Downregulation of microRNA-34 induces cell proliferation and invasion of human mesothelial cells

Our plain-English summary of Downregulation of microRNA-34 induces cell proliferation and invasion of human mesothelial cells, by N. Tanaka, S. Toyooka, J. Soh, et al (Oncology Reports, 2013).

The study

• Authors: N. Tanaka, S. Toyooka, J. Soh, K. Tsukuda, K. Shien, M. Furukawa, T. Muraoka, Y. Maki, T. Ueno, H. Yamamoto, H. Asano, T. Otsuki, S. Miyoshi
• Journal: Oncology Reports
• Published: 2013;29(6):2169-74
• Cited by: 41 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Malignant mesothelioma (MM) is an aggressive tumor with a dismal prognosis, and the molecular alterations involved in this disease remain unknown. We previously reported that microRNA-34s (miR-34s) are methylated and downregulated in MM and may play an important role in the carcinogenesis of MM. In this study, we downregulated miR-34s in human mesothelial cells to investigate the cellular effect of miR-34 knockdown. For the cell study, we used LP-9, a human mesothelial cell line, and three human primary-cultured mesothelial cell lines. RNA-based miR-34a, -34b and -34c inhibitors were transfected into these cells, and their effects on proliferation and invasion were evaluated. A scramble RNA oligonucleotide was used as a control. The protein expression status was estimated using western blotting. After miR-34 inhibitor transfection, miR-34a, -34b and -34c were downregulated in all the examined mesothelial cell lines. miR-34 inhibitor transfection significantly increased cell proliferation in all of the mesothelial cell lines, compared with the scramble control. The invasive ability also increased in the miR-34 inhibitor transfectants, compared with the scramble control, in the LP-9 cell line. Western blotting confirmed the upregulation of c-MET, phospho-c-MET, and bcl-2 proteins in LP-9 cells after miR-34 inhibitor transfection. In conclusion, our study showed that the downregulation of miR-34s induced an oncogenic phenotype in non-malignant mesothelial cells. The present study, together with the results of our previous report, strongly suggest that miR-34s play an important role in the early carcinogenic process involved in the transformation of human mesothelial cells to MM.

In plain English

This Japanese laboratory study blocked microRNA-34 molecules (miR-34a, -34b and -34c), which the authors had earlier reported as reduced in malignant mesothelioma, in non-cancerous human mesothelial cells. No asbestos was used. The authors treated one purchased peritoneal mesothelial cell line (LP-9) and three cultures grown from pleural fluid of cancer-free patients with miR-34 inhibitors or a scrambled control. The inhibitors lowered miR-34 levels and increased cell viability in all four cell types. In LP-9 cells, colony numbers, migration, invasion and the proteins c-MET, phosphorylated c-MET and Bcl-2 increased. In LP-9 cells, the growth marker Ki-67 rose significantly with the miR-34a and miR-34c inhibitors, but not significantly with the miR-34b inhibitor (P=0.09). LP-9 cells did not grow in soft agar, a test of cancer-like growth, with either treatment. The patient-derived cells did not gain the ability to migrate or invade. The authors concluded that their results strongly suggest miR-34s play an important role in early progression toward malignant mesothelioma. They took the lack of soft-agar growth to suggest that miR-34 inhibition alone was not enough and that other molecular alterations are required.

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
• Who was studied: Non-cancerous human mesothelial cells: the LP-9 peritoneal mesothelial cell line (purchased from the Coriell Cell Repository) and three primary-cultured mesothelial cell lines established from pleural effusions of cancer-free patients at Okayama University Hospital, Japan
• Exposure: No asbestos exposure was studied. Cells were treated with laboratory inhibitors of miR-34a, miR-34b and miR-34c and compared with cells given a scramble control RNA.
• Main results:
  • In all cells, compared with the scramble control, the inhibitors reduced miR-34 levels by 80-89% (miR-34a), 45-73% (miR-34b) and 68-70% (miR-34c)
  • In all four cell types, cell viability increased compared with the scramble control: 1.2- to 1.4-fold for miR-34a, 1.2- to 1.6-fold for miR-34b, 1.4- to 1.8-fold for miR-34c inhibitors
  • In LP-9 cells, the number of colonies increased significantly with the miR-34 inhibitors compared with the scramble control
  • In LP-9 cells, Ki-67-stained cells increased significantly with the miR-34a and miR-34c inhibitors (P<0.01 each) compared with control. With the miR-34b inhibitor there was only a tendency to increase (P=0.09).
  • LP-9 cells treated with either the scramble control or the miR-34 inhibitors did not grow in soft agar (no anchorage-independent growth)
  • In LP-9 cells, migration and invasion increased significantly with all miR-34 inhibitors (P<0.01) compared with control. The patient-derived cells did not migrate or invade, and did not gain these features after treatment.
  • In LP-9 cells, the inhibitors produced a slight 2.0-4.6% decrease in the G0-G1 cell fraction (data not shown)
  • In LP-9 cells, total c-MET, phosphorylated c-MET and Bcl-2 protein levels were upregulated after miR-34 inhibitor treatment
• The authors' conclusion: The authors concluded that, together with their previous report, the findings strongly suggest that miR-34s play an important role in the early carcinogenic progression of human mesothelial cells to malignant mesothelioma
• Limitations the authors state:
  • miR-34 inhibition did not produce anchorage-independent growth. The authors took this to suggest that miR-34 inhibition alone was not enough for apparent malignant transformation and that other molecular alterations are required for the carcinogenic process.
  • The authors suggested that the miR-34b inhibitor worked less efficiently than the miR-34a and miR-34c inhibitors, which may explain the non-significant Ki-67 result

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Mesothelioma, Prognosis, Carcinogenesis, Carcinogenic.

Related studies

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• Chronic exposure to carbon nanotubes induces invasion of human mesothelial cells through matrix metalloproteinase-2 — W. Lohcharoenkal, L. Wang, et al. (2013)
• The proliferative effects of asbestos-exposed peripheral blood mononuclear cells on mesothelial cells — Y. Maki, Y. Nishimura, et al. (2016)
• PIM1 knockdown inhibits cell proliferation and invasion of mesothelioma cells — A.S. Mawas, V.J. Amatya, et al. (2017)
• Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy — E. Varin, C. Denoyelle, et al. (2010)
• Strong anti-tumor effect of NVP-AUY922, a novel Hsp90 inhibitor, on non-small cell lung cancer — T. Ueno, K. Tsukuda, et al. (2012)

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