The ups and downs of STAT3 function: too much, too little and human immune dysregulation

Targeting the STAT3/IL-36G signaling pathway can be a promising approach to treat rosacea

BACKGROUND

Rosacea is an inflammatory skin disorder characterized by the release of inflammatory mediators from keratinocytes, which are thought to play a crucial role in its pathogenesis. Despite an incidence of approximately 5.5%, rosacea is associated with a poor quality of life. However, as the pathogenesis of rosacea remains enigmatic, treatment options are limited.

OBJECTIVES

To investigate the pathogenesis of rosacea and explore new therapeutic strategies.

METHODS

Transcriptome data from rosacea patients combined with immunohistochemical staining were used to investigate the activation of STAT3 in rosacea. The role of STAT3 activation in rosacea was subsequently explored by inhibiting STAT3 activation both in vivo and in vitro. The key molecules downstream of STAT3 activation were identified through data analysis and experiments. Dual-luciferase assay and ChIP-qPCR analysis were used to validate the direct binding of STAT3 to the IL-36G promoter. DARTS, in combination with experimental screening, was employed to identify effective drugs targeting STAT3 for rosacea treatment.

RESULTS

STAT3 signaling was hyperactivated in rosacea and served as a promoter of the keratinocyte-driven inflammatory response. Mechanistically, activated STAT3 directly bind to the IL-36G promoter region to amplify downstream inflammatory signals by promoting IL-36G transcription, and treatment with a neutralizing antibody (α-IL36γ) could mitigate rosacea-like inflammation. Notably, a natural plant extract (pogostone), which can interact with STAT3 directly to inhibit its activation and affect the STAT3/IL36G signaling pathway, was screened as a promising topical medication for rosacea treatment.

CONCLUSIONS

Our study revealed a pivotal role for STAT3/IL36G signaling in the development of rosacea, suggesting that targeting this pathway might be a potential strategy for rosacea treatment.

STAT3 Signaling Pathway in Health and Disease

Signal transducer and activator of transcription 3 (STAT3) is a critical transcription factor involved in multiple physiological and pathological processes. While STAT3 plays an essential role in homeostasis, its persistent activation has been implicated in the pathogenesis of various diseases, particularly cancer, bone-related diseases, autoimmune disorders, inflammatory diseases, cardiovascular diseases, and neurodegenerative conditions. The interleukin-6/Janus kinase (JAK)/STAT3 signaling axis is central to STAT3 activation, influencing tumor microenvironment remodeling, angiogenesis, immune evasion, and therapy resistance. Despite extensive research, the precise mechanisms underlying dysregulated STAT3 signaling in disease progression remain incompletely understood, and no United States Food and Drug Administration (USFDA)-approved direct STAT3 inhibitors currently exist. This review provides a comprehensive evaluation of STAT3's role in health and disease, emphasizing its involvement in cancer stem cell maintenance, metastasis, inflammation, and drug resistance. We systematically discuss therapeutic strategies, including JAK inhibitors (tofacitinib, ruxolitinib), Src Homology 2 domain inhibitors (S3I-201, STATTIC), antisense oligonucleotides (AZD9150), and nanomedicine-based drug delivery systems, which enhance specificity and bioavailability while reducing toxicity. By integrating molecular mechanisms, disease pathology, and emerging therapeutic interventions, this review fills a critical knowledge gap in STAT3-targeted therapy. Our insights into STAT3 signaling crosstalk, epigenetic regulation, and resistance mechanisms offer a foundation for developing next-generation STAT3 inhibitors with greater clinical efficacy and translational potential.

