A murine model of acute lung injury identifies growth factors to promote tissue repair and their biomarkers.

Type II alveolar epithelial cells (AEC2s) play a crucial role in the regeneration of type I AECs after acute lung injury. The mechanisms underlying the regeneration of AEC2s are not fully understood. To address this issue, here, we investigated a murine model of acute lung injury using mice expressing human Diphtheria Toxin Receptor (DTR) under the control of Lysozyme M promoter (LysM-DTR). DT injection induced the depletion of AEC2s, alveolar macrophages, and bone marrow (BM)-derived myeloid cells in LysM-DTR mice, and the mice died within 6 days after DT injection. Apoptotic AEC2s and bronchiolar epithelial cells appeared at 24 hr, whereas Ki67-positive proliferating cells appeared in the alveoli and bronchioles in the lung of LysM-DTR mice at 72-96 hr after DT injection. Transfer of wild-type BM cells into LysM-DTR mice accelerated the regeneration of AEC2s along with the up-regulation of several growth factors. Moreover, several metabolites were significantly decreased in the sera of LysM-DTR mice compared with WT mice after DT injection, suggesting that these metabolites might be biomarkers to predict AEC2s injury. Together, LysM-DTR mice might be useful to identify growth factors to promote lung repair and the metabolites to predict the severity of lung injury.

Critical Contribution of Nuclear Factor Erythroid 2-related Factor 2 (NRF2) to Electrophile-induced Interleukin-11 Production.

Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor that plays a crucial role in protection of cells from electrophile-induced toxicity through up-regulating phase II detoxifying enzymes and phase III transporters. We previously reported that oxidative stress induces up-regulation of interleukin-11 (IL-11), a member of the IL-6 family that ameliorates acetaminophen-induced liver toxicity. However, a role for IL-11 in protection of cells from electrophile-induced toxicity remains unclear. Here we show that an environmental electrophile, 1,2-naphthoquinone (1,2-NQ), but not 15d-prostaglandin J2 (PGJ2) or tert-butylhydroxyquinone (tBHQ), induced IL-11 production. Consistent with a crucial role for prolonged ERK activation in H2O2-induced IL-11 production, 1,2-NQ, but not 15d-PGJ2 or tBHQ, elicited prolonged ERK activation. Conversely, inhibition of the ERK pathway by a MEK inhibitor completely blocked 1,2-NQ-induced IL-11 production at both protein and mRNA levels, further substantiating an intimate cross-talk between ERK activation and 1,2-NQ-induced IL-11 production. Promoter analysis of the Il11 gene revealed that two AP-1 sites were essential for 1,2-NQ-induced promoter activities. Among various members of the AP-1 family, Fra-1 was up-regulated by 1,2-NQ, and its up-regulation was blocked by a MEK inhibitor. Although NRF2 was not required for H2O2-induced IL11 up-regulation, NRF2 was essential for 1,2-NQ-induced IL11 up-regulation by increasing Fra-1 proteins possibly through promoting mRNA translation of FOSL1 Finally, intraperitoneal administration of 1,2-NQ induced body weight loss in wild-type mice, which was further exacerbated in Il11ra1-/- mice compared with Il11ra1+/- mice. Together, both Fra-1 and NRF2 play crucial roles in IL-11 production that protects cells from 1,2-NQ intestinal toxicity.

Depletion of myeloid cells exacerbates hepatitis and induces an aberrant increase in histone H3 in mouse serum.

