Activation of nuclear factor-kappaB p50 homodimer/Bcl-3 complexes in nasopharyngeal carcinoma.
EBV latent infection is associated with the development of lymphoid and epithelial malignancies such as nasopharyngeal carcinoma (NPC). The EBV latent membrane protein 1 (LMP1) acts as a constitutively active tumor necrosis factor receptor and activates cellular signaling pathways such as c-Jun-NH(2)-terminal kinase, cdc42, Akt, and nuclear factor (NF)-kappaB. In epithelial cells, two regions of LMP1 induce specific forms of NF-kappaB. COOH-terminal activating region 2 only activates p52/p65 dimers, whereas COOH-terminal activating region 1 activates p50/p50, p50/p52, and p52/p65 dimers and also uniquely up-regulates the epidermal growth factor receptor (EGFR) at the mRNA level. Deregulation of specific NF-kappaB members is associated with the development of many cancers. In this study, the status of NF-kappaB activation was investigated in NPC to determine which NF-kappaB dimers may contribute to the development of NPC. Electrophoretic mobility shift assay, immunoblot, ELISA, and immunohistochemistry data demonstrate that in NPC, NF-kappaB p50 homodimers are specifically activated, and this activation is not dependent on LMP1 expression. Coimmunoprecipitation assays indicate that homodimers are bound to the transcriptional coactivator Bcl-3, and chromatin immunoprecipitation indicates that this complex is bound to NF-kappaB consensus motifs within the egfr promoter in NPC. The discrete yet striking NF-kappaB p50 activation in NPC suggests that p50/p50 homodimers may be important factors in the development of NPC and may contribute to oncogenesis through transcriptional up-regulation of target genes through their interaction with Bcl-3.