title: Prosurvival Bcl-2 family members affect autophagy only indirectly, by inhibiting Bax and Bak.
abstract: Antiapoptotic B-cell lymphoma 2 (Bcl-2) family members such as Bcl-2, myeloid cell leukemia 1 (Mcl-1), and B-cell lymphoma-X large (Bcl-xL) are proposed to inhibit autophagy by directly binding to the BH3 domain of Beclin 1/Atg6. However, these Bcl-2 family proteins also block the proapoptotic activity of Bcl-2-associated X (Bax) and Bcl-2 homologous antagonist/killer (Bak), and many inducers of autophagy also cause cell death. Therefore, when the mitochondrial-mediated apoptosis pathway is functional, interpretation of such experiments is complicated. To directly test the impact of the endogenous antiapoptotic Bcl-2 family members on autophagy in the absence of apoptosis, we inhibited their activity in cells lacking the essential cell death mediators Bax and Bak. We also used inducible lentiviral vectors to overexpress Bcl-2, Bcl-xL, or Mcl-1 in cells and subjected them to treatments that promote autophagy. In the absence of Bax and Bak, Bcl-2, Bcl-xL, and Mcl-1 had no detectable effect on autophagy or cell death in myeloid or fibroblast cell lines. On the other hand, when Bax and Bak were present, inhibiting the prosurvival Bcl-2 family members stimulated autophagy, but this correlated with increased cell death. In addition, inhibition of autophagy induced by amino acid starvation, etoposide, or interleukin-3 withdrawal did not affect cell death in the absence of Bax and Bak. These results demonstrate that the antiapoptotic Bcl-2 family members do not directly inhibit components of the autophagic pathway but instead affect autophagy indirectly, owing to their inhibition of Bax and Bak.
authors.affiliation: Cell Signalling and Cell Death Division andDepartment of Medical Biology, University of Melbourne, Parkville, VIC 3050, Australia lindqvist@wehi.edu.au.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Lindqvist
authors.affiliation: Cell Signalling and Cell Death Division andDepartment of Medical Biology, University of Melbourne, Parkville, VIC 3050, Australia.
authors.forename: Melanie
authors.initials: M
authors.lastname: Heinlein
authors.affiliation: Department of Medical Biology, University of Melbourne, Parkville, VIC 3050, AustraliaCancer and Haematology Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC 3052, Australia; and.
authors.forename: David C S
authors.initials: DC
authors.lastname: Huang
authors.affiliation: Cell Signalling and Cell Death Division andDepartment of Medical Biology, University of Melbourne, Parkville, VIC 3050, Australia.
authors.forename: David L
authors.initials: DL
authors.lastname: Vaux
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D001713:Biphenyl Compounds / Q000494:pharmacology; D015153:Blotting, Western; D002461:Cell Line, Transformed; D002470:Cell Survival / Q000235:genetics; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005434:Flow Cytometry; D051379:Mice; D018345:Mice, Knockout; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein / Q000235:genetics / Q000378:metabolism; D009596:Nitrophenols / Q000494:pharmacology; D010588:Phagosomes / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D013449:Sulfonamides / Q000494:pharmacology; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: C501332:ABT-737; C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; D001713:Biphenyl Compounds; C480860:Map1lc3b protein, mouse; C579094:Mcl1 protein, mouse; D008869:Microtubule-Associated Proteins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
keywords: ABT-737; BH3 mimetic; Bim; LC3; LC3B