Tissue-resident macrophages and bone marrow (BM)-derived monocytes play a crucial role in the maintenance of tissue homeostasis; however, their contribution to recovery from acute tissue injury is not fully understood. To address this issue, we generated an acute murine liver injury model using hepatocyte-specific Cflar-deficient (CflarHep-low ) mice. Cellular FLICE-inhibitory protein expression was down-regulated in Cflar-deficient hepatocytes, which thereby increased susceptibility of hepatocytes to death receptor-induced apoptosis. CflarHep-low mice developed acute hepatitis and recovered with clearance of apoptotic hepatocytes at 24 hours after injection of low doses of tumor necrosis factor α (TNFα), which could not induce hepatitis in wild-type (WT) mice. Depletion of Kupffer cells (KCs) by clodronate liposomes did not impair clearance of dying hepatocytes or exacerbate hepatitis in CflarHep-low mice. To elucidate the roles of BM-derived monocytes and neutrophils in clearance of apoptotic hepatocytes, we examined the effect of depletion of these cells on TNFα-induced hepatitis in CflarHep-low mice. We reconstituted CflarHep-low mice with BM cells from transgenic mice in which human diphtheria toxin receptor (DTR) was expressed under control of the lysozyme M (LysM) promoter. TNFα-induced infiltration of myeloid cells, including monocytes and neutrophils, was completely ablated in LysM-DTR BM-reconstituted CflarHep-low mice pretreated with diphtheria toxin, whereas KCs remained present in the livers. Under these experimental conditions, LysM-DTR BM-reconstituted CflarHep-low mice rapidly developed severe hepatitis and succumbed within several hours of TNFα injection. We found that serum interleukin-6 (IL-6), TNFα, and histone H3 were aberrantly increased in LysM-DTR BM-reconstituted, but not in WT BM-reconstituted, CflarHep-low mice following TNFα injection. CONCLUSION: These findings indicate an unexpected role of myeloid cells in decreasing serum IL-6, TNFα, and histone H3 levels via the suppression of TNFα-induced hepatocyte apoptosis. (Hepatology 2017;65:237-252).

The Nuclear Protein IκBζ Forms a Transcriptionally Active Complex with Nuclear Factor-κB (NF-κB) p50 and the Lcn2 Promoter via the N- and C-terminal Ankyrin Repeat Motifs.

The nuclear protein IκBζ, comprising the N-terminal trans-activation domain and the C-terminal ankyrin repeat (ANK) domain composed of seven ANK motifs, activates transcription of a subset of nuclear factor-κB (NF-κB)-dependent innate immune genes such as Lcn2 encoding the antibacterial protein lipocalin-2. Lcn2 activation requires formation of a complex containing IκBζ and NF-κB p50, a transcription factor that harbors the DNA-binding Rel homology region but lacks a trans-activation domain, on the promoter with the canonical NF-κB-binding site (κB site) and its downstream cytosine-rich element. Here we show that IκBζ productively interacts with p50 via Asp-451 in the N terminus of ANK1, a residue that is evolutionarily conserved among IκBζ and the related nuclear IκB proteins Bcl-3 and IκBNS Threonine substitution for Asp-451 abrogates direct association with the κB-site-binding protein p50, complex formation with the Lcn2 promoter DNA, and activation of Lcn2 transcription. The basic residues Lys-717 and Lys-719 in the C-terminal region of ANK7 contribute to IκBζ binding to the Lcn2 promoter, probably via interaction with the cytosine-rich element required for Lcn2 activation; glutamate substitution for both lysines results in a loss of transcriptionally active complex formation without affecting direct contact of IκBζ with p50. Both termini of the ANK domain in Bcl-3 and IκBNS function in a manner similar to that of IκBζ to interact with promoter DNA, indicating a common mechanism in which the nuclear IκBs form a regulatory complex with NF-κB and promoter DNA via the invariant aspartate in ANK1 and the conserved basic residues in ANK7.

Short form FLICE-inhibitory protein promotes TNFα-induced necroptosis in fibroblasts derived from CFLARs transgenic mice.

