Key regions of VDAC1 functioning in apoptosis induction and regulation by hexokinase.
The voltage-dependent anion channel (VDAC), located in the mitochondrial outer membrane, functions as gatekeeper for the entry and exit of mitochondrial metabolites, and thus controls cross-talk between mitochondria and the cytosol. VDAC also serves as a site for the docking of cytosolic proteins, such as hexokinase, and is recognized as a key protein in mitochondria-mediated apoptosis. The role of VDAC in apoptosis has emerged from various studies showing its involvement in cytochrome c release and apoptotic cell death as well as its interaction with proteins regulating apoptosis, including the mitochondria-bound isoforms of hexokinase (HK-I, HK-II). Recently, the functional HK-VDAC association has shifted from being considered in a predominantly metabolic light to the recognition of its major impact on the regulation of apoptotic responsiveness of the cell. Here, we demonstrate that the HK-VDAC1 interaction can be disrupted by mutating VDAC1 and by VDAC1-based peptides, consequently leading to diminished HK anti-apoptotic activity, suggesting that disruption of HK binding to VDAC1 can decrease tumor cell survival. Indeed, understanding structure-function relationships of VDAC is critical for deciphering how this channel can perform such a variety of differing functions, all important for cell life and death. By expressing VDAC1 mutants and VDAC1-based peptides, we have identified VDAC1 amino acid residues and domains important for interaction with HK and protection against apoptosis. These include negatively- and positively-charged residues, some of which are located within beta-strands of the protein. The N-terminal region of VDAC1 binds HK-I and prevents HK-mediated protection against apoptosis induced by STS, while expression of a VDAC N-terminal peptide detaches HK-I-GFP from mitochondria. These findings indicate that the interaction of HK with VDAC1 involves charged residues in several beta-strands and in the N-terminal domain. Displacing HK, serving as the 'guardian of the mitochondrion', from its binding site on VDAC1 may thus be exploited as an approach to cancer therapy.
Shoshan-Barmatz
Varda
V
Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel. vardasb@bgu.ac.il
Zakar
Miri
M
Rosenthal
Keshet
K
Abu-Hamad
Salah
S
D017209:Apoptosis; D001943:Breast Neoplasms; D002460:Cell Line; D045744:Cell Line, Tumor; D005260:Female; D006367:HeLa Cells; D006593:Hexokinase / Q000378:metabolism*; D006706:Homeostasis; D006801:Humans; D007473:Ion Channels / Q000502:physiology; D007668:Kidney; D007700:Kinetics; D014162:Transfection; D020298:U937 Cells; D050995:Voltage-Dependent Anion Channel 1 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D007473:Ion Channels; C494762:VDAC1 protein, human; D050995:Voltage-Dependent Anion Channel 1; D006593:Hexokinase