Bax-dependent regulation of Bak by voltage-dependent anion channel 2

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Item Type:	Article
Title:	Bax-dependent regulation of Bak by voltage-dependent anion channel 2
Creators Name:	Chandra, D., Choy, G., Daniel, P.T. and Tang, D.G.
Abstract:	Many studies have demonstrated a critical role of Bax in mediating apoptosis, but the role of Bak in regulating cancer cell apoptotic sensitivities in the presence or absence of Bax remains incompletely understood. Using isogenic cells with defined genetic deficiencies, here we show that in response to intrinsic, extrinsic, and endoplasmic reticulum stress stimuli, HCT116 cells show clear-cut apoptotic sensitivities in the order of Bax+/Bak+ > Bax+/Bak- >> Bax-/Bak+ >> Bax-/Bak-. Small interference RNA-mediated knockdown of Bak in Bax-deficient cells renders HCT116 cells completely resistant to apoptosis induction. Surprisingly, however, Bak knockdown in Bax-expressing cells only slightly affects the apoptotic sensitivities. Bak, like Bax, undergoes the N terminus exposure upon apoptotic stimulation in both Bax-expressing and Bax-deficient cells. Gel filtration, chemical cross-linking, and co-immunoprecipitation experiments reveal that different from Bax, which normally exists as monomers in unstimulated cells and is oligomerized by apoptotic stimulation, most Bak in unstimulated HCT116 cells exists in two distinct protein complexes, one of which contains voltage-dependent anion channel (VDAC) 2. During apoptosis, Bak and Bax form both homo- and hetero-oligomeric complexes that still retain some VDAC-2. However, the oligomeric VDAC-2 complexes are diminished, and Bak does not interact with VDAC-2 in Bax-deficient HCT116 cells. These results highlight VDAC-2 as a critical inhibitor of Bak-mediated apoptotic responses.
Keywords:	Apoptosis, Caspases, Cross-Linking Reagents, Cytochromes c, Down-Regulation, Enzyme Activation, Enzyme Inhibitors, Fluorescence Microscopy, Gel Chromatography, Immunoprecipitation, Membrane Proteins, Mitochondria, Porins, Proto-Oncogene Proteins c-bcl-2, Small Interfering RNA, Subcellular Fractions, Tertiary Protein Structure, Time Factors, Tumor Cell Line, Voltage-Dependent Anion Channel 2, Voltage-Dependent Anion Channels, Western Blotting, bcl-2 Homologous Antagonist-Killer Protein, bcl-2-Associated X Protein
Source:	Journal of Biological Chemistry
ISSN:	0021-9258
Publisher:	American Society for Biochemistry and Molecular Biology
Volume:	280
Page Range:	19051-19061
Date:	1 January 2005
Official Publication:	https://doi.org/10.1074/jbc.M501391200
PubMed:	View item in PubMed

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