The autoimmunity-associated BLK haplotype exhibits cis-regulatory effects on mRNA and protein expression that are prominently observed in B cells early in development

Biologically targeted discovery-replication scan identifies G×G interaction in relation to risk of Barrett's esophagus and esophageal adenocarcinoma

Inherited genetics represents an important contributor to risk of esophageal adenocarcinoma (EAC), and its precursor Barrett's esophagus (BE). Genome-wide association studies have identified ∼30 susceptibility variants for BE/EAC, yet genetic interactions remain unexamined. To address challenges in large-scale G×G scans, we combined knowledge-guided filtering and machine learning approaches, focusing on genes with (1) known/plausible links to BE/EAC pathogenesis (n = 493) or (2) prior evidence of biological interactions (n = 4,196). Approximately 75 × 106 SNP×SNP interactions were screened via hierarchical group lasso (glinternet) using BEACON GWAS data. The top ∼2,000 interactions retained in each scan were prioritized using p values from single logistic models. Identical scans were repeated among males only (78%), with two independent GWAS datasets used for replication. In overall and male-specific primary replications, 11 of 187 and 20 of 191 interactions satisfied p < 0.05, respectively. The strongest evidence for secondary replication was for rs17744726×rs3217992 among males, with consistent directionality across all cohorts (Pmeta = 2.19 × 10-8); rs3217992 "T" was associated with reduced risk only in individuals homozygous for rs17744726 "G." Rs3217992 maps to the CDKN2B 3' UTR and reportedly disrupts microRNA-mediated repression. Rs17744726 maps to an intronic enhancer region in BLK. Through in silico prioritization and experimental validation, we identified a nearby proxy variant (rs4841556) as a functional modulator of enhancer activity. Enhancer-gene mapping and eQTLs implicated BLK and FAM167A as targets. The first systematic G×G investigation in BE/EAC, this study uncovers differential risk associations for CDKN2B variation by BLK genotype, suggesting novel biological dependency between two risk loci encoding key mediators of tumor suppression and inflammation.

Low-frequency and rare genetic variants associated with rheumatoid arthritis risk

Rheumatoid arthritis (RA) has an estimated heritability of nearly 50%, which is particularly high in seropositive RA. HLA alleles account for a large proportion of this heritability, in addition to many common single-nucleotide polymorphisms with smaller individual effects. Low-frequency and rare variants, such as those captured by next-generation sequencing, can also have a large role in heritability in some individuals. Rare variant discovery has informed the development of drugs such as inhibitors of PCSK9 and Janus kinases. Some 34 low-frequency and rare variants are currently associated with RA risk. One variant (19:10352442G>C in TYK2) was identified in five separate studies, and might therefore represent a promising therapeutic target. Following a set of best practices in future studies, including studying diverse populations, using large sample sizes, validating RA and serostatus, replicating findings, adjusting for other variants and performing functional assessment, could help to ensure the relevance of identified variants. Exciting opportunities are now on the horizon for genetics in RA, including larger datasets and consortia, whole-genome sequencing and direct applications of findings in the management, and especially treatment, of RA.

Fyn, Blk, and Lyn kinase inhibitors: A mini-review on medicinal attributes, research progress, and future insights

Fyn, Blk, and Lyn are part of a group of proteins called Src family kinases. They are crucial in controlling cell communication and their response to the growth, changes, and immune system. Blocking these proteins with inhibitors can be a way to treat diseases where these proteins are too active. The primary mode of action of these inhibitors is to inhibit the phosphorylation of Fyn, Blk, and Lyn receptors, which in turn affects how signals pass within the cells. This review shows the structural and functional aspects of Fyn, Blk, and Lyn kinases, highlighting the significance of their dysregulation in diseases such as cancer and autoimmune disorders. The discussion encompasses the design strategies, SAR analysis, and chemical characteristics of effective inhibitors, shedding light on their specificity and potency. Furthermore, it explores the progress of clinical trials of these inhibitors, emphasizing their potential therapeutic applications.

BLK positively regulates TLR/IL-1R signaling by catalyzing TOLLIP phosphorylation

TLR/IL-1R signaling plays a critical role in sensing various harmful foreign pathogens and mounting efficient innate and adaptive immune responses, and it is tightly controlled by intracellular regulators at multiple levels. In particular, TOLLIP forms a constitutive complex with IRAK1 and sequesters it in the cytosol to maintain the kinase in an inactive conformation under unstimulated conditions. However, the underlying mechanisms by which IRAK1 dissociates from TOLLIP to activate TLR/IL-1R signaling remain obscure. Herein, we show that BLK positively regulates TLR/IL-1R-mediated inflammatory response. BLK-deficient mice produce less inflammatory cytokines and are more resistant to death upon IL-1β challenge. Mechanistically, BLK is preassociated with IL1R1 and IL1RAcP in resting cells. IL-1β stimulation induces heterodimerization of IL1R1 and IL1RAcP, which further triggers BLK autophosphorylation at Y309. Activated BLK directly phosphorylates TOLLIP at Y76/86/152 and further promotes TOLLIP dissociation from IRAK1, thereby facilitating TLR/IL-1R-mediated signal transduction. Overall, these findings highlight the importance of BLK as an active regulatory component in TLR/IL-1R signaling.

