Genistein‐induced DNA damage is repaired by nonhomologous end joining and homologous recombination in TK6 cells

Genistein (GES), a phytoestrogen, has potential chemopreventive and chemotherapeutic effects on cancer. The anticancer mechanism of GES may be related with topoisomerase II associated DNA double‐strand breaks (DSBs). However, the precise molecular mechanism remains elusive. Here, we performed genetic analyses using human lymphoblastoid TK6 cell lines to investigate whether non‐homologous DNA end joining (NHEJ) and homologous recombination (HR), the two major repair pathways of DSBs, were involved in repairing GES‐induced DNA damage. Our results showed that GES induced DSBs in TK6 cells. Cells lacking Ligase4, an NHEJ enzyme, are hypersensitive to GES. Furthermore, the sensitivity of Ligase4−/− cells was associated with enhanced DNA damage when comparing the accumulation of γ‐H2AX foci and number of chromosomal aberrations (CAs) with WT cells. In addition, cells lacking Rad54, a HR enzyme, also presented hypersensitivity and increased DNA damages in response to GES. Meanwhile, Treatment of GES‐lacking enhanced the accumulation of Rad51, an HR factor, in TK6 cells, especially in Ligase4−/−. These results provided direct evidence that GES induced DSBs in TK6 cells and clarified that both NHEJ and HR were involved in the repair of GES‐induced DNA damage, suggesting that GES in combination with inhibition of NHEJ or HR would provide a potential anticancer strategy.