Point mutations of the AML1 gene in patients with leukemia : implications in leukemogenesis, progression, and recurrence

Runt结构域转录因子AML 1/RUNX 1对确定性造血干细胞的生成和分化是必需的。AML 1是急性白血病中染色体易位的最常见靶点。一些嵌合蛋白如AML 1-MTG 8和TEL-AML 1具有野生型AML 1的反式显性特性，并作为转录抑制因子。另一方面，在没有AML 1易位的散发性急性成髓细胞白血病（AML）和具有AML易感性的家族性血小板疾病（FPD/AML）中鉴定了AML 1的Runt结构域中的突变。在这项研究中，我们确定了25例（20%）AML M0亚型患者中的5例AML 1基因突变。在2例FPD/AML患者中发现AML 1基因突变。这些观察结果表明，染色体易位或突变导致的AML 1剂量减少有助于白血病发生。对FPD/AML家系中AML 1突变体的功能分析显示AML 1基因有两种类型的突变：功能丧失突变（单倍不足）和显性阴性突变。AML 1基因显性负性错义突变的家系发生AML的可能性高于AML 1基因纯合缺失和移码突变的家系。这些观察结果表明，AML 1的剂量对于获得导致AML的第二突变至关重要，尽管这种分子机制仍有待确定。在AML中经常观察到的p15基因的甲基化是刺激细胞增殖的第二次突变的候选者。我们采用实时荧光定量RT-PCR方法分析AML中p15 mRNA的表达。我们还检测了骨髓增生异常综合征急性转化和复发性AML患者的AML 1基因突变。

A Runt domain transeriptibn factor AML1/RUNX1 is essential for generation and differentiation of difinitive hematopoietic stem cells. AML1 is the most frequent target of chromosomal translocations in acute leukemias. Several chimericproteins such as AML1-MTG8 and TEL-AML1 have transdominant properties for wild-type AML1 and acts as transcriptional repressors. On the other hand, mutations in the Runt domain of the AML1 are identified in both sporadic acute myeloblastic leukemia (AML) without AML1 translocation and familial platelet disorder with predisposition to AML (FPD/AML). In this study, we identified mutations of the AML1 gene in 5 of 25 (20%) patients with AML M0 subtype. We also found mutations of the AML1 gene in 2 pidigrees of FPD/AML. These observations indicate that a decrease in AML1 dosage resulting from chromosomal translocations or mutations contributes to leukemogenesis. Functional analysis of AML1 mutants in the FPD/AML pedigrees showed two types of mutations of the AML1 gene : loss-of-function mutations (haploinsufficiency) and a dominant negative forms of mutations. Pedigrees with dominant negative missense mutation of the AML1 appear to have a higher insidence of development of AML than those in families with genuine haploinsufficiency of the AML1 gene such as deletions and frameshift mutations. These observations suggest that dosage of AML1 is critical for acquisition of second mutation leading to AML although this molecular mechanism remains to be determined. Methylation of the p15 gene, which is frequently observed in AML, is candidate for second mutation that should stimulate cell proliferation. We are analyzing p15 mRNA expression in AML by using quantitative assay with real-time RT-PCR. We have also examined mutations of the AML1 gene in patients with acute transformation from myelodysplastic syndrome and relapsing AML.