title: bcl-X(S)-induced cell death in 3T3 cells does not require or induce caspase activation.
abstract: Using a tetracycline-regulated expression system, we have shown that expression of bcl-X(s) is sufficient to induce acute cell death in 3T3 cells, and that the manner in which these cells die is both morphologically and biochemically different from Fas/CD95-induced apoptosis. bcl-X(s) expression causes loss of the inner mitochondrial membrane potential (deltapsim) but does not induce caspase activation. Loss of viability, as determined by mitochondrial function and ethidium bromide exclusion, was not inhibited by the broad-spectrum caspase inhibitor zVAD-fmk or by expression of a dominant negative caspase 9 (9DN). However, zVAD-fmk was efficacious in inhibiting cell death triggered by an activating anti-Fas/CD95 antibody. In addition, bcl-X(s) does not possess the 5th and 6th alpha-helices (thought to be the membrane-spanning domains in bcl-2, bcl-X(L), and bax) and, therefore, should not be able to form membrane channels, thus eliminating this possible mechanism of action. The finding that bcl-X(s) kills 3T3 cells without caspase activation, along with the absence of membrane spanning domains in bcl-X(s), may, therefore, represent a novel cell death pathway for the pro-death bcl-2 family members.
authors.affiliation: Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109-0504, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Fridman
authors.forename: M A
authors.initials: MA
authors.lastname: Benedict
authors.forename: J
authors.initials: J
authors.lastname: Maybaum
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000235:genetics* / Q000378:metabolism*; D002462:Cell Membrane / Q000648:ultrastructure; D003001:Cloning, Molecular; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004789:Enzyme Activation; D007425:Intracellular Membranes / Q000502:physiology / Q000648:ultrastructure; D007700:Kinetics; D008564:Membrane Potentials; D051379:Mice; D008928:Mitochondria / Q000502:physiology / Q000648:ultrastructure; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection; D051020:bcl-X Protein; D019014:fas Receptor / Q000494:pharmacology
chemical_list: C494812:Bcl2l1 protein, mouse; D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D051020:bcl-X Protein; D019014:fas Receptor; D003609:Dactinomycin; D011065:Poly(ADP-ribose) Polymerases; C506434:Casp9 protein, mouse; D053453:Caspase 9; D020169:Caspases