Reactivation of telomerase, a specialized RNA-directed DNA polymerase that extends telomeres of eukaryotic chromosomes, is implicated in the mechanisms of cancer development. Inhibition of telomerase leads to cell death via a p53-mediated apoptotic pathway, indicating that this enzyme is a potential target for cancer therapies. Despite the high incidence of the oral squamous cells carcinoma, little is known about the mechanisms of cell death and telomerase maintenance in this cancer. Here we investigated the events involved in programmed cell death induced by oxidative stress and its implications in telomerase maintenance, in SCC-25 treated with 4 mM H₂O₂. After 6 hours of treatment, almost 40% of the cells were Annexin V positive as observed by flow cytometry. Significant increases in reactive oxygen species (ROS) production, caspase-3 activity and [Ca²⁺]_cytosol levels preceded apoptosis in these cells. Chelation of intracellular Ca²⁺ with BAPTA prevented both mitochondrial permeability transition (MPT) and the decrease in cell viability, suggesting the involvement of MPT in this process. Indeed, SCC-25 cell death was prevented by cyclosporin A, but not by FK 506. In addition, release of cytochrome c after treatment with H₂O₂ was also detected by Western blotting. Telomerase catalytic subunit (TERT) expression was decreased in the presence of H₂O₂, as observed by semi-quantitative RT-PCR. In addition, pifithrin-alpha (PFT), a p53 inhibitor, protected SCC-25 from apoptosis. Together these findings suggest that MPT, telomerase and p53 mediate H₂O₂-induced programmed cell death of SCC-25 squamous cells carcinoma.

Supported by CNPq, FAPESP, and FAEPEX/UNICAMP.