Type IV collagenases, matrix metalloproteinase (MMP) 2 and MMP9 are implicated in tumor invasion and metastasis. In patients with nasopharyngeal carcinoma (NPC), poor prognosis due to development of local and distant metastasis has been reported to be predicted by antibody titers against the Z protein which is an AP-1 family transcription factor encoded by the EBV BZLF1 immediate-early gene. Here we report that in patients with NPC, expression of Z in tumor cells correlates with advanced cervical lymph node metastasis which may suggest that Z affects tumor invasion and metastasis. We therefore tested if Z would induce expression of type IV collagenases. Transfection of Z expression plasmid into the C33A epithelial cell line increased expression of MMP9, but MMP2 expression was unaltered. Mutational analysis of the Z protein revealed that, in addition to all three functional domains of Z (dimerization domain, DNA binding domain, and activation domain), the carboxyl terminal 17 amino acids which stabilize the Z protein were necessary for induction of MMP9 expression. Analysis of the MMP9 promoter demonstrated that only AP-1 site close to the transcriptional start-site was essential for transactivation by Z. Previously we reported that Epstein-Barr virus latent membrane protein 1 (LMP1) stimulates MMP9 expression (Yoshizaki et al. Proc. Natl. Acad. Sci. 1998; 95: 3621-6). Thus, Z together with LMP1 may contribute to invasion and metastasis of NPC by inducing expression of MMP9.