Xiaohu Wang

Transcription factor achaete-scute homologue 2 initiates follicular T-helper-cell development

In immune responses, activated T cells migrate to B-cell follicles and develop into follicular T-helper (TFH) cells, a recently identified subset of CD4+ T cells specialized in providing help to B lymphocytes in the induction of germinal centres. Although Bcl6 has been shown to be essential in TFH-cell function, it may not regulate the initial migration of T cells or the induction of the TFH program, as exemplified by C-X-C chemokine receptor type 5 (CXCR5) upregulation. Here we show that expression of achaete-scute homologue 2 (Ascl2)—a basic helix–loop–helix (bHLH) transcription factor—is selectively upregulated in TFH cells. Ectopic expression of Ascl2 upregulates CXCR5 but not Bcl6, and downregulates C-C chemokine receptor 7 (CCR7) expression in T cells in vitro, as well as accelerating T-cell migration to the follicles and TFH-cell development in vivo in mice. Genome-wide analysis indicates that Ascl2 directly regulates TFH-related genes whereas it inhibits expression of T-helper cell 1 (TH1) and TH17 signature genes. Acute deletion of Ascl2, as well as blockade of its function with the Id3 protein in CD4+ T cells, results in impaired TFH-cell development and germinal centre response. Conversely, mutation of Id3, known to cause antibody-mediated autoimmunity, greatly enhances TFH-cell generation. Thus, Ascl2 directly initiates TFH-cell development.

Bcl6 expression specifies the T follicular helper cell program in vivo

A novel Bcl6 reporter mouse is used to dissect the developmental requirements, plasticity, and genetic profile of Tfh cells.

Ursolic Acid Suppresses Interleukin-17 (IL-17) Production by Selectively Antagonizing the Function of RORγt Protein

Th17 cells have recently emerged as a major player in inflammatory and autoimmune diseases via the production of pro-inflammatory cytokines IL-17, IL-17F, and IL-22. The differentiation of Th17 cells and the associated cytokine production is directly controlled by RORγt. Here we show that ursolic acid (UA), a small molecule present in herbal medicine, selectively and effectively inhibits the function of RORγt, resulting in greatly decreased IL-17 expression in both developing and differentiated Th17 cells. In addition, treatment with UA ameliorated experimental autoimmune encephalomyelitis. The results thus suggest UA as a valuable drug candidate or leading compound for developing treatments of Th17-mediated inflammatory diseases and cancer.

The Methylcytosine Dioxygenase Tet2 Promotes DNA Demethylation and Activation of Cytokine Gene Expression in T Cells

Epigenetic regulation of lineage-specific genes is important for the differentiation and function of T cells. Ten-eleven translocation (Tet) proteins catalyze 5-methylcytosine (5 mC) conversion to 5-hydroxymethylcytosine (5 hmC) to mediate DNA demethylation. However, the roles of Tet proteins in the immune response are unknown. Here, we characterized the genome-wide distribution of 5 hmC in CD4(+) T cells and found that 5 hmC marks putative regulatory elements in signature genes associated with effector cell differentiation. Moreover, Tet2 protein was recruited to 5 hmC-containing regions, dependent on lineage-specific transcription factors. Deletion of Tet2 in T cells decreased their cytokine expression, associated with reduced p300 recruitment. In vivo, Tet2 plays a critical role in the control of cytokine gene expression in autoimmune disease. Collectively, our findings suggest that Tet2 promotes DNA demethylation and activation of cytokine gene expression in T cells.

Negative regulation of IL-17-mediated signaling and inflammation by the ubiquitin-specific protease USP25

Interleukin 17 (IL-17) is important in infection and autoimmunity; how it signals remains poorly understood. In this study, we identified the ubiquitin-specific protease USP25 as a negative regulator of IL-17-mediated signaling and inflammation. Overexpression of USP25 inhibited IL-17-triggered signaling, whereas USP25 deficiency resulted in more phosphorylation of the inhibitor IκBα and kinase Jnk and higher expression of chemokines and cytokines, as well as a prolonged half-life for chemokine CXCL1–encoding mRNA after treatment with IL-17. Consistent with that, Usp25−/− mice showed greater sensitivity to IL-17-dependent inflammation and autoimmunity in vivo. Mechanistically, stimulation with IL-17 induced the association of USP25 with the adaptors TRAF5 and TRAF6, and USP25 induced removal of Lys63-linked ubiquitination in TRAF5 and TRAF6 mediated by the adaptor Act1. Thus, our results demonstrate that USP25 is a deubiquitinating enzyme (DUB) that negatively regulates IL-17-triggered signaling.

