Overexpression of EPH Receptor B2 in Malignant Mesothelioma Correlates with Oncogenic Behavior

Introduction: Malignant pleural mesothelioma (MM) is an aggressive asbestos-associated malignancy with limited therapeutic options. This study describes the overexpression of Ephrin B2 receptor (EPHB2) in MM cell lines and tumors, and the effect of its manipulation on proliferative and invasive qualities of the disease. Methods: Using expression arrays, we investigated EPHB2 in MM tumors compared with normal mesothelium. EPHB2 and downstream target expression were evaluated using reverse-transcriptase polymerase chain reaction and immunoblotting methods. The biological significance of EPHB2 in MM was evaluated using in vitro functional assays with and without targeting by EPHB2-short hairpin RNA or blocking peptide in two mesothelioma cell lines, HP-1 and H2595. Results: EPHB2 is overexpressed in all MM cell lines, but not in benign mesothelial cells, and is significantly elevated in MM tumor tissue compared with matched normal peritoneum. Targeted knockdown of EPHB2 in HP-1 and H2595 cell lines reduced its expression and that of EPHB2 downstream targets such as matrix metalloproteinase (MMP-2) and vascular endothelial growth factor, whereas caspase 2 and caspase 8 had increased expression. Inhibition of EPHB2 resulted in a significant decrease in scratch closure (1.25-fold-1.8-fold), proliferation (1.5-fold), and invasion (1.7-fold-1.8-fold) compared with the controls. Most notably, however, EPHB2 silencing resulted in a significant increase in apoptotic proteins and activity. Conclusion: EPHB2 seems to play an important role in MM pathogenesis and these findings indicate that EPHB2 could serve as a potential novel therapeutic target for treatment of the disease.