Most of what is known about the biology of Epstein-Barr virus (EBV) relates to its interaction with cells of the B lymphoid lineage. EBV was originally identified on the basis of its association with Burkitt's lymphoma, and the B lymphotropic nature of the virus is confirmed by its ability to readily infect and transform normal resting B cells in vitro (47). The virus, however, can also infect epithelial cells, and this interaction can result in malignant transformation, as exemplified by the consistent association of EBV with nasopharyngeal carcinoma (NPC) and with a proportion of gastric adenocarcinomas (44,47,53). The EBV-induced transformation of B cells in vitro is associated with the expression of two nonpolyadenylated RNAs (EBER1 and EBER2), along with a set of latent viral gene products consisting of six EBV nuclear antigens (EBNA1, EBNA2, EBNA3A, EBNA3B, EBNA3C, and EBNA leader protein) and three latent membrane proteins (LMP1, LMP2A, and LMP2B) (67). However, more restricted patterns of latent gene expression are observed in NPC and in EBV-positive gastric adenocarcinomas, where only the EBERs, EBNA1, and LMP2A are consistently expressed and the expression of LMP1 is either variable or absent (44, 67). While the association of EBV with various lymphoid and epithelial malignancies is well documented, the precise contribution of virus infection to the etiology of these tumors remains unknown.LMP1 is the major transforming protein of EBV, being absolutely essential for B-cell transformation (28) and behaving as a classical oncogenic protein in rodent fibroblast transformation assays (61). LMP1 induces the expression of lymphocyte activation antigens (62, 63) and antiapoptotic proteins (Bcl-2, TNFAIP3, and MCL1) (20,32,64) and stimulates the secretion of cytokines such as interleukin-10 (IL-10), among others (58). When expressed in epithelial cells, LMP1 induces the expression of 12). It can transform certain established epithelial cell lines and block the terminal differentiation of the cells (7,8,15,23), and it induces hyperkeratosis when expressed in transgenic mouse epidermis (65). LMP1 also induces the expression of the epidermal growth factor (EGF) receptor (41, 42, 43) and matrix metalloproteinases (35,54,59) and can down-regulate the expression of E-cadherin (16), findings which suggest that LMP1 can modulate signaling pathways that regulate the motile and invasive properties of epithelial cells. This characteristic is of particular relevance given that LMP1-positive NPC tumors are reportedly more aggressive than their LMP1-negative counterparts (24).LMP1 functions as a constitutively activated member of the tumor necrosis factor receptor superfamily, activating a number of signaling pathways in a ligand-independent manner (18, 30). LMP1 activates both the canonical and noncanonical NF-B pathways (37, 49), can induce AP-1 and p38/ATF2 activity (11,12,13,29,50,60), and has been shown previously to activate phosphatidylinositol 3-kinase (PI 3-kinase)/Akt kinase (2, 9, 39).Although the activation of t...

Although frequently expressed in Epstein-Barr virus (EBV)-positive malignancies, the contribution of the oncogenic latent membrane protein-1 (LMP1) to the pathogenesis of nasopharyngeal carcinoma remains to be fully defined. As a key effector in EBV-driven B-cell transformation in vitro, LMP1 also displays oncogenic properties in rodent fibroblasts, and exhibits similar effects in epithelial cells. LMP1 functions as a viral mimic of the TNFR family member, CD40, engaging a plethora of signaling pathways including: NF-kappaB, JNK/p38 (SAPK), PI3-kinase and ERK-MPK. The constitutive activation of these pathways appears central in the ability of LMP1 to induce multiple morphological and phenotypic alterations. Here we review the effects of LMP1 on epithelial cell growth transformation, and its putative role in the pathogenesis of nasopharyngeal carcinoma, focusing on key areas of proliferation, survival, cell motility and invasion.

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