Bcl-xL does not inhibit the function of Apaf-1.
Bcl-2 and its relative, Bcl-xL, inhibit apoptotic cell death primarily by controlling the activation of caspase proteases. Previous reports have suggested at least two distinct mechanisms: Bcl-2 and Bcl-xL may inhibit either the formation of the cytochrome c/Apaf-1/caspase-9 apoptosome complex (by preventing cytochrome c release from mitochondria) or the function of this apoptosome (through a direct interaction of Bcl-2 or Bcl-xL with Apaf-1). To evaluate this latter possibility, we added recombinant Bcl-xL protein to cell-free apoptotic systems derived from Jurkat cells and Xenopus eggs. At low concentrations (50 nM), Bcl-xL was able to block the release of cytochrome c from mitochondria. However, although Bcl-xL did associate with Apaf-1, it was unable to inhibit caspase activation induced by the addition of cytochrome c, even at much higher concentrations (1-5 microM). These observations, together with previous results obtained with Bcl-2, argue that Bcl-xL and Bcl-2 cannot block the apoptosome-mediated activation of caspase-9.
Newmeyer
D D
DD
La Jolla Institute for Allergy and Immunology, 10355 Science Center Road, San Diego, CA 92121, USA.
Bossy-Wetzel
E
E
Kluck
R M
RM
Wolf
B B
BB
Beere
H M
HM
Green
D R
DR
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D017209:Apoptosis; D053477:Apoptotic Protease-Activating Factor 1; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002474:Cell-Free System; D003574:Cytochrome c Group / Q000378:metabolism; D000939:Epitopes / Q000737:chemistry; D005260:Female; D006801:Humans; D019169:Jurkat Cells; D007700:Kinetics; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D011506:Proteins / Q000276:immunology / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D029867:Xenopus Proteins; D014982:Xenopus laevis; D051020:bcl-X Protein
C506592:APAF1 protein, human; D000906:Antibodies; D053477:Apoptotic Protease-Activating Factor 1; C494809:BCL2L1 protein, Xenopus; C494811:BCL2L1 protein, human; D003574:Cytochrome c Group; D000939:Epitopes; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D029867:Xenopus Proteins; D051020:bcl-X Protein; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases