Tadamitsu Kishimoto

Barrier tissues such as the intestine are constantly challenged by environmental stressors and must adapt to maintain integrity and prevent excessive inflammation. Although traditionally viewed as a proinflammatory effector of interferon (IFN) signaling, STAT1 is shown here to play a protective role in intestinal epithelial cells (IEC) by promoting resilience to damage and restraining IFN-induced cytotoxicity. We identify phosphorylation of threonine 748 (Thr748) on STAT1 as an evolutionarily selected adaptation—highly conserved between humans and mice—that reciprocally regulates IEC integrity and IFN responsiveness. Mice expressing a phospho-deficient T748A Stat1 mutant exhibit severe colitis-induced tissue damage comparable to Stat1-deficient littermates, underscoring the critical role of Thr748 phosphorylation in mediating Stat1-driven protection during intestinal inflammation. Bone marrow transfer experiments further demonstrate that this protective effect is nonhematopoietic. Integrated genomic and transcriptomic analyses reveal that Thr748 phosphorylation modulates STAT1 DNA binding, directly activates the Itgb4 promoter, and enhances integrin β4 expression in IEC following inflammation. In intestinal organoid models, gain- and loss-of-function experiments demonstrate that Thr748 phosphorylation drives integrin β4 expression and epithelial resilience independently of IFN-induced Tyrosine 701 (Tyr701) phosphorylation. In contrast, IFN stimulation via Tyr701 induces Zbp1—a cytotoxic nucleic acid sensor—while repressing integrin β4, resulting in epithelial injury that is mitigated by Thr748 phosphorylation. Together, these findings reveal a modular architecture of STAT1 signaling in which Thr748 phosphorylation functions as a molecular rheostat that safeguards epithelial integrity while tempering IFN-driven cytotoxic responses.

Threonine phosphorylation promotes inflammatory functions of STAT1 while restricting its interferon (IFN) signaling in innate immune responses. However, it remains unclear whether the restriction of STAT1-mediated IFN signaling conferred by threonine phosphorylation is a ubiquitous mechanism or one that is context-dependent. To address this, we utilized pristane-induced lupus, a prototype IFN-driven systemic autoimmune disease model characterized by the production of high-titer autoantibodies against nucleic acid-associated antigens. Through genetic and biochemical assays, we demonstrate that Thr748 phosphorylation is dispensable for STAT1 functionality in pristane-induced lupus. Genetically engineered mice expressing the phospho-deficient threonine 748-to-alanine (T748A) mutant STAT1 exhibited similar survival rates, high titers of anti-dsDNA IgG, and nephritis compared to their wild-type littermates. In sharp contrast, STAT1 deficiency protected mice against pristane-induced lupus, as evidenced by increased survival, low titers of anti-dsDNA IgG, and less severe nephritis in the STAT1 knockout mice compared to their T748A littermates. Our study suggests a phosphorylation-dependent modularity that governs the spectrum of STAT1 functionality in inflammatory contexts: IFN phospho-tyrosine-dependent and inflammatory phospho-threonine-dependent, with Thr748 phosphorylation driving selective inflammatory activities, particularly those not driven by the canonical JAK pathway. From a broader perspective, our findings provide deeper insights into how distinct phosphorylation events shape the combinatorial logic of signaling cassettes, thereby regulating context-dependent responses.

Castleman disease (CD) is a benign lymphoproliferative disease causing severe systemic inflammation. Interleukin-6 (IL-6) is a major pathogenesis of multicentric CD (MCD), but only 30-60% of patients respond to IL-6 inhibitors. Novel agents for IL-6 inhibitor-refractory cases are needed. Clinical data and samples are being collected on a large scale and the clinical, pathological and pathogenetic aspects are being elucidated. The pathological and clinical classification of CD is outlined. Focusing on idiopathic MCD (iMCD), this review identifies therapeutic targets and summarizes currently recommended drugs and promising therapeutic candidates. The pathogenesis of MCD has been implicated in the activation of the Janus kinase (JAK)-transcriptional signaling activator (STAT)3 pathway and the phosphatidylinositol 3-kinase (PI3K)/Akt/mechanical target of rapamycin (mTOR) signaling pathway. iMCD-TAFRO (thrombocytopenia, anasarca, fever/elevated CRP, reticulin myelofibrosis/renal dysfunction, organ enlargement) is resistant to IL-6 inhibitors, and cyclosporine and mTOR inhibitors are sometimes effective. JAK inhibitors and mTOR inhibitors may be therapeutic agents for iMCD. Recently, we have shown that peripheral helper T (Tph) cell abnormalities are at the core of iMCD pathogenesis. Therapies targeting chemokine (C-X-C motif) ligand 13 (CXCL13) produced by Tph cells and blocking the Tph-CXCL13-B cell pathway may satisfy unmet need in refractory cases.

