Ionizing radiation and arsenic trioxide sensitizes HeLa cells to Fas-induced apoptosis mediated by upregulation of Fas expression

SH Woo, MS, IC Park, PhD, MJ Park, PhD, HC Lee, MS, SH Lee, MD, SI Hong, MD, CH Rhee, MD

Laboratory of Cell Biology, Korea Cancer Center Hospital, Seoul, Nowongu Korea Republic

AIM: The mechanisms of escape from Fas/CD95-mediated apoptosis induced by immunosurveillance in tumor cells are correlated to tumorigenicity. Human cervical carcinoma cell HeLa constitutively expressed cell surface Fas antigen but was resistant to apoptosis by Fas stimulation. In this study, we examined whether ionizing radiation or arsenic trioxide could enhance Fas-induced apoptosis. Methods: HeLa cells were exposed by gamma-irradiation or arsenic trioxide and then treated with anti-Fas cytotoxic antibody (CH11). Fas-mediated apoptosis induced by CH11 was evaluated with annexin V-propidium iodide double staining, Hoechst 33258 nuclear staining, and DNA fragmentation. The upregulation of Fas receptor mRNA and protein expression were determined by RT-PCR and immunostaining. Results: Sub optimal dose of gamma-irradiation and arsenic trioxide could sensitize HeLa cells to Fas-mediated apoptosis via up-regulation of cell-surface Fas antigen. Loss of mitochondrial membrane potential by treatment of CH11 combined with gamma-irradiation or arsenic trioxide was significantly decreased. Caspase-3 was activated in cells treated with CH11 antibody and gamma radiation or arsenic trioxide. Sensitization with arsenic trioxide or gamma-radiation in Fas-mediated apoptosis was remarkably inhibited by caspase-3, 8 inhibitors. Conclusion: Our findings demonstrate that sensitization of HeLa cells to Fas-mediated apoptosis by gamma-irradiation or arsenic trioxide can be due to the up-regulation of Fas gene expression and also provide a means with which to sensitize tumors to the killing effects of cancer therapy operating through the Fas receptor.

KEY WORDS: Caspase, Mitochondrial membrane potential, Radiosesitizer.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Apoptosis - Molecular Mechanisms.