Immenschuh S, Nagae Y, Satoh H, Baumann H, Muller-Eberhard U
Department of Pediatrics, Cornell University Medical College, New York, New York 10021.
J Biol Chem. 1994 Apr 29;269(17):12654-61.
Hemopexin (Hx) is an abundant acute-phase protein (APP) that binds heme with high affinity. In rat hepatic cells, the transcription rate of the Hx gene is increased by interleukin (IL)-1 and IL-6. To investigate the cis-acting regulatory elements (REs) responsive to these hormones, chloramphenicol acetyltransferase constructs of rat and human Hx gene sequences were tested in transiently transfected hepatoma cells. An IL-6-RE was identified in the promoter of both rat and human Hx genes, the function of which was dependent on the core sequence (CCGGGAA) common in other APP genes. The previously characterized Hx A element mediated a relatively minor cytokine response as compared with the Hx IL-6-RE. The human Hx A element, in contrast to the rat and human Hx IL-6-REs, was strongly trans-activated by cotransfected CAAT enhancer-binding proteins (C/EBP)-beta and -delta. The rat gene homolog of the human Hx A element was inactive as a cytokine RE and was minimally trans-activated by C/EBP isoforms. Results of electrophoretic mobility shift assays indicated that the Hx IL-6-RE is a binding site for the IL-6-inducible nuclear protein IL-6 RE-BP, which also binds to the conserved IL-6-REs of other APP genes and is distinct from C/EBP beta.
血红素结合蛋白（Hx）是一种丰富的急性期蛋白（APP），它能以高亲和力结合血红素。在大鼠肝细胞中，Hx基因的转录速率会因白细胞介素（IL）-1和IL-6而增加。为了研究对这些激素有反应的顺式作用调控元件（REs），在瞬时转染的肝癌细胞中测试了大鼠和人类Hx基因序列的氯霉素乙酰转移酶构建体。在大鼠和人类Hx基因的启动子中都鉴定出了一个IL-6-RE，其功能依赖于其他APP基因中常见的核心序列（CCGGGAA）。与Hx IL-6-RE相比，先前鉴定的Hx A元件介导的细胞因子反应相对较小。与大鼠和人类Hx IL-6-RE不同，人类Hx A元件被共转染的CAAT增强子结合蛋白（C/EBP）-β和-δ强烈反式激活。人类Hx A元件的大鼠基因同源物作为细胞因子RE是无活性的，并且被C/EBP同工型最小程度地反式激活。电泳迁移率变动分析结果表明，Hx IL-6-RE是IL-6诱导的核蛋白IL-6 RE-BP的结合位点，该蛋白也与其他APP基因的保守IL-6-RE结合，并且与C/EBPβ不同。
