Lee J K, Tam J W, Tsai M J, Tsai S Y
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
J Biol Chem. 1992 Mar 5;267(7):4638-45.
The functional organization of the human insulin receptor (hIR) promoter was analyzed by deletion mutagenesis and protein-DNA interaction studies. A series of deletion mutants was expressed transiently in two human hepatocytes, HepG2 and PLC. The results revealed that the promoter region between -692 and -345 is essential for efficient transcription of the hIR gene. Multiple trans-acting factors were identified by band shift and footprinting analyses. Sp1 binds to a cluster of GC boxes and two GGGAGG hexamers locating at -637 to -594. Adjacent to GC boxes, there are two regions, from -550 to -530 and from -522 to -503, which bind to two novel factors, IRNF-I and IRNF-II. These two factors are distributed differentially in different cell lines. Linker scanning mutations on GC, GA boxes, or the IRNF-I binding site significantly decreased the transcriptional activity, indicating that IRNF-I and Sp1 are important for hIR promoter activity. In addition, we demonstrated that glucocorticoid-dependent transcriptional induction of hIR mRNA in vivo is conferred by a glucocorticoid response element in the hIR promoter. Taken together, these results imply that transcription of the human insulin receptor gene is regulated by multiple protein-DNA interactions occurring within the defined promoter region.
通过缺失诱变和蛋白质-DNA相互作用研究，对人胰岛素受体（hIR）启动子的功能组织进行了分析。一系列缺失突变体在两种人肝细胞HepG2和PLC中瞬时表达。结果显示，-692至-345之间的启动子区域对于hIR基因的有效转录至关重要。通过凝胶迁移和足迹分析鉴定了多个反式作用因子。Sp1结合到位于-637至-594的一组GC盒和两个GGGAGG六聚体上。在GC盒附近，有两个区域，从-550至-530以及从-522至-503，它们结合两个新因子IRNF-I和IRNF-II。这两个因子在不同细胞系中的分布存在差异。GC、GA盒或IRNF-I结合位点上的接头扫描突变显著降低了转录活性，表明IRNF-I和Sp1对hIR启动子活性很重要。此外，我们证明了hIR启动子中的糖皮质激素反应元件赋予了体内hIR mRNA的糖皮质激素依赖性转录诱导作用。综上所述，这些结果表明人胰岛素受体基因的转录受限定启动子区域内发生的多种蛋白质-DNA相互作用的调控。
