Caspase‐3 activation as a key factor for HBx‐transformed cell death

Abstract. Objectives : Nuclear factor‐kappa B (NF‐κB) activation has been associated with the tumorigenic growth of hepatitis B virus X protein (HBx)‐transformed cells. This study was aimed to find a key target for treatment of HBx‐mediated cancers. Materials and methods : NF‐κB activation, endoplasmic reticulum‐stress (ER‐stress), caspase‐3 activation, and cell proliferation were evaluated after Chang/HBx cells permanently expressing HBx viral protein were treated with inhibitors of NF‐κB, proteasome and DNA topoisomerase. Results : Inhibition of NF‐κB transcriptional activity by transient transfection with mutant plasmids encoding Akt1 and glycogen synthase kinase‐3β (GSK‐3β), or by treatment with chemical inhibitors, wortmannin and LY294002, showed little effect on the survival of Chang/HBx cells. Furthermore, IκBα (S32/36A) mutant plasmid or other NF‐κB inhibitors, 1‐pyrrolidinecarbonidithioic acid and sulphasalazine, were also shown to have little effect on the cell proliferation. By contrast, proteasome inhibitor‐1 (Pro1) and MG132 enhanced the HBx‐induced ER‐stress response and the subsequent activation of caspase‐12, ‐9 and ‐3 and reduced cell proliferation. Camptothecin (CPT), however, triggered activation of caspase‐3 without induction of caspase‐12, and reduced cell proliferation. In addition, CPT‐induced cell death was reversed by pre‐treatment with z‐DEVD, a caspase‐3‐specific inhibitor. Conclusions : Detailed exploitation of the regulators of caspase‐3 activation could open the gate for finding an efficient target for development of anticancer therapeutics against HBx‐transformed hepatocellular carcinoma.