The p53/mouse double minute 2 homolog complex deregulation in merlin-deficient tumours

Our plain-English summary of The p53/mouse double minute 2 homolog complex deregulation in merlin-deficient tumours, by S. Ammoun, M.C. Schmid, L. Zhou, et al (Molecular Oncology, 2015).

The study

• Authors: S. Ammoun, M.C. Schmid, L. Zhou, D.A. Hilton, M. Barczyk, C.O. Hanemann
• Journal: Molecular Oncology
• Published: 2015;9(1):236-48
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Deficiency of the tumour suppressor merlin leads to the development of schwannomas, meningiomas and ependymomas occurring spontaneously or as a part of the hereditary disease Neurofibromatosis type 2 (NF2). Merlin loss is also found in a proportion of other cancers like mesothelioma, melanoma, breast cancer and glioblastoma. The tumour suppressor/transcription factor p53 regulates proliferation, survival and differentiation and its deficiency plays a role in the development of many tumours. 53 can be negatively regulated by FAK, PI3K/AKT and MDM2 and possibly positively regulated by merlin in different cell lines. In this study we investigated the role of p53 in merlin-deficient tumours. Using our in vitro model of primary human schwannoma cells we have previously demonstrated that FAK is overexpressed/activated and localises into the nucleus of schwannoma cells increasing proliferation. AKT is strongly activated via platelet-derived growth factor (PDGF) - and insulin-like growth factor 1 (IGF1) - receptors increasing survival. Here we investigated p53 regulation and its role in proliferation and survival of human primary schwannoma cells using western blotting, immunocytochemistry, immunohistochemistry and proliferation, survival and transcription factor assays. In human primary schwannoma cells p53 was found to be downregulated while MDM2 was upregulated leading to increased cell proliferation and survival. p53 is regulated by merlin involving FAK, AKT and MDM2. Merlin reintroduction into schwannoma cells increased p53 levels and activity, and treatment with Nutlin-3, a drug which increases p53 stability by disrupting the p53/MDM2 complex, decreased tumour growth and reduced cell survival. These findings are important to dissect the mechanisms responsible for the development of merlin-deficient tumours and to identify new therapeutic targets. We suggest that Nutlin-3, possibly in combination with FAK or PI3K inhibitors, can be employed as a novel treatment for schwannoma and other merlin-deficient tumours.

Crown Copyright © 2014. Published by Elsevier B.V. All rights reserved.

In plain English

This laboratory study examined the protein p53 in cells from schwannomas, nerve-sheath tumours that lack a protein called merlin. It did not study asbestos or mesothelioma. Mesothelioma appears only in the background, as another cancer in which merlin loss is found. The authors grew primary human schwannoma cells and normal Schwann cells, using cells from at least three individuals in every experiment, and stained tissue from 5 schwannoma cases. Compared with normal Schwann cells, schwannoma cells had markedly lower p53 and strongly higher MDM2, a protein involved in breaking down p53. Putting merlin back into schwannoma cells increased p53 levels and activity. Reducing FAK, blocking AKT activity with wortmannin, or blocking protein breakdown with MG132 also increased p53. The drug Nutlin-3 raised p53, lowered markers of cell growth and survival, and reduced schwannoma cell proliferation and survival in culture. Combining merlin reintroduction with Nutlin-3 raised p53 further. The authors suggested that Nutlin-3, alone or with FAK or PI3K/AKT inhibitors, is a drug candidate for schwannoma and other merlin-deficient tumours.

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 cultured human primary cells, with immunohistochemistry on archived tumour tissue
• Who was studied: Primary human Schwann cells (merlin-positive) and primary human schwannoma cells (merlin-deficient), with at least three individuals per experiment. Archived tissue from 5 schwannoma cases came from Derriford Hospital, Plymouth, UK. Schwannoma cells from four patients were used for the p53 transcription factor assay. No asbestos-exposed people were studied.
• Exposure: No asbestos exposure was studied. The experimental treatments of cells were reintroduction of merlin by adenovirus, FAK knock-down by shRNA, the PI3K inhibitor wortmannin, the proteasome inhibitor MG132, and the p53/MDM2 complex inhibitor Nutlin-3.
• Main results:
  • Merlin-deficient schwannoma cells showed a marked reduction in p53 protein levels compared with merlin-positive normal Schwann cells.
  • MDM2 was strongly overexpressed in schwannoma cells compared with normal Schwann cells.
  • In schwannoma cells, merlin reintroduction significantly increased total p53 protein levels and p53 nuclear accumulation. It also increased p53 activity.
  • In schwannoma cells, merlin reintroduction did not lead to MDM2 degradation; MDM2 instead accumulated in the nucleoli.
  • FAK knock-down increased nuclear p53 levels in schwannoma cells.
  • Schwannoma cells treated with the proteasome inhibitor MG132 showed a 2.5 fold increase in p53 protein levels.
  • In schwannoma cells, the PI3K inhibitor wortmannin increased p53 levels while decreasing AKT phosphorylation/activity.
  • In schwannoma cells, merlin reintroduction and Nutlin-3 each increased p53 levels, and the combination increased them further.
  • In schwannoma cells, Nutlin-3 decreased cyclin D1 and survivin, increased cleaved caspase 3, and decreased cell proliferation and survival in a concentration- and time-dependent manner.
• The authors' conclusion: The authors suggested that Nutlin-3, alone or combined with PI3K/AKT or FAK inhibitors, is a good drug candidate for treating schwannoma and other merlin-deficient tumours.

Topics

Medical terms in this study, explained in our Lexicon: Merlin, Mesothelioma, Platelet-Derived Growth Factor (PDGF), Immunohistochemistry.

Related studies

• Combination of a p53-activating CP-31398 and an MDM2 or a FAK inhibitor produces growth suppressive effects in mesothelioma with wild-type p53 genotype — B. Zhong, M. Shingyoji, et al. (2020)
• Merlin deficiency predicts FAK inhibitor sensitivity: a synthetic lethal relationship — I.M. Shapiro, V.N. Kolev, et al. (2014)
• Analyses of merlin/NF2 connection to FAK inhibitor responsiveness in serous ovarian cancer — N.R. Shah, I. Tancioni, et al. (2014)
• E-cadherin expression is correlated with focal adhesion kinase inhibitor resistance in Merlin-negative malignant mesothelioma cells — T. Kato, T. Sato, et al. (2017)
• NF2 blocks Snail-mediated p53 suppression in mesothelioma — J.H. Cho, S.J. Lee, et al. (2015)
• Mdm2 protein expression is strongly associated with survival in malignant pleural mesothelioma — F.D. Mairinger, R.F. Walter, et al. (2014)

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