Homozygous deletion of CDKN2A/2B is a hallmark of iron-induced high-grade rat mesothelioma

Our plain-English summary of Homozygous deletion of CDKN2A/2B is a hallmark of iron-induced high-grade rat mesothelioma, by Q. Hu, S. Akatsuka, Y. Yamashita, et al (Laboratory Investigation; a Journal of Technical Methods and Pathology, 2010).

The study

• Authors: Q. Hu, S. Akatsuka, Y. Yamashita, H. Ohara, H. Nagai, Y. Okazaki, T. Takahashi, S. Toyokuni
• Journal: Laboratory Investigation; a Journal of Technical Methods and Pathology
• Published: 2010;90(3):360-73
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In humans, mesothelioma has been linked to asbestos exposure, especially crocidolite and amosite asbestos, which contain high amounts of iron. Previously, we established a rat model of iron-induced peritoneal mesothelioma with repeated intraperitoneal injections of iron saccharate and an iron chelator, nitrilotriacetate. Here, we analyze these mesotheliomas using array-based comparative genomic hybridization (aCGH) and gene expression profiling by microarray. Mesotheliomas were classified into two distinct types after pathologic evaluation by immunohistochemistry. The major type, epithelioid mesothelioma (EM), originated in the vicinity of tunica vaginalis testis, expanded into the upper peritoneal cavity and exhibited papillary growth and intense podoplanin immunopositivity. The minor type, sarcomatoid mesothelioma (SM), originated from intraperitoneal organs and exhibited prominent invasiveness and lethality. Both mesothelioma types showed male preponderance. SMs revealed massive genomic alterations after aCGH analysis, including homozygous deletion of CDKN2A/2B and amplification of ERBB2 containing region, whereas EMs showed less genomic alterations. Uromodulin was highly expressed in most of the cases. After 4-week treatment, iron deposition in the mesothelia was observed with 8-hydroxy-2'-deoxyguanosine formation. These results not only show two distinct molecular pathways for iron-induced peritoneal mesothelioma, but also support the hypothesis that oxidative stress by iron overload is a major cause of CDKN2A/2B homozygous deletion.

In plain English

This rat experiment did not use asbestos; the authors mention iron-rich crocidolite and amosite asbestos only as background. They injected 54 hybrid rats into the abdomen with an iron compound, ferric saccharate, and a second substance, nitrilotriacetate. They kept 38 untreated rats as controls and followed the animals to 26.7 months of age. Peritoneal mesothelioma developed in 16 of 24 treated males (66.7%) and 1 of 30 treated females (3.3%). No control rat developed mesothelioma. Two tumor types appeared. Epithelioid tumors grew near the lining of the testis. Sarcomatoid tumors on abdominal organs were more invasive and were lethal mainly through intestinal obstruction. Genetic testing found that four of five sarcomatoid tumors had lost both copies of the CDKN2A/2B genes (homozygous deletion), and two had extra copies of a region containing ERBB2. Epithelioid tumors showed fewer changes. After four weeks of repeated iron injections, a marker of oxidative DNA damage was increased in the abdominal lining. The authors concluded that their data strongly support that iron overload induces the CDKN2A/2B deletion.

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 (rat carcinogenesis model) with genetic and gene-expression analysis of the induced tumors
• Who was studied: 92 F1 hybrid rats (Fischer344 female crossed with Brown-Norway male): 54 iron-treated (24 male, 30 female) and 38 untreated controls (17 male, 21 female), observed to 26.7 months of age; male Wistar rats were also used in some short-term experiments
• Exposure: No asbestos. Intraperitoneal ferric saccharate (5 mg iron/kg body weight, 5 days a week for 12 weeks) and nitrilotriacetate (80 mg/kg body weight, 5 days a week for 20 weeks), starting at 4 weeks of age
• Main results:
  • Iron-treated males: 16 of 24 (66.7%) developed mesothelioma; iron-treated females: 1 of 30 (3.3%)
  • Control rats developed no mesothelioma during the observation period
  • Survival did not differ significantly between control and iron-treated groups up to 20 months of age
  • Sarcomatoid tumors were invasive and lethal, mainly through intestinal obstruction
  • Of 5 sarcomatoid mesotheliomas analyzed, 4 had homozygous deletion of CDKN2A/2B and 2 had amplification of an ERBB2-containing region
  • Epithelioid tumors (6 analyzed) showed numerous minor genomic changes, while most sarcomatoid tumors showed a variety of chromosomal changes
  • Uromodulin was overexpressed in most tumors examined by expression microarray (6 epithelioid, 2 sarcomatoid)
  • The oxidative DNA damage marker 8-hydroxy-2'-deoxyguanosine was significantly increased in the mesothelia after 4 weeks of repeated iron saccharate injections (examined 4 weeks after the start of the experiment)
• The authors' conclusion: The authors concluded that their data strongly support that iron overload induces homozygous deletion of CDKN2A/2B. They also concluded that iron overload is a major risk factor for mesothelioma.
• Limitations the authors state:
  • Many antibodies for confirming tumor type are not available for rats
  • Some sarcomatoid tumors could not be analyzed for gene expression because the animals were found dead and the RNA was of poor quality
  • How iron-caused oxidative DNA damage leads specifically to CDKN2A/2B deletion remains unknown

Topics

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

Medical terms in this study, explained in our Lexicon: Homozygous Deletion, CDKN2A, Mesothelioma, Asbestos Exposure, Crocidolite, Amosite, Peritoneal Mesothelioma, Immunohistochemistry.

Related studies

• Frequent homozygous deletion of Cdkn2a/2b in tremolite-induced malignant mesothelioma in rats — Y. Okazaki, N. Misawa, et al. (2020)
• Fluorescence in situ hybridization (FISH) provides estimates of minute and interstitial BAP1, CDKN2A, and NF2 gene deletions in peritoneal mesothelioma — S. Brich, F. Bozzi, et al. (2020)
• Iron overload as a major targetable pathogenesis of asbestos-induced mesothelial carcinogenesis — S. Toyokuni (2014)
• CDKN2A and MTAP deletions in peritoneal mesotheliomas are correlated with loss of p16 protein expression and poor survival — A.M. Krasinskas, D.L. Bartlett, et al. (2010)
• Homozygous deletion of CDKN2A in malignant mesothelioma: Diagnostic utility, patient characteristics and survival in a UK mesothelioma centre — K. Marshall, S. Jackson, et al. (2020)
• Iron overload signature in chrysotile-induced malignant mesothelioma — L. Jiang, S. Akatsuka, et al. (2012)

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