Cycloprodigiosin up-regulates inducible nitric oxide synthase gene expression in hepatocytes stimulated by interleukin-1β

Abstract

The proinflammatory cytokine interleukin-1β stimulates inducible nitric oxide synthase (iNOS) gene expression in hepatocytes via activation of a transcription factor, nuclear factor-κB (NF-κB). Nitric oxide has diverse cytoprotective and toxic effects. Cycloprodigiosin is an anticancer drug that induces apoptosis through NF-κB-dependent mechanisms. This study investigated whether cycloprodigiosin influenced NF-κB activation and induction of iNOS by interleukin-1β. Cycloprodigiosin alone had no effect on NO production by primary cultured rat hepatocytes. Simultaneous addition of cycloprodigiosin and interleukin-1β markedly stimulated the induction of iNOS mRNA and protein compared with addition of interleukin-1β alone, resulting in overproduction of NO. Cycloprodigiosin had no effect on degradation of the inhibitory subunit of NF-κB (IκBα), but lessened the recovery of IκBα levels. The electrophoretic mobility shift assay revealed that cycloprodigiosin caused an increase of NF-κB activation. Consistent with this observation, cycloprodigiosin promoted the translocation of p65 (a subunit of NF-κB) to the nucleus. Furthermore, this drug enhanced expression of the type 1 interleukin-1 receptor, and this action showed similar concentration-dependence to its induction of iNOS. These results indicate that cycloprodigiosin up-regulates the induction of iNOS by increasing NF-κB activation, at least partly through enhancement of type 1 interleukin-1 receptor expression. By regulating the expression of NF-κB-dependent genes, such as iNOS, cycloprodigiosin administration may increase NO production during hepatic injury.