Choi J K, Shen C P, Radomska H S, Eckhardt L A, Kadesch T
Department of Genetics and Pathology, University of Pennsylvania School of Medicine, Philadelphia 19104-6145, USA.
EMBO J. 1996 Sep 16;15(18):5014-21.
The E2A proteins, E12 and E47, are basic helix-loop-helix (bHLH) proteins essential for the B-cell lineage. Initially identified as immunoglobulin enhancer-binding proteins, they have also been shown to activate immunoglobulin enhancer-based reporters in transient transfection assays. Here, we examine the relationship between E2A DNA binding activity and activation of the endogenous, chromosomal immunoglobulin heavy chain (IgH) locus. Using sterile I(mu) transcription as an indicator of IgH enhancer activity, we see a direct correlation between E2A DNA binding activity and I(mu) transcription in stable BxT hybrids. We also observe a 1000-fold stimulation of endogenous I(mu) transcription in fibroblasts that express high levels of E47 and less stimulation in cells that express E12. By contrast, none of the other IgH enhancer-binding proteins tested (E2-2, Pu.1, Oct-2, OCA-B, TFE3 and USF) were able to activate I(mu) transcription. E47 overexpression also resulted in transcriptional activation of the endogenous gene encoding TdT, indicating that it, too, is a target of E2A proteins early in the B-cell lineage. Our results indicate that E2A proteins have the distinctive property of activating silent, chromatin-embedded B-cell-specific genes, underscoring their crucial role in B-cell development.
E2A蛋白E12和E47是B细胞谱系所必需的碱性螺旋-环-螺旋（bHLH）蛋白。它们最初被鉴定为免疫球蛋白增强子结合蛋白，在瞬时转染实验中也已显示能激活基于免疫球蛋白增强子的报告基因。在此，我们研究E2A DNA结合活性与内源性染色体免疫球蛋白重链（IgH）基因座激活之间的关系。以无菌I(μ)转录作为IgH增强子活性的指标，我们发现在稳定的BxT杂种细胞中，E2A DNA结合活性与I(μ)转录之间存在直接相关性。我们还观察到，在表达高水平E47的成纤维细胞中，内源性I(μ)转录受到1000倍的刺激，而在表达E12的细胞中刺激较小。相比之下，所测试的其他IgH增强子结合蛋白（E2-2、Pu.1、Oct-2、OCA-B、TFE3和USF）均不能激活I(μ)转录。E47的过表达还导致了编码末端脱氧核苷酸转移酶（TdT）的内源性基因的转录激活，这表明它也是B细胞谱系早期E2A蛋白的一个靶标。我们的结果表明，E2A蛋白具有激活沉默的、嵌入染色质的B细胞特异性基因的独特特性，突出了它们在B细胞发育中的关键作用。