Cellular FLICE-inhibitory protein (cFLIP) is a catalytically inactive homolog of the initiator caspase, caspase 8 and blocks apoptosis through binding to caspase 8. Human CFLAR gene encodes two proteins, a long form cFLIP (cFLIPL) and a short form cFLIP (cFLIPs) due to an alternative splicing. Recent studies have shown that expression of cFLIPs, but not cFLIPL promotes programmed necrosis (also referred to as necroptosis) in an immortalized human keratinocyte cell line, HaCaT. Here, we found that expression of cFLIPs similarly promoted necroptosis in immortalized fibroblasts. To further expand this observation and exclude the possibility that immortalization process of keratinocytes or fibroblasts might affect the phenotype induced by cFLIPs expression, we generated human CFLARs transgenic (Tg) mice. Primary fibroblasts derived from CFLARs Tg mice were increased in susceptibility to TNFα-induced necroptosis, but not apoptosis compared to wild-type (WT) fibroblasts. Moreover, hallmarks of necroptosis, such as phosphorylation of receptor-interacting protein kinase (RIPK)1 and RIPK3, and oligomer formation of mixed lineage kinase domain-like (MLKL) were robustly induced in CFLARs Tg fibroblasts compared to wild-type fibroblasts following TNFα stimulation. Thus, cFLIPs-dependent promotion of necroptosis is not unique to immortalized keratinocytes or fibroblasts, but also to generalized to primary fibroblasts.

DNA element downstream of the κB site in the Lcn2 promoter is required for transcriptional activation by IκBζ and NF-κB p50.

The nuclear protein IκBζ activates transcription of a subset of NF-κB-dependent innate immune genes such as Lcn2 encoding the antibacterial protein lipocalin-2. IκBζ functions as a coactivator via its interaction with NF-κB p50, which contains a DNA-binding Rel-homology domain but lacks a transcriptional activation domain. However cis-regulatory elements involved in IκBζ function have remained unknown. Here, we show that, although IκBζ by itself is unable to associate with the Lcn2 promoter, IκBζ interacts with the promoter via p50 binding to the NF-κB-binding site (κB site) and the interaction also requires the pyrimidine-rich site (CCCCTC) that localizes seven bases downstream of the κB site. The pyrimidine-rich site is also essential for IκBζ-mediated activation of the Lcn2 gene. Introduction of both sites into an IκBζ-independent gene culminates in IκBζ-p50-DNA complex formation and transcriptional activation. Furthermore, spacing between the two sites is crucial for both IκBζ-DNA interaction and IκBζ-mediated gene activation. Thus, the pyrimidine-rich IκBζ-responsive site plays an essential role in productive interaction of IκBζ with the p50-DNA complex.

Interleukin 11 confers resistance to dextran sulfate sodium-induced colitis in mice.

Intestinal homeostasis is tightly regulated by epithelial cells, leukocytes, and stromal cells, and its dysregulation is associated with inflammatory bowel diseases. Interleukin (IL)-11, a member of the IL-6 family of cytokines, is produced by inflammatory fibroblasts during acute colitis. However, the role of IL-11 in the development of colitis is still unclear. Herein, we showed that IL-11 ameliorated DSS-induced acute colitis in mouse models. We found that deletion of Il11ra1 or Il11 rendered mice highly susceptible to DSS-induced colitis compared to the respective control mice. The number of apoptotic epithelial cells was increased in DSS-treated Il11ra1- or Il11-deficient mice. Moreover, we showed that IL-11 production was regulated by reactive oxygen species (ROS) produced by lysozyme M-positive myeloid cells. These findings indicate that fibroblast-produced IL-11 plays an important role in protecting the mucosal epithelium in acute colitis. Myeloid cell-derived ROS contribute to the attenuation of colitis through the production of IL-11.

Fibroblast growth factor 18 stimulates the proliferation of hepatic stellate cells, thereby inducing liver fibrosis.

