Transcriptional regulation of the human ABO histo-blood group genes is dependent on the negative regulation through the N box upstream of the proximal promoter

我们以前的人类ABO基因的转录调控机制的研究表明，负调控元件存在于近端启动子的上游序列，这表明从ABO近端启动子的转录部分由启动子上游的沉默元件控制。在这项研究中，我们已经证实，ABO基因的表达是负调控的KATOIII细胞中的近端启动子的上游序列，并在-202和-118之间的区域是在上皮细胞和红系细胞的负调控。在KATOIII细胞中使用携带-196至-191处突变的N盒的荧光素酶报告质粒的瞬时转染实验证明，N盒是-202至-118序列中的负调控元件。使用电泳迁移率变动分析，我们表明，N盒结合的核因子，称为RACP，来自KATOIII细胞。这些结果表明，从ABO近端启动子转录的抑制部分依赖于N盒，RACP的下调可能会缓解抑制，从而导致在上皮细胞系以及红系细胞成熟过程中ABO基因的表达。

Our previous studies of the transcriptional regulatory mechanism of the human ABO gene indicated that negative regulatory elements are present in the sequence upstream of the proximal promoter, suggesting that transcription from the ABO proximal promoter is in part controlled by silencer elements just upstream of the promoter. In this study, we have confirmed that ABO gene expression is negatively regulated by the sequence upstream of the proximal promoter in KATOIII cells, and that the region between -202 and -118 is involved in the negative regulation in cells of both epithelial and erythroid lineages. Transient transfection experiments in KATOIII cells using a luciferase reporter plasmid carrying mutated N box at -196 to -191 demonstrated that the N box is a negative regulatory element in the -202 to -118 sequence. Using electrophoretic mobility shift assay, we showed that the N box binds with a nuclear factor, termed RACP, derived from KATOIII cells. These results suggest that repression of transcription from the ABO proximal promoter is partially dependent upon the N box, and that down-regulation of RACP may relieve the repression, thereby leading to expression of the ABO gene during maturation of cells in the epithelial lineage as well as the erythroid lineage.