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Anti-Inflammatory Effect of Heat Shock Protein Induction Is Related to Stabilization of IκBα Through Preventing IκB Kinase Activation in Respiratory Epithelial Cells1

Heat shock protein (HSP) induction confers protection against diverse forms of cellular and tissue injury. However, the mechanism by which HSP exerts cytoprotective effects is unclear. Because HSP induction inhibits genetic expression of pro-inflammatory cytokines, the transcription of which is dependent on NF-κB activation, we explored the relationship between the anti-inflammatory effect of HSP induction and the NF-κB/IκBα pathway. Both HS and sodium arsenite treatment increased HSP70 expression time dependently at mRNA and protein levels. Prior induction of HSP suppressed cytokine-induced IL-8 and TNF-α expression at both mRNA and protein levels. Although HSP induction did not affect total cellular expression of NF-κB, TNF-α-induced increase in NF-κB-DNA binding activity and nuclear translocation of the p65 subunit of NF-κB were inhibited by prior HSP induction, suggesting that activation of NF-κB was blocked. Cytokine-induced IκBα phosphorylation and its degradation were blocked in HSP-induced cells. Immune complex kinase assays demonstrated that TNF-α induced increase in IκB kinase activity was suppressed by prior HSP induction. These results suggest that the anti-inflammatory effect of HSP induction in respiratory epithelial cells is related to stabilization of IκBα, possibly through the prevention of IκB kinase activation, which thereby inhibits activation of NF-κB.