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DNA-damaging reagents may kill tumor cells through the generation of reactive oxygen species (ROS). Cytotoxic reagents may also induce apoptosis of cancer cells in Fas-FADD-dependent manners. In this study, we explored the possible link between these two apparently distinct pathways in T leukemia cell Jurkat. Our results demonstrated that c-irradiation, similar to cisplatin, induced apoptosis by triggering Fas aggregation and activating FADDcaspase-8 apoptotic cascade. The absence of caspase-8 or Fas greatly reduced the sensitivity to apoptosis mediated by DNA-damaging agents. In addition, apoptosis induced by cisplatin and c-irradiation, but not by Fas, was inhibited by ROS scavengers, including N-acetyl cysteine, MnTBAP, and C 60 . Importantly, these ROS scavengers effectively prevented the clustering of Fas receptor induced by cisplatin and c-irradiation. Our results suggest that cisplatin and c-irradiation promote ROS production, which in turn contributes to Fas receptor aggregation and cell death. The novel coupling between ROS and Fas clustering likely plays a significant role in apoptosis triggered by DNA-damaging reagents in Fas-expressing leukemia cells.

Transfection of human hepatoma cell lines with cloned HBV DNA resulted in the secretion of large amounts of hepatitis B surface antigen (HBsAg) and core‐related antigens (HBc/HBeAg) if well‐differentiated cell lines were employed. Synthesis of both viral antigens was the highest in cell line HuH‐7 and continued for approximately 25 days. Particles resembling hepatitis B virions (Dane particles) by morphology, density and by the presence of the preS1 surface antigen were released from the transfected HuH‐7 cells into the culture medium. These particles produced in vitro were also indistinguishable from the naturally occurring hepatitis B virions in containing the virus‐associated DNA polymerase and mature HBV genomes. Restriction analysis of these DNA molecules was compatible with the nucleotide sequence of the transfecting HBV DNA sequence. Viral surface antigens and core proteins present in the culture medium were fractionated and characterized by immunoprecipitation and SDS‐‐PAGE after labeling with [35S]methionine. Antisera specific for X‐gene products identified in cell extracts two hitherto unknown HBV gene products. This system thus provides a new approach to open questions regarding HBV‐related gene function and HBV replication.

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