The molecular role of lkaros in leukemogenesis

描述(申请人提供)：肿瘤抑制基因是一组基因，其功能经常通过突变癌细胞而丧失。我们已经确定Ikaros是一种具有新的T细胞系特异性肿瘤抑制因子特征的蛋白质。在100%外显性的情况下，小鼠体内缺乏Ikaros活性会导致白血病发生。我们已经证明，使用一种新的细胞培养系统，将Ikaros基因恢复到Ikaros缺失的T白血病细胞系会导致细胞周期停滞，并启动T细胞特异性的基因表达程序。我们还确定了细胞周期调节因子p27kip1是Ikaros转录激活的潜在遗传靶点。有趣的是，p27kip1基因表达水平的降低与bcr/abl诱导人类白血病的机制有关，这表明Ikaros零T细胞中p27kip1水平的降低可能是其显著转化倾向的关键。Ikaros在人类细胞中也可能起到肿瘤抑制作用，因为在分析的婴儿和儿童急性淋巴细胞白血病中，很高比例的Ikaros基因表达存在缺陷。这项提案中描述的实验的目标是确定Ikaros活性缺乏导致白血病发生的机制。我们将通过：1)确定对其在生长控制中的作用至关重要的Ikaros的功能/相互作用结构域；2)确定Ikaros控制p27kip1基因表达的机制；以及3)确定其在启动T细胞特异性基因表达程序中所需的功能/相互作用结构域。这些研究还将包括分析Ikaros与Brg-1和Swi/SNF染色质重塑复合体在T细胞生长控制和诱导T细胞特异性基因表达程序中的作用。定义伊卡洛斯功能的机制的困难，至少部分是由于缺乏一个易于操作的实验系统。然而，我们独特的细胞培养系统由可以通过逆转录病毒转导进行基因改变的Ikaros空T白血病细胞系组成，是确定Ikaros功能机制的有效工具。这个系统与Ikaros基因缺失的小鼠结合在一起，使我们唯一有资格确定这种新的肿瘤抑制基因的机制作用。

DESCRIPTION (provided by applicant): Tumor suppressor genes are a group of genes whose function is frequently lost through mutation cancer cells. We have identified Ikaros as a protein with characteristics of a novel T lineage specific tumor suppressor. With 100% penetrance, lack of Ikaros activity in mice results in leukemogenesis. We have shown, using a novel cell culture system, that genetic restoration of Ikaros to an Ikaros null T leukemia cell line results in cell cycle arrest and initiation of a T cell specific program of gene expression. We have also identified the cell cycle regulator, p27kip1, as a potential genetic target for transcriptional activation by Ikaros. Interestingly, decreased levels of p27kip1 gene expression have been linked to the mechanism of Bcr/Abl induced human leukemia, suggesting that decreased p27kip1 levels in Ikaros null T cells may hold the key to their remarkable propensity to transform. Ikaros may play a tumor suppressive role in human cells as well, since a high percentage of analyzed infant and childhood acute lymphocytic leukemias display defects in Ikaros gene expression. The goal of the experiments described in this proposal is to define mechanisms by which lack of Ikaros activity leads to leukemogenesis. We will do this by: 1) identifying Ikaros' functional/interaction domains essential to its role in growth control, 2) defining the mechanism by which Ikaros controls expression of the p27kip1 gene and 3) identifying Ikaros' functional/interaction domains required for its role in initiating a T cell specific program of gene expression. These studies will also include analyses of the role of Ikaros' association with Brg-1 and the Swi/Snf chromatin remodeling complexes in T cell growth control and induction of a T cell specific program of gene expression. The difficulty in defining mechanisms of Ikaros function has been due, at least in part, to lack of an easily manipulated experimental system. However, our unique cell culture system consisting of an Ikaros null T leukemia cell line that can be genetically altered using retroviral transduction is a potent tool to define mechanisms of Ikaros function. This system, in conjunction with the Ikaros null mice, makes us uniquely qualified to define the mechanistic role of this novel tumor suppressor gene.