Association of latent membrane protein 1 and matrix metalloproteinase 9 with metastasis in nasopharyngeal carcinoma

BACKGROUND Nasopharyngeal carcinoma (NPC) is a highly metastatic carcinoma whose consistent association with Epstein–Barr virus (EBV) has been established. Latent membrane protein 1 (LMP1), an EBV membrane protein expressed in latent infection, is considered to be the EBV oncoprotein. Matrix metalloproteinase 9 (MMP9), one of the MMP families, degrades Type IV collagen, a major component of extracellular matrix and is believed to be crucial for cancer invasion and metastasis. Although MMP9 is reported to be expressed in a variety of cancers, no reports concerning NPC have been published to date to the authors' knowledge. Recently, the authors have shown that LMP1 induces MMP9 in vitro cell line, which suggests the possibility of a mechanism in which LMP1 of EBV contributes to the metastasis and tumorigenesis of NPC by the induction of MMP9. METHODS The expressions of LMP1 and MMP9 were immunohistochemically examined in 38 NPC sections, and the relation of these proteins were statistically analyzed. The authors also analyzed the associations of these proteins with clinical features. RESULTS Both LMP1 and MMP9 proteins were predominantly immunolocalized in cancer nests. The expression of MMP9 showed a significant positive correlation with the expression of LMP1 (r = 0.75; P < 0.0001). Also, the expression of MMP9 correlated with lymph node metastasis (P = 0.0004). CONCLUSIONS The results suggest that the induction of MMP9 by LMP1 contributes to the metastatic potential of NPC. Cancer 2000;89:715–23. © 2000 American Cancer Society.