Heiland S, Knippers R
Division of Biology, Universität Konstanz, Germany.
Mol Cell Biol. 1995 Dec;15(12):6623-31. doi: 10.1128/MCB.15.12.6623.
We investigated the expression of the human DNA topoisomerase I (hTOP1) gene in HeLa cells and in adenovirus-transformed 293 cells. A highly conserved proximal promoter element is essential for hTOP1 promoter activity in HeLa cells but not in 293 cells. This correlates with the presence of specific promoter-binding proteins in HeLa cells and their absence in 293 cells. We identified the HeLa binding protein by screening a cDNA expression library with the specific promoter site as a probe and demonstrate now that the activating protein is identical to the nuclear factor for interleukin-6 expression (NF-IL6), a member of the C/EBP family of transcription factors. Overexpression of NF-IL6 strongly stimulates hTOP1 promoter activity in HeLa cells, suggesting that NF-IL6 is a major hTOP1-regulating protein. Because of the presence of adenovirus protein E1A, 293 cells express the hTOP1 gene more efficiently than HeLa cells but do not contain NF-IL6 activity. E1A activation of the hTOP1 promoter is suppressed by NF-IL6 overexpression. This result supports previous observations concerning a functional interaction between viral protein E1A and NF-IL6. Finally, we show that hTOP1 gene expression in differentiating macrophages is correlated with the synthesis of NF-IL6-specific mRNA.
我们研究了人类DNA拓扑异构酶I（hTOP1）基因在HeLa细胞和腺病毒转化的293细胞中的表达情况。一个高度保守的近端启动子元件对HeLa细胞中hTOP1启动子活性至关重要，但对293细胞则不然。这与HeLa细胞中存在特定的启动子结合蛋白而293细胞中不存在这些蛋白相关。我们以特定启动子位点为探针筛选cDNA表达文库来鉴定HeLa结合蛋白，现在证明该激活蛋白与白细胞介素-6表达的核因子（NF-IL6）相同，NF-IL6是转录因子C/EBP家族的成员。NF-IL6的过表达强烈刺激HeLa细胞中hTOP1启动子活性，表明NF-IL6是一种主要的hTOP1调节蛋白。由于存在腺病毒蛋白E1A，293细胞比HeLa细胞更有效地表达hTOP1基因，但不含有NF-IL6活性。NF-IL6的过表达抑制了E1A对hTOP1启动子的激活。这一结果支持了先前关于病毒蛋白E1A与NF-IL6之间功能相互作用的观察结果。最后，我们表明分化中的巨噬细胞中hTOP1基因表达与NF-IL6特异性mRNA的合成相关。