Tyrosine phosphorylation of IRF3 by BLK facilitates its sufficient activation and innate antiviral response

Viral infection triggers the activation of transcription factor IRF3, and its activity is precisely regulated for robust antiviral immune response and effective pathogen clearance. However, how full activation of IRF3 is achieved has not been well defined. Herein, we identified BLK as a key kinase that positively modulates IRF3-dependent signaling cascades and executes a pre-eminent antiviral effect. BLK deficiency attenuates RNA or DNA virus-induced ISRE activation, interferon production and the cellular antiviral response in human and murine cells, whereas overexpression of BLK has the opposite effects. BLK-deficient mice exhibit lower serum cytokine levels and higher lethality after VSV infection. Moreover, BLK deficiency impairs the secretion of downstream antiviral cytokines and promotes Senecavirus A (SVA) proliferation, thereby supporting SVA-induced oncolysis in an in vivo xenograft tumor model. Mechanistically, viral infection triggers BLK autophosphorylation at tyrosine 309. Subsequently, activated BLK directly binds and phosphorylates IRF3 at tyrosine 107, which further promotes TBK1-induced IRF3 S386 and S396 phosphorylation, facilitating sufficient IRF3 activation and downstream antiviral response. Collectively, our findings suggest that targeting BLK enhances viral clearance via specifically regulating IRF3 phosphorylation by a previously undefined mechanism.

Halofuginone ameliorates systemic lupus erythematosus by targeting Blk in myeloid-derived suppressor cells

Systemic lupus erythematosus (SLE) is a multisystemic, inflammatory autoimmune disease. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells participated in the pathogenesis of SLE. MDSCs has been considered a potential therapeutic target for lupus. As traditional Chinese medicine, Halofuginone (HF) has the extensive immunomodulatory effects on some autoimmune disorders. Our research was dedicated to discovering therapeutic efficacy of HF for lupus to explore novel mechanisms on MDSCs. We found that HF prominently alleviated the systemic symptoms especially nephritis in Imiquimod-induced lupus mice, and simultaneously repaired the immune system, reflected in the alteration of autoantibodies. HF diminished the quantity of MDSCs in lupus mice, and induced apoptosis of MDSCs. Through RNA sequencing performed on the sorted MDSC from lupus mice and HF-treated lupus mice, B lymphoid tyrosine kinase (Blk, a non-receptor cytoplasmic tyrosine kinase) was screened as the target molecule of HF. It's proven that HF had two independent effects on Blk. On the one hand, HF increased the mRNA expression of Blk in MDSCs by inhibiting the nuclear translocation of p65/p50 heterodimer. On the other hand, HF enhanced the kinase activity of Blk in MDSCs through direct molecular binding. We further investigated that Blk suppressed the phosphorylation of downstream ERK signaling pathway to increase the apoptosis of MDSCs. In conclusion, our study illustrated that HF alleviated the disease progression of lupus mice by targeting Blk to promote the apoptosis of MDSCs, which indicated the immunotherapeutic potential of HF to treat lupus.

Haplotype-specific chromatin looping reveals genetic interactions of regulatory regions modulating gene expression in 8p23.1

A major goal of genetics research is to elucidate mechanisms explaining how genetic variation contributes to phenotypic variation. The genetic variants identified in genome-wide association studies (GWASs) generally explain only a small proportion of heritability of phenotypic traits, the so-called missing heritability problem. Recent evidence suggests that additional common variants beyond lead GWAS variants contribute to phenotypic variation; however, their mechanistic underpinnings generally remain unexplored. Herein, we undertake a study of haplotype-specific mechanisms of gene regulation at 8p23.1 in the human genome, a region associated with a number of complex diseases. The FAM167A-BLK locus in this region has been consistently found in the genome-wide association studies (GWASs) of systemic lupus erythematosus (SLE) in all major ancestries. Our haplotype-specific chromatin interaction (Hi-C) experiments, allele-specific enhancer activity measurements, genetic analyses, and epigenome editing experiments revealed that: 1) haplotype-specific long-range chromatin interactions are prevalent in 8p23.1; 2) BLK promoter and cis-regulatory elements cooperatively interact with haplotype-specificity; 3) genetic variants at distal regulatory elements are allele-specific modifiers of the promoter variants at FAM167A-BLK; 4) the BLK promoter interacts with and, as an enhancer-like promoter, regulates FAM167A expression and 5) local allele-specific enhancer activities are influenced by global haplotype structure due to chromatin looping. Although systemic lupus erythematosus causal variants at the FAM167A-BLK locus are thought to reside in the BLK promoter region, our results reveal that genetic variants at distal regulatory elements modulate promoter activity, changing BLK and FAM167A gene expression and disease risk. Our results suggest that global haplotype-specific 3-dimensional chromatin looping architecture has a strong influence on local allelic BLK and FAM167A gene expression, providing mechanistic details for how regional variants controlling the BLK promoter may influence disease risk.

A risk variant for Barrett's esophagus and esophageal adenocarcinoma at chr8p23.1 affects enhancer activity and implicates multiple gene targets

Nineteen genetic susceptibility loci for esophageal adenocarcinoma (EAC) and its precursor Barrett's esophagus (BE) have been identified through genome-wide association studies (GWAS). Clinical translation of such discoveries, however, has been hindered by the slow pace of discovery of functional/causal variants and gene targets at these loci. We previously developed a systematic informatics pipeline to prioritize candidate functional variants using functional potential scores, applied the pipeline to select high-scoring BE/EAC risk loci, and validated a functional variant at chr19p13.11 (rs10423674). Here, we selected two additional prioritized loci for experimental interrogation: chr3p13/rs1522552 and chr8p23.1/rs55896564. Candidate enhancer regions encompassing these variants were evaluated using luciferase reporter assays in two EAC cell lines. One of the two regions tested exhibited allele-specific enhancer activity - 8p23.1/rs55896564. CRISPR-mediated deletion of the putative enhancer in EAC cell lines correlated with reduced expression of three candidate gene targets: B lymphocyte kinase (BLK), nei like DNA glycosylase 2 (NEIL2), and cathepsin B (CTSB). Expression quantitative trait locus (eQTL) mapping in normal esophagus and stomach revealed strong associations between the BE/EAC risk allele at rs55896564 (G) and lower expression of CTSB, a protease gene implicated in epithelial wound repair. These results further support the utility of functional potential scores for GWAS variant prioritization, and provide the first experimental evidence of a functional variant and risk enhancer at the 8p23.1 GWAS locus. Identification of CTSB, BLK, and NEIL2 as candidate gene targets suggests that altered expression of these genes may underlie the genetic risk association at 8p23.1 with BE/EAC.

