Losses of both products of the Cdkn2a/Arf locus contribute to asbestos-induced mesothelioma development and cooperate to accelerate tumorigenesis

Our plain-English summary of Losses of both products of the Cdkn2a/Arf locus contribute to asbestos-induced mesothelioma development and cooperate to accelerate tumorigenesis, by D.A. Altomare, C.W. Menges, J. Xu, et al (PloS One, 2011).

The study

• Authors: D.A. Altomare, C.W. Menges, J. Xu, J. Pei, L. Zhang, A. Tadevosyan, E. Neumann-Domer, Z. Liu, M. Carbone, I. Chudoba, A.J. Klein-Szanto, J.R. Testa
• Journal: PloS One
• Published: 2011;6(4):e18828
• Cited by: 52 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The CDKN2A/ARF locus encompasses overlapping tumor suppressor genes p16(INK4A) and p14(ARF), which are frequently co-deleted in human malignant mesothelioma (MM). The importance of p16(INK4A) loss in human cancer is well established, but the relative significance of p14(ARF) loss has been debated. The tumor predisposition of mice singly deficient for either Ink4a or Arf, due to targeting of exons 1α or 1β, respectively, supports the idea that both play significant and nonredundant roles in suppressing spontaneous tumors. To further test this notion, we exposed Ink4a(+/-) and Arf(+/-) mice to asbestos, the major cause of MM. Asbestos-treated Ink4a(+/-) and Arf(+/-) mice showed increased incidence and shorter latency of MM relative to wild-type littermates. MMs from Ink4a(+/-) mice exhibited biallelic inactivation of Ink4a, loss of Arf or p53 expression and frequent loss of p15(Ink4b). In contrast, MMs from Arf(+/-) mice exhibited loss of Arf expression, but did not require loss of Ink4a or Ink4b. Mice doubly deficient for Ink4a and Arf, due to deletion of Cdkn2a/Arf exon 2, showed accelerated asbestos-induced MM formation relative to mice deficient for Ink4a or Arf alone, and MMs exhibited biallelic loss of both tumor suppressor genes. The tumor suppressor function of Arf in MM was p53-independent, since MMs with loss of Arf retained functional p53. Collectively, these in vivo data indicate that both CDKN2A/ARF gene products suppress asbestos carcinogenicity. Furthermore, while inactivation of Arf appears to be crucial for MM pathogenesis, the inactivation of both p16(Ink4a) and p19(Arf) cooperate to accelerate asbestos-induced tumorigenesis.

In plain English

This was an animal experiment in genetically altered mice. The authors studied two overlapping tumor suppressor genes, Ink4a and Arf, located at the same DNA locus. Mice aged 6 to 8 weeks carrying one disabled copy of Ink4a, of Arf, or of both genes, plus normal (wild-type) littermates, were injected into the abdomen every 3 weeks with crocidolite asbestos, totaling 3.2 mg per mouse. Mice given titanium dioxide particles instead did not develop mesothelioma. Mesothelioma was detected sooner in the gene-altered mice. Median time from first asbestos injection was 29.6 weeks with both genes affected, 34.6 weeks for Ink4a, 38.0 weeks for Arf and 49.4 weeks for wild-type mice, and survival differences from wild-type mice were statistically significant. Tumors were mostly sarcomatoid and often seeded the abdominal lining. In tumors tested, the remaining normal copy of the affected gene was also inactivated, Arf was lost in nearly all tumors, and only one of 20 tumors lacked p53 protein. The authors concluded that both gene products suppress asbestos-induced cancer and that losing both accelerates tumor formation.

