title: A novel hypoxia-inducible spliced variant of mitochondrial death gene Bnip3 promotes survival of ventricular myocytes.
abstract: BACKGROUND
  Alternative splicing provides a versatile mechanism by which cells generate proteins with different or even antagonistic properties. Previously, we established hypoxia-inducible death factor Bnip3 as a critical component of the intrinsic death pathway.
  
  
  OBJECTIVE
  To investigate alternative splicing of Bnip3 pre-mRNA in postnatal ventricular myocytes during hypoxia.
  
  
  RESULTS
  We identify a novel previously unrecognized spliced variant of Bnip3 (Bnip3Δex3) generated by alternative splicing of exon3 exclusively in cardiac myocytes subjected to hypoxia. Sequencing of Bnip3Δex3 revealed a frame shift mutation that terminated transcription up-stream of exon5 and exon6 ablating translation of the BH3-like domain and critical carboxyl-terminal transmembrane domain crucial for mitochondrial localization and cell death. Notably, although the 26-kDa Bnip3 protein (Bnip3FL) encoded by full-length mRNA was localized to mitochondria and provoked cell death, the 8.2-kDa Bnip3Δex3 protein encoded by the truncated spliced mRNA was defective for mitochondrial targeting but interacted with Bnip3FL resulting in less association of Bnip3FL with mitochondria and diminished apoptotic and necrotic cell death. Forced expression of Bnip3FL in cardiac myocytes or Bnip3(-/-) mouse embryonic fibroblasts triggered widespread cell death that was inhibited by coexpression of Bnip3Δex3. Conversely, RNA interference targeted against sequences encompassing the unique exon2-exon4 junction of the Bnip3Δex3 sensitized cardiac myocytes to mitochondrial perturbations and cell death induced by Bnip3FL.
  
  
  CONCLUSIONS
  Given the otherwise lethal consequences of deregulated Bnip3FL expression in postmitotic cells, our findings reveal a novel intrinsic defense mechanism that opposes the mitochondrial defects and cell death of ventricular myocytes that is obligatorily linked and mutually dependent on alternative splicing of Bnip3FL during hypoxia or ischemic stress.
authors.affiliation: Institute of Cardiovascular Sciences, St Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada.
authors.forename: Hongying
authors.initials: H
authors.lastname: Gang
authors.forename: Yan
authors.initials: Y
authors.lastname: Hai
authors.forename: Rimpy
authors.initials: R
authors.lastname: Dhingra
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Gordon
authors.forename: Natalia
authors.initials: N
authors.lastname: Yurkova
authors.forename: Yaron
authors.initials: Y
authors.lastname: Aviv
authors.forename: Hongzhao
authors.initials: H
authors.lastname: Li
authors.forename: Floribeth
authors.initials: F
authors.lastname: Aguilar
authors.forename: Aaron
authors.initials: A
authors.lastname: Marshall
authors.forename: Etienne
authors.initials: E
authors.lastname: Leygue
authors.forename: Lorrie A
authors.initials: LA
authors.lastname: Kirshenbaum
mesh_terms: D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D002470:Cell Survival / Q000235:genetics; D002478:Cells, Cultured; D006352:Heart Ventricles / Q000166:cytology; D000860:Hypoxia / Q000235:genetics* / Q000473:pathology / Q000503:physiopathology; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D008817:Mice, Mutant Strains; D008928:Mitochondria / Q000502:physiology; D024101:Mitochondrial Proteins; D017202:Myocardial Ischemia / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000502:physiology*; D009336:Necrosis / Q000235:genetics / Q000473:pathology / Q000503:physiopathology; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: C505650:BNIP3 protein, rat; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D017382:Reactive Oxygen Species