TY - JOUR T1 - Use of Constitutive G Protein-Coupled Receptor Activity for Drug Discovery JF - Molecular Pharmacology JO - Mol Pharmacol SP - 125 LP - 134 VL - 57 IS - 1 AU - Grace Chen AU - James Way AU - Susan Armour AU - Chris Watson AU - Ken Queen AU - Channa K. Jayawickreme AU - Wen-Ji Chen AU - Terry Kenakin Y1 - 2000/01/01 UR - http://molpharm.aspetjournals.org/content/57/1/125.abstract N2 - This article describes the behavior of transiently transfected human receptors into melanophores and the potential use of constitutive receptor activity to screen for new drug entities. Specifically, transient transfection of melanophores with different concentrations of receptor cDNA presumably leads to increased levels of receptor expression. This leads to an increased response to agonists (both maxima and potency) and, in some cases, an agonist-independent constitutive receptor activity. Transfections with increasing concentrations of the Gs protein-coupled human calcitonin receptor type 2 (hCTR2) cDNA produced sufficient levels of constitutively activated receptor to cause elevated basal cellular responses. This was observed as a decrease in the transmittance of light through melanophores (consistent with Gs protein activation) and increased response to human calcitonin. The receptor-mediated nature of this response was confirmed by its reversal with the hCTR2 peptide inverse agonist AC512. A collection of ligands for hCTR2 either increased or decreased constitutive hCTR2 activity, suggesting that the constitutive system was a sensitive discriminator of positive and negative ligand efficacy. Similar results were obtained with Gi-protein-coupled receptors. Transient transfection of NPY1, NPY2, NPY4, CXCR4, and CCR5 cDNA produced increased light transmittance through melanophores (consistent with Gi-protein activation). NPY1 cDNA produced little constitutive response on transfection, whereas maximal levels of constitutive activity ranging from 30 to 45% were observed for the other Gi-protein-coupled receptors. Responses to agonists for these receptors increased (both maxima and potency) with increasing cDNA transfection. The receptor/Gi-protein nature of both the constitutive and agonist-mediated responses was confirmed by elimination with pertussis toxin pretreatment. These data are discussed in terms of the theoretical aspects of constitutive receptor activity and the applicability of this approach for the general screening of G protein-coupled orphan receptors. The American Society for Pharmacology and Experimental Therapeutics ER -