The role of the transcription factor Ets-1 in mitochondria to nucleus signaling

Mitochondria are unique organelles within the cell in that they contain their own genome and in conjunction with the nucleus, are able to transcribe and translate genes encoding components of the electron transport chain (ETC). In order to do so, the mitochondria must communicate with the nucleus, via the production of reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), produced as a byproduct of aerobic respiration within the mitochondria. Mitochondrial signaling is proposed to be altered in cancer cells, where the mitochondria are frequently found to harbor mutations within their mitochondrial deoxyribonucleic acid (mtDNA) and to display altered functional characteristics. Investigating the downstream consequences of such mitochondrial alterations within cancer cells, specifically the 2008/C13* ovarian carcinoma cell model, was the purpose of this study. The C13* cell variants were derived from 2008 cells following 13 consecutive cis-platinum (II)-diammine dichloride (cisplatin) treatments; as well as displaying enhanced cisplatin resistance, C13* variants contain morphologically and functionally distinct mitochondria. The transcription factor E26 transformation specific-1 (Ets-1) was observed to be specifically up-regulated in C13* cells and was thus investigated as a possible nuclear target of mitochondrial generated H2O2.; Ets-1 is the prototype of the ETS transcription factor family and is known for its ability to regulate the expression of genes involved in extracellular matrix (ECM) degradation, migration and angiogenesis. Expression of this factor is increasingly associated with aggressive cancer and poor patient outcome, emphasizing the importance of elucidating the mechanisms of aberrant expression in tumor tissues. In this study, C13* cell variants were demonstrated to produce greater amounts of ROS than the parental 2008 cells as well as to express higher levels of Ets-1 protein. Ets-1 protein levels were further shown to be up-regulated by exogenous H2O2. The ets-1 promoter was investigated in order to delineate the elements which are involved in the H2O2 mediated up-regulation. The key promoter element involved in both basal and H2O2 induced promoter activity was localized to the previously characterized enhancer region and was identified as an antioxidant response element (ARE).; Consequences of Ets-1 up-regulation in 2008 cells were investigated to determine whether the H2O2 mediated up-regulation of this factor would have a feedback effect on the mitochondria, as may be expected for a gene target of mitochondrial initiated signaling. Gene array analysis, comparing the expression of genes in 2008 cells to that in 2008 cells over-expressing Ets-1 revealed that genes encoding antioxidant defense proteins were up-regulated in the Ets-1 over-expressing cells and that several genes encoding mitochondrial proteins were down-regulated, as were genes encoding metabolic enzymes involved in generating substrates for the ETC. The overall suggestion of array results was that Ets-1 over-expressing cells should display altered metabolism, favoring an alternate energy source over oxidative phosphorylation. Such a metabolic switch was confirmed, in that Ets-1 over-expressing cells were observed to be particularly sensitive to the inhibition of glycolysis and to consume significantly less oxygen than parental cells.; This cell model was also used to investigate the effects of Ets-1 expression on cisplatin resistance. The cisplatin resistant phenotype of C13* cell variants has been proposed to be related to the altered mitochondria within these variants and thus it was hypothesized that the mitochondrial-mediated up-regulation of Ets-1 may be a component of this increased resistance. 2008 cells over-expressing Ets-1 were found to exhibit enhanced resistance to cisplatin, comparable to that of C13* cell variants. A second cell model of Ets-1 over-expression also displayed enhanced cisplatin resistance, demonstrating...