title: A novel human receptor involved in bitter tastant detection identified using Dictyostelium discoideum.
abstract: Detection of substances tasting bitter to humans occurs in diverse organisms including the social amoeba Dictyostelium discoideum. To establish a molecular mechanism for bitter tastant detection in Dictyostelium, we screened a mutant library for resistance to a commonly used bitter standard, phenylthiourea. This approach identified a G-protein-coupled receptor mutant, grlJ(-), which showed a significantly increased tolerance to phenylthiourea in growth, survival and movement. This mutant was not resistant to a structurally dissimilar potent bitter tastant, denatonium benzoate, suggesting it is not a target for at least one other bitter tastant. Analysis of the cell-signalling pathway involved in the detection of phenylthiourea showed dependence upon heterotrimeric G protein and phosphatidylinositol 3-kinase activity, suggesting that this signalling pathway is responsible for the cellular effects of phenylthiourea. This is further supported by a phenylthiourea-dependent block in the transient cAMP-induced production of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in wild-type but not grlJ(-) cells. Finally, we have identified an uncharacterized human protein γ-aminobutyric acid (GABA) type B receptor subunit 1 isoform with weak homology to GrlJ that restored grlJ(-) sensitivity to phenylthiourea in cell movement and PIP3 regulation. Our results thus identify a novel pathway for the detection of the standard bitter tastant phenylthiourea in Dictyostelium and implicate a poorly characterized human protein in phenylthiourea-dependent cell responses.
authors.affiliation: Centre for Biomedical Sciences, School of Biological Sciences, Royal Holloway University of London, Egham TW20 0EX, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Robery
authors.forename: Richard
authors.initials: R
authors.lastname: Tyson
authors.forename: Christopher
authors.initials: C
authors.lastname: Dinh
authors.forename: Adam
authors.initials: A
authors.lastname: Kuspa
authors.forename: Angelika A
authors.initials: AA
authors.lastname: Noegel
authors.forename: Till
authors.initials: T
authors.lastname: Bretschneider
authors.forename: Paul L R
authors.initials: PL
authors.lastname: Andrews
authors.forename: Robin S B
authors.initials: RS
authors.lastname: Williams
mesh_terms: D002465:Cell Movement; D002470:Cell Survival; D000242:Cyclic AMP / Q000378:metabolism; D004023:Dictyostelium / Q000502:physiology*; D017353:Gene Deletion; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D006801:Humans; D010670:Phenylthiourea / Q000737:chemistry*; D058539:Phosphatidylinositol 3-Kinase / Q000235:genetics* / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism; D018080:Receptors, GABA-B / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D013649:Taste / Q000502:physiology*; D013650:Taste Buds / Q000378:metabolism
chemical_list: D000242:Cyclic AMP; D010670:Phenylthiourea; D058539:Phosphatidylinositol 3-Kinase; D018129:Phosphatidylinositol Phosphates; D000644:Quaternary Ammonium Compounds; D043562:Receptors, G-Protein-Coupled; D018080:Receptors, GABA-B; C060974:phosphatidylinositol 3,4,5-triphosphate; C043414:denatonium
keywords: Bitter taste; Denatonium; Dictyostelium; GABABR1; PI3K; Phenylthiourea; Q8NHA5; Taste perception; grlJ