The inhibitory effect of polypeptide cSN50 on alcoholic hepatic injuries through blocking the binding of NF-κB to importin α

Abstract

Objective. To study whether alcohol and endotoxin induce inflammation, apoptosis, and expression of downstream genes TNF-α and caspase-3 through the nuclear transcription factor NF-κB, i.e., the IκB–NF-κB–importin α pathway. Methods. Flow cytometry was used to observe the apoptosis rate in human hepatoma cells (HepG2) and murine macrophages (RAW264.7) after being stimulated by alcohol and endotoxin at different concentrations. The caspase-3 activity was determined by spectrophotometry and TNF-α level in cell culture supernatant by ELISA. Western blot was used to examine the expression level of P50, importin α3 and IκBα, and indirect immunofluorescence to determine the activation level of P50, importin α3 and IκBα. Results. In human hepatoma cells, a transmembrane polypeptide, cSN50, inhibited the elevation in the level of TNF-α and caspase-3 and the expression of nuclear transport receptor importin α3 stimulated by alcohol and endotoxin. Immunofluorescence showed the nuclear translocation of NF-κB and importin α3 and cytosolic degradation of IκBα. In murine mononuclear macrophages, addition of alcohol or endotoxin or both resulted in a significant elevation of NF-κB and its downstream factors TNF-α and caspase-3 and apoptosis of RAW264.7 cells. These effects were remarkably suppressed by cSN50. However, the expression of importin α3 was not detected by Western blotting or immunofluorescence in this experiment, indicating the existence of other pathways. Conclusion. The nuclear translocation of NF-κB plays an important role in acute alcoholic hepatic injuries and the induced nuclear NF-κB activity, and its downstream gene expression can be partially suppressed by cSN50 in HepG2 and RAW264.7 cells.