Molecular basis for leukemic transformation caused by chimeric protein involving the transcription factor AML1 (PEBP2aB).

AML 1（PEBP 2 αB）编码造血相关转录因子复合物PEBP 2（CBF）的DNA结合亚基，是人类白血病相关基因畸变的最常见靶点。我们通过基因靶向实验研究了AML 1作用的分子机制以及其突变如何促进白血病的发展。主要研究结果如下：1.我们通过体内造血拯救实验证实了AML 1支持永久性造血发育的生物学活性依赖于其反式激活活性，并且其最C端的反式阻遏结构域是这种作用的关键.我们新克隆了编码AML 1c亚型的cDNA，该亚型在AML 1基因位点的远端启动子的控制下差异表达，而AML 1b亚型的表达受近端启动子的调控。AML 1b在骨髓中广泛表达，而AML 1c的表达与造血功能密切相关，并依赖于AML 1活性基因座的存在.我们分析了携带敲入的AML 1-MTG 8白血病基因的小鼠胚胎干细胞克隆在嵌合小鼠中的命运，发现敲入的克隆可以促进成年小鼠的造血组织。然而，他们从来没有发展明显的白血病，迄今为止，因为他们被保持在特定的病原体自由的气氛中，这表明这种嵌合白血病基因是必要的，但不是足够的leukemogenes.We目前正在产生的种系基因敲入小鼠携带白血病相关的点突变（S）的AML 1基因，以进一步确定该基因突变如何有助于白血病的发生。

AML1 (PEBP2αB) encodes the DNA-binding subuit for the hematopoiesis-related transcription factor complex, PEBP2 (CBF), which is the most frequent target of the human leukemia-associated gene aberrations. We investigated the molecular mechanism of actions played by AML1 and how its mutations contribute to the development of leukemia, by using gene-targeting experiments. Our results are summarized as follows :1. We established that the biologic activity of AML1 to support the development of definitive hematopoiesis depends on its trans-activating activity and that its most C-terminal trans-repression domain is dispensable for this action by in vivo hematopoietic rescue experiments.2. We newly cloned the CDNA encoding the AML1c isoform, which is differentially expressed under the control of the distal promoter of AML1 gene locus, in contrast to AML1b isoform, whose expression is regulated by the proximal promoter. While AML1b was expressed ubiquitously, the expression of AML1c appeared to be more closely related to the definitive hematopoiesis and is dependent on the presence of active AML1 gene locus.3. We analyzed the fate of the mouse embryonic stem cell clones which carry a knocked-in AML1-MTG8 leukemic gene within the chimeric mice, and found that the knock-in clones could contribute to the hematopoietic tissues of adult mice. However, they never developed overt leukemia so far as they were kept in the specific-pathogen free atmosphere, indicating that this chimeric leukemia gene is necessary but not sufficient for the leukemogenesis.We are currently generating the germline knock-in mice which carry leukemia associated point mutation(s) of AML1 gene to further define how this gene-mutation contribute to the leukemogenesis.