Transcription of Il17 and Il17f Is Controlled by Conserved Noncoding Sequence 2

T helper 17 (Th17) cells specifically transcribe the Il17 and Il17f genes, which are localized in the same chromosome region, but the underlying mechanism is unclear. Here, we report a cis element that we previously named conserved noncoding sequence 2 (CNS2) physically interacted with both Il17 and Il17f gene promoters and was sufficient for regulating their selective transcription in Th17 cells. Targeted deletion of CNS2 resulted in impaired retinoic acid-related orphan receptor gammat (RORγt)-driven IL-17 expression in vitro. CNS2-deficient T cells also produced substantially decreased amounts of IL-17F. These cytokine defects were associated with defective chromatin remodeling in the Il17-Il17f gene locus, possibly because of effects on CNS2-mediated recruitment of histone-modifying enzymes p300 and JmjC domain-containing protein 3 (JMJD3). CNS2-deficient animals were also shown to be resistant to experimental autoimmune encephalomyelitis (EAE). Our results thus suggest that CNS2 is sufficient and necessary for Il17 and optimal Il17f gene transcription in Th17 cells.

Ubiquitin-Specific Protease 25 Regulates TLR4-Dependent Innate Immune Responses Through Deubiquitination of the Adaptor Protein TRAF3

The deubiquitinase USP25 prevents excessive proinflammatory signaling by Toll-like receptor 4. Maintaining a Balanced Response Activation of Toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS) stimulates two signaling pathways that are mediated by distinct adaptor proteins and depend on ubiquitination. The first, which requires the adaptor MyD88 (myeloid differentiation marker 88), results in production of proinflammatory cytokines, whereas the second, which involves the adaptors TRIF (Toll–interleukin-1 receptor domain–containing adaptor-inducing interferon-β) and TRAF3 (tumor necrosis factor receptor–associated factor 3), results in production of the modulatory cytokine interferon-α (IFN-α). Zhong et al. found that the deubiquitinase USP25 (ubiquitin-specific protease 25) was required for this second pathway. LPS stimulated the association of USP25 with TLR4 and TRAF3, and loss of USP25 resulted in enhanced ubiquitination and degradation of TRAF3 and inhibition of IFN-α production. As a result, USP25-deficient mice produced more inflammatory cytokines and less IFN-α and were more susceptible to death in response to LPS than were their wild-type counterparts. These data suggest that USP25 is required to maintain balanced TLR4 signaling and prevent an excessive inflammatory response. Protein ubiquitination plays a critical role in Toll-like receptor (TLR) signaling and innate immunity. Although several E3 ubiquitin ligases have been identified downstream of TLRs, the regulation of protein deubiquitination in TLR-triggered innate immune responses is poorly understood. We identified ubiquitin-specific protease 25 (USP25) as a regulator of TLR signaling. USP25 was recruited to the TLR4 signaling complex, and it associated with the adaptor proteins tumor necrosis factor receptor–associated factor 3 (TRAF3) and TRAF6 after stimulation of TLR4 with its ligand lipopolysaccharide (LPS). USP25 specifically reversed the Lys48-linked ubiquitination of TRAF3 that was mediated by the E3 ubiquitin ligase cIAP2 (cellular inhibitor of apoptosis 2). Deficiency in USP25 enhanced the extent of ubiquitination of TRAF3 and accelerated its degradation after TLR4 activation, which potentiated TLR4-induced activation of NF-κB (nuclear factor κB) and MAPK (mitogen-activated protein kinase) signaling, but inhibited activation of the transcription factor IRF3 (interferon regulatory factor 3). USP25-deficient mice exhibited increased susceptibility to LPS-induced septic shock compared to their wild-type counterparts, which was associated with enhanced production of proinflammatory cytokines and decreased production of interferon-α. Thus, by inhibiting the degradation of TRAF3 during TLR4 activation, USP25 enables a balanced innate immune response.

