Preferential Binding to Elk-1 by SLE-Associated <i>IL10</i> Risk Allele Upregulates <i>IL10</i> Expression

<div><p>Immunoregulatory cytokine interleukin-10 (IL-10) is elevated in sera from patients with systemic lupus erythematosus (SLE) correlating with disease activity. The established association of <i>IL10</i> with SLE and other autoimmune diseases led us to fine map causal variant(s) and to explore underlying mechanisms. We assessed 19 tag SNPs, covering the <i>IL10</i> gene cluster including <i>IL19</i>, <i>IL20</i> and <i>IL24</i>, for association with SLE in 15,533 case and control subjects from four ancestries. The previously reported <i>IL10</i> variant, rs3024505 located at 1 kb downstream of <i>IL10</i>, exhibited the strongest association signal and was confirmed for association with SLE in European American (EA) (<i>P</i> = 2.7×10⁻⁸, OR = 1.30), but not in non-EA ancestries. SNP imputation conducted in EA dataset identified three additional SLE-associated SNPs tagged by rs3024505 (rs3122605, rs3024493 and rs3024495 located at 9.2 kb upstream, intron 3 and 4 of <i>IL10</i>, respectively), and SLE-risk alleles of these SNPs were dose-dependently associated with elevated levels of <i>IL10</i> mRNA in PBMCs and circulating IL-10 protein in SLE patients and controls. Using nuclear extracts of peripheral blood cells from SLE patients for electrophoretic mobility shift assays, we identified specific binding of transcription factor Elk-1 to oligodeoxynucleotides containing the risk (G) allele of rs3122605, suggesting rs3122605 as the most likely causal variant regulating <i>IL10</i> expression. Elk-1 is known to be activated by phosphorylation and nuclear localization to induce transcription. Of interest, phosphorylated Elk-1 (p-Elk-1) detected only in nuclear extracts of SLE PBMCs appeared to increase with disease activity. Co-expression levels of p-Elk-1 and IL-10 were elevated in SLE T, B cells and monocytes, associated with increased disease activity in SLE B cells, and were best downregulated by ERK inhibitor. Taken together, our data suggest that preferential binding of activated Elk-1 to the <i>IL10</i> rs3122605-G allele upregulates <i>IL10</i> expression and confers increased risk for SLE in European Americans.</p>