Hippo pathway gene mutations in malignant mesothelioma: revealed by RNA and targeted exon sequencing

Our plain-English summary of Hippo pathway gene mutations in malignant mesothelioma: revealed by RNA and targeted exon sequencing, by A. Miyanaga, M. Masuda, K. Tsuta, et al (Journal of Thoracic Oncology, 2015).

The study

• Authors: A. Miyanaga, M. Masuda, K. Tsuta, K. Kawasaki, Y. Nakamura, T. Sakuma, H. Asamura, A. Gemma, T. Yamada
• Journal: Journal of Thoracic Oncology
• Published: 2015;10(5):844-851
• Cited by: 99 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Introduction: Malignant mesothelioma (MM) is an aggressive neoplasm causatively associated with exposure to asbestos. MM is rarely responsive to conventional cytotoxic drugs, and the outcome remains dismal. It is, therefore, necessary to identify the signaling pathways that drive MM and to develop new therapeutics specifically targeting the molecules involved.

Methods: We performed comprehensive RNA sequencing of 12 MM cell lines and four clinical samples using so-called next-generation sequencers.

Results: We found 15 novel fusion transcripts including one derived from chromosomal translocation between the large tumor suppressor 1 (LATS1) and presenilin-1 (PSEN1) genes. LATS1 is one of the central players of the emerging Hippo signaling pathway. The LATS1-PSEN1 fusion gene product lacked the ability to phosphorylate yes-associated protein and to suppress the growth of a MM cell line. The wild-type LATS1 allele was undetectable in this cell line, indicating two-hit genetic inactivation of its tumor suppressor function. Using pathway-targeted exon sequencing, we further identified a total of 11 somatic mutations in four Hippo pathway genes (neurofibromatosis type 2 [NF2], LATS2, RASSF1, and SAV1) in 35% (8 of 23) of clinical samples. Nuclear staining of yes-associated protein was detected in 55% (24 of 44) of the clinical samples. Expression and/or phosphorylation of the Hippo signaling proteins, RASSF1, Merlin (NF2), LATS1, and LATS2, was frequently absent.

Conclusions: The frequent alterations of Hippo pathway molecules found in this study indicate the therapeutic feasibility of targeting this pathway in patients with MM.

In plain English

This laboratory study looked for genetic changes in malignant mesothelioma, focusing on a group of genes called the Hippo pathway, which helps regulate cell growth. It did not study asbestos exposure. The authors sequenced genes in mesothelioma cell lines and in tumor samples from patients treated in Tokyo between 1995 and 2012. RNA sequencing of 12 cell lines and paired samples from four patients found 15 new fusion genes. One, joining LATS1 and PSEN1 in the MSTO-211H cell line, produced a protein that, unlike normal LATS1, did not suppress that cell line's growth. Neither this fusion nor LATS1 mutations were found in 44 patient samples. Sequencing 40 Hippo pathway genes in tumors from 23 patients found somatic mutations in 8 of 23 (35%), in the NF2, LATS2, RASSF1 and SAV1 genes. Nuclear staining for the YAP protein was seen in 24 of 44 tumors (55%). The authors were unable to detect any link between these changes and patient characteristics or outcome. The authors concluded that the frequent Hippo pathway changes indicate that targeting this pathway in treatment may be feasible.

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 genetic study: whole-exon, RNA and Hippo-pathway-targeted exon sequencing, plus protein and cell-growth experiments, in mesothelioma cell lines and patient tumor samples
• Who was studied: 19 malignant mesothelioma cell lines. Fresh frozen tumor and normal tissue from 23 patients. Tissue sections from 44 patients with malignant mesothelioma (including the 23) who had panpleuropneumonectomy or pleural biopsy at the National Cancer Center Hospital, Tokyo, Japan, between 1995 and 2012.
• Exposure: Not studied. The article does not report asbestos or fiber exposure for the patients. It examined genetic and protein changes in tumors.
• Main results:
  • RNA sequencing of 12 cell lines and paired normal and tumor samples from four patients identified 15 novel fusion transcripts.
  • In the MSTO-211H cell line, both copies of LATS1 were inactivated, one by deletion and one by the LATS1–PSEN1 rearrangement.
  • Normal LATS1 suppressed the growth of MSTO-211H cells. The LATS1–PSEN1 fusion product lacked this growth-suppressing activity.
  • Neither LATS1 mutation nor the LATS1–PSEN1 fusion was detected in the 44 clinical samples.
  • In cell lines, protein expression was lost for RASSF1 in 89% (17 of 19), Merlin (NF2) in 68% (13 of 19), LATS1 in 28% (5 of 18) and LATS2 in 63% (12 of 19).
  • Somatic mutations in Hippo pathway genes were found in 35% (8 of 23) of patients' tumors.
  • Among the 23 patients' tumors, mutation frequencies were NF2 22% (5 of 23), LATS2 17% (4 of 23), RASSF1 4% (1 of 23) and SAV1 4% (1 of 23).
  • Nuclear staining for YAP was seen in 55% (24 of 44) of primary mesotheliomas.
  • Silencing YAP1 in the laboratory inhibited growth of mesothelioma cells.
  • The authors could not detect any demographic or prognostic significance of nuclear YAP or Hippo pathway gene mutations in patients.
• The authors' conclusion: The authors concluded that the frequent alterations of Hippo pathway molecules indicate it is feasible to target this pathway therapeutically in mesothelioma patients.
• Limitations the authors state:
  • For the whole-exon sequencing of cell lines, no matching normal samples were available, so the authors could not tell whether the alterations were somatic mutations.
  • The number of clinical samples analyzed was limited.
  • The core kinase proteins of the pathway act as tumor suppressors and cannot be considered therapeutic targets. YAP's activity is unlikely to be manipulated by small-molecule compounds.

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, Neoplasm, Translocation, Hippo Signaling Pathway, Somatic Mutation, Merlin.

Related studies

• Immunohistochemistry for NF2, LATS1/2, and YAP/TAZ Fails to Separate Benign From Malignant Mesothelial Proliferations — B.S. Sheffield, J. Lorette, et al. (2016)
• The hippo pathway provides novel insights into lung cancer and mesothelioma treatment — X.L. Liu, R. Zuo, et al. (2018)
• The Emerging Role of the Hippo Pathway in Lung Cancers: Clinical Implications — S.L. Teoh, S. Das (2017)
• LIM-domain protein AJUBA suppresses malignant mesothelioma cell proliferation via Hippo signaling cascade — I. Tanaka, H. Osada, et al. (2015)
• TAZ activation by Hippo pathway dysregulation induces cytokine gene expression and promotes mesothelial cell transformation — A. Matsushita, T. Sato, et al. (2019)
• LATS2 is a tumor suppressor gene of malignant mesothelioma — H. Murakami, T. Mizuno, et al. (2011)

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