BRCA1 deficiency promotes DNA damage in cochlear hair cells with activation of ATM-p53 pathway independent of CHK2

Platinum-based chemotherapy drugs, including cisplatin (CDDP), are known to cause irreversible hearing loss. We recently discovered that BRCA1 facilitates the repair of CDDP-induced DNA double-strand breaks (DSBs) in cochlear hair cells (HCs) and prevents hearing loss. However, the checkpoint pathways activated in response to DSBs in HCs, and the mechanisms by which Brca1 regulates these pathways, remain unclear. In this study, we demonstrate that CDDP induces significant DSBs in outer HCs (OHCs), accompanied by phosphorylation of ATM, CHK2, and p53 at serine‑15 (S15) and S20, leading to apoptosis. In contrast, CDDP induces fewer DSBs in inner HCs (IHCs), with phosphorylation of ATM and p53 at S20, but not CHK2, promoting cell survival. Brca1 deficiency further increases phosphorylation of ATM and p53 at S15 in CDDP-treated OHCs. In response to CDDP, phosphorylation of CHK2 is not detected, but phosphorylation of p53 at S20 is enhanced in Brca1-deficient OHCs, whereas, phosphorylation of p53 at S20 is significantly increased in both Brca1-deficient and proficient IHCs. The expression patterns of phosphorylated ATM, CHK2, and p53 in response to CDDP in cultured explants and cell lines differ markedly from those observed in Brca1-deficient and proficient mice in vivo. These findings suggest that CDDP induces extensive DSBs in OHCs, activating the ATM-CHK2-p53 pathway to promote cell death, while Brca1 deficiency exacerbates CDDP-induced DSBs and activates ATM-p53 signaling independent of CHK2, accelerating OHC loss. Additionally, these results demonstrate that CDDP induces modest DSBs in IHCs with activation of the ATM-p53 pathway, independent of CHK2 and BRCA1, leading to cell survival.