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Molecular Immunology

Publications

2026

  • Janus kinase 2 activation loop as a regulator of catalysis and trans-activation

    Protein kinases regulate essential cellular processes such as apoptosis, proliferation, and growth. Precise regulation of kinase activity is critical for proper signal transduction and is often mediated by activation-loop phosphorylation. Janus kinases (JAKs) employ a unique regulatory mechanism: they remain autoinhibited by their pseudokinase domains until cytokine stimulation triggers dimerization and trans-phosphorylation of two activation-loop tyrosines. Despite its relevance for JAK...

  • A rare JAK2 mutation associated with adult-onset Still's disease and exacerbated vaccine-induced innate immune response

    CONCLUSION: The JAK2R947Q germline variant identified in a patient with AOSD displays enhanced activation upon cytokine stimulation. Our results also suggest that the vaccine-induced innate immune transcriptome response could be used as benchmark in the functional assessment of genetic variants in key genetic pathways controlling immune response.

  • Heritability and Transcriptional Impact of JAK3, STAT5A and STAT6 Variants in a Tyrolean Family

    The Janus Kinase (JAK) and Signal Transducers and Activators of Transcription (STAT) pathways regulate a range of biological processes, including immune response and hematopoiesis. While a major research focus has been on somatic human mutations in disease, less is known about the heritability of germline variants and their physiological impact. This study addresses an important issue in population genetics: the context-dependent effects and incomplete penetrance of rare genetic variants in...

  • Pharmacological targeting of the JAK-STAT pathway: new concepts and emerging indications

    Type I/II cytokine receptors mediate cytokine-specific biological responses by employing a defined combination of four Janus kinases (JAKs) and seven signal transducers and activators of transcription (STATs) for cellular signal transduction. Deregulation of the JAK-STAT pathway leads to various diseases, with JAK and STAT proteins representing attractive therapeutic targets. Fifteen JAK inhibitors are approved for several immunological and haematological diseases, offering significant benefits...

2025

  • Investigation of the transcriptional impact of rare germline JAK/STAT variants found in a Tyrolean alpine community

    The impact of most missense variants in immune regulatory genes on steady-state immune transcriptome expression in healthy individuals in real-world conditions remains largely unexplored. Here, we investigated the transcriptional impact of 21 germline variants in JAK, TYK2, and STAT family genes identified within a healthy Austrian alpine cohort. Of the 98 participants 35 carried only one variant and 32 carried two or more variants. Allele frequencies (AF) of these germline mutations, based on...

  • JAK2/JAK2V617F heterodimers activate STAT1 and AhR to promote thrombocytosis

    In this issue of JEM, Zhou et al. (https://doi.org/10.1084/jem.20250153) report that hematopoietic progenitors heterozygous for the JAK2V617F mutation preferentially activate STAT1, promoting platelet production and thrombocythemia, whereas homozygous progenitors activate STAT5, leading to erythrocytosis and polycythemia.

  • Clonal hematopoiesis is associated with distinct rheumatoid arthritis phenotypes

    Clonal hematopoiesis (CH) becomes more prevalent with aging and may influence inflammatory diseases by altering immune function. While CH of indeterminate potential (CHIP) promotes inflammation in nonmalignant conditions, its relationship with rheumatoid arthritis (RA) remains unknown. We analyzed CHIP mutations in RA using two population-level cohorts and patients with newly diagnosed RA. CHIP was associated with prevalent RA in 10,089 FINRISK study participants with whole-exome sequencing (OR,...

  • Molecular basis of JAK kinase regulation guiding therapeutic approaches: Evaluating the JAK3 pseudokinase domain as a drug target

    Janus kinases (JAK1-3, TYK2) are critical mediators of cytokine signaling and their role in hematological and inflammatory and autoimmune diseases has sparked widespread interest in their therapeutic targeting. JAKs have unique tandem kinase structure consisting of an active tyrosine kinase domain adjacent to a pseudokinase domain that is a hotspot for pathogenic mutations. The development of JAK inhibitors has focused on the active kinase domain and the developed drugs have demonstrated good...

2024

  • Molecular basis of JAK kinase regulation guiding therapeutic approaches: Evaluating the JAK3 pseudokinase domain as a drug target

    Janus kinases (JAK1-3, TYK2) are critical mediators of cytokine signaling and their role in hematological and inflammatory and autoimmune diseases has sparked widespread interest in their therapeutic targeting. JAKs have unique tandem kinase structure consisting of an active tyrosine kinase domain adjacent to a pseudokinase domain that is a hotspot for pathogenic mutations. The development of JAK inhibitors has focused on the active kinase domain and the developed drugs have demonstrated good...

