Amino acid-stimulated Ca2+ oscillations produced by the Ca2+-sensing receptor are mediated by a phospholipase C/inositol 1,4,5-trisphosphate-independent pathway that requires G12, Rho, filamin-A, and the actin cytoskeleton.
The G protein-coupled Ca(2+)-sensing receptor (CaR) is an allosteric protein that responds to two different agonists, Ca(2+) and aromatic amino acids, with the production of sinusoidal or transient oscillations in intracellular Ca(2+) concentration ([Ca(2+)](i)). Here, we examined whether these differing patterns of [Ca(2+)](i) oscillations produced by the CaR are mediated by separate signal transduction pathways. Using real time imaging of changes in phosphatidylinositol 4,5-biphosphate hydrolysis and generation of inositol 1,4,5-trisphosphate in single cells, we found that stimulation of CaR by an increase in the extracellular Ca(2+) concentration ([Ca(2+)](o)) leads to periodic synthesis of inositol 1,4,5-trisphosphate, whereas l-phenylalanine stimulation of the CaR does not induce any detectable change in the level this second messenger. Furthermore, we identified a novel pathway that mediates transient [Ca(2+)](i) oscillations produced by the CaR in response to l-phenylalanine, which requires the organization of the actin cytoskeleton and involves the small GTPase Rho, heterotrimeric proteins of the G(12) subfamily, the C-terminal region of the CaR, and the scaffolding protein filamin-A. Our model envisages that Ca(2+) or amino acids stabilize unique CaR conformations that favor coupling to different G proteins and subsequent activation of distinct downstream signaling pathways.
Rey
Osvaldo
O
Unit of Signal Transduction and Gastrointestinal Cancer, Division of Digestive Diseases, Department of Medicine, UCLA-CURE Digestive Diseases Research Center, David Geffen School of Medicine, University of California at Los Angeles, 90095, USA.
Young
Steven H
SH
Yuan
Jingzhen
J
Slice
Lee
L
Rozengurt
Enrique
E
D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000495:Allosteric Site; D000596:Amino Acids / Q000737:chemistry*; D015153:Blotting, Western; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D002460:Cell Line; D003285:Contractile Proteins / Q000737:chemistry*; D003599:Cytoskeleton / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D064448:Filamins; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000378:metabolism*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008840:Microfilament Proteins / Q000737:chemistry*; D009991:Oscillometry; D010649:Phenylalanine / Q000737:chemistry; D011487:Protein Conformation; D011493:Protein Kinase C / Q000737:chemistry; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
D000199:Actins; D000596:Amino Acids; D003285:Contractile Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D064448:Filamins; D008840:Microfilament Proteins; D044169:Receptors, Calcium-Sensing; D010649:Phenylalanine; D015544:Inositol 1,4,5-Trisphosphate; C089212:protein kinase D; D011493:Protein Kinase C; D010738:Type C Phospholipases; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D020741:rho GTP-Binding Proteins; D002118:Calcium