Activated TNF-alpha/NF-kappaB signaling via down-regulation of Fas-associated factor 1 in asbestos-induced mesotheliomas from Arf knockout mice

Our plain-English summary of Activated TNF-alpha/NF-kappaB signaling via down-regulation of Fas-associated factor 1 in asbestos-induced mesotheliomas from Arf knockout mice, by D.A. Altomare, C.W. Menges, J. Pei, et al (Proceedings of the National Academy of Sciences of the United States of America, 2009).

The study

• Authors: D.A. Altomare, C.W. Menges, J. Pei, L. Zhang, K.L. Skele-Stump, M. Carbone, A.B. Kane, J.R. Testa
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 2009;106(9):3420-5
• Cited by: 61 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The human CDKN2A locus encodes 2 distinct proteins, p16(INK4A) and p14(ARF) [mouse p19(Arf)], designated INK4A (inhibitor of cyclin dependent kinase 4) and ARF (alternative reading frame) here, that are translated from alternatively spliced mRNAs. Human ARF is implicated as a tumor suppressor gene, mainly in association with the simultaneous deletion of INK4A. However, questions remain as to whether loss of ARF alone is sufficient to drive tumorigenesis. Here, we report that mice deficient for Arf are susceptible to accelerated asbestos-induced malignant mesothelioma (MM). MMs arising in Arf (+/-) mice consistently exhibit biallelic inactivation of Arf, but, unexpectedly, do not acquire additional recurrent genetic alterations that we previously identified in asbestos-induced MMs arising in Nf2 (+/-) mice. Array CGH analysis was used to detect a recurrent deletion at chromosome 4C6 in MMs from Arf (+/-) mice. A candidate gene in this region, Faf1 (FAS-associated factor 1), was further explored, because it encodes a protein implicated in tumor cell survival and in the pathogenesis of some human tumor types. We confirmed hemizygous loss of Faf1 and down-regulation of Faf1 protein in a series of MMs from Arf (+/-) mice, and we then showed that Faf1 regulates TNF-alpha-mediated NF-kappaB signaling, a pathway previously implicated in asbestos-induced oncogenesis of human mesothelial cells. Collectively, these data indicate that Arf inactivation has a significant role in driving MM pathogenesis, and implicate Faf1 as a key component in the TNF-alpha/NF-kappaB signaling node that has now been independently implicated in asbestos-induced oncogenesis.

In plain English

This was a laboratory study in mice. The authors repeatedly injected crocidolite asbestos into the abdominal cavity of male mice that carried one disabled copy of the Arf tumor suppressor gene (Arf +/- mice) and of normal (wild-type) littermates. Comparison mice received titanium dioxide particles instead. Twenty-six Arf +/- and 27 wild-type asbestos-treated mice completed the protocol. Malignant mesothelioma appeared after a median of 42 weeks in Arf +/- mice, compared with 56 weeks in wild-type mice. None of the titanium dioxide-treated mice developed mesothelioma. In all 11 tumor cultures from Arf +/- mice, the remaining normal Arf copy was lost. Genetic scanning pointed to loss of one copy of a gene called Faf1. Faf1 protein was reduced in 6 of 7 tumors from Arf +/- mice, in 4 of 7 from wild-type mice, and in 7 of 7 human mesothelioma cell lines. Cell experiments linked low Faf1 to increased TNF-alpha/NF-kappaB signaling. The authors concluded that Arf loss has a significant independent role in mesothelioma. They also concluded that impairing the p53 pathway increases the risk of asbestos-mediated cancer.

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: Animal experiment (genetically modified mice injected with asbestos), followed by laboratory analyses of tumor cells
• Who was studied: Male mice lacking one copy of the Arf gene (Arf +/-, per the abstract) and wild-type littermates. Completing the protocol were 26 Arf +/- and 27 wild-type mice treated with asbestos, and 13 Arf +/- and 18 wild-type mice treated with titanium dioxide. Some experiments also used human mesothelioma cell lines and tumors.
• Exposure: Repeated intraperitoneal (abdominal cavity) injections of UICC-grade crocidolite asbestos. Control mice were injected with titanium dioxide particles.
• Main results:
  • Median time to detection of mesothelioma was 42 weeks after first asbestos exposure in Arf +/- mice, compared with 56 weeks in wild-type mice. The log-rank test showed shorter survival in Arf +/- mice; the P value was printed as 4.63E-13, with the symbol before it lost in the text.
  • None of the titanium dioxide-treated control mice developed mesothelioma.
  • Invasion into lymphatics or muscle was seen in 8 of 25 mesotheliomas from asbestos-treated Arf +/- mice and in 9 of 22 from wild-type mice, which the authors described as equivalent.
  • The remaining normal Arf copy was lost in all 11 primary mesothelioma cultures from Arf +/- mice. In wild-type mice, 5 of 7 (71%) mesotheliomas had loss of functional Arf.
  • Loss of p53 was not seen in any of the 11 mesotheliomas from Arf +/- mice.
  • Genetic analysis of tumor cells from 4 Arf +/- mice found one recurrent change, a focal loss on chromosome 4, band C6, in all 4. It turned out to be an inherited copy number variant. Next to it was a region where one copy (hemizygous loss) was missing, and this region contained the Faf1 gene.
  • Faf1 protein was reduced in 6 of 7 mesotheliomas from Arf +/- mice and in 4 of 7 from wild-type mice.
  • FAF1 protein was reduced in 7 of 7 human mesothelioma cell lines compared with normal mesothelial cells. Loss of FAF1 staining was seen in 12 of 14 human mesothelioma tumors.
  • Restoring Faf1 in Faf1-deficient mouse tumor cells reduced nuclear p65 levels and NF-kappaB activity. Knocking Faf1 down by up to 63% in Faf1-positive cells increased NF-kappaB activity.
• The authors' conclusion: The authors concluded that their findings support a significant independent role for Arf loss in mesothelioma. They also concluded that this study, together with earlier ones, shows that genetic or viral alterations impairing the p53 pathway increase the risk of asbestos-mediated cancer.
• Limitations the authors state:
  • Other candidate genes in the deleted region (Dmrta2 and Elavl4/HuD) were not investigated.
  • Two Arf +/- mice and 1 wild-type mouse did not complete asbestos treatment and could not be analyzed for cause of death.
  • The tumors in Arf +/- mice were not highly invasive. The authors took this to suggest that other genetic changes are needed for extensive invasion and spread.

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, CDKN2A, Tumor Suppressor Gene, Carcinogenesis, Mesothelial Cells.

Related studies

• TNF-alpha inhibits asbestos-induced cytotoxicity via a NF-kappaB-dependent pathway, a possible mechanism for asbestos-induced oncogenesis — H. Yang, M. Bocchetta, et al. (2006)
• TNF-alpha receptor knockout mice are protected from the fibroproliferative effects of inhaled asbestos fibers — J.Y. Liu, D.M. Brass, et al. (1998)
• Role of transcription factor NF-kappaB in asbestos-induced TNFalpha response from macrophages — N. Cheng, X. Shi, et al. (1999)
• Transforming growth factor-beta(1) overexpression in tumor necrosis factor-alpha receptor knockout mice induces fibroproliferative lung disease — J.Y. Liu, P.J. Sime, et al. (2001)
• Losses of both products of the Cdkn2a/Arf locus contribute to asbestos-induced mesothelioma development and cooperate to accelerate tumorigenesis — D.A. Altomare, C.W. Menges, et al. (2011)
• Bortezomib inhibits nuclear factor-kappaB dependent survival and has potent in vivo activity in mesothelioma — A. Sartore-Bianchi, F. Gasparri, et al. (2007)

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