Genetic variants related to systemic lupus erythematosus revealed using bioinformatics

Objectives

Systemic lupus erythematosus (SLE) is an autoimmune disease involving multiple organs and is characterized by immune inflammation. The pathogenesis of SLE is complex and involves genetic and environmental components.

Methods

In this study, single nucleotide polymorphisms (SNPs) closely related to SLE were searched through integration analysis of public gene expression profiles from Gene Expression Omnibus and European Bioinformatics Institute data, and immunochip data in a genome-wide association study.

Results

SLE-associated SNPs were identified in 17 genes common among datasets. The mRNA expression levels of three genes among them were verified to differ between SLE patients and healthy controls subjects based on real-time polymerase chain reaction and sequencing of peripheral blood mononuclear cells (PBMCs). The GG genotype frequency of rs116253043 in LY6G6D was significantly lower in SLE patients and the GC genotype frequency of rs328 on LPL was significantly higher in SLE patients than in controls. VARS2 levels were significantly higher in SLE PBMCs than controls, but there was no significant difference in allele or genotype frequencies of the two SNPs (rs115470445 [C/T] and rs114394807 [A/G]) between groups.

Conclusion

Our results suggest that the GG genotype of rs116253043 plays a protective role against SLE, whereas the C allele of rs328 is a risk factor for SLE and rs116253043 with the GC genotype is an SLE-susceptibility SNP.

Hygiene Hypothesis as the Etiology of Kawasaki Disease: Dysregulation of Early B Cell Development

Kawasaki disease (KD) is an acute systemic vasculitis that occurs predominantly in children under 5 years of age. Despite much study, the etiology of KD remains unknown. However, epidemiological and immunological data support the hygiene hypothesis as a possible etiology. It is thought that more sterile or clean modern living environments due to increased use of sanitizing agents, antibiotics, and formula feeding result in a lack of immunological challenges, leading to defective or dysregulated B cell development, accompanied by low IgG and high IgE levels. A lack of B cell immunity may increase sensitivity to unknown environmental triggers that are nonpathogenic in healthy individuals. Genetic studies of KD show that all of the KD susceptibility genes identified by genome-wide association studies are involved in B cell development and function, particularly in early B cell development (from the pro-B to pre-B cell stage). The fact that intravenous immunoglobulin is an effective therapy for KD supports this hypothesis. In this review, I discuss clinical, epidemiological, immunological, and genetic studies showing that the etiopathogenesis of KD in infants and toddlers can be explained by the hygiene hypothesis, and particularly by defects or dysregulation during early B cell development.

Src Family Protein Kinase Controls the Fate of B Cells in Autoimmune Diseases

There are more than 80 kinds of autoimmune diseases known at present, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), systemic sclerosis (SSc), inflammatory bowel disease (IBD), as well as other disorders. Autoimmune diseases have a characteristic of immune responses directly attacking own tissues, leading to systematic inflammation and subsequent tissue damage. B cells play a vital role in the development of autoimmune diseases and differentiate into plasma cells or memory B cells to secrete high-affinity antibody or provide long-lasting function. Drugs targeting B cells show good therapeutic effects for the treatment of autoimmune diseases, such as rituximab (anti-CD20 antibody). Src family protein kinases (SFKs) are believed to play important roles in a variety of cellular functions such as growth, proliferation, and differentiation of B cell via B cell antigen receptor (BCR). Lck/Yes-related novel protein tyrosine kinase (LYN), BLK (B lymphocyte kinase), and Fyn are three different kinds of SFKs mainly expressed in B cells. LYN has a dual role in the BCR signal. On the one hand, positive signals are beneficial to the development and maturation of B cells. On the other hand, LYN can also inhibit excessively activated B cells. BLK is involved in the proliferation, differentiation, and immune tolerance of B lymphocytes, and further affects the function of B cells, which may lead to autoreactive or regulatory cellular responses, increasing the risk of autoimmune diseases. Fyn may affect the development of autoimmune disorders via the differentiation of B cells in the early stage of B cell development. This article reviews the recent advances of SFKs in B lymphocytes in autoimmune diseases.

Association of BLK and BANK1 Polymorphisms and Interactions With Rheumatoid Arthritis in a Latin-American Population

Introduction

BLK has been identified as a risk factor to rheumatoid arthritis (RA) primarily in Asian or European-derived populations. However, this finding has not been evaluated in other populations such as Latin-Americans, except for Colombians. On the other hand, BANK1 single nucleotide variants (SNVs) have been scarcely studied in RA patients.

Objective

The aim of this study was to determine whether the BLK rs2736340T/C, rs13277113A/G, and BANK1 rs10516487G/A (R61H) and rs3733197G/A (A383T) polymorphisms are risk factors to RA in a sample of patients from Central Mexico.

