Ephrin-A1 induces cell retraction to exert three- dimensional traction stress on the substrate via a PI3K- dependent pathway

The Eph family of receptor tyrosine kinases and their ligands, Ephrins, have been shown to play important roles in regulating cell migration, polarization, and cell- matrix and cell-cell adhesions. Specifically, Ephrin-A1 has been shown to regulate cell retraction via activating EphA receptors that signal to the PI3K pathway. In the current study using differential interference contrast (DIC) microscopy, Ephrin-A1 treatment of mouse embryonic fibroblasts (MEFs) caused cell edge retraction in the wild type, but not in those with PI3K subunit p85[beta] knockout, indicating that the Ephrin-A1 induction of cell retraction is p85[beta]-dependent. To quantify the p85[beta]-mediated stress generation in MEFs under Ephrin- A1 treatment, three-dimensional images of the displacement of beads embedded in the polyacrylamide substrate were acquired with confocal microscopy and determined with image processing programs, and the traction stress were computed in tangential and normal directions with finite element analysis. The results demonstrated that the tangential traction stress of wild-type MEFs increased after Ephrin-A1 treatment, while no significant change was observed in p85[beta]-knockout MEFs. Ephrin-A1/Fc also caused the reduction of paxillin-containing focal adhesions in endothelial cell (EC) monolayer without affecting intercellular junctions; this reduction of cell- substrate attachment without affecting intercellular stress would change the stress balance and cause the uplifting of the monolayer, indicating the potential of acting as a regulator for the attachment of EC monolayer to its substrate, and thus may be applied to the coating material to guild cell attachment and migration in regulating EC behavio