Liver fibrosis results from chronic liver injury triggered by factors such as viral infection, excess alcohol intake, and lipid accumulation. However, the mechanisms underlying liver fibrosis are not fully understood. Here, we demonstrate that the expression of fibroblast growth factor 18 (Fgf18) is elevated in mouse livers following the induction of chronic liver fibrosis models. Deletion of Fgf18 in hepatocytes attenuates liver fibrosis; conversely, overexpression of Fgf18 promotes liver fibrosis. Single-cell RNA sequencing reveals that overexpression of Fgf18 in hepatocytes results in an increase in the number of Lrat+ hepatic stellate cells (HSCs), thereby inducing fibrosis. Mechanistically, FGF18 stimulates the proliferation of HSCs by inducing the expression of Ccnd1. Moreover, the expression of FGF18 is correlated with the expression of profibrotic genes, such as COL1A1 and ACTA2, in human liver biopsy samples. Thus, FGF18 promotes liver fibrosis and could serve as a therapeutic target to treat liver fibrosis.

Rescue of TRAF3-null mice by p100 NF-kappa B deficiency.

Proper activation of nuclear factor (NF)-kappaB transcription factors is critical in regulating fundamental biological processes such as cell survival and proliferation, as well as in inflammatory and immune responses. Recently, the NF-kappaB signaling pathways have been categorized into the canonical pathway, which results in the nuclear translocation of NF-kappaB complexes containing p50, and the noncanonical pathway, which involves the induced processing of p100 to p52 and the formation of NF-kappaB complexes containing p52 (Bonizzi, G., and M. Karin. 2004. Trends Immunol. 25:280-288). We demonstrate that loss of tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3) results in constitutive noncanonical NF-kappaB activity. Importantly, TRAF3-/- B cells show ligand-independent up-regulation of intracellular adhesion molecule 1 and protection from spontaneous apoptosis during in vitro culture. In addition, we demonstrate that loss of TRAF3 results in profound accumulation of NF-kappaB-inducing kinase in TRAF3-/- cells. Finally, we show that the early postnatal lethality observed in TRAF3-deficient mice is rescued by compound loss of the noncanonical NF-kappaB p100 gene. Thus, these genetic data clearly demonstrate that TRAF3 is a critical negative modulator of the noncanonical NF-kappaB pathway and that constitutive activation of the noncanonical NF-kappaB pathway causes the lethal phenotype of TRAF3-deficient mice.

IκBζ controls IL-17-triggered gene expression program in intestinal epithelial cells that restricts colonization of SFB and prevents Th17-associated pathologies.

Control of gut microbes is crucial for not only local defense in the intestine but also proper systemic immune responses. Although intestinal epithelial cells (IECs) play important roles in cytokine-mediated control of enterobacteria, the underlying mechanisms are not fully understood. Here we show that deletion of IκBζ in IECs in mice leads to dysbiosis with marked expansion of segmented filamentous bacteria (SFB), thereby enhancing Th17 cell development and exacerbating inflammatory diseases. Mechanistically, the IκBζ deficiency results in decrease in the number of Paneth cells and impairment in expression of IL-17-inducible genes involved in IgA production. The decrease in Paneth cells is caused by aberrant activation of IFN-γ signaling and a failure of IL-17-dependent recovery from IFN-γ-induced damage. Thus, the IL-17R-IκBζ axis in IECs contributes to the maintenance of intestinal homeostasis by serving as a key component in a regulatory loop between the gut microbiota and immune cells.

Control of canonical NF-kappaB activation through the NIK-IKK complex pathway.

Articles in recent years have described two separate and distinct NF-kappaB activation pathways that result in the differential activation of p50- or p52-containing NF-kappaB complexes. Studies examining tumor-necrosis factor receptor-associated factors (TRAFs) have identified positive roles for TRAF2, TRAF5, and TRAF6, but not TRAF3, in canonical (p50-dependent) NF-kappaB activation. Conversely, it recently was reported that TRAF3 functions as an essential negative regulator of the noncanonical (p52-dependent) NF-kappaB pathway. In this article, we provide evidence that TRAF3 potently suppresses canonical NF-kappaB activation and gene expression in vitro and in vivo. We also demonstrate that deregulation of the canonical NF-kappaB pathway in TRAF3-deficient cells results from accumulation of NF-kappaB-inducing kinase (NIK), the essential kinase mediating noncanonical NF-kappaB activation. Thus, our data demonstrate that inhibition of TRAF3 results in coordinated activation of both NF-kappaB activation pathways.