STAT Signature Dish: Serving Immunity with a Side of Dietary Control

Immunity is a fundamental aspect of animal biology, defined as the host's ability to detect and defend against harmful pathogens and toxic substances to preserve homeostasis. However, immune defenses are metabolically demanding, requiring the efficient allocation of limited resources to balance immune function with other physiological and developmental needs. To achieve this balance, organisms have evolved sophisticated signaling networks that enable precise, context-specific responses to internal and external cues. These networks are essential for survival and adaptation in multicellular systems. Central to this regulatory architecture is the STAT (signal transducer and activator of Transcription) family, a group of versatile signaling molecules that govern a wide array of biological processes across eukaryotes. STAT signaling demonstrates remarkable plasticity, from orchestrating host defense mechanisms to regulating dietary metabolism. Despite its critical role, the cell-specific and context-dependent nuances of STAT signaling remain incompletely understood, highlighting a significant gap in our understanding. This review delves into emerging perspectives on immunity, presenting dynamic frameworks to explore the complexity and adaptability of STAT signaling and the underlying logic driving cellular decision-making. It emphasizes how STAT pathways integrate diverse physiological processes, from immune responses to dietary regulation, ultimately supporting organismal balance and homeostasis.

STAT3 orchestrates immune dynamics in hepatocellular carcinoma: A pivotal nexus in tumor progression

Hepatocellular carcinoma (HCC) presents a formidable challenge in oncology, attributed to its association with chronic liver diseases and global prevalence. The immune microenvironment profoundly influences HCC progression, balancing immune suppression and antitumor responses. The Signal Transducer and Activator of Transcription 3 (STAT3) is central to this equilibrium, orchestrating immune dynamics and intertwining tumor progression with immune evasion mechanisms. Dysregulated STAT3 signaling, activated by various stimuli, including cytokines and growth factors, promotes an immunosuppressive milieu within HCC tumors, fostering tumor survival and proliferation while hindering immune surveillance. Non-coding RNAs and other molecules regulate this process, modulating STAT3 activity and influencing immune cell function. Moreover, therapeutic interventions targeting the STAT3 pathway, alongside advancements in radiotherapy, cancer vaccines, and diabetes-related drugs, offer promising strategies in HCC management. Integrating natural compounds with immunotherapy emerges as a novel approach, leveraging their ability to enhance antitumor immunity and counter immune evasion strategies. Understanding the multifaceted role of STAT3 and its interactions within the immune landscape of HCC is paramount for devising effective therapeutic interventions and improving patient outcomes.

Inhibition of DYRK1B BY C81 impedes inflammatory processes in leukocytes by reducing STAT3 activity

Chronic inflammatory diseases are a significant global burden and are associated with dysregulated resolution of inflammation. Therefore, promoting the process of resolution is a promising therapeutic approach. This study presents the potent anti-inflammatory and pro-resolving effects of a natural product-derived compound called C81. Administration of C81 in a therapeutic window resolved inflammation in the murine imiquimod-induced psoriasis model, and reduced microglial infiltration in a laser-induced choroidal neovascularisation model. Investigations into the underlying mechanisms of C81 identified the DYRK1B/STAT3 axis as a new regulator of inflammatory processes in leukocytes. The inhibition of DYRK1B by C81 resulted in attenuated STAT3 phosphorylation. The depletion of STAT3-regulated gene expression led to the inhibition of leukocyte adhesion and migration due to reduced integrin activation, and in addition to the inhibition of the release of pro-inflammatory mediators such as cytokines and eicosanoids. Importantly, the pro-resolving effects of C81 included the cell type-specific induction of apoptosis in neutrophils and a subsequent increase in efferocytosis. In conclusion, we report the DYRK1B/STAT3 axis as a novel and promising therapeutic target for activating the resolution of inflammation.

Functional validation of a novel STAT3 'variant of unknown significance' identifies a new case of STAT3 GOF syndrome and reveals broad immune cell defects

INTRODUCTION

Signal transducer and activator of transcription 3 (STAT3) orchestrates crucial immune responses through its pleiotropic functions as a transcription factor. Patients with germline monoallelic dominant negative or hypermorphic STAT3 variants, who present with immunodeficiency and/or immune dysregulation, have revealed the importance of balanced STAT3 signaling in lymphocyte differentiation and function, and immune homeostasis. Here, we report a novel missense variant of unknown significance in the DNA-binding domain of STAT3 in a patient who experienced hypogammaglobulinemia, lymphadenopathy, hepatosplenomegaly, immune thrombocytopenia, eczema, and enteropathy over a 35-year period.

