Phosphorylation-dependent Regnase-1 release from endoplasmic reticulum is critical in IL-17 response.

Regnase-1 (also known as Zc3h12a or MCPIP-1) is an endoribonuclease involved in mRNA degradation of inflammation-associated genes. Regnase-1 is inactivated in response to external stimuli through post-translational modifications including phosphorylation, yet the precise role of phosphorylation remains unknown. Here, we demonstrate that interleukin (IL)-17 induces phosphorylation of Regnase-1 in an Act1-TBK1/IKKi-dependent manner, especially in nonhematopoietic cells. Phosphorylated Regnase-1 is released from the endoplasmic reticulum (ER) into the cytosol, thereby losing its mRNA degradation function, which leads to expression of IL-17 target genes. By using CRISPR/Cas-9 technology, we generated Regnase-1 mutant mice, in which IL-17-induced Regnase-1 phosphorylation is completely blocked. Mutant mice (Regnase-1AA/AA and Regnase-1ΔCTD/ΔCTD ) were resistant to the IL-17-mediated inflammation caused by T helper 17 (Th17) cells in vivo. Thus, Regnase-1 plays a critical role in the development of IL-17-mediated inflammatory diseases via the Act1-TBK1-IKKi axis, and blockade of Regnase-1 phosphorylation sites may be promising for treatment of Th17-associated diseases.

Presenilin 1 Regulates NF-κB Activation via Association with Breakpoint Cluster Region and Casein Kinase II.

We recently reported that NF-κB-mediated inflammation caused by breakpoint cluster region (BCR) is dependent on the α subunit of casein kinase II (CK2α) complex. In the current study, we demonstrate that presenilin 1 (Psen1), which is a catalytic component of the γ-secretase complex and the mutations of which are known to cause familial Alzheimer disease, acts as a scaffold of the BCR-CK2α-p65 complex to induce NF-κB activation. Indeed, Psen1 deficiency in mouse endothelial cells showed a significant reduction of NF-κB p65 recruitment to target gene promoters. Conversely, Psen1 overexpression enhanced reporter activation under NF-κB responsive elements and IL-6 promoter. Furthermore, the transcription of NF-κB target genes was not inhibited by a γ-secretase inhibitor, suggesting that Psen1 regulates NF-κB activation in a manner independent of γ-secretase activity. Mechanistically, Psen1 associated with the BCR-CK2α complex, which is required for phosphorylation of p65 at serine 529. Consistently, TNF-α-induced phosphorylation of p65 at serine 529 was significantly decreased in Psen1-deficient cells. The association of the BCR-CK2α-p65 complex was perturbed in the absence of Psen1. These results suggest that Psen1 functions as a scaffold of the BCR-CK2α-p65 complex and that this signaling cascade could be a novel therapeutic target for various chronic inflammation conditions, including those in Alzheimer disease.

BATF2 inhibits immunopathological Th17 responses by suppressing Il23a expression during Trypanosoma cruzi infection.

Inappropriate IL-17 responses are implicated in chronic tissue inflammation. IL-23 contributes to Trypanosoma cruzi-specific IL-17 production, but the molecular mechanisms underlying regulation of the IL-23-IL-17 axis during T. cruzi infection are poorly understood. Here, we demonstrate a novel function of BATF2 as a negative regulator of Il23a in innate immune cells. IL-17, but not IFN-γ, was more highly produced by CD4+ T cells from spleens and livers of T. cruzi-infected Batf2-/- mice than by those of wild-type mice. In this context, Batf2-/- mice showed severe multiorgan pathology despite reduced parasite burden. T. cruzi-induced IL-23 production was increased in Batf2-/- innate immune cells. The T. cruzi-induced enhanced Th17 response was abrogated in Batf2-/-Il23a-/- mice. The interaction of BATF2 with c-JUN prevented c-JUN-ATF-2 complex formation, inhibiting Il23a expression. These results demonstrate that IFN-γ-inducible BATF2 in innate immune cells controls Th17-mediated immunopathology by suppressing IL-23 production during T. cruzi infection.

Breakpoint Cluster Region-Mediated Inflammation Is Dependent on Casein Kinase II.