  • Author Correction: AI is a viable alternative to high throughput screening: a 318-target study

    No abstract

  • JAK inhibitor selectivity: new opportunities, better drugs?

    Cytokines function as communication tools of the immune system, serving critical functions in many biological responses and shaping the immune response. When cytokine production or their biological activity goes awry, the homeostatic balance of the immune response is altered, leading to the development of several pathologies such as autoimmune and inflammatory disorders. Cytokines bind to specific receptors on cells, triggering the activation of intracellular enzymes known as Janus kinases...

  • Functional and Structural Characterization of Clinical-Stage Janus Kinase 2 Inhibitors Identifies Determinants for Drug Selectivity

    Janus kinase 2 (JAK2) plays a critical role in orchestrating hematopoiesis, and its deregulation leads to various blood disorders, most importantly myeloproliferative neoplasms (MPNs). Ruxolitinib, fedratinib, momelotinib, and pacritinib are FDA-/EMA-approved JAK inhibitors effective in relieving symptoms in MPN patients but show variable clinical profiles due to poor JAK selectivity. The development of next-generation JAK2 inhibitors is hampered by the lack of comparative functional analysis...

  • AI is a viable alternative to high throughput screening: a 318-target study

    High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that...

  • Molecular basis of JAK2 activation in erythropoietin receptor and pathogenic JAK2 signaling

    Janus kinase 2 (JAK2) mediates type I/II cytokine receptor signaling, but JAK2 is also activated by somatic mutations that cause hematological malignancies by mechanisms that are still incompletely understood. Quantitative superresolution microscopy (qSMLM) showed that erythropoietin receptor (EpoR) exists as monomers and dimerizes upon Epo stimulation or through the predominant JAK2 pseudokinase domain mutations (V617F, K539L, and R683S). Crystallographic analysis complemented by kinase...

2023

  • New scaffolds for type II JAK2 inhibitors overcome the acquired G993A resistance mutation

    Recurrent JAK2 alterations are observed in myeloproliferative neoplasms, B-cell acute lymphoblastic leukemia, and other hematologic malignancies. Currently available type I JAK2 inhibitors have limited activity in these diseases. Preclinical data support the improved efficacy of type II JAK2 inhibitors, which lock the kinase in the inactive conformation. By screening small molecule libraries, we identified a lead compound with JAK2 selectivity. We highlight analogs with on-target biochemical and...

  • The RNA-binding protein Snd1/Tudor-SN regulates hypoxia-responsive gene expression

    Snd1 is an evolutionarily conserved RNA-binding protein implicated in several regulatory processes in gene expression including activation of transcription, mRNA splicing, and microRNA decay. Here, we have investigated the outcome of Snd1 gene deletion in the mouse. The knockout mice are viable showing no gross abnormalities apart from decreased fertility, organ and body size, and decreased number of myeloid cells concomitant with decreased expression of granule protein genes. Deletion of Snd1...

  • Development of an enzyme-coupled activity assay for Janus kinase 2 inhibitor screening

    JAK2 transmits signals of several important cytokines, such as growth hormone and erythropoietin. The interest toward the therapeutic targeting of JAK2 was boosted in 2005, when the somatic JAK2 V617F mutation, responsible for the majority of myeloproliferative neoplasms (MPNs) was discovered. JAK2 inhibitors have been approved for MPN therapy and they are effective in alleviating symptoms and improving the quality of life of the patients, but they do not lead to molecular remission. This calls...

  • Differences in JAK Isoform Selectivity Among Different Types of JAK Inhibitors Evaluated for Rheumatic Diseases Through In Vitro Profiling

    CONCLUSION: Inhibition of JAK kinase activity did not directly translate into cellular inhibition of JAK/STAT signaling. Despite differences in JAK selectivity, the cytokine inhibition profiles of currently approved Jakinibs were highly similar, with preference for JAK1-mediated cytokines. Novel types of Jakinibs showed narrow cytokine inhibition profile specific for JAK3- or TYK2-mediated signaling.

  • Identification of Novel Small Molecule Ligands for JAK2 Pseudokinase Domain

    Hyperactive mutation V617F in the JAK2 regulatory pseudokinase domain (JH2) is prevalent in patients with myeloproliferative neoplasms. Here, we identified novel small molecules that target JH2 of JAK2 V617F and characterized binding via biochemical and structural approaches. Screening of 107,600 small molecules resulted in identification of 55 binders to the ATP-binding pocket of recombinant JAK2 JH2 V617F protein at a low hit rate of 0.05%, which indicates unique structural characteristics of...

