SUMOylation of EphB4 enhances its stability in prostate cancer.

The receptor tyrosine kinase EphB4 is frequently overexpressed in epithelial cancers, including prostate cancer (PCa). SUMOylation is a post-translational modification that influences protein interactions, localisation and stability. This study investigated how SUMOylation regulates EphB4 localisation, stability and function in PCa. EphB4 SUMOylation was analysed in PCa cell lines and its contribution to stability assessed using siRNA or chemical inhibition of SUMOylation. An EphB4 mutant protein (K616R) was expressed in PCa cells and proteasomal inhibition was used to assess its stability. Cell migration was measured using a scratch wound assay. Immunoprecipitation was used to determine if mutant EphB4 could be SUMOylated on other residues. EphB4 in PCa cells is constitutively modified by SUMO2/3 and acquires SUMO1 modification when stimulated with ephrin-B2 ligand. SUMOylation of K616 is critical for EphB4 stability. K616R EphB4 protein is degraded by the proteasome, and this is associated with reduced MYC protein and slower migration. Immunoprecipitation revealed that additional SUMOylated lysines may also contribute to EphB4 function. SUMOylation at K616 stabilises EphB4, promotes MYC signalling and PCa cell migration. These findings identify a novel mechanism regulating EphB4 and highlight SUMOylation as a potential target in EphB4-driven cancers.