Exosomal miR-16-5p as a target for malignant mesothelioma

Our plain-English summary of Exosomal miR-16-5p as a target for malignant mesothelioma, by P.B. Munson, E.M. Hall, N.H. Farina, et al (Scientific Reports, 2019).

The study

• Authors: P.B. Munson, E.M. Hall, N.H. Farina, H.I. Pass, A. Shukla
• Journal: Scientific Reports
• Published: 2019;9(1):11688
• Cited by: 45 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an asbestos-induced cancer arising on the mesothelial surface of organ cavities. MM is essentially incurable without a means of early diagnosis and no successful standard of care. These facts indicate a deep chasm of knowledge that needs to be filled. Our group recently delved into MM tumor biology from the perspective of exosome-contained microRNAs (miRNAs). We discovered that the most abundant miRNAs in MM cancer exosomes were tumor suppressors, particularly miR-16-5p. This observation lead us to hypothesize that MM cells preferentially secreted tumor-suppressor miRNAs via exosomes. Through separate avenues of potential therapeutic advance, we embarked on an innovative strategy to kill MM tumor cells. We employed small molecule inhibitors to block exosome secretion, thereby reducing miR-16-5p exosome loss and replenishing cellular miR-16-5p leading to reduced tumorigenic capacity and miR-16-5p target oncoproteins CCND1 and BCL2. Additionally, we force-fed MM tumor exosomes back to MM tumor cells, which led to cell death, and a reduction in the same oncoproteins. We recapitulated these results with direct transfection of miR-16-5p, confirmed that this is a cancer-cell specific effect, and elucidated a part of the miR-16-5p mechanism of exosome loading.

In plain English

This was a laboratory study of cells grown in dishes. No patients or animals were studied, and asbestos was not used in the experiments. The authors compared exosomes (tiny packets released by cells) from human pleural mesothelioma cell lines with exosomes from normal mesothelial cells. A microarray found 20 microRNAs higher and 110 lower in the cancer-cell exosomes. One microRNA, miR-16-5p, was higher in exosomes from three of the four cancer lines tested, but not from the biphasic line HP-1. Inside the cancer cells it was lower than in normal cells. Drugs that blocked exosome release raised miR-16-5p inside Hmeso cancer cells, lowered two cancer-related proteins (CCND1 and BCL2) in those cells, and increased cell death from cisplatin. Feeding cancer cells their own exosomes killed them but did not affect non-cancer LP9 mesothelial cells. Adding miR-16-5p directly gave similar results. Lowering the protein HuR reduced miR-16-5p in exosomes. The authors concluded that mesothelioma cells preferentially release miR-16-5p through exosomes in vitro. They noted that exosomes carry many other molecules, and they plan animal experiments.

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) experiments on human cell lines: microarray and qPCR of exosome microRNAs, drug inhibition of exosome release, adding exosomes back to cells, microRNA and siRNA transfection
• Who was studied: Human pleural malignant mesothelioma cell lines H2373, H2595, HP-1 and Hmeso, compared with human primary pleural mesothelial cells (HPM3) and immortalized peritoneal mesothelial cells (LP9/TERT-1)
• Exposure: No asbestos exposure was part of the experiments. Cells were treated with exosome-release inhibitors GW4869 (40 µM) or bisindolylmaleimide-I (10 µM) plus chloramidine (50 µM) for 72 hours, with or without cisplatin. Cells were also given their own exosomes, miR-16-5p mimics, or HuR siRNA.
• Main results:
  • Compared with exosomes from primary mesothelial cells, exosomes from mesothelioma cells had 20 microRNAs upregulated and 110 downregulated
  • miR-16-5p, miR-222-3p and miR-30a-5p were upregulated in exosomes from the epithelioid lines Hmeso and H2595. The sarcomatoid line H2373 showed upregulation only of miR-16-5p and miR-30a-5p, and the biphasic line HP-1 showed no upregulation.
  • Inside the mesothelioma cells, the microRNAs tested were all lower than in primary mesothelial cells HPM3
  • Blocking exosome release in Hmeso cells reduced exosomal miR-16-5p and increased miR-16-5p inside the cells
  • The B&C inhibitor combination alone caused significant cell death. GW alone did not significantly reduce cell viability.
  • Exosome inhibition increased cisplatin-induced cell death in these in vitro studies
  • Protein levels of CCND1 and BCL2 decreased in Hmeso cells after exosome release was blocked
  • Migration and invasion of Hmeso and H2373 cells were significantly reduced when exosome release was blocked
  • Mesothelioma cells given their own concentrated exosomes showed significant cell death. This was seen in the epithelioid lines Hmeso and H2595 and the sarcomatoid line H2373.
  • Cancer exosomes killed only the cancer cells that produced them and had no effect on LP9 mesothelial cells. LP9 exosomes had a somewhat growth-promoting effect on Hmeso cancer cells.
  • Adding miR-16-5p directly to Hmeso cells reduced CCND1 and BCL2 proteins and reduced viable cells, both alone and with cisplatin
  • Lowering HuR protein in Hmeso cells raised miR-16-5p inside the cells and lowered it in exosomes
• The authors' conclusion: The authors concluded that, in vitro, mesothelioma cells preferentially secrete miR-16-5p through exosomes. In their view, blocking exosome release raises miR-16-5p in the cells, lowers cancer-related proteins, and reduces the cells' tumor-forming capacity.
• Limitations the authors state:
  • Exosomes contain many molecules besides miR-16-5p and other tumor-suppressor microRNAs, and the interplay of these other molecules still needs study
  • Experiments in whole animals had not yet been done. The authors list them as future work.

Topics

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

Related studies

• Mouse serum exosomal proteomic signature in response to asbestos exposure — P. Munson, Y.W. Lam, et al. (2018)
• P53-regulated miR-320a targets PDL1 and is downregulated in malignant mesothelioma — C. Costa, P. Indovina, et al. (2020)
• Vorinostat eliminates multicellular resistance of mesothelioma 3D spheroids via restoration of Noxa expression — D. Barbone, P. Cheung, et al. (2012)
• Targeting of the Hedgehog signal transduction pathway suppresses survival of malignant pleural mesothelioma cells in vitro — M. You, J. Varona-Santos, et al. (2014)
• miR-193a-3p is a potential tumor suppressor in malignant pleural mesothelioma — M. Williams, M.B. Kirschner, et al. (2015)
• Restoring expression of miR-16: a novel approach to therapy for malignant pleural mesothelioma — G. Reid, M.E. Pel, et al. (2013)

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