Does p53 Status Affect the Sensitivity of the Comet Assay?

It has been shown that cells having mutant p53 are more sensitive to genotoxic effects than cells having wild-type p53. To determine whether p53 status affects the sensitivity of the comet assay, we compared the results of the comet assay in WTK1 cells having mutant p53 and TK6 cells having wild-type p53 in the presence and absence of DNA repair inhibitors. Cells were exposed to methyl nitrosourea (MNU), ethyl nitrosourea (ENU), methyl methanesulfonate (MMS), ethyl methanesulfonate (EMS), and bleomycin (BLM) for 2 h in the presence or absence of araC and hydroxyurea (araC/HU) or irradiated to UVC. UVC irradiated cells were cultured for 2 h with or without araC/HU. Immediately after the exposure to chemical mutagens or 2 h after UVC irradiation, slides for the comet assay were prepared. In the absence of araC/HU, the lowest genotoxic doses (LGDs) were higher in TK6 than in WTK1 cells, showing that wild-type p53 reduces comet assay sensitivity. On the other hand, in the presence of araC/HU, the LGDs were almost the same in WTK1 and TK6 cells. In the presence of araC/HU, positive responses to UVC irradiation were observed earlier in TK6 than in WTK1 cells. Therefore, SSB formation followed by SSB rejoining during the nucleotide excision repair process is considered to occur earlier in TK6 than in WTK1 cells, which results in a lower comet assay sensitivity in cells having wild-type p53. Comet assay response to mutagens inducing DNA damages that are repaired by the excision repair system tended to be affected by p53 status.