Regulation of T cell differentiation by the AP-1 transcription factor JunB.

JunB, a component of the activator protein-1 (AP-1) transcription factor, is known to exhibit an important role in bone formation and bone marrow cell proliferation. During T helper type 2 (Th2) cell differentiation, JunB contributes to the regulation of interleukin (IL)-4 expression, and AP-1 and nuclear factor of activated T cell (NFAT) constitute a heteromer and contribute to IL-2 production. However, the role of JunB in other T cells has not been investigated. In 2017, it was revealed that JunB, in collaboration with basic leucine zipper ATF-like transcription factor (BATF), regulates the expression of Th17-related genes. Furthermore, JunB was found to play an important role in regulatory T (Treg) cell differentiation, contributing to CD25 expression and IL-2 production. IL-2 is a T cell activator and has been shown as a necessary factor for Treg proliferation. Here, we review the role of JunB in T cells based on basic research data and discuss the potential for its clinical applications.

MIND bomb 2 prevents RIPK1 kinase activity-dependent and -independent apoptosis through ubiquitylation of cFLIPL.

Mind bomb 2 (MIB2) is an E3 ligase involved in Notch signalling and attenuates TNF-induced apoptosis through ubiquitylation of receptor-interacting protein kinase 1 (RIPK1) and cylindromatosis. Here we show that MIB2 bound and conjugated K48- and K63-linked polyubiquitin chains to a long-form of cellular FLICE-inhibitory protein (cFLIPL), a catalytically inactive homologue of caspase 8. Deletion of MIB2 did not impair the TNF-induced complex I formation that mediates NF-κB activation but significantly enhanced formation of cytosolic death-inducing signalling complex II. TNF-induced RIPK1 Ser166 phosphorylation, a hallmark of RIPK1 death-inducing activity, was enhanced in MIB2 knockout cells, as was RIPK1 kinase activity-dependent and -independent apoptosis. Moreover, RIPK1 kinase activity-independent apoptosis was induced in cells expressing cFLIPL mutants lacking MIB2-dependent ubiquitylation. Together, these results suggest that MIB2 suppresses both RIPK1 kinase activity-dependent and -independent apoptosis, through suppression of RIPK1 kinase activity and ubiquitylation of cFLIPL, respectively.

Interleukin-11-expressing fibroblasts have a unique gene signature correlated with poor prognosis of colorectal cancer.

Interleukin (IL)-11 is a member of the IL-6 family of cytokines and is involved in multiple cellular responses, including tumor development. However, the origin and functions of IL-11-producing (IL-11+) cells are not fully understood. To characterize IL-11+ cells in vivo, we generate Il11 reporter mice. IL-11+ cells appear in the colon in murine tumor and acute colitis models. Il11ra1 or Il11 deletion attenuates the development of colitis-associated colorectal cancer. IL-11+ cells express fibroblast markers and genes associated with cell proliferation and tissue repair. IL-11 induces the activation of colonic fibroblasts and epithelial cells through phosphorylation of STAT3. Human cancer database analysis reveals that the expression of genes enriched in IL-11+ fibroblasts is elevated in human colorectal cancer and correlated with reduced recurrence-free survival. IL-11+ fibroblasts activate both tumor cells and fibroblasts via secretion of IL-11, thereby constituting a feed-forward loop between tumor cells and fibroblasts in the tumor microenvironment.

Regulation of Toll/IL-1-receptor-mediated gene expression by the inducible nuclear protein IkappaBzeta.

