SIRT3 interacts with the daf-16 homolog FOXO3a in the Mitochondria, as well as increases FOXO3a Dependent Gene expression

Abstract

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.

The Protein Deacetylase SIRT3 Prevents Oxidative Stress-induced Keratinocyte Differentiation

“…Keratinocytes-SIRT3 acts through several targets to both reduce superoxide production and enhance the oxidative stress response and detoxification mechanisms (8,(11)(12)(13)(14)(15)(16)(17). Consistent with the repression of mitochondrial oxidative stress by SIRT3, mitochondrial superoxide levels decreased in SIRT3-overexpressing keratinocytes (Fig.…”

“…Decreased availability of the sirtuin co-substrate NAD ϩ may lead to decreased SIRT3 activity in keratinocytes during differentiation. Given the well established role of SIRT3 as a regulator of mitochondrial oxidative stress (8,(11)(12)(13)(14)(15)(16)(17)(18), mitochondrial superoxide levels increased in both primary and immortalized keratinocytes with differentiation. We identified SIRT3 as a key regulator of this phenotype; constitutive SIRT3 deficiency resulted in increased mitochondrial superoxide levels, whereas constitutive SIRT3 expression reduced mitochondrial ROS.…”

“…It binds and deacetylates several mitochondrial proteins that promote mitochondrial oxidative metabolism, such as electron transport chain subunits and fatty acid oxidation enzymes (9,10). SIRT3 also dampens mitochondrial oxidative stress via deacetylation and subsequent activation of SOD2 and isocitrate dehydrogenase (8,(11)(12)(13)(14)(15)(16)(17)(18).…”

SirT3 Regulates the Mitochondrial Unfolded Protein Response

“…Whether this effect is due to a direct association between FOXO3A and SirT3 in the mitochondria (16,17) is a matter of debate. However, our data suggest that the effect of SirT3 on FOXO3A is likely to be indirect.…”

“…Moreover, SirT3 has been linked to augmented transcription of MnSOD and catalase, both known targets of the transcription factor FOXO3A (15). The SirT3-dependent deacetylation of FOXO3A promotes both its nuclear translocation and its transcriptional activity (16,17). Therefore, mechanistically, the reduction of SirT3 levels leads to an elevation in ROS levels by compromising the mitochondrial antioxidant machinery.…”