Elevated extracellular calcium can prevent apoptosis via the calcium-sensing receptor.
The calcium-sensing receptor (CaR) is a membrane-bound, G-protein-coupled receptor present on parathyroid cells which monitors the level of extracellular calcium (Ca2+o) and transduces signals involved in serum calcium regulation. Expression of CaR protein in tissues with functions unrelated to systemic calcium homeostasis, including the brain, suggests that extracellular calcium (Ca2+o) may act as a first messenger to regulate diverse cellular functions. To test this hypothesis, we examined the effect of increasing Ca2+o on apoptosis induced by Sindbis Virus in AT-3 prostate carcinoma cells. We found a steep increase in cell survival with between 5 and 7 mM added Ca2+o (EC50 = 6.1 mM). Magnesium, a less potent agonist of the calcium sensing receptor, was also protective (EC50 = 23.4 mM). Northern and immunocytochemical analyses confirmed the presence of the CaR message and protein in AT-3 prostate carcinoma cells. Enforced expression of CaR protein by stable transfection in human embryonic kidney (HEK)-293 cells, which normally don't express the receptor, resulted in resistance to SV-induced apoptosis in the presence of elevated Ca2+o. In addition to preventing SV-induced death, elevated Ca2+o also abrogated apoptosis induced by c-Myc overexpression/serum deprivation in rat 1A fibroblasts, and these fibroblasts were shown to express CaR message and protein. Altogether, these observations suggest that Ca2+o can act with the CaR to prevent apoptosis and define a novel mechanism by which calcium ions can regulate cell survival.
Beth Israel-Deaconess Medical Center and Harvard Medical School, Harvard University, Boston, Massachusetts, USA.
K I
KI
Lin
N
N
Chattopadhyay
M
M
Bai
R
R
Alvarez
C V
CV
Dang
J M
JM
Baraban
E M
EM
Brown
R R
RR
Ratan
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015152:Blotting, Northern; D002118:Calcium / Q000008:administration & dosage / Q000494:pharmacology*; D002460:Cell Line; D004622:Embryo, Mammalian; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney; D008297:Male; D011471:Prostatic Neoplasms; D051381:Rats; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000235:genetics / Q000502:physiology*; D012845:Sindbis Virus / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured
D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; C473605:extracellular calcium cation-sensing receptor, rat; D002118:Calcium