METHODS

In vitro demonstration of prolonged STAT3 activation due to delayed dephosphorylation, and enhanced transcriptional activity, confirmed this to be a novel pathogenic STAT3 gain-of-function variant. Peripheral blood lymphocytes from this patient, and patients with confirmed STAT3 Gain-of-function Syndrome, were collected to investigate mechanisms of disease pathogenesis.

RESULTS

B cell dysregulation was evidenced by a loss of class-switched memory B cells and a significantly expanded CD19hiCD21lo B cell population, likely influenced by a skewed CXCR3+ TFH population. Interestingly, unlike STAT3 dominant negative variants, cytokine secretion by activated peripheral blood STAT3 GOF CD4+ T cells and frequencies of Treg cells were intact, suggesting CD4+ T cell dysregulation likely occurs at sites of disease rather than the periphery.

CONCLUSION

This study provides an in-depth case study in confirming a STAT3 gain-of-function variant and identifies lymphocyte dysregulation in the peripheral blood of patients with STAT3 gain-of-function syndrome. Identifying cellular biomarkers of disease provides a flow cytometric-based screen to guide validation of additional novel STAT3 gain-of-function variants as well as provide insights into putative mechanisms of disease pathogenesis.

Defining Mechanistic Links Between the Non-Coding Variant rs17673553 in CLEC16A and Lupus Susceptibility

Systemic lupus erythematosus (SLE) is a complex autoimmune disorder characterized by widespread inflammation and autoantibody production. Its development and progression involve genetic, epigenetic, and environmental factors. Although genome-wide association studies (GWAS) have repeatedly identified a susceptibility signal at 16p13, its fine-scale source and its functional and mechanistic role in SLE remain unclear. We used bioinformatics to prioritize likely functional variants and validated the top candidate through various experimental techniques, including clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing in B cells. To assess the functional impact of the proposed causal variant in C-type lectin domain family 16, member A (CLEC16A), we compared autophagy levels between wild-type (WT) and knock-out (KO) cells. Systematic bioinformatics analysis identified the highly conserved non-coding intronic variant rs17673553, with the risk allele apparently affecting enhancer function and regulating several target genes, including CLEC16A itself. Luciferase reporter assays followed by chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP-qPCR) validated this enhancer activity, demonstrating that the risk allele increases the binding of enhancer histone marks (H3K27ac and H3K4me1), the CTCF-binding factor, and key immune transcription factors (GATA3 and STAT3). Knock-down of GATA3 and STAT3 via siRNA led to a significant decrease in CLEC16A expression. These regulatory effects on the target gene were further confirmed using CRISPR-based genome editing and CRISPR-dCas9-based epigenetic activation/silencing. Functionally, WT cells exhibited higher levels of starvation-induced autophagy compared to KO cells, highlighting the role of CLEC16A and the rs17673553 locus in autophagy regulation. These findings suggest that the rs17673553 locus-particularly the risk allele-drives significant allele-specific chromatin modifications and binding of multiple transcription factors, thereby mechanistically regulating the expression of target autophagy-associated genes, including CLEC16A itself. This mechanism could potentially explain the association between rs17673553 and SLE, and could underlie the signal at 16p13.

Crosstalk between circular RNAs and the STAT3 signaling pathway in human cancer

Circular RNAs (circRNAs) are endogenous covalently closed single-stranded RNAs produced by reverse splicing of pre-mRNA. Emerging evidence suggests that circRNAs contribute to cancer progression by modulating the oncogenic STAT3 signaling pathway, which plays key roles in human malignancies. STAT3 signaling-related circRNAs expression appears to be extensively dysregulated in diverse cancer types, where they function either as tumor suppressors or oncogenes. However, the biological effects of STAT3 signaling-related circRNAs and their associations with cancer have not been systematically studied before. Given this, shedding light on the interaction between circRNAs and STAT3 signaling pathway in human malignancies may provide several novel insights into cancer therapy. In this review, we provide a comprehensive introduction to the molecular mechanisms by which circRNAs regulate STAT3 signaling in cancer progression, and the crosstalk between STAT3 signaling-related circRNAs and other signaling pathways. We also further discuss the role of the circRNA/STAT3 axis in cancer chemotherapy sensitivity.

