Summary
The EphB/ephrinB receptor-ligand system is pivotal for the development of the embryonic
vasculature and for angiogenesis in the adult organism. We observed that (i) the expression
of ephrinB2 and ephrinB1 is up-regulated in capillaries during inflammation, that
(ii) these ligands are localised on the luminal endothelial surface, and that (iii)
they interact with the ephrinB-receptor EphB2 on monocyte/macrophages. This study
delineates the impact of ephrinB-mediated reverse signalling on the integrity and
proinflammatory differentiation of the endothelium. To this end, in vitro analyses with human cultured endothelial cells reveal that knockdown of ephrinB2
or ephrinB1 impairs monocyte transmigration through the endothelium. While ephrinB2
but not ephrinB1 interacts with PECAM-1 (CD31) in this context, reverse signalling
by ephrinB1 but not ephrinB2 elicits a c-Jun N-terminal kinase (JNK)-dependent up-regulation
of E-selectin expression. Furthermore, treatment of endothelial cells with soluble
EphB2 receptor bodies or EphB2-overexpressing mouse myeloma cells links ephrinB2 to
PECAM-1 and induces its Src-dependent phosphorylation while diminishing Src homology
phosphotyrosyl phosphatase-2 (SHP-2) activity and increasing endothelial cell permeability.
We conclude that extravasation of EphB2 positive leukocyte populations is facilitated
by lowering the integrity of endothelial cell junctions and enhancing the pro-inflammatory
phenotype of the endothelium through activation of ephrinB ligands.
Keywords
Inflammation - ephrinB1 - ephrinB2 - EphB2 - monocytes - endothelial cells