| Objective: To investigate the expression of Tfam, OGG1 and POLG, which are relative to mitochondrial DNA repair system, regulated byγirradiation in oral squamous cell carcino- ma cells. And enhance apoptotic damage ofγ-rays insensitive squamous cell carcinoma cells by inhibiting the mitochondrial DNA repair system.Methods: OSC-2 and OSC-5 cells were cultured in vitro and treated withγirradiation. OSC cells survival rate was calculated with MTT assay and Flow Cytometry. Using GC/MS determined the levels of 8-OHdG in nucleolus and mitochondria. Using PCR detected the mRNA level ofΔmtDNA. Using Western blot, RNA interference, RT-PCR detected the protein and mRNA level of mRNA, Tfam, OGG1 and POLG.Results: After OSC-2 cells and OSC-5 cells were irradiated at a dose of 30 Gy, the cell proliferation rate were (35.33±6.03) % and (75.67±4.16) % respectively, the levels of 8-OHdG and ?mtDNA in nDNA and mtDNA increased (P<0.05), the level of Tfam mRNA increased too, but higher Tfam mRNA levels were observed in OSC-5 cells at 6 h after irradiation. Besides, the expression of OGG1, POLG and pAKT/PI-3K was also stronger in the irradiated OSC-5 cells. In OSC-5 cells,γirradiation alone did not induce deletion of mtDNA, but pretreatment of the cells with bothγirradiation and the PI-3K or Akt inhibitor clearly induced ?mtDNA. Pretreatment with LY 294002 or InhibitorⅥ, down-regulated the expression of Tfam mRNA,OGG1 and POLG proteins and increased 8-OHdG syn- thesis,and increased apoptosis. What's more, each siRNA down-regulated the correspond- ing protein expression (P<0.05). Transfection of the siRNAs increased apoptosis of the irradiated cells.Conclusions:γirradiation up-regulated the OSC-5 cells'(γirradiation insensitive squa- mous cell carcinoma cells) expression of Tfam, OGG1 and POLG which reative with the activation of PI-3K/Akt signway. And enhance apoptotic damage ofγirradiation insen- sitive squamous cell carcinoma cells by inhibiting the mtDNA repair system. |
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