Peroxiredoxin 3 is a redox-dependent target of thiostrepton in malignant mesothelioma cells

Our plain-English summary of Peroxiredoxin 3 is a redox-dependent target of thiostrepton in malignant mesothelioma cells, by K. Newick, B. Cunniff, K. Preston, et al (PloS One, 2012).

The study

• Authors: K. Newick, B. Cunniff, K. Preston, P. Held, J. Arbiser, H. Pass, B. Mossman, A. Shukla, N. Heintz
• Journal: PloS One
• Published: 2012;7(6):e39404
• Cited by: 45 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Thiostrepton (TS) is a thiazole antibiotic that inhibits expression of FOXM1, an oncogenic transcription factor required for cell cycle progression and resistance to oncogene-induced oxidative stress. The mechanism of action of TS is unclear and strategies that enhance TS activity will improve its therapeutic potential. Analysis of human tumor specimens showed FOXM1 is broadly expressed in malignant mesothelioma (MM), an intractable tumor associated with asbestos exposure. The mechanism of action of TS was investigated in a cell culture model of human MM. As for other tumor cell types, TS inhibited expression of FOXM1 in MM cells in a dose-dependent manner. Suppression of FOXM1 expression and coincidental activation of ERK1/2 by TS were abrogated by pre-incubation of cells with the antioxidant N-acetyl-L-cysteine (NAC), indicating its mechanism of action in MM cells is redox-dependent. Examination of the mitochondrial thioredoxin reductase 2 (TR2)-thioredoxin 2 (TRX2)-peroxiredoxin 3 (PRX3) antioxidant network revealed that TS modifies the electrophoretic mobility of PRX3. Incubation of recombinant human PRX3 with TS in vitro also resulted in PRX3 with altered electrophoretic mobility. The cellular and recombinant species of modified PRX3 were resistant to dithiothreitol and SDS and suppressed by NAC, indicating that TS covalently adducts cysteine residues in PRX3. Reduction of endogenous mitochondrial TRX2 levels by the cationic triphenylmethane gentian violet (GV) promoted modification of PRX3 by TS and significantly enhanced its cytotoxic activity. Our results indicate TS covalently adducts PRX3, thereby disabling a major mitochondrial antioxidant network that counters chronic mitochondrial oxidative stress. Redox-active compounds like GV that modify the TR2/TRX2 network may significantly enhance the efficacy of TS, thereby providing a combinatorial approach for exploiting redox-dependent perturbations in mitochondrial function as a therapeutic approach in mesothelioma.

In plain English

This was a laboratory study, not a study of asbestos-exposed people. The authors studied how the antibiotic thiostrepton (TS) acts on human malignant mesothelioma (MM) cell lines versus a mesothelial cell line (LP9). In tissue-bank samples, most MM tumors of every subtype showed the protein FOXM1 in the nuclei of 50% or more of cells. FOXM1 messenger RNA was higher in tumor than in normal mesothelium from four patients (p = 0.0017). MM cell lines produced about 2 to 3 times more mitochondrial oxidants than LP9. TS lowered FOXM1, an effect blocked by the antioxidant N-acetyl-L-cysteine. TS altered PRX3, a mitochondrial antioxidant protein, in cells and as purified protein. Gentian violet (GV) increased this alteration. In four-day growth tests on HM cells, the authors estimated by statistical model that a fixed TS dose plus increasing GV was about 3.3-fold more potent than GV alone, and a fixed low GV dose plus increasing TS about 175-fold more potent than TS alone. The authors concluded that TS disables a mitochondrial antioxidant network by binding PRX3. They noted that cell culture differs from tumors in the body.

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: cell culture experiments with human mesothelioma and mesothelial cell lines, experiments on purified recombinant protein, and staining of tumor tissue microarrays
• Who was studied: Human pleural MM cell lines (HM, HP-1, H2373 and others), compared with the hTERT-immortalized human mesothelial cell line LP9. Tissue microarrays from the Mesothelioma Virtual Tissue Bank, described as covering 46 tumors, of which 13 with unspecified histology were excluded. Tumor and matched normal mesothelium came from four patients.
• Exposure: No asbestos exposure was studied. The cells were treated with the antibiotic thiostrepton (TS), alone or combined with gentian violet (GV), with or without pre-treatment with the antioxidant N-acetyl-L-cysteine (NAC).
• Main results:
  • In the MM tumor tissue arrays, most tumors of every subtype expressed nuclear FOXM1 in 50% or more of cells.
  • FOXM1 mRNA was higher in tumor tissue than in matched normal mesothelium from four patients (p = 0.0017).
  • MM cell lines produced about 2 to 3 times more mitochondrial oxidants than LP9 mesothelial cells.
  • In HM mesothelioma cells, pre-incubation with the antioxidant NAC completely blocked the effect of TS on FOXM1 expression.
  • TS produced a modified form of purified recombinant PRX3 that ran on gels like the modified PRX3 seen in TS-treated cells.
  • In HM cells, gentian violet combined with TS markedly increased the levels of modified PRX3.
  • In a four-day HM cell growth assay, a fixed dose of TS (about half the dose that inhibited growth by half) plus increasing GV was estimated by a four-parameter regression model to be about 3.3-fold more potent than increasing GV alone.
  • In a separate four-day HM cell growth assay, a constant low dose of GV plus increasing TS was estimated to be about 175 times more potent than increasing TS alone.
• The authors' conclusion: The authors concluded that TS disables the mitochondrial TR2-TRX2-PRX3 antioxidant network by covalently binding PRX3, and that GV enhances this binding by inhibiting expression of TRX2.
• Limitations the authors state:
  • The experiments were in cell culture. The approach still needs testing in models closer to tumors in the body, and the ratio of TS to GV that favors tumor over normal cells still has to be worked out.
  • The specific parts of PRX3 that TS binds to were not identified.
  • How disruption of PRX3 and higher mitochondrial oxidant levels reduce FOXM1 expression is not known.
  • TS probably acts on other redox-dependent targets in MM cells that were not studied.

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: Malignant Mesothelioma, Oxidative Stress, Asbestos Exposure, Mesothelioma.

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