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

本研究的目的是了解基因表达促进红系细胞分化的调控机制。我们利用培养细胞中的报告基因分析方法研究了辅酶A酶原(CPO)基因的调控机制。CPO基因在红系细胞中特异地活跃，但在非红系细胞中不活跃。我们发现了一个新的CPRE基序，它似乎对该基因的差异表达具有重要意义。我们还研究了Nrf3和Bach1的功能，这两个基因是cnc转录因子家族的成员。在该家族成员中，核因子-E2P45被认为是红系分化的关键转录因子。对Nrf3的分子解剖发现了一个新的与caspase9相互作用的基序。生化分析表明，Bach1与血红素有关。与血红素结合的Bach1失去了与DNA的结合能力，表明Bach1的抑制活性被血红素取消。Bach1基因缺失的小鼠一直表现出血红素加氧酶1基因的结构性激活，该基因是Bach1的候选靶基因。因此，这些数据支持这样的观点，即Bach1是血红素浓度的传感器，并将血红素丰度转化为基因表达。

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.