Signal Transducer And Activator Of Transcription 3 Mutations Research Articles

Clinical Relevance of Gain- and Loss-of-Function Germline Mutations in STAT1: A Systematic Review.

Background: Germline mutations in signal transducer and activator of transcription 1 (STAT1), which lead to primary immunodeficiency, are classified as defects in intrinsic and innate immunity. To date, no comprehensive overview comparing GOF with LOF in early-onset immunodeficiency has been compiled.Objective: To collect and systematically review all studies reporting STAT1 GOF and LOF cases, and to describe the clinical, diagnostic, molecular, and therapeutic characteristics of all the conditions.Methods: A systematic review of the PubMed, EMBASE, Web of Science, Scopus, and Cochrane to identify articles published before May 23, 2020. Data pertaining to patients with a genetic diagnosis of STAT1 GOF or LOF germline mutations, along with detailed clinical data, were reviewed.Results: The search identified 108 publications describing 442 unique patients with STAT1 GOF mutations. The patients documented with chronic mucocutaneous candidiasis (CMC; 410/442), lower respiratory tract infections (210/442), and autoimmune thyroid disease (102/442). Th17 cytopenia was identified in 87.8% of those with GOF mutations. Twenty-five patients with GOF mutations received hematopoietic stem cell transplantation (HSCT), and 10 died several months later. Twelve of 20 patients who received JAK inhibitor therapy showed improved symptoms. Twenty-one publications described 39 unique patients with STAT1 LOF mutations. The most common manifestations were Mendelian susceptibility to mycobacterial diseases (MSMD) (29/39), followed by osteomyelitis (16/39), and lymphadenopathy (9/39). Missense, indel, and frameshift mutations were identified as LOF mutations. There were no obvious defects in lymphocyte subsets or immunoglobulin levels. Eighteen patients required antimycobacterial treatment. Three patients received HSCT, and one of the three died from fulminant EBV infection.Conclusions: STAT1 GOF syndrome is a clinical entity to consider when confronted with a patient with early-onset CMC, bacterial respiratory tract infections, or autoimmune thyroid disease as well as Th17 cytopenia and humoral immunodeficiency. HSCT is still not a reasonable therapeutic choice. Immunoglobulin replacement therapy and JAK inhibitors are an attractive alternative. STAT1 LOF deficiency is a more complicated underlying cause of early-onset MSMD, osteomyelitis, respiratory tract infections, and Herpesviridae infection. Anti-mycobacterial treatment is the main therapeutic choice. More trials are needed to assess the utility of HSCT.

Analysis of a single-institution cohort of patients with Felty's syndrome and T-cell large granular lymphocytic leukemia in the setting of rheumatoid arthritis

T-cell large granular lymphocytic leukemia (T-LGLL) is a lymphoproliferative disorder characterized by a persistent increase in the number of large granular lymphocytes (LGLs), neutropenia, and splenomegaly. Clinical manifestations of T-LGLL in the setting of rheumatoid arthritis (RA) are often identical to those in which one would suspect Felty's syndrome (FS). These disorders are distinguished by the presence of T-cell clonality, which is present in T-LGLL but not in FS. Mutations in the signal transducer and activator of transcription 3 (STAT3) and 5b (STAT5b) genes can be used as molecular markers of T-LGLL, but their prevalence in FS is unknown.Eighty-one patients with RA and unexplained neutropenia or/and an increase in the number of LGLs above 2 × 109/L were stratified into RA-associated T-LGLL (N = 56) or FS (N = 25) groups based on the presence or absence of T-cell clonality. STAT3 and STAT5b gene mutations were assessed in each group by means of allele-specific polymerase chain reaction assays. Clinical, immunological, laboratory data and the results of immunophenotyping of blood and bone marrow lymphocytes were also evaluated.Mutations of the STAT3 gene and an increase in the number of LGLs above 2 × 109/L were detected in RA-associated T-LGLL, but not in FS (39% vs 0% and 21% vs 0%, respectively). Mutations in the STAT5b gene were not observed in either group. Expression of CD57, CD16, and CD5−/dim on CD3+CD8+ T-lymphocytes was observed in both RA-associated T-LGLL and FS.STAT3 gene mutations or LGL counts over 2 × 109/L in RA patients are indicative of T-LGLL.

