Latent membrane protein 1 mediates the resistance of nasopharyngeal carcinoma cells to TRAIL-induced apoptosis by activation of the PI3K/Akt signaling pathway

The 5-year survival rate of nasopharyngeal carcinoma (NPC) is still disappointing despite the much improved technologies in its treatment. Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) can selectively induce apoptosis in most tumor cells while sparing normal cells. However, its potential in the treatment of NPC has been limited by the eventual emergence of drug resistance. Latent membrane protein 1 (LMP1) is a major oncogene of the human DNA tumor virus Epstein-Barr virus (EBV) and is associated with the development of NPC and the emergence of chemo-resistance in NPC. In this study, we investigated the potential role of LMP1 in TRAIL resistance in CNE-1 NPC cells. Results show that overexpression of LMP1 could induce TRAIL resistance in NPC cells without influencing death receptors. The LMP1-induced TRAIL resistance is associated with increased expression of FLIP and elevated cleavage of caspase-8 without altering the TRAIL-mediated mitochondrial events and Bid cleavage. Knockdown of the FLIP gene with siRNA prevented the LMP1-induced TRAIL resistance. Furthermore, we found that overexpression of LMP1 activated Akt. Inhibition of Akt with LY294002 completely prevented the LMP1-induced FLIP expression and TRAIL resistance. Together, these results show that LMP1 can inhibit the TRAIL-mediated apoptosis through activation of PI3K/Akt and expression of FLIP in CNE-1 NPC cells, and may provide new methods to prevent and reverse drug resistance in NPC.