Differential regulation of nitric oxide synthase mRNA expression by lipopolysaccharide and pro-inflammatory cytokines in fetal hepatocytes treated with cycloheximide

The effect of cycloheximide (CHX) on the mRNA expression of the cytokine-inducible, calcium-independent nitric oxide synthase (iNOS) was investigated in fetal hepatocytes stimulated with lipopolysaccharide (LPS) or pro-inflammatory cytokines. In the presence of CHX the LPS-dependent iNOS mRNA levels were reduced, whereas the response to pro-inflammatory cytokines was enhanced, Because iNOS transcription is highly dependent on the activation of nuclear factor kappa B (NF-kappa B), this factor was evaluated by electrophoretic mobility shift assays, and a close correlation between NF-kappa B activity and iNOS mRNA levels was observed. CHX itself potentiated the degradation of the I kappa B alpha and I kappa B beta inhibitory subunits (I kappa B is inhibitory kappa B) of the NF-kappa B complex, and therefore the loss of LPS-dependent iNOS mRNA expression cannot be attributed to a blockage in the activation of NF-kappa B. These results suggest the existence of a CHX-sensitive pathway in the expression of iNOS mediated by LPS, a mechanism that is not involved in the response to pro-inflammatory cytokines.