DIFFERENTIAL ACTIVATION OF HEAT-SHOCK AND NUCLEAR FACTOR KAPPA-B TRANSCRIPTION FACTORS IN POSTISCHEMIC REPERFUSED RAT-LIVER

The aim of this study was to investigate the behavior of the transcrip tion factors, heat-shock factor (HSF) and nuclear factor kappa B (NF-k appa B), in postischemic reperfused liver, with particular attention p aid to possible differences in the time-course and mechanism of activa tion, which map help in defining their role in the response of the liv er to reperfusion. Ischemia was induced by clamping the hilar pedicle of the left lateral and median liver lobes; the clamp was removed afte r 1 hour. Some rats were treated intraperitoneally with IL-1 receptor antagonist (IL-1RA) 30 minutes before ischemia and at the time of repe rfusion. Binding of NF-kappa B to the corresponding consensus sequence is activated after 30 minutes of reperfusion, and is still increased 1 hour after reperfusion. Activation is suppressed in rats treated wit h IL-1RA; NF-kappa B persists in the cytosol associated with the inhib itor, I kappa B, and can be artifactually activated in vitro. Super-ge l shift experiments revealed that the two subunits, p50 and p65, are i nvolved in the activation of binding. In contrast, binding of HSF to t he corresponding consensus sequence, heat shock element (HSE), is alre ady activated at the end of ischemia, shows a further increase after 3 0 minutes of reperfusion, but declines 1 hour after reperfusion; more importantly, it is not inhibited by pretreatment of the rat with IL-1R A. In conclusion, although both HSF and NF-kappa B are activated by is chemia-reperfusion, there are clear differences in time-course and mec hanism of activation of the two transcription factors. Activation of H SF depends directly on some events occurring during ischemia; NF-kappa B is activated only after reperfusion and the concurrent oxidative st ress, by an indirect mechanism that can be suppressed by IL-1RA. The p ossibility of dissociating the activation of these two transcription f actors in postischemic reperfusion can have a prospective clinical rel evance.