Metabolic control of TH17 and induced Treg cell balance by an epigenetic mechanism

Metabolism has been shown to integrate with epigenetics and transcription to modulate cell fate and function. Beyond meeting the bioenergetic and biosynthetic demands of T-cell differentiation, whether metabolism might control T-cell fate by an epigenetic mechanism is unclear. Here, through the discovery and mechanistic characterization of a small molecule, (aminooxy)acetic acid, that reprograms the differentiation of T helper 17 (TH17) cells towards induced regulatory T (iTreg) cells, we show that increased transamination, mainly catalysed by GOT1, leads to increased levels of 2-hydroxyglutarate in differentiating TH17 cells. The accumulation of 2-hydroxyglutarate resulted in hypermethylation of the Foxp3 gene locus and inhibited Foxp3 transcription, which is essential for fate determination towards TH17 cells. Inhibition of the conversion of glutamate to α-ketoglutaric acid prevented the production of 2-hydroxyglutarate, reduced methylation of the Foxp3 gene locus, and increased Foxp3 expression. This consequently blocked the differentiation of TH17 cells by antagonizing the function of transcription factor RORγt and promoted polarization into iTreg cells. Selective inhibition of GOT1 with (aminooxy)acetic acid ameliorated experimental autoimmune encephalomyelitis in a therapeutic mouse model by regulating the balance between TH17 and iTreg cells. Targeting a glutamate-dependent metabolic pathway thus represents a new strategy for developing therapeutic agents against TH17-mediated autoimmune diseases.

An Interleukin-25-Mediated Autoregulatory Circuit in Keratinocytes Plays a Pivotal Role in Psoriatic Skin Inflammation

SUMMARY Psoriasis is a chronic autoinflammatory skin disease. Although interleukin‐17, derived from lymphocytes, has been shown to be critical in psoriasis, the initiation and maintenance of chronic skin inflammation has not been well understood. IL‐25 (also called IL‐17E), another IL‐17 family cytokine, is well known to regulate allergic responses and type 2 immunity. Here we have shown that IL‐25, also highly expressed in the lesional skin of psoriasis patients, was regulated by IL‐17 in murine skin of a imiquimod (IMQ)‐induced psoriasis model. IL‐25 injection induced skin inflammation, whereas germline or keratinocyte‐specific deletion of IL‐25 caused resistance to IMQ‐induced psoriasis. Via IL‐17RB expression in keratinocytes, IL‐25 stimulated the proliferation of keratinocytes and induced the production of inflammatory cytokines and chemokines, via activation of the STAT3 transcription factor. Thus, our data demonstrate that an IL‐17‐induced autoregulatory circuit in keratinocytes is mediated by IL‐25 and suggest that this circuit could be targeted in the treatment of psoriasis patients. Graphical Abstract Figure. No caption available. HighlightsIL‐25 is highly expressed in psoriasisIL‐25 treatment induces psoriasis‐like skin inflammationIL‐25 in keratinocytes is necessary for psoriasis‐like skin inflammationIL‐25 promotes keratinocyte proliferation and pro‐inflammatory response In Brief The inflammatory mechanism of psoriasis remains incompletely understood. In this issue, Xu et al. identified IL‐25 as a key pathogenic factor regulating the proliferation of keratinocytes and psoriasis development in an autocrine expression manner.

Ubc9 Is Required for Positive Selection and Late-Stage Maturation of Thymocytes

SUMOylation is an important posttranslational modification that regulates protein function in diverse biological processes. However, its role in early T cell development has not been genetically studied. UBC9 is the only E2 enzyme for all SUMOylation. In this study, by selectively deleting Ubc9 gene in T cells, we have investigated the functional roles of SUMOylation in T cell development. Loss of Ubc9 results in a significant reduction of CD4 and CD8 single-positive lymphocytes in both thymus and periphery. Ubc9-deficient cells exhibit defective late-stage maturation post the initial positive selection with increased apoptosis and impaired proliferation, among which attenuated IL-7 signaling was correlated with the decreased survival of Ubc9-deficent CD8 single-positive cells. Furthermore, NFAT nuclear retention induced by TCR signals was regulated by SUMOylation during thymocytes development. Our study thus reveals a novel posttranslational mechanism underlying T cell development.