BCL-3 and NF-κB p50 Attenuate Lipopolysaccharide-induced Inflammatory Responses in Macrophages

Abstract

Lipopolysaccharide (LPS) induces expression of tumor necrosis factor ␣ (TNF␣) and other pro-inflammatory cytokines in macrophages. Following its induction, TNF␣ gene transcription is rapidly attenuated, in part due to the accumulation of NF-B p50 homodimers that bind to three B sites in the TNF␣ promoter. Here we have investigated the inhibitory role of BCL-3, an IBlike protein that interacts exclusively with p50 and p52 homodimers. BCL-3 was induced by LPS with delayed kinetics and was associated with p50 in the nucleus. Forced expression of BCL-3 suppressed LPS-induced transcription from the TNF␣ promoter and inhibited two artificial promoters composed of TNF␣ B sites that preferentially bind p50 dimers. BCL-3-mediated repression was reversed by trichostatin A and was enhanced by overexpression of HDAC-1, indicating that transcriptional attenuation involves recruitment of histone deacetylase. Analysis of macrophages from p50 and BCL-3 knock-out mice revealed that both transcription factors negatively regulate TNF␣ expression and that BCL-3 inhibits IL-1␣ and IL-1␤. In contrast, induction of the anti-inflammatory cytokine IL-10 was reduced in BCL-3 null macrophages. BCL-3 was not required for the production of p50 homodimers but BCL-3 expression was severely diminished in p50-deficient cells. Together, these findings indicate that p50 and BCL-3 function as anti-inflammatory regulators in macrophages by attenuating transcription of pro-inflammatory cytokines and activating IL-10 expression.

NF-κB and the immune response

“…It has long been known that cells such as macrophages become resistant to repeated proinflammatory stimuli. BCL-3, which is induced late following LPS stimulation, in combination with p50 dimers has been shown to have a role in the inhibition of repeated LPS responses in macrophages, a phenomenon also referred to as LPS tolerance (Wessells et al, 2004). Furthermore by selectively affecting chromatin remodeling, BCL-3 mediates repression of proinflammatory genes, but also facilitates expression of the antiinflammatory gene IL-10.…”

NF-κB in immunobiology

“…Following LPS stimulation, Bcl-3 is induced and binds p50 dimers, with which it can repress the expression of a subset of NF-κB target genes. In this manner, Bcl-3 mediates the selective inhibition of repeated LPS responses in macrophages [143]. Although clearly not the only mechanism, induced transcriptional repression by Bcl-3/p50 likely contributes to LPS-tolerance.…”

Interleukin-10 inhibits tumor necrosis factor-α production in lipopolysaccharide-stimulated RAW 264.7 cells through reduced MyD88 expression

“…10,11 The effect of IL-10 on NF-κB activation in LPS-stimulated RAW 264.7 cells was examined by a luciferase reporter gene assay ( Fig. 2A).…”