Th17-specific demethylation and methylation-sensitive STAT3 binding at a DNA element in the IL-17 promoter (88.13)

Abstract

Abstract CD4+ helper T cells can be instructed by non-antigen-specific signals to differentiate into functionally distinct subsets with exclusive patterns of cytokine production. Activation in the presence of TGFbeta and IL-6 results in the development of Th17 cells that produce IL-17, an inflammatory cytokine that is not expressed by Th1 or Th2 lineage cells. The promoter region of the IL-17A gene contains 12 CpG dinucleotides, leading us to test whether the IL-17 gene is regulated epigenetically by DNA methylation. In Th1 and Th2 cells, all CpG dinucleotides were heavily methylated (80-100%), with the exception of the -33 dinucleotide adjacent to the TATA element, which was 70% methylated in all cell lineages. The Th17 differentiation program was associated with a selective, 4-fold increase in demethylation (from 90% to 60%) at CpG dinucleotides -144 and +13 bp from the transcriptional start site. Interestingly, the -144 CpG is located within a consensus element (CCpGTCA) for STAT3, a transcription factor that is required for IL-17 gene induction and Th17 differentiation. We find that STAT3 from Th17 nuclear extracts binds with high affinity to this CCpGTCA element in vitro, but shows low affinity binding to the methylated CmeCpGTCA element. These results suggest that signals from the TGFbeta and/or IL-6 receptors lead to demethylation of a STAT3 element in the IL17A promoter, and epigenetically program the IL-17 locus for transactivation by STAT3 in the Th17 lineage.