First somatic mutation of E2F1 in a critical DNA binding residue discovered in well-differentiated papillary mesothelioma of the peritoneum

Our plain-English summary of First somatic mutation of E2F1 in a critical DNA binding residue discovered in well-differentiated papillary mesothelioma of the peritoneum, by W. Yu, W. Chan-On, M. Teo, et al (Genome Biology, 2011).

The study

• Authors: W. Yu, W. Chan-On, M. Teo, C.K. Ong, I. Cutcutache, G.E. Allen, B. Wong, S.S. Myint, K.H. Lim, P.M. Voorhoeve, S. Rozen, K.C. Soo, P. Tan, B.T. Teh
• Journal: Genome Biology
• Published: 2011;12(9):R96
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Well differentiated papillary mesothelioma of the peritoneum (WDPMP) is a rare variant of epithelial mesothelioma of low malignancy potential, usually found in women with no history of asbestos exposure. In this study, we perform the first exome sequencing of WDPMP.

Results: WDPMP exome sequencing reveals the first somatic mutation of E2F1, R166H, to be identified in human cancer. The location is in the evolutionarily conserved DNA binding domain and computationally predicted to be mutated in the critical contact point between E2F1 and its DNA target. We show that the R166H mutation abrogates E2F1's DNA binding ability and is associated with reduced activation of E2F1 downstream target genes. Mutant E2F1 proteins are also observed in higher quantities when compared with wild-type E2F1 protein levels and the mutant protein's resistance to degradation was found to be the cause of its accumulation within mutant over-expressing cells. Cells over-expressing wild-type E2F1 show decreased proliferation compared to mutant over-expressing cells, but cell proliferation rates of mutant over-expressing cells were comparable to cells over-expressing the empty vector.

Conclusions: The R166H mutation in E2F1 is shown to have a deleterious effect on its DNA binding ability as well as increasing its stability and subsequent accumulation in R166H mutant cells. Based on the results, two compatible theories can be formed: R166H mutation appears to allow for protein over-expression while minimizing the apoptotic consequence and the R166H mutation may behave similarly to SV40 large T antigen, inhibiting tumor suppressive functions of retinoblastoma protein 1.

In plain English

This laboratory study examined the genes of one tumor: a well-differentiated papillary mesothelioma of the peritoneum (WDPMP) from a 41-year-old Chinese woman. The authors sequenced the protein-coding parts of the genome (the exome) in her tumor, her blood and a cell line grown from the tumor. They found none of the large DNA gains or losses they looked for, and they confirmed small acquired changes (somatic mutations) in three genes: E2F1, PPFIBP2 and TRAF7. The E2F1 change, called R166H, lies in the part of the protein that binds DNA. In one mesothelioma cell line, MSTO-211H, the mutant protein bound DNA less well than the normal protein. In two cell lines, it switched on two target genes less strongly, and it built up in cells because it broke down more slowly. Cells making the normal protein grew slightly slower than cells making the mutant, whose growth was comparable to control cells. The authors reported no significant effect of the mutant on growth. The authors offered two compatible theories for how the mutation might act. The article does not report the patient's asbestos history.

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 of a single patient's tumor (exome sequencing), followed by computer modeling and cell-culture experiments
• Who was studied: One patient: a 41-year-old Chinese woman diagnosed with WDPMP after biopsy. Her tumor, her blood and a cell line grown from the tumor were studied. Experiments also used two established mesothelioma cell lines, MSTO-211H and NCI-H28. The patient was reported disease-free 8 months after surgery.
• Exposure: No asbestos or other fiber exposure was studied, and the article does not report the patient's asbestos history. In the laboratory, cells were made to over-produce either normal (wild-type) or mutant (R166H) E2F1 protein in two mesothelioma cell lines.
• Main results:
  • Exome sequencing showed no large DNA deletion or amplification events in the tumor, the tumor cell line or the blood sample.
  • Somatic mutations were confirmed in three genes in this tumor: PPFIBP2, TRAF7 and E2F1.
  • The E2F1 R166H mutation was present on one of the two copies of the gene (heterozygous).
  • The DNA-binding test (ChIP assay) was done in one cell line, MSTO-211H. In that test, mutant E2F1 bound DNA less well than normal E2F1.
  • In MSTO-211H cells, activity of the target genes SIRT1 and APAF1 was significantly lower with mutant E2F1 than with normal E2F1 (P = 0.032 for SIRT1 and P = 0.005 for APAF1).
  • Mutant E2F1 protein built up in cells. This was not explained by differences in how well the gene was delivered into the cells (transfection efficiency).
  • In a breakdown test over 3 hours in MSTO-211H cells, mutant protein levels stayed almost constant, while normal E2F1 levels fell over time.
  • Cells over-producing normal E2F1 grew slightly slower, and cells over-producing the mutant grew slightly faster.
  • Growth of cells over-producing the mutant was comparable to that of control cells carrying an empty vector. The authors stated that the mutant did not show a significant effect on cell proliferation.
• The authors' conclusion: The authors concluded that two compatible theories could explain the results. First, the mutant E2F1 decreases cell death (apoptosis), while other E2F family members make up for its lost cell-cycle role. Second, the mutant behaves like the SV40 large T antigen, interfering with the tumor-suppressing role of the retinoblastoma protein (Rb) and allowing the normal copy to drive cell division.
• Limitations the authors state:
  • The computer modeling could not establish the mutation's effect on DNA binding, which led to the laboratory experiments.
  • Both cell lines used already lacked the CDKN2A gene. The authors suggested this may be why cells making the mutant did not grow more than control cells.
  • The exome capture technology over-represented small sections of the exome.

Topics

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

Medical terms in this study, explained in our Lexicon: Somatic Mutation, Well-Differentiated Papillary Mesothelioma, Peritoneum, Mesothelioma, Asbestos Exposure, SV40.

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