Abstract 1085: Nuclear localization and function of EphB4 in prostate cancer cells

Abstract EphB4 is a member of the largest group of receptor tyrosine kinases. EphB4 is significantly overexpressed in prostate cancer where it contributes to tumour progression as demonstrated through knock down of EphB4 in both in vitro and in vivo cell models. EphB4's interaction with its preferred ligand ephrin-B2 may lead, in some cases, to tumour suppression, suggesting therefore that ligand-independent effects are oncogenic. EphB4 is usually located to the plasma membrane, but using an in-house specific monoclonal antibody we have identified EphB4 in the nucleus of prostate cancer cell lines and patient tumour samples. Accordingly, we hypothesise that EphB4 can directly regulate gene expression in prostate cancer cells and that this may be at least one mechanism through which the ligand-independent effects on tumour progression may be manifested. Using chromatin immunoprecipitation with the specific EphB4 antibody we were able to precipitate numerous DNA sequences that are currently being validated. Using confocal microscopy we have discovered that EphB4 colocalises with SUMO-1 (small ubiquitin-like modifier-1). SUMOylation is a posttranslational modification by which one or multiple SUMO molecules are attached to certain lysine residues of a target protein and this can result in cytoplasmic-nuclear shuttling. In silico analysis of EphB4 revealed that it contains a highly conserved potential sumoylation site, K616. This is a highly novel and significant finding in the Eph receptor field and may provide a mechanism by which EphB4 localises to the nucleus. Further characterisation of EphB4 sumoylation and nuclear translocation is currently being undertaken. This study provides novel insight into Eph receptor biology and may identify a major new mechanism by which EphB4 can control gene expression and potentially influence cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1085. doi:10.1158/1538-7445.AM2011-1085