Inhibition of NADPH oxidase 4 induces apoptosis in malignant mesothelioma: Role of reactive oxygen species

Our plain-English summary of Inhibition of NADPH oxidase 4 induces apoptosis in malignant mesothelioma: Role of reactive oxygen species, by M. Tanaka, Y. Miura, H. Numanami, et al (Oncology Reports, 2015).

The study

• Authors: M. Tanaka, Y. Miura, H. Numanami, S. Karnan, A. Ota, H. Konishi, Y. Hosokawa, M. Hanyuda
• Journal: Oncology Reports
• Published: 2015;34(4):1726-32
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive tumor that is characterized by dysregulated growth and resistance to apoptosis. Reactive oxygen species (ROS)-generating NADPH oxidase (Nox) family enzymes have been suggested to be involved in neoplastic proliferation. Both the antioxidant N-acetylcysteine (NAC) and the inhibitor of flavoprotein-dependent oxidase, diphenylene iodonium (DPI), inhibited the cell viability of MPM cells in a dose-dependent manner. To examine whether Nox-mediated ROS generation confers antiapoptotic activity and thus a growth advantage to MPM cells, we analyzed the mRNA expression of Nox family members using quantitative RT-PCR in 7 MPM cell lines and a normal mesothelial cell line. Nox4 mRNA was expressed in all of the examined MPM cell lines, whereas little or no Nox2, Nox3 and Nox5 mRNA expression was detected. In 2 MPM cell lines, Nox4 mRNA expression was significantly higher than that in a normal mesothelial cell line. siRNAs targeting Nox4 suppressed ROS generation and cell viability in the MPM cell lines. In addition, DPI treatment and knockdown of Nox4 attenuated phosphorylation of AKT and ERK. Taken together, our results indicate that Nox4-mediated ROS, at least in part, transmit cell survival signals and their depletion leads to apoptosis, thus highlighting the Nox4-ROS-AKT signaling pathway as a potential therapeutic target for MPM treatment.

In plain English

This was a laboratory study of mesothelioma cells grown in dishes. It did not study patients or asbestos exposure, although blood cells from healthy donors were used for comparison. Working in Japan, the authors used seven malignant pleural mesothelioma cell lines and one normal mesothelial cell line (Met-5A). They asked whether reactive oxygen species (ROS), made by enzymes called NADPH oxidases (Nox), help mesothelioma cells survive. The antioxidant N-acetylcysteine (NAC) and the enzyme inhibitor diphenylene iodonium (DPI) reduced the viability of five mesothelioma cell lines, more so at higher doses. DPI lowered ROS levels and significantly induced apoptosis (programmed cell death), reported as 27% and 26% in two cell lines. Nox4 was expressed in all the mesothelioma cell lines. Two lines, ACC-MESO4 and MSTO-211H, had higher Nox4 levels than the normal cell line. In those two lines, blocking Nox4 lowered ROS, reduced cell viability by 30% and induced apoptosis by 13%. The authors concluded that ROS made by Nox4, at least in part, carry survival signals in a subset of mesothelioma cells. They suggested this pathway as a possible treatment target.

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 (in vitro) experiment on human cell lines
• Who was studied: Seven malignant pleural mesothelioma cell lines and one normal mesothelial cell line (Met-5A), obtained from the Aichi Cancer Center Research Institute, Japan. For comparison, the authors also used blood cells (PBMCs) from normal individuals and several lymphoma/leukemia cell lines.
• Exposure: No asbestos exposure was studied. The cells were treated with the antioxidant N-acetylcysteine (NAC), vitamin E, or the flavoenzyme inhibitor diphenylene iodonium (DPI), or were given siRNAs that block the Nox4 gene.
• Main results:
  • In five mesothelioma cell lines, NAC and DPI each reduced cell viability, more so at higher doses. DPI IC50 values ranged from 0.8 µM (ACC4-MESO) to 2.5 µM (Y8-MESO).
  • Vitamin E and DPI lowered the ROS signal (DCF fluorescence) in mesothelioma cells. The reading was printed as 2.1x104 in untreated cells, 0.7x104 with vitamin E and 0.1x104 with DPI.
  • DPI significantly induced apoptosis in two mesothelioma cell lines, reported as 27% and 26%.
  • Nox4 mRNA was expressed in all the mesothelioma cell lines, with little or no Nox2, Nox3 or Nox5. Nox1 was detected in ACC-MESO4.
  • Nox4 expression was high in ACC-MESO4 and MSTO-211H cells compared with the normal mesothelial cell line Met-5A (P<0.01).
  • In two mesothelioma cell lines, siRNAs against Nox4 reduced intracellular ROS by 50% and cell viability by 30%. The transfection induced apoptosis by 13%.
  • Blocking Nox4 and treating with DPI both reduced the phosphorylation (activation) of the survival-signaling proteins AKT and ERK.
• The authors' conclusion: The authors concluded that ROS generated by Nox4, at least in part, transmit cell survival signals in a subset of mesothelioma cells, and that removing ROS leads to apoptosis. They suggested the Nox4-ROS-AKT pathway as a possible new therapeutic target for malignant pleural mesothelioma.
• Limitations the authors state:
  • Blocking Nox4 did not completely stop ROS production. The authors said other Nox enzymes and mitochondria may also contribute.
  • The study used cell lines only. The authors said the link between Nox4 expression in primary mesothelioma tumors and patient prognosis remains to be investigated.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Apoptosis, Mesothelioma, Reactive Oxygen Species (ROS), Pleural Mesothelioma, Mesothelial Cells.

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• Reactive oxygen species a double-edged sword for mesothelioma — S. Benedetti, B. Nuvoli, et al. (2015)

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