Clinical and laboratory predictors of monogenic very early onset inflammatory bowel disease.

BACKGROUND: Inflammatory bowel disease (IBD) is a chronic inflammatory disease of the gastrointestinal tract. Treatment for patients who have a monogenic cause of their IBD, often the youngest children, known as very early onset IBD (VEO-IBD), can be different from standard treatment for polygenic cases. Yet, ascertainment of these patients is difficult. METHODS: We analyzed cases of VEO-IBD to understand the breadth of monogenic etiology and to identify clinical, laboratory, and flow cytometric correlates of this subpopulation. RESULTS: Genetic causes of very early onset inflammatory bowel disease are highly diverse ranging from pure epithelial defects to classic T cell defects. Flow cytometry, other than testing for chronic granulomatous disease, has a low sensitivity for monogenic etiologies. Poor growth was a clinical feature associated with monogenic causality. CONCLUSIONS: Genetic testing is, at this moment, the most robust method for the identification of monogenic cases of very early onset IBD.

IL-1 Transcriptional Responses to Lipopolysaccharides Are Regulated by a Complex of RNA Binding Proteins.

The IL1A and IL1B genes lie in close proximity on chromosome 2 near the gene for their natural inhibitor, IL1RN Despite diverse functions, they are all three inducible through TLR4 signaling but with distinct kinetics. This study analyzed transcriptional induction kinetics, chromosome looping, and enhancer RNA production to understand the distinct regulation of these three genes in human cells. IL1A, IL1B, and IL1RN were rapidly induced after stimulation with LPS; however, IL1B mRNA production was less inhibitable by iBET151, suggesting it does not use pause-release regulation. Surprisingly, chromatin looping contacts between IL1A and IL1B were highly intermingled, although those of IL1RN were distinct, and we focused on comparing IL1A and IL1B transcriptional pathways. Our studies demonstrated that enhancer RNAs were produced from a subset of the regulatory regions, that they were critical for production of the mRNAs, and that they bound a diverse array of RNA binding proteins, including p300 but not CBP. We, furthermore, demonstrated that recruitment of p300 was dependent on MAPKs. Integrator is another RNA binding protein recruited to the promoters and enhancers, and its recruitment was more dependent on NF-κB than MAPKs. We found that integrator and NELF, an RNA polymerase II pausing protein, were associated with RNA in a manner that facilitated interaction. We conclude that IL1A and IL1B share many regulatory contacts, signaling pathways, and interactions with enhancer RNAs. A complex of protein interactions with enhancer RNAs emphasize the role of enhancer RNAs and the overall structural aspects of transcriptional regulation.

Chromatin Modifications in 22q11.2 Deletion Syndrome.

PURPOSE: Chromosome 22q11.2 deletion syndrome is a common inborn error of immunity. The early consequences of thymic hypoplasia are low T cell numbers. Later in life, atopy, autoimmunity, inflammation, and evolving hypogammaglobulinemia can occur and the causes of these features are not understood. This study utilized an unbiased discovery approach to define alterations in histone modifications. Our goal was to identify durable chromatin changes that could influence cell behavior. METHODS: CD4 T cells and CD19 B cells underwent ChIP-seq analysis using antibodies to H3K4me3, H3K27ac, and H4ac. RNA effects were defined in CD4 T cells by RNA-seq. Serum cytokines were examined by Luminex. RESULTS: Histone marks of transcriptional activation at CD4 T cell promoters and enhancers were globally increased. The promoter activation signature had elements related to T cell activation and inflammation, concordant with effects seen in the transcriptome. B cells, in contrast, had a minimally altered epigenetic landscape in 22q11.2. Both cell types had an "edge" effect with markedly altered chromatin adjacent to the deletion. CONCLUSIONS: People with 22q11.2 deletion have altered CD4 T cell chromatin and a transcriptome concordant with the changes in the epigenome. These effects support a disease model where qualitative changes to T cells occur in addition to quantitative defects that have been well characterized. This study offers unique insight into qualitative differences in the T cells in 22q11.2 deletion, an aspect that has received limited attention.

Mucosal Invariant T cells are Diminished in Very Early-Onset Inflammatory Bowel Disease.

