Chemosensitization by Knockdown of Adenine Nucleotide Translocase-2

Abstract

Mitochondrial membrane permeabilization (MMP) is a ratelimiting step of apoptosis, including in anticancer chemotherapy. Adenine nucleotide translocase (ANT) mediates the exchange of ADP and ATP on the inner mitochondrial membrane in healthy cells. In addition, ANT can cooperate with Bax to form a lethal pore during apoptosis. Humans possess four distinct ANT isoforms, encoded by four genes, whose transcription depends on the cell type, developmental stage, cell proliferation, and hormone status. Here, we show that the ANT2 gene is up-regulated in several hormonedependent cancers. Knockdown of ANT2 by RNA interference induced no major changes in the aspect of the mitochondrial network or cell cycle but provoked minor increase in mitochondrial transmembrane potential and reactive oxygen species level and reduced intracellular ATP concentration without affecting glycolysis. At expression and functional levels, ANT2 depletion was not compensated by other ANT isoforms. Most importantly, ANT2, but not ANT1, silencing facilitated MMP induction by lonidamine, a mitochondriontargeted antitumor compound already used in clinical studies for breast, ovarian, glioma, and lung cancer as well as prostate adenoma. The combination of ANT2 knockdown with lonidamine induced apoptosis irrespective of the Bcl-2 status. These data identify ANT2 as an endogenous inhibitor of MMP and suggest that its selective inhibition could constitute a promising strategy of chemosensitization. (Cancer Res 2006; 66(18): 9143-52)

Adenine nucleotide translocase family: four isoforms for apoptosis modulation in cancer

“…Of note, as almost all the SP1-binding sites in the ANT2 promoter are epigenetically masked by methylated CpG islands, it is plausible that the transcriptional activation of the gene is deregulated. Intrigued by the enhanced ANT2 content in some cancer cells (Faure Vigny et al, 1996;Le Bras et al, 2006), we and others examined the possibility that ANT2 could have cytoprotective effects, that is proliferative and/or anti-apoptotic effects. Thus, it has been speculated that (1) ANT2 could function in a reverse manner to import ATP into the mitochondrial matrix to compensate for the reduced mitochondrial ATP production in cancer cells (Chevrollier et al, 2005a) and (2) could interact preferentially with Bcl-2 to favor a stabilization of mitochondrial membranes through the inhibition of MMP (Belzacq et al, 2003).…”

“…In humans, the four ANT genes have similar structures and encode similar proteins, with sequence homology among between 80 and 90% between the various isoforms Le Bras et al, 2005). The initial classification was based on the measurements of ANT1 to ANT3 mRNA levels in rodents and human organs (Lunardi and Attardi, 1991;Faure Vigny et al, 1996;Giraud et al, 1998;Le Bras et al, 2006). ANT1 mRNA level has been found by reverse transcription polymerase chain reaction (RT-PCR) to be the predominant isoform in heart, brain and muscle, ANT2 mRNA level being the most abundant isoform in proliferative tissues such as lymphoid cells and the liver, and ANT3 being expressed at low levels independently of the tissue type.…”

“…ANT1 mRNA level has been found by reverse transcription polymerase chain reaction (RT-PCR) to be the predominant isoform in heart, brain and muscle, ANT2 mRNA level being the most abundant isoform in proliferative tissues such as lymphoid cells and the liver, and ANT3 being expressed at low levels independently of the tissue type. In breast (MCF7), colon (HT29), cervix (HeLa) and hepato-carcinoma (HepG2) cells, ANT2 mRNA is more abundant than ANT1 (Lunardi and Attardi, 1991;Faure Vigny et al, 1996;Giraud et al, 1998;Le Bras et al, 2006). Of note, we recently reported that ANT2 mRNA is significantly overexpressed in primary tissues derived from patients with cancer of the breast, uterus, ovary, lung, thyroid gland, bladder and testis as compared with the respective normal tissue (Le .…”

“…More recently, a third major breakthrough has been made in terms of role of ANT in apoptosis. Thus, ANT is expressed as four tissue-specific isoforms, ANT1 to ANT4, and we and others postulated that each ANT isoform might have a specific role in influencing cell fate, notably in cancer cells (Bauer et al, 1999;Zamora et al, 2004a;Le Bras et al, 2006;Gallerne et al, 2010). In this review, we recapitulate our knowledge of the role that the various isoforms of ANT play in apoptosis, examine the expression and the function of the four ANT isoforms in cancer cells and discuss recent evidence to propose a novel classification of ANT isoforms and their function in cancer cell death.…”

Disruption of the hexokinase–VDAC complex for tumor therapy

“…The PTPC scaffold involves proteins in the outer mitochondrial membrane, in particular the voltage-dependent anion channel (VDAC), as well as in the inner mitochondrial membrane, including the adenine nucleotide translocase (ANT) (Brenner and Grimm, 2006) and perhaps other members from the mitochondrial carrier protein family such as the inorganic phosphate carrier (Alcala et al, 2008). Although several ANT isoforms facilitate MOMP (Vieira et al, 2001), others, such as ANT2, stabilize mitochondrial membranes (Le Bras et al, 2006). As ANT2 is overexpressed in highly proliferating (and in particular in tumor) cells, small interfering RNAs that downregulate its levels may constitute a valid strategy for the selective induction of tumor cell death (Jang et al, 2008).…”