Pulmonary arterial hypertension (PAH) is characterized by stenosis and occlusions of small pulmonary arteries, leading to elevated pulmonary arterial pressure and right heart failure. Although accumulating evidence shows the importance of interleukin (IL)-6 in the pathogenesis of PAH, the target cells of IL-6 are poorly understood. Using mice harboring the floxed allele of gp130 , a subunit of the IL-6 receptor, we found substantial Cre recombination in all hematopoietic cell lineages from the primitive hematopoietic stem cell level in SM22α-Cre mice. We also revealed that a CD4 ⁺ cell-specific gp130 deletion ameliorated the phenotype of hypoxia-induced pulmonary hypertension in mice. Disruption of IL-6 signaling via deletion of gp130 in CD4 ⁺ T cells inhibited phosphorylation of signal transducer and activator of transcription 3 (STAT3) and suppressed the hypoxia-induced increase in T helper 17 cells. To further examine the role of IL-6/gp130 signaling in more severe PH models, we developed Il6 knockout (KO) rats using the CRISPR/Cas9 system and showed that IL-6 deficiency could improve the pathophysiology in hypoxia-, monocrotaline-, and Sugen5416/hypoxia (SuHx)-induced rat PH models. Phosphorylation of STAT3 in CD4 ⁺ cells was also observed around the vascular lesions in the lungs of the SuHx rat model, but not in Il6 KO rats. Blockade of IL-6 signaling had an additive effect on conventional PAH therapeutics, such as endothelin receptor antagonist (macitentan) and soluble guanylyl cyclase stimulator (BAY41-2272). These findings suggest that IL-6/gp130 signaling in CD4 ⁺ cells plays a critical role in the pathogenesis of PAH.

The intestinal epithelium not only facilitates the absorption of nutrients, but also plays a pivotal role in guarding intestinal homeostasis and preventing opportunistic gut microbiome invasions. The intestinal epithelial cells have diverse and coordinated regulatory networks that provide intricate lines of defense, in order to maintain the integrity of the intestinal barrier. The epithelial defense comprises the anatomical structure of intestinal epithelial cells as a stout physical barrier and its covering mucus layer containing diverse antimicrobial peptides. In addition, epithelial cells are well-equipped with diverse microbial sensors, which upon activation induce the expression of downstream immunomodulatory networks of cytokines and chemokines. In this review, we summarize the intestinal epithelial cells’ defense mechanisms and their role in maintaining intestinal homeostasis.

AT-rich interactive domain 5a (Arid5a) is a member of the arid family of proteins, which contain a helix-turn-helix domain and an ability to bind to nucleic acids. Current evidence suggests that Arid5a performs dual functions as a transcription factor and an RNA-binding protein in immune, nonimmune, and/ or tumor cells depending on its cellular localization. The contribution of Arid5a to the development of inflammation, autoimmunity, and obesity through its transcriptional and posttranscriptional regulatory functions has broadly been reviewed. Recent studies have indeed revealed an association of Arid5a with cancers, including breast, pancreatic, colorectal, and lung cancers and glioma. Notably, Arid5a affects various aspects of cellular homeostasis, including invasion, metastasis, epithelial-to-mesenchymal transition, immune evasion, adipogenesis and M1-like tumor-associated macrophage (TAM)-to-M2-like TAM transition. This review aims to summarize current knowledge of Arid5a from a cancer perspective and highlights recent advances in Arid5a-related cancer research. This review may improve the understanding of Arid5a-mediated molecular mechanisms and their relevance to cancers.

