title: DNase activation by hypoxia-acidosis parallels but is independent of programmed cell death.
abstract: OBJECTIVE
  Hypoxia, acidosis and programmed cell death are each hallmarks of acute myocardial infarction (AMI). We previously described a death pathway of cardiac myocytes mediated by hypoxia-acidosis that was characterized by activation of the Bcl2-family protein Bnip3 and programmed necrosis. The pathway included extensive DNA fragmentation that was sensitive to inhibition of the mitochondrial permeability transition pore (mPTP) and calpain inhibitors, but not caspase inhibitors. We did not identify the DNases responsible for DNA cleavage.
  
  
  METHODS
  Neonatal rat cardiomyocytes were subjected to hypoxia with and without concurrent acidosis, and the cellular localization of apoptosis-inducing factor (AIF), DNase II and caspase-dependent DNase (CAD) were determined.
  
  
  RESULTS
  Here we report the occurrence of biphasic pH-dependent translocations of AIF and DNase II but no change in CAD or its inhibitor ICAD. AIF co-localized with the mitochondria under aerobic and hypoxia-neutral conditions but translocated to the nucleus at pH ~6.7 coincident with a decrease of the mitochondrial membrane potential. DNase II co-localized with lysosomes under normoxia and hypoxia-neutral conditions, and translocated to the nucleus at pH ~6.1 coincident with the appearance of single strand DNA cuts. Inhibition of the mPTP pore with BH4-TAT peptide, calpain inhibition with PD150606, or knockdown (KD) of Bnip3 failed to prevent nuclear translocation of these DNase although Bnip3 KD blocked mitochondrial fission.
  
  
  CONCLUSIONS
  These results suggest that caspase-independent DNA fragmentation is precisely regulated and occurs in parallel but independently from programmed necrosis mediated by hypoxia-acidosis.
authors.affiliation: Department of Molecular and Cellular Pharmacology and the Vascular Biology Institute, University of Miami School of Medicine, Miami, FL 33136, USA.
authors.forename: John W
authors.initials: JW
authors.lastname: Thompson
authors.forename: Regina M
authors.initials: RM
authors.lastname: Graham
authors.forename: Keith A
authors.initials: KA
authors.lastname: Webster
mesh_terms: D000138:Acidosis; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D051033:Apoptosis Inducing Factor / Q000378:metabolism; D015153:Blotting, Western; D015687:Cell Hypoxia; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D004789:Enzyme Activation; D007150:Immunohistochemistry; D009206:Myocardium / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D021381:Protein Transport; D051381:Rats
chemical_list: D051033:Apoptosis Inducing Factor; D004706:Endodeoxyribonucleases; C019329:deoxyribonuclease II