Abstract 1236: Ephrin signaling in medulloblastoma

Eph receptor and ephrin ligand expression profiles have been associated with poor outcome in several malignancies, but to date, there have been no comprehensive studies characterizing Eph/ephrin expression and signaling function in medulloblastoma (MB), the most common malignant brain tumor of childhood. Determining if Eph receptors and ephrin ligands have a functional role in MB tumorigenesis would be important to our understanding of the molecular regulation of MB and for identifying more effective and less toxic targeted therapies for MB. A few studies have shown that the level of specific Eph receptor mRNA expression and Eph tyrosine kinase activity appears to be increased in MB, particularly in those subtypes with a propensity to metastasize. However, to our knowledge, this is the first study to comprehensively characterize the ephrin receptor and ligand expression profile (mRNA and protein) of MB tumors and to demonstrate the functional effects of ephrin signaling in medulloblastoma cells in vitro. We hypothesize that interactions between specific Eph receptor and ligands results in bidirectional signaling that is critical for MB cell proliferation and migration. We have generated profiles characterizing Eph receptor and cognate ligand expression at the mRNA and protein level in two medulloblastoma cell lines and in 29 (mRNA) and 60 (protein) human medulloblastoma tissues. Based on our data, the candidates of interest for functional characterization are Eph receptors B1 and B2, expressed in over 98% of tumors, and the cognate ephrin ligands b1 and b2. Of these targets, only ephrin b2 was detected in developing fetal cerebellum, with positive expression by IHC restricted to the purkinje cells, suggesting that these ephrin family members are tumor-specific. To assess the functional role of these molecules in MB cells, we knocked down ephrin b2 and ephrin b1 using siRNA. Cells with altered Eph/ephrin expression were then compared to control transfectants for the ability to signal downstream through Src and for changes in cell function using bioassays of proliferation (MTT) and migration (scratch assay). We demonstrate that ephrin b2 is diffusely expressed in 100% of medulloblastoma tumors analyzed, signals through src oncogene, and promotes MB cell proliferation. In contrast, ephrin b1 is heterogeneously expressed in 20% of tumors analyzed, localizes to cells with high MIB proliferative index within the tumor that are associated with an aggressive phenotype of medulloblastoma, and promotes MB cell migration. Together, these data indicate that ephrin b1 and b2 have distinct and differential functional roles in the regulation of Eph signaling and cellular behavior in MB cells. Further preclinical investigation of these specific targets in MB in vivo is warranted to validate these Eph family members as potential novel therapeutic targets in MB. The complete tumor expression profiles and functional data of altered Eph/ephrin expression in MB cells will be presented. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1236. doi:1538-7445.AM2012-1236