Roles of heme in the regulation of gene expression and cell differentiation of erythroid cells

本研究旨在了解促进红细胞分化的基因表达调控机制。我们在培养细胞中采用报告基因法研究了coproporphyrinogen （CPO）基因的基因调控机制。CPO基因在红系细胞中有特异性活性，而在非红系细胞中无特异性活性。我们发现了一个新的基序CPRE，它似乎对基因的差异表达很重要。我们还检测了CNC转录因子家族成员Nrf3和Bach1的功能。在这个家族的成员中，NF-E2 p45被认为是红系分化的关键转录因子。Nrf3的分子解剖揭示了一个与caspase 9相互作用的新基序。生化分析显示Bach1与血红素结合。血红素结合的Bach1失去了其DNA结合能力，表明血红素消除了Bach1的抑制活性。与此一致的是，Bach1缺失的小鼠表现出血红素加氧酶1基因的组成性激活，该基因是Bach1的候选靶基因。因此，这些数据支持了Bach1是血红素浓度传感器并将血红素丰度转化为基因表达的观点。

The purpose of this study is to understand the regulatory mechanisms of gene expression promoting erythroid cell differentiation. We examined the gene regulatory mechanisms of coproporphyrinogen (CPO) gene using reporter assays in cultured cells. The CPO gene is specifically active in erythroid cells but not in non-erythroid cells. We identified a novel motif CPRE, which appeared to be important for the differential expression of the gene. We also examined the function of Nrf3 and Bach1, which are members of the CNC transcription factor family. Among the members of this family, NF-E2 p45 is considered as a key transcription factor for erythroid differentiation. Molecular dissection of Nrf3 revealed a novel motif interacting with caspase 9. Biochemical analysis revealed that Bach1 associates with heme. Heme-bound Bach1 lost its DNA binding ability, suggesting that repressor activity of Bach1 is abrogated by heme. Consistently, Bach1-null mice displayed constitutive activation of heme-oxygenase 1 gene, which is a candidate target gene of Bach1. Thus, these data support the contention that Bach1 is a sensor of heme concentration and translates the heme abundance into the gene expression.