title: PKA and ERK1/2 are involved in dopamine D₁ receptor-induced heterologous desensitization of the δ opioid receptor.
abstract: OBJECTIVE
  Chronic administration of cocaine attenuates delta opioid receptor (DOPR) signaling in the striatum and the desensitization is mediated by the indirect actions of cocaine on dopamine D1 receptors (D1R). In addition, DOPR and D1R co-exist in some rat striatal neurons. In the present study, we examined the underlying mechanism of DOPR desensitization by D1R activation.
  
  
  METHODS
  NG 108-15 cells stably expressing HA-rat D1 receptor (HA-D1R) and Chinese hamster ovary (CHO) cells stably expressing both FLAG-mouse DOPR (FLAG-DOPR) and HA-D1R were used as the cell models. Receptor binding, [(35)S]GTPγS binding, receptor phosphorylation and western blot were conducted to examine DOPR affinity, expression, internalization, downregulation, desensitization, phosphorylation and phosphorylated ERK1/2.
  
  
  RESULTS
  Pretreatment with either the DOPR agonist DPDPE or the D1R agonist SKF-82958 for 30min attenuated DPDPE-stimulated [(35)S]GTPγS binding to G proteins, demonstrating homologous and heterologous desensitization of the DOPR, respectively. SKF-82958 pretreatment did not affect the level of DOPR or affinity of DOPR antagonist or agonists, nor did it induce phosphorylation, internalization or down-regulation of the DOPR in the CHO-FLAG-DOPR/HA-D1R cells. Pretreatment of cells with inhibitors of PKA, MEK1 and PI3K, but not PKC, attenuated SKF-82958-induced desensitization of the DOPR. The D1R agonist SKF-82958 enhanced phosphorylation of ERK1/2, and pretreatment with inhibitors of MEK1 and PI3K, but not PKA and PKC, reduced the effect. These results indicate that activation of ERK1/2 and/or PKA, but not PKC, is involved in D1 receptor-induced heterologous desensitization of the DOPR.
  
  
  CONCLUSIONS
  This study provides possible mechanisms underlying D1R activation-induced DOPR desensitization.
authors.affiliation: Department of Pharmacology and Center for Substance Abuse Research, School of Medicine, Temple University, Philadelphia, PA 19140, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Xu
authors.forename: Chongguang
authors.initials: C
authors.lastname: Chen
authors.forename: Jian-Guo
authors.initials: JG
authors.lastname: Li
authors.forename: Kelly
authors.initials: K
authors.lastname: Dimattio
authors.forename: Yujun
authors.initials: Y
authors.lastname: Wang
authors.forename: Ellen
authors.initials: E
authors.lastname: Unterwald
authors.forename: Lee-Yuan
authors.initials: LY
authors.lastname: Liu-Chen
mesh_terms: D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D015153:Blotting, Western; D016466:CHO Cells; D002460:Cell Line; D003042:Cocaine / Q000494:pharmacology; D006224:Cricetinae; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000502:physiology*; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D051379:Mice; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology; D051381:Rats; D017447:Receptors, Dopamine D1 / Q000187:drug effects / Q000502:physiology*; D017465:Receptors, Opioid, delta / Q000187:drug effects / Q000502:physiology*
chemical_list: D001549:Benzamides; D001552:Benzazepines; D010879:Piperazines; D017447:Receptors, Dopamine D1; D017465:Receptors, Opioid, delta; C088464:4-(alpha-(4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N,N-diethylbenzamide; C071262:SK&F 82958; D017868:Cyclic AMP-Dependent Protein Kinases; D003042:Cocaine