RT Journal Article
SR Electronic
T1 CPCCOEt, a Noncompetitive Metabotropic Glutamate Receptor 1 Antagonist, Inhibits Receptor Signaling Without Affecting Glutamate Binding
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 453
OP 461
VO 55
IS 3
A1 Stephane Litschig
A1 Fabrizio Gasparini
A1 Doris Rueegg
A1 Natacha Stoehr
A1 Peter Josef Flor
A1 Ivo Vranesic
A1 Laurent Prézeau
A1 Jean-Philippe Pin
A1 Christian Thomsen
A1 Rainer Kuhn
YR 1999
UL http://molpharm.aspetjournals.org/content/55/3/453.abstract
AB Metabotropic glutamate receptors (mGluRs) are a family of G protein-coupled receptors characterized by a large, extracellular N-terminal domain comprising the glutamate-binding site. In the current study, we examined the pharmacological profile and site of action of the non-amino-acid antagonist 7-hydroxyiminocyclopropan[b]chromen-1a-carboxylic acid ethyl ester (CPCCOEt). CPCCOEt selectively inhibited glutamate-induced increases in intracellular calcium at human mGluR1b (hmGluR1b) with an apparent IC50 of 6.5 μM while having no agonist or antagonist activity at hmGluR2, -4a, -5a, -7b, and -8a up to 100 μM. Schild analysis indicated that CPCCOEt acts in a noncompetitive manner by decreasing the efficacy of glutamate-stimulated phosphoinositide hydrolysis without affecting the EC50 value or Hill coefficient of glutamate. Similarly, CPCCOEt did not displace [3H]glutamate binding to membranes prepared from mGluR1a-expressing cells. To elucidate the site of action, we systematically exchanged segments and single amino acids between hmGluR1b and the related subtype, hmGluR5a. Substitution of Thr815 and Ala818, located at the extracellular surface of transmembrane segment VII, with the homologous amino acids of hmGluR5a eliminated CPCCOEt inhibition of hmGluR1b. In contrast, introduction of Thr815 and Ala818 at the homologous positions of hmGluR5a conferred complete inhibition by CPCCOEt (IC50 = 6.6 μM), i.e., a gain of function. These data suggest that CPCCOEt represents a novel class of G protein-coupled receptor antagonists inhibiting receptor signaling without affecting ligand binding. We propose that the interaction of CPCCOEt with Thr815 and Ala818 of mGluR1 disrupts receptor activation by inhibiting an intramolecular interaction between the agonist-bound extracellular domain and the transmembrane domain. The American Society for Pharmacology and Experimental Therapeutics