Cyclin E Regulation in Normal and Neoplastic Hematopoiesis

描述(由申请人提供)：血细胞发育依赖于精确控制的基因表达程序，该程序管理特定谱系的祖细胞的承诺和成熟。除了在谱系承诺过程中调节基因表达的转录因子外，完整的细胞周期控制机制对正常的血细胞成熟至关重要。在研究调节S时相进入的蛋白质Cyclin E异常的生理后果的敲入小鼠模型中，我们发现红细胞异常成熟，红系祖细胞的增殖、凋亡和异常形态增加。这些特征是早期骨髓增生异常综合征(MDS)患者的造血细胞特征。我们假设，在正常的造血过程中，细胞周期蛋白E的适当调节是至关重要的，而细胞周期调控失控有助于MDS和白血病等血液疾病的发病。Fbw7泛素连接酶是细胞周期蛋白E活性的主要调节因子，也控制着与细胞生长和增殖有关的其他重要致癌蛋白的丰度。在急性白血病中发现Fbw7功能缺失突变，与骨髓发育不良和白血病相关的信号通路突变可能会削弱Fbw7介导的细胞周期蛋白E的降解。我们最近发现，P53肿瘤抑制因子在红系祖细胞中被激活，这是对Fbw7介导的细胞周期蛋白E降解受损的DNA损伤型反应。在包括目标1的拟议研究中，我们将首先定义高水平的细胞周期蛋白E及其引起的分子反应如何改变正常的红系细胞成熟。MDS是一组由造血干细胞缺陷引起的异质性血液疾病。在目标2中提出的研究中，我们将检验Fbw7介导的细胞周期蛋白E调节对维持正常的造血干细胞功能至关重要的假设。在晚期MDS中发现了p53突变，这与进展为弗兰克白血病有关。在目标3中，我们将验证一种假说，即P53功能受损与造血祖细胞中异常调节的细胞周期蛋白E协同在体内诱导肿瘤发生。我们将建立小鼠骨髓移植模型来验证这一假设，方法是通过直接通过等位基因缺失或通过另一种致癌底物Fbw7 c-jun的异常表达来禁用细胞周期蛋白E敲入的造血细胞中的p53功能。公共卫生相关性：由MDS演变而来的骨髓增生异常综合征和急性白血病尤其难以治疗，通常会导致死亡。迫切需要更好地了解这些疾病的分子发病机制，这是这些研究的长期目标之一，以便制定更有效的治疗策略。 公共卫生相关性：骨髓增生异常综合征和急性白血病是血液的恶性疾病，对于老年人来说，这些疾病尤其难以治疗，通常会导致死亡。迫切需要了解这些疾病发生的不同方式，以便在未来开发更好的治疗方法。研究人员最近发现，一种控制细胞分裂的蛋白质(称为周期蛋白E)，当它被异常调控时，会导致血细胞发育缺陷，其中一些类似于一些骨髓发育不良患者的缺陷。研究人员现在提议研究高周期蛋白E水平如何导致这些血细胞缺陷，并导致骨髓衰竭和癌症。

DESCRIPTION (provided by applicant): Blood cell development depends on precisely controlled gene expression programs that govern the commitment and maturation of progenitor cells along specific lineages. In addition to transcription factors that regulate gene expression during the course of lineage commitment, intact cell cycle control mechanisms are critical to normal blood cell maturation. In a mouse knock-in model developed to study the physiologic consequences of dysregulated cyclin E, a protein that regulates S-phase entry, we found abnormal red blood cell maturation, with increased proliferation, apoptosis, and dysplastic morphologies in erythroid progenitors. These features are characteristics of hematopoietic cells of patients with early-stage myelodysplastic syndromes (MDS). We hypothesize that proper regulation of cyclin E is critical during normal hematopoiesis and that deregulated cell cycle controls contribute to the pathogenesis of blood diseases such as MDS and leukemia. The Fbw7 ubiquitin ligase is a major regulator of cyclin E activity and also controls the abundance of other important oncogenic proteins involved in cell growth and proliferation. Fbw7 loss-of-function mutations are found in acute leukemias, and mutations in signaling pathways associated with myelodysplasia and leukemias can impair Fbw7- mediated cyclin E degradation. We recently found that the p53 tumor suppressor is activated in erythroid progenitor cells in a DNA damage-type response to impaired Fbw7-mediated cyclin E degradation. In the proposed studies comprising Aim 1, we will first define how high cyclin E and the molecular response it evokes alters normal erythroid cell maturation. MDS is a heterogeneous group of blood diseases caused by hematopoietic stem cell defects. In studies proposed in Aim 2, we will test the hypothesis that Fbw7-mediated cyclin E regulation critically maintains normal hematopoietic stem cell function. Mutations in p53 are found in advanced stage MDS, which is associated with progression to frank leukemia. In Aim 3, we will test the hypothesis that compromised p53 function cooperates with dysregulated cyclin E in hematopoietic progenitors to induce neoplasia in vivo. We will develop mouse marrow transplantation models to test this hypothesis by disabling p53 function in cyclin E knock-in hematopoietic cells, either directly by allelic deletion or indirectly via dysregulated expression of another oncogenic substrate of Fbw7, c-Jun. PUBLIC HEALTH RELEVANCE: Myelodysplastic syndromes and acute leukemias that evolve from MDS are especially difficult to treat, usually causing death. There is urgent need for a better understanding of the molecular pathogenesis of these diseases, one long-term goal of these studies, in order for more effective treatment strategies to be devised. PUBLIC HEALTH RELEVANCE: Myelodysplastic syndromes and acute leukemias are malignant diseases of the blood, and in older adults these diseases are especially difficult to treat and usually cause death. There is urgent need for understanding the different ways in which these diseases occur so that better treatments can be developed in the future. The investigators recently found that one of the proteins that controls cell division (called "cyclin E"), when it is abnormally regulated, causes defects in blood cell development, some of which resemble those found in some patients with myelodysplasia. The investigators now propose to study how high cyclin E levels cause these blood cell defects and contribute to bone marrow failure and cancers.