Bromodomain containing protein 9 (BRD9), a member of the non-canonical BRG1/BRM-associated factor (ncBAF) chromatin remodeling complex, has been implicated as a synthetic lethal target in AML but its function in normal human hematopoiesis is unknown. In hematopoietic stem and progenitor cells (HSPC) genomic or chemical inhibition of BRD9 led to a proliferative disadvantage and loss of stem cells in vitro. Human HSPCs with reduced BRD9 protein levels produced lower numbers of immature mixed multipotent GEMM colonies in semi-solid media. In lineage-promoting culture conditions, cells with reduced BRD9 levels failed to differentiate into the megakaryocytic lineage and showed delayed differentiation into erythroid cells but enhanced terminal myeloid differentiation. HSPCs with BRD9 knock down (KD) had reduced long-term multilineage engraftment in a xenotransplantation assay. An increased number of downregulated genes in RNAseq analysis after BRD9 KD coupled with a gain in chromatin accessibility at the promoters of several repressive transcription factors (TF) suggest that BRD9 functions in the maintenance of active transcription during HSC differentiation. In particular, the hematopoietic master regulator GATA1 was identified as one of the core TFs regulating the gene networks modulated by BRD9 loss in HSPCs. BRD9 inhibition reduced a GATA1-luciferase reporter signal, further suggesting a role for BRD9 in regulating GATA1 activity. BRD9 is therefore an additional example of epigenetic regulation of human hematopoiesis.

含布罗莫结构域蛋白 9 (BRD9) 是非经典 BRG1/BRM 相关因子 (ncBAF) 染色质重塑复合物的成员，已被认为是 AML 中的合成致死靶标，但其在正常人类造血中的功能尚不清楚。在造血干细胞和祖细胞 (HSPC) 中，BRD9 的基因组或化学抑制导致体外干细胞增殖不利和损失。 BRD9 蛋白水平降低的人类 HSPC 在半固体培养基中产生较少数量的未成熟混合多能 GEMM 集落。在谱系促进培养条件下，BRD9水平降低的细胞无法分化为巨核细胞谱系，并且显示出延迟分化为红系细胞，但增强了终末骨髓分化。在异种移植试验中，敲低 BRD9 (KD) 的 HSPC 减少了长期多谱系植入。 BRD9 KD 后 RNAseq 分析中下调基因的数量增加，加上几个抑制性转录因子 (TF) 启动子处染色质可及性的增加，表明 BRD9 在 HSC 分化过程中维持活性转录方面发挥作用。特别是，造血主调节因子 GATA1 被确定为调节 HSPC 中 BRD9 缺失所调节的基因网络的核心 TF 之一。 BRD9 抑制减少了 GATA1-荧光素酶报告信号，进一步表明 BRD9 在调节 GATA1 活性中的作用。因此，BRD9 是人类造血作用表观遗传调控的另一个例子。