DIFFERENTIAL REGULATION OF NITRIC-OXIDE SYNTHASE MESSENGER-RNA EXPRESSION BY LIPOPOLYSACCHARIDE AND PRO-INFLAMMATORY CYTOKINES IN FETAL HEPATOCYTES TREATED WITH CYCLOHEXIMIDE

The effect of cycloheximide (CHX) on the mRNA expression of the cytoki ne-inducible, calcium-independent nitric oxide synthase (iNOS) was inv estigated in fetal hepatocytes stimulated with lipopolysaccharide (LPS ) or pro-inflammatory cytokines. In the presence of CHX the LPS-depend ent iNOS mRNA levels were reduced, whereas the response to pro-inflamm atory cytokines was enhanced, Because iNOS transcription is highly dep endent on the activation of nuclear factor kappa B (NF-kappa B), this factor was evaluated by electrophoretic mobility shift assays, and a c lose correlation between NF-kappa B activity and iNOS mRNA levels was observed. CHX itself potentiated the degradation of the I kappa B alph a and I kappa B beta inhibitory subunits (I kappa B is inhibitory kapp a B) of the NF-kappa B complex, and therefore the loss of LPS-dependen t iNOS mRNA expression cannot be attributed to a blockage in the activ ation of NF-kappa B. These results suggest the existence of a CHX-sens itive pathway in the expression of iNOS mediated by LPS, a mechanism t hat is not involved in the response to pro-inflammatory cytokines.