Cetuximab enhances cisplatin-induced endoplasmic reticulum stress-associated apoptosis in laryngeal squamous cell carcinoma cells by inhibiting expression of TXNDC5

Cisplatin and cetuximab, an anti-epidermal growth factor receptor (EGFR) monoclonal humanized antibody, have been used for treatment of laryngeal squamous cell carcinoma (LSCC). It has been demonstrated that cisplatin and inhibition of EGFR signaling may induce endoplasmic reticulum (ER) stress-associated apoptosis. However, ER protein thioredoxin domain-containing protein 5 (TXNDC5) reportedly protects cells from ER stress-associated apoptosis. The present study investigated the interaction between cisplatin, cetuximab and TXNDC5 on ER stress-associated apoptosis in LSCC cells. AMC-HN-8 human LSCC cells with or without TXNDC5 overexpression or knockdown were treated with cisplatin (5, 10, 20 and 40 mu M) and/or cetuximab (10, 50, 100 and 150 mu g/ml), for 12, 24, 36 and 48 h. Cisplatin and cetuximab concentration- and time-dependently increased and decreased the expression of TXNDC5 in AMC-HN-8 cells, respectively. Knockdown of TXNDC5 markedly augmented cisplatin-induced levels of CCAAT/enhancer-binding protein homologous protein (CHOP), caspase-3 activity and apoptosis; while overexpression of TXNDC5 largely eliminated cetuximab-induced levels of CHOP, caspase-3 activity and apoptosis. Cisplatin and cetuximab demonstrated a combinatorial effect on increasing the levels of CHOP, caspase-3 activity and apoptosis, which was largely eliminated by overexpression of TXNDC5 or a reactive oxygen species (ROS) scavenger/antagonist. In addition, promoter/luciferase reporter assays revealed that cisplatin and cetuximab regulated the expression of TXNDC5 at the gene transcription/promoter level. In conclusion, the findings suggested that ER stress-associated apoptosis is a major mechanism underlying the apoptotic effect of cisplatin and cetuximab on LSCC cells; cetuximab enhanced cisplatin-induced ER stress-associated apoptosis in LSCC cells largely by inhibiting the expression of TXNDC5 and thereby increasing ROS production; cisplatin and cetuximab had stimulatory and inhibitory effects on the TXNDC5 gene promoter, respectively. The present study offered novel insights into the pharmacological effects of cisplatin and cetuximab on LSCC. It also suggested that TXNDC5 may be a potential therapeutic target for LSCC.