Nuclear factor kB is required for the transcriptional control of type II NO synthase in regenerating liver

Abstract

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 kappaB (NF-kappaB). Analysis of the kappaB inhibitory (I) proteins showed an important role for IkappaBalpha in the process of NF-kappaB activation, whereas the contribution of IkappaBbeta 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 IkappaB 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-kappaB activation for iNOS expression. These data suggest that there is an important role for the restricted NF-kappaB activation in the temporal pattern of iNOS expression in regenerating liver.