PU.1-dependent enhancer inhibition separates clonal hematopoiesis from malignant transformation (oxBS-Seq). PU.1-dependent enhancer inhibition separates clonal hematopoiesis from malignant transformation (oxBS-Seq)

Hematopoietic stem cells sustain life-long blood production. While they are the known cellular origin of aging-associated myeloid malignancies, such as acute myeloid leukemia (AML), mechanisms driving their malignant transformation have remained elusive. Epigenetic dysregulation following acquired loss-of-function mutations of DNA methyl-cytosine dioxygenase Ten-Eleven Translocation-2 (TET2) occurs frequently in the elderly leading to cytosine hypermethylation in and around DNA binding sites of master transcription factors, including PU.1. Here we show that Tet2 deficient hematopoietic stem and progenitor cells (HSPC) undergo malignant transformation upon compromised PU.1 gene regulation. Leukemic stem and progenitor cells show hypermethylation at PU.1 binding sites and fail to activate PU.1-depenent myeloid enhancers, and are hallmarked by a defined signature of impaired genes shared with human AML. Our study demonstrates that Tet2 and PU.1 cooperate in suppressing leukemogenesis in HSPC and establishes a methylation sensitive PU.1-dependent gene network as a unifying feature in acute myeloid leukemia. Overall design: oxidative bisulfite sequencing of cKit+ HSPC purified from UREHETTet2HET and UREHETTet2KO mice and age-matched controls

造血干细胞可维持终身造血功能。尽管它们是衰老相关髓系恶性肿瘤（如急性髓系白血病（acute myeloid leukemia，AML））的已知细胞起源，但驱动其恶性转化的机制仍不明朗。DNA甲基胞嘧啶双加氧酶Ten-Eleven Translocation-2（TET2）发生获得性功能丧失突变后引发的表观遗传失调，在老年人群中较为常见，可导致包括PU.1在内的核心转录因子DNA结合位点及其侧翼区域出现胞嘧啶超甲基化。本研究发现，Tet2缺陷型造血干祖细胞（hematopoietic stem and progenitor cells，HSPC）在PU.1基因调控受损时会发生恶性转化。白血病干祖细胞在PU.1结合位点呈现超甲基化，无法激活PU.1依赖的髓系增强子，其特征为存在与人类急性髓系白血病共有的受损基因特征谱。本研究证实，Tet2与PU.1协同抑制造血干祖细胞中的致白血病过程，并确立了甲基化敏感的PU.1依赖基因网络作为急性髓系白血病的统一特征。整体实验设计：对从UREHETTet2HET、UREHETTet2KO小鼠及同月龄对照小鼠中纯化的cKit+造血干祖细胞进行氧化亚硫酸氢盐测序（oxidative bisulfite sequencing）。