Staphylococcus aureus and Hyper-IgE Syndrome.

Hyper-immunoglobulin E syndrome (HIES) is a primary immunodeficiency disease characterized by recurrent Staphylococcus aureus (S. aureus) infections, eczema, skeletal abnormalities and high titers of serum immunoglobulin E. Although the genetic basis of HIES was not known for almost a half century, HIES most frequently exhibits autosomal dominant trait that is transmitted with variable expressivity. Careful genetic studies in recent years identified dominant-negative mutations in human signal transducer and activator of transcription 3 (STAT3) gene as the cause of sporadic and dominant forms of HIES. The STAT3 mutations were localized to DNA-binding, SRC homology 2 (SH2) and transactivating domains and disrupted T helper 17 (TH17) cell differentiation and downstream expression of TH17 cytokines IL-17 and IL-22. Deficiency of IL-17 and IL-22 in turn is responsible for suboptimal expression of anti-staphylococcal host factors, such as neutrophil-recruiting chemokines and antimicrobial peptides, by human keratinocytes and bronchial epithelial cells. TH17 cytokines deficiency thereby explains the recurrent staphylococcal lung and skin infections of HIES patients.

The pathogenic T387A missense mutation in the gene encoding signal transducer and activator of transcription 1 exhibits a differential gene expression profile

Heterozygous gain-of-function (GOF) mutations in the interferon-driven transcription factor STAT1 (signal transducer and activator of transcription 1) cause chronic mucocutaneous candidiasis (CMC). In this study, we characterized the molecular basis of a CMC-associated missense mutation by introducing a threonine-to-alanine exchange in the STAT1 DNA-binding domain at position 387. This substitution had previously been described in a CMC patient with suppurative eyelid infection and cutaneous abscesses, which are both unusual symptoms in this immunodeficiency. The STAT1-T387A mutant generated was compared to the wild-type protein and, in addition, to the missense mutant in the neighbouring position 386. Our results showed that the T387A mutant displayed distinct properties different from the wild-type molecule, namely elevated levels of tyrosine phosphorylation in conjunction with increased DNA-binding activity, hyperactive transcriptional regulation, and prolonged nuclear accumulation. The elevated tyrosine phosphorylation of the T387A mutant did not result in an increased mRNA production above the level of the wild-type molecule for all transcripts tested, indicating that the transcriptional activity of this mutant is largely gene-dependent. Nonetheless, these data demonstrate that the pathogenic T387A mutation associated with an atypical CMC symptomatology is biochemically similar to other well-characterized GOF mutants, while the H386A mutant was indistinguishable from the wild-type molecule. Our findings are in line with the assumption that the phenotype of this dominant STAT1 GOF mutation probably results from a disturbed shift in the equilibrium between the parallel and antiparallel dimer conformation, which is required for physiological gene activation.

Helicobacter pylori infection induces STAT3 phosphorylation on Ser727 and autophagy in human gastric epithelial cells and mouse stomach

Helicobacter pylori (H. pylori) infection is considered as one of the principal risk factors of gastric cancer. Constitutive activation of the signal transducer and activator of transcription 3 (STAT3) plays an important role in inflammation-associated gastric carcinogenesis. In the canonical STAT3 pathway, phosphorylation of STAT3 on Tyr705 is a major event of STAT3 activation. However, recent studies have demonstrated that STAT3 phosphorylated on Ser727 has an independent function in mitochondria. In the present study, we found that human gastric epithelial AGS cells infected with H. pylori resulted in localization of STAT3 phosphorylated on Ser727 (P-STAT3Ser727), predominantly in the mitochondria. Notably, H. pylori-infected AGS cells exhibited the loss of mitochondrial integrity and increased expression of the microtubule-associated protein light chain 3 (LC3), the autophagosomal membrane-associated protein. Treatment of AGS cells with a mitophagy inducer, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), resulted in accumulation of P-STAT3Ser727 in mitochondria. In addition, the elevated expression and mitochondrial localization of LC3 induced by H. pylori infection were attenuated in AGS cells harboring STAT3 mutation defective in Ser727 phosphorylation (S727A). We also observed that both P-STAT3Ser727 expression and LC3 accumulation were increased in the mitochondria of H. pylori-inoculated mouse stomach.

