Over‐expression of phosphatase of regenerating liver‐3 correlates with tumor progression and poor prognosis in nasopharyngeal carcinoma

This study aimed at clarifying the expression of phosphatase of regenerating liver‐3 (PRL‐3), one member of protein tyrosine phosphatase (PTP) superfamily, in nasopharyngeal carcinoma (NPC) and its correlation with clinicopathologic features, including the survival of patients with NPC. Real‐time PCR and Western blot showed that the expression level of PRL‐3 was markedly higher in NPC cell lines than that in the normal nasopharyngeal epithelial cell at both mRNA and protein levels. Immunohistochemical analysis revealed overexpression of PRL‐3 in 97 of 174 (55.7%) paraffin‐embedded archival NPC biopsies. Statistical analysis showed that PRL‐3 expression was positively correlated with N classification (p = 0.033), distant metastasis (M classification, p = 0.048) and clinical stage (p = 0.005) of patients. Patients with higher PRL‐3 expression had shorter overall survival time, whereas patients with lower level of PRL‐3 had better survival. Multivariate analysis suggested that PRL‐3 expression might be an independent prognostic indicator for the survival of patients with NPC. Disruption of endogenous PRL‐3 protein through a siRNA knockdown technique was shown to suppress the invasion ability and migration potency of 5‐8F and HONE1 cells, substantially. Interestingly, we also found that no significant effect on the proliferation of 5‐8F and HONE1 cells was observed after PRL‐3 was down‐regulated. Our results suggest that PRL‐3 protein is a valuable marker for progression of NPC patients. High PRL‐3 expression is associated with poor overall survival in patients with NPC. © 2008 Wiley‐Liss, Inc.