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High mobility group box 1 (HMGB1) can be actively secreted by macrophages/monocytes in response to exogenous and endogenous inflammatory stimuli (such as bacterial endotoxin, TNF‐α, IL‐1, and IFN‐γ) or passively released by necrotic cells and mediates innate and adaptive inflammatory responses to infection and injury. Here, we demonstrated that a reactive oxygen species, hydrogen peroxide (H2O2), induces active and passive HMGB1 release from macrophage and monocyte cultures in a time‐ and dose‐dependent manner. At nontoxic doses (e.g., 0.0125–0.125 mM), H2O2induced HMGB1 cytoplasmic translocation and active release within 3–24 h. At higher concentrations (e.g., 0.25 mM), however, H2O2exhibited cytotoxicity to macrophage and monocyte cell cultures and consequently, triggered active and passive HMGB1 release. In addition, H2O2stimulated potential interaction of HMGB1 with a nuclear export factor, chromosome region maintenance (CRM1), in macrophage/monocyte cultures. Inhibitors specific for the JNK (SP600125) and MEK (PD98059), but not p38 MAPK (SB203580), abrogated H2O2‐induced, active HMGB1 release. Together, these data establish an important role for oxidative stress in inducing active HMGB1 release, potentially through a MAPK‐ and CRM1‐dependent mechanism.

The objective of this study was to evaluate the negative regulatory role of heat shock protein 70 (HSP70) on endotoxin-induced activation of inflammatory cytokine signaling pathways in a macrophage cell line. Our studies show that elevation of HSP70 either by activation of the heat shock response (HSR) or through forced expression of the hsp70.1 gene downregulates cytokine expression. Our experiments showed that activation of the HSR and HSP70 overexpression could inhibit LPS-mediated expression of the proinflammatory cytokines TNF- and IL-1 at the mRNA and protein levels. We also investigated the effects of HSP70 elevation on signaling pathways downstream of LPS and its receptors, including the NF-B and mitogen-activated protein kinase (MAPK) pathways. The effects of HSP70 on cytokine expression were correlated with its effects on activation of NF-B, a known activator of the tnfand Il-1genes. Overexpression of HSP70 inhibited the nuclear translocation of p65, the transcriptionally active component of the NF-B complex, and prevented the degradation of IB, the regulator of NF-B activity. However, HSP70 elevation did not markedly inhibit signaling through the MAPK arm of the LPS-induced pathway, suggesting that the effects of HSP70 are mediated primarily through the NF-B cascade. Our experiments therefore suggested that elevated levels of HSP70 inhibit LPS-induced production of inflammatory cytokines by a mechanisms involving inactivation of NF-B but cast doubt on significant role for the MAPK pathway in these effects.

The purpose of this study was to evaluate the kinetic changes and the localization of high-mobility group box 1 protein (HMGB1) and to observe the effect of heat shock response (HSR) on the expression and release of HMGB1 in lipopolysaccharide (LPS)-activated murine macrophage-like RAW 264.7 cells. Reverse transcriptase (RT)-PCR and Western blot were used to examine HMGB1 expression after LPS treatment. The intracellular localization of HMGB1 in normal or LPS-activated cells was investigated by immunocytochemical analysis and HMGB1 released from cultured macrophages by Western blot. HSR was performed by incubating RAW 264.7 cells at 42.5°C for 1 h then recovery at 37°C for 12 h. The effect of HSR on expression and release of HMGB1 was observed. The results showed that a decrease of HMGB1 mRNA expression was observed at 18 h after LPS (500 ng/mL) treatment, although the total intracellular HMGB1 protein levels were not affected. A visible translocation of HMGB1 from the nuclear to the cytoplasm was observed at 20 h after stimulation with LPS (500 ng/mL). Furthermore, HMGB1 was released into the medium by LPS-activated RAW 264.7 cells in a time- and dose-dependent manner. Heat shock pretreatment significantly inhibited LPS-induced release of HMGB1 and the translocation of HMGB1 from the nucleus to the cytoplasm in RAW 264.7 cells. These findings suggest that the release of HMGB1 by LPS-activated macrophages is a late event in the pathogenesis of sepsis and that HSR could inhibit the release and translocation of HMGB1 induced by LPS.

Introduction It was recently suggested that heat shock protein (HSP)70, an intracellular protein, is a potential mediator of inflammatory disease when it is released into the extracellular compartment. Although elevated HSP70 levels have been identified in rheumatoid arthritis (RA) synovial tissues and RA synovial fluid compared with patients with osteoarthritis and healthy individuals, it remains unclear what role extracellular HSP70 plays in the pathogenesis of RA. This study was conducted to investigate the effects of extracellular HSP70 on the production of RA-associated cytokines in fibroblast-like synoviocytes from patients with RA and to elucidate the mechanisms involved.Methods IL-6, IL-8 and monocyte chemoattractant protein (MCP)-1 levels in culture supernatants were measured using enzyme-linked immunosorbent assays. Activation of mitogen-activated protein kinases (MAPKs), such as extracellular signal-regulated protein kinases (ERKs), c-Jun amino-terminal kinase (JNK) and p38 MAPK, was detected using Western blotting. Nuclear translocation of nuclear factor-κB (NF-κB) and degradation of the inhibitory protein IκBα were examined using immunohistochemistry and Western blotting.Results Human HSP70 downregulated IL-6, IL-8 and MCP-1 production in RA fibroblast-like synoviocytes induced by tumour necrosis factor (TNF)-α in a concentration dependent manner. HSP70 inhibited the activation of ERK, JNK and p38 MAPK in fibroblast-like synoviocytes stimulated by TNF-α. Furthermore, HSP70 also significantly inhibited nuclear translocation of nuclear factor-κB and degradation of IκBα induced by TNF-α.Conclusion Extracellular HSP70 has an anti-inflammatory effect on RA by downregulating production of IL-6, IL-8 and MCP-1 in fibroblast-like synoviocytes, which is mediated through inhibited activation of the MAPKs and NF-κB signal pathways.