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TNFAIP3 (A20) and Susceptibility to Systemic Lupus Erythematosus

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Systemic lupus erythematosus (SLE) is characterized by a loss of immunologic tolerance to a multitude of self-antigens. Widespread innate and adaptive immune dysfunction includes interferon pathway dysregulation, high titer autoantibody production, and deficiencies in complement function and immune complex clearance. Inflammatory processes result in systemic end-organ damage. Despite decades of research, the underlying genetic basis of lupus is clearly complex and incompletely understood. Our laboratory identified TNFAIP3, a potent negative regulator of NF-?B signaling, as an SLE risk gene. In addition to SLE, genetic variants in the region of TNFAIP3 are associated rheumatoid arthritis, psoriasis, Crohn's disease, celiac disease, type 1 diabetes, Sjogren's syndrome, systemic sclerosis and juvenile rheumatoid arthritis suggesting that TNFAIP3 is a master regulator of autoimmunity. Therefore, clarifying the mechanisms that regulate TNFAIP3 expression and function are likely to have broad impact on human health. By fine mapping in SLE cohorts of multiple ethnicities and deep sequencing of TNFAIP3 risk haplotypes, we isolated two functional variants (rs148314165, rs200820567) responsible for association with SLE in the region of TNFAIP3. We showed that rs148314165 and rs200820567 (referred to as the TT>A variants) reside in an enhancer element that binds NF-?B and SATB1 enabling the interaction of the enhancer with the TNFAIP3 promoter through long-range DNA looping. Impaired binding of NF-?B to the enhancer harboring the TT>A risk allele, inhibits interaction of the enhancer with the TNFAIP3 promoter resulting in reduced A20 expression. These results reveal a novel functional mechanism by which rs148314165 and rs200820567 attenuate A20 expression and support a causal role for these variants in the predisposition to autoimmune disease. The primary scientific objective of this proposal will be to build upon these discoveries by elucidating mechanisms of TNFAIP3 transcriptional control that influence autoimmune disease risk. In the next funding period we will define the dynamic chromatin state for the TT>A enhancer and other SLE enhancers in primary B cells following stimulation using ChIP-sequencing (Aim 1), characterize the transcription factors and chromatin modifiers that assemble on the TT>A enhancer (Aim 2) and explore the functional effect of a putative novel enhancer 55 kb upstream of the TNFAIP3 promoter (Aim 3). All of these studies will be performed in the context of the SLE risk and nonrisk haplotypes to maximize the clinical relevance of our findings. These studies will serve to clarify new functional mechanisms that regulate TNFAIP3 expression and lay the groundwork for developing of rational therapeutics to restore homeostatic potency of TNFAIP3 in autoimmune disease.
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