%0 Journal Article %A Yong Chen %A Chongguang Chen %A Yulin Wang %A Lee-Yuan Liu-Chen %T Ligands Regulate Cell Surface Level of the Human κ Opioid Receptor by Activation-Induced Down-Regulation and Pharmacological Chaperone-Mediated Enhancement: Differential Effects of Nonpeptide and Peptide Agonists %D 2006 %R 10.1124/jpet.106.107987 %J Journal of Pharmacology and Experimental Therapeutics %P 765-775 %V 319 %N 2 %X Two peptide agonists, eight nonpeptide agonists, and five nonpeptide antagonists were evaluated for their capacity to regulate FLAG (DYKDDDDK)-tagged human κ opioid receptors (hKORs) stably expressed in Chinese hamster ovary cells after incubation for 4 h with a ligand at a concentration ∼1000-fold of its EC50 (agonist) or Ki (antagonist) value. Dynorphins A and B decreased the fully glycosylated mature form (55-kDa) of FLAG-hKOR by 70%, whereas nonpeptide full agonists [2-(3,4-dichlorophenyl)-N-methyl-N-[(2R)-2-pyrrolidin-1-ylcyclohexyl-]acetamide (U50,488H), 17-cyclopropylmethyl-3,14-dihydroxy-4,5-epoxy-6-[N-methyl-trans-3-(3-furyl) acrylamido] morphinan hydrochloride (TRK-820), ethylketocyclazocine, bremazocine, asimadoline, and (RS)-[3-[1-[[(3,4-dichlorophenyl)acetyl]-methylamino]-2-(1-pyrrolidinyl)ethyl]phenoxy] acetic acid hydrochloride (ICI 204,448) caused 10–30% decreases. In contrast, pentazocine (partial agonist) and etorphine (full agonist) up-regulated by ∼15 and 25%, respectively. The antagonists naloxone and norbinaltorphimine also significantly increased the 55-kDa receptor, whereas selective μ, δ, and D1 receptor antagonists had no effect. Naloxone up-regulated the receptor concentration- and time-dependently and enhanced the receptor maturation extent, without affecting its turnover. Treatment with brefeldin A (BFA), which disrupts Golgi, resulted in generation of a 51-kDa form that resided intracellularly. Naloxone up-regulated the new species, indicating that its action site is in the endoplasmic reticulum as a pharmacological chaperone. After treatment with BFA, all nonpeptide agonists up-regulated the 51-kDa form, whereas dynorphins A and B did not, indicating that nonpeptide agonists act as pharmacological chaperones, but peptide agonists do not. BFA treatment enhanced down-regulation of the cell surface receptor induced by nonpeptide agonists, but not that by peptide agonists, and unmasked etorphine- and pentazocine-mediated receptor down-regulation. These results demonstrate that ligands have dual effects on receptor levels: enhancement by chaperone-like effects and agonist-promoted down-regulation, and the net effect reflects the algebraic sum of the two. The American Society for Pharmacology and Experimental Therapeutics %U https://jpet.aspetjournals.org/content/jpet/319/2/765.full.pdf