Mitochondrial SOD2 regulates epithelial–mesenchymal transition and cell populations defined by differential CD44 expression

Abstract

Epithelial-mesenchymal transition (EMT) promotes cancer cell invasion, metastasis and treatment failure. EMT may be activated in cancer cells by reactive oxygen species (ROS). EMT may promote conversion of a subset of cancer cells from a CD44Low-CD24High (CD44L) epithelial phenotype to a CD44High-CD24-/Low (CD44H) mesenchymal phenotype, the latter associated with increased malignant properties of cancer cells. ROS are required for cells undergoing EMT while excessive ROS may induce cell death or senescence; however, little is known as to how cellular antioxidant capabilities may be regulated during EMT. Mitochondrial superoxide dismutase 2 (SOD2) is frequently overexpressed in oral and esophageal cancers. Here, we investigate mechanisms of SOD2 transcriptional regulation in EMT as well as the functional role of this antioxidant in EMT. Using well-characterized genetically engineered oral and esophageal human epithelial cell lines coupled with RNA interference (RNAi) and flow cytometric approaches, we find that transforming growth factor (TGF)-β stimulates EMT, resulting in conversion of CD44L to CD44H cells, the latter of which display SOD2 upregulation. SOD2 induction in transformed keratinocytes was concurrent with suppression of TGF-β-mediated induction of both ROS and senescence. SOD2 gene expression appeared to be transcriptionally regulated by NF-κB and ZEB2, but not ZEB1. Moreover, SOD2-mediated antioxidant activity may restrict conversion of CD44L cells to CD44H cells at the early stages of EMT. This data provides novel mechanistic insights into the dynamic expression of SOD2 during EMT. Additionally, we delineate a functional role for SOD2 in EMT via the influence of this antioxidant upon distinct CD44L and CD44H subsets of cancer cells that have been implicated in oral and esophageal tumor biology.

Autophagy mediates epithelial cytoprotection in eosinophilic oesophagitis

“…We have previously demonstrated that ROS-scavenging enzymes regulate epithelial-mesenchymal transition (EMT). 19 As EMT has been implicated in EoE pathogenesis, 38 39 it will be interesting to investigate roles for antioxidants in maintaining epithelial homeostasis in response to EoE inflammation.…”

“…Western blotting was performed as described previously 19 with antibodies and conditions listed in online supplementary information.…”

“…Flow cytometry was performed to determine AV content (Cyto-ID) and reactive oxygen species (ROS) (2 0 ,7 0 -dichlorodihydrofluorescein diacetate (DCF)) as described previously 19 and detailed in online supplementary information.…”

Defining the momiome: Promiscuous information transfer by mobile mitochondria and the mitochondrial genome

“…Epithelial-to-mesenchymal transition (EMT) provides metastatic potential to tumors and renders them resistant to therapies targeted to the primary cancers. Available literature supports a role for mitochondria in the EMT process [180, 310–312]. As stated previously, mtDNA content and/or copy number is frequently reduced in tumors [44, 313].…”

“…The EMT marker gene fibronectin and high mobility group AT-hook 2 (HMGA2), a central mediator of EMT and metastatic progression, have been shown to be inhibited by exogenous expression of mitochondrial antioxidant thioredoxin (TXN2) [312]. Another study implicates a role for mitochondrial antioxidant enzyme, superoxide dismutase 2 (SOD2), in the regulation of EMT [310]. These observations suggest a novel mitochondria-dependent mechanism that regulates TGF-β-mediated gene expression associated with EMT [310, 312].…”