Bcl-2 and Bax regulate the channel activity of the mitochondrial adenine nucleotide translocator

Abstract

Bcl-2 family protein including anti-apoptotic (Bcl-2) or pro-apoptotic (Bax) members can form ion channels when incorporated into synthetic lipid bilayers. This contrasts with the observation that Bcl-2 stabilizes the mitochondrial membrane barrier function and inhibits the permeability transition pore complex (PTPC). Here we provide experimental data which may explain this apparent paradox. Bax and adenine nucleotide translocator (ANT), the most abundant inner mitochondrial membrane protein, can interact in arti®cial lipid bilayers to yield an e cient composite channel whose electrophysiological properties di er quantitatively and qualitatively from the channels formed by Bax or ANT alone. The formation of this composite channel can be observed in conditions in which Bax protein alone has no detectable channel activity. Cooperative channel formation by Bax and ANT is stimulated by the ANT ligand atractyloside (Atr) but inhibited by ATP, indicating that it depends on the conformation of ANT. In contrast to the combination of Bax and ANT, ANT does not form active channels when incorporated into membranes with Bcl-2. Rather, ANT and Bcl-2 exhibit mutual inhibition of channel formation. Bcl-2 prevents channel formation by Atr-treated ANT and neutralizes the cooperation between Bax and ANT. Our data are compatible with a meÂnage aÁ trois model of mitochondrial apoptosis regulation in which ANT, the likely pore forming protein within the PTPC, interacts with Bax or Bcl-2 which in¯uence its pore forming potential in opposing manners.

Bax and Bcl-xL independently regulate apoptotic changes of yeast mitochondria that require VDAC but not adenine nucleotide translocator

“…Bax was shown to interact with ANT, and enhance the atractyloside (ANT inhibitor)-induced opening of ANT (Marzo et al, 1998;Brenner et al, 2000). We con®rmed the interaction of Bax and ANT both in vitro and in vivo (Shimizu et al, 1999;and data not shown).…”

“…Bcl-2 and Bcl-x L were reported to bind with ANT (Marzo et al, 1998;Shimizu et al, 1999;Brenner et al, 2000). Therefore, we next examined the role of ANT in the prevention of Dc loss and cytochrome c release by Bcl-x L .…”

“…It has also been reported that Bax interacts directly with ANT and enhances ANT opening induced by atractyloside (an ANT inhibitor), and that ANTde®cient yeast are resistant to Bax-induced cell death, suggesting that ANT may also be a functional target of Bax (Marzo et al, 1998;Brenner et al, 2000). To investigate the detailed mechanisms of Bax-induced mitochondrial changes, we assessed the e ect of Bax on mitochondria isolated from ANT-and VDAC-de®cient yeasts.…”

Hierarchical involvement of Bak, VDAC1 and Bax in cisplatin-induced cell death

“…The exact composition of the PTPC is rather variable between different cells and is influenced by the existence of several isoforms of its constituents (such as hexokinase-1, hexokinase-2, VDAC1-3, adenine nucleotide translocase-1 to -4) (Brenner and Grimm, 2006;Grimm and Brdiczka, 2007;Kroemer et al, 2007). Although several studies have insisted on the fact that Bax/Bak-mediated MMP and PTPC-dependent MMP would occur in a completely independent, mechanistically distinct fashion, other reports suggest that proteins from the Bcl-2 family can functionally and physically interact with the PTPC (Marzo et al, 1998;Brenner et al, 2000;Belzacq et al, 2002). In this context, it has been suggested that VDAC2 would exert antiapoptotic functions by sequestering Bak (Cheng et al, 2003;Chandra et al, 2005) whereas other VDAC isoforms (possibly VDAC1 and VDAC3) would interact cooperatively with Bax to induce apoptosis (Shimizu et al, 1999(Shimizu et al, , 2001.…”

NGF Withdrawal Induces Apoptosis in CESS B Cell Line through p38 MAPK Activation and Bcl-2 Phosphorylation

“…A direct binding with mitochondrial proteins, such as adenine nucleotide traslocator (ANT) and the voltage-dependent anion channel (VDAC), has also been suggested as part of the regulatory functions of Bcl-2 voted to prevent cytochrome c release (5,6). The delicate nature of these protein-protein interactions explains why factors affecting Bcl-2 protein expression and/or function are able to modulate apoptotic cell death.…”