BCOR, encoding BCL-6 corepressor (BCOR), is X-linked and targeted by somatic mutations in various hematological malignancies including myelodysplastic syndrome (MDS). We previously reported that mice lacking Bcor exon 4 (Bcor DE4/y ) in the hematopoietic compartment developed NOTCH-dependent acute T-cell lymphoblastic leukemia (T-ALL). Here, we analyzed mice lacking Bcor exons 9 and 10 (Bcor DE9-10/y ), which express a carboxyl-terminal truncated BCOR that fails to interact with core effector components of polycomb repressive complex 1.1. Bcor D E9-10/y mice developed lethal T-ALL in a similar manner to Bcor DE4/y mice, whereas Bcor D E9-10/y hematopoietic cells showed a growth advantage in the myeloid compartment that was further enhanced by the concurrent deletion of Tet2. Tet2 D / D Bcor D E9-10/y mice developed lethal MDS with progressive anemia and leukocytopenia, inefficient hematopoiesis, and the morphological dysplasia of blood cells. Tet2 D / D Bcor D E9-10/y MDS cells reproduced MDS or evolved into lethal MDS/myeloproliferative neoplasms in secondary recipients. Transcriptional profiling revealed the derepression of myeloid regulator genes of the Cebp family and Hoxa cluster genes in Bcor DE9-10/y progenitor cells and the activation of p53 target genes specifically in MDS erythroblasts where massive apoptosis occurred. Our results reveal a tumor suppressor function of BCOR in myeloid malignancies and highlight the impact of Bcor insufficiency on the initiation and progression of MDS. (Blood. 2018;132(23): 2470-2483)
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This work was supported, in part, by Grants-in-Aid for Scientific Research (#15H02544) and Scientific Research on Innovative Areas “Stem Cell Aging and Disease” (#26115002) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and grants from the Yasuda Memorial Medical Foundation and Tokyo Biochemical Research Foundation.