Elucidation of ABO blood group gene expression though chromatin remodeling

ABO血型在输血和身份识别中具有重要意义。然而，调控人类ABO基因表达的机制仍然不清楚。根据UCSC Genome Browser(http://genome.ucsc.edu)，)提供的公开表达数据中人红白血病细胞系K562中ABO基因的DNA酶I超敏位点，我们制备了包括这些位点的报告质粒构建体。随后的荧光素酶分析表明，在内含子1中有一个新的正调控元件。该元件被证明以红系细胞特异性的方式增强ABO启动子的活性。凝胶迁移率改变分析表明，它与组织限制性转录因子GATA-1和GATA-2结合。GATA基序的突变取消了该因子的结合，降低了该元件的调节活性。因此，GATA转录因子似乎参与了该元件的细胞特异性活动。此外，我们发现BM表型与涉及该元件的内含子1的部分缺失以及GATA位点的单点突变导致该元件的活性降低有关。因此，红系细胞特异性调控元件的缺失或单点突变可能下调B^m等位基因的转录，导致红系细胞中B抗原表达减少，但在粘液分泌细胞中不会。这些结果支持ABO内含子1中的增强子样元件在红系细胞中具有重要功能的观点。

The ABO blood group is of great importance in blood transfusion and personal identification. However, the mechanisms regulating human ABO gene expression remain obscure. On the basis of DNase I hypersensitive sites in and upstream of ABO in the human erythroleukemia cell line K562 in publicly available expression data from the UCSC Genome Browser (http://genome.ucsc.edu), we prepared reporter plasmid constructs including these sites. Subsequent luciferase assays indicated a novel positive regulatory element in intron 1. This element was shown to enhance ABO promoter activity in an erythroid cell-specific manner. Electrophoretic mobility shift assays demonstrated that it bound to the tissue-restricted transcription factor GATA-1 and GATA-2. Mutation of the GATA motifs to abrogate binding of this factor reduced the regulatory activity of the element. Thus, GATA transcription factors seem to be involved in the cell-specific activity of the element. Furthermore, we found that Bm phenotypes were associated with a partial deletion in intron 1 involving the element as well as a single point mutation of GATA site leading to reduced activity of the element. Therefore, it is plausible that deletion or a single point mutation of the erythroid cell-specific regulatory element could down-regulate transcription in the B^m allele, leading to reduction of B antigen expression in cells of erythroid lineage, but not in mucus-secreting cells. These results support the contention that the enhancer-like element in intron 1 of ABO has a significant function in erythroid cells.