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Osteoblast calcium‐sensing receptor has characteristics of ANF/7TM receptors
Author(s) -
Pi Min,
Quarles L. Darryl
Publication year - 2005
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.20500
Subject(s) - calcium sensing receptor , luciferase , extracellular , chemistry , receptor , g protein coupled receptor , gq alpha subunit , endocrinology , mapk/erk pathway , medicine , signal transduction , rhoa , microbiology and biotechnology , calcium , biology , biochemistry , parathyroid hormone , transfection , organic chemistry , gene
There is evidence for a functionally important extracelluar calcium‐sensing receptor in osteoblasts, but there is disagreement regarding its identity. Candidates are CASR and a putative novel calcium‐sensing receptor, called Ob.CASR. To further characterize Ob.CASR and to distinguish it from CASR, we examined the extracellular cation‐sensing response in MC3T3‐E1 osteoblasts and in osteoblasts derived from CASR null mice. We found that extracellular cations activate ERK and serum response element (SRE)‐luciferase reporter activity in osteoblasts lacking CASR. Amino acids, but not the calcimimetic NPS‐R568, an allosteric modulator of CASR, also stimulate Ob.CASR‐dependent SRE‐luciferase activation in MC3T3‐E1 osteoblasts. In addition, we found that the dominant negative Gαq(305–359) construct inhibited cation‐stimulated ERK activation, consistent with Ob.CASR coupling to Gαq‐dependent pathways. Ob.CASR is also a target for classical GPCR desensitization mechanisms, since β‐arrestins, which bind to and uncouple GRK phosphorylated GPCRs, attenuated cation‐stimulated SRE‐luciferase activity in CASR deficient osteoblasts. Finally, we found that Ob.CASR and CASR couple to SRE through distinct signaling pathways. Ob.CASR does not activate RhoA and C3 toxin fails to block Ob.CASR‐induced SRE‐luciferase activity. Mutational analysis of the serum response factor (SRF) and ternary complex factor (TCF) elements in SRE demonstrates that Ob.CASR predominantly activates TCF‐dependent mechanisms, whereas CASR activates SRE‐luciferase mainly through a RhoA and SRF‐dependent mechanism. The ability of Ob.CASR to sense cations and amino acids and function like a G‐protein coupled receptor suggests that it may belong to the family of receptors characterized by an evolutionarily conserved amino acid sensing motif (ANF) linked to an intramembranous 7 transmembrane loop region (7TM). © 2005 Wiley‐Liss, Inc.