title: Agonist-specific down-regulation of the human delta-opioid receptor.
abstract: Down-regulation of the delta-opioid receptor contributes to the development of tolerance to delta-opioid receptor agonists. The involvement of the carboxy terminus of the mouse delta-opioid receptor in peptide agonist-mediated down-regulation has been established. In the present study, we examined the down-regulation of the truncated human delta-opioid receptor by structurally distinct delta-opioid receptor agonists. Chinese hamster ovary (CHO) cells, expressing the full-length or truncated epitope-tagged human delta-opioid receptors were incubated with various delta-opioid receptor agonists (100 nM, 24 h), and membrane receptor levels were determined by [(3)H]naltrindole saturation binding. Each delta-opioid receptor agonist tested down-regulated the full-length receptor. Truncation of the carboxy terminus abolished down-regulation by all delta-opioid receptor agonists, except SNC80 ((+)-4-[(alphaR)-alpha-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]N,N-diethylbenzamide). In addition, truncation of the C-terminus completely attenuated [D-Pen(2)-D-Pen(5)]enkephalin (DPDPE), but not SNC80-mediated [32P] incorporation into the protein immunoreactive with an anti-epitope-tagged antibody. These findings suggest that SNC80-mediated phosphorylation and down-regulation of the human delta-opioid receptor involves other receptor domains in addition to the carboxy terminus. Pertussis toxin treatment did not block SNC80-mediated down-regulation of the truncated Et-hDOR, indicating that the down-regulation is independent of G(i/o) protein activation and subsequent downstream signaling.
authors.affiliation: Department of Pharmacology, The University of Arizona Health Sciences Center, Tucson, AZ 85724, USA.
authors.forename: Takashi
authors.initials: T
authors.lastname: Okura
authors.forename: Eva V
authors.initials: EV
authors.lastname: Varga
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Hosohata
authors.forename: Edita
authors.initials: E
authors.lastname: Navratilova
authors.forename: Scott M
authors.initials: SM
authors.lastname: Cowell
authors.forename: Kenner
authors.initials: K
authors.lastname: Rice
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nagase
authors.forename: Victor J
authors.initials: VJ
authors.lastname: Hruby
authors.forename: William R
authors.initials: WR
authors.lastname: Roeske
authors.forename: Henry I
authors.initials: HI
authors.lastname: Yamamura
mesh_terms: D000595:Amino Acid Sequence; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001549:Benzamides / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D009271:Naltrexone / Q000031:analogs & derivatives* / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010879:Piperazines / Q000494:pharmacology*; D011869:Radioligand Assay; D017465:Receptors, Opioid, delta / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D014316:Tritium
chemical_list: D000701:Analgesics, Opioid; D001549:Benzamides; D010879:Piperazines; D017465:Receptors, Opioid, delta; D011993:Recombinant Fusion Proteins; D014316:Tritium; C088464:4-(alpha-(4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N,N-diethylbenzamide; D009271:Naltrexone; D020881:Enkephalin, D-Penicillamine (2,5)-; D037342:Pertussis Toxin; C055382:naltrindole