Tissue transglutaminase (TG2) enables survival of human malignant pleural mesothelioma cells in hypoxia

Our plain-English summary of Tissue transglutaminase (TG2) enables survival of human malignant pleural mesothelioma cells in hypoxia, by S. Zonca, G. Pinton, Z. Wang, et al (Cell Death & Disease, 2017).

The study

• Authors: S. Zonca, G. Pinton, Z. Wang, M.F. Soluri, D. Tavian, M. Griffin, D. Sblattero, L. Moro
• Journal: Cell Death & Disease
• Published: 2017;8(2):e2592
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant pleural mesothelioma (MPM) is an aggressive tumor linked to environmental/occupational exposure to asbestos, characterized by the presence of significant areas of hypoxia. In this study, we firstly explored the expression and the role of transglutaminase 2 (TG2) in MPM cell adaptation to hypoxia. We demonstrated that cells derived from biphasic MPM express the full-length TG2 variant at higher levels than cells derived from epithelioid MPM and normal mesothelium. We observed a significant induction of TG2 expression and activity when cells from biphasic MPM were grown as a monolayer in chronic hypoxia or packed in spheroids, where the presence of a hypoxic core was demonstrated. We described that the hypoxic induction of TG2 was HIF-2 dependent. Importantly, TGM2-v1 silencing caused a marked and significant reduction of MPM cell viability in hypoxic conditions when compared with normoxia. Notably, a TG2-selective irreversible inhibitor that reacts with the intracellular active form of TG2, but not a non-cell-permeable inhibitor, significantly compromised cell viability in MPM spheroids. Understanding the expression and function of TG2 in the adaptation to the hypoxic environment may provide useful information for novel promising therapeutic options for MPM treatment.

In plain English

This laboratory study used cells, not patients or asbestos exposure. The authors studied the enzyme TG2 in normal mesothelial cells (MET5A) and two malignant pleural mesothelioma cell lines, REN (epithelioid) and MSTO-211H (biphasic). Compared with the normal cells, the full-length TG2 message was 9-fold higher in REN cells and 22-fold higher in MSTO-211H cells. When MSTO-211H cells were grown at 1% oxygen (hypoxia), TG2 levels and activity rose, and the rise in TG2 expression depended on a protein called HIF-2alpha. Blocking TG2 production significantly reduced cell survival in low oxygen but had only a moderate effect at normal oxygen. In packed cell clusters (spheroids), blocking TG2 production, or using a TG2 inhibitor that enters cells (1-155), reduced cell survival. An inhibitor that cannot enter cells (R281) had no evident effect at 25 μM. At 250 μM it abolished the measured TG2 transamidating activity but still did not compromise cell survival. The authors concluded that TG2 has a role in these cells' adaptation to low oxygen and that inhibiting it may offer a new treatment avenue. They said further studies are needed.

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) study of human cell lines, grown as flat cultures and as 3D multicellular spheroids
• Who was studied: Three human cell lines: MET5A (derived from mesothelium), REN (epithelioid malignant pleural mesothelioma) and MSTO-211H (biphasic malignant pleural mesothelioma). No patients or animals were studied.
• Exposure: No asbestos exposure was studied. Cells were grown at 1% oxygen (hypoxia) or normal oxygen. TG2 was silenced with siRNA, and spheroids were treated with 25 μM of the cell-permeable TG2 inhibitor 1-155 or the non-cell-permeable inhibitor R281.
• Main results:
  • Compared with normal mesothelial MET5A cells, full-length TG2 (TGM2-v1) transcripts were increased 9-fold in epithelioid-derived REN cells and 22-fold in biphasic-derived MSTO-211H cells.
  • In MSTO-211H cells, silencing TG2 significantly reduced cell viability in hypoxia, with only a moderate effect at normal oxygen.
  • In MSTO-211H cells, TG2 was significantly increased at mRNA and protein level after 48 hours in hypoxia compared with normoxia.
  • The hypoxia-driven increase in TG2 (TGM2-v1) expression in MSTO-211H cells depended on HIF-2alpha.
  • In MSTO-211H spheroids, TG2 expression and transamidating activity were higher at 72 hours than at 24 hours.
  • In MSTO-211H spheroids, silencing TG2 significantly reduced cell viability. The cell-permeable inhibitor 1-155 (25 μM) reproduced these results. The non-cell-permeable inhibitor R281 at 25 μM had no evident effect.
  • A ten times higher dose of R281 (250 μM) abolished the measured transamidating activity in spheroids, but spheroid viability was not compromised.
• The authors' conclusion: The authors concluded that TG2 expression and function play a role in the adaptation of mesothelioma cells to hypoxia, and that inhibiting TG2 may provide a novel therapeutic avenue for this disease.
• Limitations the authors state:
  • The authors stated that how TG2 regulates cell death requires additional studies.
  • The authors stated that they cannot fully rule out a role for intracellular TG2 transamidating activity. They measured this activity with BAP and have no direct evidence that BAP enters cells in their model.

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: Pleural Mesothelioma, Hypoxia, Occupational Exposure, Biphasic Mesothelioma, Epithelioid, Mesothelium.

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