title: Characterization of Imidazopyridine Compounds as Negative Allosteric Modulators of Proton-Sensing GPR4 in Extracellular Acidification-Induced Responses.
abstract: G protein-coupled receptor 4 (GPR4), previously proposed as the receptor for sphingosylphosphorylcholine, has recently been identified as the proton-sensing G protein-coupled receptor (GPCR) coupling to multiple intracellular signaling pathways, including the Gs protein/cAMP and G13 protein/Rho. In the present study, we characterized some imidazopyridine compounds as GPR4 modulators that modify GPR4 receptor function. In the cells that express proton-sensing GPCRs, including GPR4, OGR1, TDAG8, and G2A, extracellular acidification stimulates serum responsive element (SRE)-driven transcriptional activity, which has been shown to reflect Rho activity, with different proton sensitivities. Imidazopyridine compounds inhibited the moderately acidic pH-induced SRE activity only in GPR4-expressing cells. Acidic pH-stimulated cAMP accumulation, mRNA expression of inflammatory genes, and GPR4 internalization within GPR4-expressing cells were all inhibited by the GPR4 modulator. We further compared the inhibition property of the imidazopyridine compound with psychosine, which has been shown to selectively inhibit actions induced by proton-sensing GPCRs, including GPR4. In the GPR4 mutant, in which certain histidine residues were mutated to phenylalanine, proton sensitivity was significantly shifted to the right, and psychosine failed to further inhibit acidic pH-induced SRE activation. On the other hand, the imidazopyridine compound almost completely inhibited acidic pH-induced action in mutant GPR4. We conclude that some imidazopyridine compounds show specificity to GPR4 as negative allosteric modulators with a different action mode from psychosine, an antagonist susceptible to histidine residues, and are useful for characterizing GPR4-mediated acidic pH-induced biological actions.
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Ayaka
authors.initials: A
authors.lastname: Tobo
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Tobo
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakakura
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Ebara
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Tomura
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Mogi
authors.affiliation: Laboratory of Pharmacology, College of Pharmacy, Pusan National University, Busan, Republic of Korea.
authors.forename: Dong-Soon
authors.initials: DS
authors.lastname: Im
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Naoya
authors.initials: N
authors.lastname: Murata
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kuwabara
authors.affiliation: Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Ito
authors.affiliation: Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan.
authors.forename: Hayato
authors.initials: H
authors.lastname: Fukuda
authors.affiliation: Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Arisawa
authors.affiliation: Faculty of Pharmaceutical Science, Hokkaido University, Sapporo, Japan; Center for Research and Education on Drug Discovery, Hokkaido University, Sapporo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Shuto
authors.affiliation: Department of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Nakaya
authors.affiliation: Department of Pharmacology and Toxicology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Kurose
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Sato
authors.affiliation: Laboratory of Signal Transduction, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Japan.
authors.forename: Fumikazu
authors.initials: F
authors.lastname: Okajima
mesh_terms: D000494:Allosteric Regulation; D019943:Amino Acid Substitution; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D057809:HEK293 Cells; D061307:Human Umbilical Vein Endothelial Cells; D006801:Humans; D007093:Imidazoles / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding; D011522:Protons; D011725:Pyridines / Q000737:chemistry / Q000494:pharmacology*; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D007093:Imidazoles; D011522:Protons; D011725:Pyridines; D043562:Receptors, G-Protein-Coupled