OBJECTIVES: Very early-onset inflammatory bowel disease (VEO-IBD) arises in children less than 6 years old, a critical time for immunologic development and maturation of the intestinal microbiome. Non-conventional lymphocytes, defined here as mucosal-associated invariant T cells and innate lymphocytes, require microbial products for either development or expansion, aspects that could be altered in very early-onset inflammatory bowel disease. Our objective was to define conventional leukocyte and non-conventional lymphocyte populations in controls and patients using multiparameter flow cytometry to test the hypothesis that their frequencies would be altered in a chronic inflammatory state associated with significant dysbiosis. METHODS: Multiparameter flow cytometry was used in a control cohort of 105 subjects to define age-effects, not previously comprehensively examined for these cell types in humans. Differences were defined between 263 unique age-matched patients with VEO-IBD and 105 controls using Student t-test. Subjects were divided into two age groups at the time of sampling to control for age-related changes in immune composition. RESULTS: Intermediate monocytes were consistently decreased in patients with VEO-IBD compared to controls. Mucosal-associated invariant T cells were significantly lower in patients with long-standing disease. Levels were less than half of those seen in the age-matched control cohort. The innate lymphoid cells type 2 population was expanded in the youngest patients. CONCLUSION: Mucosal-associated invariant T cells are diminished years after presentation with inflammatory bowel disease. This durable effect of early life intestinal inflammation may have long-term consequences. Diminished mucosal-associated invariant T cells could impact host defense of intestinal infections.

Prolactin activates IRF1 and leads to altered balance of histone acetylation: Implications for systemic lupus erythematosus.

Objectives: Prolactin is known to be associated with autoimmune disease; however, the mechanisms are incompletely understood. Previous studies have highlighted the effects on B-cell tolerance and monocyte/macrophage activation. One study found that prolactin could activate IRF1, a transcription factor implicated in SLE and interferon responses. We hypothesized that prolactin elicited transcriptional regulation though an epigenetic process related to IRF1 activation in monocytes. This study examined IRF1 activation and downstream epigenetic effects.Methods: Protein analysis, qRT-PCR, and ChIP assays were used in a human monocytic cell line and primary monocytes to define changes related to acute and chronic prolactin exposure.Results: We found that prolactin acutely induced both expression and activation of IRF1. Prolactin induced interactions of IRF1 with the histone acetyltransferase co-activators CBP and p300. Chronic prolactin induced expression of multiple histone modifying proteins and genes within the interferon signature suggesting that the prolonged exposure to prolactin resets the landscape and balance of chromatin modifying enzymes.Conclusion: These data provide insight into the mechanism of the association of prolactin with autoimmunity. We found effects at the level of epigenetics, an area not previously explored. Our data support a role for chronic prolactin regulating the expression of genes setting the landscape of chromatin modifying enzymes and driving the interferon signature. This novel finding is of relevance in systemic lupus erythematosus, where clinical effects of hyperprolactinemia have been recognized.

Toll-like receptor 2 stimulation augments esophageal barrier integrity.

BACKGROUND: Germline-encoded innate immune pattern recognition receptors (PRR) are expressed at epithelial surfaces and modulate epithelial defenses. Evidence suggests that stimulation of the Toll-like receptor (TLR) family of PRR may regulate epithelial barrier integrity by upregulating tight junction (TJ) complex protein expression, but it is not known whether this mechanism is utilized in esophageal epithelial cells. TJ complex proteins maintain intact barrier function and are dysregulated in atopic disorders including eosinophilic esophagitis. METHODS: Pattern recognition receptors expression was assessed in EoE and control primary esophageal epithelial cells, demonstrating robust expression of TLR2 and TLR3. The three-dimensional air-liquid interface culture (ALI) model was used to test whether TLR2 or TLR3 stimulation alters epithelial barrier function using an in vitro model of human epithelium. Transepithelial electrical resistance (TEER) and FITC-Dextran permeability were evaluated to assess membrane permeability. ALI cultures were evaluated by histology, immunohistochemistry, Western blotting, and chromatin immunoprecipitation (ChIP). RESULTS: TLR3 stimulation did not change TEER in the ALI model. TLR2 stimulation increased TEER (1.28- to 1.31-fold) and decreased paracellular permeability to FITC-Dextran, and this effect was abolished by treatment with anti-TLR2 blocking antibody. TJ complex proteins claudin-1 and zonula occludens-1 were upregulated following TLR2 stimulation, and ChIP assay demonstrated altered histone 4 acetyl binding at the TJP1 enhancer and CLDN1 enhancer and promoter following zymosan treatment, implying the occurrence of durable chromatin changes. CONCLUSIONS: Our findings implicate the TLR2 pathway as a potential regulator of esophageal epithelial barrier function and suggest that downstream chromatin modifications are associated with this effect.

