Melatonin enhances cisplatin-induced cell death through inhibition of DERL1 in mesenchymal-like CD44 high OSCC cells

Melatonin is a hormone that is primarily produced in the pineal gland and is involved in wide range of biological functions. However, the impact of melatonin on chemotherapy-induced cell death remains to be elucidated in oral squamous cell carcinoma (OSCC) cells. The objective of this study was to clarify the role of melatonin in cisplatin-induced cytotoxicity in CD44 OSCC cells. CD44 OSCC cells were cultured on fibronectin-coated hydrogel. A lactate dehydrogenase cytotoxicity assay was performed to evaluate cisplatin-induced cell death. The effect of melatonin on cisplatin-induced cell death and Derlin-1 (DERL1) endoplasmic reticulum membrane protein expression was investigated. CD44 OSCC cells exhibited mesenchymal-like features when cultured on fibronectin-coated hydrogel. Mesenchymal-like CD44 OSCC cells demonstrated strong resistance to cisplatin-induced cell death compared with epithelial-like CD44 OSCC cells. DERL1 mRNA and DERL1 protein expression levels were significantly higher in mesenchymal-like CD44 cells compared with epithelial-like CD44 cells. Cisplatin-induced cell death was significantly enhanced after DERL1 siRNA knockdown, suggesting that DERL1 is involved in resistance to cisplatin-induced cell death. Melatonin significantly inhibited DERL1 expression and enhanced cisplatin-induced cell death in mesenchymal-like CD44 cells. miR-181c-5p expression was significantly upregulated in the presence of melatonin. Furthermore, melatonin-inhibited DERL1 expression was significantly recovered by miR-181c-5p inhibitor. In addition, melatoninenhanced cisplatin-induced cell death was attenuated by miR-181c-5p inhibitor. These results suggest that melatonin-induced miR-181c-5p enhances cisplatin-induced cell death through inhibition of DERL1 in mesenchymal-like CD44 cells. Melatonin plays a vital role in promoting cisplatin-induced cytotoxicity in mesenchymal-like CD44 OSCC cells.