Journal of the National Cancer Institute Advance Access published online on August 26, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn253
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ARTICLES |
Identification of Chromatin Remodeling Genes Arid4a and Arid4b as Leukemia Suppressor Genes
Affiliations of authors: Department of Molecular and Human Genetics, Baylor College of Medicine (MYW, ALB) and Department of Pathology, Baylor College of Medicine, Texas Children’s Hospital (KWE), Houston, TX
Correspondence to: Arthur L. Beaudet, MD, Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 (e-mail: abeaudet{at}bcm.edu).
Background: Leukemia evolves through a multistep process from premalignancy to malignancy. Epigenetic alterations, including histone modifications, have been proposed to play an important role in tumorigenesis. The involvement of two chromatin remodeling genes, retinoblastoma-binding protein 1 (Rbbp1/Arid4a) and Rbbp1-like 1 (Rbbp1l1/Arid4b), in leukemogenesis was not characterized.
Methods: The leukemic phenotype of mice deficient for Arid4a with or without haploinsufficiency for Arid4b was investigated by serially monitoring complete blood counts together with microscopic histologic analysis and flow cytometric analysis of bone marrow and spleen from the Arid4a–/– mice or Arid4a–/–Arid4b+/– mice. Regulation in bone marrow cells of downstream genes important for normal hematopoiesis was analyzed by reverse transcription–polymerase chain reaction. Genotypic effects on histone modifications were examined by western blotting and immunofluorescence analysis. All statistical tests were two-sided.
Results: Young (2–5 months old) Arid4a-deficient mice had ineffective blood cell production in all hematopoietic lineages. Beyond 5 months of age, the Arid4a–/– mice manifested monocytosis, accompanied by severe anemia and thrombocytopenia. These sick Arid4a–/– mice showed bone marrow failure with myelofibrosis associated with splenomegaly and hepatomegaly. Five of 42 Arid4a–/– mice and 10 of 12 Arid4a–/–Arid4b+/– mice progressed to acute myeloid leukemia (AML) and had rapid further increases of leukocyte counts. Expression of Hox genes (Hoxb3, Hoxb5, Hoxb6, and Hoxb8) was decreased in Arid4a-deficient bone marrow cells with or without Arid4b haploinsufficiency, and FoxP3 expression was reduced in Arid4a–/–Arid4b+/– bone marrow. Increases of histone trimethylation of H3K4, H3K9, and H4K20 (fold increases in trimethylation = 32, 95% confidence interval [CI] = 27 to 32; 45, 95% CI = 41 to 49; and 2.2, 95% CI = 1.7 to 2.7, respectively) were observed in the bone marrow of Arid4a-deficient mice.
Conclusions: Arid4a-deficient mice initially display ineffective hematopoiesis, followed by transition to chronic myelomonocytic leukemia (CMML)–like myelodysplastic/myeloproliferative disorder, and then transformation to AML. The disease processes in the Arid4a-deficient mice are very similar to the course of events in humans with CMML and AML. This mouse model has the potential to furnish additional insights into the role of epigenetic alterations in leukemogenesis, and it may be useful in developing novel pharmacological approaches to treatment of preleukemic and leukemic states.
| CONTEXT AND CAVEATS Prior knowledge Epigenetic modifications of DNA have been proposed to play an important role in carcinogenesis. The involvement of two chromatin remodeling genes, Arid4a and Arid4b, in the etiology of leukemia was unknown. Study design Mice deleted for Arid4a or mice deleted for Arid4a and haploinsufficient for Arid4b were characterized in terms of blood counts, bone marrow abnormalities as revealed by histologic analysis, gene transcription, and epigenetic modification in their bone marrow cells. Contribution The fact that the genetically modified mice progressed to acute myeloid leukemia suggests a critical role for epigenetic modifications mediated by Arid4a and Arid4a in suppression of leukemogenesis. Implications The mouse model described here may be useful for studying the etiology of leukemia and the role that epigenetic modification plays in this process. Limitations The suitability of the mouse strains described here as a model for human leukemia and the precise roles of Arid4a and Arid4b in chromatin remodeling remain to be determined. From the Editors
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Manuscript received January 25, 2008; revised May 13, 2008; accepted June 19, 2008.
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J Natl Cancer Inst 2008 100: 1191.