NIK­ and IKKß­binding protein contributes to gastric cancer chemoresistance by promoting epithelial­mesenchymal transition through the NF­κB signaling pathway.

Systematic chemotherapy is indispensable for gastric cancer patients with advanced stage disease, but the occurrence of chemoresistance drastically limits treatment effectiveness. There is a tremendous need for identifying the underlying mechanism of chemoresistance. NIK­ and IKKß­binding protein (NIBP) (also known as TRAPPC9, trafficking protein particle complex 9) is a regulator of the cytokine­induced NF­κB signaling pathway which has been proven to play pivotal roles in the progression of various malignancies. Nevertheless, it is still ambiguous whether NIBP is involved in the chemoresistance of gastric cancer. The aim of the present study was to investigate the effect of NIBP on chemotherapy resistance of gastric cancer (GC) and to research the mechanisms of Ginkgo biloba extract 761 (EGb 761®) on reversing chemoresistence which has been confirmed in our previous study. In the present study, the results of immumohistochemisty revealed that the positive staining rates of NIBP, NF­κB p65 and NF­κB p­p65 in gastric cancer tissues were obviously higher than those in normal tissues. Furthermore, a close correlation was found to exist between the expression of NIBP and NF­κB p65 (p­p65) in gastric cancer tissues. Moreover, the overexpression of NIBP was closely related to tumor differentiation, depth of invasion, clinical stage and lymphatic metastasis in gastric cancer. Western blot analysis, real­time PCR, MTT assay and flow cytometric analysis were performed and the results demonstrated that compared with the gastric cancer SGC­7901 cells, the expression of NIBP, NF­κB p65, NF­κB p­p65 and mesenchymal marker vimentin were significantly increased in gastric cancer multidrug­resistant SGC­7901/CDDP cells, and the epithelial cell marker ZO­1 was significantly decreased. Meanwhile, it was found that SGC­7901/CDDP cells were accompanied by spindle­like mesenchymal appearance and upregulation of stem cell marker CD133 which has been verified to be an upstream regulatory gene of epithelial­mesenchymal transition (EMT). Further research confirmed that downregulation of NIBP by Ginkgo biloba extract (EGb) 761 EGb 761 suppressed the cis­diamminedichloroplatinum(II) (CDDP)­induced NF­κB signaling pathway, EMT and the expression of CD133 in SGC­7901 and SGC­7901/CDDP cells. Altogether, these data indicate that the NIBP­regulated NF­κB signaling pathway plays a pivotal role in the chemoresistance of gastric cancer by promoting CD133­induced EMT.