Materials and Methods

We studied 957 women; 487 controls and 470 patients with RA by means of a TaqMan® SNP genotyping assay with fluorescent probes for the BLK rs13277113A/G, rs2736340T/C and BANK1 10516487G/A (R61H) and rs3733197G/A (A383T) variants.

Result

The BLK rs2736340T/C and rs13277113A/G variants were associated with risk for RA: C vs T; OR 1.39, p = 0.001, and G vs A; OR 1.37, p = 0.004, respectively. In addition, there was also an association between BANK1 R61H and RA: A vs G; OR 1.49, p = 0.003, but no with BANK1 A383T. We also identified an interaction significant between genotypes of BLK rs2736340T/C-BANK1 rs10516487G/A and RA: OR 1.65, p = 0.0001.

Conclusions

Our data suggest that both BLK and BANK1 confer susceptibility to RA in Mexican patients. The individual association of BANK1 rs1054857G/A with RA had not been previously reported in a particular population (except for pooled patients from several countries), therefore, our study presents the first evidence of association between this BANK1 variant and RA.

Functional rare and low frequency variants in BLK and BANK1 contribute to human lupus

Systemic lupus erythematosus (SLE) is the prototypic systemic autoimmune disease. It is thought that many common variant gene loci of weak effect act additively to predispose to common autoimmune diseases, while the contribution of rare variants remains unclear. Here we describe that rare coding variants in lupus-risk genes are present in most SLE patients and healthy controls. We demonstrate the functional consequences of rare and low frequency missense variants in the interacting proteins BLK and BANK1, which are present alone, or in combination, in a substantial proportion of lupus patients. The rare variants found in patients, but not those found exclusively in controls, impair suppression of IRF5 and type-I IFN in human B cell lines and increase pathogenic lymphocytes in lupus-prone mice. Thus, rare gene variants are common in SLE and likely contribute to genetic risk.

Function-altering variants of immune-related genes cause rare autoimmune syndromes, whereas their contribution to common autoimmune diseases remains uncharacterized. Here the authors show that rare variants of lupus-associated genes are present in the majority of lupus patients and healthy controls, but only the variants found in lupus patients alter gene function.

The rheumatic disease-associated FAM167A-BLK locus encodes DIORA-1, a novel disordered protein expressed highly in bronchial epithelium and alveolar macrophages

Triggering of autoimmunity that leads to rheumatic disease has been suggested to depend upon gene-environment interactions occurring in epithelial barriers and associated immune cells. Genetic studies have identified associations of the FAM167A-BLK locus with rheumatoid arthritis, systemic lupus erythematosus (SLE) and Sjögren's syndrome. While BLK (B lymphocyte kinase) has a well-established role in B cells, family with sequence similarity to 167 member A (FAM167A) and its gene family remain uncharacterized. To begin to understand the role of FAM167A in rheumatic disease pathogenesis, we explored this gene family and cloned and investigated the gene products. Expression of quantitative trait locus analysis was performed in immune cells. FAM167A and FAM167B were cloned from human peripheral blood mononuclear cells (PBMC). Gene conservation and protein properties were analysed by online tools, mRNA expression measured in mouse organs by quantitative polymerase chain reaction (qPCR) and protein expression investigated in human tissues by immunohistochemistry. We found that autoimmune risk genotypes within the FAM167A-BLK locus lead to increased expression of FAM167A. The FAM167 gene family includes two members, FAM167A and FAM167B, which are not homologous to any other annotated gene but are evolutionarily conserved. The encoded proteins, which we denote 'disordered autoimmunity' (DIORA)-1 and DIORA-2, respectively, are characterized by a high content of intrinsic disorder. Notably, DIORA-1 has its highest expression in the lung, detectable in both bronchial epithelium and alveolar macrophages with an endosomal localization pattern. In summary, the FAM167A gene is associated with several rheumatic diseases and encodes a novel disordered protein, DIORA-1, which is expressed highly in the lung, consistent with a potential role in disease pathogenesis.

Plasma Cell Differentiation Pathways in Systemic Lupus Erythematosus

Plasma cells (PCs) are responsible for the production of protective antibodies against infectious agents but they also produce pathogenic antibodies in autoimmune diseases, such as systemic lupus erythematosus (SLE). Traditionally, high affinity IgG autoantibodies are thought to arise through germinal center (GC) responses. However, class switching and somatic hypermutation can occur in extrafollicular (EF) locations, and this pathway has also been implicated in SLE. The pathway from which PCs originate may determine several characteristics, such as PC lifespan and sensitivity to therapeutics. Although both GC and EF responses have been implicated in SLE, we hypothesize that one of these pathways dominates in each individual patient and genetic risk factors may drive this predominance. While it will be important to distinguish polymorphisms that contribute to a GC-driven or EF B cell response to develop targeted treatments, the challenge will be not only to identify the differentiation pathway but the molecular mechanisms involved. In B cells, this task is complicated by the cross-talk between the B cell receptor, toll-like receptors (TLR), and cytokine signaling molecules, which contribute to both GC and EF responses. While risk variants that affect the function of dendritic cells and T follicular helper cells are likely to primarily influence GC responses, it will be important to discover whether some risk variants in the interferon and TLR pathways preferentially influence EF responses. Identifying the pathways of autoreactive PC differentiation in SLE may help us to understand patient heterogeneity and thereby guide precision therapy.

CD4+ and B Lymphocyte Expression Quantitative Traits at Rheumatoid Arthritis Risk Loci in Patients With Untreated Early Arthritis: Implications for Causal Gene Identification

OBJECTIVE

Rheumatoid arthritis (RA) is a genetically complex disease of immune dysregulation. This study sought to gain further insight into the genetic risk mechanisms of RA by conducting an expression quantitative trait locus (eQTL) analysis of confirmed genetic risk loci in CD4+ T cells and B cells from carefully phenotyped patients with early arthritis who were naive to therapeutic immunomodulation.

