Cell-specific Transcription of Leukotriene C4Synthase Involves a Kruppel-like Transcription Factor and Sp1

Abstract Leukotriene C4synthase (LTC4S) is responsible for the biosynthesis of cysteinyl leukotrienes that participate in allergic and asthmatic inflammation. We analyzed 2.1 kilobases of the 5′-flanking region of the human LTC4S gene, which contains three DNase I hypersensitivity sites, for its transcriptional activity when fused to a promoterless and enhancerless luciferase gene. Deletion analysis revealed a nonspecific basal promoter region between nucleotides −122 and −56 upstream of the translation start site which contains a consensus Sp1 binding site and a putative initiator element (Inr) and cell-specific enhancer regions further upstream. A single mutation of either the Sp1 binding site between nucleotides −120 and −115 or the Inr (CAGAC) between nucleotides −66 and −62 reduced the expression of the reporter gene by ∼60%, whereas double mutations decreased the expression by ∼80%. The incubation of nuclear extracts from THP-1 and K562 cells with a 32P-labeled oligonucleotide containing the Sp1 site or the Inr sequence gave gel-shifted complexes that were blocked by their respective cold oligonucleotides, and antisera specific for Sp1 and Sp3 provided supershifts for the former. Linker-scanning mutations of a cell-specific regulatory region revealed that mutations from nucleotides −165 to −125 reduced reporter activity. This region contains a tandem CACCC repeat (at nucleotides −149 to −145 and −139 to −135). An oligonucleotide containing the distal CACCC motif was gel shifted by THP-1 cell nuclear extract and was supershifted by antisera to Sp1 and Sp3. Cotransfection of an Sp1 expression plasmid into Drosophila SL2 cells with a −228 to −3 LTC4S reporter construct transactivated the reporter gene, whereas mutations at the CACCC repeat region reduced Sp1 transactivation by ∼66%. Similarly, the Kruppel-like factor Zf9/CPBP (core promoter-binding protein) transactivated the −228 construct in COS cells but not its CACCC mutant construct. These findings indicate the involvement of Sp1 and an Inr in non-cell-specific regulation and a Kruppel-like transcription factor and Sp1 in the cell-specific regulation of the LTC4S gene. These are the first such analyses of a member of a newly recognized superfamily of membrane-associated proteins involved in eicosanoid and glutathione metabolism, which contains key proteins involved in the generation of both prostanoids and cysteinyl leukotrienes.