The Time-Dependent Serial Gene Response to Zeocin Treatment Involves Caspase-Dependent Apoptosis in HeLa Cells

Zeocin, a member of the bleomycin/phleomycin family of antibiotics, is known to bind DNA and to induce apoptosis in cervical cancer cells, but the mechanism underlying this apoptotic response is poorly understood. The present study was undertaken to elucidate time‐dependent serial transcript patterns in the HeLa cervical carcinoma cell line, following treatment with Zeocin. The HeLa cell proliferation rate was found to gradually decrease following Zeocin exposure, in a time‐ and dose‐dependent manner. RNA transcript level measurements, for time‐dependent serial gene expression profiling, were determined at 0, 6, 12, 18 and 24 hr using a 0.5 k apoptosis functional microarray chip. Further statistical analysis, using a significance test at a 95% confidence level, for transcripts with a greater than 2‐fold change on the array chips, identified 49 up‐regulated and 57 down‐regulated genes. Our gene expression profile data indicate that Zeocin treatment induces an initial release of cytochrome c, the down‐regulation of Bcl‐XL, ENDOG, DAXX and MDM2, and the up‐regulation of CASP and BID. This suggests that a p53‐independent mitochondrial caspase cascade pathway is primarily involved in Zeocin‐induced apoptosis. Such caspase‐dependent cytotoxic activity also implies that this cell death pathway occurs via the caspase 8 and BID genes. However, disruption of either FAS or TNFR1 signaling did not interfere with the Zeocin induced apoptotic response in our experimental system. We hypothesize that Zeocin could be active against cervical cancer cell resistance to conventional chemotherapy and postulate that Zeocin is a novel candidate for the development of new chemotherapeutic treatments of gynecological cancers.