The breakpoint cluster region (BCR) is known as a kinase and cause of leukemia upon fusing to Abl kinase. In this study, we demonstrate that BCR associated with the α subunit of casein kinase II (CK2α), rather than BCR itself, is required for inflammation development. We found that BCR knockdown inhibited NF-κB activation in vitro and in vivo. Computer simulation, however, suggested that the putative BCR kinase domain has an unstable structure with minimal enzymatic activity. Liquid chromatography-tandem mass spectrometry analysis showed that CK2α associated with BCR. We found the BCR functions are mediated by CK2α. Indeed, CK2α associated with adaptor molecules of TNF-αR and phosphorylated BCR at Y177 to establish a p65 binding site after TNF-α stimulation. Notably, p65 S529 phosphorylation by CK2α creates a p300 binding site and increased p65-mediated transcription followed by inflammation development in vivo. These results suggest that BCR-mediated inflammation is dependent on CK2α, and the BCR-CK2α complex could be a novel therapeutic target for various inflammatory diseases.

KDEL receptor 1 regulates T-cell homeostasis via PP1 that is a key phosphatase for ISR.

KDEL receptors are responsible for retrotransporting endoplasmic reticulum (ER) chaperones from the Golgi complex to the ER. Here we describe a role for KDEL receptor 1 (KDELR1) that involves the regulation of integrated stress responses (ISR) in T cells. Designing and using an N-ethyl-N-nitrosourea (ENU)-mutant mouse line, T-Red (naïve T-cell reduced), we show that a point mutation in KDELR1 is responsible for the reduction in the number of naïve T cells in this model owing to an increase in ISR. Mechanistic analysis shows that KDELR1 directly regulates protein phosphatase 1 (PP1), a key phosphatase for ISR in naïve T cells. T-Red KDELR1 does not associate with PP1, resulting in reduced phosphatase activity against eIF2α and subsequent expression of stress responsive genes including the proapoptotic factor Bim. These results demonstrate that KDELR1 regulates naïve T-cell homeostasis by controlling ISR.

Role of Inflammation Amplifier-Induced Growth Factor Expression in the Development of Inflammatory Diseases.

Inflammation is a fundamental response induced by the immune system to protect the body against pathogens, tissue damage, and stress. At the same time, recent studies have suggested that chronically induced inflammation is involved in various human diseases and disorders. Thus, understanding the molecular mechanisms of chronic inflammation could provide therapeutic value. Many mediators such as cytokines or chemokines regulate inflammatory responses. Among them, interleukin(IL)-6 is a prominent cytokine that induces and maintains inflammatory reactions. It is expressed by activated CD4+ T cells and also non-immune cells such as fibroblasts and epithelial cells. We discovered an inflammation-induction machinery, the inflammation amplifier, which is activated by the simultaneous stimulation of nuclear factor-kappa B (NF-κB) and signal transducers and activator of transcription 3 (STAT3) via various cytokines like IL-17 and IL-6 in non-immune cells. Activation of the inflammation amplifier induces a synergistic increase of IL-6, inflammatory chemokines, and growth factors. Using genome-wide screening, we identified several growth factors as mediators of the inflammation amplifier. In this review, we highlight the role of growth factors in the inflammation mechanism with special attention on the inflammation amplifier.

The reverse-direction method links mass experimental data to human diseases.

Genome-wide analyses such as DNA microarray, RNA sequencing and RNA interference-based high-throughput screening are prevalent to decipher a biological process of interest, and provide a large quantity of data to be processed. An ultimate goal for researchers must be extrapolation of their data to human diseases. We have conducted functional genome-wide screenings to elucidate molecular mechanisms of the inflammation amplifier, a NFκB/STAT3-dependent machinery that potently drives recruitment of immune cells to promote inflammation. Using a public database of genome-wide association studies (GWAS), we recently reported the reverse-direction method by which our mass screening data were successfully linked to many human diseases. As an example, the epiregulin-epidermal growth factor receptor pathway was identified as a regulator of the inflammation amplifier, and associated with human diseases by GWAS. In fact, serum epiregulin levels were higher in patients with chronic inflammatory disorders. The reverse-direction method can be a useful tool to narrow mass data down to focus on human disease-related genes.

Inflammation amplifier, a new paradigm in cancer biology.

