LMP1 activates NF-kappa B via degradation of I kappa B alpha in nasopharyngeal carcinoma cells.
OBJECTIVE
To elucidate the mechanisms by which Epstein-Barr virus-encoded latent membrane protein 1 activates NF-kappa B 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, I kappa B alpha and I kappa B beta, was analyzed by Western blotting. The subcellular localization of NF-kappa B (p65) was detected by indirect immunofluorescence assay. The NF-kappa B transactivity was studied by transient transfection and reporter gene assay.


RESULTS
I kappa B alpha was phosphorylated and degraded after the inducible expression of LMP1, although the total protein levels remained stable. The steady-state level of total I kappa B beta protein may have resulted from the initiation of an autoregulation loop after the activation of NF-kappa B. No change in the I kappa B beta level was detected. NF-kappa B (p65) was translocated from the cytoplasm to the nucleus following degradation of I kappa B alpha. After the introduction of the dominant-negative mutant of I kappa B alpha (Del 71) into Tet-on-LMP1-HNE2 cells, both nuclear translocation and transactivation of NF-kappa B induced by LMP1 was significantly inhibited.


CONCLUSIONS
The results indicated that in nasopharyngeal carcinoma cells, LMP1 activated NF-kappa B via phosphorylation and degradation of I kappa B alpha, but not I kappa B beta. The dominant-negative mutant of I kappa B alpha (Del 71) could completely inhibit both the nuclear translocation and transactivation of NF-kappa B induced by LMP1.
Yin
L
L
Cancer Research Institute, Hunan Medical University, Changsha 410078, China.
Liao
W
W
Deng
X
X
Tang
M
M
Gu
H
H
Li
X
X
Yi
W
W
Cao
Y
Y
D001692:Biological Transport; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D020672:I-kappa B Proteins; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D009303:Nasopharyngeal Neoplasms / Q000378:metabolism / Q000821:virology*; D010766:Phosphorylation; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D014763:Viral Matrix Proteins / Q000502:physiology*
D004268:DNA-Binding Proteins; C037662:EBV-associated membrane antigen, Epstein-Barr virus; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D014763:Viral Matrix Proteins; D000072000:NF-KappaB Inhibitor alpha