We also found a significant down regulation in the e pression of the Nrf2 downstream genes GCLM, GCLC and NQO1 in breast, prostate and kidney cancer respect ively, suggesting that Nrf2 protein activity might also be reduced in these tumors. Of note, analysis of Keap1 e pression in these datasets showed no significant differences between normal and tu mors samples, e cept for lymphoma tumors where Keap1 e pression was found up regulated when compared to normal tissue. Ne t we investigated whether Nrf2 levels are associ ated with survival in patients with cancer. Analysis of available survival datasets obtained from GEO and TCGA databases showed that lower e pression of Nrf2 is associated with a significantly poorer out come in skin cutaneous melanoma and in kidney clear cell carcinoma.

Similarly, low Nrf2 e pression was associ ated with biochemical recurrence in prostate cancer, but we found no relation positive or negative to prognosis in any of the other cancers studied. The analysis of those cancers where we found an association between Nrf2 e pression and survival revealed that the mRNA level of Nrf2 was posi tively correlated to its downstream targets in KIRC and PRAD GSE21034, but not in SKCM. These data suggest that the Nrf2 pathway activity can be dimin ished in those tumors e hibiting low Nrf2 e pression. Discussion Intracellular redo homeostasis is altered in cancer, where increased levels of ROS favor a pro o idant microenviron ment. Here we show that MSC accumulate ROS dur ing oncogenic transformation, and that transformed MSC become o idative stress dependent, since treatment with antio idants decreases ROS levels and impairs their tu morigenic potential.

Moreover, the increase in ROS coin cides with the down regulation of genes involved in the cellular antio idant machinery, including most antio idant enzymes, genes implicated in glutathione homeostasis, and those involved in the biosynthesis of NADPH. It is believed that a significant amount of the intracellular ROS is produced by mitochondria. However, ROS can also be produced by non mitochondrial sources such as membrane bound NADPH o idases. While the vast majority of the pro o idant enzymes in our list of ROS genes do not change during MSC transformation, microarray and qRT PCR analysis showed in creased e pression of NADPH o idase 4 and aldehyde o idase 1 during MSC transformation. Although the precise contribution of these enzymes to ROS accumulation is AV-951 unknown and needs further investigation, our data overall suggest that a defective cellular antio idant system may largely con tribute to the high levels of ROS observed during MSC transformation. We also found that e pression of Nrf2 decreased during the process of MSC transformation.