2022

2021

  • Tofacitinib Suppresses Several JAK-STAT Pathways in Rheumatoid Arthritis <em>In Vivo</em> and Baseline Signaling Profile Associates With Treatment Response

    CONCLUSIONS: Tofacitinib suppresses multiple JAK-STAT pathways in cytokine and cell population specific manner in RA patients in vivo. Besides directly inhibiting JAK activation, tofacitinib downregulates the expression of JAK-STAT pathway components. This may modulate the effects of tofacitinib on JAK-STAT pathway activation in vivo and explain some of the differential findings between the current study and previous in vitro studies. Finally, baseline immunological markers associate with the...

  • <em>IRF2BP2</em> Mutation Is Associated with Increased STAT1 and STAT5 Activation in Two Family Members with Inflammatory Conditions and Lymphopenia

    Interferon regulatory factor 2 binding protein 2 (IRF2BP2) is a transcriptional coregulator that has an important role in the regulation of the immune response. IRF2BP2 has been associated with the Janus kinase (JAK)-signal transducers and activators of transcription (STAT) pathway, but its exact role remains elusive. Here, we identified a novel clinical variant, IRF2BP2 c.625_665del, from two members of a family with inflammatory conditions and investigated the function of IRF2BP2 and...

  • Janus Kinases in Leukemia

    Janus kinases (JAKs) transduce signals from dozens of extracellular cytokines and function as critical regulators of cell growth, differentiation, gene expression, and immune responses. Deregulation of JAK/STAT signaling is a central component in several human diseases including various types of leukemia and other malignancies and autoimmune diseases. Different types of leukemia harbor genomic aberrations in all four JAKs (JAK1, JAK2, JAK3, and TYK2), most of which are activating somatic...

2020

  • JAK2S523L, a novel gain-of-function mutation in a critical autoregulatory residue in JAK2V617F- MPNs

    The SH2-JH2 linker domain of JAK2 has been implicated in the negative regulation of JAK2 activity. In 2 patients with myeloproliferative neoplasms (MPNs), we identified and characterized the novel JAK2 mutation S523L, which occurs in a key residue in the linker region. In 1 case, acquisition of JAK2S523L was associated with thrombocytosis and bone marrow megakaryocytic hyperplasia, and there were no other somatic alterations in this patient. The second patient with JAK2S523Lmutation presented...

2019

  • Characterization of JAK1 Pseudokinase Domain in Cytokine Signaling

    The Janus kinase-signal transducer and activator of transcription protein (JAK-STAT) pathway mediates essential biological functions from immune responses to haematopoiesis. Deregulated JAK-STAT signaling causes myeloproliferative neoplasms, leukaemia, and lymphomas, as well as autoimmune diseases. Thereby JAKs have gained significant relevance as therapeutic targets. However, there is still a clinical need for better JAK inhibitors and novel strategies targeting regions outside the conserved...

  • Janus kinases to jakinibs: from basic insights to clinical practice

    Cytokines are critical mediators of diverse immune and inflammatory diseases. Targeting cytokines and cytokine receptors with biologics has revolutionized the treatment of many of these diseases, but targeting intracellular signalling with Janus kinase (JAK) inhibitors (jakinibs) now represents a major new therapeutic advance. We are still in the first decade since these drugs were approved and there is still much to be learned about the mechanisms of action of these drugs and the practical use...

  • Selective JAKinibs: Prospects in Inflammatory and Autoimmune Diseases

    Cytokines, many of which signal through the JAK-STAT (Janus kinase-Signal Transducers and Activators of Transcription) pathway, play a central role in the pathogenesis of inflammatory and autoimmune diseases. Currently three JAK inhibitors have been approved for clinical use in USA and/or Europe: tofacitinib for rheumatoid arthritis, psoriatic arthritis and ulcerative colitis, baricitinib for rheumatoid arthritis, and ruxolitinib for myeloproliferative neoplasms. The clinical JAK inhibitors...

  • Janus kinase 2 activation mechanisms revealed by analysis of suppressing mutations

    CONCLUSIONS: These results suggest that therapeutic approaches targeting the JH2 ATP binding site and αC could be effective in inhibiting most pathogenic mutations. JH2 ATP site targeting has the potential for reduced side effects by retaining erythropoietin and IFN-γ functions. Simultaneously, however, we identified the JH2 αC interface as a potential target for pathway-selective JAK inhibitors in patients with diseases with unmutated JAK2, thus providing new insights into the development of...

  • The regulation of JAKs in cytokine signaling and its breakdown in disease

    The JAK-STAT signal transduction pathway is responsible for mediating signals of over fifty cytokines, growth factors and hormones. Signaling through the JAK-STAT pathway is regulated on multiple levels, including intramolecular regulation by the JAK pseudokinase domain, and intermolecular regulation by a host of regulatory proteins. The advent of accessible genomic tools have provided a wealth of information on disease-associated mutations in the JAK-STAT pathway and its regulatory components....

