Article

Mediation of the Antiapoptotic Activity of Bcl-xL Protein upon Interaction with VDAC1 Protein

Department of Life Sciences and the National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
Journal of Biological Chemistry (Impact Factor: 4.57). 05/2012; 287(27):23152-61. DOI: 10.1074/jbc.M112.345918
Source: PubMed

ABSTRACT

The mitochondrial protein, the voltage-dependent anion channel (VDAC), is implicated in the control of apoptosis, including via its interaction with the pro- and antiapoptotic proteins. We previously demonstrated the direct interaction of Bcl2 with VDAC, leading to reduced channel conductance. VDAC1-based peptides interacted with Bcl2 to prevent its antiapoptotic activity. Here, using a variety of approaches, we show the interaction of the antiapoptotic protein, Bcl-xL, with VDAC1 and reveal that this interaction mediates Bcl-xL protection against apoptosis. C-terminally truncated Bcl-xL(Δ21) interacts with purified VDAC1, as revealed by microscale thermophoresis and as reflected in the reduced channel conductivity of bilayer-reconstituted VDAC1. Overexpression of Bcl-xL prevented staurosporine-induced apoptosis in cells expressing native VDAC1 but not certain VDAC1 mutants. Having identified mutations in VDAC1 that interfere with the Bcl-xL interaction, certain peptides representing VDAC1 sequences, including the N-terminal domain, were designed and generated as recombinant and synthetic peptides. The VDAC1 N-terminal region and two internal sequences were found to bind specifically, and in a concentration- and time-dependent manner, to immobilized Bcl-xL(Δ21), as revealed by surface plasmon resonance. Moreover, expression of the recombinant peptides in cells overexpressing Bcl-xL prevented protection offered by the protein against staurosporine-induced apoptosis. These results point to Bcl-xL acting as antiapoptotic protein, promoting tumor cell survival via binding to VDAC1. These findings suggest that interfering with Bcl-xL binding to the mitochondria by VDAC1-based peptides may serve to induce apoptosis in cancer cells and to potentiate the efficacy of conventional chemotherapeutic agents.

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    • "Cytochrome c activates caspases which eventually leads to cell death. Anti-apoptotic Bcl-2 proteins maintain mitochondrial integrity by sequestering pro-apoptotic members (Arbel, Ben-Hail, & Shoshan-Barmatz, 2012; Kinnally, Peixoto, Ryu, & Dejean, 2011; Shore, 2009). Glycolytic enzyme hexokinase (HK) interacts with VDAC, and this interaction makes the cells resistant to several apoptotic stimuli. "
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    • "For instance, many experiments performed by White et al. were based on mitochondrial Ca 2+ uptake experiments in permeabilized cells where all VDAC1 channels across the mitochondrial outer membrane will participate in mitochondrial Ca 2+ uptake[114]. In contrast, experiments in other studies relied on mitochondrial Ca 2+ uptake measurements in intact cells exposed to agonists for which Ca 2+ would be preferentially transferred via ER-mitochondrial contact sites[113,115,116]. Nevertheless, since a stimulatory effect of VDAC1 by Bcl-XL has never been shown in direct measurements based on purified VDAC1 channels, the molecular properties and the relevance of the VDAC1/ Bcl-XL connection in promoting mitochondrial Ca 2+ transfer ought to be further scrutinized. "
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    • "mitochondrial membrane, VDACs interact directly with a plethora of pro-and anti-apoptotic factors, either members of the Bcl-2 protein family such as Bcl-xL (Arbel et al., 2012; Malia and Wagner, 2007), Bid/tBid(Rostovtseva et al., 2004), Bax/Bak, (Shimizu et al., 2001), hexokinases (Godbole et al., 2013) or Bnip3 (Chaanine et al., 2013). The precise molecular functions and stoichiometries of these VDAC/apoptotic factor complexes are poorly understood, although tentative structural predictions for several VDAC/effector complexes have been suggested (G.Veresov and Davidovskii, 2014). "
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