Objective: In our previous work, we found that hypoxia induces apoptosis in oncogenically transformed rodent cells and loss of the p53 tumor suppressor gene significantly reduces hypoxia induced cell death. In this report, we show that transformation of wild-type p53 expressing primary cervical epithelial cells with the E6 and E7 genes from high risk human papillomavirus (HPV) type 16 dramatically enhances their susceptibility to hypoxia induced apoptosis.Materials and Methods: Subconfluent primary normal human cervical epithelial cells and normal human fibroblasts were infected with retroviral vectors containing HPV16 E6 and E7 and the neomycin selectable marker using previously described techniques. Clones were selected and isolated in neomycin containing media. Expotentially growing cells were treated with hypoxia (0.02% O 2 ) using specially designed chambers, irradiated (800 cGy) using a cesium source, or grown under aerobic conditions (20% O 2 ) as a control. After treatment, cells were stained with Hoescht and propidium iodide and viewed with a fluorescent microscope for analysis of apoptotic cells. To determine increase in expression of p53, immunoblots were performed using whole cell extracts.Results: After a 48 hour exposure to hypoxic conditions, 40% of E6 and E7 transformed cervical cells exhibit morphologic features indicative of apoptosis, compared to 5% of untransformed cervical cells. Exposure of HPV E6 and E7 transformed cells to ionizing radiation, however, did not initiate apoptosis. Immunoblot assays show induction of p53 under hypoxic conditions but not by ionizing radiation, indicating that hypoxia is able to induce p53 in the presence of E6 and that hypoxia activates p53 by a pathway which is distinct from that of ionizing radiation. Furthermore, hypoxia did not induce apoptosis in normal human fibroblasts transformed with E6 and E7, suggesting that the cellular response to hypoxia is influenced by the cell type.Conclusion: These results suggest a clinically relevant model for HPV mediated tumorigenesis whereby hypoxia differentially induces apoptosis in minimally transformed cervical epithelial cells based on their apoptotic potential. Thus, cervical cells lacking an apoptotic program may have a survival advantage over cells with an intact apoptotic program, leading to a tumor that may respond poorly to radiotherapy or chemotherapy.