Impaired Bcl3 Up-regulation Leads to Enhanced Lipopolysaccharide-induced Interleukin (IL)-23P19 Gene Expression in IL-10 super(-/-) Mice

Genetic and biochemical analyses show that IL-23p19 plays a central role in mediating bacteria-induced colitis in interleukin-10-deficient (IL-10 super(-/-)) mice. The molecular mechanisms responsible for the dysregulated innate host response leading to enhanced IL-23 gene expression in IL-10 super(-/-) mice are poorly understood. In this study, we investigated the role of Bcl3 in controlling LPS-induced IL-23p19 gene expression in bone marrow-derived dendritic cells (BMDC) isolated from IL-10 super(-/-) mice. We report higher IL-23p19 mRNA accumulation and protein secretion in LPS-stimulated BMDC isolated from IL-10 super(-/-) compared with WT mice. Lipopolysaccharide (LPS)-induced B cell leukemia 3 (Bcl3) expression was strongly impaired (90% decrease) in IL-10 super(-/-) BMDC compared with WT BMDC. Chromatin immunoprecipitation demonstrated enhanced RelA binding to the IL-23p19 promoter in IL-10 super(-/-) compared with WT BMDC. Bcl3 overexpression decreased LPS-induced IL-23p19 gene expression in IL-10 super(-/-) BMDC, which correlated with enhanced NF- Kappa B p50 binding and decreased RelA binding to the gene promoter. Conversely, Bcl3 knockdown enhanced LPS-induced IL-23p19 gene expression in WT BMDC. Moreover, LPS-induced IL-23p19 gene expression was significantly enhanced in Bcl3 super(-/-) BMDC compared with WT BMDC. In conclusion, enhanced LPS-induced IL-23p19 gene expression in IL-10 super(-/-) mice is due to impaired Bcl3 expression leading to diminished p50 and enhanced RelA recruitment to the IL-23p19 promoter.