LeBrun D P, Cleary M L
Department of Pathology, Stanford University Medical Center, California 94305.
Oncogene. 1994 Jun;9(6):1641-7.
The t(1;19) chromosomal translocation is observed in pre-B cell acute lymphoblastic leukemias and results in expression of chimeric E2A-PBX1 proteins that contain transcriptional activation domains from E2A and the homeodomain of PBX1. Since homeodomains mediate DNA-binding, a potential model for the action of E2A-PBX1 is that it disrupts the transcriptional regulation of genes normally controlled by PBX1 or its closely-related family members PBX2 or PBX3. Using a binding site selection assay, we identified a consensus nucleotide sequence ATCAATCA specifically bound by the PBX1 homeodomain and those of its closely-related family members PBX2 and PBX3. An endogenous protein with the properties of PBX3b specifically bound to this sequence in nuclear extracts of precursor B cells. Transfection of reporter genes containing PBX binding sites linked to a minimal promoter demonstrated transactivation by E2A-PBX1 fusion protein dependent upon presence of the homeodomain. In contrast, wild-type PBX proteins were incapable of activating transcription. The striking differences in transcriptional properties of fusion and wild-type PBX proteins provides strong functional evidence for the importance of aberrant transcriptional regulation in the genesis of t(1;19)-bearing leukemias.
在前B细胞急性淋巴细胞白血病中观察到t(1;19)染色体易位，其导致嵌合E2A-PBX1蛋白的表达，该蛋白包含来自E2A的转录激活结构域和PBX1的同源结构域。由于同源结构域介导DNA结合，E2A-PBX1作用的一个潜在模型是它破坏了通常由PBX1或其密切相关的家族成员PBX2或PBX3控制的基因的转录调控。使用结合位点选择试验，我们鉴定了一个共有核苷酸序列ATCAATCA，它被PBX1同源结构域及其密切相关的家族成员PBX2和PBX3特异性结合。一种具有PBX3b特性的内源性蛋白在B前体细胞的核提取物中特异性结合到该序列。转染含有与最小启动子相连的PBX结合位点的报告基因表明，E2A-PBX1融合蛋白的反式激活依赖于同源结构域的存在。相反，野生型PBX蛋白不能激活转录。融合型和野生型PBX蛋白转录特性的显著差异为异常转录调控在携带t(1;19)白血病发生中的重要性提供了有力的功能证据。