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 (in vivo carcinogenesis study in genetically modified mice)
• Who was studied: Mice heterozygous for Ink4a, for Arf, or for both Ink4a and Arf (doubly heterozygous), plus wild-type littermates. Ink4a and Arf are overlapping tumor suppressor genes at the Cdkn2a/Arf locus. All mice were in a comparable FVB/N genetic background and were 6 to 8 weeks old at first injection. The main text does not give the number of mice in each group; it refers to a supporting file.
• Exposure: Crocidolite asbestos (UICC), injected into the abdominal cavity (intraperitoneally) every 3 weeks starting at 6 to 8 weeks of age, for a total of 3.2 mg per mouse. The per-injection dose prints as '400 mg', which cannot be right given the stated total and must be 400 micrograms. Control mice received titanium dioxide (TiO2) particles.
• Main results:
  • Median time from first asbestos exposure to mesothelioma detection was 29.6 weeks for doubly heterozygous Ink4a;Arf mice, 34.6 weeks for Ink4a heterozygous mice, 38.0 weeks for Arf heterozygous mice, and 49.4 weeks for wild-type mice.
  • A log-rank test on survival curves showed significant differences between wild-type mice and the Ink4a-deficient (p = 0.0342), Arf-deficient (p = 0.0312) and Ink4a;Arf-deficient (p less than 0.0001) groups.
  • Tumor latency did not differ significantly between Ink4a-deficient and Arf-deficient mice. Latency was decreased in Ink4a;Arf-deficient mice (p less than 0.0001), which the authors described as accelerated relative to mice deficient for either gene alone.
  • Mesothelioma incidence was increased in Ink4a and Arf heterozygous mice relative to wild-type littermates. The counts are not given in the main text.
  • Mesothelioma did not develop in the titanium dioxide-treated control mice.
  • Sarcomatoid mesotheliomas were prevalent in all asbestos-treated mice. Tumors frequently presented with ascites and diffuse peritoneal seeding of the serosal lining.
  • Mesotheliomas from all three heterozygous groups showed biallelic inactivation (inactivation of both copies) of the predisposing tumor suppressor gene.
  • In mesotheliomas from Ink4a heterozygous mice, 4 of 5 tested also showed loss of Arf and p15(Ink4b).
  • In mesothelioma cultures from Arf heterozygous mice, Ink4a expression was lost in 3 of 6 and p15(Ink4b) was retained in 5 of 6.
  • Mesotheliomas from doubly heterozygous mice showed biallelic inactivation of both Ink4a and Arf, while Ink4b was retained in 6 of 7 samples tested.
  • Arf was lost in nearly all tumors. The only tumor (#200) that retained Arf expression lacked p53 expression.
  • Only 1 of the 20 asbestos-induced mesotheliomas showed loss of p53 expression.
  • In mesothelioma cells that had lost Arf, the p53 pathway appeared to remain functional, judged by the cells' response to DNA damage.
• The authors' conclusion: The authors concluded that both products of the Cdkn2a/Arf locus (p16(Ink4a) and p19(Arf)) suppress asbestos carcinogenicity. They also concluded that Arf inactivation appears critical for mesothelioma development, and that inactivation of both genes cooperates to accelerate asbestos-induced tumor formation.
• Limitations the authors state:
  • In a few cases diagnosis was difficult, because mesotheliomas may arise anywhere in the abdominal cavity and may not be obvious in the sampled tissues.

Topics

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

Medical terms in this study, explained in our Lexicon: CDKN2A, Mesothelioma, Carcinogenesis, Tumor Suppressor Gene, Latency.

Related studies

• Activated TNF-alpha/NF-kappaB signaling via down-regulation of Fas-associated factor 1 in asbestos-induced mesotheliomas from Arf knockout mice — D.A. Altomare, C.W. Menges, et al. (2009)
• Germline mutation of Bap1 accelerates development of asbestos-induced malignant mesothelioma — J. Xu, Y. Kadariya, et al. (2014)
• Aberrant methylation of the CDKN2a/p16INK4a gene promoter region in preinvasive bronchial lesions: a prospective study in high-risk patients without invasive cancer — A. Lamy, R. Sesboüé, et al. (2002)
• Alterations of the p16(INK4) locus in human malignant mesothelial tumors — T. Hirao, R. Bueno, et al. (2002)
• Long-Fiber Carbon Nanotubes Replicate Asbestos-Induced Mesothelioma with Disruption of the Tumor Suppressor Gene Cdkn2a (Ink4a/Arf) — T. Chernova, F.A. Murphy, et al. (2017)
• Homozygous deletion of CDKN2A/2B is a hallmark of iron-induced high-grade rat mesothelioma — Q. Hu, S. Akatsuka, et al. (2010)

Browse more research in PloS One, or return to medical research.