Role of Rel/NF-kappaB transcription factors in apoptosis of human hepatocellular carcinoma cells.

Abstract

Primary hepatocellular carcinoma (HCC) is one of the 10 most common human carcinomas in the world. The mechanism by which HCC cells resist apoptosis induced by various treatment modalities is poorly understood. The authors sought to determine whether Rel/NF-kappaB transcription factors play a key role in controlling apoptosis in human HCCcells. We assessed constitutive and inducible activation of NF-kappaB in hepatitis B virus (HBV)-positive (Hep3B) and in hepatitis virus-negative (Chang, HepG2) HCC cells, as well as the role of known inhibitors of NF-kappaB activity. The current study data demonstrate that 1) RelA/NF-kappaB activity is activated constitutively in Hep3B cells, as determined by electrophoretic mobility shift assays; 2) RelA/NF-kappaB reporter gene activity is inhibited specifically by dominant-negative mutants of IkappaB(alpha), IKK1, IKK2, MEKK1, and MEKK3 and it is activated by overexpression of wild-type MEKK3, suggesting that upstream kinase cascades induce phosphorylation of IkappaB(alpha) and activate RelA/NF-kappaB in Hep3B cells; 3) overexpression of the HBV x gene fails to activate NF-kappaB in HepG2 and Chang cell lines; 4) The NF-kappaB-inducible gene, bcl-xl, is overexpressed in Hep3B cells and is inhibited by the proteosome inhibitor PS341, which prevents IkappaBalpha degradation and RelA/NF-kappaB activation; and 5) inhibition of constitutive RelA/NF-kappaB activity by PS341 sensitizes Hep3B cells to doxorubicin-induced apoptosis. These results are consistent with the role of RelA/NF-kappaB activity in the regulation of apoptosis through activation of its downstream target genes and suggest that signaling pathways that control RelA/NF-kappaB activity may be important targets for novel therapeutic approaches in the treatment of human HCC.