Cisplatin is a widely used chemotherapeutic agent. However, its clinical application remains limited due to the high incidence of severe ototoxicity. It has been reported that the unfolded protein response (UPR) is involved in cisplatin-induced ototoxicity. However, the specific mechanism underlying its effect remains unclear. Therefore, the present study aimed to explore the sequential changes in the key UPR signaling branch and its potential pro-apoptotic role in cisplatin-induced ototoxicity. The hair cell-like OC-1 cells were treated with cisplatin for different periods and then the expression levels of the UPR- and apoptosis-related proteins were determined. The results showed that the apoptotic rate of cells was gradually increased with prolonged cisplatin treatment. Furthermore, the sequential changes in three UPR signaling branches were evaluated. The expression levels of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) were gradually increased with up to 12 h of cisplatin treatment. The aforementioned expression profile was consistent with that observed for the apoptosis-related proteins. Subsequently, the proportion of apoptotic cells was notably decreased in CHOP-silenced hair cell-like OC-1 cells following treatment with cisplatin. Moreover, we found significant hair cells loss and a higher level of CHOP in cisplatin-treated cochlear explants in a time-dependent manner. Overall, the present study demonstrated that the protein kinase RNA‑like endoplasmic reticulum kinase (PERK)/ATF4/CHOP signaling branch could play an important role in cisplatin-induced cell apoptosis. Furthermore, the current study suggested that CHOP may be considered as a promising therapeutic target for cisplatin-induced ototoxicity.
Keywords: C/EBP homologous protein; Cisplatin; apoptosis; ototoxicity; unfolded protein response.