B cell development in chromosome 22q11.2 deletion syndrome.

Chromosome 22q11.2 deletion syndrome is a common immune deficiency associated with thymic hypoplasia. Most patients did not survive until the mid-1980s and now there is a growing adult population. B cell and immunoglobulin defects have been described and appear to be increased in the adult population. We used flow cytometry, B cell stimulation and repertoire analysis to understand B cell function. B cell production at early stages appeared to be normal in patients but adult patients exhibited a deficit of switched memory B cells. Follicular helper T cells were present at higher percentages in patients and they exhibited a more activated phenotype in patients compared to controls. In spite of that, somatic hypermutation was decreased in patients compared to controls at all ages. Fewer mutations per clone were seen, strongly implicating aberrant T cell help. Therefore, patients with chromosome 22q11.2 deletion syndrome have a progressive decrease in switched memory B cells and evidence of compromised T cell help. In children, evidence of compromised T cell help is limited to decreased somatic hypermutation. With age, greater manifestations become apparent even though a minority of patients have hypogammaglobulinemia. As this population ages, this has important implications for management.

Exome sequencing analysis reveals variants in primary immunodeficiency genes in patients with very early onset inflammatory bowel disease.

BACKGROUND & AIMS: Very early onset inflammatory bowel disease (VEO-IBD), IBD diagnosed at 5 years of age or younger, frequently presents with a different and more severe phenotype than older-onset IBD. We investigated whether patients with VEO-IBD carry rare or novel variants in genes associated with immunodeficiencies that might contribute to disease development. METHODS: Patients with VEO-IBD and parents (when available) were recruited from the Children's Hospital of Philadelphia from March 2013 through July 2014. We analyzed DNA from 125 patients with VEO-IBD (age, 3 wk to 4 y) and 19 parents, 4 of whom also had IBD. Exome capture was performed by Agilent SureSelect V4, and sequencing was performed using the Illumina HiSeq platform. Alignment to human genome GRCh37 was achieved followed by postprocessing and variant calling. After functional annotation, candidate variants were analyzed for change in protein function, minor allele frequency less than 0.1%, and scaled combined annotation-dependent depletion scores of 10 or less. We focused on genes associated with primary immunodeficiencies and related pathways. An additional 210 exome samples from patients with pediatric IBD (n = 45) or adult-onset Crohn's disease (n = 20) and healthy individuals (controls, n = 145) were obtained from the University of Kiel, Germany, and used as control groups. RESULTS: Four hundred genes and regions associated with primary immunodeficiency, covering approximately 6500 coding exons totaling more than 1 Mbp of coding sequence, were selected from the whole-exome data. Our analysis showed novel and rare variants within these genes that could contribute to the development of VEO-IBD, including rare heterozygous missense variants in IL10RA and previously unidentified variants in MSH5 and CD19. CONCLUSIONS: In an exome sequence analysis of patients with VEO-IBD and their parents, we identified variants in genes that regulate B- and T-cell functions and could contribute to pathogenesis. Our analysis could lead to the identification of previously unidentified IBD-associated variants.

Noncoding RNAs and LRRFIP1 regulate TNF expression.

Noncoding RNAs have been implicated in the regulation of expression of numerous genes; however, the mechanism is not fully understood. We identified bidirectional, long noncoding RNAs upstream of the TNF gene using five different methods. They arose in a region where the repressors LRRFIP1, EZH2, and SUZ12 were demonstrated to bind, suggesting a role in repression. The noncoding RNAs were polyadenylated, capped, and chromatin associated. Knockdown of the noncoding RNAs was associated with derepression of TNF mRNA and diminished binding of LRRFIP1 to both RNA targets and chromatin. Overexpression of the noncoding RNAs led to diminished expression of TNF and recruitment of repressor proteins to the locus. One repressor protein, LRRFIP1, bound directly to the noncoding RNAs. These data place the noncoding RNAs upstream of TNF gene as central to the transcriptional regulation. They appear to serve as a platform for the assembly of a repressive complex.

A de novo whole gene deletion of XIAP detected by exome sequencing analysis in very early onset inflammatory bowel disease: a case report.

