Bortezomib overcomes TRAIL resistance in Burkitt's lymphoma by enhancing apoptosis via reactive oxygen species‑mediated DR5 upregulation and MAPK pathway activation

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) selectively kills tumor cells and exerts minimal toxic effects on normal cells. However, resistance to TRAIL-induced apoptosis is a major obstacle in the clinical application of TRAIL. Bortezomib can enhance the tumor-killing effect of TRAIL in certain tumors, but understanding in Burkitt's lymphoma (BL), especially in TRAIL-resistant BL cells, is limited. Therefore, the present study aimed to assess the synergistic effect of bortezomib and TRAIL in BL. Using the Raji cell line, the least susceptible to TRAIL among BL cell lines, the present study assessed the effect and mechanism by which bortezomib reverses resistance to TRAIL. Cell proliferation inhibition was assessed using the Cell Counting Kit-8 assay. Apoptosis was assessed by flow cytometry. Intracellular reactive oxygen species (ROS) were detected with DCFH-DA, and mitochondrial membrane potential was measured using JC-1. Expression levels of apoptosis proteins and MAPK signaling pathway-related proteins were analyzed by western blot. Combination of bortezomib and TRAIL strongly and synergistically inhibited Raji and CA46 BL cell proliferation. Furthermore, the combination of bortezomib and TRAIL was associated with the following: Induction of apoptosis; increased levels of ROS; presence of mitochondrial membrane potential disorders; upregulation of the levels of apoptosis-related proteins cleaved caspase 8/9/3 and cleaved poly (ADP-ribose) polymerase; and downregulation of the levels of antiapoptotic factors Bcl-2 and Bcl-xl. In addition, bortezomib induced a significant increase in the expression levels of death receptor 5 (DR5), a TRAIL receptor. Pretreatment with the antioxidant N-acetylcysteine inhibited not only ROS upregulation but also DR5 upregulation induced by bortezomib in Raji cells. Furthermore, the present study revealed that the combination of bortezomib and TRAIL could regulate the levels of MAPK signaling pathway-related proteins, such as phosphorylated extracellular signal-regulated kinase 1/2, phosphorylated (p-)p38, p-c-Jun, p-activating transcription factor 2 and phosphorylated stress-activated protein kinase/c-Jun N-terminal kinase. Therefore, the results indicate that bortezomib may enhance Raji cell sensitivity to TRAIL via ROS-dependent upregulation of DR5, induce apoptosis through the MAPK signaling pathway, and subsequently inhibit cell proliferation. Additionally, bortezomib combined with TRAIL had a potential synergistic apoptosis-inducing effect in TRAIL-resistant BL cells.