Enhanced expression of the leukotriene C-4 synthase due to overactive transcription of an allelic variant associated with aspirin-intolerant asthma

Aspirin-intolerant asthma (AIA), a distinct clinical syndrome affecting abo ut 10% of adult asthmatics, appears to be unusually dependent on cysteine l eukotriene (cys-LT) overproduction by pulmonary eosinophils, The gene codin g for leukotriene (LT) C-4 synthase (LTC4S), the enzyme controlling cys-LT biosynthesis, exists as two common alleles distinguished by an A to C trans version at a site 444 nucleotides upstream of the translation start. We tes ted the hypothesis that this single nucleotide polymorphism (SNP) affects b inding of transcription factors and influences the transcription rate, pred isposing to AIA, Gel shift assay studies revealed that the C-444 allele, co nferring an activator protein-2 binding sequence, is an additional target f or a transcription factor of histone H4 consensus. Introduction of the H4TF -2 decoy oligonucleotide into LTC4S-positive, differentiated HL-60 cells de creased accumulation of LTC4 to 68%. Transfection of COS-7 with promoter co nstruct increased expression of beta-galactosidase reporter for the C-444 v ariant. The C-444 allelic frequency was significantly higher in AIA patient s (n = 76) as compared with matched aspirin-tolerant asthmatics (n = 110) a nd healthy controls (n = 75), Patients with AIA had also upregulated LTC4S messenger RNA expression in peripheral blood eosinophils, An inhaled provoc ation test with lysine-aspirin led to an increase in urinary output of LTE4 , which reached statistical significance only in carriers of the C-444 alle le, Our results suggest that a transcription factor, present in dividing an d bone marrow resident progenitors of eosinophils, triggers LTC4S transcrip tion in carriers of a common C-444 allele due to binding with the histone H 4 promoter element of the gene. Genetic predisposition to cys-LT pathway up regulation, a hallmark of AlA can be related to overactive expression of th e LTC4S C-444 allele.