A modern view of LGL leukemia

ABSTRACT

Large granular lymphocytic leukemia (LGLL) is a rare lymphoproliferative chronic disorder characterized by expansion of either T or natural killer (NK) cytotoxic cells. In contrast to Epstein-Barr virus-induced aggressive NK-LGLL, chronic T-LGLL and NK-LGLL are indolent diseases affecting older patients with a median age of 66.5 years. LGLL is frequently associated with autoimmune disorders, most frequently rheumatoid arthritis. An auto-/alloantigen is tentatively implicated in disease initiation. Large granular lymphocyte expansion is then triggered by proinflammatory cytokines such as interleukin-15, macrophage inflammatory protein 1 (MIP-1), and RANTES (regulated upon activation, normal T cell expressed, and secreted). This proinflammatory environment contributes to deregulation of proliferative and apoptotic pathways. After the initial description of the JAK-STAT pathway signaling activation in the majority of patients, recurrent STAT3 gain-of-function mutations have been reported. The JAK-STAT pathway plays a key role in LGL pathogenesis by promoting survival, proliferation, and cytotoxicity. Several recent advances have been made toward understanding the molecular landscapes of T- and NK-LGLL, identifying multiple recurrent mutations affecting the epigenome, such as TET2 or KMT2D, and cross talk with the immune microenvironment, such as CCL22. Despite an indolent course, published series suggest that the majority of patients eventually need treatment. However, it is noteworthy that many patients may have a long-term observation period without ever requiring therapy. Treatments rely upon immunosuppressive drugs, namely cyclophosphamide, methotrexate, and cyclosporine. Recent advances have led to the development of targeted approaches, including JAK-STAT inhibitors, cytokine targeting, and hypomethylating agents, opening new developments in a still-incurable disease.

7D, a small molecule inhibits dengue infection by increasing interferons and neutralizing-antibodies via CXCL4:CXCR3:p38:IRF3 and Sirt1:STAT3 axes respectively

There are a limited number of effective vaccines against dengue virus (DENV) and significant efforts are being made to develop potent anti-virals. Previously, we described that platelet-chemokine CXCL4 negatively regulates interferon (IFN)-α/β synthesis and promotes DENV2 replication. An antagonist to CXCR3 (CXCL4 receptor) reversed it and inhibited viral replication. In a concurrent search, we identified CXCR3-antagonist from our compound library, namely 7D, which inhibited all serotypes of DENV in vitro. With a half-life of ~2.85 h in plasma and no significant toxicity, 7D supplementation (8 mg/kg-body-weight) to DENV2-infected IFNα/β/γR-/-AG129 or wild-type C57BL6 mice increased synthesis of IFN-α/β and IFN-λ, and rescued disease symptoms like thrombocytopenia, leukopenia and vascular-leakage, with improved survival. 7D, having the property to inhibit Sirt-1 deacetylase, promoted acetylation and phosphorylation of STAT3, which in-turn increased plasmablast proliferation, germinal-center maturation and synthesis of neutralizing-antibodies against DENV2 in mice. A STAT3-inhibitor successfully inhibited these effects of 7D. Together, these observations identify compound 7D as a stimulator of IFN-α/β/λ synthesis via CXCL4:CXCR3:p38:IRF3 signaling, and a booster for neutralizing-antibody generation by promoting STAT3-acetylation in plasmablasts, capable of protecting dengue infection.

Molecular Mechanism Analysis of Intensive Light-Induced Retinal Damages

Introduction: The retina is a light-sensitive tissue, and intensive light exposure leads to light-induced retinal damage. It is pointed out that photoreceptor damage is responsible for the decrease in retina function. The aim of this study was to detect the main genes and biological terms which are involved in retinal response to intensive light exposure. Methods: The effect of intensive light on the mouse retina function was searched in the Gene Expression Omnibus (GEO) database. The data of GSE22818 were assessed by the GEO2R program. The significant differentially expressed genes (DEGs) were determined and evaluated via directed protein-protein interaction (PPI) network analysis. The critical significant DEGs were enriched via gene ontology analysis to find the related biological processes, molecular function, and biochemical pathways. Results: Data analysis indicates that the high intensity of light induces gene expression alteration in the retina. 105 significant DEGs were identified as the main responsive genes to light damage in the retina. STAT3, JUN, IL6ST, SOCS3, ATF3, JUNB, FOSL1, CCL2, ICAM1, FGF2, AGT, MYC, LIF, CISH, and EGR1 were introduced as the critical affected genes. STAT3, JUN, IL6ST, SOCS3, and ATF3 and "Positive regulation of the receptor signaling pathway via JAK-STAT" were highlighted as the key elements of molecular events. Conclusion: It can be concluded that regulation of the key DEGs and the dependent biological terms can effectively provide tools to prevent the development of light-induced retinal damage.

