miR-1 induces growth arrest and apoptosis in malignant mesothelioma

Our plain-English summary of miR-1 induces growth arrest and apoptosis in malignant mesothelioma, by Y. Xu, M. Zheng, R.E. Merritt, et al (Chest, 2013).

The study

• Authors: Y. Xu, M. Zheng, R.E. Merritt, J.B. Shrager, H.A. Wakelee, R.A. Kratzke, C.D. Hoang
• Journal: Chest
• Published: 2013;144(5):1632-1643
• Cited by: 42 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: We investigated microRNA expression profiles of malignant pleural mesothelioma (MPM) specimens to identify novel microRNA that are potentially involved in the oncogenic transformation of human pleural cells.

Methods: microRNA microarray transcriptional profiling studies of 25 MPM primary tumors were performed. We used normal pleural tissue from an unmatched patient cohort as normal comparators. To confirm microarray data, we used real-time quantitative polymerase chain reaction. Representative cell lines H513 and H2052 were used in functional analyses of miR-1.

Results: In addition to several novel MPM-associated microRNAs, we observed that the expression level of miR-1 was significantly lower in tumors as compared with normal pleural specimens. Subsequently, pre-miR of miR-1 was introduced into MPM cell lines to overexpress this microRNA. Phenotypic changes of these altered cells were assayed. The cellular proliferation rate was significantly inhibited after overexpression of miR-1. Early and late apoptosis was increased markedly in miR-1-transfected cell lines. Taken together, these data suggested that overexpression of miR-1 induced apoptosis in these MPM cell lines, acting as a tumor suppressor. We confirmed our observations by assessing in the transduced MPM cells cell cycle-related, proapoptotic, and antiapoptotic genes, which all showed coordinated, significant changes characteristic of the apoptotic phenotype.

Conclusions: Further investigation and validation of our microRNA database of MPM may elucidate previously unrecognized molecular pathways and/or mechanisms by identifying novel microRNAs that are involved in malignant transformation. Our study has now found miR-1 to be one of these MPM-associated microRNAs, with potential pathogenic and therapeutic significance.

In plain English

This laboratory study, by researchers at Stanford University and the University of Minnesota, compared small regulatory molecules called microRNAs in 25 malignant pleural mesothelioma tumors (18 epithelial, 4 biphasic, 3 sarcomatoid) with normal parietal pleura from six different patients without cancer. The article does not report the patients' asbestos exposure. Using a chip that tested 1,145 microRNAs, the authors found 49 microRNAs higher and 65 lower in tumors than in normal pleura. One of them, miR-1, was 6.6-fold lower in tumors. A second test in four tumors confirmed the lower level. The authors then added miR-1 to two mesothelioma cell lines grown in the laboratory, H513 and H2052, raising its level more than eightfold. These cells grew less than control cells, with significant differences at days 3 and 6, and showed more signs of programmed cell death (apoptosis). Genes linked to growth arrest and cell death rose, and two genes that protect against cell death fell. The authors proposed that miR-1 may act as a tumor suppressor in mesothelioma. They noted as a limitation that the normal tissue came from unmatched patients.

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 study: microRNA microarray profiling of human tumor and normal pleural tissue, followed by experiments in two mesothelioma cell lines
• Who was studied: 25 malignant pleural mesothelioma tumor specimens from the University of Minnesota Cancer Center (18 epithelial, 4 biphasic, 3 sarcomatoid; 11 women and 14 men aged 35 to 70). Comparison tissue was normal parietal pleura from 6 unmatched patients without mesothelioma or other cancers, from the Stanford Cancer Center Tissue Bank (2 women and 4 men aged 58 to 71). Two cell lines from the National Cancer Institute were also used: H513 (epithelial) and H2052 (sarcomatoid). Collection dates are not given.
• Exposure: Asbestos exposure was not studied or reported for these patients. The experimental exposure was introducing a miR-1 precursor (pre-miR) into the H513 and H2052 mesothelioma cell lines, compared with a transfection-reagent control and a scrambled RNA control.
• Main results:
  • Using criteria of fold change greater than 2 and adjusted P value less than .05, 49 microRNAs were overexpressed and 65 underexpressed in the 25 tumors compared with the 6 normal pleura specimens.
  • On the microarray, miR-1 was 6.6-fold lower in tumors than in normal pleura (adjusted P value 1.1E-02). Related microRNAs miR-206 (12.1-fold) and miR-133b (16.7-fold) were also lower.
  • Quantitative real-time PCR in four representative tumors, compared with pooled normal pleura, confirmed that miR-1 was underexpressed in each. Reported fold changes were 11.45, 12.85, 14.36 and 2.56 lower.
  • After the precursor was introduced, miR-1 levels rose on average more than eightfold in both cell lines.
  • Growth of miR-1-transfected cells was lower than in control cells. The differences were significant at day 3 and day 6.
  • Both cell lines showed a significant increase in apoptotic cells after miR-1 transfection by the Annexin V assay (p less than .05). A second assay showed more staining for late-stage apoptosis in miR-1-transfected cells than in controls.
  • In miR-1-transfected cells, cell cycle genes p16 and p21 and proapoptotic genes p53 and BAX increased, while the antiapoptotic genes Survivin and BCL-2 decreased. All changes were reported as significant (p less than .05).
  • Computer prediction found 29 possible miR-1 target genes common to three databases. Three of these (BDNF, DDX3X and YWHAZ) were annotated as associated with apoptosis.
• The authors' conclusion: The authors concluded that mesothelioma tissues consistently express very low levels of miR-1 across histologic subtypes, and that introducing miR-1 into mesothelioma cells induced apoptosis. They proposed that miR-1 may function as a putative tumor suppressor in mesothelioma and may be worth exploring as a therapeutic strategy. They stated that further studies are needed to identify its gene targets.
• Limitations the authors state:
  • The normal comparison tissue was unmatched, nonmalignant pleura from different patients. The authors stated that patient-matched normal pleura is not feasible in this diffuse disease.
  • The sample size was too small to support robust correlations between microRNA profiles and clinical or pathologic variables.
  • The microarray could not cover all known human microRNAs (about 1,898 in miRBase release 18).
  • Whether miR-1 acts directly or indirectly on apoptosis genes was not determined.

Topics

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

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

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• Phosphatidylinositol Induces Caspase-Independent Apoptosis of Malignant Pleural Mesothelioma Cells by Accumulating AIF in the Nucleus — S. Kanemura, A. Tsuchiya, et al. (2015)
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