title: Pseudomonas exotoxin A-mediated apoptosis is Bak dependent and preceded by the degradation of Mcl-1.
abstract: Pseudomonas exotoxin A (PE) is a bacterial toxin that arrests protein synthesis and induces apoptosis. Here, we utilized mouse embryo fibroblasts (MEFs) deficient in Bak and Bax to determine the roles of these proteins in cell death induced by PE. PE induced a rapid and dose-dependent induction of apoptosis in wild-type (WT) and Bax knockout (Bax(-/-)) MEFs but failed in Bak knockout (Bak(-/-)) and Bax/Bak double-knockout (DKO) MEFs. Also a loss of mitochondrial membrane potential was observed in WT and Bax(-/-) MEFs, but not in Bak(-/-) or in DKO MEFs, indicating an effect of PE on mitochondrial permeability. PE-mediated inhibition of protein synthesis was identical in all 4 cell lines, indicating that differences in killing were due to steps after the ADP-ribosylation of EF2. Mcl-1, but not Bcl-x(L), was rapidly degraded after PE treatment, consistent with a role for Mcl-1 in the PE death pathway. Bak was associated with Mcl-1 and Bcl-x(L) in MEFs and uncoupled from suppressed complexes after PE treatment. Overexpression of Mcl-1 and Bcl-x(L) inhibited PE-induced MEF death. Our data suggest that Bak is the preferential mediator of PE-mediated apoptosis and that the rapid degradation of Mcl-1 unleashes Bak to activate apoptosis.
authors.affiliation: Laboratory of Molecular Biology, National Cancer Institute, 37 Convent Drive, Bethesda, MD 20892-4264, USA.
authors.forename: Xing
authors.initials: X
authors.lastname: Du
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Youle
authors.forename: David J
authors.initials: DJ
authors.lastname: FitzGerald
authors.forename: Ira
authors.initials: I
authors.lastname: Pastan
mesh_terms: D036002:ADP Ribose Transferases / Q000633:toxicity*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D001427:Bacterial Toxins / Q000633:toxicity*; D002478:Cells, Cultured; D005098:Exotoxins / Q000633:toxicity*; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D051379:Mice; D018345:Mice, Knockout; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011500:Protein Synthesis Inhibitors / Q000633:toxicity; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D037521:Virulence Factors / Q000633:toxicity*; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051020:bcl-X Protein / Q000378:metabolism; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D005098:Exotoxins; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D011500:Protein Synthesis Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D037521:Virulence Factors; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D000097668:Pseudomonas aeruginosa Exotoxin A; C494773:Bak1 protein, mouse; C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; C579094:Mcl1 protein, mouse
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