The clinical, immunological and genetic features of 12 Chinese patients with STAT3 mutations

BackgroundLoss-of-function (LOF) mutations in signal transducer and activator of transcription 3 (STAT3) is one of the causes of STAT3 hyperimmunoglobulin E (IgE) syndrome (STAT3-HIES), while gain-of-function (GOF) mutations in STAT3 lead to immune dysregulation diseases. We retrospectively analyzed the age, common clinical symptoms, immunologic and molecular manifestations in 11 patients with LOF STAT3 mutations and 1 patient with a GOF STAT3 mutation.MethodsTwelve patients were enrolled in our study. Serum immunoglobulin measurements, lymphocyte subset detection and whole-exome sequencing were performed.ResultsThe median age at diagnosis of STAT3-HIES patients was 4.74 years. Eczema, recurrent respiratory infections, fevers, abscesses and Staphylococcus aureus infections were the classic manifestations. Elevated serum IgE levels are not always observed in conjunction with high eosinophil counts. A moderate viral DNA load was also measured in peripheral blood mononuclear cells. We noticed that c. 1144C>T was the most common mutation site, followed by c.1311C>A. Additionally, c.1311C>A and c. 1826G>C are two novel mutations. Eight patients achieved notable improvement after receiving intravenous immunoglobulin.ConclusionWe updated the current knowledge of this topic. We found an earlier median age at diagnosis, a higher survival rate, and a general lack of nonimmunological abnormalities; we also described the treatment details and novel mutations involve in STAT3-HIES and compared STAT3 LOF and GOF mutations.

STAT3 modulates reprogramming efficiency of human somatic cells; insights from autosomal dominant Hyper IgE syndrome caused by STAT3 mutations.

ABSTRACTHuman induced pluripotent stem cell (iPSC) technology has opened exciting opportunities for stem-cell-based therapy. However, its wide adoption is precluded by several challenges including low reprogramming efficiency and potential for malignant transformation. Better understanding of the molecular mechanisms of the changes that cells undergo during reprograming is needed to improve iPSCs generation efficiency and to increase confidence for their clinical use safety. Here, we find that dominant negative mutations in STAT3 in patients with autosomal-dominant hyper IgE (Job's) syndrome (AD-HIES) result in greatly reduced reprograming efficiency of primary skin fibroblasts derived from skin biopsies. Analysis of normal skin fibroblasts revealed upregulation and phosphorylation of endogenous signal transducer and activator of transcription 3 (STAT3) and its binding to the NANOG promoter following transduction with OKSM factors. This coincided with upregulation of NANOG and appearance of cells expressing pluripotency markers. Upregulation of NANOG and number of pluripotent cells were greatly reduced throughout the reprograming process of AD-HIES fibroblasts that was restored by over-expression of functional STAT3. NANOGP8, the human-specific NANOG retrogene that is often expressed in human cancers, was also induced during reprogramming, to very low but detectable levels, in a STAT3-dependent manner. Our study revealed the critical role of endogenous STAT3 in facilitating reprogramming of human somatic cells.

Jakinibs for the Treatment of Immune Dysregulation in Patients With Gain–of–Function Signal Transducer and Activator of Transcription 1 (STAT1) or STAT3 Mutations

