Tsc1-Tp53 loss induces mesothelioma in mice, and evidence for this mechanism in human mesothelioma

Our plain-English summary of Tsc1-Tp53 loss induces mesothelioma in mice, and evidence for this mechanism in human mesothelioma, by Y. Guo, L.R. Chirieac, R. Bueno, et al (Oncogene, 2014).

The study

• Authors: Y. Guo, L.R. Chirieac, R. Bueno, H. Pass, W. Wu, I.A. Malinowska, D.J. Kwiatkowski
• Journal: Oncogene
• Published: 2014;33(24):3151-60
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Mesothelioma is diagnosed in ∼2500 patients in the United States every year, most often arising in the pleural space, but also occurring as primary peritoneal mesothelioma. The vast majority of patients with mesothelioma die of their disease within 3 years. We developed a new mouse model of mesothelioma by bladder or intraperitoneal injection of adenovirus Cre into mice with conditional alleles of each of Tp53 and Tsc1. Such mice began to develop malignant ascites about 6 months after injection, which was due to peritoneal mesothelioma, on the basis of tumor morphology and immunohistochemical staining. Mesothelioma cell lines were established, which showed loss of both Tsc1 and Tp53, with mammalian target of rapamycin complex (mTORC)1 activation. Treatment of mice with malignant ascites due to mesothelioma with rapamycin led to a marked reduction in ascites, extended survival and a 95-99% reduction in the mesothelioma tumor volume, in comparison with vehicle-treated mice. To see whether TSC1/TSC2 loss was a common genetic event in human mesothelioma, we examined nine human mesothelioma cell lines, and found that four of nine showed persistent activation of mTORC1, although none had loss of TSC1 or TSC2. A tissue microarray analysis of 198 human mesothelioma specimens showed that 33% of cases had reduced TSC2 expression and 60% showed activation of mTOR, indicating that mTOR activation is common in human mesothelioma, suggesting that it is a potential therapeutic target.

In plain English

This laboratory study reported a new mouse model of peritoneal mesothelioma. Adenovirus Cre was injected into the bladder or peritoneum of mice with conditional Tsc1 and Tp53 alleles. After bladder injection, Tsc1ccTp53cc mice began dying from 6 months, with median survival 10.2 months, and mesothelioma was found in 16 (73%) of 22 assessable mice; other genotypes had less early mortality (p=0.0003) and none developed ascites. After intraperitoneal injection, median survival was 8.5 months, 89% of Tsc1ccTp53cc mice died within a year, and mesothelioma was documented in 17 (85%) of 20 assessable mice. In treatment experiments ascites was first drained; mice then given rapamycin 3 mg/kg IP three times weekly for 5 weeks showed more than 95% reduction in mesothelioma volume (two mice, bladder cohort, with no ascites at necropsy) and about 98% (four mice, IP cohort), while the single vehicle-treated mouse in each cohort regained ascites and died within two weeks. Of 9 human cell lines (eight derived directly from mesothelioma; Met5A from SV40-transduced primary mesothelial cells), all expressed TSC1 and TSC2, but four, including Met5A, showed constitutive mTORC1 activation; all were sensitive to Torin1. In a tissue microarray of 198 human mesothelioma specimens, 33% had reduced TSC2 staining and 60% positive pS6 staining.

