title: Role of ceramide in Ca2+-sensing receptor-induced apoptosis.
abstract: Increased extracellular Ca(2+) ([Ca(2+)](o)) can damage tissues, but the molecular mechanisms by which this occurs are poorly defined. Using HEK 293 cell lines that stably overexpress the Ca(2+)-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, caspase-3 activation, and increased 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 wild-type CaR-expressing cells with pertussis toxin inhibited CaR-induced [(3)H]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 [Ca(2+)](o) showed no evidence of activation of the apoptotic pathway. In conclusion, we report the involvement of the CaR in stimulating programmed cell death via a pathway involving GTP binding protein alpha subunit (Galpha(i))-dependent ceramide accumulation, activation of stress-activated protein kinase/c-Jun N-terminal kinase, c-Jun phosphorylation, caspase-3 activation, and DNA cleavage.
authors.affiliation: Department of Medicine, Case Western Reserve University, Cleveland, OH, USA.
authors.forename: Zhenzhen
authors.initials: Z
authors.lastname: Wu
authors.forename: Rajnish
authors.initials: R
authors.lastname: Tandon
authors.forename: Jenny
authors.initials: J
authors.lastname: Ziembicki
authors.forename: Junko
authors.initials: J
authors.lastname: Nagano
authors.forename: Kristine M
authors.initials: KM
authors.lastname: Hujer
authors.forename: R Tyler
authors.initials: RT
authors.lastname: Miller
authors.forename: Chunfa
authors.initials: C
authors.lastname: Huang
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000494:pharmacology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002518:Ceramides / Q000096:biosynthesis / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D048055:Mitogen-Activated Protein Kinase 8 / Q000378:metabolism; D037342:Pertussis Toxin / Q000494:pharmacology; D044169:Receptors, Calcium-Sensing / Q000502:physiology*; D015290:Second Messenger Systems / Q000502:physiology*
chemical_list: D002518:Ceramides; D044169:Receptors, Calcium-Sensing; D045304:Cytochromes c; D037342:Pertussis Toxin; D048031:JNK Mitogen-Activated Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D048670:MAP Kinase Kinase 4; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D002118:Calcium