Constitutive activation of NF-κB in human hepatocellular carcinoma:: Evidence of a cytoprotective role

Activation of nuclear factor-kappa B (NF-kappa B) can promote or inhibit apoptosis. Oxidative stress is an important mechanism by which certain anticancer drugs kill cancer cells, and is also one of the mechanisms that activate NF-kappa B. We therefore examined hepatic expression of the NF-kappa B monomer p65 in human hepatocellular carcinoma (HCC) tissue samples from eight patients and compared it with their respective samples of surrounding liver tissues. We also studied the effect of NF-kappa B inhibition in human HCC cells exposed to oxidative stress, by infecting HuH7 cells with a recombinant adenovirus carrying mutant I kappa B alpha (mI kappa B alpha). Cultured HuH7 cells were infected with mI kappa B alpha or beta-galactosidase (beta-Gal) for 24 hr followed by treatment with increasing concentrations of H2O2. Cytotoxicity, NF-kappa B translocation, NF-kappa B DNA binding, cell proliferation, and apoptosis were determined. The monomer p65 was overexpressed in six of eight human HCC tissues. In HuH7 cells, introduction of mI kappa B alpha potently inhibited the translocation, activation, and DNA binding of NF kappa B . In control (beta-Gal-infected) HuH7 cells, exposure to H2O2 produced a dose-dependent increase in apoptosis, regardless of NF-kappa B status. mI kappa B alpha-mediated inhibition of NF-kappa B activation sensitized HuH7 cells to H2O2-induced inhibition of cell growth, and further promoted cell death. Addition of H2O2 (200 - 500 mu M) to control or mI kappa B alpha-infected HuH7 cells enhanced caspase-3 activity and cleavage. Adenovirus-mediated transfer of mI kappa B alpha potently inhibits NF-kappa B activity in HuH7 cells, and this enhances oxidative stress-induced cell killing.