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Abstract：
The protein product of the Toll-like receptor (TLR) 4 gene has been implicated in the signal transduction events induced by lipopolysaccharide (LPS). In mice, destructive mutations of Tlr4 impede the normal response to LPS and cause a high susceptibility to Gram-negative infection. Expression of TLR4 mRNA in humans is restricted to a small number of cell types, including LPS-responsive myeloid cells, B-cells, and endothelial cells. To investigate the molecular basis for TLR4 expression in cells of myeloid origin, we cloned the human TLR4 gene and analyzed its putative 5\'-proximal promoter. In transient transfections a region of only 75 base pairs upstream of the major transcription initiation site was sufficient to induce maximal luciferase activity in THP-1 cells. The sequence of this region is similar in human and mouse TLR4 genes and lacks a TATA box, typical Sp1-sites or CCAAT box sequences. Instead, it contains consensus-binding sites for Ets family transcription factors, octamer-binding factors, and a composite interferon response factor/Ets motif. The activity of the promoter in macrophages was strictly dependent on the integrity of both half sites of the composite interferon response factor/Ets motif, which was constitutively bound by the myeloid and B-cell-specific transcription factor PU.1 and interferon consensus sequence-binding protein. These results indicate that the two tissue-restricted transcription factors PU.1 and interferon consensus sequence-binding protein participate in the basal regulation of human TLR4 in myeloid cells. Cloning of the human TLR4 gene provides a basis for further investigation of the possible impact of genetic variations on the susceptibility to infection and sepsis.
摘要：
Toll样受体（TLR）4基因的蛋白质产物与脂多糖（LPS）诱导的信号转导事件有关。在老鼠身上,Tlr4的破坏性突变会阻碍对LPS的正常反应，并导致对革兰氏阴性感染的高度易感性。TLR4mRNA在人类中的表达仅限于少数细胞类型，包括LPS反应性骨髓细胞，B细胞,和内皮细胞。探讨TLR4在骨髓来源细胞中表达的分子基础,我们克隆了人TLR4基因，并分析了其推定的5'-近端启动子。在瞬时转染中，主要转录起始位点上游仅75个碱基对的区域足以在THP-1细胞中诱导最大的荧光素酶活性。该区域的序列在人和小鼠TLR4基因中相似，并且缺少TATA框，典型的Sp1位点或CCAAT盒序列。相反，它包含Ets家族转录因子的共有结合位点，八聚体结合因子，和复合干扰素应答因子/Ets基序。启动子在巨噬细胞中的活性严格依赖于复合干扰素应答因子/Ets基序的两个半位点的完整性,由髓样和B细胞特异性转录因子PU.1和干扰素共有序列结合蛋白组成性结合。这些结果表明，两个组织限制性转录因子PU.1和干扰素共有序列结合蛋白参与人TLR4在骨髓细胞中的基础调节。人TLR4基因的克隆为进一步研究遗传变异对感染和败血症易感性的可能影响提供了基础。
