Activation of Cdc2 contributes to apoptosis in HPV E6 expressing human keratinocytes in response to therapeutic agents

Infection with human papillomaviruses (HPV) is strongly associated with the development of cervical cancer. The HPV E6 oncogene induces apoptosis in cervical cancer precursor lesions but the mechanism is poorly understood. While it is expected that inactivation of p53 by E6 should lead to a reduction in apoptosis, E6 also sensitizes cells to apoptosis under some experimental conditions. Here, we demonstrate that expression of E6 in human keratinocytes rendered sensitization to chemotherapeutic agents. The cell death was shown to be by apoptosis involving caspase activation and the mitochondria pathway. To explore mechanisms involved in sensitization of E6 expressing cells to apoptosis, we used a proteomic approach to identify proteins differentially expressed in E6 expressing and control keratinocytes. Among nearly a thousand proteins examined, Cdc2 was demonstrated to be the most dramatically up-regulated protein in E6 expressing cells. p53 degradation appears to be important for the up-regulation of Cdc2 by E6. Using genetic, pharmacologic, and siRNA strategies, a role for Cdc2 in E6 expression-conferred apoptosis was demonstrated. Thus, these results have important therapeutic implications in enhancing the efficacy of chemotherapy.