METHODS

RNA and DNA were isolated from purified B and/or CD4+ T cells obtained from the peripheral blood of 344 patients with early arthritis. Genotyping and global gene expression measurements were carried out using Illumina BeadChip microarrays. Variants in linkage disequilibrium (LD) with non-HLA RA single-nucleotide polymorphisms (defined as r2 ≥ 0.8) were analyzed, seeking evidence of cis- or trans-eQTLs according to whether the associated probes were or were not within 4 Mb of these LD blocks.

RESULTS

Genes subject to cis-eQTL effects that were common to both CD4+ and B lymphocytes at RA risk loci were FADS1, FADS2, BLK, FCRL3, ORMDL3, PPIL3, and GSDMB. In contrast, those acting on METTL21B, JAZF1, IKZF3, and PADI4 were unique to CD4+ lymphocytes, with the latter candidate risk gene being identified for the first time in this cell subset. B lymphocyte-specific eQTLs for SYNGR1 and CD83 were also found. At the 8p23 BLK-FAM167A locus, adjacent genes were subject to eQTLs whose activity differed markedly between cell types; in particular, the FAM167A effect displayed striking B lymphocyte specificity. No trans-eQTLs approached experiment-wide significance, and linear modeling did not identify a significant influence of biologic covariates on cis-eQTL effect sizes.

CONCLUSION

These findings further refine the understanding of candidate causal genes in RA pathogenesis, thus providing an important platform from which downstream functional studies, directed toward particular cell types, may be prioritized.

Immunological function of Blimp-1 in dendritic cells and relevance to autoimmune diseases

Previous studies have identified the immunological functions of transcription factor B lymphocyte-induced maturation protein-1 (Blimp-1) in various adaptive immune cell types such as T and B lymphocytes. More recently, it has been shown that Blimp-1 extends its functional roles to dendritic cells (DCs) and macrophages, two cell types belonging to the innate immune system. The protein acts as a direct and indirect regulator of target genes by recruiting chromatin modification factors and by regulating microRNA expression, respectively. In DCs, Blimp-1 has been identified as one of the components involved in antigen presentation. Genome-wide association studies identified polymorphisms associated with multiple autoimmune diseases such as system lupus erythematosus, rheumatoid arthritis, and inflammatory bowel disease in PRDM1, the gene encoding Blimp-1 protein. In this review, we will discuss the immune regulatory functions of Blimp-1 in DCs with a main focus on the tolerogenic mechanisms of Blimp-1 required to protect against the development of autoimmune diseases.

DNA-reactive B cells in lupus

IgG anti-DNA antibodies are both diagnostic and pathogenic for systemic lupus erythematosus (SLE). They contribute to tissue inflammation through direct tissue binding and to systemic inflammation through activation of Toll-like receptors by nucleic acid-containing immune complexes. IgG DNA-reactive antibodies originate when B cell tolerance mechanisms are impaired. The heterogeneous immune perturbations in SLE lead to the survival and activation of DNA-reactive B cells in various B cell subsets at distinct stages of B cell maturation and differentiation. We propose that the spectrum of B cell alterations and failed tolerance mechanisms for DNA-reactive B cells in lupus patients is best understood by studying genetic risk alleles. This implies that the B cells producing IgG anti-DNA antibodies and the failed tolerance mechanisms(s) will differ across patients. A better understanding of these differences should lead to better patient stratification, improved outcomes of clinical trials, and the identification of novel therapeutic targets.

Recent Advances in Defining the Genetic Basis of Rheumatoid Arthritis

Rheumatoid arthritis (RA) is the most common inflammatory arthritis and exhibits genetic overlap with other autoimmune and inflammatory disorders. Although predominant associations with the HLA-DRB1 locus have been known for decades, recent data have revealed additional insight into the likely causative variants within HLA-DRB1 as well as within other HLA loci that contribute to disease risk. In addition, more than 100 common variants in non-HLA loci have been implicated in disease susceptibility. Genetic factors are involved not only in the development of RA, but also with various disease subphenotypes, including production and circulating levels of autoantibodies and joint destruction. The major current challenge is to integrate these new data into a precise understanding of disease pathogenesis, including the critical cell types and molecular networks involved as well as interactions with environmental factors. We predict that delineating the functional effects of genetic variants is likely to drive new diagnostic and therapeutic approaches to the disease.

Autoimmune disease-associated haplotypes of BLK exhibit lowered thresholds for B cell activation and expansion of Ig class-switched B cells

OBJECTIVE

B lymphoid kinase (BLK) is associated with rheumatoid arthritis (RA) and several other B cell-associated autoimmune disorders. BLK risk variants are consistently associated with reduced BLK expression, but the mechanisms by which reduced expression alters human B cell function to confer autoimmune disease susceptibility are unknown. This study was undertaken to characterize the BLK risk haplotype and to determine associated B cell functional phenotypes involved in autoimmunity.

METHODS

The BLK risk haplotype association with RA (determined using whole-genome sequencing data) was confirmed in 2,526 RA cases and 2,134 controls. Peripheral blood mononuclear cells (PBMCs) from RA patients, healthy adults, and umbilical cord blood were used to study B cell functional phenotypes associated with the BLK risk genotype. Association of the BLK haplotype with B cell phenotypes was analyzed using cell culture and flow cytometry.