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: Experimental study: genetically engineered mouse model with drug treatment, plus immunoblotting of human cell lines and immunohistochemistry on a human tissue microarray
• Who was studied: Mice with conditional Tsc1 and/or Tp53 alleles (bladder-injected: 13 p53ww/TSC1ww, 26 p53cc/TSC1cc, 23 p53ww/TSC1cc, 22 p53cc/TSC1ww; IP-injected: 18, 27, 23 and 12 respectively); 9 human cell lines, eight derived directly from mesothelioma and Met5A from SV40-transduced primary mesothelial cells; a tissue microarray of 198 human pleural mesothelioma specimens from Brigham and Women's Hospital
• Exposure: Genetic: Cre-mediated loss of Tsc1 and Tp53 by adenovirus Cre injection (2x10^9 pfu into bladder, or 10^9 pfu intraperitoneally) at 2-3 months of age; treatment exposure was rapamycin 3 mg/kg IP three times weekly, or Torin1 in cell culture. No asbestos exposure was studied.
• Main results:
  • Bladder-injected Tsc1ccTp53cc mice began dying 6 months after injection, with median survival 10.2 months
  • Mice of the other three genotypes after bladder injection had much less early mortality (p=0.0003) and none developed ascites
  • Among bladder-injected p53cc/TSC1cc mice, 15 of 26 (58%) died and mesothelioma was found in 16 (73%) of the 22 mice in which it could be assessed; no mesothelioma occurred in the other three genotypes
  • After IP injection of adenovirus Cre, Tsc1ccTp53cc mice had median survival 8.5 months, 89% died during one year of follow-up, and mesothelioma was documented in 85% (17 of the 20 assessable mice)
  • In the bladder-injection cohort, ascites was aspirated before treatment began; the two rapamycin-treated mice had no ascites and more than 95% reduction in mesothelioma volume at necropsy, while the single vehicle-treated mouse died within two weeks
  • In the IP-injection cohort, four rapamycin-treated mice showed about 98% overall reduction in tumor volume after 5 weeks; the one vehicle-treated mouse regained weight with ascites and survived only two weeks
  • All 9 human cell lines expressed TSC1 and TSC2; 4 of 9 (H2591, H2595, H2596 and the SV40-transduced mesothelial line Met5A) showed constitutive mTORC1 activation without serum
  • All 9 cell lines were sensitive to Torin1 with IC50 below 300 nM, and 3 lines below 50 nM; 5 of 9 lines showed no NF2 expression, which did not correlate with mTORC1 or AKT activation or Torin1 sensitivity
  • In the 198-case human mesothelioma tissue microarray, 33% of cases had reduced TSC2 staining and 60% had positive pS6(S235/236) staining; the association between high pS6 and reduced TSC2 was a trend (p = 0.0867)
• The authors' conclusion: The authors concluded that loss of Tp53 and Tsc1 act as gatekeeper mutations enabling mesothelioma development in the mouse, and that although no TSC1 or TSC2 loss was found in the human cell lines, reduced TSC2 expression and mTORC1 activation in human specimens suggest frequent pathway activation and a potential therapeutic target.
• Limitations the authors state:
  • The cell line analysis involved relatively few mesothelioma cell lines, prompting the additional tissue microarray study
  • Cause of death could not be determined in many mice because necropsy was not possible
  • The lack of correlation between NF2 loss and mTORC1 activation was unexplained and the authors stated further investigation is needed

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Peritoneal Mesothelioma, Ascites, Immunohistochemistry.

Related studies

• BAP1 loss induces mitotic defects in mesothelioma cells through BRCA1-dependent and independent mechanisms — A. Singh, S. Busacca, et al. (2023)
• Loss of BAP1 expression is very rare in peritoneal and gynecologic serous adenocarcinomas and can be useful in the differential diagnosis with abdominal mesothelioma — J. Andrici, J. Jung, et al. (2016)
• BAP1 Is Altered by Copy Number Loss, Mutation, and/or Loss of Protein Expression in More Than 70% of Malignant Peritoneal Mesotheliomas — N. Leblay, F. Leprêtre, et al. (2017)
• Minimal asbestos exposure in germline BAP1 heterozygous mice is associated with deregulated inflammatory response and increased risk of mesothelioma — A. Napolitano, L. Pellegrini, et al. (2016)
• Functional Genomic Screen in Mesothelioma Reveals that Loss of Function of BRCA1-Associated Protein 1 Induces Chemoresistance to Ribonucleotide Reductase Inhibition — A. Okonska, S. Bühler, et al. (2020)
• Restored expression of the MYO18B gene suppresses orthotopic growth and the production of bloody pleural effusion by human malignant pleural mesothelioma cells in SCID mice — N. Edakuni, K. Ikuta, et al. (2006)

Browse more research in Oncogene, or return to medical research.