Overexpression of PBK/TOPK Contributes to Tumor Development and Poor Outcome of Esophageal Squamous Cell Carcinoma

Background: PDZ-binding kinase/T-celloriginated protein kinase (PBK/TOPK) is a serine-threonine kinase and overexpressed in various types of cancer. PBK/TOPK is associated with tumor cell development and progression through suppression of p53 function. In this study, we tested whether PBK acts as a cancer-promoting factor by being overexpressed in esophageal squamous cell carcinoma (ESCC). Materials and Methods: We analyzed PBK/TOPK expression in 15 ESCC cell lines, and 54 primary ESCC tumors that were curatively resected between 1994 and 2007. Results: Overexpression of the PBK/TOPK protein was detected in 93% (14/15) ESCC cell lines and 19% (10/54) primary ESCC tumor samples, and significantly correlated with macroscopic appearance and tumor depth. PBK/TOPK positivity was independently associated with worse outcome in multivariate analysis (p=0.0235, hazard ratio=3.58). Knockdown of PBK/TOPK using specific siRNAs inhibited the cell proliferation, invasion/migration of PBK/TOPK-overexpressing ESCC cell lines. Conclusion: These findings suggest that PBK/TOPK plays a crucial role in tumor malignant potential through its overexpression in ESCC.