Epstein-Barr Virus Latent Membrane Protein 2A Promotes Invasion of Nasopharyngeal Carcinoma Cells through ERK/Fra-1-Mediated Induction of Matrix Metalloproteinase 9

Abstract

Epstein-Barr virus (EBV)-associated nasopharyngeal carcinoma (NPC) is highly metastatic, and this malignant feature may be promoted by an EBV oncoprotein, latent membrane protein 2A (LMP2A). Acting as a signal regulator, LMP2A can enhance invasiveness and motility of epithelial cells. Downstream from the LMP2A-triggered signaling events, it is largely unknown what key effector proteins are induced and essentially promote cell invasion. In the present study, we found that in NPC cells, LMP2A upregulated matrix metalloproteinase 9 (MMP9), a metastasis-associated protease. LMP2A increased MMP9 expression at both the mRNA and protein levels. It also activated the MMP9 promoter, in which two AP-1 elements were required for the promoter activation. Among AP-1 transcription factors, Fra-1 was induced by LMP2A and is essential for LMP2A-triggered MMP9 expression. Induction of Fra-1 was dependent on the LMP2A-activated ERK1/2 pathway, and induction of the ERK1/2–Fra-1–MMP9 axis required PY motifs in the amino-terminal domain of LMP2A. Notably, LMP2A-promoted invasion of NPC cells was blocked when MMP9 expression, Fra-1 induction, or ERK1/2 activation was inhibited. In addition, we found an association of LMP2A with MMP9 expression in NPC tumor biopsy specimens, where Fra-1 was a major mediation factor. This study reveals an underlying mechanism of LMP2A-induced cell invasion, from signal transduction to upregulation of a critical protease. Considering that MMP9 can also be upregulated by another EBV oncoprotein, LMP1, this protease may be a pivotal effector at which the EBV-induced, invasion-promoting mechanisms converge, serving as an attractive therapeutic target for NPC treatment.