ICSBP Function During Myeloid Differentiation

描述(由申请人提供)：几行证据表明干扰素共识序列结合蛋白(ICSBP或IRF8)具有髓系白血病肿瘤抑制因子的功能。首先，骨髓增生异常综合征(MDS)和慢性粒细胞白血病(CML)患者的骨髓样本中ICSBP-表达减少。其次，IRF8基因定向干扰的小鼠表现出一种CML样的骨髓增生性疾病，随着时间的推移，这种疾病会发展为急性髓系白血病(AML)。这些结果表明，ICSBP缺乏本身就足以诱导骨髓增殖，但更多的突变是发展为AML所必需的。然而，最初确定的靶基因并不表明ICSBP缺乏导致这两种事件的机制。例如，我们发现ICSBP激活了编码吞噬细胞NADPH-氧化酶蛋白gp91PHOx和p67Phox的基因的转录。其他研究人员发现了其他与吞噬细胞功能有关的ICSBP靶基因。因此，ICSBP缺乏降低了髓系特异性基因的转录，这可能是分化障碍的原因之一。然而，ICSBP缺陷的髓系祖细胞表现出对凋亡的抵抗，对造血细胞因子的超敏，以及积累额外的遗传损伤的倾向。介导这些效应的真正的ICSBP靶基因尚未被鉴定。在之前的资助期间，我们一直在寻找这样的目标基因。通过染色质免疫沉淀和CpG岛芯片筛选，我们鉴定了ICSBP靶基因，这些基因编码与细胞增殖和凋亡相关的蛋白(Nore1、Fap1和可溶性鸟氨酸环化酶组分)。这些靶基因的鉴定支持ICSBP缺乏足以导致骨髓增殖性疾病的假设。我们还发现了通过调节Wnt/2连环蛋白途径(Gas2、Dapper2和calain 2和12)参与造血干细胞扩增的靶基因。此外，我们还鉴定了一个ICSBP靶基因，该基因参与了造血细胞(Fanconi F)的一个关键DNA修复途径。这与靶基因表达异常的ICSBP缺陷细胞容易获得额外的基因突变，导致分化障碍和AML的假设是一致的。我们将通过以下具体目标来推进我们的假设：目标1：确定在ICSBP缺乏的造血中，与凋亡相关的靶基因的异常表达是否有助于骨髓增殖。目的：探讨调控DNA修复和造血干细胞扩增的靶基因表达异常是否在ICSBP缺乏的造血系统中易患急性髓系白血病。目的3：确定与ICSBP缺乏协同导致髓系恶性肿瘤疾病进展的基因损伤。公共卫生相关性：识别ICSBP靶基因可能会提示共同的最终途径，这对骨髓增殖是足够的，对髓系原始细胞危机的易感性是必要的。这种途径的功能特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具有合理的靶点。

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.