MicroRNA-31 Regulates Chemosensitivity in Malignant Pleural Mesothelioma

Our plain-English summary of MicroRNA-31 Regulates Chemosensitivity in Malignant Pleural Mesothelioma, by H.L. Moody, M.J. Lind, S.G. Maher (Molecular Therapy. Nucleic Acids, 2017).

The study

• Authors: H.L. Moody, M.J. Lind, S.G. Maher
• Journal: Molecular Therapy. Nucleic Acids
• Published: 2017;8:317-329
• Cited by: 40 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is associated with an extremely poor prognosis, and most patients initially are or rapidly become unresponsive to platinum-based chemotherapy. MicroRNA-31 (miR-31) is encoded on a genomic fragile site, 9p21.3, which is reportedly lost in many MPM tumors. Based on previous findings in a variety of other cancers, we hypothesized that miR-31 alters chemosensitivity and that miR-31 reconstitution may influence sensitivity to chemotherapeutics in MPM. Reintroduction of miR-31 into miR-31 null NCI-H2452 cells significantly enhanced clonogenic resistance to cisplatin and carboplatin. Although miR-31 re-expression increased chemoresistance, paradoxically, a higher relative intracellular accumulation of platinum was detected. This was coupled to a significantly decreased intranuclear concentration of platinum. Linked with a downregulation of OCT1, a bipotential transcriptional regulator with multiple miR-31 target binding sites, we subsequently identified an indirect miR-31-mediated upregulation of ABCB9, a transporter associated with drug accumulation in lysosomes, and increased uptake of platinum to lysosomes. However, when overexpressed directly, ABCB9 promoted cellular chemosensitivity, suggesting that miR-31 promotes chemoresistance largely via an ABCB9-independent mechanism. Overall, our data suggest that miR-31 loss from MPM tumors promotes chemosensitivity and may be prognostically beneficial in the context of therapeutic sensitivity.

Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

In plain English

This laboratory study used two cell lines from the epithelioid type of malignant pleural mesothelioma. No patients and no asbestos exposure were studied. The authors added microRNA-31 (miR-31), a small gene-regulating molecule, to a line lacking it (NCI-H2452) and blocked it in a line that makes it (P31). They treated the cells with the platinum chemotherapy drugs cisplatin and carboplatin. NCI-H2452 cells given miR-31 survived the drugs better: colony survival rose by 9.6 ± 1.6 with cisplatin and 19.3 ± 0.2 with carboplatin. These cells held more platinum overall but about 50% less in the nucleus, where the drug damages DNA, and they showed less DNA damage. miR-31 also increased a transporter protein, ABCB9. Yet adding ABCB9 alone made cells more sensitive to cisplatin (surviving fraction 64 ± 19 versus 93 ± 9; p = 0.0516, called near significance). The authors concluded that miR-31 promotes chemotherapy resistance largely through a mechanism independent of ABCB9, and that its loss from tumors may make them more chemotherapy-sensitive. They noted the work was done only in cultured cells.

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 in cultured mesothelioma cell lines grown in 2D culture, with genetic manipulation of miR-31 and ABCB9
• Who was studied: Two malignant pleural mesothelioma cell lines of the epithelioid subtype: NCI-H2452, which lacks miR-31, and P31, which expresses miR-31. No human participants.
• Exposure: Laboratory manipulation of miR-31: re-introduced into NCI-H2452 cells and suppressed in P31 cells. Cells were then treated with the platinum chemotherapy drugs cisplatin and carboplatin. Radiation and 5-fluorouracil were also tested. In separate experiments, the transporter ABCB9 was overexpressed in NCI-H2452 cells. Asbestos exposure was not studied.
• Main results:
  • In NCI-H2452 cells, re-introducing miR-31 significantly increased the surviving fraction after cisplatin treatment, by 9.6 ± 1.6.
  • In NCI-H2452 cells, re-introducing miR-31 increased the surviving fraction after carboplatin treatment, by 19.3 ± 0.2.
  • In P31 cells, suppressing miR-31 was reported as making the cells more sensitive to cisplatin, with an 8.4 ± 0.2 significant change in surviving fraction.
  • Without chemotherapy, changing miR-31 levels did not significantly change how fast the cells multiplied.
  • Sensitivity to radiation was not changed by miR-31 status.
  • A marker of DNA damage (gamma-H2A.X) was lower in NCI-H2452 cells given miR-31 and higher in P31 cells with miR-31 suppressed, after both cisplatin and carboplatin.
  • Total platinum inside NCI-H2452 cells given miR-31 was significantly higher than in control cells (p = 0.0112). Suppressing miR-31 in P31 cells did not change overall platinum levels.
  • Platinum in the cell nucleus fell by approximately 50% when miR-31 was re-expressed in NCI-H2452 cells (figure legend: p = 0.0028).
  • The text reports a 0.28 ± 0.07 ppm increase in platinum in the lysosomal fraction with miR-31 re-expression. The figure legend describes this as a trend that was not statistically significant.
  • No significant differences were found in the drug-efflux proteins ATP7A and ATP7B. There was a non-significant trend (p = 0.0722) toward more of the drug-influx protein CTR1.
  • Re-introducing miR-31 raised gene-level expression of the lysosomal transporter ABCB9 (p = 0.0251) and protein-level expression (p = 0.0325). The lysosome marker LAMP1 did not change.
  • OCT1, a protein that regulates other genes, was reduced when miR-31 was re-introduced into NCI-H2452 cells. This analysis used n = 2.
  • NCI-H2452 cells overexpressing ABCB9 alone had a surviving fraction of 64 ± 19 after cisplatin, compared with 93 ± 9 in vector control cells. The text calls this 29% more sensitive; the figure legend reports near significance (p = 0.0516).
  • When ABCB9 and miR-31 were overexpressed together, DNA damage induction was reduced. The authors took this to mean that ABCB9 does not make cells chemosensitive when miR-31 is present.
  • Levels of reactive oxygen species and glutathione did not differ significantly between control cells and miR-31-expressing cells.
• The authors' conclusion: The authors concluded that miR-31 expression promotes resistance to platinum chemotherapy in these mesothelioma cells. They proposed that this works through reduced movement of the drug into the nucleus, by a mechanism they had not yet identified. They described this mechanism as largely independent of ABCB9: ABCB9 changes alone were not sufficient to explain the resistance. They also concluded that loss of miR-31 from tumors may make them more sensitive to chemotherapy.
• Limitations the authors state:
  • The experiments used only cell lines grown in 2D laboratory culture, not living organisms.
  • The vector-driven overexpression method may limit the significance of the ABCB9 experiments.
  • ABCB9 sat in different places inside the cell when it was raised by miR-31 than when it was overexpressed directly, which may explain the different responses.
  • The authors stated that the findings would need support from a mesothelioma mouse model and from patient-derived samples.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Prognosis, Chemotherapy, Cisplatin, Carboplatin.

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