RESUMO
The transcription factor nuclear factor kappaB (NFkappaB) is an essential antagonist of apoptosis during liver regeneration and embryonal development of hepatocytes. Several reports have indicated that NFkappaB may also inhibit the programmed cell death induced by cytokines, ionizing radiation, or cytotoxic drugs in some cancer cell lines. Because hepatocellular carcinomas (HCCs) are one of the most resistant tumors to systemic chemotherapy, we investigated the activation of NFkappaB and the consequence of its inhibition by an IkappaBalpha-super repressor during tumor necrosis factor alpha (TNFalpha)- and chemotherapy-induced apoptosis in HCC cell lines. We demonstrate that both TNFalpha and adriamycin activate NFkappaB in hepatoma cells. Activation of NFkappaB could be blocked through an adenoviral vector expressing the IkappaBalpha super repressor, regardless of the activating agent. Inhibition of NFkappaB enhanced the apoptosis induced by TNFalpha, whereas IkappaBalpha had an anti-apoptotic effect on chemotherapy-induced programmed cell death. A strong inhibition of chemotherapy- and TNFalpha-induced apoptosis by dominant-negative Fas-associated death domain indicated an essential contribution of death receptor-mediated apoptosis. To elucidate the different role of NFkappaB in chemotherapy-induced apoptosis, we investigated the expression of Fas (CD95) and Fas ligand (CD95 ligand), which have been described as important mediators of chemotherapy-induced cell death and as target genes of NFkappaB. However, our investigations demonstrated that in hepatoma cells, the chemotherapy-induced up-regulation of Fas (CD95) and Fas ligand (CD95 ligand) is not transcriptionally mediated through NFkappaB. Thus, other molecular mechanisms must account for the anti-apoptotic effect of IkappaBalpha in adriamycin-induced death of hepatoma cells. In summary, our investigations indicate that the activation of NFkappaB in response to cytotoxic drugs, in contrast to TNFalpha, exerts a pro-apoptotic stimulus rather than an anti-apoptotic function, which has implications for therapy of HCCs.