PBK Expression Promotes the Aggressive Phenotypes of Mesothelioma

Mesothelioma is one of the most aggressive neoplasms worldwide that has a particularly poor prognosis. We have previously discovered that oxytocin receptors (OXTR) are highly expressed in mesothelioma and that OXTR knockdown significantly decreases the proliferation of mesothelioma cells with high OXTR expression. In this study, we performed quantitative proteomic profiling of two mesothelioma cell lines with high OXTR expression using mass spectrometry to investigate the downstream signals of OXTR in mesothelioma cells. We found that OXTR knockdown significantly downregulated PDZ-binding kinase (PBK)-a serine/threonine protein kinase belonging to the bispecific MAPKK family. PBK knockdown significantly suppressed proliferation, migration, and colony formation in mesothelioma cells with high PBK expression and decreased Akt and MAPK phosphorylation levels. Furthermore, immunohistochemical analysis of PBK in surgical specimens obtained from patients with mesothelioma showed that high PBK expression was strongly associated with poor overall survival (log-rank test p = 0.0031; hazard ratio 3.339 and 95% confidence interval 1.12-10.00) and recurrence-free survival (log-rank test p = 0.0024; hazard ratio 3.355 and 95% confidence interval 1.25-9.04). In addition, the clinical significance of PBK expression was validated in mesothelioma using datasets from TCGA. Multivariable Cox regression analysis, incorporating stage and OXTR mRNA expression, demonstrated that PBK mRNA expression was the strongest independent predictor of OS. Our findings indicate that PBK plays a crucial role in the aggressiveness of mesothelioma, making it a promising therapeutic target and potential prognostic biomarker for mesothelioma.