1) at ETS/IRF composite elements (EICE), description of AP-1/IRF composite elements (AICE) reveals how these factors function together to bind distinct elements

co-operatively, and may explain some of their distinct functions in T-cell subsets, dendritic cells and B cells. At AICE, combinatorial integration is possible through both varied AP-1 dimer composition and choice of IRF family co-factors. For example, IRF8 co-operates with BATF3/JUN to instruct homeostatic classical dendritic cell (cDC) differentiation, and with BATF/JUN during inflammatory cDC differentiation.[40] BATF/JUN and IRF4 co-operative binding at AICE motifs is required for instruction of Th17 GDC-0973 order differentiation and B-cell class switch recombination.[12,

30, 31, 40] Further, it is likely that co-operation of these AP-1/IRF complexes with different STAT family members can confer additional integration of environmental cues for interpretation of combinatorial motifs in regulatory DNA elements. Transcriptional programmes that integrate environmental signals with cell intrinsic features instruct cellular phenotypes, including plasticity. In this context, it is interesting to compare and contrast the transcriptional strategies of FOXP3 and RORγt in control of Treg and Th17 cell identity, respectively. Recent mechanistic insights into the transcriptional regulation of Foxp3 and Rorc and their targets explain some of the characteristics of the Treg and Th17 cellular phenotype. For example, both FOXP3 and RORγt have in common an activity that largely reinforces, stabilizes and maintains a chromatin PS-341 and gene activation landscape initiated

by ERFs. More specifically, these factors augment the expression of critical lineage-specific genes such as il2ra, ctla4, il10, il10ra, cd5, icos and notably, Foxp3 itself, in the case of FOXP3, and il17a, il17f, il1r1 and il23r for RORγt (Fig. 1). This target gene selection reflects the distinct behaviour and biology of Th17 and Treg cells. RORγt augments il23r expression in a positive feedback loop, as STAT3 signalling downstream of IL-23R activates Rorc expression. However, this feedback loop, and maintained expression selleck of Rorc and Th17 lineage fidelity, is dependent on the persistence of environmental IL-23 and transforming growth factor-β (TGF-β), and altered environmental signals, especially IL-12 and interferon-γ, can subvert Rorc expression and the Th17 transcriptional programme, converting cells to the Th1 lineage (Fig. 2).[42-44] In contrast, FOXP3 regulates its own expression upon engagement of a positive feedback loop following activation and CpG demethylation at a Foxp3-intronic enhancer (CNS2), a heritable feature of mature Treg cells, effectively buffering mature Treg cells from changes in environmental signals.[45] These differences may reflect important phenotypic features of these distinct cell types.