Smith K S, Jacobs Y, Chang C P, Cleary M L
Department of Pathology, Stanford University Medical Center, California 94305, USA.
Oncogene. 1997 Jun 19;14(24):2917-26. doi: 10.1038/sj.onc.1201249.
The chimeric oncoprotein E2a-Pbx1 results from fusion of the E2A and PBX1 genes following t(1;19) chromosomal translocations in B cell precursor acute leukemias. Experimentally B cell progenitors do not tolerate constitutive expression of E2a-Pbx1 which contrasts with transformation of several other cell types following its stable expression both in vitro and in vivo. To further investigate the effects of E2a-Pbx1 on the B cell progenitors, we conditionally expressed E2a-Pbx1 under control of a metal response element in hematopoietic precursor cell lines in vitro. Inducible expression of E2a-Pbx1 resulted in cell death with the morphologic and molecular features of apoptosis. A structure-function analysis demonstrated that induction of apoptosis was not a dominant-negative effect of the E2a moiety but, rather, required the DNA-binding homeodomain of Pbx1. E2a-Pbx1-induced apoptosis proceeded through a BCL2-responsive checkpoint eventuating in PARP inactivation but did require p53. Constitutive expression of E2a-Pbx1 did not induce apoptosis or continued cycling of Rat-1 fibroblasts in low serum conditions. These studies demonstrate that E2a-Pbx1 initiates programmed cell death of hematopoietic precursers by a mechanism that requires its chimeric transcriptional properties, but, unlike other nuclear oncoproteins, is independent of p53.
嵌合癌蛋白E2a-Pbx1是在B细胞前体急性白血病中t(1;19)染色体易位后由E2A和PBX1基因融合产生的。实验表明，B细胞祖细胞不能耐受E2a-Pbx1的组成型表达，这与在体外和体内稳定表达E2a-Pbx1后其他几种细胞类型的转化形成对比。为了进一步研究E2a-Pbx1对B细胞祖细胞的影响，我们在体外造血前体细胞系中，在金属反应元件的控制下条件性表达E2a-Pbx1。E2a-Pbx1的可诱导表达导致细胞死亡，并具有凋亡的形态学和分子特征。结构-功能分析表明，凋亡的诱导不是E2a部分的显性负效应，而是需要Pbx1的DNA结合同源结构域。E2a-Pbx1诱导的凋亡通过BCL2反应性检查点进行，最终导致PARP失活，但确实需要p53。在低血清条件下，E2a-Pbx1的组成型表达不会诱导凋亡或导致Rat-1成纤维细胞持续循环。这些研究表明，E2a-Pbx1通过一种需要其嵌合转录特性的机制启动造血前体细胞的程序性细胞死亡，但与其他核癌蛋白不同，它不依赖于p53。
