Sweet taste receptor interacting protein CIB1 is a general inhibitor of InsP3-dependent Ca2+ release in vivo.
In a search for sweet taste receptor interacting proteins, we have identified the calcium- and integrin-binding protein 1 (CIB1) as specific binding partner of the intracellular carboxyterminal domain of the rat sweet taste receptor subunit Tas1r2. In heterologous human embryonic kidney 293 (HEK293) cells, the G protein chimeras Galpha(16gust44) and Galpha(15i3) link the sweet taste receptor dimer TAS1R2/TAS1R3 to an inositol 1,4,5-trisphosphate (InsP3)-dependent Ca2+ release pathway. To demonstrate the influence of CIB1 on the cytosolic Ca2+ concentration, we used sweet and umami compounds as well as other InsP3-generating ligands in FURA-2-based Ca2+ assays in wild-type HEK293 cells and HEK293 cells expressing functional human sweet and umami taste receptor dimers. Stable and transient depletion of CIB1 by short-hairpin RNA increased the Ca2+ response of HEK293 cells to the InsP3-generating ligands ATP, UTP and carbachol. Over-expression of CIB1 had the opposite effect as shown for the sweet ligand saccharin, the umami receptor ligand monosodium glutamate and UTP. The CIB1 effect was dependent on the thapsigargin-sensitive Ca2+ store of the endoplasmic reticulum (ER) and independent of extracellular Ca2+. The function of CIB1 on InsP3-evoked Ca2+ release from the ER is most likely mediated by its interaction with the InsP3 receptor. Thus, CIB1 seems to be an inhibitor of InsP3-dependent Ca2+ release in vivo.
Hennigs
Jan K
JK
Institut für Biochemie und Molekularbiologie II, Molekulare Zellbiologie, Zentrum für Experimentelle Medizin, Hamburg, Germany
Burhenne
Nicole
N
Stähler
Frauke
F
Winnig
Marcel
M
Walter
Bettina
B
Meyerhof
Wolfgang
W
Schmale
Hartwig
H
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016257:Fura-2; D006801:Humans; D007202:Indicators and Reagents; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000187:drug effects / Q000378:metabolism; D008024:Ligands; D034622:RNA Interference; D051381:Rats; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000502:physiology; D013649:Taste / Q000187:drug effects / Q000235:genetics*; D013650:Taste Buds / Q000187:drug effects / Q000378:metabolism*; D014059:Tongue / Q000378:metabolism; D014544:Uridine Triphosphate / Q000378:metabolism / Q000494:pharmacology
C109198:CIB1 protein, human; D002135:Calcium-Binding Proteins; D004791:Enzyme Inhibitors; D007202:Indicators and Reagents; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008024:Ligands; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D002217:Carbachol; D002118:Calcium; D016257:Fura-2; D014544:Uridine Triphosphate