SIRT3 interacts with the daf-16 homolog FOXO3a in the mitochondria, as well as increases FOXO3a dependent gene expression.

Cellular longevity is a complex process relevant to age-related diseases including but not limited to chronic illness such as diabetes and metabolic syndromes. Two gene families have been shown to play a role in the genetic regulation of longevity; the Sirtuin and FOXO families. It is also established that nuclear Sirtuins interact with and under specific cellular conditions regulate the activity of FOXO gene family proteins. Thus, we hypothesize that a mitochondrial Sirtuin (SIRT3) might also interact with and regulate the activity of the FOXO proteins. To address this we used HCT116 cells overexpressing either wild-type or a catalytically inactive dominant negative SIRT3. For the first time we establish that FOXO3a is also a mitochondrial protein and forms a physical interaction with SIRT3 in mitochondria. Overexpression of a wild-type SIRT3 gene increase FOXO3a DNA-binding activity as well as FOXO3a dependent gene expression. Biochemical analysis of HCT116 cells over expressing the deacetylation mutant, as compared to wild-type SIRT3 gene, demonstrated an overall oxidized intracellular environment, as monitored by increase in intracellular superoxide and oxidized glutathione levels. As such, we propose that SIRT3 and FOXO3a comprise a potential mitochondrial signaling cascade response pathway.

Histone deacetylase inhibitor and demethylating agent chromatin compaction and the radiation response by cancer cells.

It now appears that epigenetics plays a central role in transformation, both in vitro and in vivo. The expression and regulation of DNA methylation and the subsequent chromatin structure are significantly altered in tumor cells, suggesting a direct role in the process of in vivo cellular transformation. If epigenetics and posttranslational modifications of histones play a role in transformation, then it seems logical that the genes regulating chromatin compaction may also be molecular targets and markers in profiling tumor cell resistance. Local remodeling of chromatin is a key step in the regulation of gene expression, and altering the expression of these genes might also favorably alter how tumor cells respond to anticancer agents. Several new agents that alter chromatin compaction, either methyltransferase or histone deacetylases inhibitors, are progressing through clinical trials and have shown promising preclinical interactions when combined with radiation. In this review, we discuss the potential for histone deacetylases inhibitors as radiosensitizing agents.

Thioredoxin and thioredoxin reductase as redox-sensitive molecular targets for cancer therapy.

Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of altered intracellular processes including cell cycle regulation, excessive growth factor pathway activation, and decreased apoptosis. Metabolites from these processes result in significant cellular oxidative stress that must be buffered to prevent permanent cell damage and cell death. Tumor cells depend on a complex set of respiratory pathways to generate the necessary energy as well as redox-sensitive pro-survival signaling pathways and factors to cope with and defend against the detrimental effects of oxidative stress. It has been hypothesized that redox-sensitive signaling factors such as thioredoxin reductase-1 (TR) and thioredoxin (TRX) may represent central pro-survival factors that would allow tumor cells to evade the damaging and potentially cytotoxic effects of endogenous and exogenous agents that induce oxidative stress. The overarching theme of this review is an extension of the hypothesis that tumor cells use these redox sensitive pro-survival signaling pathways/factors, which are up-regulated due to increased tumor cell respiration, to evade the cytotoxic effects of anticancer agents. These observations suggest that redox-sensitive signaling factors may be potential novel molecular targets for drug discovery.