Alleles of the proximal promoter of BAT1, a putative anti-inflammatory gene adjacent to the TNF cluster, reduce transcription on a disease-associated MHC haplotype.

Abstract

BAT1 belongs to the DEAD-box family of proteins, and is encoded in the central region of the MHC, a region containing genes affecting immunopathological disorders including Type 1 diabetes. We showed that BAT1 can reduce inflammatory cytokine production, supporting its candidacy as a disease gene. Here we examined the proximal promoter region of BAT1. Ten single nucleotide polymorphisms were identified in approximately 1.4 kb of sequence, defining at least seven alleles. Sections of the BAT1 promoter region were amplified from cells homozygous for the MHC haplotypes associated with susceptibility (HLA-A1, B8, DR3; 8.1 haplotype) and resistance (HLA-A3, B7, DR15; 7.1 haplotype) to diabetes and cloned into a promoter-less luciferase-encoding plasmid. Jurkat cells transiently transfected with fragments from the 8.1 haplotype exhibited a lower luciferase activity than those transfected with fragments from the 7.1 haplotype, indicating reduced transcription. The effect was clearest with the 520 bp immediately upstream of the transcriptional start site. Electrophoretic mobility shift assays using oligonucleotides spanning polymorphic sites within the 520 bp (proximal) promoter fragment showed haplotype-specific binding of nuclear proteins. In view of the anti-inflammatory role of BAT1, reduced production on a disease-associated haplotype constitutes a novel and self-consistent model for the effect of central MHC genes on disease.