Next, compared with the control group, elevated expression of γH2AX, a marker of DSBs, was detected using WB in the 20 μM etoposide or 10 μM MK4827 treated groups, implying that DSBs had been successfully induced (Figure 3C, D). Further, compared with fibroblasts, decreased expression of RAD51 was detected in the six STS cell lines, which suggested that HRR was impaired in the STS cell lines. Here, RAD51 is linked to telomere syndrome.