Identification of chromatin remodeling genes Arid4a and Arid4b as leukemia suppressor genes.
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.
Wu
Mei-Yi
MY
Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Eldin
Karen W
KW
Beaudet
Arthur L
AL
D000818:Animals; D001772:Blood Cell Count; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics*; D042002:Chromatin Assembly and Disassembly / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D004195:Disease Models, Animal; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D015973:Gene Expression Regulation, Leukemic; D016147:Genes, Tumor Suppressor; D007942:Leukemia, Experimental / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D056465:Retinoblastoma-Binding Protein 1; D020133:Reverse Transcriptase Polymerase Chain Reaction
C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C515305:Rbbp1l1 protein, mouse; D056465:Retinoblastoma-Binding Protein 1