BACKGROUND: Children with very early-onset inflammatory bowel disease (VEO-IBD), those diagnosed at less than 5 years of age, are a unique population. A subset of these patients present with a distinct phenotype and more severe disease than older children and adults. Host genetics is thought to play a more prominent role in this young population, and monogenic defects in genes related to primary immunodeficiencies are responsible for the disease in a small subset of patients with VEO-IBD. CASE PRESENTATION: We report a child who presented at 3 weeks of life with very early-onset inflammatory bowel disease (VEO-IBD). He had a complicated disease course and remained unresponsive to medical and surgical therapy. The refractory nature of his disease, together with his young age of presentation, prompted utilization of whole exome sequencing (WES) to detect an underlying monogenic primary immunodeficiency and potentially target therapy to the identified defect. Copy number variation analysis (CNV) was performed using the eXome-Hidden Markov Model. Whole exome sequencing revealed 1,380 nonsense and missense variants in the patient. Plausible candidate variants were not detected following analysis of filtered variants, therefore, we performed CNV analysis of the WES data, which led us to identify a de novo whole gene deletion in XIAP. CONCLUSION: This is the first reported whole gene deletion in XIAP, the causal gene responsible for XLP2 (X-linked lymphoproliferative Disease 2). XLP2 is a syndrome resulting in VEO-IBD and can increase susceptibility to hemophagocytic lymphohistocytosis (HLH). This identification allowed the patient to be referred for bone marrow transplantation, potentially curative for his disease and critical to prevent the catastrophic sequela of HLH. This illustrates the unique etiology of VEO-IBD, and the subsequent effects on therapeutic options. This cohort requires careful and thorough evaluation for monogenic defects and primary immunodeficiencies.

TNFSF13 insufficiency disrupts human colonic epithelial cell-mediated B cell differentiation.

Cytokines mediating epithelial and immune cell interactions modulate mucosal healing- a process that goes awry with chronic inflammation as in inflammatory bowel disease. TNFSF13 is a cytokine important for B cell maturation and function, but roles for epithelial TNFSF13 and putative contribution to inflammatory bowel disease are poorly understood. We evaluated functional consequences of a novel monoallelic TNFSF13 variant using biopsies, tissue-derived colonoids and induced pluripotent stem cell (iPSC)-derived colon organoids. TNFSF13 variant colonoids exhibited a >50% reduction in secreted TNFSF13, increased epithelial proliferation, and reduced apoptosis, which was confirmed in iPSC-derived colon organoids. Single cell RNA-sequencing, flow cytometry, and co-immunoprecipitation identified FAS as the predominant colonic epithelial receptor for TNFSF13. Imaging mass cytometry revealed an increase in epithelial-associated B cells in TNFSF13 variant colon tissue sections. Finally, TNFSF13 variant colonoids co-cultured with memory B cells demonstrated a reduction in the production of IgA+ plasma cells compared to control colonoid co-cultures. Our findings support a role for epithelial TNFSF13 as a regulator of colonic epithelial growth and epithelial crosstalk with B cells.

Rituximab-treated patients have a poor response to influenza vaccination.

The efficacy of influenza vaccination in patients treated with rituximab is a clinically important question. Rheumatology clinics are populated with patients receiving rituximab for a broad array of disorders. Although several studies have explored the efficacy of other vaccines in rituximab-treated populations, results have been conflicting. We wished to define influenza vaccine efficacy in a rituximab-treated cohort. We examined 17 evaluable subjects treated with rituximab for rheumatologic conditions. T cell subsets, B cells subsets, T cell function, and B cell function were evaluated at specific time points along with hemagglutinination inhibition titers after receiving the standard inactivated influenza vaccine. T cell subset counts were significantly different than controls but did not change with rituximab. B cells depleted in all patients but were in various stages of recovery at the time of vaccination. Influenza vaccine responsiveness was poor overall, with only 16 % of subjects having a four-fold increase in titer. Pre-existing titers were retained throughout the study, however. The ability to respond to the influenza vaccine appeared to be related to the degree of B cell recovery at the time of vaccination. This study emphasizes that antibody responses to vaccine are impaired in subjects treated with rituximab and supports the concept that B cell recovery influences influenza vaccine responsiveness.

Urinary HER2, TWEAK and VCAM-1 levels are associated with new-onset proteinuria in paediatric lupus nephritis.

