Hunger S P, Li S, Fall M Z, Naumovski L, Cleary M L
Section of Pediatric Hematology/Oncology, Department of Pediatrics, University of Colorado School of Medicine, Denver, CO, USA.
Blood. 1996 Jun 1;87(11):4607-17.
Genes encoding transcription factors are frequently altered by chromosomal translocations in acute lymphoblastic leukemia (ALL), suggesting that aberrant transcriptional regulation plays a prominent role in leukemogenesis. E2A-hepatic leukemia factor (HLF), a chimeric transcription factor created by the t(17;19), consists of the amino terminal portion of E2A proteins, including two experimentally defined transcriptional activation domains (TADs), fused to the HLF DNA binding and protein dimerization basic leucine zipper (bZIP) domain. To understand the mechanisms by which E2A-HLF induces leukemia and the crucial functions contributed by each constituent of the chimera, it is essential to define the normal transcriptional regulatory properties of HLF and related bZIP proteins. To address these questions, we cloned the human homologue of TEF/VBP, a bZIP protein closely related to HLF. Using a binding site selection assay, we found that TEF bound preferentially to the consensus sequence 5'-GTTACGTAAT-3', which is identical to the previously determined HLF recognition site. TEF and HLF activated transcription of consensus site-containing reporter genes in several different cell types with similar potencies. Using GAL4 chimeric proteins, a TAD was mapped to a discrete approximate 40 amino acid region of TEF and HLF within which they share 72% amino acid identity and 85% similarity. The TEF/HLF activation domain (THAD) has a predicted helical secondary structure, but shares no sequence homology with previously reported TADs. The THAD contained most, if not all, of the transcriptional activation properties present in both TEF and HLF and its deletion completely abrogated transcriptional activity of TEF and HLF in both mammalian cells and yeast. Thus, TEF and HLF share indistinguishable DNA-binding and transcriptional regulatory properties, whose alteration in leukemia may be pathogenetically important.
在急性淋巴细胞白血病（ALL）中，编码转录因子的基因常因染色体易位而发生改变，这表明异常的转录调控在白血病发生过程中起着重要作用。E2A-肝白血病因子（HLF）是一种由t(17;19)产生的嵌合转录因子，由E2A蛋白的氨基末端部分组成，包括两个实验确定的转录激活域（TADs），与HLF的DNA结合和蛋白质二聚化碱性亮氨酸拉链（bZIP）域融合。为了了解E2A-HLF诱导白血病的机制以及嵌合体各组成部分所起的关键作用，明确HLF和相关bZIP蛋白的正常转录调控特性至关重要。为了解决这些问题，我们克隆了与HLF密切相关的bZIP蛋白TEF/VBP的人类同源物。通过结合位点选择试验，我们发现TEF优先结合共有序列5'-GTTACGTAAT-3'，该序列与先前确定的HLF识别位点相同。TEF和HLF在几种不同细胞类型中以相似的效力激活含共有位点的报告基因的转录。使用GAL4嵌合蛋白，一个TAD被定位到TEF和HLF的一个离散的约40个氨基酸区域，它们在该区域内氨基酸同一性为72%，相似性为85%。TEF/HLF激活域（THAD）具有预测的螺旋二级结构，但与先前报道的TADs没有序列同源性。THAD包含了TEF和HLF中存在的大部分（如果不是全部）转录激活特性，其缺失完全消除了TEF和HLF在哺乳动物细胞和酵母中的转录活性。因此，TEF和HLF具有难以区分的DNA结合和转录调控特性，其在白血病中的改变可能在发病机制上具有重要意义。
