Aflatoxin B1 (AFB1)-induced hepatocellular carcinoma Kagura-2 cells overexpress c-myc oncogene, which has been implicated in both cell proliferation and apoptosis. To gain an insight into the molecular mechanism of AFB1 hepatocarcinogenesis, Kagura-2 cell death induced by an anticancer agent, sodium 5, 6-benzylideneascorbate (SBA), was studied. The dying cells showed typical characteristics of apoptosis such as nuclear fragmentation, chromosomal condensation and DNA fragmentation by internucleosomal cleavage. The apoptotic death was inhibited by the addition of cycloheximide (CHX), suggesting the requirement for new protein synthesis. However, the induction of Ca2+/Mg2+-dependent endonuclease activities and the alteration of c-myc gene expression in SBA-induced apoptosis were hardly detected. In addition, SBA-induced apoptosis was markedly suppressed by dexamethasone (DEX), insulin and P3 fraction, which was separated from the conditioned medium of Kagura-2 cells (K2CM) by Sephadex G-200 column chromatography and could stimulate Kagura-2 cell growth. P3 fraction also inhibited DNA fragmentation of Kagura-2 cells induced by serum deprivation. These results suggest that SBA induces apoptosis through the interference with the function of growth/survival factors acting in an autocrine and/or a paracrine mechanism or their signal transduction pathways. It is also possible that growth/survival factors play a critical role in the multistep hepatocarcinogenesis of AFB1 together with the deregulated expression of c-myc oncogene.