To investigate the efficacy of jakinib therapy in patients with gain-of-function (GOF) signal transducer and activator of transcription 1 (STAT1) or signal transducer and activator of transcription 3 (STAT3) mutations.The study included 17 total patients with either a STAT1 GOF (n = 11) or STAT3 GOF (n = 6) mutation who were treated with jakinibs (ruxolitinib or tofacitinib). Patients came from 11 international centers.This was a retrospective study to describe disease-related clinical manifestations and determine indication for treatment, dosage, length of treatment, treatment response, and treatment-associated complications. All subjects underwent thorough pre- and posttreatment clinical and laboratory evaluations and follow-up (follow-up period: 1–34 months).Fourteen patients (82%) responded favorably with clinical improvement to jakinib treatment. Observed clinical improvements included resolution of enteropathy leading to total parenteral nutrition independence, better lung function, improved autoimmune cytopenias, decreased arthritis symptoms, and remission of hemophagocytic lymphohistiocytosis. All patients with STAT1 GOF had resolved chronic mucocutaneous candidiasis with treatment. Most patients tolerated the jakinibs well with minimal or transient adverse effects. An increase in herpes zoster infections (none systemic and all cleared with antiviral agents) was observed in some patients. Four patients died despite treatment with a jakinib. The majority of these patients were critically ill with severe invasive infection or progressive lung disease. One patient died due to posttransplant complications.Jakinibs are both safe and effective in the treatment of patients with STAT1 or STAT3 GOF mutations with clinical manifestations of autoimmunity and/or immune dysregulation.Patients with STAT1 and STAT3 GOF mutations often present in early childhood with severe and/or refractory infections, lymphoproliferation, autoinflammation, and autoimmunity. Jakinibs allow for a targeted therapeutic approach to block the cytokine-induced JAK activation in STAT1 and STAT3 GOF diseases. This is the first study to evaluate the use and clinical impact of jakinibs in STAT1 and STAT3 GOF. The results are overwhelmingly encouraging, with the majority of patients having clinical improvement and reduction or resolution of autoimmune manifestations after treatment with a jakinib. Use of jakinibs late in disease progression or when critically ill was associated with mortality, suggesting early initiation may improve efficacy. This study has significant clinical impact in the treatment of STAT1 and STAT3 GOF and reinforces the notion that early genetic diagnosis of primary immunodeficiency diseases may lead to targeted therapeutic options and improved clinical outcomes.

The activating p.Ser466Arg change in STAT1 causes a peculiar phenotype with features of interferonopathies

Signal Transducer and Activator of Transcription 1 (STAT1) is a DNA-binding signal transducer that regulates transcription of specific genes in response to IFNγ and IFNα/β stimulation. Loss-of-function mutations impairing STAT1 activity are known to confer susceptibility to intracellular bacterial and viral diseases. Conversely, the few known activating mutations of STAT1 allow predisposition to chronic mucocutaneous candidiasis disease, and occur in patients with combined immunodeficiency and defective Th1 and Th17 responses. Here, we report on a de novo gain-of-function (GoF) STAT1 mutation (c.1398C>G, p.Ser466Arg) identified by exome sequencing in an individual with brain calcification, arthritis, recurrent pericarditis, leukopenia, thrombocytopenia and low C3 levels, a phenotype resembling an interferonopathy. The Ser466Arg change affects a highly conserved residue located in the DNA binding domain of the protein and the amino acid substitution was documented to have an activating role both in vitro and in vivo. Altogether, clinical features and functional studies are compatible with hyperactivation of the Interferon pathways, highlighting a role of STAT1 GoF mutation in clinical phenotypes fitting interferonopathies.

Identification of a distinct subset of disease-associated gain-of-function missense mutations in the STAT1 coiled-coil domain as system mutants

Heterozygous gain-of-function (GOF) mutations in the cytokine-regulated transcription factor STAT1 (signal transducer and activator of transcription 1) lead to chronic mucocutaneous candidiasis (CMC). However, the molecular basis of these pathogenic missense mutations is largely unknown. In this study, we characterized in more detail the CMC-associated GOF substitution mutation of arginine-to-tryptophan at position 274 (R274W) and, in addition, the adjacent glutamine-to-alanine mutation at position 275 (Q275A). Both mutants displayed elevated tyrosine phosphorylation levels, prolonged nuclear accumulation, and increased transcriptional responses to interferon-γ (IFNγ) stimulation. No difference was observed between wild-type (WT) and mutant STAT1 in DNA sequence-specificity or dissociation kinetics from high-affinity DNA-binding elements known as gamma-activated sites (GAS). Furthermore, all variants exhibited similar cooperative DNA binding. Unexpectedly, in vitro dephosphorylation rates using the recombinant STAT1-inactivating Tc45 phosphatase in both the absence and presence of double-stranded GAS elements were similar in all STAT1 variants. Likewise, the rate of tyrosine phosphorylation by Janus kinase 2 (JAK2) was unaltered as compared to the WT molecule, excluding that the phenotype of these mutants is caused by either defective Tc45-catalyzed dephosphorylation or JAK2-induced hyper-activation. Interestingly, within 10 min of IFNγ exposure, the majority of R274W and Q275A molecules had entered the nucleus, whereas the wild-type protein remained predominantly cytosolic. Thus, the exchange of critical residues located at the binding interface in the antiparallel dimer conformer led to a premature accumulation of phospho-STAT1 in the nuclear compartment. In summary, our data show that the hyper-activity of the GOF mutations results, at least in part, from the premature nuclear import of the tyrosine-phosphorylated molecules and not from alterations in their phosphorylation or dephosphorylation rates.

