Mechanisms of FUS1/TUSC2 deficiency in mesothelioma and its tumorigenic transcriptional effects

Our plain-English summary of Mechanisms of FUS1/TUSC2 deficiency in mesothelioma and its tumorigenic transcriptional effects, by A.V. Ivanova, S.V. Ivanov, L. Prudkin, et al (Molecular Cancer, 2009).

The study

• Authors: A.V. Ivanova, S.V. Ivanov, L. Prudkin, D. Nonaka, Z. Liu, A. Tsao, I. Wistuba, J. Roth, H.I. Pass
• Journal: Molecular Cancer
• Published: 2009;8:91
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: FUS1/TUSC2 is a novel tumor suppressor located in the critical 3p21.3 chromosomal region frequently deleted in multiple cancers. We previously showed that Tusc2-deficient mice display a complex immuno-inflammatory phenotype with a predisposition to cancer. The goal of this study was to analyze possible involvement of TUSC2 in malignant pleural mesothelioma (MPM) - an aggressive inflammatory cancer associated with exposure to asbestos.

Methods: TUSC2 insufficiency in clinical specimens of MPM was assessed via RT-PCR (mRNA level), Representational Oligonucleotide Microarray Analysis (DNA level), and immunohistochemical evaluation (protein level). A possible link between TUSC2 expression and exposure to asbestos was studied using asbestos-treated mesothelial cells and ROS (reactive oxygen species) scavengers. Transcripional effects of TUSC2 in MPM were assessed through expression array analysis of TUSC2-transfected MPM cells.

Results: Expression of TUSC2 was downregulated in approximately 84% of MM specimens while loss of TUSC2-containing 3p21.3 region observed in approximately 36% of MPMs including stage 1 tumors. Exposure to asbestos led to a transcriptional suppression of TUSC2, which we found to be ROS-dependent. Expression array studies showed that TUSC2 activates transcription of multiple genes with tumor suppressor properties and down-regulates pro-tumorigenic genes, thus supporting its role as a tumor suppressor. In agreement with our knockout model, TUSC2 up-regulated IL-15 and also modulated more than 40 other genes (approximately 20% of total TUSC2-affected genes) associated with immune system. Among these genes, we identified CD24 and CD274, key immunoreceptors that regulate immunogenic T and B cells and play important roles in systemic autoimmune diseases. Finally, clinical significance of TUSC2 transcriptional effects was validated on the expression array data produced previously on clinical specimens of MPM. In this analysis, 42 TUSC2 targets proved to be concordantly modulated in MM serving as disease discriminators.

Conclusion: Our data support immuno-therapeutic potential of TUSC2, define its targets, and underscore its importance as a transcriptional stimulator of anti-tumorigenic pathways.

In plain English

This laboratory study examined TUSC2 (also called FUS1), which the authors describe as a tumor suppressor gene, in malignant pleural mesothelioma. TUSC2 messenger RNA was lower in 25 of 30 tumors than in matched normal tissue (described as unaffected peritoneum). In tissue samples from 105 mesothelioma cases, 89 had TUSC2 protein staining scores below 220, a level never seen in normal mesothelial tissue. No link with tumor stage was seen. Earlier DNA data on 22 tumors showed loss of the chromosome region containing TUSC2 in 8, including one of five stage 1 patients. When cultured mesothelial cells were exposed to crocidolite asbestos for 24 hours, TUSC2 levels fell. Pretreating the cells with catalase or superoxide dismutase, which remove reactive oxygen species, prevented this fall. Forcing TUSC2 expression in a mesothelioma cell line changed 195 genes at least twofold, including immune-related genes such as IL15. The authors concluded that their data provide the first evidence that TUSC2 plays an essential tumor suppressive role in asbestos-induced 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 analysis of mesothelioma tissue specimens (RT-PCR, immunohistochemistry, DNA copy number data) with cell culture experiments (asbestos exposure, reactive oxygen species scavengers, and gene expression microarray of TUSC2-transfected mesothelioma cells)
• Who was studied: Matched tumor and control specimens from 30 MPM patients for RNA analysis. Tissue microarrays with 105 MPM cases (30 from Karmanos Cancer Institute, Detroit; 75 from MD Anderson Cancer Center, Houston). Previously produced DNA copy number data on 22 MPM specimens. Previously produced expression array data on 30 MPM and 7 control specimens. Cultured cells: the mesothelial cell line Met5A, primary mesothelial cells, the H2595 mesothelioma cell line and four additional MPM cell lines.
• Exposure: In cell culture, crocidolite asbestos at 2.5 micrograms per square centimetre for 24 hours, with or without 30-minute pretreatment with catalase (500 U/ml) or superoxide dismutase (250 U/ml). Also forced expression (transfection) of the TUSC2 gene in mesothelioma cells.
• Main results:
  • TUSC2 mRNA was down-regulated in 25 of 30 MPM tumors compared with matched normal tissue
  • TUSC2 protein: 89 of 105 MPM tumors, including stage I, had a staining score below 220, a score never seen in normal mesothelial tissue
  • The difference in TUSC2 protein between epithelial and sarcomatoid/biphasic tumors was not statistically significant (p = 0.09)
  • The TUSC2-containing 3p21.3 chromosome region was under-represented in 8 of 22 MPM samples, including 1 of 5 stage 1 patients
  • After 24 hours of asbestos exposure, TUSC2 expression decreased in both types of mesothelial cells tested
  • Pretreatment with catalase or superoxide dismutase prevented the asbestos-induced TUSC2 decrease
  • In H2595 mesothelioma cells, forced TUSC2 expression changed 228 probes corresponding to 195 genes at least 2-fold compared with empty-vector cells
  • 21 genes with anti-tumorigenic properties (including BCL2L11, FOXN3, GAS1, NME5) were up-regulated by TUSC2 in H2595 cells
  • IL15 was 2-fold up-regulated by TUSC2 in H2595 cells
  • Compared with earlier clinical array data, more than 21 genes down-regulated by TUSC2 in H2595 cells were up-regulated in MPM specimens, and 24 genes up-regulated by TUSC2 were suppressed in MPM
• The authors' conclusion: The authors concluded that their data provide the first evidence that the TUSC2 protein plays an essential tumor suppressive role in asbestos-induced mesothelioma, and that restoring TUSC2 activity in MPM patients may have therapeutic implications.
• Limitations the authors state:
  • Mutational analysis is still needed to determine whether TUSC2 is a true transcriptional regulator
  • Loss of the TUSC2 chromosome region (in about 36% of tumors) does not explain the reduced mRNA seen in up to about 83% of tumors
  • The function of many of the identified immune-related target genes is not yet known

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Pleural Mesothelioma, Mesothelial Cells, Reactive Oxygen Species (ROS).

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