Ovarian cancer is the leading cause of gynecologic cancer-related deaths and novel therapeutic strategies are required. Programmed cell death 1 and programmed cell death ligand 1 (PD-L1), which are key mediators of host immune tolerance, are associated with ovarian cancer progression. Recent evidence indicates the importance of IFNγ-induced PD-L1 for immune tolerance in ovarian cancer. This study aimed to reveal the therapeutic potential of suppressor of cytokine signaling 1 (SOCS-1), an endogenous inhibitor of the Janus kinase (JAK)–STAT signaling pathway, for the treatment of ovarian cancer. IHC assessment revealed that patients with ovarian cancer with high intratumoral STAT1 activation exhibited poor prognosis compared with patients with low STAT1 activation (P < 0.05). Stimulation of OVISE, OVTOKO, OV2944-HM-1 (HM-1), and CT26 cell lines with IFNγ induced STAT1 phosphorylation and PD-L1 expression. Adenovirus-mediated SOCS-1 gene delivery (AdSOCS-1) in HM-1 and CT26 cells in vitro potently inhibited IFNγ-induced STAT1 phosphorylation and PD-L1 upregulation, similar to the addition of JAK inhibitor I, but failed to inhibit their proliferation. Notably, intratumoral injection of AdSOCS-1, but not AdLacZ, significantly inhibited the tumor growth of HM-1 and CT26 cells subcutaneously transplanted in immunocompetent syngeneic mice. AdSOCS-1 reduced PD-L1 expression on tumors and restored the activation of tumor-infiltrating CD8+ T cells. Moreover, the antitumor effect of AdSOCS-1 was significantly attenuated by PD-L1 Fc-fusion protein administration in vivo, suggesting that the effect of AdSOCS-1 is mainly attributable to enhancement of tumor immunity. This study highlights the potential clinical utility of SOCS-1 as an immune checkpoint inhibitor. Mol Cancer Ther; 17(9); 1941–50. ©2018 AACR.

Ovarian cancer is the leading cause of gynecologic cancer-related deaths and novel therapeutic strategies are required. Programmed cell death 1 and programmed cell death ligand 1 (PD-L1), which are key mediators of host immune tolerance, are associated with ovarian cancer progression. Recent evidence indicates the importance of IFNγ-induced PD-L1 for immune tolerance in ovarian cancer. This study aimed to reveal the therapeutic potential of suppressor of cytokine signaling 1 (SOCS-1), an endogenous inhibitor of the Janus kinase (JAK)–STAT signaling pathway, for the treatment of ovarian cancer. IHC assessment revealed that patients with ovarian cancer with high intratumoral STAT1 activation exhibited poor prognosis compared with patients with low STAT1 activation (P < 0.05). Stimulation of OVISE, OVTOKO, OV2944-HM-1 (HM-1), and CT26 cell lines with IFNγ induced STAT1 phosphorylation and PD-L1 expression. Adenovirus-mediated SOCS-1 gene delivery (AdSOCS-1) in HM-1 and CT26 cells in vitro potently inhibited IFNγ-induced STAT1 phosphorylation and PD-L1 upregulation, similar to the addition of JAK inhibitor I, but failed to inhibit their proliferation. Notably, intratumoral injection of AdSOCS-1, but not AdLacZ, significantly inhibited the tumor growth of HM-1 and CT26 cells subcutaneously transplanted in immunocompetent syngeneic mice. AdSOCS-1 reduced PD-L1 expression on tumors and restored the activation of tumor-infiltrating CD8+ T cells. Moreover, the antitumor effect of AdSOCS-1 was significantly attenuated by PD-L1 Fc-fusion protein administration in vivo, suggesting that the effect of AdSOCS-1 is mainly attributable to enhancement of tumor immunity. This study highlights the potential clinical utility of SOCS-1 as an immune checkpoint inhibitor. Mol Cancer Ther; 17(9); 1941–50. ©2018 AACR.

The diverse biological activity of interleukin-6 (IL-6) contributes to the maintenance of homeostasis. Emergent infection or tissue injury induces rapid production of IL-6 and activates host defense through augmentation of acute-phase proteins and immune responses. However, excessive IL-6 production and uncontrolled IL-6 receptor signaling are critical to pathogenesis. Over the years, therapeutic agents targeting IL-6 signaling, such as tocilizumab, a humanized anti-IL-6 receptor antibody, have shown remarkable efficacy for rheumatoid arthritis, Castleman disease, and juvenile idiopathic arthritis, and their efficacy in other diseases is continually being reported. Emerging evidence has demonstrated the benefit of tocilizumab for several types of acute inflammatory diseases, including cytokine storms induced by chimeric antigen receptor T cell therapy and coronavirus disease 2019 (COVID-19). Here, we refocus attention on the biology of IL-6 and summarize the distinct pathological roles of IL-6 signaling in several acute and chronic inflammatory diseases.