Negative Regulation of STAT3 Protein-mediated Cellular Respiration by SIRT1 Protein

Abstract

In mammals, the transcriptional activity of signal transducer and activator of transcription 3 (STAT3) is regulated by the deacetylase SIRT1. However, whether the newly described nongenomic actions of STAT3 toward mitochondrial oxidative phosphorylation are dependent on SIRT1 is unclear. In this study, Sirt1 gene knock-out murine embryonic fibroblast (MEF) cells were used to delineate the role of SIRT1 in the regulation of STAT3 mitochondrial function. Here, we show that STAT3 mRNA and protein levels and the accumulation of serine-phosphorylated STAT3 in mitochondria were increased significantly in Sirt1-KO cells as compared with wild-type MEFs. Various mitochondrial bioenergetic parameters, such as the oxygen consumption rate in cell cultures, enzyme activities of the electron transport chain complexes in isolated mitochondria, and production of ATP and lactate, indicated that Sirt1-KO cells exhibited higher mitochondrial respiration as compared with wildtype MEFs. Two independent approaches, including ectopic expression of SIRT1 and siRNA-mediated knockdown of STAT3, led to reduction in intracellular ATP levels and increased lactate production in Sirt1-KO cells that were approaching those of wild-type controls. Comparison of profiles of phospho-antibody array data indicated that the deletion of SirT1 was accompanied by constitutive activation of the proinflammatory NF-B pathway, which is key for STAT3 induction and increased cellular respiration in Sirt1-KO cells. Thus, SIRT1 appears to be a functional regulator of NF-B-dependent STAT3 expression that induces mitochondrial biogenesis. These results have implications for understanding the interplay between STAT3 and SIRT1 in pro-inflammatory conditions.Sirtuins, or silent information regulator proteins, are a conserved family of seven proteins that regulate distinct biological pathways in mammals (1). The sirtuin, SIRT1, a NAD-dependent deacetylase, is located in the nucleus and plays crucial roles in genome organization and stability, stress response, glucose homeostasis, cell differentiation, DNA repair, and cell cycle control (2, 3). It also regulates processes such as cell survival, inflammation, mitochondrial biogenesis, and oxidative damage (4). Although the promotion of mitochondrial biogenesis by SIRT1 has been ascribed to deacetylation of the master regulator PGC-1␣ and FOXO1 (5, 6), little is known about how SIRT1 controls the energy production of the cell. Proper mitochondrial function is crucial for maintenance of metabolic homeostasis and activation of appropriate stress responses that have been implicated in life span extension and aging (7). The process of oxidative phosphorylation to generate ATP represents one of the principal bioenergetic functions of mitochondria, and yet the molecular mechanisms by which deregulation of SIRT1 expression and/or activity alters the capacity of mitochondria to meet energy demands have only begun to be elucidated.The signal transducer and activator of transcription 3 (STAT3) transcription factor is a key antiapo...

SirT1 and STAT3 protect retinal pigmented epithelium cells against oxidative stress

“…Bernier et al (22) reported negative regulation of STAT3 protein-mediated cellular respiration by SirT1 in murine embryonic fibroblast cells (21), and a previous study provided further support for these results (41). As previously demonstrated, pSTAT3 stimulated expression of the STAT3 gene [unphosphorylated STAT3 (U-STAT3)], which exerted persistent activity (42).…”

“…Based on the known roles of SirT1 and STAT3 in oxidative stress, it was hypothesized that there is crosstalk between the two molecules during oxidative stress. Interactions between SirT1 and STAT3, which have versatile roles in various microenvironments, had previously been identified (20,21). However, whether or not there was crosstalk between the two molecules during oxidative stress in RPEs and what the mechanism of crosstalk was, remained to be elucidated.…”

Cyclophilin D Extramitochondrial Signaling Controls Cell Cycle Progression and Chemokine-directed Cell Motility*

“…Although the biochemical requirements of this pathway are still controversial (39), there is evidence that mitochondrial STAT3 may improve organelle performance and antagonize apoptosis during acute vascular injury (40), consistent with a non-transcriptional function of STAT3 in cellular responses (41). At variance with this paradigm, STAT3 induced by CypD depletion did not significantly accumulate in mitochondria, and its phosphorylation on Ser-727, a marker of the mitochondrial pool of the molecule (25,26), was not affected in CypD-targeted cells.…”

“…Confirming the specificity of this response, CypD targeting in different cell types did not affect STAT3 phosphorylation on Ser-727 (Fig. 5D), an activation marker of mitochondria-localized STAT3 (25,26).…”

“…Intriguingly, an oncogenic pool of STAT3 has been identified in mitochondria (37) and implicated in regulation of oxidative phosphorylation (38), potentially modulated by the SIRT1 deacetylase (25). Although the biochemical requirements of this pathway are still controversial (39), there is evidence that mitochondrial STAT3 may improve organelle performance and antagonize apoptosis during acute vascular injury (40), consistent with a non-transcriptional function of STAT3 in cellular responses (41).…”