Mechanism(s) of TAL-1/SCL-mediated Leukemogenesis

描述(申请人提供)：大多数儿童T细胞急性淋巴细胞白血病(T-ALL)病例涉及肿瘤特异性激活TAL-1/SCL。TAL-1是一种在造血祖细胞和红系细胞中表达的碱性螺旋-环-螺旋(BHLH)蛋白，一旦与E蛋白(如E12、E47、Heb)结合就能与DNA结合，E蛋白是调节淋巴系发育的关键转录因子。在人和小鼠白血病细胞中检测到稳定的Tal-1/E47或Heb异源二聚体，表明Tal-1通过干扰E蛋白功能而参与白血病(S)。与这一想法一致，E2A缺陷的小鼠会患上T细胞白血病/淋巴瘤，而表达TAL-1的DNA结合突变体的小鼠会患上疾病。TAL-1E/2A转化途径与人类T-ALL有关，涉及LIM-Only基因LMO1/LM02，最近发现该基因在基因治疗诱导的T-ALL中被激活。 本研究的总体目标是以小鼠为模型系统，以TALL/SCL为模型系统，明确白血病发生的机制(S)。我们对Tal-1/E2a+L-和TAI-1/Heb+I-小鼠的初步研究为Tal-1通过干扰E47/Heb进行转化提供了遗传学证据。Tal-1/scl如何抑制E47/Heb的转录活性以及新的TAI-1/E47/LMO2靶基因是否与疾病有关是提出的工作目标(目标1)。另一个目标是使用有条件的TAL-1转基因模型(目标2)，检查TAL-1表达对胸腺细胞分化、凋亡和基因表达的直接和直接影响。利用逆转录病毒插入突变技术，我们发现在TAL L1诱导的白血病中，激活的Notch 1、显性阴性的Ikaros和myc是协同作用基因。最后一个目标是确定激活的Notch1、显性阴性的Ikaros和myc如何促进Tal-1白血病的发生，以及Tal-1肿瘤是否仍然依赖于这些次级突变的持续表达(目标3)。

DESCRIPTION (provided by applicant): Most cases of pediatric T cell acute lymphoblastic leukemia (T-ALL) involve tumor-specific activation of TAL-1/SCL. TAL-1, a basic helix-loop-helix (bHLH) protein expressed in hematopoietic progenitors and erythroid cells, binds DNA once bound to E proteins (e.g., E12, E47, HEB), critical bHLH transcription factors, which regulate lymphoid development. Stable tal-1/E47 or HEB heterodimers are detected in human and mouse leukemic cells, suggesting that tal-1 contributes to leukemia by interfering with E protein function(s). Consistent with this idea, E2A-deficient mice develop T cell leukemia/lymphoma, and mice expressing a DNA binding mutant of tal-1 develop disease. The TAL-1E/2A transformation pathway is implicated in human T-ALL involving the LIM-only genes LMO1/LM02, recently found activated in gene therapy-induced T-ALL. The overall goal of this research program is to define the mechanism(s) of leukemogenesis by tall/ scl using the mouse as a model system. Our preliminary studies of tal-1/E2A+l- and taI-1/HEB+I- mice provide genetic evidence that tal-1 transforms by interfering with E47/HEB. How tal-1/scl inhibits E47/HEB transcriptional activity and whether novel taI-1/E47/LMO2 target genes contribute to disease are objectives of the work proposed (Aim 1). An additional goal is to examine the immediate and direct effects of tal-1 expression on thymocyte differentiation, apoptosis, and gene expression, using a conditional tal-1 transgenic model (Aim 2). Using retroviral insertional mutagenesis, we identified activated notch 1, dominant negative ikaros, and myc as cooperating genes in tal l1-induced leukemia. A final objective is to determine how activated notch 1, dominant negative ikaros, and myc contribute to tal-1 leukemogenesis and whether tal-1 tumors remain dependent on the continuous expression of these secondary mutations (Aim 3)