A nontoxic dose of chrysotile can malignantly transform Met-5A cells, in which microRNA-28 has inhibitory effects

Our plain-English summary of A nontoxic dose of chrysotile can malignantly transform Met-5A cells, in which microRNA-28 has inhibitory effects, by F. Zhang, X. Yuan, H. Sun, et al (Journal of Applied Toxicology, 2021).

The study

• Authors: F. Zhang, X. Yuan, H. Sun, X. Yin, Y. Gao, M. Zhang, Z. Jia, M. Yu, S. Ying, H. Xia, L. Ju, Y. Xiao, H. Tao, J. Lou, L. Zhu
• Journal: Journal of Applied Toxicology
• Published: 2021;41(11):1879-1892
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile, which is classified as a class I carcinogen by the International Agency for Research on Cancer (IARC), has extensive application in the industry and can lead to lung or other cancers. However, whether chrysotile causes malignant mesothelioma and its molecular mechanism remain debatable. Thus, this study aimed to demonstrate the mesothelioma-inducing potential of chrysotile at the mesothelial cellular level and the function of microRNA-28 in malignantly transformed mesothelial MeT-5A cells. MeT-5A cells malignantly transformed by a nontoxic dose of chrysotile were named Asb-T, and miR-28 expression was downregulated in Asb-T cells. Restoration of miR-28 expression inhibited the proliferation, migration and invasion of Asb-T cells. We verified that IMPDH is a putative target of miR-28. The expression of IMPDH was significantly higher in Asb-T MeT-5A cells than in control cells, whereas the opposite trend was observed with miR-28 overexpression. Additionally, inhibition of IMPDH had similar effects as miR-28 overexpression. After miR-28 was elevated or IMPDH was inhibited, Ras activation was reduced, and its downstream pathways (the Erk and Akt signalling pathways) were inhibited. Surprisingly, the content of miR-28 in the blood of mesothelioma patients was higher than that in control subjects. Overall, nontoxic doses of chrysotile can cause malignant transformation of MeT-5A cells. Moreover, miR-28 inhibits the proliferation, migration and invasion of Asb-T MeT-5A cells, negatively regulates the expression of IMPDH through the Ras signalling pathway and may be an important therapeutic target.

© 2021 John Wiley & Sons, Ltd.

In plain English

In this laboratory study, the authors exposed a line of normal human pleural mesothelial cells (MeT-5A) to standard UICC chrysotile asbestos at 5 micrograms per square centimetre, for 24 hours once a week, 28 times. They described this dose as nontoxic. The treated cells then formed colonies in soft agar, a sign of malignant transformation: 18.33 per 1000 cells, versus 0 for untreated cells. They also grew faster. The treated cells had less of a regulatory molecule called microRNA-28 (miR-28) and more of an enzyme called IMPDH. Adding extra miR-28, or blocking IMPDH, reduced the transformed cells' growth, migration and invasion and lowered Ras signalling activity. The authors also tested blood plasma from Southeast China: 21 mesothelioma patients, 50 people occupationally exposed to asbestos, and 50 healthy controls. miR-28 was higher in the patients than in the healthy controls. The authors concluded that a nontoxic chrysotile dose can malignantly transform these cells and that miR-28 may act as a tumour suppressor. They noted that their human sample was small.

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) cell-culture experiment on a human mesothelial cell line, plus a small comparison of a blood marker (plasma miR-28) in people with and without mesothelioma
• Who was studied: Cells: the normal human pleural mesothelial cell line MeT-5A, chrysotile-transformed (called Asb-T) and untreated. People: 121 plasma samples from Southeast China. These came from 50 healthy controls with no asbestos exposure and normal chest X-rays, 21 patients diagnosed with malignant mesothelioma (patient blood collected 2014 to 2016), and 50 people occupationally exposed to asbestos without imaging changes.
• Exposure: UICC standard chrysotile asbestos (supplied by the Association of Fiber Science and Technology, Japan). Cells were treated with 5 μg/cm2 for 24 hours once a week, 28 times in total, then cultured for 15 more weeks. Some cells were also given short-term treatment for 24, 48 and 72 hours. The asbestos-exposed people were occupationally exposed; no further exposure details are given.
• Main results:
  • Chrysotile-treated MeT-5A cells formed colonies in soft agar at 18.33 per 1000 cells, versus 0 for PBS-treated control cells (p less than 0.001).
  • Compared with control MeT-5A cells, the chrysotile-transformed cells had a significantly shorter doubling time (p less than 0.01), meaning they multiplied faster.
  • miR-28 levels were significantly lower in chrysotile-transformed cells than in control cells, and IMPDH protein was significantly higher.
  • Adding extra miR-28 (a miR-28 mimic) to transformed cells significantly lowered their viability compared with transformed cells given a control mimic (p less than 0.01). It also suppressed their migration and invasion.
  • In a test run in a different cell line (U87), miR-28-5p reduced activity of a reporter carrying the IMPDH1 binding site. The authors took this as support that IMPDH1 is a direct target of miR-28.
  • Blocking IMPDH in transformed cells had effects similar to adding miR-28 on cell growth, migration and invasion.
  • Ras activation was higher in transformed cells than in control cells and was significantly reduced after miR-28 was added or IMPDH was targeted.
  • Plasma miR-28 was higher in mesothelioma patients than in healthy controls.
  • Plasma miR-28 was slightly lower in the asbestos-exposed group than in healthy controls, but the difference was not statistically significant.
  • As a test for telling mesothelioma patients apart from others, plasma miR-28 had an area under the curve of 0.7301 (95% CI 0.60 to 0.86) against healthy controls and 0.7434 (0.61 to 0.88) against the asbestos-exposed group.
• The authors' conclusion: The authors concluded that a nontoxic dose of chrysotile can malignantly transform mesothelial cells in the laboratory. They also concluded that miR-28 could be a tumour suppressor whose reduction may be involved in pleural mesothelioma and asbestos-related cancer development.
• Limitations the authors state:
  • miR-28 levels differed between the cells and the human plasma, so the authors said MeT-5A cells may not be an equivalent stand-in for plasma from human patients.
  • The human study did not have enough subjects.
  • The patients were not followed up, so the link between miR-28 level and prognosis could not be checked.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, MeT-5A Cells, IARC, Malignant Mesothelioma, Mesothelioma, Malignant Transformation.

Related studies

• Genome-wide profiling reveals novel microRNAs in hand-spinning-specific chrysotile exposure — J. Jia, X. Guo, et al. (2019)
• Safety and activity of microRNA-loaded minicells in patients with recurrent malignant pleural mesothelioma: a first-in-man, phase 1, open-label, dose-escalation study — N. van Zandwijk, N. Pavlakis, et al. (2017)
• Inhibitory effects of anti-oxidants on apoptosis of a human polyclonal T-cell line, MT-2, induced by an asbestos, chrysotile-A — F. Hyodoh, A. Takata-Tomokuni, et al. (2005)
• Role of PARP1 on DNA damage induced by mineral silicate chrysotile in bronchial epithelial and pleural mesothelial cells — M. Zhang, H. Xia, et al. (2021)
• Extensive temporal transcriptome and microRNA analyses identify molecular mechanisms underlying mitochondrial dysfunction induced by multi-walled carbon nanotubes in human lung cells — P. Nymark, P. Wijshoff, et al. (2015)
• MicroRNA expression in lung tissues of asbestos-exposed mice: Upregulation of miR-21 and downregulation of tumor suppressor genes Pdcd4 and Reck — Y. Hiraku, J. Watanabe, et al. (2021)

Browse more research in Journal of Applied Toxicology, or return to medical research.