Role of C-myb in Hematopoiesis and Cancer

描述(申请人提供)：现已确定c-myb基因编码两种蛋白质，p75-Myb和p89-Myb，在造血细胞的发育、增殖和肿瘤发生中起关键作用。由于c-myb基因的结构性缺失会导致胚胎死亡，因此无法准确评估该基因在维持成人造血中的作用。为了克服这一问题，并研究该基因在成人造血中的功能，我们使用Cre-loxP重组系统来实现c-myb的组织特异性缺失。在最近发表的一项研究中，我们建立了两个T细胞特异性c-myb基因敲除小鼠模型mybF/F/Lck Cre和mybF/F/CD4Cre，它们在T细胞发育的两个特定阶段删除c-myb。对这些小鼠的研究使我们能够确定c-myb在T细胞发育和功能中的作用。与p75-c-Myb的功能相比，p89c-Myb在造血中的作用尚不清楚。为了研究p89c-myb亚型的功能，我们建立了一个外显子9A缺失的小鼠模型，结果是，这个突变的小鼠不能产生p89-c-Myb。当逆转录病毒诱导的小鼠髓系白血病表达c-myb的C端截短形式(称为t-myb)时，c-myb在白血病发生中的作用被确立，该c-myb具有增强的反式激活和转化活性。为了确定MYB基因截断在小鼠发育和造血过程中的生物学效应，我们培育了一株有条件地表达c-Myb C端缺失突变体的小鼠。在这个应用中，我们建议使用这些强大的小鼠遗传模型来确定c-Myb的p75和p89亚型在造血中所起的作用，以及c-Myb的C端截短在造血和白血病发生中的后果。本研究的目的是：1.通过基因芯片和蛋白质组学分析，确定c-Myb调控DP期T细胞发育的分子机制，并在体内和体外条件下评估这些改变的基因和蛋白质的功能。2.探讨c-myb在成人造血和髓系发育中的作用。3.明确c-myb在造血干细胞(HSC)发育和功能中的作用。4.确定c-myb的选择性剪接形式p89c-myb和c-myb的基因截短版本t-myb在髓系祖细胞和造血干细胞的谱系承诺、增殖和存活中的作用；以及5.检测c-myb在BCRABL介导的髓系细胞转化中的作用。

DESCRIPTION (provided by applicant): It is now well established that the c-myb gene encodes for two proteins, p75-Myb and p89-Myb, and plays a critical role in the development, proliferation and oncogenesis of hematopoietic cells. Because constitutive loss of the c-myb gene leads to embryonic lethality, it has not been possible to accurately assess the role of this gene in the maintenance of adult hematopoiesis. To overcome this problem and to investigate the function of this gene in adult hematopoiesis, we used the Cre-LoxP recombination system to achieve tissue-specific deletion of c-myb. In a recently published study, we have generated two T cell-specific c-myb knockout mouse models mybF/F/LckCre and mybF/F/CD4Cre, which delete c-myb at two specific stages of T cell development. Studies with these mice have allowed us to define the role of c-myb in T cell development and function. In contrast to the function of p75-c-Myb, the role of p89c-Myb in hematopoiesis is not known. To examine the function of the p89c- myb isoform, we have generated a mouse model where exon 9A is deleted, and as a consequence, this mutant mouse is incapable of producing the p89-c-Myb. A role for c-myb in leukemogenesis was established when It was shown that retrovirus-induced mouse myeloid leukemias express a C- terminal truncated form of c-myb (termed t-myb), which exhibits enhanced transactivating and transformation activities. To determine the biological effects of myb gene truncation during mouse development and hematopoiesis, we have generated a strain of mice which express a C-terminal deletional mutant of c-Myb conditionally. In this application, we propose to use these powerful mouse genetic models to determine the roles played by p75 and p89 isoforms of c-Myb in hematopoiesis and the consequence of C-terminal truncation of c-Myb in hematopoiesis and leukemogenesis. The aims are: 1. To ascertain the molecular mechanisms by which c-Myb regulates T-cell development at the DP stage, gene array and proteomics analysis will be performed, and the functions of those altered genes and proteins will be assessed using both in vivo and in vitro conditions. 2. To determine the role of c-myb in adult hematopoiesis and myeloid development. 3. To define the role of c-myb in Hematopoietic Stem Cell (HSC) development and function. 4. To determine the roles of an alternatively spliced form of c-myb, the p89c-myb, and a genetically truncated version of c-myb, t- myb, in lineage commitment, proliferation and survival of myeloid progenitors and HSCs; and 5. To examine the role of c-myb in BCRABL-mediated transformation of myeloid cells.