JunB regulates homeostasis and suppressive functions of effector regulatory T cells.

Koizumi, Shin-Ichi; Sasaki, Daiki; Hsieh, Tsung-Han; Taira, Naoyuki; Arakaki, Nana; Yamasaki, Shinichi; Wang, Ke; Sarkar, Shukla et al. · Nat Commun · 2018

basic_science · Level V

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Abstract

Foxp3-expressing CD4<sup>+</sup> regulatory T (Treg) cells need to differentiate into effector Treg (eTreg) cells to maintain immune homeostasis. T-cell receptor (TCR)-dependent induction of the transcription factor IRF4 is essential for eTreg differentiation, but how IRF4 activity is regulated in Treg cells is still unclear. Here we show that the AP-1 transcription factor, JunB, is expressed in eTreg cells and promotes an IRF4-dependent transcription program. Mice lacking JunB in Treg cells develop multi-organ autoimmunity, concomitant with aberrant activation of T helper cells. JunB promotes expression of Treg effector molecules, such as ICOS and CTLA4, in BATF-dependent and BATF-independent manners, and is also required for homeostasis and suppressive functions of eTreg. Mechanistically, JunB facilitates the accumulation of IRF4 at a subset of IRF4 target sites, including those located near Icos and Ctla4. Thus, JunB is a critical regulator of IRF4-dependent Treg effector programs, highlighting important functions for AP-1 in Treg-mediated immune homeostasis.

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