RESULTS

Two insertion/deletions were found on the RA risk haplotype in BLK, and the reduction in BLK expression associated with the risk haplotype was confirmed in primary B lymphocytes. Carriers of the RA-associated haplotype had evidence of lower basal B cell receptor (BCR) signaling activity, yet their B cells were hyperactivatable, with enhanced up-regulation of CD86 after BCR crosslinking and greater T cell stimulatory capacity. The number of isotype-switched memory B cells was also significantly increased in subjects carrying the risk haplotype.

CONCLUSION

A major mechanism underlying the BLK association with autoimmune disease involves lowered thresholds for BCR signaling, enhanced B cell-T cell interactions, and altered patterns of isotype switching.

The SLE variant Ala71Thr of BLK severely decreases protein abundance and binding to BANK1 through impairment of the SH3 domain function

The B-lymphocyte kinase (BLK) gene is associated genetically with several human autoimmune diseases including systemic lupus erythematosus. We recently described that the genetic risk is given by two haplotypes: one covering several strongly linked single-nucleotide polymorphisms within the promoter of the gene that correlated with low transcript levels, and a second haplotype that includes a rare nonsynonymous variant (Ala71Thr). Here we show that this variant, located within the BLK SH3 domain, is a major determinant of protein levels. In vitro analyses show that the 71Thr isoform is hyperphosphorylated and promotes kinase activation. As a consequence, BLK is ubiquitinated, its proteasomal degradation enhanced and the average life of the protein is reduced by half. Altogether, these findings suggest that an intrinsic autoregulatory mechanism previously unappreciated in BLK is disrupted by the 71Thr substitution. Because the SH3 domain is also involved in protein interactions, we sought for differences between the two isoforms in trafficking and binding to protein partners. We found that binding of the 71Thr variant to the adaptor protein BANK1 is severely reduced. Our study provides new insights on the intrinsic regulation of BLK activation and highlights the dominant role of its SH3 domain in BANK1 binding.

The Genotype and Phenotype (GaP) registry: a living biobank for the analysis of quantitative traits

We describe the development of the Genotype and Phenotype (GaP) Registry, a living biobank of normal volunteers who are genotyped for genetic markers related to human disease. Participants in the GaP can be recalled for hypothesis driven study of disease associated genetic variants. The GaP has facilitated functional studies of several autoimmune disease associated loci including Csk, Blk, PDRM1 (Blimp-1) and PTPN22. It is likely that expansion of such living biobank registries will play an important role in studying and understanding the function of disease associated alleles in complex disease.

Concordance of increased B1 cell subset and lupus phenotypes in mice and humans is dependent on BLK expression levels

Polymorphisms in the B lymphoid tyrosine kinase (BLK) gene have been associated with autoimmune diseases, including systemic lupus erythematosus, with risk correlating with reduced expression of BLK. How reduced expression of BLK causes autoimmunity is unknown. Using Blk(+/+) , Blk(+/-) , and Blk(-/-) mice, we show that aged female Blk(+/-) and Blk(-/-) mice produced higher anti-dsDNA IgG Abs and developed immune complex-mediated glomerulonephritis, compared with Blk(+/+) mice. Starting at young age, Blk(+/-) and Blk(-/-) mice accumulated increased numbers of splenic B1a cells, which differentiated into class-switched CD138(+) IgG-secreting B1a cells. Increased infiltration of B1a-like cells into the kidneys was also observed in aged Blk(+/-) and Blk(-/-) mice. In humans, we found that healthy individuals had BLK genotype-dependent levels of anti-dsDNA IgG Abs as well as increased numbers of a B1-like cell population, CD19(+)CD3(-)CD20(+)CD43(+)CD27(+), in peripheral blood. Furthermore, we describe the presence of B1-like cells in the tubulointerstitial space of human lupus kidney biopsies. Taken together, our study reveals a previously unappreciated role of reduced BLK expression on extraperitoneal accumulation of B1a cells in mice, as well as the presence of IgG autoantibodies and B1-like cells in humans.

Integration of disease association and eQTL data using a Bayesian colocalisation approach highlights six candidate causal genes in immune-mediated diseases

The genes and cells that mediate genetic associations identified through genome-wide association studies (GWAS) are only partially understood. Several studies that have investigated the genetic regulation of gene expression have shown that disease-associated variants are over-represented amongst expression quantitative trait loci (eQTL) variants. Evidence for colocalisation of eQTL and disease causal variants can suggest causal genes and cells for these genetic associations. Here, we used colocalisation analysis to investigate whether 595 genetic associations to ten immune-mediated diseases are consistent with a causal variant that regulates, in cis, gene expression in resting B cells, and in resting and stimulated monocytes. Previously published candidate causal genes were over-represented amongst genes exhibiting colocalisation (odds ratio > 1.5), and we identified evidence for colocalisation (posterior odds > 5) between cis eQTLs in at least one cell type and at least one disease for six genes: ADAM15, RGS1, CARD9, LTBR, CTSH and SYNGR1. We identified cell-specific effects, such as for CTSH, the expression of which in monocytes, but not in B cells, may mediate type 1 diabetes and narcolepsy associations in the chromosome 15q25.1 region. Our results demonstrate the utility of integrating genetic studies of disease and gene expression for highlighting causal genes and cell types.

