Four Gy IR causes a significant number of DNA base lesions and SSBs which can be effectively repaired by all three vector-expressing osteosarcoma cell lines, while these lesions were left unrepaired or repaired more slowly in miR-513a-5p-expressing cells (Figure 4B and 4C), suggesting that the AP endonuclease activity of APE1, together with the BER and SSBR capacity, were impaired in stably-expressing miR-513a-5p osteosarcoma cells. Here, APEX1 is linked to osteosarcoma.