Background/Purpose: Genome-wide association studies have identified a strong association between a single risk haplotype of the UBE2L3gene and Systemic Lupus Erythematosus (SLE), as well as multiple autoimmune diseases (rheumatoid arthritis, juvenile idiopathic arthritis, inflammatory bowel disease, psoriasis). UBE2L3 is an E2 ubiquitin-conjugating enzyme specific for RING/HECT hybrid or HECT E3 ligases. Linear ubiquitination is a newly described form of ubiquitination, whose only known function is controlling activation of NF-kB, mediated by the linear ubiquitination chain assembly complex (LUBAC).

Methods: UBE2L3 genotype data from GWAS in SLE was imputed up to 1000 Genomes level. UBE2L3 function was studied in vitro using standard molecular biology techniques in HEK293 cells, or ex vivo using B cells and/or monocytes from healthy individuals or SLE patients (NF-kB translocation by Imagestream, multicolour flow cytometry of B cell subsets) stratified by UBE2L3genotype.

Results: Data from SLE GWAS, imputed to 1000 Genomes level identified rs140490 as the most strongly associated UBE2L3 SNP, located at -270bp of the promoter region (P=8.6×10^-14; OR 1.30, 95%CI: 1.21-1.39). Microarray /western blot studies found that the rs140490 risk allele increased UBE2L3 expression in B cells and monocytes from PBMC. Overexpression of UBE2L3 in combination with LUBAC in HEK293-NF-kB reporter cell line led to a marked upregulation in NF-kB activity, which was abolished by dominant-negative mutant UBE2L3[C86S]. RNAi blockade of UBE2L3 antagonised TNF signalling by inhibiting IκBα processing. Ex vivo human B cells and monocytes were isolated from genotyped healthy twins stimulated with CD40L or TNF respectively and NF-kB translocation quantified by Imagestream analysis. rs140490 genotype was correlated with both basal NF-kB activation in healthy human individuals, as well as the sensitivity of NF-kB to CD40 stimulation in B cells and TNF stimulation in monocytes. UBE2L3 expression was 3-4-fold elevated in peripheral blood plasmablasts and plasma cells (P<0.0001), with increased UBE2L3 expression in plasma cells from SLE patients compared to controls (P=0.01). UBE2L3 expression was significantly elevated in Ki-67⁺ B cells consistent with a functional role in B cell proliferation. Consistent with the functional effect of UBE2L3 on CD40 driven NF-kB activation in human B cells, rs140490 genotype correlated with increasing plasmablast and plasma cell differentiation in SLE patients (P<0.001).

Conclusion: Our study is the first to show that the UBE2L3 risk haplotype exerts a critical rate-limiting effect on TNF and CD40 activation of NF-kB in primary human cells, and that this effect is mediated through LUBAC. By tracking NF-kB nuclear translocation in B cells and monocytes from genotyped individuals, we have shown that the UBE2L3 risk variant amplifies both basal NF-kB activation and sensitivity of NF-kB to stimulation in ex vivo cells, leading to increased plasma cell proliferation in SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ube2l3-genotype-influences-plasma-cell-proliferation-in-systemic-lupus-erythematosus-by-regulation-of-nf-%ce%bab-by-the-linear-ubiquitination-assembly-complex/