title: Characterization of bitter taste responses of intestinal STC-1 cells.
abstract: Cellular responses of STC-1 cells to two bitter tastants (denatonium and caffeine) were investigated using a calcium-imaging technique and compared with the response to bombesin. Caffeine is known to stimulate taste receptor cells, but the properties of its signaling have not been well studied. STC-1 cells responded to all three molecules in a dose-dependent manner, and when a reverse transcriptase-polymerase chain reaction (RT-PCR) for denatonium receptor was performed, the product of predicted size was detected in STC-1 cells. Furthermore, all three signaling pathways were blocked by a phospholipase C (PLC) inhibitor, demonstrating the essential involvement of PLC in cellular responses. To study the regulatory system of G protein signaling in STC-1 cells, we searched G protein-coupled receptor kinases (GRKs) by the degenerate-primer PCR method and found that GRK2 is expressed. We also demonstrated that three GRKs (GRK2, GRK3 and GRK5) are differentially distributed in the circumvallate papilla while only GRK2 is present in taste bud cells. Finally, we overexpressed GRK2 in SCT-1 cells and found that bombesin-induced response was strongly inhibited by GRK2 but denatonium-activated signaling was not affected. In the case of caffeine, response was decreased by expression of GRK2 only when cells were activated by 1 mM caffeine. Thus, we showed that STC-1 cells emerge as a cell model for studying the molecular mechanism of bitter taste signaling, and could indicate properties of caffeine-induced signaling in comparison with other signaling.
authors.affiliation: Department of Bio-Science, Faculty of Bio-Science, Nagahama Institute of Bio-Science and Technology, Shiga 526-0829, Japan.
authors.forename: Ikuo
authors.initials: I
authors.lastname: Masuho
authors.forename: Michihiro
authors.initials: M
authors.lastname: Tateyama
authors.forename: Osamu
authors.initials: O
authors.lastname: Saitoh
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001839:Bombesin / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D054770:G-Protein-Coupled Receptor Kinase 3; D054774:G-Protein-Coupled Receptor Kinase 5; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013649:Taste / Q000187:drug effects / Q000502:physiology*; D013650:Taste Buds / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D014162:Transfection; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D000644:Quaternary Ammonium Compounds; D043562:Receptors, G-Protein-Coupled; D002110:Caffeine; C043414:denatonium; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C517850:GRK3 protein, mouse; D051552:beta-Adrenergic Receptor Kinases; D054774:G-Protein-Coupled Receptor Kinase 5; C517895:Grk5 protein, mouse; D001839:Bombesin