Transcriptional activation of the human heme oxygenase gene as a cellular defence mechanism

点击翻译按钮获取中文摘要

(1) Identification of the enhancer element responsible for the heme-mediated transcriptional activation of the heme oxygenase gene (HO gene). Using transient expression assays of chimeric fusion genes containing the luciferase gene downstream from the 5'-flanking region of the human HO gene, we found that the putative heme-responsive element is located about 4 kb upstream from the transcriptional initiation site. We have localized the element within the region of about 100 bp and are currently determining its sequence, Furthermore, we are searching for a nuclear protein that interacts with this element.(2) Identification of the putative silencer element that negatively acts on the heat shock element (HSE) of the human HO gene. Despite the presence of a HSE (-384/-370) in the 5'-flanking region of the human HO gene, heme oxygenase is not induced in cultured human cells following heat shock treatment. However, a synthetic human HO HSE is able to confer the heat-inducibility of the reoporter gene on the cells transfected with a fusion gene. These results suggest the presence of a silencer sequence that may repress the human HO gene expression. Using various constructs lacking the sequence in the vicinity of the HSE, we found that the sequence (-341/-320) may act as a negative regulator for the human HO gene expression.(3) Identification of a nuclear protein that recognizes the sequence, containing an atypical HSE, of the rat HO gene promoter. The rat HO gene promoter contains the two HSEs, a classic and an atypical HSE. The atypical HSE, consisting of two copies of inverted repeats of NGAAN, is bound by both heat shock transcription factor (HSF) and a newly identified factor. In contrast to HSF, the DNA-binding activity of the latter protein is constitutively expressed. We provide evidence that this protein may modulate the heat shock-mediated induction of the rat HO gene.