Epigenomic elements enriched in the promoters of autoimmunity susceptibility genes

Abstract

Genome-wide association studies have identified a number of autoimmune disease-susceptibility genes. Whether or not these loci share any regulatory or functional elements, however, is an open question. Finding such common regulators is of considerable research interest in order to define systemic therapeutic targets. The growing amount of experimental genomic annotations, particularly those from the ENCODE project, provide a wealth of opportunities to search for such commonalities. We hypothesized that regulatory commonalities might not only delineate a regulatory landscape predisposing to autoimmune diseases, but also define functional elements distinguishing specific diseases. We further investigated if, and how, disease-specific epigenomic elements can identify novel genes yet to be associated with the diseases. We evaluated transcription factors, histone modifications, and chromatin state data obtained from the ENCODE project for statistically significant over- or under-representation in the promoters of genes associated with Systemic Lupus Erythematosus (SLE), Rheumatoid Arthritis (RA), and Systemic Sclerosis (SSc). We identified BATF, BCL11A, IRF4, NFkB, PAX5, and PU.1 as transcription factors over-represented in SLE- and RA-susceptibility gene promoters. H3K4me1 and H3K4me2 epigenomic marks were associated with SLE susceptibility genes, and H3K9me3 was common to both SLE and RA. In contrast to a transcriptionally active signature in SLE and RA, SSc-susceptibility genes were depleted in activating epigenomic elements. Using epigenomic elements enriched in SLE and RA, we identified additional immune and B cell signaling-related genes with the same elements in their promoters. Our analysis suggests common and disease-specific epigenomic elements that may define novel therapeutic targets for controlling aberrant activation of autoimmune susceptibility genes.