title: Calcium plays a key role in paraoxon-induced apoptosis in EL4 cells by regulating both endoplasmic reticulum- and mitochondria-associated pathways.
abstract: OBJECTIVE
  Paraoxon (POX) is one of the most toxic organophosphorus pesticides, but its toxic mechanisms associated with apoptosis remain unclear. The aim of this study was to investigate calcium-associated mechanisms in POX-induced apoptosis in EL4 cells.
  
  
  METHODS
  EL4 cells were exposed to POX for 0-16 h. EGTA was used to chelate Ca(2+ ) in extracellular medium, and heparin and procaine were used to inhibit Ca(2+ )efflux from the endoplasmic reticulum (ER). Z-ATAD-FMK was used to inhibit caspase-12 activity. The apoptotic rate assay, western blotting and immunocytochemistry (ICC) were used to reveal the mechanisms of POX-induced apoptosis.
  
  
  CONCLUSIONS
  POX significantly increased the expression and activation of caspase-12 and caspase-3, enhanced expression of calpain 1 and calpain 2, and induced the release of cyt c, but did not change the expression of Grp 78. Inhibiting caspase-12 activity alleviated POX-induced upregulation of calpain 1 and caspase-3, promoted POX-induced upregulation of calpain 2, and reduced POX-induced cyt c release, suggesting that there was a cross-talk between the ER-associated pathway and mitochondria-associated apoptotic signals. Attenuating intracellular calcium concentration with EGTA, heparin or procaine decreased POX-induced upregulation of calpain 1, calpain 2, caspase-12 and caspase-3, and reduced POX-induced cyt c release. After pretreatment with EGTA or procaine, POX significantly promoted expression of Grp 78.
  
  
  CONCLUSIONS
  Calcium played a key role in POX-induced apoptosis in EL4 cells by regulating both ER- and mitochondria-associated pathways. The cross-talk of ER- and mitochondria-associated pathways was accomplished through calcium signal.
authors.affiliation: a Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University , Lanzhou , People's Republic of China.
authors.forename: Lan
authors.initials: L
authors.lastname: Li
authors.affiliation: a Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University , Lanzhou , People's Republic of China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Du
authors.affiliation: a Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University , Lanzhou , People's Republic of China.
authors.forename: Furong
authors.initials: F
authors.lastname: Ju
authors.affiliation: a Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University , Lanzhou , People's Republic of China.
authors.forename: Shunxiang
authors.initials: S
authors.lastname: Ma
authors.affiliation: a Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences, Lanzhou University , Lanzhou , People's Republic of China.
authors.forename: Shengxiang
authors.initials: S
authors.lastname: Zhang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D018929:Cell Culture Techniques; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D004785:Environmental Pollutants / Q000633:toxicity*; D051379:Mice; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D010261:Paraoxon / Q000633:toxicity*
chemical_list: D004785:Environmental Pollutants; D010261:Paraoxon; D002118:Calcium
keywords: Calpain 1; Grp 78; calpain 2; caspase-12; cyt c