Activation of the heat shock factor 1 by serine protease inhibitors. An effect associated with nuclear factor-kappaB inhibition.

Heat shock proteins (HSPs) have a cytoprotective role in several human diseases, including ischemia and viral infection. Nuclear factor-kappaB (NF-kappaB) is a critical regulator of inflammation and virus replication. Here we report that a class of serine protease inhibitors with NF-kappaB-inhibitory activity are potent HSP inducers via activation of heat shock transcription factor 1 (HSF1) in human cells. 3,4-Dichloroisocoumarin, the most effective compound, rapidly induces HSF1 DNA binding activity and phosphorylation, leading to transcription and translation of heat shock genes for a period of several hours. HSF1 activation is independent of de novo protein synthesis and is correlated in a concentration- and time-dependent manner with NF-kappaB inhibition. Cysteine protease inhibitors E64 and calpain inhibitor II, which do not block NF-kappaB activation, do not induce HSF DNA binding activity. HSP induction by 3,4-dichloroisocoumarin is associated with antiviral activity during rhabdovirus infection. These results identify a new class of HSP inducers and indicate a link between the regulatory pathways of HSF and NF-kappaB, suggesting novel strategies to simultaneously switch on cytoprotective genes and down-regulate inflammatory and viral genes.