Variants on the UBE2L3-YDJC autoimmune disease risk haplotype increase UBE2L3 gene expression by modulating CTCF and YY1 binding.

Objective Genetic variants spanning the ubiquitin-conjugating enzyme E2 L3 (UBE2L3) gene are associated with increased expression of the UBE2L3-encoded E2 ubiquitin-conjugating enzyme, UbcH7, that facilitates activation of proinflammatory NF-κB signaling, and susceptibility to autoimmune diseases. This study aims to delineate how genetic variants carried on the UBE2L3-YDJC autoimmune risk haplotype function to drive hypermorphic UBE2L3 expression. Methods We used bioinformatic analyses, electrophoretic mobility shift assays, and luciferase reporter assays to identify and functionally characterize allele-specific effects of risk variants positioned in chromatin accessible regions of immune cells. Chromatin conformation capture (3C)-qPCR, ChIP-qPCR, and siRNA knockdown assays were performed on patient-derived EBV-transformed B cells homozygous for the UBE2L3-YDJC non-risk or risk haplotype to determine if the risk haplotype increases UBE2L3 expression by altering the regulatory chromatin architecture in the region. Results Five of the seven prioritized variants demonstrated allele-specific increases in nuclear protein binding affinity and regulatory activity. HiChIP and 3C-qPCR uncovered a long-range interaction between the UBE2L3 promoter (rs140490, rs140491, rs11089620) and downstream YDJC promoter (rs3747093) that was strengthened in the presence of the UBE2L3-YDJC risk haplotype, and correlated with the loss of CTCF binding and gain of YY1 binding at the risk alleles. Depleting YY1 by siRNA disrupted the long-range interaction between the two promoters and reduced UBE2L3 expression. Conclusion The UBE2L3-YDJC autoimmune risk haplotype increases UBE2L3 expression through strengthening a YY1-mediated interaction between the UBE2L3 and YDJC promoters.