Submitted on February 23, 2005
Revised on March 30, 2005
Accepted on March 30, 2005
Role of ceramide in Ca2+-sensing receptor-induced apoptosis
Zhenzhen Wu, Rajnish Tondon, Jenny Ziembicki, Junko Nagano, Kirstine M. Hujer, R. Tyler Miller, and Chunfa Huang
Medicine/Nephrology, Case Western Reserve University, Cleveland, OH 44106
Corresponding Author: chunfa.huang{at}case.edu
Elevated extracellular Ca2+ (Cao2+can damage tissues, but the molecular mechanisms by which this occurs are poorly defined. Using HEK 293 cell lines that stably over-express the Ca2+-sensing receptor (CaR), a G protein coupled receptor, we demonstrate that activation of the CaR leads to apoptosis which was determined by nuclear condensation, DNA fragmentation, CPP32 (caspase-3) activation, and elevation of cytosolic cytochrome c. This CaR-induced apoptotic pathway is initiated by CaR-induced accumulation of ceramide which plays an important role in inducing cell death signals by distinct G protein independent signaling pathways. Pretreatment of CaRWT-expressing cells with pertussis toxin inhibited CaR-induced [3H]ceramide formation, c-Jun phosphorylation and caspase-3 activation. The ceramide accumulation, c-Jun phosphorylation and caspase-3 activation by the CaR can be abolished by sphingomyelinase and ceramide synthase inhibitors in different time frames. Cells that express a nonfunctional mutant CaR that were exposed to the same levels of Cao2+ showed no evidence of activation of the apoptotic pathway. Taken together, we report the involvement of the CaR in stimulating programmed cell death via a pathway involving G
i-dependent ceramide accumulation, activation of stress activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), c-Jun phosphorylation, caspase-3 activation, and DNA cleavage.
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