Targeting YAP in malignant pleural mesothelioma

Our plain-English summary of Targeting YAP in malignant pleural mesothelioma, by W.Q. Zhang, Y.Y. Dai, P.C. Hsu, et al (Journal of Cellular and Molecular Medicine, 2017).

The study

• Authors: W.Q. Zhang, Y.Y. Dai, P.C. Hsu, H. Wang, L. Cheng, Y.L. Yang, Y.C. Wang, Z.D. Xu, S. Liu, G. Chan, B. Hu, H. Li, D.M. Jablons, L. You
• Journal: Journal of Cellular and Molecular Medicine
• Published: 2017;21(11):2663-2676
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma is an aggressive cancer that is resistant to current therapy. The poor prognosis of mesothelioma has been associated with elevated Yes-associated protein (YAP) activity. In this study, we evaluated the effect of targeting YAP in mesothelioma. First, we comprehensively studied YAP activity in five mesothelioma cell lines (211H, H2052, H290, MS-1 and H2452) and one normal mesothelial cell line (LP9). We found decreased phospho-YAP to YAP protein ratio and consistently increased GTIIC reporter activity in 211H, H2052 and H290 compared to LP9. The same three cell lines (IC50 s < 1 μM) were more sensitive than LP9 (IC50 = 3.5 μM) to the YAP/TEAD inhibitor verteporfin. We also found that verteporfin significantly reduced YAP protein level, mRNA levels of YAP downstream genes and GTIIC reporter activity in the same three cell lines, indicating inhibition of YAP signaling by verteporfin. Verteporfin also impaired invasion and tumoursphere formation ability of H2052 and H290. To validate the effect of specific targeting YAP in mesothelioma cells, we down-regulated YAP by siRNA. We found siYAP significantly decreased YAP transcriptional activity and impaired invasion and tumoursphere formation ability of H2052 and H290. Furthermore, forced overexpression of YAP rescued GTIIC reporter activity and cell viability after siYAP targeting 3'UTR of YAP. Finally, we found concurrent immunohistochemistry staining of ROCK2 and YAP (P < 0.05). Inhibition of ROCK2 decreased GTIIC reporter activity in H2052 and 211H suggesting that Rho/ROCK signaling also contributed to YAP activation in mesothelioma cells. Our results indicate that YAP may be a potential therapeutic target in mesothelioma.

© 2017 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.

In plain English

This laboratory study examined a protein called YAP in mesothelioma. It did not study asbestos exposure. The authors tested five human mesothelioma cell lines and one normal mesothelial cell line, LP9. Three mesothelioma lines (211H, H2052 and H290) showed signs of higher YAP activity than LP9. They were also more sensitive to the drug verteporfin: the concentration that halved cell viability was 418.1 to 788.6 nM in these lines, compared with 3915 nM in LP9. Verteporfin, and separately silencing YAP with siRNA, lowered YAP activity and reduced invasion by H2052 and H290 cells. Both also reduced tumoursphere formation by H290 cells. In tumour samples from 60 patients, nuclear YAP staining was moderate to strong in 68.3%. ROCK2 staining went together with strong YAP staining (P less than 0.05), and blocking ROCK2 lowered YAP activity in two cell lines. YAP activation was not associated with patient survival, which the authors said may reflect the small sample size. The authors concluded that YAP may be a potential therapeutic target in mesothelioma.

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 of human cell lines (drug and gene-silencing experiments), plus immunohistochemistry staining of patient tumour samples
• Who was studied: Five human mesothelioma cell lines (211H, H2052, H2452, H290, MS-1) and one normal human mesothelial cell line (LP9). Also primary mesothelioma tumour samples from 60 patients undergoing surgery at the University of California, San Francisco, with normal pleura tissue from 7 of them as controls. Dates of sample collection are not given.
• Exposure: No asbestos or fiber exposure was studied. The cells were treated with verteporfin (a YAP/TEAD inhibitor, mainly at 1 or 3 micromolar), with siRNAs that silence YAP, with siRNAs against RhoA, ROCK1 and ROCK2, and with the Rho-kinase inhibitor GSK269962A.
• Main results:
  • In three mesothelioma cell lines (211H, H2052 and H290), the ratio of phosphorylated (inactive) YAP to total YAP was significantly lower than in the normal LP9 line, indicating higher YAP activation.
  • The verteporfin concentration that halved cell viability (IC50) was 418.1 nM in 211H, 689.3 nM in H2052 and 788.6 nM in H290 cells.
  • The verteporfin IC50 was much higher in MS-1 (2027 nM), H2452 (3485 nM) and normal LP9 cells (3915 nM).
  • Verteporfin lowered YAP-driven reporter activity in a dose-dependent way in H2052, H290 and 211H cells.
  • Verteporfin reduced the invasive ability of H2052 and H290 cells.
  • Silencing YAP with siRNA reduced invasion to 26.2% of control in H290 cells (printed as 'H90') and to 56.7% of control in H2052 cells.
  • In H290 cells, about 10 tumourspheres formed from 4000 cells treated with control siRNA, compared with 2 after YAP siRNA.
  • In H2052 cells, YAP siRNA-2 reduced reporter activity by 47.7% and cell viability by 49.7%. Forced YAP overexpression rescued these by 67.4% and 58.1%, respectively.
  • Among the 60 patient tumour samples, nuclear YAP staining was negative in 6.7%, weak in 25.0% and moderate to strong in 68.3%.
  • In the patient samples, ROCK2 staining occurred together with strong nuclear YAP staining (P less than 0.05). The authors found no significant concurrent expression of ROCK1 with YAP.
  • Silencing RhoA or ROCK2 significantly decreased YAP reporter activity in H2052 and 211H cells.
  • YAP activation in the patient samples was not associated with overall or disease-free survival.
• The authors' conclusion: The authors concluded that YAP is an oncogenic driver and may be a potential therapeutic target in mesothelioma. They also suggested that clinical trials of verteporfin may be warranted.
• Limitations the authors state:
  • The authors said the lack of association between YAP and survival may be because of the small sample size.
  • H2052 cells could not form compact tumourspheres, for reasons the authors did not know, so sphere results come from H290 only.
  • 211H cells were left out of the invasion and sphere assays because verteporfin killed many of them, which complicated interpretation.
  • The authors noted that other groups have reported off-target effects of verteporfin, which would require modifying the drug to make it more specific.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Mesothelioma, Malignant Mesothelioma, Prognosis, Mesothelioma, Mesothelial Cells, Immunohistochemistry.

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