Mitochondrial ROS Induce Partial Dedifferentiation of Human Mesothelioma via Upregulation of NANOG

Our plain-English summary of Mitochondrial ROS Induce Partial Dedifferentiation of Human Mesothelioma via Upregulation of NANOG, by F. Sedlic, F. Seiwerth, A. Sepac, et al (Antioxidants, 2020).

The study

• Authors: F. Sedlic, F. Seiwerth, A. Sepac, S. Sikiric, M. Cindric, M. Milavic, L. Batelja Vuletic, M. Jakopovic, S. Seiwerth
• Journal: Antioxidants
• Published: 2020;9(7)
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The expression of pluripotency factors is a key regulator of tumor differentiation status and cancer stem cells. The purpose of this study was to examine the expression of pluripotency factors and differentiation status of human mesothelioma and the role of mitochondria in their regulation. We tested the expression of OCT4/POU5F1, NANOG, SOX2, PI3K-AKT pathway and BCL2 genes and proteins in 65 samples of human mesothelioma and 19 samples of normal mesothelium. Mitochondrial membrane potential, reactive oxygen species (ROS) generation and expression of pluripotency factors were also tested in human mesothelioma cell line. Human mesothelium and mesothelioma expressed SOX2, NANOG, PI3K and AKT genes and proteins and POU5F1 gene, whereby NANOG, SOX2 and phosphorylated (activated) AKT were upregulated in mesothelioma. NANOG protein expression was elevated in less differentiated samples of human mesothelioma. The expression of genes of PI3K-AKT pathway correlated with pluripotency factor genes. Mesothelioma cells had functional, but depolarized mitochondria with large capacity to generate ROS. Mitochondrial ROS upregulated NANOG and mitoTEMPO abrogated it. In conclusion, human mesothelioma displays enhanced expression of NANOG, SOX2 and phosphorylated AKT proteins, while elevated NANOG expression correlates with poor differentiation of human mesothelioma. Mitochondria of mesothelioma cells have a large capacity to form ROS and thereby upregulate NANOG, leading to dedifferentiation of mesothelioma.

In plain English

This laboratory study, by researchers in Zagreb, Croatia, did not study asbestos exposure. The authors examined archived tissue from 65 cases of malignant pleural mesothelioma and 19 normal pleuras, covering 2000 to 2018. They measured proteins and genes linked to how immature, or less differentiated, cells are. They also ran experiments on one mesothelioma cell line, Mero-14. NANOG and SOX2 proteins were more highly expressed in mesothelioma than in normal tissue. OCT4 protein was not found in either, and the matching genes were less expressed in mesothelioma. NANOG protein was significantly higher in the pleomorphic subtype than in the tubulopapillary subtype. In the cell line, mitochondria were on average less polarized than in a non-cancerous cell line. A chemical, antimycin A, raised reactive oxygen species eight fold at 10 micromolar. Doses of 2.5 and 5 micromolar increased NANOG, but 10 micromolar did not, and a mitochondrial antioxidant, mitoTEMPO, blocked the effect. The authors concluded that poor differentiation of mesothelioma is associated with higher NANOG, which can be induced by mitochondrial reactive oxygen species.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study: immunohistochemistry and PCR on archived human tissue samples, plus experiments on a human mesothelioma cell line
• Who was studied: Archived samples from the Department of Pathology, University of Zagreb School of Medicine and Clinical Hospital Center Zagreb: 19 randomly selected normal pleuras and 65 cases of malignant pleural mesothelioma, from 2000 to 2018. The patients were 61 males and 4 females with an average age of 60 years. Gene (PCR) analysis used 9 normal pleura controls and 34 mesothelioma samples diagnosed 2016 to 2018. The experiments used the human mesothelioma cell line Mero-14.
• Exposure: Asbestos exposure was not studied. In the cell-line experiments, cells were treated with antimycin A (2.5, 5 and 10 µM) to stimulate mitochondrial reactive oxygen species, with mitoTEMPO to scavenge them, and in one experiment with wortmannin (10 µM) to block the PI3K/AKT pathway.
• Main results:
  • NANOG and SOX2 proteins were expressed more in mesothelioma than in normal mesothelium (by a semi-quantitative staining index). OCT4 protein was not expressed in either.
  • NANOG protein was significantly more expressed in the pleomorphic than in the tubulopapillary mesothelioma subtype. SOX2 showed no difference among subtypes.
  • At the gene level, the opposite was seen: POU5F1, NANOG and SOX2 genes were less expressed in mesothelioma than in mesothelium.
  • Activated (phosphorylated) AKT protein was more extensively expressed in mesothelioma. Activated PI3K was expressed to a similar extent in both tissues. BCL2 protein was lower in mesothelioma.
  • In mesothelioma samples, the pluripotency genes correlated with at least one PI3K or AKT gene but not with BCL2. In Mero-14 cells, wortmannin did not significantly reduce NANOG or SOX2 protein.
  • Mero-14 mesothelioma cells had functional mitochondria that were on average less polarized than those of a non-cancerous human endothelial cell line.
  • Baseline reactive oxygen species in Mero-14 cells were low, but rose with antimycin A dose, increasing eight fold at 10 µM.
  • In Mero-14 cells, 2.5 and 5 µM antimycin A increased NANOG expression in a dose-dependent way, while 10 µM had no effect. mitoTEMPO abolished the effect of 5 µM antimycin A. OCT4, SOX2 and the control proteins were not affected.
• The authors' conclusion: The authors concluded that poor differentiation of human mesothelioma is associated with enhanced NANOG expression, which can be induced by mitochondrial reactive oxygen species. They also concluded that NANOG and SOX2 may have diagnostic potential.
• Limitations the authors state:
  • The authors note that protein expression in tissue slides could only be measured with a semi-quantitative index, because tissue slides contain multiple cell layers.
  • The authors note that, in human mesothelioma samples, the relationships between pluripotency factors and the PI3K-AKT pathway could only be tested by correlating gene expression.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, STEM, Mesothelium, Reactive Oxygen Species (ROS).

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