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Identification of the rheumatoid arthritis shared epitope binding site on calreticulin.

ABSTRACT: BACKGROUND:The rheumatoid arthritis (RA) shared epitope (SE), a major risk factor for severe disease, is a five amino acid motif in the third allelic hypervariable region of the HLA-DRbeta chain. The molecular mechanisms by which the SE affects susceptibility to--and severity of--RA are unknown. We have recently demonstrated that the SE acts as a ligand that interacts with cell surface calreticulin (CRT) and activates innate immune signaling. In order to better understand the molecular basis of SE-RA association, here we have undertaken to map the SE binding site on CRT. PRINCIPAL FINDINGS:Surface plasmon resonance (SPR) experiments with domain deletion mutants suggested that the SE binding site is located in the P-domain of CRT. The role of this domain as a SE-binding region was further confirmed by a sulfosuccinimidyl-2-[6-(biotinamido)-2-(p-azido-benzamido) hexanoamido] ethyl-1,3-dithiopropionate (sulfo-SBED) photoactive cross-linking method. In silico analysis of docking interactions between a conformationally intact SE ligand and the CRT P-domain predicted the region within amino acid residues 217-224 as a potential SE binding site. Site-directed mutagenesis demonstrated involvement of residues Glu(217) and Glu(223)--and to a lesser extent residue Asp(220)--in cell-free SPR-based binding and signal transduction assays. SIGNIFICANCE:We have characterized here the molecular basis of a novel ligand-receptor interaction between the SE and CRT. The interaction represents a structurally and functionally well-defined example of cross talk between the adaptive and innate immune systems that could advance our understanding of the pathogenesis of autoimmunity.

SUBMITTER: Ling S

PROVIDER: S-EPMC2908537 | biostudies-literature | 2010 Jul

REPOSITORIES: biostudies-literature

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Identification of the rheumatoid arthritis shared epitope binding site on calreticulin.

Ling Song S Cheng Andrew A Pumpens Paul P Michalak Marek M Holoshitz Joseph J

PloS one 20100722 7

<h4>Background</h4>The rheumatoid arthritis (RA) shared epitope (SE), a major risk factor for severe disease, is a five amino acid motif in the third allelic hypervariable region of the HLA-DRbeta chain. The molecular mechanisms by which the SE affects susceptibility to--and severity of--RA are unknown. We have recently demonstrated that the SE acts as a ligand that interacts with cell surface calreticulin (CRT) and activates innate immune signaling. In order to better understand the molecular b ...[more]

PMID: 20661469

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Project description:IntroductionShared epitope (SE) is present in high proportions of anti-citrullinated protein antibody (ACPA) + patients with rheumatoid arthritis (RA) and is associated with poor prognosis. We assessed the role of SE in RA prognosis, in relation to ACPA positivity.MethodsPatients enrolled in the Brigham and Women's RA Sequential Study were included. Changes from baseline in disease activity (Disease Activity Score in 28 joints using C-reactive protein [DAS28 (CRP)], Clinical Disease Activity Index [CDAI], Simplified Disease Activity Index [SDAI]) to 1 year were assessed. Baseline characteristics were compared by SE and ACPA status (±; chi-squared, Kruskal-Wallis). Association between number of SE alleles and ACPA status (logistic regression models), relationships between baseline characteristics and changes in disease activity (adjusted linear regression model), and effect of ACPA on the association between SE and changes in disease activity (mediation analysis) were studied.ResultsNine hundred twenty-six patients were included. SE + versus SE - patients had significantly longer disease duration and higher disease activity scores and were more likely to have erosive disease, have higher comorbidity burden, and be RF + (all p < 0.05). Among patients with one or two SE alleles (vs. 0), odds of being ACPA + were 1.97 (p = 0.0003) and 3.82 (p < 0.0001), respectively. SE + versus SE - patients had worse disease activity scores as indicated by mean increases in DAS28 (CRP) of 0.22, CDAI of 2.07, and SDAI of 2.43 over 1 year (all p < 0.05). Direct effect of SE + accounted for 76.4-80.1% of total effect in disease activity increases.ConclusionsSE is strongly associated with ACPA positivity and higher disease activity in patients with RA. SE was associated with greater increases in disease activity over 1 year, which was partially mediated by the presence of ACPA.Trial registrationClinicalTrials.gov identifier: NCT01793103; registration date: February 15, 2013, retrospectively registered.

Project description:ObjectivesThe human leukocyte antigen-shared epitope (HLA-SE) alleles and smoking are the most prominent genetic and environmental risk factors for rheumatoid arthritis (RA). However, at which pre-arthritis stage (asymptomatic/symptomatic) they exert their effect is unknown. We aimed to determine whether HLA-SE and smoking are involved in the onset of autoantibody positivity, symptoms (clinically suspect arthralgia (CSA)) and/or progression to clinical arthritis.MethodsWe performed meta-analyses on results from the literature on associations of HLA-SE and smoking with anti-citrullinated protein antibodies (ACPAs) in the asymptomatic population. Next, we studied associations of HLA-SE and smoking with autoantibody positivity at CSA onset and with progression to clinical inflammatory arthritis (IA) during follow-up. Associations in ACPA-positive patients with CSA were validated in meta-analyses with other arthralgia cohorts. Analyses were repeated for rheumatoid factor (RF), anti-carbamylated protein antibodies (anti-CarP) and anti-acetylated protein antibodies (AAPA).ResultsMeta-analyses showed that HLA-SE is not associated with ACPA positivity in the asymptomatic population (OR 1.06 (95% CI:0.69 to 1.64)), whereas smoking was associated (OR 1.37 (95% CI: 1.15 to 1.63)). At CSA onset, both HLA-SE and smoking associated with ACPA positivity (OR 2.08 (95% CI: 1.24 to 3.49), OR 2.41 (95% CI: 1.31 to 4.43)). During follow-up, HLA-SE associated with IA development (HR 1.86 (95% CI: 1.23 to 2.82)), in contrast to smoking. This was confirmed in meta-analyses in ACPA-positive arthralgia (HR 1.52 (95% CI: 1.08 to 2.15)). HLA-SE and smoking were not associated with RF, anti-CarP or AAPA-positivity at CSA onset. Longitudinally, AAPA associated with IA development independent from ACPA and RF (HR 1.79 (95% CI: 1.02 to 3.16)), anti-CarP did not.ConclusionsHLA-SE and smoking act at different stages: smoking confers risk for ACPA and symptom development, whereas HLA-SE mediates symptom and IA development. These data enhance the understanding of the timing of the key risk factors in the development of RA.

Dataset Information

Identification of the rheumatoid arthritis shared epitope binding site on calreticulin.

Publications

Identification of the rheumatoid arthritis shared epitope binding site on calreticulin.

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