Cancer and neurodegeneration are different classes of diseases that share the involvement of mitochondria in their pathogenesis. Whereas the high glycolytic rate (the so-called Warburg metabolism) and the suppression of apoptosis are key elements for the establishment and maintenance of cancer cells, mitochondrial dysfunction and increased cell death mark neurodegeneration. As a main actor in the regulation of cell metabolism and apoptosis, VDAC may represent the common point between these two broad families of pathologies. Located in the outer mitochondrial membrane, VDAC forms channels that control the flux of ions and metabolites across the mitochondrion thus mediating the organelle's cross-talk with the rest of the cell. Furthermore, the interaction with both pro-apoptotic and anti-apoptotic factors makes VDAC a gatekeeper for mitochondria-mediated cell death and survival signaling pathways. Unfortunately, the lack of an evident druggability of this protein, since it has no defined binding or active sites, makes the quest for VDAC interacting molecules a difficult tale. Pharmacologically active molecules of different classes have been proposed to hit cancer and neurodegeneration. In this work, we provide an exhaustive and detailed survey of all the molecules, peptides, and microRNAs that exploit VDAC in the treatment of the two examined classes of pathologies. The mechanism of action and the potential or effectiveness of each compound are discussed.

Edited by Linda SpremulliApoptosis is thought to play a critical role in several pathological processes, such as neurodegenerative diseases (i.e. Parkinson's and Alzheimer's diseases) and various cardiovascular diseases. Despite the fact that apoptotic mechanisms are well defined, there is still no substantial therapeutic strategy to stop or even slow this process. Thus, there is an unmet need for therapeutic agents that are able to block or slow apoptosis in neurodegenerative and cardiovascular diseases. The outer mitochondrial membrane protein voltage-dependent anion channel 1 (VDAC1) is a convergence point for a variety of cell survival and death signals, including apoptosis. Recently, we demonstrated that VDAC1 oligomerization is involved in mitochondrion-mediated apoptosis. Thus, VDAC1 oligomerization represents a prime target for agents designed to modulate apoptosis. Here, high-throughput compound screening and medicinal chemistry were employed to develop compounds that directly interact with VDAC1 and prevent VDAC1 oligomerization, concomitant with an inhibition of apoptosis as induced by various means and in various cell lines. The compounds protected against apoptosis-associated mitochondrial dysfunction, restoring dissipated mitochondrial membrane potential, and thus cell energy and metabolism, decreasing reactive oxidative species production, and preventing detachment of hexokinase bound to mitochondria and disruption of intracellular Ca 2؉ levels. Thus, this study describes novel drug candidates with a defined mechanism of action that involves inhibition of VDAC1 oligomerization, apoptosis, and mitochondrial dysfunction. The compounds VBIT-3 and VBIT-4 offer a therapeutic strategy for treating different diseases associated with enhanced apoptosis and point to VDAC1 as a promising target for therapeutic intervention.Mitochondria play crucial roles in cellular energy generation and metabolism, maintenance of the cell redox potential, calcium homeostasis, pH control and fatty acid oxidation, cell signaling, proliferation, differentiation, aging, and death (1). It is therefore not surprising that mitochondrial dysfunction is associated with various human diseases (1, 2).Located at the outer mitochondrial membrane (OMM), 2 the voltage-dependent anion channel (VDAC) serves as a mitochondrial gatekeeper. Three VDAC isoforms have been discovered (3), but only for VDAC1 is there a complete set of structural and functional information available. VDAC1 controls the metabolic and energy cross-talk between mitochondria and the rest of the cell, mediating the fluxes of ions, nucleotides, and other metabolites across the OMM (4 -7).

We have investigated the transmembrane topology of the bovine heart mitochondrial porin by means of proteases and antibodies raised against the amino-terminal region of the protein. The antisera against the human N-terminus reacted with porin in Western blots of NaDodSO4-solubilized bovine heart mitochondria and with the membrane-bound porin in enzyme-linked immunosorbent assay (ELISA). The immunoreaction with mitochondria coated on microtiter wells showed that the amino-terminal region of the protein is not embedded in the lipid bilayer but is exposed to the cytosol. Back-titration of unreacted anti-N-terminal antibodies after their incubation with intact mitochondria demonstrated that the porin N-terminus is also exposed in "noncoated" mitochondria. No difference in antisera reactivity was observed between intact and broken mitochondria. Intact and broken mitochondria were subjected to proteolysis by specific proteases. The membrane-bound bovine heart porin was strongly resistant to proteolysis, but a few specific cleavage sites were observed. Staphylococcus aureus V8 protease gave a large 24K N-terminal peptide, trypsin produced a 12K N-terminal and an 18K C-terminal peptide, and chymotrypsin gave two peptides of Mr 19.5K and 12.5K, which were both recognized by the antiserum against the human N-terminus. Carboxypeptidase A was ineffective in cleaving the membrane-bound porin in both intact and broken mitochondria. Thus, the carboxy-terminal part of the protein is probably not exposed to the water phase. The cleavage patterns of membrane-bound porin, obtained with S. aureus V8 protease, trypsin, and chymotrypsin, showed no difference between intact and broken mitochondria, thus indicating that all porin molecules have the same orientation in the membrane. The computer analysis of the sequence of human B-lymphocyte porin suggested that 16 beta-strands can span the phospholipid bilayer. This result, together with the overall information presented, allowed us to draw a possible scheme of the transmembrane arrangement of mammalian mitochondrial porin.