Tumor-associated inflammation can induce various molecules expressed from the tumors themselves or surrounding cells to create a microenvironment that potentially promotes cancer development. Inflammation, particularly chronic inflammation, is often linked to cancer development, even though its evolutionary role should impair nonself objects including tumors. The inflammation amplifier, a hyperinducer of chemokines in nonimmune cells, is the principal machinery for inflammation and is activated by the simultaneous stimulation of NF-κB and STAT3. We have redefined inflammation as local activation of the inflammation amplifier, which causes an accumulation of various immune cells followed by dysregulation of local homeostasis. Genes related to the inflammation amplifier have been genetically associated with various human inflammatory diseases. Here, we describe how cancer-associated genes, including interleukin (IL)-6, Ptgs2, ErbB1, Gas1, Serpine1, cMyc, and Vegf-α, are strongly enriched in genes related to the amplifier. The inflammation amplifier is activated by the stimulation of cytokines, such as TNF-α, IL-17, and IL-6, resulting in the subsequent expression of various target genes for chemokines and tumor-related genes like BCL2L11, CPNE7, FAS, HIF1-α, IL-1RAP, and SOD2. Thus, we conclude that inflammation does indeed associate with the development of cancer. The identified genes associated with the inflammation amplifier may thus make potential therapeutic targets of cancers.

The gateway theory: bridging neural and immune interactions in the CNS.

The central nervous system (CNS) is considered an immune-privileged tissue protected by a specific vessel structure, the blood-brain barrier (BBB). Upon infection or traumatic injury in the CNS, the BBB is breached, and various immune cells are recruited to the affected area. In the case of autoimmune diseases in the CNS like multiple sclerosis (MS), autoreactive T cells against some CNS-specific antigens can theoretically attack neurons throughout the CNS. The affected CNS regions in MS patients can be detected as multiple focal plaques in the cerebrum, thoracic cord, and other regions. Vision problems are often associated with the initial phase of MS, suggesting a disturbance in the optic nerves. These observations raise the possibility that there exist specific signals that direct autoreactive T cells past the BBB and into particular sites of the CNS. Using a mouse model of MS, experimental autoimmune encephalomyelitis (EAE), we recently defined the mechanism of the pathogenesis in which regional neural stimulations modulate the status of the blood vessel endothelium to allow the invasion of autoreactive T cells into specific sites of the CNS via the fifth lumbar cord. This gate for autoreactive T cells can be artificially manipulated by removing gravity forces on the hind legs or by electric pulses to the soleus muscles, quadriceps, and triceps of mice, resulting in an accumulation of autoreactive T cells in the intended regions via the activation of regional neurons. Gating blood vessels by regional neural stimulations, a phenomenon we call the gateway theory, has potential therapeutic value not only in preventing autoimmunity, but also in augmenting the effects of cancer immunotherapies.

Regulation of immune cell infiltration into the CNS by regional neural inputs explained by the gate theory.

The central nervous system (CNS) is an immune-privileged environment protected by the blood-brain barrier (BBB), which consists of specific endothelial cells that are brought together by tight junctions and tight liner sheets formed by pericytes and astrocytic end-feet. Despite the BBB, various immune and tumor cells can infiltrate the CNS parenchyma, as seen in several autoimmune diseases like multiple sclerosis (MS), cancer metastasis, and virus infections. Aside from a mechanical disruption of the BBB like trauma, how and where these cells enter and accumulate in the CNS from the blood is a matter of debate. Recently, using experimental autoimmune encephalomyelitis (EAE), an animal model of MS, we found a "gateway" at the fifth lumber cord where pathogenic autoreactive CD4+ T cells can cross the BBB. Interestingly, this gateway is regulated by regional neural stimulations that can be mechanistically explained by the gate theory. In this review, we also discuss this theory and its potential for treating human diseases.

Ecto-nucleoside triphosphate diphosphohydrolase 7 controls Th17 cell responses through regulation of luminal ATP in the small intestine.

