ICSBP Function During Myeloid Differentiation

描述（由申请人提供）：几条证据表明，干扰素一致序列结合蛋白（ICSBP或IRF8）具有髓系白血病肿瘤抑制因子的功能。首先，icsbp在骨髓增生异常综合征（MDS）和慢性髓性白血病（CML）患者的骨髓样本中表达降低。其次，靶向破坏irf8基因的小鼠表现出cml样骨髓增殖性疾病，随着时间的推移发展为急性髓性白血病（AML）。这些结果表明，icsbp缺乏本身足以诱导骨髓增殖，但需要额外的突变才能进展为AML。然而，最初确定的靶基因并没有提示icsbp缺乏症易患这两种事件的机制。例如，我们发现ICSBP可以激活编码吞噬细胞nadph氧化酶蛋白gp91PHOX和p67phox的基因的转录。其他研究人员发现了参与吞噬细胞功能的其他icsbp靶基因。因此，icsbp缺乏降低了骨髓特异性基因转录，这可能导致分化受阻。然而，缺乏icsbp的骨髓祖细胞表现出对凋亡的抵抗，对造血细胞因子的过敏，以及积累额外遗传病变的倾向。介导这些作用的真正的icsbp靶基因尚未确定。在之前的资助期间，我们致力于鉴定这些靶基因。通过染色质免疫沉淀和CpG岛芯片筛选，我们确定了ICSBP靶基因，该基因编码参与增殖（神经纤维蛋白1）和凋亡（Nore1， Fap1和可溶性鸟苷酸环化酶成分）的蛋白质。这些靶基因的鉴定支持了icsbp缺乏足以诱导骨髓增生性疾病的假设。我们还发现了通过调节Wnt/2catenin通路参与造血干细胞扩增的靶基因（Gas2、Dapper2、calpain2和12）。此外，我们发现了一个icsbp靶基因参与造血细胞的关键DNA修复途径（Fanconi F）。这与icsbp缺陷细胞异常靶基因表达容易获得额外基因突变的假设是一致的，从而导致分化阻滞和AML。我们将通过以下具体目标来实现我们的假设：目的1：确定细胞凋亡相关靶基因的异常表达是否有助于icsbp缺陷造血的骨髓增殖。目的2：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导致icsbp缺陷造血的AML。目的3：确定与icsbp缺乏合作导致髓系恶性肿瘤疾病进展的遗传病变。公共卫生相关性：确定icsbp靶基因可能提示共同的最终途径，这是髓细胞增殖的充分条件，也是髓细胞危象易感性的必要条件。这一途径的功能表征对于识别人类髓系恶性肿瘤疾病进展的早期标志物以及CML和MDS等疾病的分子治疗方法的合理靶点具有重要意义。

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.