P53-regulated miR-320a targets PDL1 and is downregulated in malignant mesothelioma

Our plain-English summary of P53-regulated miR-320a targets PDL1 and is downregulated in malignant mesothelioma, by C. Costa, P. Indovina, E. Mattioli, et al (Cell Death & Disease, 2020).

The study

• Authors: C. Costa, P. Indovina, E. Mattioli, I.M. Forte, C.A. Iannuzzi, L. Luzzi, C. Bellan, S. De Summa, E. Bucci, D. Di Marzo, M. De Feo, L. Mutti, F. Pentimalli, A. Giordano
• Journal: Cell Death & Disease
• Published: 2020;11(9):748
• Cited by: 35 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive cancer, related to asbestos exposure, which has a dismal prognosis. MPM diagnosis is late and often challenging, suggesting the need to identify more reliable molecular biomarkers. Here, we set out to identify differentially expressed miRNAs in epithelioid, biphasic, and sarcomatoid MPMs versus normal mesothelium and explored specific miRNA contribution to mesothelial tumorigenesis. We screened an LNA™-based miRNA-microrray with 14 formalin-fixed paraffin-embedded (FFPE) MPMs and 6 normal controls. Through real-time qRT-PCR we extended the analysis of a miRNA subset and further investigated miR-320a role through state-of-the-art techniques. We identified 16 upregulated and 32 downregulated miRNAs in MPMs versus normal tissue, including the previously identified potential biomarkers miR-21, miR-126, miR-143, miR-145. We showed in an extended series that miR-145, miR-10b, and miR-320a levels can discriminate tumor versus controls with high specificity and sensitivity. We focused on miR-320a because other family members were found downregulated in MPMs. However, stable miR-320a ectopic expression induced higher proliferation and migration ability, whereas miR-320a silencing reduced these processes, not supporting a classic tumor-suppressor role in MPM cell lines. Among putative targets, we found that miR-320a binds the 3'-UTR of the immune inhibitory receptor ligand PDL1 and, consistently, miR-320a modulation affects PDL1 levels in MPM cells. Finally, we showed that p53 over-expression induces the upregulation of miR-320a, along with miR-200a and miR-34a, both known to target PDL1, and reduces PDL1 levels in MPM cells. Our data suggest that PDL1 expression might be due to a defective p53-regulated miRNA response, which could contribute to MPM immune evasion or tumorigenesis through tumor-intrinsic roles.

In plain English

This laboratory study looked at microRNAs, small molecules that control genes, in malignant pleural mesothelioma. Archived tumor samples from a university hospital in Siena, Italy, were compared with normal pleura removed during heart bypass surgery. In 14 tumors (6 epithelioid, 4 sarcomatoid, 4 biphasic) and 6 normal samples, 48 microRNAs differed: 16 were higher and 32 lower in tumors. In an extended series that added 18 tumors, three of them (miR-145, miR-10b and miR-320a) were confirmed lower in tumors. Each separated tumor from normal tissue with sensitivity and specificity over 80%. In mesothelioma cell lines, raising miR-320a increased cell growth, and lowering it reduced growth. miR-320a attached to the messenger RNA of PDL1, a protein linked to tumors evading the immune system, and lowered PDL1 messenger RNA and protein levels. Making the cells produce more p53 raised miR-320a and lowered PDL1. The authors concluded that PDL1 levels might reflect a faulty p53-controlled microRNA response. The article does not report patients' asbestos exposure. The authors said the cell-line findings need testing in other models.

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: microarray profiling of microRNAs in archived tumor and normal tissue, checked by qRT-PCR, followed by experiments in mesothelioma cell lines
• Who was studied: 32 formalin-fixed paraffin-embedded malignant pleural mesothelioma specimens from the Azienda Ospedaliera Universitaria Senese archives. 14 were used for the microarray (6 epithelioid, 4 sarcomatoid, 4 biphasic) and 18 for the extended qRT-PCR series. Controls were 6 normal mediastinal pleura samples taken during aortocoronary-bypass surgery from individuals of the same age range. Mesothelioma cell lines MSTO-211H, NCI-H28, NCI-H2052 and IST-MES2 were also used, plus HEK-293 cells. Dates of collection are not given.
• Exposure: Asbestos exposure was not studied, and the article gives no exposure information for the patients. The study compared tumor with normal tissue. In cell lines, the authors raised or lowered miR-320a levels and over-expressed p53.
• Main results:
  • In the 14 tumors compared with the 6 normal samples, 48 microRNAs were differentially expressed: 16 higher and 32 lower in mesothelioma.
  • By qRT-PCR, miR-145, miR-10b and miR-320a differed between tumors and controls (Mann–Whitney p values 0.0020, 0.0233 and 0.0026 respectively). Lower levels of all three in tumors were confirmed in the extended series.
  • In ROC analysis separating tumor from control samples, the area under the curve was 0.8818 (95% CI 0.7455 to 1.018) for miR-145, 0.8629 (95% CI 0.6643 to 1.061) for miR-10b and 0.9375 (95% CI 0.8574 to 1.018) for miR-320a. Sensitivity and specificity were over 80% for all three.
  • miR-320a was lower in the mesothelioma specimens, particularly in the biphasic and sarcomatoid types, which the authors describe as the most aggressive.
  • In IST-MES2 and MSTO-211H cell lines, stable over-expression of miR-320a increased the proliferation rate. Silencing miR-320a in MSTO-211H decreased proliferation. Increased migration in over-expressing clones reached statistical significance only for clone cl9.
  • miR-320a acted directly on the PDL1 gene's 3′-UTR, a control region of the gene's messenger RNA, in a luciferase reporter test in HEK-293 cells. Adding miR-320a lowered PDL1 messenger RNA and protein in IST-MES2, NCI-H28 and MSTO-211H cells, and silencing it raised PDL1.
  • In all mesothelioma cell lines tested, over-expressing p53 raised miR-320a (and also miR-34a and miR-200a) and lowered PDL1 messenger RNA and protein. Blocking miR-320a or miR-200a binding raised PDL1; blocking miR-34a did not.
• The authors' conclusion: The authors concluded that PDL1 expression might be due to a defective p53-regulated microRNA response, which could contribute to mesothelioma immune evasion or tumor development. In their view, miR-320a might serve as a diagnostic or prognostic biomarker but would not be a feasible therapeutic target.
• Limitations the authors state:
  • The effects of miR-320a on cell behavior were seen in two cell lines (IST-MES2 and MSTO-211H). They still need to be tested in other mesothelioma cell lines and models to see whether they apply generally.
  • Larger, uniform cohorts that include normal tissue, mesotheliomas and benign pleural conditions are needed before miR-320 family members can be considered clinically useful biomarkers.
  • It is not established whether the lower miR-320a in tumors results from inactivation of the p53 pathway (a passenger rather than a driver change).

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Pleural Mesothelioma, Asbestos Exposure, Prognosis, Biomarker, Epithelioid, Biphasic Mesothelioma, Sarcomatoid.

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