Downregulation of Epstein-Barr virus-encoded latent membrane protein-1 by arsenic trioxide in nasopharyngeal carcinoma cells

Aims and background: It was documented that nasopharyngeal carcinoma (NPC) is associated with Epstein-Barr virus (EBV) and that EBV-encoded latent membrane protein-1 expression (LMP1) plays an important role in the pathogenesis of NPC. In preclinical studies, arsenic trioxide (AS(2)O(3)) has been identified as a promising anticancer agent for treatment of NPC. The purpose of this study is to investigate if this agent can inhibit the expression of LMP1 and therefore lead to growth inhibition of NPC cells in vitro. Methods: LMPl1positive NPC cells, HNE1-LMP1, were treated with 3 mu mol/L of As2O3 for 96 hours. The LMP1 protein expression and mRNA level in HNE1-LMP1 cells were determined by western blot, confocal immunofluorescence staining and semiquantitative reverse transcriptase reaction (RT-PCR). Apoptosis was determined by light microscopy and the TUNEL method. Alterations in the cell cycle distribution were also investigated by flow cytometry. MTT assay and colony formation assay were used to detect the proliferation of the cells. The LMP1-negative parental cell lines HNE1 and HNE2 were used as control in an attempt to elucidate the role of LMP1 in the anticancer effect of AS(2)O(3) on NPC cells. Results: The expression of LMP1 at the protein and mRNA level was reduced after exposure to 3 mu mol/L AS(2)O(3). This dose of As2O3 significantly induced apoptosis and growth retardation of HNE1-LMP1 cells. In addition, more HNEl-LMP1 cells were induced to G0/G1 and G2/M arrest. The same dose of As2O3 had a moderate effect on HNE1 and HNE2 cells. Conclusion: Arsenic trioxide can inhibit LMP1 expression and dictate apoptosis and alterations of cell cycle distribution as well as growth retardation. LMP1-positive NPC cells are more sensitive to AS(2)O(3) treatment than LMP1-negative NPC cells.