OBJECTIVE: Lupus nephritis is a key driver of morbidity and mortality in SLE. Detecting active nephritis on a background of pre-existing renal damage is difficult, leading to potential undertreatment and accumulating injury. An unmet need is a biomarker that distinguishes active lupus nephritis, particularly important in paediatrics where minimising invasive procedures is desirable. METHODS: This was a multicentre, prospective study of 113 paediatric patients with biopsy-proven lupus nephritis. Clinical data and urine were obtained every 3-4 months and patients averaged 2 years on study with seven time points. Urine was analysed for human epidermal growth factor receptor 2 (HER2), tumour necrosis factor-like weak inducer of apoptosis and vascular cell adhesion molecule-1 (VCAM-1) by ELISA. We defined active disease as either a rise in serum creatinine ≥0.3 mg/dL from baseline or a rise in renal Systemic Lupus Erythematosus Disease Activity Index score from the previous visit. These markers were also studied in patients with acute kidney injury, juvenile idiopathic arthritis (JIA), amplified pain syndrome and healthy controls. RESULTS: The rate of active disease was 56% over an average of 2 years of follow-up. HER2 and VCAM-1 were significantly elevated at time points with active disease defined by increased serum creatinine compared with time points with inactive disease or patients who never flared. All three biomarkers were associated with new-onset proteinuria and VCAM-1 was elevated at time points preceding new-onset proteinuria. These biomarkers were not increased in acute kidney injury or JIA. CONCLUSION: All three biomarkers were associated with new onset proteinuria and increased VCAM-1 may predict impending proteinuria. These biomarkers provide potential non-invasive measures for monitoring that may be more sensitive to impending flare than conventional measures.

RNA sequencing identifies global transcriptional changes in peripheral CD4+ cells during active oesophagitis and following epicutaneous immunotherapy in eosinophilic oesophagitis.

OBJECTIVE: There are no disease-modifying therapies for the treatment of eosinophilic oesophagitis (EoE), which is driven by non-IgE-mediated allergic inflammation. A recent clinical trial of milk epicutaneous immunotherapy (EPIT) has shown initial promise, with 47% of treated EoE patients tolerating milk without recurrence of disease. Mechanisms of EPIT in EoE have not been studied in humans. Here, we identify transcriptional changes in the peripheral CD4+ T-cell compartment during active EoE and following EPIT. METHODS: RNA isolation, sequencing and integrative data analysis were performed on peripheral CD4+ T cells isolated from 15 of 20 patients enrolled in a clinical trial of EPIT for EoE. Gene expression changes in peripheral CD4+ T cells were examined during diet therapy and following trial of milk antigen EPIT. RESULTS: We identify 244 differentially expressed genes in peripheral blood CD4+ cells of EoE patients consuming versus those eliminating milk, and 129 DEGs in CD4+ cells were isolated after EPIT versus after placebo (FDR ≤ 0.05). Gene set enrichment analysis identifies enrichment of hallmark interferon-α and interferon-γ response pathways in peripheral CD4+ T cells from EoE patients during active disease on a milk-containing diet. We demonstrate overlap of this gene signature with the altered gene expression signature seen in EoE patient biopsy tissue. EPIT therapy response is associated with significant enrichment in pathways related to T-cell receptor signalling (P = 1.16 × 10-14), antigen presentation and costimulation, and cytokine signalling (P = 1.11 × 10-16), as well as upregulation of genes associated with regulatory T-cell function. CONCLUSIONS: EoE is associated with distinct global transcriptional changes in CD4+ T cells, one feature of which is an IFN response signature. Clinically favorable response to EPIT is likely multifactorial but is associated with a distinct transcriptional profile in peripheral CD4+ cells supporting the hypothesis that EPIT alters peripheral CD4+ responses in EoE patients.

Immune Dysregulation in Human ITCH Deficiency Successfully Treated with Hematopoietic Cell Transplantation.

BACKGROUND: Mutations in ITCH, which encodes an E3 ubiquitin-protein ligase, can result in systemic autoimmunity and immunodeficiency. The clinical phenotype and mechanism of disease have not been fully characterized, resulting in a paucity of therapeutic options for this potentially fatal disease. OBJECTIVE: We aimed to (1) expand the understanding about the phenotype of human ITCH deficiency (2) further characterize the associated immune dysregulation, and (3) report the first successful hematopoietic cell transplant (HCT) in a patient with ITCH deficiency. METHODS: Disease profiling was performed in a patient with multisystem immune dysregulation. Whole exome sequencing with trio analysis and functional validation of candidate disease variants were performed, including mRNA and protein expression. Analyses to further delineate the immunophenotype included quantitative evaluation of lymphoid and myeloid subsets with flow cytometry and mass cytometry. RESULTS: A patient with multisystem immune dysregulation presenting with growth failure, very-early-onset inflammatory bowel disease, arthritis, uveitis, psoriasis, and type 1 diabetes mellitus underwent whole exome sequencing, which identified novel compound heterozygous mutations in ITCH. Reduced expression of ITCH mRNA and absent ITCH protein were found. Abnormalities in both lymphoid and myeloid lineages were identified. The patient underwent HCT. He demonstrated excellent immune reconstitution and resolution of many manifestations of his systemic disease. CONCLUSIONS: Here we report ITCH deficiency with unique clinical features of colonic very-early-onset inflammatory bowel disease, arthritis, and uveitis in the setting of immune dysregulation and further characterize the underlying immune dysregulation. We demonstrate that HCT can be an effective, and potentially curative, therapy for ITCH deficiency.

