Investigating the functions of EphB4 in prostate cancer

Abstract

Prostate Cancer is the most commonly diagnosed cancer and the second most common cause of cancer death in Canadian men after lung cancer. Factors that promote metastasis in prostate cancer include the ability of prostate cancer cells to proliferate uncontrollably, and migrate and invade into tissues away from a localized prostate adenocarcinoma. Eph receptors are the largest family of receptor tyrosine kinases and their role in cancer progression has recently taken interest due to their identification, expression and activity in several cancer types. The work presented herein examines the potential impact of EphB4 tyrosine kinase receptor on proliferation, migration and invasion of prostate carcinoma cell lines, PC3, Du-145, and LNCaP. Comparison of EphB4 protein levels between prostate tumor cell lines and normal prostate epithelial cells indicated that EphB4 was generally overexpressed in prostate cancer. To understand the role of EphB4 in prostate cancer, we employed siRNA to deplete EphB4 expression, or alternatively, by activating EphB4 receptor by exogenous addition of EphrinB2-Fc. Proliferation of prostate carcinoma cell lines was not affected when EphB4 was reduced using siRNA, nor when EphB4 was activated with EphrinB2. Additionally, activating EphB4 was not found to promote downstream activation of the PI3/AKT pathway hence did not affect cell survival. Cellular migration of PC3, Du-145 and LNCaP cells, as determined by Wound-healing migration assays, was significantly decreased when EphB4 protein was reduced. However, stimulating the EphB4 receptor using EphrinB2-Fc did not show significant changes in migration. A closer examination of Rho-GTPase proteins that regulate cytoskeleton reorganization and motility led to our finding that activation of EphB4 by EphrinB2-Fc increases activity of Rac and Cdc42. Furthermore, EphB4 plays an important part in invasion of PC3 cells as it was found that cells with reduced EphB4 expression had decreased invasion, while increased invasion was observed after EphB4 was activated with EphrinB2-Fc. These findings suggest that EphB4 could play important roles in prostate cancer metastasis and, with further investigations, it may be possible to develop cancer therapies based on targeting the EphB4 receptor.