Analysis of the mechanism of leukemogenesis in leukemia cells carrying mutation of AML1 and PEBP2β genes

AML1基因被认为是与白血病相关的最常见的染色体易位目标。它编码异源二聚体转录因子Runt域家族中的α亚单位，并调节各种与造血相关的基因的表达。AML1易位在t(8；21)(q22；q22)急性髓细胞白血病(AML)中产生AML1-ETO(MTG8)等嵌合蛋白，在t(12；21)急性淋巴细胞白血病(ALL)中产生ETV6(TEL)-AML1嵌合蛋白。这些嵌合蛋白中的所有11个都保留了整个Runt结构域，该结构域负责与β亚单位(β)结合和异源二聚。我们在160例白血病中发现8例AML1基因点突变，2例沉默突变，4例杂合性错义突变，2例双等位无义突变或移码突变。3例错义突变既没有DNA结合，也没有反式激活。编码截短的AML1蛋白的双等位无义突变体几乎丧失了所有功能，可能在导致AML的白血病发生中发挥作用。另一方面，我们在120例白血病中未发现PEBP_2β基因突变。在本研究中，我们还检测了AML1基因在AML M0亚型中的突变，以验证亚型与AML1基因突变的关系。在30例M0患者中，有6例检测到AML1基因移码突变，导致AML1单倍体缺失。最近的研究表明，AML1基因单倍体功能不全会导致与AML发病倾向相关的家族性血小板紊乱。因此，AML1基因的单倍性缺失与白血病的易感性或进展有关。

The AML1 gene is known as the most frequent target of chromosomal translocations associated with leukemia. It encodes the α-subunit in the Runt domain family of heterodimeric transcriptional factors and acts to regulate the expression of various gene specific to hematopoiesis. The Translocations involving AML1 produce chimeric proteins such as AML1-ETO (MTG8) in acute myeloblastic leukemia (AML) with t(8;21)(q22;q22) and ETV6 (TEL)-AML1 in pediatric acute lymphoblastic leukemia(ALL)with t(12;21). A11 of these chimeric proteins retain thc entire Runt domain which is responsible for DNA binding and heterodimerization withβsubunit (PEBP2β). We round point mutations of the AML1 gene in 8 of 160 leukemias; 2 silent mutations, 4 heterozygous missense mutations, and 2 biallelic nonsense or frameshift mutations. Missense mutations in 3 patients showed neither DNA binding nor transactivation. The biallelic nonsense mutants encoding truncated AML1 proteins lost almost all functions and may play a role in leukemogenesis leading to AML. On the other hand,we found no mutation of the PEBP2βgene in 120 leukemias. In this study, we also examined mutation of the AML1 gene in AML M0 subtype to verify relationship between subtype and the AML1 gene mutation. In 6 of 30 patients with M0, we detected frameshift mutations of the AML1 gene, resulting in haploinsufficiency of the AML1. It was recently demonstrated that haploinsufficiency of AML1 causes familial platelet disorder associated with propensity to develop AML. Therefore, the haploinsufficiency of the AML1 is relevant to the predisposition or progression of leukemia.