Two different STAT1 gain-of-function mutations lead to diverse IFN-\u03b3-mediated gene expression

Signal transducer and activator of transcription 1 (STAT1) regulates multiple biological processes downstream of a variety of cytokine receptors in many cell types. Heterozygous gain-of-function (GOF) mutations in STAT1 have been associated with a diverse phenotype encompassing chronic mucocutaneous candidiasis (CMCC) and declining immunity. There is no clear correlation between STAT1 domain-specific mutations and phenotype, and it remains unclear why GOF mutations in STAT1 result in such a wide spectrum of clinical presentations. To begin exploring this dilemma, we have studied the patterns of gene expression mediated by two different GOF mutations. Analysis of IFN-γ response elements using RNA microarrays in cells transfected with the rare H629Y mutant or the common R274G mutant showed distinct patterns of gene expression. We show here that the impact of GOF mutations in STAT1 is variant-specific. This difference in gene expression may explain the diversity in clinical manifestations experienced by these patients.

ZNF341 controls STAT3 expression and thereby immunocompetence.

Signal transducer and activator of transcription 3 (STAT3) is a central regulator of immune homeostasis. STAT3 levels are strictly controlled, and STAT3 impairment contributes to several diseases including the monogenic autosomal-dominant hyper-immunoglobulin E (IgE) syndrome (AD-HIES). We investigated patients of four consanguineous families with an autosomal-recessive disorder resembling the phenotype of AD-HIES, with symptoms of immunodeficiency, recurrent infections, skeletal abnormalities, and elevated IgE. Patients presented with reduced STAT3 expression and diminished T helper 17 cell numbers, in absence of STAT3 mutations. We identified two distinct homozygous nonsense mutations in ZNF341, which encodes a zinc finger transcription factor. Wild-type ZNF341 bound to and activated the STAT3 promoter, whereas the mutant variants showed impaired transcriptional activation, partly due to nuclear translocation failure. In summary, nonsense mutations in ZNF341 account for the STAT3-like phenotype in four autosomal-recessive kindreds. Thus, ZNF341 is a previously unrecognized regulator of immune homeostasis.

Signal Transducer and Activator of Transcription 3 Control of Human T and B Cell Responses.

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that is activated downstream of many key cytokine receptors expressed by lymphocytes. As such, it plays a critical role in regulating B cells as well as CD4+ and CD8+ T cells. Patients with clinically significant immunodeficiency and immune dysregulation resulting from loss-of-function or gain-of-function mutations in STAT3 have been described. These individuals provide insight into the critical role of this transcription factor in the regulation of immune responses and the balance between effective immune protection and autoimmunity.

Novel signal transducer and activator of transcription 1 mutation disrupts small ubiquitin-related modifier conjugation causing gain of function