Toll-like receptors (TLRs) recognize microbial components and trigger the inflammatory and immune responses against pathogens. IkappaBzeta (also known as MAIL and INAP) is an ankyrin-repeat-containing nuclear protein that is highly homologous to the IkappaB family member Bcl-3 (refs 1-6). Transcription of IkappaBzeta is rapidly induced by stimulation with TLR ligands and interleukin-1 (IL-1). Here we show that IkappaBzeta is indispensable for the expression of a subset of genes activated in TLR/IL-1R signalling pathways. IkappaBzeta-deficient cells show severe impairment of IL-6 production in response to a variety of TLR ligands as well as IL-1, but not in response to tumour-necrosis factor-alpha. Endogenous IkappaBzeta specifically associates with the p50 subunit of NF-kappaB, and is recruited to the NF-kappaB binding site of the IL-6 promoter on stimulation. Moreover, NF-kappaB1/p50-deficient mice show responses to TLR/IL-1R ligands similar to those of IkappaBzeta-deficient mice. Endotoxin-induced expression of other genes such as Il12b and Csf2 is also abrogated in IkappaBzeta-deficient macrophages. Given that the lipopolysaccharide-induced transcription of IkappaBzeta occurs earlier than transcription of these genes, some TLR/IL-1R-mediated responses may be regulated in a gene expression process of at least two steps that requires inducible IkappaBzeta.

Regenerating islet-derived protein (Reg)3ß plays a crucial role in attenuation of ileitis and colitis in mice.

Regenerating islet-derived protein (Reg)3ß belongs to a member of the Reg family of proteins and has pleiotropic functions, including antimicrobial activity and tissue repair. However, whether Reg3ß plays a protective role in the development of colitis and ileitis has not been fully investigated. We generated transgenic mice expressing a short form of cellular FLICE-inhibitory protein (cFLIPs) that promotes necroptosis, a regulated form of cell death. cFLIPs transgenic (CFLARs Tg) mice develop severe ileitis in utero. Although Reg3ß is undetectable in the small intestine of wild-type embryos, its expression is aberrantly elevated in the small intestine of CFLARs Tg embryos. To test whether elevated Reg3ß attenuates or exacerbates ileitis in CFLARs Tg mice, we generated a Reg3b -/- strain. Reg3b -/- mice grew to adulthood without apparent abnormalities. Deletion of Reg3b in CFLARs Tg mice exacerbated the embryonic lethality of CFLARs Tg mice. Dextran sulfate sodium-induced colitis, characterized by body weight loss and infiltration of neutrophils, was exacerbated in Reg3b -/- compared to wild-type mice. Moreover, the expression of Interleukin 6, an inflammatory cytokine and Chitinase-like 3, a marker for tissue repair macrophages was elevated in the colon of Reg3b -/- mice compared to wild-type mice after DSS treatment. Together, these results suggest that attenuation of colitis and ileitis is a result of Reg3ß's real function.

Protein synthesis inhibitors enhance the expression of mRNAs for early inducible inflammatory genes via mRNA stabilization.

Expression of inflammatory genes is regulated at multiple steps, including transcriptional activation and mRNA stabilization. During an investigation into the requirement of de novo protein synthesis for the induction of inflammatory genes, it was revealed that protein synthesis inhibitors unexpectedly potentiated the induction of mRNAs for primary response genes, while the inhibitors suppressed the induction of secondary inducible genes as previously described. Stimulus-induced nuclear translocation and promoter recruitment of NF-kappaB, which is responsible for the transcriptional activation of many inflammatory genes, were largely unaffected by the inhibitors. Instead, these inhibitors prolonged the half-lives of all of the primary inducible mRNAs tested. Thus, these findings emphasize the important contribution of regulated mRNA longevity to gene expression induced by pro-inflammatory stimulation.

Development of novel methods that monitor necroptosis and the release of DAMPs at the single cell resolution.

