Tumor necrosis factor induces GSK3 kinase–mediated cross-tolerance to endotoxin in macrophages

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Abstract
Tumor necrosis factor promotes potent inflammatory immune responses that can result in pathological tissue damage. Ivashkiv and colleagues show that it induces a regulatory feedback pathway that dampens inflammatory signaling via the kinase GSK3. Endotoxin tolerance, a key mechanism for suppressing excessive inflammatory cytokine production, is induced by prior exposure of macrophages to Toll-like receptor (TLR) ligands. Induction of cross-tolerance to endotoxin by endogenous cytokines has not been investigated. Here we show that prior exposure to tumor necrosis factor (TNF) induced a tolerant state in macrophages, with less cytokine production after challenge with lipopolysaccharide (LPS) and protection from LPS-induced death. TNF-induced cross-tolerization was mediated by suppression of LPS-induced signaling and chromatin remodeling. TNF-induced cross-tolerance was dependent on the kinase GSK3, which suppressed chromatin accessibility and promoted rapid termination of signaling via the transcription factor NF-κB by augmenting negative feedback by the signaling inhibitors A20 and IκBα. Our results demonstrate an unexpected homeostatic function for TNF and a GSK3-mediated mechanism for the prevention of prolonged and excessive inflammation.