Two functional lupus-associated BLK promoter variants control cell-type- and developmental-stage-specific transcription

Efforts to identify lupus-associated causal variants in the FAM167A/BLK locus on 8p21 are hampered by highly associated noncausal variants. In this report, we used a trans-population mapping and sequencing strategy to identify a common variant (rs922483) in the proximal BLK promoter and a tri-allelic variant (rs1382568) in the upstream alternative BLK promoter as putative causal variants for association with systemic lupus erythematosus. The risk allele (T) at rs922483 reduced proximal promoter activity and modulated alternative promoter usage. Allelic differences at rs1382568 resulted in altered promoter activity in B progenitor cell lines. Thus, our results demonstrated that both lupus-associated functional variants contribute to the autoimmune disease association by modulating transcription of BLK in B cells and thus potentially altering immune responses.

Reduced B lymphoid kinase (Blk) expression enhances proinflammatory cytokine production and induces nephrosis in C57BL/6-lpr/lpr mice

BLK, which encodes B lymphoid kinase, was recently identified in genome wide association studies as a susceptibility gene for systemic lupus erythematosus (SLE), and risk alleles mapping to the BLK locus result in reduced gene expression. To determine whether BLK is indeed a bona fide susceptibility gene, we developed an experimental mouse model, namely the Blk^+/−.lpr/lpr (Blk^+/−.lpr) mouse, in which Blk expression levels are reduced to levels comparable to those in individuals carrying a risk allele. Here, we report that Blk is expressed not only in B cells, but also in IL-17-producing γδ and DN αβ T cells and in plasmacytoid dendritic cells (pDCs). Moreover, we found that solely reducing Blk expression in C57BL/6-lpr/lpr mice enhanced proinflammatory cytokine production and accelerated the onset of lymphoproliferation, proteinuria, and kidney disease. Together, these findings suggest that BLK risk alleles confer susceptibility to SLE through the dysregulation of a proinflammatory cytokine network.

Association between a C8orf13-BLK polymorphism and polymyositis/dermatomyositis in the Japanese population: an additive effect with STAT4 on disease susceptibility

Background

Accumulating evidence has shown that several non-HLA genes are involved in the susceptibility to polymyositis/dermatomyositis. This study aimed to investigate the involvement of C8orf13–BLK, one of the strongest candidate genes for autoimmune diseases, in susceptibility to polymyositis/dermatomyositis in the Japanese population. A possible gene–gene interaction between C8orf13–BLK and STAT4, which we recently showed to be associated with Japanese polymyositis/dermatomyositis, was also analyzed.

Methods

A single-nucleotide polymorphism in C8orf13–BLK (dbSNP ID: rs13277113) was investigated in the Japanese population using a TaqMan assay in 283 polymyositis patients, 194 dermatomyositis patients, and 656 control subjects.

Results

The C8orf13–BLK rs13277113A allele was associated with overall polymyositis/dermatomyositis (P<0.001, odds ratio [OR] 1.44, 95% confidence interval [CI] 1.19–1.73), as well as polymyositis (P = 0.011, OR 1.32, 95% CI 1.06–1.64) and dermatomyositis (P<0.001, OR 1.64, 95% CI 1.26–2.12). No association was observed between the C8orf13–BLK rs13277113A allele and either interstitial lung disease or anti-Jo-1 antibody positivity. The C8orf13–BLK rs13277113 A and STAT4 rs7574865 T alleles had an additive effect on polymyositis/dermatomyositis susceptibility. The strongest association was observed in dermatomyositis, with an OR of 3.07 (95% CI; 1.57–6.02) for the carriers of four risk alleles at the two SNP sites, namely, rs1327713 and rs7574865.

Conclusions

This study established C8orf13–BLK as a new genetic susceptibility factor for polymyositis/dermatomyositis. Both C8orf13–BLK and STAT4 exert additive effects on disease susceptibility. These observations suggested that C8orf13–BLK, in combination with STAT4, plays a pivotal role in creating genetic susceptibility to polymyositis/dermatomyositis in Japanese individuals.

Genome-wide association study of dermatomyositis reveals genetic overlap with other autoimmune disorders

OBJECTIVE

To identify new genetic associations with juvenile and adult dermatomyositis (DM).

METHODS

We performed a genome-wide association study (GWAS) of adult and juvenile DM patients of European ancestry (n = 1,178) and controls (n = 4,724). To assess genetic overlap with other autoimmune disorders, we examined whether 141 single-nucleotide polymorphisms (SNPs) outside the major histocompatibility complex (MHC) locus, and previously associated with autoimmune diseases, predispose to DM.

RESULTS

Compared to controls, patients with DM had a strong signal in the MHC region consisting of GWAS-level significance (P < 5 × 10(-8)) at 80 genotyped SNPs. An analysis of 141 non-MHC SNPs previously associated with autoimmune diseases showed that 3 SNPs linked with 3 genes were associated with DM, with a false discovery rate (FDR) of <0.05. These genes were phospholipase C-like 1 (PLCL1; rs6738825, FDR = 0.00089), B lymphoid tyrosine kinase (BLK; rs2736340, FDR = 0.0031), and chemokine (C-C motif) ligand 21 (CCL21; rs951005, FDR = 0.0076). None of these genes was previously reported to be associated with DM.

CONCLUSION

Our findings confirm the MHC as the major genetic region associated with DM and indicate that DM shares non-MHC genetic features with other autoimmune diseases, suggesting the presence of additional novel risk loci. This first identification of autoimmune disease genetic predispositions shared with DM may lead to enhanced understanding of pathogenesis and novel diagnostic and therapeutic approaches.

