Abstract:Objective To elucidate the mechanisms by which Epstein-Barr virus-encoded latent membrane protein 1 activates NF-κB in nasopharyngeal carcinoma cells.Methods A tetracycline-regulated LMP1-expressing nasopharyngeal carcinoma cell line, Tet-on-LMP1-HNE2, was used as the cell model. The kinetics of the expression of proteins, including LMP1, IκBα and IκBβ, was analyzed by Western blotting. The subcellular localization of NF-κB (p65) was detected by indirect immunofluorescence assay. The NF-κB transactivity was studied by transient transfection and reporter gene assay. Results IκBα was phosphorylated and degraded after the inducible expression of LMP1, although the total protein levels remained stable. The steady-state level of total IκBβ protein may have resulted from the initiation of an autoregulation loop after the activation of NF-κB. No change in the IκBβ level was detected. NF-κB (p65) was translocated from the cytoplasm to the nucleus following degradation of IκBα. After the introduction of the dominant-negative mutant of IκBα (Del 71) into Tet-on-LMP1-HNE2 cells, both nuclear translocation and transactivation of NF-κB induced by LMP1 was significantly inhibited. Conclusions The results indicated that in nasopharyngeal carcinoma cells, LMP1 activated NF-κB via phosphorylation and degradation of IκBα, but not IκBβ. The dominant-negative mutant of IκBα (Del 71) could completely inhibit both the nuclear translocation and transactivation of NF-κB induced by LMP1.