Necroptosis is a regulated form of necrosis that depends on receptor-interacting protein kinase (RIPK)3 and mixed lineage kinase domain-like protein (MLKL). While danger-associated molecular pattern (DAMP)s are released from dead cells and involved in various pathological conditions, the mechanisms underlying regulation of the release of DAMPs are not fully understood. Apoptosis and pyroptosis can be detected by several types of sensors such as Forster resonance energy transfer (FRET) biosensors, termed SCAT1 (a sensor for caspase 1 activation based on FRET) and SCAT3, respectively. These sensors have provided better understanding of pyroptosis and apoptosis in vitro and in vivo. However, there have been no biosensors to monitor necroptosis. Development of a FRET biosensor that monitors necroptosis and generation of transgenic mice expressing such FRET biosensor might be useful to understand the mechanisms underlying the execution of necroptosis and also the consequences of necroptosis in vivo. In our recent study (Nat Commun, 9(1):4457), we developed a FRET biosensor for necroptosis, termed SMART (a sensor for MLKL activation by RIPK3 based on FRET). SMART is composed of a fragment of MLKL and monitors necroptosis, but not apoptosis or necrosis. Moreover, we recently developed a platform called Live-Cell Imaging for Secretion activity (LCI-S) to monitor protein secretion at the single cell level. This platform has enabled us to monitor the release of HMGB1 (High Mobility Group Box 1), one of the DAMPs, at the single cell level and reveals two different modes of the release of HMGB1 from necroptotic cells.

JunB plays a crucial role in development of regulatory T cells by promoting IL-2 signaling.

The AP-1 transcription factor JunB plays crucial roles in multiple biological processes, including placental formation and bone homeostasis. We recently reported that JunB is essential for development of Th17 cells, and thus Junb-deficient mice are resistant to experimental autoimmune encephalomyelitis. However, the role of JunB in CD4+ T cells under other inflammatory disease conditions is unknown. Here we show that mice lacking JunB in CD4+ T cells (Junbfl/flCd4-Cre mice) were more susceptible to dextran sulfate sodium (DSS)-induced colitis because of impaired development of regulatory T (Treg) cells. Production of interleukin (IL)-2 and expression of CD25, a high affinity IL-2 receptor component, were decreased in Junb-deficient CD4+ T cells in vitro and in vivo. Naive CD4+ T cells from Junbfl/flCd4-Cre mice failed to differentiate into Treg cells in the absence of exogenously added IL-2 in vitro. A mixed bone marrow transfer experiment revealed that defective Treg development of Junb-deficient CD4+ T cells was not rescued by co-transferred wild-type cells, indicating a significance of the cell-intrinsic defect. Injection of IL-2-anti-IL-2 antibody complexes induced expansion of Treg cells and alleviated DSS-induced colitis in Junbfl/flCd4-Cre mice. Thus JunB plays a crucial role in the development of Treg cells by facilitating IL-2 signaling.

Necroptosis of Intestinal Epithelial Cells Induces Type 3 Innate Lymphoid Cell-Dependent Lethal Ileitis.

A short form of cellular FLICE-inhibitory protein encoded by CFLARs promotes necroptosis. Although necroptosis is involved in various pathological conditions, the detailed mechanisms are not fully understood. Here we generated transgenic mice wherein CFLARs was integrated onto the X chromosome. All male CFLARs Tg mice died perinatally due to severe ileitis. Although necroptosis was observed in various tissues of CFLARs Tg mice, large numbers of intestinal epithelial cells (IECs) died by apoptosis. Deletion of Ripk3 or Mlkl, essential genes of necroptosis, prevented both necroptosis and apoptosis, and rescued lethality of CFLARs Tg mice. Type 3 innate lymphoid cells (ILC3s) were activated and recruited to the small intestine along with upregulation of interleukin-22 (Il22) in CFLARs Tg mice. Deletion of ILC3s or Il22 rescued lethality of CFLARs Tg mice by preventing apoptosis, but not necroptosis of IECs. Together, necroptosis-dependent activation of ILC3s induces lethal ileitis in an IL-22-dependent manner.