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Am J Physiol Cell Physiol 292: C1388-C1397, 2007. First published November 29, 2006; doi:10.1152/ajpcell.00490.2006
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GROWTH, DIFFERENTIATION, AND APOPTOSIS

Phosphorothioate oligonucleotides reduce mitochondrial outer membrane permeability to ADP

¹Department of Biology, University of Maryland, College Park, Maryland; ²Department of Biomedical Engineering, Columbia University, New York, New York; ³Johns Hopkins University, School of Public Health, Baltimore, Maryland; and ⁴Albert Einstein-Montefiore Cancer Center, Department of Oncology, Montefiore Medical Center, Bronx, New York

Submitted 15 September 2006 ; accepted in final form 25 November 2006

G3139, an antisense Bcl-2 phosphorothioate oligodeoxyribonucleotide, induces apoptosis in melanoma and other cancer cells. This apoptosis happens before and in the absence of the downregulation of Bcl-2 and thus seems to be Bcl-2-independent. Binding of G3139 to mitochondria and its ability to close voltage-dependent anion-selective channel (VDAC) have led to the hypothesis that G3139 acts, in part, by interacting with VDAC channels in the mitochondrial outer membrane (21). In this study, we demonstrate that G3139 is able to reduce the mitochondrial outer membrane permeability to ADP by a factor of 6 or 7 with a K_i between 0.2 and 0.5 µM. Because VDAC is responsible for this permeability, this result strengthens the aforesaid hypothesis. Other mitochondrial respiration components are not affected by [G3139] up to 1 µM. Higher levels begin to inhibit respiration rates, decrease light scattering and increase uncoupled respiration. These results agree with accumulating evidence that VDAC closure favors cytochrome c release. The speed of this effect (within 10 min) places it early in the apoptotic cascade with cytochrome c release occurring at later times. Other phosphorothioate oligonucleotides are also able to induce VDAC closure, and there is some length dependence. The phosphorothioate linkages are required to induce the reduction of outer membrane permeability. At levels below 1 µM, phosphorothioate oligonucleotides are the first specific tools to restrict mitochondrial outer membrane permeability.

respiration; voltage-dependent anion-selective channel; apoptosis; cell death