RKIP Downregulation Associated With The Metastasis and Activation of NF-κB Signaling Pathway in Nasopharyngeal Carcinoma

To identify the proteins associated with nasopharyngeal carcinoma (NPC) oncogenesis, a two-dimensional electrophoresis and mass spectrometry was used to screen for differential proteins between NPC and adjacent normal nasopharyngeal epithelial tissue (ANNET). As a result, 21 differential proteins were identified, and Raf kinase inhibitor protein (RKIP) was one of the nine downregulated proteins in NPC compared to ANNET. To investigate for the role and mechanisms of RKIP in the metastasis of NPC, Western blot and immunohistochemistry was respectively used to detect RKIP expression in 5-8F and 6-10B NPC cell lines with the different metastatic potentials, as well as in the normal nasopharyngeal epithelial tissue (NNET), primary NPC and NPC metastasis. Furthermore, 5-8F and 6-10B cells were stably transfected with plasmids that expressed sense and antisense RKIP cDNA, respectively, or with empty vector to establish the stable transfected cell lines. The effects of RKIP expression on in, vitro cell invasion, and the activity of NF-kappa B signaling pathway were analyzed in the transfected cell lines. The results showed that RKIP was significantly downregulated in 5-8F compared with 6-10B, in NPC compared with NNET, and not detectable in NPC metastasis. Overexpressed RKIP in 5-8F could decrease its lit vitro cell invasion, whereas downregulated RKIP in 6-10B could increase its in, vitro cell invasion. Overexpressed RKIP in 5-8F could decrease phosphorylated-I kappa B-alpha level and tansactivation activity of NF-kappa B, whereas downregulated RKIP in 6-10B could increase phosphorylated-I kappa B-alpha level and tansactivation activity of NF-kappa B. Taken together, the results suggest that RKIP may be a NPC cell metastasis suppressor, and decreased RKIP expression is associated with the increased metastasis capability of NPC cells possibly through the activation of NF-kappa B signaling pathway.