Epigenetic regulation of the expression of Il12 and Il23 and autoimmune inflammation by the deubiquitinase Trabid

Cells of the innate immune system, including dendritic cells (DCs) and macrophages, have an important role in regulating the nature and magnitude of adaptive immune responses1. They recognize microbial components via pattern-recognition receptors, including various Tolllike receptors (TLRs), which trigger intracellular signaling events that induce the maturation and function of these cells. DCs function as the main antigen-presenting cells required for activation of naive T cells2. In addition, DCs and macrophages produce a plethora of cytokines that regulate the differentiation of CD4+ T cells and promote inflammatory responses3. However, deregulated production of proinflammatory cytokines by cells of the innate immune system also contributes to autoimmune and inflammatory diseases. The interleukin 12 (IL-12) family of cytokines, particularly IL-12 and IL-23, are proinflammatory cytokines produced by DCs and macrophages, as well as by fibroblasts in response to microbial infection4–6. IL-12 is composed of the subunits IL-12α and IL-12β and acts as a key mediator in the differentiation of CD4+ T cells toward the type 1 helper T cell (TH1 cell) lineage, characterized by production of the signature cytokine interferon-γ (IFN-γ)7. IL-23, composed of IL-12β and the specific subunit IL-23α, functions to amplify and maintain the TH17 subset of CD4+ helper T cells6,7. The genes encoding IL-12 (Il12a and Il12b; collectively called ‘Il12’ here) and IL-23 (Il23a and Il12b; collectively called ‘Il23’ here) are induced in response to stimulation by various TLR ligands, and IL-12 and IL-23 have been linked to autoimmune and inflammatory diseases6. However, the mechanisms that regulate the induction of Il12 and Il23 are incompletely understood. The transcriptional regulator c-Rel, of the NF-κB family of transcription factors, mediates TLR-stimulated expression of Il12 and Il23 (refs. 8,9). In addition to activating NF-κB and other transcription factors, TLR signals induce chromatin remodeling at the Il12b promoter, which might be important for accessibility of the promoter region to specific transcription factors10,11. As seen with Il12b, chromatin remodeling allows accessibility of the Il12a promoter to specific transcription factors, such as c-Rel and C/EBP12. Similarly, stimulation via TLRs results in histone modifications of the nucleosome located at the Il23a promoter13,14. Each nucleosome contains the core histones H2A, H2B, H3 and H4, which are characteristically regulated by post-translational modifications, including methylation and demethylation15. Published work has indicated Jmjd2d is a demethylase that mediates the demethylation of histone H3 that is involved in the induction of Il12b in DCs15,16. However, how Jmjd2d is regulated has remained unclear. Here we identified the deubiquitinase (DUB) Trabid (‘tumornecrosis factor receptor–associated factor–binding protein domain’; also called ‘Zranb1’), as a crucial regulator of TLR-stimulated expression of IL-12 and IL-23. Trabid belongs to the OTU family of DUBs and ‘preferentially’ hydrolyzes lysine 29 (K29)and Lys33 (K33)linked ubiquitin chains17–19. In vitro studies of cancer cell lines have suggested a role for Trabid in the regulation of Wnt signaling, but this function remains controversial20,21. By using a gene-targeting approach, we found that Trabid deficiency in DCs and macrophages impaired the induction of Il12 and Il23 without affecting the induction