The heat shock response inhibits inducible nitric oxide synthase gene expression by blocking I kappa-B degradation and NF-kappa B nuclear translocation.

We investigated the mechanisms by which the heat shock response inhibits inducible nitric oxide synthase (iNOS) gene expression. Incubation of cultured murine lung epithelium (MLE-15) at temperatures ranging from 39 to 43 degrees C, for 1 h, demonstrated that only severe thermal stress (41 to 43 degrees C) was sufficient to induce the heat shock response. Thermal stress inhibited cytokine-mediated iNOS gene expression only when associated with induction of the heat shock response. Transient transfection assays with an iNOS promoter-reporter gene construct demonstrated that the heat shock response inhibited cytokine-mediated iNOS promoter activity. Electromobility gel shift assays demonstrated that the heat shock response inhibited cytokine-mediated NF-kappa B nuclear translocation. The heat shock response also inhibited cytokine-mediated I kappa-B degradation. These data suggest that the heat shock response inhibits iNOS gene expression by transcriptional mechanisms involving the NF-kappa B/ I kappa-B pathway.