Extracellular ATP is released from live cells in controlled conditions, as well as dying cells in inflammatory conditions, and, thereby, regulates T cell responses, including Th17 cell induction. The level of extracellular ATP is closely regulated by ATP hydrolyzing enzymes, such as ecto-nucleoside triphosphate diphosphohydrolases (ENTPDases). ENTPDase1/CD39, which is expressed in immune cells, was shown to regulate immune responses by downregulating the ATP level. In this study, we analyzed the immunomodulatory function of ENTPDase7, which is preferentially expressed in epithelial cells in the small intestine. The targeted deletion of Entpd7 encoding ENTPDase7 in mice resulted in increased ATP levels in the small intestinal lumen. The number of Th17 cells was selectively increased in the small intestinal lamina propria in Entpd7(-/-) mice. Th17 cells were decreased by oral administration of antibiotics or the ATP antagonist in Entpd7(-/-) mice, indicating that commensal microbiota-dependent ATP release mediates the enhanced Th17 cell development in the small intestinal lamina propria of Entpd7(-/-) mice. In accordance with the increased number of small intestinal Th17 cells, Entpd7(-/-) mice were resistant to oral infection with Citrobacter rodentium. Entpd7(-/-) mice suffered from severe experimental autoimmune encephalomyelitis, which was associated with increased numbers of CD4(+) T cells producing both IL-17 and IFN-γ. Taken together, these findings demonstrate that ENTPDase7 controls the luminal ATP level and, thereby, regulates Th17 cell development in the small intestine.

Regional neural activation defines a gateway for autoreactive T cells to cross the blood-brain barrier.

Although it is believed that neural activation can affect immune responses, very little is known about the neuroimmune interactions involved, especially the regulators of immune traffic across the blood-brain barrier which occurs in neuroimmune diseases such as multiple sclerosis (MS). Using a mouse model of MS, experimental autoimmune encephalomyelitis, we show that autoreactive T cells access the central nervous system via the fifth lumbar spinal cord. This location is defined by IL-6 amplifier-dependent upregulation of the chemokine CCL20 in associated dorsal blood vessels, which in turn depends on gravity-induced activation of sensory neurons by the soleus muscle in the leg. Impairing soleus muscle contraction by tail suspension is sufficient to reduce localized chemokine expression and block entry of pathogenic T cells at the fifth lumbar cord, suggesting that regional neuroimmune interactions may offer therapeutic targets for a variety of neurological diseases.

Local microbleeding facilitates IL-6- and IL-17-dependent arthritis in the absence of tissue antigen recognition by activated T cells.

Cognate antigen recognition by CD4(+) T cells is thought to contribute to the tissue specificity of various autoimmune diseases, particularly those associated with class II MHC alleles. However, we show that localized class II MHC-dependent arthritis in F759 mice depends on local events that result in the accumulation of activated CD4(+) T cells in the absence of cognate antigen recognition. In this model, transfer of in vitro polarized Th17 cells combined with the induction of experimental microbleeding resulted in CCL20 production, the accumulation of T cells in the joints, and local production of IL-6. Disease induction required IL-17A production by transferred T cells, IL-6 and CCL20 expression, and STAT3 signaling in type I collagen-expressing cells. Our data suggest a model in which the development of autoimmune disease in F759 mice depends on four events: CD4(+) T cell activation regardless of antigen specificity, local events that induce T cell accumulation, enhanced sensitivity to T cell-derived cytokines in the tissue, and activation of IL-6 signaling in the tissue. This model provides a possible explanation for why tissue-specific antigens recognized by activated CD4(+) T cells have not been identified in many autoimmune diseases, especially those associated with class II MHC molecules.

IL-6 positively regulates Foxp3+CD8+ T cells in vivo.

Although recent studies have identified regulatory roles for Foxp3(+)CD8(+) T cells, the mechanisms that induce their development and underlie their functions in vivo have not been elucidated. Here, we show that IL-6 positively regulates the Foxp3(+)CD8(+) T-cell development and function. The Foxp3(+)CD8(+) T cells that differentiated in vitro in the presence of IL-6 suppressed autoimmune colitis and arthritis in vivo. Moreover, Foxp3(+)CD8(+) T cells that developed in vivo in the presence of enhanced IL-6 signaling suppressed the development of a spontaneous T(h)17 cell-mediated autoimmune arthritis. Thus, we concluded that Foxp3(+)CD8(+) T cells develop in response to IL-6 and regulate chronic inflammation in T(h)17 cell-mediated F759 autoimmune arthritis. These results suggested that Foxp3(+)CD8(+) T cells may develop in response to IL-6 under certain inflammatory conditions in vivo and may regulate some other chronic inflammation diseases.