Investigation into the potential mechanism and therapeutic targets of Cangzhu Erchen decoction for the treatment of chronic obstructive pulmonary disease based on bioinformatics and network pharmacology

This study aimed to elucidate the molecular mechanisms underlying the therapeutic effects of Cangzhu Erchen decoction (CZECD) in the treatment of chronic obstructive pulmonary disease (COPD) using microarray analysis, network pharmacology, and molecular docking. The active components and candidate targets of CZECD were obtained using the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform and Swiss Target Prediction. COPD-related targets were collected from 5 databases. Access to drug-disease interface targets in the Venny platform. The Cytoscape program and the STRING database were used for protein-protein interaction analysis and subsequent core target screening. The DAVID database was used for Gene Ontology (GO) functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes enrichment pathway analysis, while AutoDockTools was used for molecular docking to confirm binding affinity between drugs and key targets. A total of 140 compounds from CZECD and 5100 COPD-related targets were identified. SRC, PIK3CA, STAT3, PIK3R1, AKT1, HSP90AA1, PIK3CB, GRB2, PIK3CD, and MAPK1 were identified as the major targets of CZECD in its anti-COPD activity. GO and Kyoto Encyclopedia of Genes and Genomes enrichment studies revealed that CZECD mainly affects biological processes such as protein phosphorylation, xenobiotic response, positive regulation of the MAPK cascade, and inflammatory responses. Cancer, PI3K/AKT, and MAPK were the key pathways mediating these effects. The positive association between the core targets and the compounds was further validated by molecular docking. CZECD exerts its therapeutic role in COPD mainly through multiple compounds, targets, and pathways.

STAT3 gain of function: Too much of a good thing in the skin!

Germline activating mutations in STAT3 cause a multi-systemic autoimmune and autoinflammatory condition. By studying a mouse model, Toth et al. (https://doi.org/10.1084/jem.20232091) propose a role for dysregulated IL-22 production by Th17 cells in causing some aspects of immune-mediated skin inflammation in human STAT3 GOF syndrome.

Stat3 Regulates Developmental Hematopoiesis and Impacts Myeloid Cell Function via Canonical and Non-Canonical Modalities

INTRODUCTION

Signal transducer and activator of transcription (STAT) 3 is extensively involved in the development, homeostasis, and function of immune cells, with STAT3 disruption associated with human immune-related disorders. The roles ascribed to STAT3 have been assumed to be due to its canonical mode of action as an inducible transcription factor downstream of multiple cytokines, although alternative noncanonical functional modalities have also been identified. The relative involvement of each mode was further explored in relevant zebrafish models.

METHODS

Genome editing with CRISPR/Cas9 was used to generate mutants of the conserved zebrafish Stat3 protein: a loss of function knockout (KO) mutant and a mutant lacking C-terminal sequences including the transactivation domain (ΔTAD). Lines harboring these mutations were analyzed with respect to blood and immune cell development and function in comparison to wild-type zebrafish.

RESULTS

The Stat3 KO mutant showed perturbation of hematopoietic lineages throughout primitive and early definitive hematopoiesis. Neutrophil numbers did not increase in response to lipopolysaccharide (LPS) or granulocyte colony-stimulating factor (G-CSF) and their migration was significantly diminished, the latter correlating with abrogation of the Cxcl8b/Cxcr2 pathway, with macrophage responses perturbed. Intriguingly, many of these phenotypes were not shared by the Stat3 ΔTAD mutant. Indeed, only neutrophil and macrophage development were disrupted in these mutants with responsiveness to LPS and G-CSF maintained, and neutrophil migration actually increased.

