Rac1 and Rac2 Guanosine Triphosphatases in Erythroid Function and Differentiation

描述(由申请人提供)： Rho鸟苷三磷酸酶(GTP酶)rac1和rac2调节多种细胞类型的肌动蛋白细胞骨架、微管动力学、基因转录、增殖和存活。在不同的造血细胞系中，它们在肌动蛋白的组织、细胞存活和增殖中具有重叠和不同的作用。然而，它们在红系前体和红细胞中的作用尚未得到评估。利用基因靶向的小鼠，我们发现，在红系中，rac1和rac2 GTP酶的缺失导致了显著的表型：轻度贫血伴相对网织红细胞增多，既有溶血(红细胞细胞骨架结构异常，机械稳定性降低)，也有天然的红细胞生成障碍。红细胞生成主要在早期阶段受到影响，此时干细胞因子(SCF)起着关键作用。因此，我们假设RAC GTP酶(1)动态调节红细胞细胞骨架的结构和功能，(2)在红系前体的归巢、增殖、存活和分化中发挥关键作用，可能与通过SCF受体c-Kit激活的信号通路交叉。为了验证我们的假设，我们提出了一个系统的表征Rac GTP酶缺陷对RBC细胞骨架中肌动蛋白聚合机制的影响，分析了肌动蛋白相关蛋白，并评估了RAC与其他Rho GTP酶和信号分子可能的相互作用。同时，我们将研究Rac1“/”；Rac2“/”小鼠红细胞生成的扰动，寻找Rac GTP酶整合来自一种或多种促红细胞细胞因子的多种信号，影响红细胞生成的机制/S。这两个被提出的目的旨在探索和测试RAC GTP酶如何调节红系发育、形态发生以及RBC细胞骨架及其组分的结构-功能关系。中心目标是确定参与正常红系发育和红细胞膜结构生物学的关键分子信号通路。从长远来看，这项研究有望为溶血性贫血的发病机制提供新的视角，并为以异常红细胞生成和红细胞存活率下降为特征的人类疾病提供潜在的治疗靶点。(摘要结束)

DESCRIPTION (provided by applicant): The Rho guanosine triphosphatases (GTPases) Rac1 and Rac2 regulate actin cytoskeleton, microtubule dynamics, gene transcription, proliferation, and survival in multiple cell types. They have been shown to have overlapping as well as distinct roles in actin organization, cell survival, and proliferation in various hematopoietic cell lineages. However their role in erythroid precursors and erythrocytes has not been evaluated. Using gene-targeted mice we have found that deficiency of Rac1 and Rac2 GTPases causes a significant phenotype in erythroid lineage: mild anemia with relative reticulocytosis, both hemolytic (abnormal structure of the erythrocyte cytoskeleton with decreased mechanical stability) and dyserythropoietic in nature. Erythropoiesis is affected mainly at the early stages, when stem cell factor (SCF) plays a critical role. We therefore hypothesize that Rac GTPases (1) dynamically regulate the structure and function of the erythrocyte cytoskeleton, and (2) play a critical role in homing, proliferation, survival, and differentiation of erythroid precursors, likely intersecting signaling pathways activated via the SCF receptor, c-Kit. To test our hypotheses, we propose a systematic characterization of the effects of Rac GTPase deficiency on the actin polymerization mechanics in the RBC cytoskeleton, with analysis of the actin-associated proteins and evaluation of possible cross-talk of Rac with other Rho GTPases and signaling molecules. In parallel, we will investigate the perturbations of erythropoiesis in Rac1"/";Rac2"/" mice, seeking the mechanism/s by which Rac GTPases, integrating multiple signals from one or more of the erythropoietic cytokines, affect erythropoiesis. These two proposed aims intent to explore and test how Rac GTPases regulate erythroid development, morphogenesis, and structure-function relation of the RBC cytoskeleton and its components. The central goal is to define critical molecular signaling pathways that participate in normal erythroid development and RBC structural membrane biology. In the long-term, this research is expected to offer new perspectives on the pathogenesis of hemolytic anemia and provide potential therapeutic targets in human disease characterized by abnormal erythropoiesis and decreased RBC survival. (End of Abstract)