Abstract
Bax induces mitochondrial-dependent cell death signals in mammalian cells. However, the mechanism of how Bax is kept inactive has remained unclear. Yeast-based functional screening of Bax inhibitors from mammalian cDNA libraries identified Ku70 as a new Bax suppressor. Bax-mediated apoptosis was suppressed by overexpression of Ku70 in mammalian cells, but enhanced by downregulation of Ku70. We found that Ku70 interacts with Bax, and that the carboxyl terminus of Ku70 and the amino terminus of Bax are required for this interaction. Bax is known to translocate from the cytosol to mitochondria when cells receive apoptotic stimuli. We found that Ku70 blocks the mitochondrial translocation of Bax. These results suggest that in addition to its previously recognized DNA repair activity in the nucleus, Ku70 has a cytoprotective function in the cytosol that controls the localization of Bax.
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Acknowledgements
We thank R. Takahashi (Riken Brain Science Research Institute), M. Miura (Riken Brain Research Institute), D. Green (La Jolla Institute for Allergy and Immunology), J. Reed (The Burnham Institute), J. Gorski (Blood Research Institute) and D. Wang for their invaluable suggestions, critical reviewing of the manuscript and encouragement. This work was supported in part by the Blood Center Research Foundation, Northwest Mutual Foundation, Taiho Pharmaceutical Company Ltd. for S.M., and in part by National Institute of Health/National Cancer Institute grant # CA78530 to D.A.B. Supplementary Information accompanies the paper on www.nature.com/naturecellbiology.
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Figure S1 a, Flow cytometric propidium iodide (PI) exclusion analysis. (PPT 2857 kb)
Figure S2 a-d, „Entire gels” of co-immunoprecipitation (co-ip) of endogenous Ku70 and Bax.
Figure S3 a-d, The interaction between Ku70 and Bax in primary mouse brain (a and b) and primary mouse fibroblasts (c and d).
Figure S4 a, Ku70-deficiency alone does not induce membrane integration of Bax in mitochondria.
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Sawada, M., Sun, W., Hayes, P. et al. Ku70 suppresses the apoptotic translocation of Bax to mitochondria. Nat Cell Biol 5, 320–329 (2003). https://doi.org/10.1038/ncb950
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DOI: https://doi.org/10.1038/ncb950
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