BCOR controls maintenance of haematopoietic stem cell quiescence and regulates myeloid cell proliferation and differentiation [Affymetrix]

BCOR is a component of a variant Polycomb group repressive complex 1 (PRC1) complex. Recently, we and others reported recurrent somatic BCOR loss-of-function mutations in myelodysplastic syndrome and acute myelogenous leukaemia (AML). However the role of BCOR in normal hematopoiesis is largely unknown. Here, we explored the function of BCOR in myeloid cells using myeloid murine cell models with Bcor conditional loss-of-function or overexpression alleles. Bcor mutant bone marrow cells showed significantly higher proliferation and differentiation rates with reduced protein levels of RING1B, a ubiquitin ligase subunit of PRC1 family complexes. Global RNA expression profiling in murine cells and AML patient samples with BCOR loss-of-function mutation suggested that loss of BCOR expression is associated with proliferation and myeloid differentiation and decreased stem cell quiescence. Further, we used a MLL-AF9 murine model of AML and found that loss of Bcor increased serial replating efficiency, enhanced MLL-AF9 in blocking cell differentiation, and increased expression of Evi1 which is associated with leukemic transformation. Our results strongly suggest that BCOR plays an indispensable role in maintaining hematopoietic stem cell (HSC) quiescence by inhibiting myeloid stem cell proliferation and differentiation and offer a mechanistic explanation for how BCOR regulates gene expression such as Hox genes.

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Cao Q, Gearhart MD, Gery S, Shojaee S, Yang H, Sun H, Lin DC, Bai JW, Mead M, Zhao Z, Chen Q, Chien WW, Alkan S, Alpermann T, Haferlach T, Müschen M, Bardwell VJ, Koeffler HP