A concerted activation of transcription factors involved in the transactivation of type II NO synthase (iNOS) gene occurred after partial hepatectomy (PH), resulting in the transient expression of iNOS. The corresponding mRNA and protein levels of iNOS reached a maximum at 4 h and 8 h post-PH respectively. This induction was preceded by an early and transient activation of nuclear factor κB (NF-κB). Analysis of the κB inhibitory (I) proteins showed an important role for IκBα in the process of NF-κB activation, whereas the contribution of IκBβ was less evident. Interferon regulatory factor 1, which has been described as an important activator of iNOS expression, was up-regulated after PH but failed to bind to the corresponding DNA binding sequences of the iNOS promoter. The transcriptional control of iNOS after PH, was compared with the events associated with the hepatic expression of this enzyme in animals challenged with lipopolysaccharide, showing a differential pattern of transcription-factor activation and IκB degradation between both models. Transfection of hepatoma cell lines with iNOS promoter constructs, followed by stimulation with post-PH sera, revealed the requirement of NF-κB activation for iNOS expression. These data suggest that there is an important role for the restricted NF-κB activation in the temporal pattern of iNOS expression in regenerating liver.
These authors have contributed equally to the work.