Apoptotic cytosol facilitates Bax translocation to mitochondria that involves cytosolic factor regulated by Bcl-2.
Proapoptotic members of the Bcl-2 family, including Bax, Bak, and Bid, directly trigger the mitochondrial release of apoptogenic cytochrome c and apoptosis-inducing factor into the cytoplasm. One of the crucial steps before Bax can exert its proapoptotic activity is translocation from the cytoplasm to the mitochondria, but the molecular mechanism of this translocation is not understood. To investigate the mechanism of apoptosis-associated Bax translocation, we used an in vitro system comprising isolated mitochondria and cytosol. We found that both endogenous and exogenous added recombinant Bax translocated to the mitochondria more efficiently in the presence of cytosol from cells with VP16-induced apoptosis than with cytoplasm from normal cells. This apoptosis-dependent promotion of Bax translocation was not seen with cytosol that was prepared from VP16-treated cells expressing Bcl-2. Cytosol from cells with VP16-induced apoptosis, but not that from normal cells or Bcl-2-expressing cells, induced cytochrome c release from isolated mitochondria, which, as assessed by immunodepletion experiments, was mainly mediated by Bax. These results suggest that Bcl-2 exerts its antiapoptotic activity partly by inhibiting the translocation of Bax through the modification of cytosolic factors that are involved in such translocation during apoptosis.
Nomura
M
M
The First Department of Surgery, Osaka University Graduate School of Medicine, Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Corporation, Osaka.
Shimizu
S
S
Ito
T
T
Narita
M
M
Matsuda
H
H
Tsujimoto
Y
Y
D017209:Apoptosis; D001692:Biological Transport; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006367:HeLa Cells; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D013997:Time Factors; D014162:Transfection; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; D003574:Cytochrome c Group; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D005047:Etoposide; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases