Cyclin E Regulation in Normal and Neoplastic Hematopoiesis

描述（由申请人提供）：血细胞的发育依赖于精确控制的基因表达程序，该程序控制着特定谱系中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血细胞成熟至关重要。在小鼠敲入模型中，研究了调节s期进入的蛋白cyclin E失调的生理后果，我们发现红细胞成熟异常，增生、凋亡增加，红细胞祖细胞形态发育异常。这些特征是早期骨髓增生异常综合征（MDS）患者造血细胞的特征。我们假设细胞周期蛋白E的适当调控在正常造血过程中是至关重要的，并且细胞周期控制的失调有助于MDS和白血病等血液疾病的发病机制。Fbw7泛素连接酶是细胞周期蛋白E活性的主要调节因子，也控制着参与细胞生长和增殖的其他重要致癌蛋白的丰度。在急性白血病中发现了Fbw7功能丧失突变，与骨髓发育不良和白血病相关的信号通路突变可损害Fbw7介导的细胞周期蛋白E降解。我们最近发现，在fbw7介导的细胞周期蛋白E降解受损的DNA损伤型反应中，p53肿瘤抑制因子在红系祖细胞中被激活。在包括Aim 1的拟议研究中，我们将首先定义高周期蛋白E及其引起的分子反应如何改变正常的红细胞成熟。MDS是一种由造血干细胞缺陷引起的异质性血液病。在Aim 2中提出的研究中，我们将验证fbw7介导的周期蛋白E调节对维持正常造血干细胞功能至关重要的假设。p53突变在晚期MDS中发现，这与进展为白血病有关。在Aim 3中，我们将验证p53功能受损与造血祖细胞中细胞周期蛋白E失调共同诱导体内肿瘤形成的假设。我们将开发小鼠骨髓移植模型来验证这一假设，通过在cyclin E敲入的造血细胞中禁用p53功能，直接通过等位基因缺失或间接通过Fbw7的另一种致癌底物c-Jun的表达失调。公共卫生相关性：骨髓增生异常综合征和由MDS演变而来的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，这是这些研究的一个长期目标，以便制定更有效的治疗策略。

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.