Ischemia/reperfusion injury in the liver of BALB/c mice activates AP-1 and nuclear factor κB independently of IκB degradation

Abstract

For many inherited and acquired hepatic diseases, liver transplantation is the only possible therapeutic strategy. Ischemia/reperfusion (I/R) damage to donor tissue is thought to be one component that may play a role in the decline of posttransplant tissue function and ultimately rejection. The transcription factors, AP-1 and nuclear factor κB (NF-κB), play important roles in the acute cellular responses to tissue damage, as well as the inflammatory phase following I/R. We have found that the DNA binding activity of AP-1 was dramatically increased following warm ischemia at 1 to 3 hours postreperfusion. Induced DNA binding activity was composed of predominately c-Jun and JunD hetero- and homodimers as determined by electrophoretic mobility supershift assays. This increase in AP-1 activity occurred in the absence of significant changes in the steady-state protein levels of c-Jun and JunB. Maximal activation of Jun amino-terminal kinase (JNK) occurred within the 25 to 30 minutes postreperfusion, just before the peak in AP-1 DNA binding. These findings suggest that phosphorylation may play an important role in regulating AP-1 transcriptional complexes. Furthermore, JunD protein levels slightly increased at 3 hours postreperfusion, concordant with changes in AP-1 DNA binding activity. The activation of NF-κB at 1 hour postreperfusion was independent of proteolytic degradation of IκB-α or IκB-β. This activation of NF-κB DNA binding activity in the nucleus was preceded by an increase in tyrosine phosphorylation of IκB-α. These studies suggest that JNK, IκB tyrosine kinase, and JunD are potential targets for therapeutic intervention during liver I/R injury.