Molecular dissection of the leukemia-associated transcription factor, AML1/RUNX1,in hematopoietic regulation

急性髓系白血病1(AML1；又称Runt相关转录因子1：RUNX1)是一种转录因子，在明确的造血早期发育中起关键作用，也是白血病相关基因异常的最常见靶点。在这项研究中，我们通过胚胎干细胞和整个小鼠水平的造血挽救试验，检测了它的功能以及正常和白血病的造血。我们的发现概括如下：1.AML1的转录抑制功能是通过其C端的VWRPY基序介导的，在整个小鼠的早期造血发育中并不是必不可少的。2.纯合子携带缺失VWRPY基序的敲入的AML1等位基因的基因组修饰小鼠品系显示，遗传保守的VWRPY基序在胸腺的早期发育和CD4表达中起重要作用。3.通过对170例白血病或相关疾病的筛查，我们在外显子3到6中发现了5个(2.9%)新的突变，与矮小结构域相对应。除1例沉默突变外，其余4例均为功能缺失型等位基因：其中2例为N-末端附近移码突变，另外2例为插入突变，位于矮小结构域C-末端附近，经实验证实为非功能性突变。这些数据进一步强调，AML1的一个等位基因丢失是人类白血病发生的早期事件。

Acute Myeloid Leukemia 1 (AML1; also called as Runt-Related Transcription Factor 1: RUNX1) encodes a transcription factor which plays a pivotal role in early development of definitive hematopoiesis, and is the most frequent target of the leukemia-associated gene aberration. In this study, we examined its function along with normal and leukemic hematopoiesis by means of hematopoietic rescue assay at embryonic stem cell and entire mouse levels. What we found are summarized as follows:1.Transcription-repressive function of AML1,which is mediated through its C-terminal VWRPY-motif, is not essential for the early hematopoietic development in the context of the entire mouse.2.Genome-modified mouse lines which homozygously harbor knocked-in AML1 allele lacking of VWRPY-motif revealed that the genetically conserved VWRPY-motif plays an important role in early development of thymus and CD4-expression.3.By screening 170 cases of leukemia or related disorders, we found five (2.9%) novel mutations within the exons 3 through 6,which correspond to the runt domain. Apart from a case with a silent mutation, the remaining four cases were all loss-of-function type of the allele : Two of them were frame-shift near the N-terminus, and the other two, I150ins and K168,were insertion mutations near the C-terminal end of the runt domain which were experimentally proven to be non-functional. These data further underscore the notice that one-allele loss of AML1 serves as an early event of human leukemogenesis.