Sumoylation is a posttranslational reversible modification of cellular proteins through the conjugation of small ubiquitin-related modifier (SUMO) and comprises an important regulator of protein function. We sought to characterize the molecular mechanism of a novel mutation at the SUMO motif on signal transducer and activator of transcription 1 (STAT1). STAT1 sequencing and functional characterization were performed in transfection experiments by using immunoblotting and immunoprecipitation in STAT1-deficient cell lines. Transcriptional response and target gene activation were also investigated in PBMCs. We identified a novel STAT1 mutation (c.2114A>T, p.E705V) within the SUMO motif (702IKTE705) in a patient with disseminated Rhodococcus species infection, Norwegian scabies, chronic mucocutaneous candidiasis, hypothyroidism, and esophageal squamous cell carcinoma. The mutation is located in the tail segment and is predicted to disrupt STAT1 sumoylation. Immunoprecipitation experiments performed in transfected cells confirmed absent STAT1 sumoylation for E705V, whereas it was present in wild-type (WT) STAT1 cells, as well as the loss-of-function mutants L706S and Y701C. Furthermore, stimulation with IFN-γ led to enhanced STAT1 phosphorylation, enhanced transcriptional activity, and target gene expression in the E705V-transfected compared with WT-transfected cells. Computer modeling of WT and mutant STAT1 molecules showed variations in the accessibility of the phosphorylation site Y701, which corresponded to the loss-of-function and gain-of-function variants. This is the first report of a mutation in the STAT1 sumoylation motif associated with clinical disease. These data reinforce sumoylation as a key posttranslational regulatory modification of STAT1 and identify a novel mechanism for gain-of-function STAT1 disease in human subjects.

Autosomal dominant gain of function STAT1 mutation and severe bronchiectasis

BackgroundIn a substantial number of patients with non-cystic fibrosis (CF) bronchiectasis an etiology cannot be found. Various complex immunodeficiency syndromes account for a significant portion of these patients but the mechanism elucidating the predisposition for suppurative lung disease often remains unknown. ObjectiveTo investigate the cause and mechanism predisposing a patient to severe bronchiectasis. MethodsA patient presenting with severe non-CF bronchiectasis was investigated. Whole exome analysis (WES) was performed and complemented by extensive immunophenotyping. ResultsThe genetic analysis revealed an autosomal dominant gain-of-function mutation (AD- GOF) in the signal transducer and activator of transcription 1 (STAT1) in the patient. STAT1 phosphorylation studies showed increased phosphorylation of STAT1 after stimulation with interferon γ (IFN-γ). Immunophenotyping showed normal counts of CD4 and CD8 T cells, B and NK cells, but a reduction of all memory B cells especially class switched memory B cells. Minor changes in the CD8 T cell subpopulations were seen. ConclusionsEarly use of WES in the investigation of non-CF bronchiectasis was highly advantageous. The degree of impairment in class-switched memory B cells may predispose patients with AD- GOF mutations in STAT1 to suppurative sinopulmonary disease.

A Novel Heterozygous Mutation in the STAT1 SH2 Domain Causes Chronic Mucocutaneous Candidiasis, Atypically Diverse Infections, Autoimmunity, and Impaired Cytokine Regulation.

Chronic mucocutaneous candidiasis (CMC) is a primary immunodeficiency characterized by persistent or recurrent skin and mucosal surface infections with Candida species. Different gene mutations leading to CMC have been identified. These include various heterozygous gain-of-function (GOF) mutations in signal transducer and activator of transcription 1 (STAT1) that are not only associated with infections but also with autoimmune manifestations. Recently, two STAT1 GOF mutations involving the Src homology 2 (SH2) domain have been reported, while so far, over 50 mutations have been described mainly in the coiled coil and the DNA-binding domains. Here, we present two members of a Dutch family with a novel STAT1 mutation located in the SH2 domain. T lymphocytes of these patients revealed STAT1 hyperphosphorylation and higher expression of STAT1 target genes. The clinical picture of CMC in our patients could be explained by diminished production of interleukin (IL)-17 and IL-22, cytokines important in the protection against fungal infections.

Gain-of-function STAT1 mutations are associated with intracranial aneurysms

Chronic mucocutaneous candidiasis, characterized by persistent or recurrent fungal infections, represents the clinical hallmark in gain-of-function (GOF) signal transducer and activator of transcription 1 (STAT1) mutation carriers. Several cases of intracranial aneurysms have been reported in patients with GOF STAT1 mutation but the paucity of reported cases likely suggested this association still as serendipity. In order to endorse this association, we link the development of intracranial aneurysms with STAT1 GOF mutation by presenting the two different cases of a patient and her mother, and demonstrate upregulated phosphorylated STAT4 and IL-12 receptor β1 upon stimulation in patient's blood cells. We also detected increased transforming growth factor (TGF)-β type 2 receptor expression, particularly in CD14+ cells, and a slightly higher phosphorylation rate of SMAD3. In addition, the mother of the patient developed disseminated bacille Calmette-Guérin disease after vaccination, speculating that GOF STAT1 mutations may confer a predisposition to weakly virulent mycobacteria.

