Gallic acid induces DNA damage and inhibits DNA repair-associated protein expression in human oral cancer SCC-4 cells.

Gallic acid (GA), a phenolic compound naturally present in plants, used as an antioxidant additive in food and in the pharmaceutical industry, may have cancer chemopreventive properties. In the present study, we investigated whether GA induced DNA damage and affected DNA repair-associated protein expression in human oral cancer SCC-4 cells. Flow cytometry assays were used to measure total viable cells and results indicated that GA decreased viable cells dose-dependently. The comet assay and 4',6-Diamidino-2-phenylindole dihydrochloride (DAPI) staining were used to measure DNA damage, as well as condensation and it was shown that GA induced DNA damage (comet tail) and DNA condensation in a dose-dependent manner. DNA gel electrophoresis was used to examine DNA fragmentation and we found that GA induced DNA ladder (fragmentation). Using western blotting it was shown that GA inhibited the protein expressions of MDC1, O(6)-methylguanine-DNA methyltransferase (MGMT), p-H2A.X, p53, DNA-dependent serine/threonine protein kinase (DNA-PK) and 14-3-3 proteins sigma (14-3-3σ) but increased p-p53, phosphate-ataxia-telangiectasia (p-H2A.X) and ataxia telangiectasia mutated and Rad3-related (p-ATR), phosphate-ataxia telangiectasia mutated (p-ATM) and breast cancer susceptibility protein 1 (BRCA1) in a 24-h treatment. The protein translocation was examined by confocal laser microscopy and results indicated that GA increased the levels of p-H2A.X, MDC1 and p-p53 in SCC-4 cells. In conclusion, we found that GA-induced cell death may proceed through the induced DNA damage and suppressed DNA repair-associated protein expression in SCC-4 cells.