ICSBP Function During Myeloid Differentiation

描述（由申请人提供）：几条证据表明干扰素共有序列结合蛋白（ICSBP或IRF 8）作为髓系白血病肿瘤抑制因子发挥作用。首先，ICSBP表达在来自骨髓增生异常综合征（MDS）和慢性髓性白血病（CML）受试者的骨髓样品中降低。第二，IRF 8基因靶向破坏的小鼠表现出CML样骨髓增生性疾病，其随着时间的推移进展为急性髓性白血病（AML）。这些结果表明，ICSBP缺陷单独足以诱导骨髓增生，但额外的突变是必要的进展为AML。然而，最初确定的靶基因并没有提出一个机制，ICSBP缺乏症倾向于这些事件。例如，我们发现ICSBP激活编码吞噬细胞NADPH氧化酶蛋白gp 91 PHOX和p67 phox的基因的转录。其他研究者确定了参与吞噬细胞功能的其他ICSBP靶基因。因此，ICSBP缺乏降低骨髓特异性基因转录，这可能有助于分化阻滞。然而，ICSBP缺陷型骨髓祖细胞表现出对细胞凋亡的抵抗、对造血细胞因子的超敏反应以及积累额外遗传病变的倾向。真正的ICSBP靶基因介导这些影响尚未确定。在上一个资助期内，我们致力找出这些目标基因。使用染色质免疫沉淀和CpG岛微阵列筛选，我们鉴定了ICSBP靶基因，其编码参与增殖（神经纤维蛋白1）和凋亡（Nore 1、Fap 1和可溶性鸟苷酸环化酶组分）的蛋白。这些靶基因的鉴定支持ICSBP缺乏足以诱导骨髓增生性疾病的假设。我们还鉴定了通过调节Wnt/2catenin途径参与造血干细胞扩增的靶基因（Gas 2、Dapper 2和calpain 2和12）。此外，我们确定了一个ICSBP靶基因参与造血细胞中的关键DNA修复途径（Fanconi F）。这与靶基因表达异常的ICSBP缺陷细胞易于获得额外的基因突变，导致分化阻滞和AML的假设一致。我们将通过以下具体目标来实现我们的假设：目标1：确定在ICSBP缺陷型造血中，骨髓增生相关靶基因的异常表达是否有助于骨髓增生。目标二：确定调节DNA修复和造血干细胞扩增的靶基因的异常表达是否易使ICSBP缺陷型造血中的AML发生。目的3：确定与ICSBP缺乏协同导致骨髓恶性肿瘤疾病进展的遗传性病变。公共卫生相关性：识别ICSBP靶基因可能提示共同的最终途径，这对于骨髓增殖是足够的，并且对于骨髓原始细胞危象的易感性是必要的。这种途径的功能表征对于鉴定人类髓系恶性肿瘤疾病进展的早期标志物和疾病（如CML和MDS）的分子治疗方法的合理靶点具有意义。

DESCRIPTION (provided by applicant): Several lines of evidence suggest that the interferon consensus sequence binding protein (ICSBP or IRF8) functions as a myeloid leukemia tumor-suppressor. First, ICSBP-expression is decreased in bone marrow samples from subjects with myelodysplastic syndrome (MDS) and chronic myeloid leukemia (CML). Second, mice with targeted disruption of the IRF8-gene exhibit a CML-like myeloproliferative disorder which progresses to acute myeloid leukemia (AML) over time. These results suggest that ICSBP-deficiency alone is adequate to induce myeloproliferation, but additional mutations are necessary for progression to AML. However, initially identified target-genes did not suggest a mechanism by which ICSBP-deficiency predisposes to either of these events. For example, we found that ICSBP activates transcription of genes encoding the phagocyte NADPH-oxidase proteins, gp91PHOX and p67phox. Other investigators identified additional ICSBP-target-genes involved in phagocyte function. Therefore, ICSBP-deficiency decreases myeloid-specific gene transcription, which may contribute to differentiation block. However, ICSBP-deficient myeloid progenitor cells exhibit resistance to apoptosis, hypersensitivity to hematopoietic cytokines, and the tendency to accumulate additional genetic lesions. Genuine ICSBP-target-genes mediating these effects had not been identified. During the previous funding period, we pursued identification of such target-genes. Using chromatin immuno-precipitation and CpG island microarray screening, we identified ICSBP- target-genes which encode proteins involved in proliferation (Neurofibromin 1) and apoptosis (Nore1, Fap1 and a soluble guanylate cyclase component). Identification of these target-genes supports the hypothesis that ICSBP-deficiency is sufficient to induce a myeloproliferative disorder. We also identified target-genes involved in hematopoietic stem cell expansion via regulation of the Wnt/2catenin pathway (Gas2, Dapper2 and calpain2 and 12). Additionally, we identified an ICSBP-target-gene involved in a key DNA repair pathway in hematopoietic cells (Fanconi F). This is consistent with the hypothesis that abnormal target-gene expression ICSBP-deficient cells predisposes to acquisition of additional genetic mutations, leading to differentiation block and AML. We will pursue our hypotheses through the following specific aims; Aim 1: Determine if abnormal expression of apoptosis-related target-genes contributes to myeloproliferation in ICSBP-deficient hematopoiesis. Aim 2: Determine if abnormal expression of target-genes which regulate DNA-repair and hematopoietic stem cell expansion predisposes to AML in ICSBP-deficient hematopoiesis. Aim 3: Identify genetic lesions that cooperate with ICSBP-deficiency to lead to disease progression in myeloid malignancy. PUBLIC HEALTH RELEVANCE: Identifying ICSBP-target-genes may suggest common final pathways which is sufficient for myeloproliferation and necessary for susceptibility to myeloid blast crisis. Functional characterization of such a pathway has implications for identifying early markers of disease progression in human myeloid malignancy and rational targets for molecular therapeutic approaches to diseases such as CML and MDS.