Cell-specific transcriptional regulation of human leukotriene B(4) receptor gene.
Leukotriene B(4) (LTB(4)) is a lipid mediator that activates leukocytes and is involved in host defense and inflammation. BLT1, a high-affinity receptor for LTB(4) (originally termed BLT), is expressed exclusively in inflammatory cells and is inducible in macrophages upon activation. The mechanisms of tissue-specific expression and induction of BLT1 are important for the understanding of mechanism of onset and the potential treatment of inflammatory disorders. Here, we report the genomic structure and a promoter analysis of the human BLT1 gene, with an emphasis on the mechanism of cell-specific transcription. No TATA or CAAT elements exist around the transcription initiation sites, but a GC-rich sequence is observed in this region. A reporter gene assay revealed that a region approximately 80 basepair upstream from the initiator sequence is required for the basal transcription of the BLT1 gene. Sp1 was found to be a major activator of basal transcription by electrophoretic mobility shift assays and site-directed mutagenesis. The CpG sites of the BLT1 promoter region were highly methylated in BLT1-nonexpressing cells, but not methylated in BLT1-expressing cells. Further, methylation of this region in vitro inhibited the promoter activity to approximately 15% of the control. Thus, methylation at CpG sites in the promoter region is important for cell-specific transcription of the BLT1 gene. The promoter region of the BLT1 gene is localized within the open reading frame (ORF) of the BLT2 gene, which encodes a low-affinity receptor for LTB(4) (Yokomizo, T., K. Kato, K. Terawaki, T. Izumi, and T. Shimizu. 2000. J. Exp. Med. 192:421-431). To our knowledge, this is the first example of "promoter in ORF" in higher eukaryotes.
Department of Biochemistry and Molecular Biology, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan.
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Kato
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Yokomizo
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Izumi
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Shimizu
D020121:5' Untranslated Regions; D001483:Base Sequence; D018899:CpG Islands; D019175:DNA Methylation; D018076:DNA, Complementary; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D005786:Gene Expression Regulation; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D011401:Promoter Regions, Genetic; D018102:Receptors, Leukotriene B4 / Q000235:genetics*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D020298:U937 Cells
D020121:5' Untranslated Regions; D018076:DNA, Complementary; D018102:Receptors, Leukotriene B4