The Phosphorylation of EphB2 Receptor Regulates Migration and Invasion of Human Glioma Cells

Abstract

Eph receptor tyrosine kinases and their ligands, ephrins, mediate neurodevelopmental processes such as boundary formation, axon guidance, vasculogenesis, and cell migration. We determined the expression profiles of the Eph family members in five glioma cell lines under migrating and nonmigrating conditions. EphB2 mRNA was overexpressed in all five during migration (1.2-2.8-fold). We found abundant EphB2 protein as well as strong phosphorylation of EphB2 in migrating U87 cells. Confocal imaging showed EphB2 localized in lamellipodia of motile U87 cells. Treatment with ephrin-B1/Fc chimera stimulated migration and invasion of U87, whereas treatment with a blocking EphB2 antibody significantly inhibited migration and invasion. Forced expression of EphB2 in U251 cells stimulated cell migration and invasion and diminished adhesion concomitant with the tyrosine phosphorylation of EphB2. U251 stably transfected with EphB2 showed more scattered and more pronounced invasive growth in an ex vivo rat brain slice. In human brain tumor specimens, EphB2 expression was higher in glioblastomas than in low-grade astrocytomas or normal brain; patterns of phosphorylated EphB2 matched the expression levels. Laser capture microdissection of invading glioblastoma cells revealed elevated EphB2 mRNA (1.5-3.5-fold) in 7 of 7 biopsy specimens. Immunohistochemistry demonstrated EphB2 localization primarily in glioblastoma cells (56 of 62 cases) and not in normal brain. This is the first demonstration that migrating glioblastoma cells overexpress EphB2 in vitro and in vivo; glioma migration and invasion are promoted by activation of EphB2 or inhibited by blocking EphB2. Dysregulation of EphB2 expression or function may underlie glioma invasion.