Expression of iNOS in cultured rat pulmonary artery smooth muscle cells is inhibited by the heat shock response.

The heat shock response is a highly conserved stress response known to alter patterns of gene expression in many cell types. We hypothesized that interleukin-1 beta (IL-1 beta)-mediated inducible nitric oxide synthase (iNOS) gene expression would be inhibited after induction of the heat shock response in cultured rat pulmonary artery smooth muscle cells (RPASMC). Exposure of RPASMC to sodium arsenite or heat led to expression of heat shock protein-70 (HSP-70) in a time- and concentration-dependent manner. Prior induction of the heat shock response inhibited IL-1 beta-mediated iNOS gene expression in a time- and dose-dependent manner. The inhibitory effects were not due to cytotoxicity, since cell viability was not affected by either sodium arsenite, heat, IL-1 beta, or their combination. Transcriptional analysis via transient transfection of the murine macrophage iNOS promoter [-1592 and -367 base pairs (bp)], upstream from the reporter gene luciferase, revealed that the heat shock response did not affect IL-1 beta-mediated promoter activation, as measured by luciferase activity. We conclude that induction of the heat shock response inhibits IL-1 beta-mediated iNOS gene expression in cultured RPASMC.