CONCLUSION

This study has identified roles for zebrafish Stat3 within hematopoietic stem cells impacting multiple lineages throughout primitive and early definitive hematopoiesis, myeloid cell responses to G-CSF and LPS and neutrophil migration. Many of these roles showed conservation, but notably several involved noncanonical modalities, providing additional insights for relevant diseases.

The complex relationship between large granular lymphocyte leukemia and rheumatic disease

INTRODUCTION

Large granular lymphocytic (LGL) leukemia is a rare lymphoproliferative disorder characterized by an expansion of clonal T or NK lymphocytes. Neutropenia-related infections represent the main clinical manifestation. Even if the disease follows an indolent course, most patients will ultimately need treatment in their lifetime. Interestingly, LGL leukemia is characterized by a high frequency of autoimmune disorders with rheumatoid arthritis being the most frequent.

AREAS COVERED

This review covers the pathophysiology, clinic-biological features and the advances made in the treatment of LGL leukemia. A special focus will be made on the similarities in the pathophysiology of LGL leukemia and the frequently associated rheumatic disorders.

EXPERT OPINION

Recent advances in the phenotypic and molecular characterization of LGL clones have uncovered the key role of JAK-STAT signaling in the pathophysiology linking leukemic cells expansion and autoimmunity. The description of the molecular landscape of T- and NK-LGL leukemia and the improved understanding of the associated rheumatic disorders open the way to the development of new targeted therapies effective on both conditions.

Intractable diarrhea in an infant-autoimmune enteropathy: A case report

Autoimmune enteropathy is a rare cause of chronic intractable diarrhea and is present in <1 in 100,000 infants. We report the case of a 9-month-old boy who presented with intractable diarrhea and vomiting. Genetic panel testing revealed a STAT3 heterozygous mutation in exon 6, suggesting infantile-onset multisystem autoimmune disease-1. The patient was initially treated with steroids and sulfasalazine. However, on tapering steroids, he had another episode of diarrhea and was subsequently put on baricitinib to which he responded.

Signal Transducer and Activator of Transcription Proteins at the Nexus of Immunodeficiency, Autoimmunity and Cancer

The signal transducer and activator of transcription (STAT) family of proteins has been demonstrated to perform pivotal roles downstream of a myriad of cytokines, particularly those that control immune cell production and function. This is highlighted by both gain-of-function (GOF) and loss-of-function (LOF) mutations being implicated in various diseases impacting cells of the immune system. These mutations are typically inherited, although somatic GOF mutations are commonly observed in certain immune cell malignancies. This review details the growing appreciation of STAT proteins as a key node linking immunodeficiency, autoimmunity and cancer.

Transcription factor genetics and biology in predisposition to bone marrow failure and hematological malignancy

Transcription factors (TFs) play a critical role as key mediators of a multitude of developmental pathways, with highly regulated and tightly organized networks crucial for determining both the timing and pattern of tissue development. TFs can act as master regulators of both primitive and definitive hematopoiesis, tightly controlling the behavior of hematopoietic stem and progenitor cells (HSPCs). These networks control the functional regulation of HSPCs including self-renewal, proliferation, and differentiation dynamics, which are essential to normal hematopoiesis. Defining the key players and dynamics of these hematopoietic transcriptional networks is essential to understanding both normal hematopoiesis and how genetic aberrations in TFs and their networks can predispose to hematopoietic disease including bone marrow failure (BMF) and hematological malignancy (HM). Despite their multifaceted and complex involvement in hematological development, advances in genetic screening along with elegant multi-omics and model system studies are shedding light on how hematopoietic TFs interact and network to achieve normal cell fates and their role in disease etiology. This review focuses on TFs which predispose to BMF and HM, identifies potential novel candidate predisposing TF genes, and examines putative biological mechanisms leading to these phenotypes. A better understanding of the genetics and molecular biology of hematopoietic TFs, as well as identifying novel genes and genetic variants predisposing to BMF and HM, will accelerate the development of preventative strategies, improve clinical management and counseling, and help define targeted treatments for these diseases.