2018

  • Hyperactivation of Oncogenic JAK3 Mutants Depend on ATP Binding to the Pseudokinase Domain

    Janus kinase 3 (JAK3) tyrosine kinase has a central role in the control of lymphopoiesis, and mutations in JAK3 can lead to either severe combined immunodeficiency or leukemia and lymphomas. JAK3 associates with the common gamma chain (γc) receptor and functions in a heteromeric signaling pair with JAK1. In IL-2 signaling JAK1 is the effector kinase for STAT5 phosphorylation but the precise molecular regulatory mechanisms of JAK1 and JAK3 and their individual domains are not known. The...

  • Janus kinase 2 activation mechanisms revealed by analysis of suppressing mutations

    CONCLUSIONS: These results suggest that therapeutic approaches targeting the JH2 ATP binding site and αC could be effective in inhibiting most pathogenic mutations. JH2 ATP site targeting has the potential for reduced side effects by retaining erythropoietin and IFN-γ functions. Simultaneously, however, we identified the JH2 αC interface as a potential target for pathway-selective JAK inhibitors in patients with diseases with unmutated JAK2, thus providing new insights into the development of...

  • The regulation of JAKs in cytokine signaling and its breakdown in disease

    The JAK-STAT signal transduction pathway is responsible for mediating signals of over fifty cytokines, growth factors and hormones. Signaling through the JAK-STAT pathway is regulated on multiple levels, including intramolecular regulation by the JAK pseudokinase domain, and intermolecular regulation by a host of regulatory proteins. The advent of accessible genomic tools have provided a wealth of information on disease-associated mutations in the JAK-STAT pathway and its regulatory components....

  • Proprotein convertase enzyme FURIN is upregulated in primary Sjögren's syndrome

    CONCLUSIONS: The proprotein convertase FURIN is significantly upregulated in pSS. Elevated FURIN levels associate with high levels of the Th1 type cytokine IFN-γ and long duration of dry eye symptoms. Patients with high FURIN levels show signs of lower disease activity suggesting that FURIN might have a protective role in pSS.

  • Oncoprotein Tudor-SN is a key determinant providing survival advantage under DNA damaging stress

    Herein, Tudor-SN was identified as a DNA damage response (DDR)-related protein that plays important roles in the early stage of DDR. X-ray or laser irradiation could evoke the accumulation of Tudor-SN to DNA damage sites in a poly(ADP-ribosyl)ation-dependent manner via interaction with PARP-1. Additionally, we illustrated that the SN domain of Tudor-SN mediated the association of these two proteins. The accumulated Tudor-SN further recruited SMARCA5 (ATP-dependent chromatin remodeller) and GCN5...

2017

  • Identification and Characterization of JAK2 Pseudokinase Domain Small Molecule Binders

    Janus kinases (JAKs) regulate hematopoiesis via the cytokine-mediated JAK-STAT signaling pathway. JAKs contain tandem C-terminal pseudokinase (JH2) and tyrosine kinase (JH1) domains. The JAK2 pseudokinase domain adopts a protein kinase fold and, despite its pseudokinase designation, binds ATP with micromolar affinity. Recent evidence shows that displacing ATP from the JAK2 JH2 domain alters the hyperactivation state of the oncogenic JAK2 V617F protein while sparing the wild type JAK2 protein. In...

  • An Activating STAT3 Mutation Causes Neonatal Diabetes through Premature Induction of Pancreatic Differentiation

    Activating germline mutations in STAT3 were recently identified as a cause of neonatal diabetes mellitus associated with beta-cell autoimmunity. We have investigated the effect of an activating mutation, STAT3^(K392R), on pancreatic development using induced pluripotent stem cells (iPSCs) derived from a patient with neonatal diabetes and pancreatic hypoplasia. Early pancreatic endoderm differentiated similarly from STAT3^(K392R) and healthy-control cells, but in later stages, NEUROG3 expression...

2016

  • Cytokine-induced STAT1 activation is increased in patients with primary Sjögren's syndrome

    Limited data are available regarding the intracellular responses to different cytokines in primary Sjögren's syndrome (pSS). We studied the signal transducer and activator of transcription (STAT) activation profile in response to cytokine stimulations in peripheral blood mononuclear cells (PBMCs) from pSS patients by multicolor flow cytometry. The expression of the suppressors of cytokine signaling (SOCS), and interferon (IFN)-γ target genes in PBMCs was studied using quantitative reverse...