To determine the mechanism by which STK4/MST1 signaling controls EPHA3 expression, we first assessed the abundance of the Ephrin A (EphA) and Ephrin B (EphB) receptor subtypes and their respective ligands in the well-characterized human prostate cancer cell lines LNCaP, C4-2, 22Rv1, and PC3. Here, STK4 is linked to prostate carcinoma.