title: Bnip3 mediates permeabilization of mitochondria and release of cytochrome c via a novel mechanism.
abstract: Bnip3 is a member of the BH3-only subfamily of pro-apoptotic Bcl-2 proteins and is associated with loss of cardiac myocytes after a myocardial infarction. Previous studies have demonstrated that Bnip3 induces mitochondrial dysfunction, but the mechanisms involved in this process remain unknown. In this study, we demonstrate that Bnip3 induces permeabilization of the mitochondria via a novel mechanism that is different from other BH3-only proteins. We found that Bnip3 induced mitochondrial swelling and cytochrome c release in isolated heart mitochondria in vitro. Another BH3-only protein, tBid, also caused release of cytochrome c but failed to induce swelling of mitochondria. Swelling of mitochondria is a characteristic of mitochondrial permeability transition pore (mPTP) opening, but Bnip3-mediated mitochondrial swelling was insensitive to cyclosporine A, an inhibitor of the mPTP and independent of cyclophilin D (cypD), an essential component of the mPTP. Bnip3 also induced permeabilization of the mitochondrial membranes as evident by calcein release from the matrix in both wild type (WT) and cypD deficient mouse embryonic fibroblasts (MEFs). Moreover, Bnip3 induced mitochondrial matrix remodeling and large amplitude swelling of the inner membrane, which led to disassembly of OPA1 complexes and release from the mitochondria. Thus, these studies suggest that Bnip3 mediates mitochondrial permeabilization by a novel mechanism that is different from other BH3-only proteins.
authors.affiliation: Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Drive MC 0748, La Jolla, CA 92093-0748, USA.
authors.forename: Melissa N
authors.initials: MN
authors.lastname: Quinsay
authors.forename: Youngil
authors.initials: Y
authors.lastname: Lee
authors.forename: Shivaji
authors.initials: S
authors.lastname: Rikka
authors.forename: M Richard
authors.initials: MR
authors.lastname: Sayen
authors.forename: Jeffery D
authors.initials: JD
authors.lastname: Molkentin
authors.forename: Roberta A
authors.initials: RA
authors.lastname: Gottlieb
authors.forename: Asa B
authors.initials: AB
authors.lastname: Gustafsson
mesh_terms: D000818:Animals; D016923:Cell Death; D003432:Cross-Linking Reagents / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D005452:Fluoresceins / Q000737:chemistry; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron / Q000379:methods; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: C505650:BNIP3 protein, rat; C508686:BNip3 protein, mouse; D003432:Cross-Linking Reagents; D005452:Fluoresceins; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D045304:Cytochromes c; C007740:fluorexon