title: The multidomain proapoptotic molecules Bax and Bak are directly activated by heat.
abstract: During apoptosis, engagement of the mitochondrial pathway involves a decisive event characterized by the release of mitochondrial intermembrane space proteins, such as cytochrome c. This permeabilization of the mitochondrial outer membrane depends on activation and oligomerization of multidomain Bcl-2-family proteins Bax or Bak. Although specific members of the Bcl-2 family can activate these proapoptotic proteins, we found that heat directly activated Bax or Bak to induce cytochrome c release. A preparation of mitochondria heated at 43 degrees C released cytochrome c in association with Bak oligomerization, and Bcl-xL prevented these events. Similarly, heat induced the oligomerization of recombinant Bax, conferring an ability to permeabilize mitochondria. Compared with wild-type cells, bax(-/-)bak(-/-) mouse embryonic fibroblasts and mitochondria isolated from these cells were resistant to heat-induced cytochrome c release. Cytosol from untreated cells inhibited heat-activated Bax or Bak; however, depletion of cytosolic Bcl-xL ablated this protection. Although mitochondria heated in the presence of cytosol did not release cytochrome c, they displayed a dramatic increase in sensitivity to permeabilization by the BH3-only protein Bid. Additionally, a peptide corresponding to the BH3 domain of Puma counteracted the inhibitory effect of cytosol and permitted heat-activated Bak to permeabilize the mitochondria. Therefore, heat represents a condition under which multidomain proapoptotic proteins are activated, and this activation is regulated by both antiapoptotic and BH3-only members of the Bcl-2 family. Our results support an emerging paradigm, wherein the activation of Bax or Bak and the blockade of antiapoptotic Bcl-2 proteins are pivotal steps in the mitochondrial pathway of apoptosis.
authors.affiliation: Division of Cellular Immunology, La Jolla Institute for Allergy and Immunology, San Diego, CA 92121, USA.
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Pagliari
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kuwana
authors.forename: Christine
authors.initials: C
authors.lastname: Bonzon
authors.forename: Donald D
authors.initials: DD
authors.lastname: Newmeyer
authors.forename: Shine
authors.initials: S
authors.lastname: Tu
authors.forename: Helen M
authors.initials: HM
authors.lastname: Beere
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Green
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002478:Cells, Cultured; D045304:Cytochromes c / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006358:Hot Temperature; D051379:Mice; D018345:Mice, Knockout; D008930:Mitochondria, Liver / Q000378:metabolism / Q000502:physiology*; D051336:Mitochondrial Membranes / Q000378:metabolism*; D010539:Permeability; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism*; D051020:bcl-X Protein / Q000378:metabolism
chemical_list: C494773:Bak1 protein, mouse; C494812:Bcl2l1 protein, mouse; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D045304:Cytochromes c