Variants at multiple loci implicated in both innate and adaptive immune responses are associated with Sjögren's syndrome

Sjögren’s syndrome is a common autoimmune disease (~0.7% of European Americans) typically presenting as keratoconjunctivitis sicca and xerostomia. In addition to strong association within the HLA region at 6p21 (P_meta=7.65×10⁻¹¹⁴), we establish associations with IRF5-TNPO3 (P_meta=2.73×10⁻¹⁹), STAT4 (P_meta=6.80×10⁻¹⁵), IL12A (P_meta =1.17×10⁻¹⁰), FAM167A-BLK (P_meta=4.97×10⁻¹⁰), DDX6-CXCR5 (P_meta=1.10×10⁻⁸), and TNIP1 (P_meta=3.30×10⁻⁸). Suggestive associations with P_meta<5×10⁻⁵ were observed with 29 regions including TNFAIP3, PTTG1, PRDM1, DGKQ, FCGR2A, IRAK1BP1, ITSN2, and PHIP amongst others. These results highlight the importance of genes involved in both innate and adaptive immunity in Sjögren’s syndrome.

On the structural plasticity of the human genome: chromosomal inversions revisited

With the aid of novel and powerful molecular biology techniques, recent years have witnessed a dramatic increase in the number of studies reporting the involvement of complex structural variants in several genomic disorders. In fact, with the discovery of Copy Number Variants (CNVs) and other forms of unbalanced structural variation, much attention has been directed to the detection and characterization of such rearrangements, as well as the identification of the mechanisms involved in their formation. However, it has long been appreciated that chromosomes can undergo other forms of structural changes - balanced rearrangements - that do not involve quantitative variation of genetic material. Indeed, a particular subtype of balanced rearrangement – inversions – was recently found to be far more common than had been predicted from traditional cytogenetics. Chromosomal inversions alter the orientation of a specific genomic sequence and, unless involving breaks in coding or regulatory regions (and, disregarding complex trans effects, in their close vicinity), appear to be phenotypically silent. Such a surprising finding, which is difficult to reconcile with the classical interpretation of inversions as a mechanism causing subfertility (and ultimately reproductive isolation), motivated a new series of theoretical and empirical studies dedicated to understand their role in human genome evolution and to explore their possible association to complex genetic disorders. With this review, we attempt to describe the latest methodological improvements to inversions detection at a genome wide level, while exploring some of the possible implications of inversion rearrangements on the evolution of the human genome.

Integrative analyses for functional mechanisms underlying associations for rheumatoid arthritis

OBJECTIVE

Extensive association analyses including genome-wide association studies (GWAS) and powerful metaanalysis studies have identified a long list of loci associated with rheumatoid arthritis (RA) in very large populations, but most of them established statistical associations of genetic markers and RA only at the DNA level, without supporting evidence of functional relevance. Our study serves as a trial to detect the functional mechanisms underlying associations for RA by searching publicly available datasets and results.

METHODS

Based on publicly available datasets and results, we performed integrative analyses (gene relationships across implicated loci analysis, differential gene expression analysis, and functional annotation clustering analysis) and combined them with the expression quantitative trait locus (eQTL) results to dissect functional mechanisms underlying the associations for RA.

RESULTS

By searching 2 GWAS, Integrator and PheGenI, we selected 98 RA association results (p < 10(-5)). Among these associations, we found that 8 single-nucleotide polymorphisms (SNP; rs1600249, rs2736340, rs3093023, rs3093024, rs4810485, rs615672, rs660895, and rs9272219) serve as cis-effect regulators of the corresponding eQTL genes (BLK and CD4 in non-HLA region; CCR6, HLA-DQA1, and HLA-DQB1 in HLA region) that also were differentially expressed in RA-related cell groups. These 5 genes are closely related with immune response in function.

CONCLUSION

Our results showed the functional mechanisms underlying the associations of 8 SNP and the corresponding genes. This study is an example of mining publicly available datasets and results in validation of significant disease-association results. Using public data resources for integrative analyses may provide insights into the molecular genetic mechanisms underlying human diseases.

CSK regulatory polymorphism is associated with systemic lupus erythematosus and influences B-cell signaling and activation

C-src tyrosine kinase, Csk, physically interacts with the intracellular phosphatase Lyp (PTPN22) and can modify the activation state of downstream Src kinases, such as Lyn, in lymphocytes. We identified an association of Csk with systemic lupus erythematosus (SLE) and refined its location to an intronic polymorphism rs34933034 (OR 1.32, p = 1.04 × 10⁻⁹). The risk allele is associated with increased CSK expression and augments inhibitory phosphorylation of Lyn. In carriers of the risk allele, B cell receptor (BCR)-mediated activation of mature B cells, as well as plasma IgM, are increased. Moreover, the fraction of transitional B cells is doubled in the cord blood of carriers of the risk allele compared to non-risk haplotypes due to an expansion of the late transitional cells, a stage targeted by selection mechanisms. This suggests that the Lyp-Csk complex increases susceptibility to lupus at multiple maturation and activation points of B cells.

GWAS implicates a role for quantitative immune traits and threshold effects in risk for human autoimmune disorders

Genome wide association studies in human autoimmune disorders have provided a long list of alleles with rather modest degrees of risk. A large fraction of these associations are probably owing to either quantitative differences in gene expression or amino acid changes that regulate quantitative aspects of the immune response. While functional studies are still lacking for most of these associations, we present examples of autoimmune disease risk alleles that influence quantitative changes in lymphocyte activation, cytokine signaling and dendritic cell function. The analysis of immune quantitative traits associated with autoimmune loci is clearly going to be an important component of understanding the pathogenesis of autoimmunity. This will require both new and more efficient ways of characterizing the normal immune system, as well as large population resources in which genotype-phenotype correlations can be convincingly demonstrated. Future development of new therapies will depend on understanding the mechanistic underpinnings of immune regulation by these new risk loci.