TGF-β synergizes with defects in the Hippo pathway to stimulate human malignant mesothelioma growth

Our plain-English summary of TGF-β synergizes with defects in the Hippo pathway to stimulate human malignant mesothelioma growth, by M. Fujii, T. Toyoda, H. Nakanishi, et al (The Journal of Experimental Medicine, 2012).

The study

• Authors: M. Fujii, T. Toyoda, H. Nakanishi, Y. Yatabe, A. Sato, Y. Matsudaira, H. Ito, H. Murakami, Y. Kondo, E. Kondo, T. Hida, T. Tsujimura, H. Osada, Y. Sekido
• Journal: The Journal of Experimental Medicine
• Published: 2012;209(3):479-94
• Cited by: 191 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is an incurable malignancy that is caused by exposure to asbestos and is accompanied by severe fibrosis. Because MM is usually diagnosed at an advanced stage and clinical identification of early lesions is difficult, its molecular pathogenesis has not been completely elucidated. Nearly 75% of MM cases have inactivating mutations in the NF2 (neurofibromatosis type 2; Merlin) gene or in downstream signaling molecules of the Hippo signaling cascade, which negatively regulates the transcription factor Yes-associated protein (YAP). In this study, we demonstrate a functional interaction between the Hippo and TGF-β pathways in regulating connective tissue growth factor (CTGF). Expression of CTGF in MM cells was induced by the formation of a YAP-TEAD4-Smad3-p300 complex on the CTGF promoter. Knocking down CTGF expression in MM cells prolonged the survival of xenografted mice, and a significant association was seen between CTGF expression and extracellular matrix deposition in MM xenografts and in patient tissue specimens. We further suggest that CTGF may influence the malignancy of mesothelioma because of the different histological expression patterns observed in human MM tissues. These data suggest that CTGF is an important modulator of MM growth and pathology and represents a novel therapeutic target for this disease.

In plain English

This laboratory study looked at how two cell-signaling systems work together in malignant mesothelioma cells. One is the TGF-β pathway. The other is the Hippo pathway, which is often damaged in mesothelioma through genes such as NF2 and LATS2. Asbestos exposure itself was not studied. The authors used human mesothelioma cell lines, mice with tumor cells implanted in the chest cavity, and tumor tissue from 24 patients. In all patient samples, staining showed active TGF-β signaling in cell nuclei, whatever the tumor subtype. In cells, the proteins YAP, TEAD4, Smad3 and p300 formed a complex on the CTGF gene that drove its expression. Silencing CTGF with two different shRNA constructs reduced NCI-H290 cell growth to a mean of 77.2% and 84% of control growth. In mice, the TGF-β blocker SD-208, or lowering CTGF, prolonged survival. The text gives no p-values for these survival results. In patient tissue, strong CTGF was seen mainly in sarcomatoid tumors. The authors concluded that the complex controlling CTGF is a novel 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 combining experiments on human malignant mesothelioma cell lines, mouse xenograft experiments (tumor cells injected into the chest cavity of nude mice), and immunohistochemical staining of patient tumor tissue
• Who was studied: Human malignant mesothelioma cell lines (including NCI-H290, Y-MESO-27, MSTO-211H, NCI-H2052) and the nonmalignant mesothelial cell line MeT-5A; female athymic nude mice (n = 8 per experiment for CTGF knockdown); tumor tissue from 24 patients classified by subtype (epithelioid, biphasic, sarcomatoid) at Aichi Cancer Center, Japan
• Exposure: No asbestos exposure was studied. The experiments examined TGF-β signaling: TGF-β treatment, and the TGF-β type I receptor kinase inhibitor SD-208 given to mice at 60 mg/kg by oral gavage. They also used cell lines with Hippo-pathway defects (NF2 deleted in NCI-H290, LATS2 deleted in Y-MESO-27) and genetic knockdown of YAP and CTGF.
• Main results:
  • Nuclear staining for p-Smad2, a sign of active TGF-β signaling, was seen in all patient mesothelioma tissue specimens, regardless of histological subtype.
  • In TGF-β-treated MeT-5A and Y-MESO-27 cells, 42% of the commonly up-regulated genes (16 of 38) were ECM-related (connective tissue) proteins.
  • A complex of YAP, TEAD4, Smad3 and p300 formed on the CTGF gene promoter, and the authors reported this was crucial for CTGF expression in mesothelioma cells.
  • Knocking down CTGF with two different CTGF-targeting shRNA constructs reduced NCI-H290 cell growth to a mean of 77.2% (shCTGF#1) and 84% (shCTGF#2) of the nontarget control.
  • In nude mice with NCI-H290 tumors in the chest cavity, 60 mg/kg SD-208 lowered p-Smad2 in the tumors and prolonged survival. No p-value is given in the text.
  • Mice implanted with NCI-H290 cells in which CTGF was knocked down survived longer (n = 8). No p-value is given in the text.
  • In the 24 patient tissues, CTGF expression in mesothelioma cells was mainly seen in sarcomatoid-type tissues.
  • The authors reported a strong association between CTGF expression in mesothelioma cells and the amount of surrounding stroma. No statistical test for this association is reported in the text.
• The authors' conclusion: The authors concluded that CTGF expression was controlled by the YAP-TEAD4-Smad3-p300 complex in the nucleus of mesothelioma cells, which they identified as a novel therapeutic target in mesothelioma.
• Limitations the authors state:
  • The authors could not detect the YAP-Smad3 binding at natural (endogenous) levels in mesothelioma cells.
  • Some samples did not fit the YAP-CTGF relationship: Y-MESO-9 cells and some epithelioid patient tissues had high nuclear YAP but low CTGF. The authors suggested other, undiscovered mechanisms may be involved.
  • The authors stated that how CTGF exerts its effects has not yet been clarified.

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, Fibrosis, Merlin, Deposition, Mesothelioma, Pathology.

Related studies

• Convergent signaling in the regulation of connective tissue growth factor in malignant mesothelioma: TGFβ signaling and defects in the Hippo signaling cascade — M. Fujii, H. Nakanishi, et al. (2012)
• TAZ activation by Hippo pathway dysregulation induces cytokine gene expression and promotes mesothelial cell transformation — A. Matsushita, T. Sato, et al. (2019)
• LIM-domain protein AJUBA suppresses malignant mesothelioma cell proliferation via Hippo signaling cascade — I. Tanaka, H. Osada, et al. (2015)
• Transforming growth factor-β-induced protein (TGFBI) suppresses mesothelioma progression through the Akt/mTOR pathway — G. Wen, M. Hong, et al. (2011)
• Hippo pathway gene mutations in malignant mesothelioma: revealed by RNA and targeted exon sequencing — A. Miyanaga, M. Masuda, et al. (2015)
• Fibroblast growth factor receptor inhibition is active against mesothelioma and synergizes with radio- and chemotherapy — K. Schelch, M.A. Hoda, et al. (2014)

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