NF-κB protects rat ARL-6 hepatocellular carcinoma cells against hydrogen peroxide-induced apoptosis

Abstract

Background/Aims: Refractoriness of some tumours to apoptosis has been related to over-expression of NF-κB, while NF-κB inhibition can promote apoptosis in several cell types. We compared NF-κB activation profiles between normal rat hepatocytes and ARL-6 rat hepatocellular carcinoma (HCC) cells exposed to hydrogen peroxide (H2O2), and examined whether NF-κB activation could explain the observed resistance to apoptosis of ARL-6 cells. We then infected ARL-6 cells with recombinant adenovirus containing mutant (non-degradable) I?B? (Adv-mI?B?), and examined whether this rendered ARL-6 cells more sensitive to oxidative stress-induced apoptosis. Methods: Cultured primary rat hepatocytes and ARL-6 cells were treated with graded doses of H2O2. To block NF-κB, ARL-6 cells were incubated with Adv-mIκBα for 24 h. Cytotoxicity, NF-κB activation, cell proliferation, and apoptosis were determined. Results: H2O2 induced more apoptosis in primary hepatocytes than ARL-6 cells, and the relative resistance of ARL-6 cells to H2O2-induced apoptosis was associated with more pronounced NF-κB activity. In ARL-6 cells, nuclear translocation of NF-κB took place within 2 h of administering H2O2 and remained prominent at 36 h. Adv-mI?B? sensitized ARL-6 cells to H2O2-induced apoptosis, but cell proliferation was minimally suppressed. Conclusions: Compared with normal hepatocytes, ARL-6 cells are refractory to apoptosis after exposure to H2O2, and this is associated with NF-κB activation. Conversely, NF-κB inhibition sensitises ARL-6 cells to H2O2-induced apoptosis. Sustained NF-?B activation in these HCC cells may protect them against apoptosis produced by oxidative stress.