NFkB1 inhibits NOD2-induced cytokine secretion through ATF3-dependent and -independent mechanisms (P1252)

Abstract

Abstract NOD2, an intracellular sensor of bacterial peptidoglycan, is associated to Crohn’s disease (CD). In the intestine, NOD2 is continuously stimulated. Upon chronic NOD2 stimulation in human monocyte-derived macrophages (MDM), cytokine secretion is significantly attenuated upon restimulation of NOD2 or other pattern recognition receptors (PRR); cytokine downregulation is a prominent feature of intestinal tolerance. NFkB1 (p50/p105) is a critical transcription factor regulating PRR responses. However, the role of NFkB1 in NOD2-mediated tolerance reported is not known. Knocking down NFkB1 expression in primary human MDM significantly reversed NOD2-induced cytokine downregulation. MAPK and IkBa activation was dramatically reduced in NOD2-initiated tolerance; this reduced signaling was reversed upon NFkB1 knockdown. Furthermore, upon NOD2-initiated tolerance, NFkB1 knockdown significantly reversed the regulation of both activating (H3K4Me2, H4Ac) and inhibitory (H3K27Me3) histone modifications within cytokine gene promoters. Upon chronic NOD2 stimulation, the transcriptional repressor, ATF3, was induced and bound to the promoters of cytokine genes; both features were reversed upon NFkB1 knockdown. Restoring ATF3 expression under these NFkB1 knockdown conditions significantly restored NOD2-initiated tolerance. We therefore define a clear role for NFkB1 in the mechanisms through which the CD-associated protein NOD2 downregulates cytokines.