title: In non-transformed cells Bak activates upon loss of anti-apoptotic Bcl-XL and Mcl-1 but in the absence of active BH3-only proteins.
abstract: Mitochondrial apoptosis is controlled by proteins of the B-cell lymphoma 2 (Bcl-2) family. Pro-apoptotic members of this family, known as BH3-only proteins, initiate activation of the effectors Bcl-2-associated X protein (Bax) and Bcl-2 homologous antagonist/killer (Bak), which is counteracted by anti-apoptotic family members. How the interactions of Bcl-2 proteins regulate cell death is still not entirely clear. Here, we show that in the absence of extrinsic apoptotic stimuli Bak activates without detectable contribution from BH3-only proteins, and cell survival depends on anti-apoptotic Bcl-2 molecules. All anti-apoptotic Bcl-2 proteins were targeted via RNA interference alone or in combinations of two in primary human fibroblasts. Simultaneous targeting of B-cell lymphoma-extra large and myeloid cell leukemia sequence 1 led to apoptosis in several cell types. Apoptosis depended on Bak whereas Bax was dispensable. Activator BH3-only proteins were not required for apoptosis induction as apoptosis was unaltered in the absence of all BH3-only proteins known to activate Bax or Bak directly, Bcl-2-interacting mediator of cell death, BH3-interacting domain death agonist and p53-upregulated modulator of apoptosis. These findings argue for auto-activation of Bak in the absence of anti-apoptotic Bcl-2 proteins and provide evidence of profound differences in the activation of Bax and Bak.
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Senft
authors.affiliation: Institute of Medical Microbiology and Hygiene, University Medical Center Freiburg, 79104 Freiburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Weber
authors.affiliation: Division of Clinical Pharmacology, Department of Internal Medicine, Ludwig-Maximilian University, 80336 Munich, Germany.|Center of Integrated Protein Science CIPS-M, Division of Clinical Pharmacology, Department of Internal Medicine, Ludwig-Maximilian University, 80336 Munich, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Saathoff
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Berking
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.
authors.forename: M V
authors.initials: MV
authors.lastname: Heppt
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Kammerbauer
authors.affiliation: Division of Clinical Pharmacology, Department of Internal Medicine, Ludwig-Maximilian University, 80336 Munich, Germany.|Center of Integrated Protein Science CIPS-M, Division of Clinical Pharmacology, Department of Internal Medicine, Ludwig-Maximilian University, 80336 Munich, Germany.|Section of Gastroenterology and Endocrinology, Medizinische Klinik Innenstadt, Ludwig-Maximilian University, 80336 Munich, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Rothenfusser
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Kellner
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.|Department of Dermatology and Allergology, University of Szeged, 6720 Szeged, Hungary.
authors.forename: Z
authors.initials: Z
authors.lastname: Kurgyis
authors.affiliation: Department of Dermatology and Allergology, Ludwig-Maximilian University, 80337 Munich, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Besch
authors.affiliation: Institute of Medical Microbiology and Hygiene, University Medical Center Freiburg, 79104 Freiburg, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Häcker
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000648:ultrastructure; D005347:Fibroblasts; D006801:Humans; D015603:Keratinocytes; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000172:deficiency / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000172:deficiency* / Q000378:metabolism; D014162:Transfection; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000378:metabolism*; D051020:bcl-X Protein / Q000172:deficiency* / Q000378:metabolism
chemical_list: C494772:BAK1 protein, human; C494811:BCL2L1 protein, human; C579095:MCL1 protein, human; D033681:Mitochondrial Membrane Transport Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D019253:Proto-Oncogene Proteins c-bcl-2; C581062:RTL10 protein, human; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051020:bcl-X Protein