The effect of different families of detergents on the solubilization and purification of the pore-forming protein (porin) of the mitochondrial outer membrane of bovine heart was investigated in detail. With Tritons, dimethylamine oxides and zwittergents, porin solubilization with respect to total mitochondrial membrane protein was more efficient with the more hydrophobic members of each series. With most detergents the protein eluted as protein-detergent micelles in the void volume of hydroxyapatite/cehte columns. In contrast, the protein was bound to the column material and was eluted after the addition of salt to the elution buffer when the detergents octylglucoside, zwittergent 2-314 and lauryl (dimethyl)-amine oxide were used. The protein purified in the presence of the latter detergent had a higher pore-forming activity in lipid bilayer membranes compared to porin isolated in the presence of Triton X-100. The binding of porin to the hydroxyapatite/celite column was used to study the lipid content of the active pore-forming complex. The analysis revealed that the complex contained no phospholipid but rather five molecules of cholesterol/polypeptide chain.The mitochondria1 outer membrane contains general diffusion pores which are responsible for the free permeability of this membrane towards small hydrophilic solutes [l]. The active component of this molecular sieve is a protein, called mitochondrial porin or voltage-dependent anion channel [2 -41. Mitochondria1 porins were isolated from a variety of eukaryotic cells and their pore-forming properties were studied in reconstitution experiments with planar lipid bilayers and liposomes [2 -51. According to these investigations the mitochondrial pore has a diameter of about 2 nm in the open state and is slightly anion-selective at low transmembrane potentials. Voltages larger than 20 mV result in a shift of the pore into closed states, which have a reduced permeability towards hydrophilic solutes and a completely different selectivity from the open state.The role of the mitochondrial outer membrane in the physiology and metabolism of mitochondria was underestimated in the past. It has been described as a simple barrier that prevented the destruction of the mitochondrial inner membrane during osmotic swelling. More recent papers gave some insight into the function of the mitochondrial outer Abbreviations. (cHxN)zC, dicyclohexylcarbodiimide; CaE3, octyl trioxyethylene; CsE4, octyl tetraoxyethylene; CsE5, octyl pentaoxyethylene; C8(HE)S0, octyl (hydroxyethyl) sulfoxide; Cs(DHP)SO, octyl (dihydroxypropane) sulfoxide; DDAO, decyl (dimethyl)-amine oxide; LDAO, lauryl (dimethy1)-amine oxide; IysoPtdCho, lysophosphatidylcholine; MEGA 6, exanoyl-N-methylglucamide; MEGA 7, heptanoyl-N-methylglucamide; MEGA 8, octanoyl-N-methylglucamide; MEGA 9, nonaoyl-N-methylglucamide; MEGA 10, decanoyl-N-methylglucamide; MEGA 1 1 , undecanoyl-N-methylglucamide; MEGA 12, dodecanoyl-N-methylglucamide; NDAO, nonaoyl (dimethyl)-amine oxide; octyl-POE, octyl-polydisperse-oligo(oxyethy1-ene);...

VDACs three isoforms (VDAC1, VDAC2, VDAC3) are integral proteins of the outer mitochondrial membrane whose primary function is to permit the communication and exchange of molecules related to the mitochondrial functions. We have recently reported about the peculiar over-oxidation of VDAC3 cysteines. In this work we have extended our analysis, performed by tryptic and chymotryptic proteolysis and UHPLC/High Resolution ESI-MS/MS, to the other two isoforms VDAC1 and VDAC2 from rat liver mitochondria, and we have been able to find also in these proteins over-oxidation of cysteines. Further PTM of cysteines as succination has been found, while the presence of selenocysteine was not detected. Unfortunately, a short sequence stretch containing one genetically encoded cysteine was not covered both in VDAC2 and in VDAC3, raising the suspect that more, unknown modifications of these proteins exist. Interestingly, cysteine over-oxidation appears to be an exclusive feature of VDACs, since it is not present in other transmembrane mitochondrial proteins eluted by hydroxyapatite. The assignment of a functional role to these modifications of VDACs will be a further step towards the full understanding of the roles of these proteins in the cell.