Aberrant expression of FoxP3 in a human T cell line possessing regulatory T cell‑like function and exposed continuously to asbestos fibers

Our plain-English summary of Aberrant expression of FoxP3 in a human T cell line possessing regulatory T cell‑like function and exposed continuously to asbestos fibers, by M. Maeda, H. Matsuzaki, S. Yamamoto, et al (Oncology Reports, 2018).

The study

• Authors: M. Maeda, H. Matsuzaki, S. Yamamoto, S. Lee, N. Kumagai-Takei, K. Yoshitome, Y. Min, N. Sada, Y. Nishimura, T. Otsuki
• Journal: Oncology Reports
• Published: 2018;40(2):748-758
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Prompted by the known carcinogenic activity of asbestos, our investigations revealed that asbestos causes a reduction in antitumor immunity. One mechanism involves the enhancement of regulatory T (Treg) cell function and volume assayed using MT‑2 original cells (Org), an HTLV‑1 immortalized human T cell line which possesses Treg‑like function. Continuous and relatively low‑dose exposure of MT‑2 to asbestos fibers yielded sublines resistant to asbestos‑induced apoptosis and enhanced Treg function via cell‑cell contact mechanisms and increased the production of soluble factors such as interleukin (IL)‑10 and transforming growth factor (TGF)‑β. Additionally, cell cycle progression was accelerated in these sublines. Subsequently, the status of the Treg‑specific transcription factor FoxP3 was examined. Unexpectedly, FoxP3 mRNA levels decreased in the sublines, although significant changes in protein expression were absent. Methylation analysis of CpG sites located in the promoter region of FoxP3 in original MT‑2 cells and sublines showed almost complete methylation in Org and slight hypomethylation in the sublines. Although treatment with the demethylating agent 5‑aza‑deoxycytidine tended to upregulate FoxP3 expression, the methylation status did not match the mRNA expression and enhanced function. Additionally, the expression of other transcription factors related to Treg did not differ between Org and subline CB1. Collectively, aberrant expression and methylation patterns of FoxP3 were detected in human T cells continuously exposed to asbestos, although cell function was enhanced by asbestos exposure. Future analyses to identify factors responsible for Treg functional enhancements induced by asbestos, such as the investigation of surface molecules, are needed for the development of strategies to prevent the occurrence of asbestos‑induced cancers.

In plain English

This laboratory study used MT-2, an HTLV-1-immortalized human T cell line. MT-2 behaves like regulatory T (Treg) cells, which the authors note can weaken antitumor immunity. The authors had earlier grown MT-2 sublines with continuous low-dose exposure (5 to 10 µg/ml) to chrysotile A, chrysotile B or crocidolite for over eight months. Here they examined FoxP3, a key Treg gene, in both. FoxP3 mRNA was higher in the original cells than in the sublines, but FoxP3 protein showed no clear difference. In the original cells and sublines CA1, CB1 and CR1, almost all FoxP3 control-region sites tested were methylated. At position -216, 77% of clones were methylated in the original cells, versus 25%, 11% and 53% in CA1, CB1 and CR1. A demethylating drug seemed to raise FoxP3, without statistical significance. Among other Treg-related genes, CTLA4 mRNA was significantly lower in sublines CB1 and CB2. GITR, IKZF2, SATB1 and AML1 (the last three tested only in the original cells and CB1) showed no significant differences. The authors concluded that what causes the sublines' enhanced Treg function remains unknown.

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) study comparing an original human T cell line with sublines previously generated by continuous asbestos exposure
• Who was studied: MT-2, a human HTLV-1-immortalized polyclonal T cell line described as having Treg-like function: the original cells (Org) and asbestos-exposed sublines (CA1-3, CB1-3, CR1-4; not all were used in every test)
• Exposure: Continuous, relatively low-dose exposure to chrysotile A, chrysotile B or crocidolite at 5 to 10 µg/ml for more than eight months
• Main results:
  • FoxP3 mRNA was higher in the original cells than in sublines CA1 to 3 and CB1 to 3
  • FoxP3 protein did not appear to differ significantly between the original cells and the sublines
  • Methylation of eleven CpG sites in the FoxP3 promoter region was measured in the original cells and in sublines CA1, CB1 and CR1 only
  • Almost all of these CpG sites were methylated, both in the original cells and in the three sublines examined
  • At CpG position -216, the percentage of methylated clones was 77% in the original cells, 25% in CA1, 11% in CB1 and 53% in CR1
  • Subline CB1 also showed lower methylation at other sites: 27% at -419, 72% at -256 and 56% at -139
  • mRNA levels of the methyltransferases DNMT1, DNMT2, DNMT3a and DNMT3b varied between the original cells and sublines CA1, CB1 and CR1, but the differences were not statistically significant
  • In the original cells and subline CB1, the demethylating agent 5-aza-dC seemed to increase FoxP3 mRNA and protein, without statistical significance
  • CTLA4 mRNA was significantly lower in sublines CB1 and CB2; other sublines showed no significant changes
  • By flow cytometry, CTLA4 tended to be higher in sublines CB1 to 3, but the changes were not significant
  • GITR showed no significant differences between the original cells and sublines CA1 to 3 and CB1 to 3
  • mRNA of the Treg-related transcription factors IKZF2, SATB1 and AML1 did not differ significantly between the original cells and CB1, the only subline tested for these genes
• The authors' conclusion: The authors concluded that the cellular and molecular changes responsible for the enhanced Treg function of the asbestos-exposed MT-2 sublines remain unknown
• Limitations the authors state:
  • The authors note that the results may reflect the nature of the MT-2 cell line, since gene expression in cell lines may change during long-term culture compared with normal cells

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Apoptosis, Asbestos Exposure.

Related studies

• Accelerated cell cycle progression of human regulatory T cell-like cell line caused by continuous exposure to asbestos fibers — S. Lee, H. Matsuzaki, et al. (2017)
• Enhancement of regulatory T cell-like suppressive function in MT-2 by long-term and low-dose exposure to asbestos — C. Ying, M. Maeda, et al. (2015)
• Increased production of matrix metalloproteinase-7 (MMP-7) by asbestos exposure enhances tissue migration of human regulatory T-like cells — S. Lee, S. Yamamoto, et al. (2021)
• Enhanced expression of nicotinamide nucleotide transhydrogenase (NNT) and its role in a human T cell line continuously exposed to asbestos — S. Yamamoto, S. Lee, et al. (2020)
• Inflammatory Alteration of Human T Cells Exposed Continuously to Asbestos — N. Kumagai-Takei, S. Yamamoto, et al. (2018)
• The Effects of Asbestos Fibers on Human T Cells — N. Kumagai-Takei, S. Lee, et al. (2020)

Browse more research in Oncology Reports, or return to medical research.