Endogenous retrovirus expression activates type-I interferon signaling in an experimental mouse model of mesothelioma development

Our plain-English summary of Endogenous retrovirus expression activates type-I interferon signaling in an experimental mouse model of mesothelioma development, by S. Sun, F. Frontini, W. Qi, et al (Cancer Letters, 2021).

The study

• Authors: S. Sun, F. Frontini, W. Qi, A. Hariharan, M. Ronner, M. Wipplinger, C. Blanquart, H. Rehrauer, J.F. Fonteneau, E. Felley-Bosco
• Journal: Cancer Letters
• Published: 2021;507:26-38
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Early events in an experimental model of mesothelioma development include increased levels of editing in double-stranded RNA (dsRNA). We hypothesised that expression of endogenous retroviruses (ERV) contributes to dsRNA formation and type-I interferon signaling. ERV and interferon stimulated genes (ISGs) expression were significantly higher in tumor compared to non-tumor samples. 12 tumor specific ERV ("MesoERV1-12") were identified and verified by qPCR in mouse tissues. "MesoERV1-12" expression was lower in mouse embryonic fibroblasts (MEF) compared to mesothelioma cells. "MesoERV1-12" levels were significantly increased by demethylating agent 5-Aza-2'-deoxycytidine treatment and were accompanied by increased levels of dsRNA and ISGs. Basal ISGs expression was higher in mesothelioma cells compared to MEF and was significantly decreased by JAK inhibitor Ruxolitinib, by blocking Ifnar1 and by silencing Mavs. "MesoERV7" promoter was demethylated in asbestos-exposed compared to sham mice tissue as well as in mesothelioma cells and MEF upon 5-Aza-CdR treatment. These observations uncover novel aspects of asbestos-induced mesothelioma whereby ERV expression increases due to promoter demethylation and is paralleled by increased levels of dsRNA and activation of type-I IFN signaling. These features are important for early diagnosis and therapy.

Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.

In plain English

This laboratory study combined re-analysis of RNA-sequencing data from an earlier mouse model of asbestos-induced mesothelioma with experiments in mouse cell lines. Mice had been injected intraperitoneally with crocidolite (400 micrograms per mouse, eight times over 21 weeks, 3.2 mg total) or saline, and killed at 33 weeks. The authors found that the A-to-G RNA editing index rose in crocidolite-exposed groups (P less than 0.001), that long terminal repeat elements were the most abundant transposable elements changed, and that tumour samples had significantly more reads mapping to endogenous retrovirus (ERV) sequences (P less than 0.01). Twelve tumour-associated sequences, called MesoERV1-12, were expressed more in mesothelioma cells (RN5, AK7) than in mouse embryonic fibroblasts (P less than 0.0001), formed double-stranded RNA, and increased after treatment with the demethylating agent 5-Aza-2'-deoxycytidine. Interferon-stimulated gene levels fell with Ruxolitinib, with Ifnar1 blockade and with Mavs silencing. The MesoERV7 promoter was more demethylated in crocidolite-exposed than sham tissue (P less than 0.05). The authors concluded that demethylation-driven ERV expression activates type-I interferon signaling during mesothelioma development.

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: Experimental laboratory study: re-analysis of RNA-sequencing data from a previously reported mouse model of crocidolite-induced mesothelioma, combined with in vitro cell culture experiments and methylation analysis of archived mouse tissue
• Who was studied: Tissues from B6;129S2-Nf2tm1Tyj/J mice backcrossed on a C57Bl/6J background exposed to crocidolite or sham (three groups: sham, crocidolite-exposed with pre-neoplastic lesions, crocidolite-exposed bearing tumors), plus mouse embryonic fibroblasts and mouse mesothelioma cell lines RN5, AK7 and AB1
• Exposure: Crocidolite (blue asbestos) asbestos, 400 micrograms per mouse intraperitoneally every 3 weeks for eight rounds, total 3.2 mg per mouse; in cells, 25 nM 5-Aza-2'-deoxycytidine, 1 microM Ruxolitinib, IFN-beta, Ifnar1-blocking antibody and Mavs siRNA
• Main results:
  • The A-to-G RNA editing index increased significantly in the crocidolite-exposed mouse groups compared with sham
  • Tumor samples from the mouse model had significantly more reads mapping to ERV sequences
  • Twelve tumor-expressed ERV sequences, named MesoERV1-12, of the ERV1 family, were identified from four mesothelioma-enriched sequences sharing a 90 bp region located in 21 genomic regions
  • MesoERV1-12 expression was higher in RN5 and AK7 mesothelioma cells than in mouse embryonic fibroblasts, whereas control MuLV_pol_U92 did not differ
  • RNaseIII digestion reduced MesoERV1-12 detection and J2 anti-dsRNA pull-down enriched MesoERV1-12 transcripts in AK7 and RN5 cells, supporting dsRNA structure
  • 5-Aza-CdR treatment increased MesoERV1-12 expression in MEF and in RN5 and AK7 cells, with increased dsRNA, while MuLV_pol_U92 was unchanged
  • In the RNA-seq data, 26 interferon stimulated genes, in addition to Adar1, were expressed more highly in tumor samples than in samples from crocidolite-exposed mice without tumor
  • Ddx58 and Ifitm1 expression was increased in asbestos-exposed mouse samples
  • In RN5 mesothelioma cells, silencing Mavs, Ruxolitinib treatment and IFNAR1-blocking antibody each decreased Rig-I and Ifitm1 levels
  • The MesoERV7 promoter was significantly more demethylated in tissues from crocidolite-exposed mice than from sham mice, and promoter methylation decreased in RN5 cells after 5-Aza-CdR
  • In TCGA mesothelioma patient data, overexpression of 6 of the identified ISGs was associated with best overall survival
• The authors' conclusion: The authors concluded that mesothelioma development is accompanied by promoter demethylation-driven ERV expression that forms double-stranded RNA and activates type-I interferon signaling without viral infection, which they consider relevant to early diagnosis and therapy
• Limitations the authors state:
  • Because of limited sample availability, all crocidolite samples (tumor and inflamed mesothelium) had to be pooled for the methylation comparison with sham samples
  • The effect size of the tissue demethylation finding was low, possibly because of contaminating non-tumor cells
  • Quantitative methylation specific PCR could not be performed in MEF because of low basal demethylation and extra PCR fragments
  • The possible role of ERV loci in driving long noncoding RNA expression was not explored in this study

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Fibroblast.

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• Frequent Homozygous Deletions of Type I Interferon Genes in Pleural Mesothelioma Confer Sensitivity to Oncolytic Measles Virus — T. Delaunay, C. Achard, et al. (2020)
• RNA editing in mesothelioma: a look forward — A. Hariharan, S. Sun, et al. (2020)
• Potential for interferon-alpha-based therapy in mesothelioma: assessment in a murine model — H. Bielefeldt-Ohmann, D.R. Fitzpatrick, et al. (1995)
• How asbestos drives the tissue towards tumors: YAP activation, macrophage and mesothelial precursor recruitment, RNA editing, and somatic mutations — H. Rehrauer, L. Wu, et al. (2018)
• Inflammation precedes the development of human malignant mesotheliomas in a SCID mouse xenograft model — J.M. Hillegass, A. Shukla, et al. (2010)

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