I kappa B alpha gene therapy in tumor necrosis factor-alpha- and chemotherapy-mediated apoptosis of hepatocellular carcinomas

The transcription factor nuclear factor kappaB (NF kappaB) is an essential antagonist of apoptosis during liver regeneration and embryonal development of hepatocytes. Several reports have indicated that NF kappaB may also inh ibit the programmed cell death induced by cytokines, ionizing radiation, or cytotoxic drugs in some cancer cell lines. Because hepatocellular carcinom as (HCCs) are one of the most resistant tumors to systemic chemotherapy, we investigated the activation of NF kappaB and the consequence of its inhibi tion by an I kappaB alpha -super repressor during tumor necrosis factor alp ha (TNF alpha)- and chemotherapy-induced apoptosis in HCC cell lines. We de monstrate that both TNF alpha and adriamycin activate NF kappaB in hepatoma cells. Activation of NF kappaB could be blocked through an adenoviral vect or expressing the I kappaB alpha -super repressor, regardless of the activa ting agent. Inhibition of NF kappaB enhanced the apoptosis induced by TNF a lpha, whereas I kappaB alpha had an anti-apoptotic effect on chemotherapy-i nduced programmed cell death. A strong inhibition of chemotherapy- and TNF alpha -induced apoptosis by dominant-negative Fas-associated death domain i ndicated an essential contribution of death receptor-mediated apoptosis. To elucidate the different role of NF kappaB in chemotherapy-induced apoptosi s, 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 NF kappaB. However, our investigations d emonstrated that in hepatoma cells, the chemotherapy-induced up-regulation of fas (CD95) and Fas ligand (CD95 ligand) is not transcriptionally mediate d through NF kappaB. Thus, other molecular mechanisms must account for the anti-apoptotic effect of I kappaB alpha in adriamycin-induced death of hepa toma cells. In summary, our investigations indicate that the activation of NF kappaB in response to cytotoxic drugs, in contrast to TNF alpha, exerts a pro-apoptotic stimulus rather than an anti-apoptotic function, which has implications for therapy of HCCs.