title: Regulation of Rac1 GTPase activity by quinine through G-protein and bitter taste receptor T2R4.
abstract: Rac1 belongs to the Rho family of small GTPases and regulates actin cytoskeleton reorganization. T2R4 is a bitter taste receptor belonging to the G protein-coupled receptor family of proteins. In addition to mediating bitter taste perception from the tongue, T2R4s are found in extra-oral tissues, e.g., nasal epithelium, airways, brain, testis suggesting a much broader physiological function for these receptors. Anti-malarial drug and a bitter tasting compound, quinine, is a known agonist for T2R4, whereas BCML (Nα,Nα-Bis(carboxymethyl)-L-lysine) acts as an inverse agonist. Using western blot and Ca++mobilization assays, the effects of quinine on Rac1 activity in HEK293T cells stably expressing T2R4/Gα16/44, T2R4, or Gα16/44and transiently transfected with HA-Rac1 were investigated. Quinine treatment caused a significant reduction in the amount of active Rac1, whereas in the presence of BCML, quinine failed to cause any significant change in active Rac1. No significant change in Rac1 activity was observed in BAPTA-AM plus quinine-treated Gα16/44cells, suggesting possibility of a pathway in addition to the canonical Ca++-dependent pathway. A noticeable role for Gα16/44independent of T2R4 is observed in quinine-mediated Rac1 inactivation. Further, a significant difference in quinine-induced Ca++response in T2R4/Gα16/44or T2R4 cells was observed validating the partial role of calcium and importance of Gα16/44. This study is the first to show an inhibitory downstream action of a T2R4 agonist on Rac1 function. Further investigation will help in better understanding the downstream signal transduction network of T2R4 and its extra-oral physiological roles.
authors.affiliation: Department of Oral Biology, University of Manitoba, Rm. D328, Winnipeg, MB, R3E 0W2, Canada.|Manitoba Chemosensory Biology Research Group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada.
authors.forename: Crystal
authors.initials: C
authors.lastname: Sidhu
authors.affiliation: Department of Oral Biology, University of Manitoba, Rm. D328, Winnipeg, MB, R3E 0W2, Canada.|Manitoba Chemosensory Biology Research Group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada.
authors.forename: Appalaraju
authors.initials: A
authors.lastname: Jaggupilli
authors.affiliation: Department of Oral Biology, University of Manitoba, Rm. D328, Winnipeg, MB, R3E 0W2, Canada.|Manitoba Chemosensory Biology Research Group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada.
authors.forename: Prashen
authors.initials: P
authors.lastname: Chelikani
authors.affiliation: Department of Oral Biology, University of Manitoba, Rm. D328, Winnipeg, MB, R3E 0W2, Canada. Rajinder.Bhullar@umanitoba.ca.|Manitoba Chemosensory Biology Research Group, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada. Rajinder.Bhullar@umanitoba.ca.|Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, MB, R3E 0W2, Canada. Rajinder.Bhullar@umanitoba.ca.
authors.forename: Rajinder P
authors.initials: RP
authors.lastname: Bhullar
mesh_terms: D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D011803:Quinine / Q000494:pharmacology*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D000098706:Taste Receptors, Type 2
chemical_list: C107953:RAC1 protein, human; D043562:Receptors, G-Protein-Coupled; D000098706:Taste Receptors, Type 2; D011803:Quinine; C112631:G protein alpha 16; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020830:rac1 GTP-Binding Protein
keywords: Bitter taste receptor; G protein-coupled receptor; G-alpha protein; Quinine; Rac1 inactivation