Colonoids From Patients With Pediatric Inflammatory Bowel Disease Exhibit Decreased Growth Associated With Inflammation Severity and Durable Upregulation of Antigen Presentation Genes.

BACKGROUND: Defining epithelial cell contributions to inflammatory bowel disease (IBD) is essential for the development of much needed therapies for barrier repair. Children with very early onset (VEO)-IBD have more extensive, severe, and refractory disease than older children and adults with IBD and, in some cases, have defective barrier function. We therefore evaluated functional and transcriptomic differences between pediatric IBD (VEO and older onset) and non-IBD epithelium using 3-dimensional, biopsy-derived organoids. METHODS: We measured growth efficiency relative to histopathological and clinical parameters in patient enteroid (ileum) and colonoid (colon) lines. We performed RNA-sequencing on patient colonoids and subsequent flow cytometry after multiple passages to evaluate changes that persisted in culture. RESULTS: Enteroids and colonoids from pediatric patients with IBD exhibited decreased growth associated with histological inflammation compared with non-IBD controls. We observed increased LYZ expression in colonoids from pediatric IBD patients, which has been reported previously in adult patients with IBD. We also observed upregulation of antigen presentation genes HLA-DRB1 and HLA-DRA, which persisted after prolonged passaging in patients with pediatric IBD. CONCLUSIONS: We present the first functional evaluation of enteroids and colonoids from patients with VEO-IBD and older onset pediatric IBD, a subset of which exhibits poor growth. Enhanced, persistent epithelial antigen presentation gene expression in patient colonoids supports the notion that epithelial cell-intrinsic differences may contribute to IBD pathogenesis.

Constrained chromatin accessibility in PU.1-mutated agammaglobulinemia patients.

The pioneer transcription factor (TF) PU.1 controls hematopoietic cell fate by decompacting stem cell heterochromatin and allowing nonpioneer TFs to enter otherwise inaccessible genomic sites. PU.1 deficiency fatally arrests lymphopoiesis and myelopoiesis in mice, but human congenital PU.1 disorders have not previously been described. We studied six unrelated agammaglobulinemic patients, each harboring a heterozygous mutation (four de novo, two unphased) of SPI1, the gene encoding PU.1. Affected patients lacked circulating B cells and possessed few conventional dendritic cells. Introducing disease-similar SPI1 mutations into human hematopoietic stem and progenitor cells impaired early in vitro B cell and myeloid cell differentiation. Patient SPI1 mutations encoded destabilized PU.1 proteins unable to nuclear localize or bind target DNA. In PU.1-haploinsufficient pro-B cell lines, euchromatin was less accessible to nonpioneer TFs critical for B cell development, and gene expression patterns associated with the pro- to pre-B cell transition were undermined. Our findings molecularly describe a novel form of agammaglobulinemia and underscore PU.1's critical, dose-dependent role as a hematopoietic euchromatin gatekeeper.

Characterization of LRRFIP1.

LRRFIP1 has been identified as a regulator of toll-like receptor (TLR) pathway signaling; however, little is known about its own regulation and function. This study was undertaken to characterize the biochemical properties and its regulation. Over-expression of full length LRRFIP1 led to enhanced responses to lipopolysaccharide (LPS). We examined its expression in monocytic cell lines because they express a broad range of TLRs. We found that its level of expression was not altered by LPS or phorbol myristate acetate (PMA) but that it was up-regulated by nicotine, influenza infection, and serum starvation. Phosphorylation was examined because of the bioinformatically predicted serine phosphorylation sites. Serine phosphorylation was detected and was altered by both poly I:C and nicotine. Finally, we examined the regulation of intracellular localization in response to dsRNA and found that LRRFIP1 colocalized with labeled dsRNA in monocyte lysosomal structures but not with lysosomes lacking dsRNA. These data suggest that LRRFIP1 is phosphorylated in response to immunologic stimuli and it is directed to lysosomal structures.