and the affinity of the receptor, Kd. Tunicamycin treatment produced a decrease in Bmax with no apparent alteration in Kd values. Cycloheximide and tunicamycin did not potentiate the rate or magnitude of etorphine-induced down-regulation or desensitization of opiate receptor in NG108-15 cells. Furthermore, there was an apparent antagonism in cycloheximide action on receptor down-regulation. The reappearance of opiate binding sites after agonist removal was affected by these two inhibitors. Cycloheximide and tunicamycin eliminated the increase in [3H]diprenorphine binding in the chronic etorphine-treated cells after agonist removal. These two inhibitors did not alter the resensitization of hybrid cells to etorphine. Thus, the site of opiate agonist action to induce receptor down-regulation and desensitization is not at the site of protein synthesis or protein glycosylation. These data substantiate previously reported observations that receptor down-regulation and receptor desensitization are two different cellular adaptation processes.
authors.forename: P Y
authors.initials: PY
authors.lastname: Law
authors.forename: H G
authors.initials: HG
authors.lastname: Ungar
authors.forename: D S
authors.initials: DS
authors.lastname: Hom
authors.forename: H H
authors.initials: HH
authors.lastname: Loh
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000242:Cyclic AMP / Q000096:biosynthesis; D003513:Cycloheximide / Q000494:pharmacology*; D004174:Diprenorphine / Q000378:metabolism; D005048:Etorphine / Q000494:pharmacology; D005910:Glioma / Q000378:metabolism; D005944:Glucosamine / Q000031:analogs & derivatives*; D006801:Humans; D006822:Hybrid Cells / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011957:Receptors, Opioid / Q000187:drug effects* / Q000378:metabolism; D014316:Tritium; D014415:Tunicamycin / Q000494:pharmacology*
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D011506:Proteins; D011957:Receptors, Opioid; D014316:Tritium; D014415:Tunicamycin; D004174:Diprenorphine; D005048:Etorphine; D003513:Cycloheximide; D000242:Cyclic AMP; D005944:Glucosamine