Graded responses to variable TCR signaling are encoded in the affinities of AICE-containing enhancers responding to BATF and IRF4 [gene expression]

Variable strengths of T cell receptor (TCR) signaling can produce divergent outcomes for T cell development and function. The mechanisms leading to different outcomes are incompletely understood, but may include distinct activation thresholds for different transcription factors as well as distinct sensitivities among target genes to transcription factors. IRF4 is one transcription factor implicated in responses to variable TCR signal strength. IRF4 expression increases uniformly with increasing TCR signal strength (i.e., analog), but it is unclear how IRF4 induced distinct genes at different levels, rather than different amounts of the same genes. Here, we analyzed global gene expression in TH2 cells and used ChIP-seq to define the relationship between TCR signal strength, enhancer occupancy and transcriptional activity for BATF/IRF4-dependent genes. We show that enhancers exhibit a spectrum of affinity for the BATF/IRF4 ternary complex mediate graded responsiveness of individual genes to increasing TCR signal strength. Differential gene induction by BATF and IRF4 occurs through interaction with enhancer elements of different affinity for BATF/IRF4 complexes. The increased resolution of factor binding site identified using ChIP-exo allowed the identification of a novel AICE2 motif binding BATF/IRF4 with higher affinity and that this may explain the protective role of a single nucleotide polymorphism in the CTLA-4 locus known to decrease the incidence of autoimmune diseases.

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Iwata A, Durai V, Tussiwand R, Briseño CG, Wu X, Grajales-Reyes GE, Egawa T, Murphy TL, Murphy KM