Underhill D A, Hammond G L
MRC Group in Fetal and Neonatal Health, University of Western Ontario, London, Canada.
Gene. 1995 Sep 11;162(2):205-11. doi: 10.1016/0378-1119(95)00337-6.
Corticosteroid-binding globulin (CBG) transports and modulates the bioavailability of glucocorticoids in blood plasma. It is produced predominantly by the liver, but is also produced in a complex spatial and temporal pattern during development and is regulated hormonally. The rat Cbg promoter (pCbg) has therefore been cloned to allow identification of cis-acting sequence elements that could contribute to its regulation. Five protein-binding sites (P1 to P5) were identified within 236 bp immediately 5' of the transcription start point by DNase I footprinting with rat liver nuclear extracts. These P1-P5 sites are highly conserved in the human pCbg, and resemble recognition sequences for HNF-1, CP-2, DBP, HNF-3 and C/EBP or NF-1L6, respectively. Electrophoretic mobility-shift assays indicted that the P1 element most likely binds HNF-1, and transient transfection assays with luciferase reporter plasmids demonstrated that P1-P5 represent a positive component of rat pCbg activity, whereas additional 5' sequences repressed promoter activity 2-4-fold in H4IIEC3 rat hepatoblastoma cells.
皮质类固醇结合球蛋白（CBG）在血浆中转运并调节糖皮质激素的生物利用度。它主要由肝脏产生，但在发育过程中也以复杂的时空模式产生，并受激素调节。因此，大鼠Cbg启动子（pCbg）已被克隆，以确定可能有助于其调控的顺式作用序列元件。通过用大鼠肝核提取物进行DNase I足迹实验，在转录起始点上游236 bp内鉴定出五个蛋白质结合位点（P1至P5）。这些P1 - P5位点在人类pCbg中高度保守，分别类似于肝细胞核因子-1（HNF-1）、CP-2、DBP、HNF-3和C/EBP或NF-1L6的识别序列。电泳迁移率变动分析表明，P1元件最有可能结合HNF-1，并且用荧光素酶报告质粒进行的瞬时转染实验表明，P1 - P5代表大鼠pCbg活性的正性成分，而在H4IIEC3大鼠肝癌细胞中，额外的5'序列使启动子活性受到2至4倍的抑制。
