Heat shock inhibits NF-kB activation in a dose- and time-dependent manner

Background. The heat shock response (HSR) attenuates NF-kappa B mediated activation of the acute inflammatory response by inhibiting IkB degradation. The HSR also confers a protective phenotype upon cells through production of heat shock proteins (HSP). However, the exact conditions that induce the HSR and stimulate the production of protective HSP are poorly defined. Consequently, we hypothesized that the inhibition of NF-kappa B activation through the HSR is dependent both on the degree of cellular injury and the length of the recovery period from the heat shock. Methods. RAW 264.7 murine macrophages were heated to 43 degrees C for 15 (mild heat shock), 45 (moderate heat shock), or 90 min (severe heat shock), allowed to recover at 37 degrees C for 0 to 24 h, and then exposed to 100 ng/ml. of Escherichia coli (055:B5) lipopolysaccharide (LPS). Cellular viability, HSP expression, and the activation of NF-kappa B after LPS exposure were determined by alamarBlue assay, immunoblot, and electrophoretic mobility shift assay, respectively. Results. Transient attenuation of NF-kappa B activation and I kappa B preservation was observed only with moderate heat shock and 1 h of recovery. Mild heat shock had no effect on LPS-induced NF-kappa B activation or I kappa B degradation. Severe heat shock completely inhibited NF-kappa B activation and preserved I kappa B protein levels. Heat shock proteins were detectable 30 min after moderate heat shock, with maximal and sustained levels 2 to 24 h after heat shock. Conclusion. The attenuation of NF-kappa B activation after heat shock is both dose- and time-dependent. (c) 2005 Elsevier Inc. All rights reserved.