Wu Z, Chiang J Y
Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, P.O. Box 95, Rootstown, OH 44272, USA.
Gene. 2001 Jul 11;272(1-2):191-7. doi: 10.1016/s0378-1119(01)00541-8.
Oxysterol 7 alpha-hydroxylase catalyzes hydroxylation of oxysterols and neurosterols and plays a role in the alternative bile acid synthesis pathway. This gene is widely expressed in many organs and peripheral tissues and may protect tissues from the toxicity of oxysterols. Mutation in CYP7B1 caused neonatal cholestasis. To examine the regulatory mechanisms governing CYP7B1 expression, the 5' flanking sequence of the CYP7B1 was analyzed and revealed a CpG island of about 1.2 kb. Transient transfection assays of deletion mutants of the CYP7B1 promoter-luciferase reporter gene in human liver-derived HepG2, fibroblast NT1088, and human embryonic kidney 293 cell lines revealed that the region from -291 to +189 was critical for gene transcription. Three GC box sequences located between -25 and +10 were essential for basal transcription because mutations of these sequences markedly reduced promoter activity. Sp1 and Sp3 bound to these sequences as demonstrated by DNase I footprinting assays and electrophoretic mobility shift assay. Thus, regulation of CYP7B1 transcription by Sp1 may play a pivotal role in regulating oxysterol levels, which regulate cholesterol metabolism.
氧化甾醇7α-羟化酶催化氧化甾醇和神经甾体的羟基化反应，并在胆汁酸合成的替代途径中发挥作用。该基因在许多器官和外周组织中广泛表达，可能保护组织免受氧化甾醇的毒性影响。CYP7B1基因的突变会导致新生儿胆汁淤积。为了研究调控CYP7B1表达的机制，对CYP7B1基因的5'侧翼序列进行了分析，发现了一个约1.2 kb的CpG岛。在人肝源性HepG2细胞系、成纤维细胞NT1088和人胚肾293细胞系中对CYP7B1启动子-荧光素酶报告基因的缺失突变体进行瞬时转染分析，结果显示-291至+189区域对基因转录至关重要。位于-25至+10之间的三个GC盒序列对基础转录至关重要，因为这些序列的突变会显著降低启动子活性。DNase I足迹分析和电泳迁移率变动分析表明，Sp1和Sp3与这些序列结合。因此，Sp1对CYP7B1转录的调控可能在调节氧化甾醇水平中起关键作用，而氧化甾醇水平又调控胆固醇代谢。
