Unraveling crucial roles of homeobox gene Hlx in hematopoiesis and leukemogenesis

描述（由申请人提供）：虽然干细胞的分离在过去几十年中取得了显著进展，但对调节干细胞自我更新和谱系定型的精确机制的理解仍然有限。在造血过程中，造血干细胞（HSC）的后代定向分化为特定的细胞谱系，最终产生终末分化细胞。转录因子被认为能够驱动一组特征性的谱系特异性靶点的表达， 基因，指示前体细胞采取一定的分化程序。转录因子活性的失调在白血病中具有重要作用，暗示这些基因是血液和其他形式癌症中治疗干预的潜在靶点。当我们在小鼠急性髓性白血病（AML）模型中分析纯化的白血病前造血干细胞和祖细胞（HSPC）时，我们发现新型非成簇同源框基因H2.0样同源框（Hlx）上调4倍，表明Hlx可能参与健康造血和恶性转化。我们的初步研究表明，Hlx的过表达破坏健康的骨髓分化，并赋予无限的连续克隆形成和骨髓单核细胞分化阻滞造血干细胞和祖细胞在体外。此外，Hlx的过表达导致表型HSC的损失和体内扩增的异常骨髓祖细胞群体的持续存在。我们还发现，Hlx调节的基因网络的谱系承诺和骨髓分化的HSPC的重要。引人注目的是，我们发现Hlx在大多数AML患者中过表达，并且Hlx表达是AML患者存活的最强预测因子之一。我们还发现，Hlx下调抑制鼠和人AML细胞在体外的生长。该项目旨在了解Hlx如何调节HSC和髓样分化过程中的这些关键功能。为了表征Hlx在干细胞和祖细胞的谱系定型中以及在髓样分化和急性髓样白血病细胞中的作用，我们将利用遗传小鼠模型、干细胞移植测定和体内和体外Hlx水平的靶向降低。为了阐明Hlx的作用机制，我们将研究我们通过转录谱确定的下游途径，并进行染色质免疫沉淀，以建立Hlx作为能够直接调节其靶基因的转录因子。

DESCRIPTION (provided by applicant): While isolation of stem cells has advanced dramatically in the last few decades, understanding of the precise mechanisms that regulate the self-renewal and lineage commitment of a stem cell is still limited. During hematopoiesis, progeny of hematopoietic stem cells (HSC) become committed to differentiate into specific cell lineages to ultimately generate terminally differentiated cells. Transcription factors have been recognized for their ability to drive expression of a characteristic set of lineage-specific target genes, instructing a precursor cell to adopt a certain differentiation program. Dysregulation of transcription factor activity has an important role in leukemia, implicating these genes as potential targets for therapeutic intervention in blood, and other forms of cancer. When we analyzed purified pre-leukemic hematopoietic stem and progenitor cells (HSPC) in a murine acute myeloid leukemia (AML) model, we found 4-fold upregulation of a novel non-clustered homeobox gene, H2.0-like homeobox (Hlx), suggesting that Hlx may be involved in healthy hematopoiesis and malignant transformation. Our preliminary studies indicate that overexpression of Hlx disrupts healthy myeloid differentiation and confers unlimited serial clonogenicity and a myelomonocytic differentiation block to hematopoietic stem and progenitor cells in vitro. Furthermore, overexpression of Hlx causes loss of phenotypic HSC and persistence of an expanded, aberrant myeloid progenitor population in vivo. We also find that Hlx regulates a network of genes important for lineage commitment and myeloid differentiation of HSPC. Strikingly, we find that Hlx is overexpressed in the majority of patients with AML, and that Hlx expression is one of the strongest predictors of AML patient survival. We also find that Hlx downregulation inhibits growth of murine and human AML cells in vitro. This project aims to understand how Hlx is regulating these critical functions in HSC and during myeloid differentiation. To characterize the roles of Hlx in lineage commitment of stem and progenitor cells, as well as in myeloid differentiation and acute myeloid leukemia cells, we will utilize genetic murine models, stem cell transplantation assays and targeted reduction of Hlx levels in vivo and in vitro. To elucidate the mechanism of action of Hlx, we will study downstream pathways we have identified by transcriptional profiling and perform chromatin-immunoprecipitation to establish Hlx as a transcription factor capable of directly regulating its target genes.