No abstract

As a distinct type of head and neck cancer, non-keratinizing nasopharyngeal carcinoma (NPC) is closely associated with EBV infection and massive lymphoid infiltration. The unique histological features suggest that local inflammation plays an important role in NPC tumourigenesis. We comprehensively characterized NF-κB signalling, a key inflammatory pathway which might contribute to the tumourigenesis of this EBV-associated cancer. By EMSA, western blotting, and immunohistochemical staining, constitutive activation of distinct NF-κB complexes, either p50/p50/Bcl3 or p50/RelB, was found in almost all EBV-positive NPC tumours. siRNA or chemical inhibition of NF-κB signalling significantly inhibited the growth of EBV-positive NPC cells C666-1. Gene expression profiling identified a number of NF-κB target genes involved in cell proliferation, apoptosis, immune response, and transcription. We further confirmed that p50 signals modulate the expression of multiple oncogenes (MYB, BCL2), chemokines, and chemokine receptors (CXCL9, CXCL10, CX3CL1, and CCL20). The findings support a crucial role of these constitutively activated NF-κB signals in NPC tumourigenesis and local inflammation. In addition to expression of the viral oncoprotein LMP1, genetic alteration of several NF-κB regulators (eg TRAF3, TRAF2, NFKBIA, A20) also contributes to the aberrant NF-κB activation in EBV-associated NPC. Except for LMP1-expressing C15 cells, all NPC tumour lines harbour at least one of these genetic alterations. Importantly, missense mutations of TRAF3, TRAF2, and A20 were also detected in 3/33 (9.1%) primary tumours. Taken together with the reported LTBR amplification in 7.3% of primary NPCs, genetic alterations in NF-κB pathways occurred in at least 16% of cases of this cancer. The findings indicate that distinct NF-κB signals are constitutively activated in EBV-positive NPC cells by either multiple genetic changes or EBV latent genes.

Non-keratinizing nasopharyngeal carcinoma (NPC) is closely associated with Epstein-Barr virus (EBV) infection. The EBV-encoded latent membrane protein 1 (LMP1) is believed to play an important role in NPC pathogenesis by virtue of its ability to activate multiple cell signalling pathways which collectively promote cell proliferation, transformation, angiogenesis, and invasiveness, as well as modulation of energy metabolism. In this study, we report that LMP1 increases cellular uptake of glucose and glutamine, enhances LDHA activity and lactate production, but reduces pyruvate kinase activity and pyruvate concentrations. LMP1 also increases the phosphorylation of PKM2, LDHA, and FGFR1, as well as the expression of PDHK1, FGFR1, c-Myc, and HIF-1α, regardless of oxygen availability. Collectively, these findings suggest that LMP1 promotes aerobic glycolysis. With respect to FGFR1 signalling, LMP1 not only increases FGFR1 expression, but also up-regulates FGF2, leading to constitutive activation of the FGFR1 signalling pathway. Furthermore, two inhibitors of FGFR1 (PD161570 and SU5402) attenuate LMP1-mediated aerobic glycolysis, cellular transformation (proliferation and anchorage-independent growth), cell migration, and invasion in nasopharyngeal epithelial cells, identifying FGFR1 signalling as a key pathway in LMP1-mediated growth transformation. Immunohistochemical staining revealed that high levels of phosphorylated FGFR1 are common in primary NPC specimens and that this correlated with the expression of LMP1. In addition, FGFR1 inhibitors suppress cell proliferation and anchorage-independent growth of NPC cells. Our current findings demonstrate that LMP1-mediated FGFR1 activation contributes to aerobic glycolysis and transformation of epithelial cells, thereby implicating FGF2/FGFR1 signalling activation in the EBV-driven pathogenesis of NPC.