Alanine-scanning mutagenesis of human signal transducer and activator of transcription 1 to estimate loss- or gain-of-function variants

Germline heterozygous mutations in human signal transducer and activator of transcription 1 (STAT1) can cause loss of function (LOF), as in patients with Mendelian susceptibility to mycobacterial diseases, or gain of function (GOF), as in patients with chronic mucocutaneous candidiasis. LOF and GOF mutations are equally rare and can affect the same domains of STAT1, especially the coiled-coil domain (CCD) and DNA-binding domain (DBD). Moreover, 6% of patients with chronic mucocutaneous candidiasis with a GOF STAT1 mutation have mycobacterial disease, obscuring the functional significance of the identified STAT1 mutations. Current computational approaches, such as combined annotation-dependent depletion, do not distinguish LOF and GOF variants. We estimated variations in the CCD/DBD of STAT1. We mutagenized 342 individual wild-type amino acids in the CCD/DBD (45.6% of full-length STAT1) to alanine and tested the mutants for STAT1 transcriptional activity. Of these 342 mutants, 201 were neutral, 30 were LOF, and 111 were GOF mutations in a luciferase assay. This assay system correctly estimated all previously reported LOF mutations (100%) and slightly fewer GOF mutations (78.1%) in the CCD/DBD of STAT1. We found that GOF alanine mutants occurred at the interface of the antiparallel STAT1 dimer, suggesting that they destabilize this dimer. This assay also precisely predicted the effect of 2 hypomorphic and dominant negative mutations, E157K and G250E, in the CCD of STAT1 that we found in 2 unrelated patients with Mendelian susceptibility to mycobacterial diseases. The systematic alanine-scanning assay is a useful tool to estimate the GOF or LOF status and the effect of heterozygous missense mutations in STAT1 identified in patients with severe infectious diseases, including mycobacterial and fungal diseases.

STAT3-gain of function mutation as a cause of severe bronchiectasis and multi-organ autoimmunity; A case report

Background: Signal transducer and activator of transcription 3 (STAT3) is a member of a family of proteins involved in the regulation of inflammation, differentiation, proliferation and survival. Loss or gain-of-function mutations in STAT3 lead to infectious and autoimmune complications. Recently, STAT3 gain-of-function mutations have been associated with the development of a multi-organ autoimmune syndrome. Case presentation: Here, we describe a 38-year-old male who presented with severe diffuse bronchiectasis in addition to gastrointestinal, dermatological, and malignant manifestations. Following negative workup, whole exome sequencing, validated by Sanger sequencing, revealed a heterozygous missense mutation in the STAT3 gene, c.1261G>A (p.G421R). FACS analysis of peripheral T lymphocytes revealed low levels of CD4+CD25+FoxP3 and CD8+CD25+FoxP3 regulatory T cells (Tregs). Following treatment with two cycles of tocilizumab, an interleukin-6 receptor antibody, a significant increase in the level of Tregs was observed, accompanied by clinical improvement. Conclusion: This case sheds light on the emerging role of STAT3 gain of function mutation in the pathogenesis of autoimmune diseases and development of bronchiectasis, and further addresses the therapeutic role of IL-6 blocker treatment in this syndrome.

A novel presentation of homozygous loss-of-function STAT-1 mutation in an infant with hyperinflammation—A case report and review of the literature

We present an infant with a novel homozygous, loss-of-function signal transducer and activator of transcription 1 (STAT-1) mutation, revealed by whole-exome sequencing and manifesting as multisystem hyperinflammation without mycobacterial disease. Autosomal-recessive (AR) complete STAT-1 deficiency has been described only a handful of times previously, but all have presented characteristically and dramatically during infancy with disseminated nonvirulent mycobacterial disease.1-3 We add a novel presentation of complete STAT-1 deficiency, successfully treated by stem cell transplantation (SCT), alongside a current literature review.