Analysis of multi-step processes of leukemia-genesis in childhood leukemia.

（1）由t（12 ; 21）易位产生的TEL-AML 1融合基因是儿童白血病中最常见的异常，并且仅与B细胞白血病相关。我们用小鼠模型探讨了易位导致白血病的机制。虽然我们能够看到融合能够阻断B细胞分化，并扩大细胞群体，但小鼠没有发展成白血病。因此，我们接下来寻找可能与白血病发生相关的其他遗传异常。为此，我们利用阵列-CGH方法分析了临床白血病样品和细胞系。我们发现所有的病例除了TEL-AML 1易位外，还有至少2种遗传异常。其中，非易位等位基因上的TEL缺失最常见，其次是参与细胞周期调控的基因，如BTG 1，p16 INK 4a/ARF。在TEL-AML 1细胞系Reh中发现丢失的基因产物的强制表达抑制细胞增殖。这些发现表明这些基因的丢失可能是白血病发生的部分原因。（2）越来越多的证据表明，特定转录因子的特定亚型与白血病有关。Runx 1/AML 1转录因子有两种亚型，但它们的不同作用及其与白血病发生的可能关系尚未得到很好的研究。我们发现，短亚型，AML 1a，只表达在CD 34阳性的未成熟干/祖细胞之间的人脐带血细胞。因此，我们接下来使用逆转录病毒/慢病毒转导小鼠/人造血细胞，以观察AML 1a的表达是否对体外和体内的干/祖细胞活性有任何影响。我们发现AML 1a的表达赋予细胞自我更新的能力，生长优势，更高的植入潜力。我们的结论是，这样实现的血细胞扩增更有可能获得额外的遗传命中，从而导致白血病。

(1)TEL-AML1 fusion gene, generated by t(12 ; 21) translocation, is the commonest abnormality in childhood leukemia, and is exclusively associated with B cell leukemia. We have addressed the mechanism whereby the translocation generates the leukemia, using mouse model. Although we are able to see the fusion is able to block B cell differentiation, and expand cell population, mice did not develop leukemia. We therefore next searched for additional genetic abnormalities which could be linked leukemia-genesis. To this end, we analyzed clinical leukemia samples and cell lines by the use of array-CGH method. We then found that all the cases had at least 2 genetic abnormalities, in addition to TEL-AML1 translocation. Among these, loss of TEL on the untranslocated allele was most commonly found, followed by losses of genes involved in cell cycle regulation, such as BTG1, p16INK4a/ARF. Enforced expressions of the gene products found lost in Reh, a TEL-AML1 cell line, inhibited the cell proliferation. These findings suggest the losses of the genes may partly account for the leukemia-genesis.(2)Evidence is accumulating that a specific isoform of a given transcription factor is associated with leukemia. There are two isoforms in Runx1/AML1 transcription factor, but their differential roles and possible association with leukemia-genesis have not been well explored. We found that the short isoform, AML1a, is expressed exclusively in CD34-positive immature stem/progenitors among human cord blood cells. We therefore next transduced mouse/human hematopoietic cells using retrovirus/lentivirus to see if the expression of AML1a has any impact on stem/progenitor activities both in vitro and in vivo. We then found that AML1a expression confers cells self-renewal activities, growth advantage, higher engraftment potential. We concluded that the blood cell expansion thus achieved is more likely to obtain additional genetic hits, and thus leading to leukemia.