NF-κB RelB suppresses the inflammatory gene expression programs of dendritic cells by competing with RelA for binding to target gene promoters

A group of autoinflammatory disorders termed relopathies arise as a consequence of NF-κB dysregulation. Genetic loss of the NF-κB subunit RelB in humans and mice leads to autoimmunity and lethal multi-organ inflammatory pathology. Our recent study showed that this inflammatory pathology is independent of type I interferon signaling, and further identified dysregulation of a set of pro-inflammatory NF-κB target genes. However, it remains unknown how the loss of RelB leads to the dysregulation of these NF-κB motif-containing pro-inflammatory genes. Here, we report epigenome profiling studies revealing that RelB is associated with pro-inflammatory genes in dendritic cells. While these genes recruit RelA binding upon exposure to a maturation stimulus, we observed substantially more RelA recruitment in the absence of RelB. For these genes, we found that elevated RelA recruitment is correlated with elevated gene expression. To test whether RelB may compete with RelA for binding to NF-κB-regulated gene promoters via competition for κB sites, we generated a new mouse strain (RelB^DB/DB) that harbors targeted point mutations in the RelB DNA binding domain that eliminates high-affinity DNA binding. We found that this targeted mutation in the RelB DNA binding domain is sufficient to drive multi-organ inflammatory pathology. These results provide insights into the biological mechanism of RelB as a suppressor of pro-inflammatory gene expression and autoimmune pathology.