NFκB and caspase-3 activity in apoptotic hepatocytes of galactosamine-sensitized mice treated with TNfα

Abstract

Tumor necrosis factor-α (TNFα) induces apoptosis in hepatocytes only under transcriptional arrest induced by galactosamine (GAIN). In this study we demonstrated the shuttle of the transcription factor NFκB (nuclear factor-kappa B) in the liver tissue of mice within 30 min-4.5 hr hours after GaIN/TNFα treatment. NFκB translocation from cytoplasm to the nucleus is initiated by its separation from the inhibitory IκB proteins which include IκBα, IκBβ, and IκBε. Thirty minutes after GaIN/TNFα administration, NFκBp65 in hepatocellular nuclei becomes increasingly detectable and reaches its highest level after 2.5 hr. Then export back into cytoplasm begins but, surprisingly, approximately 30% of NFκB remains in the nuclear fraction and appears as an immunoprecipitate in the nuclei of apoptotic hepatocytes. Non-apoptotic hepatocytes do not show any reaction product in the nuclei 4.5 hr after treatment. Correspondingly, the amount of dissociated IκBβ decreases in the cytoplasm up to 2.5 hr and increases again afterwards, although it does not reach the level of the control samples. No evidence of IκBβ in the nuclei was found either immunocytochemically or biochemically. Caspase-3 activity, which is responsible for apoptosis, increases significantly after 3.5 hr. At that time, apoptotic hepatocytes can occasionally be observed and, 4.5 hr after GaIN/TNFα treatment, constitute approximately 30% of the hepatocytes.