The role of PI3K in Ephrin-A1 induced cell retraction

The Eph family of receptor tyrosine kinases and their cognate ligands, the Ephrins, form a coordinated program of cell contact-mediated migration control, polarity establishment, and tissue architecture development. Specifically, the ligand Ephrin-A1 has been shown to regulate cell morphology and motility through the activation of EphA receptors, which signal to the small GTPase RhoA, leading to actin cytoskeleton remodeling and cell retraction away from regions of high Ephrin-A1 concentration. The aim of this study is to investigate the molecular signaling events, which regulate Ephrin-A1- induced morphological remodeling and cell retraction. My results indicate that Ephrin-A1-induced cell retraction is mediated by PI3K-p85[Beta]-dependent signaling to RhoA, MLC2, and the actin cytoskeleton. Treatment of wildtype MEFs or NIH3T3 fibroblasts with Ephrin-A1 is sufficient to induce the rapid activation of RhoA, the phosphorylation of MLC2, and actin reorganization, leading to marked cell retraction. In contrast, p85[Beta]-/- MEFs exhibited markedly impaired RhoA activation, decreased MLC2 phosphorylation, and lack of actin reorganization or cell retraction following Ephrin-A1 stimulation. Signaling to RhoA, MLC2, and the induction of cell retraction could be rescued in p85[Beta]-/- MEFs, following the re-expression of the p85[Beta] gene. Furthermore, we have shown that Ephrin-A1, when used as a surface coating, prevents cell adhesion/spreading or migration onto the coated surface. Moreover, Ephrin-A1 treatment results in the dephosphorylation of paxillin and induces the reorganization of phospho-paxillin-containing focal adhesions. The present study contributes significantly to the understanding of the molecular signaling pathways that regulate Ephrin-A1-mediated cell retraction and adhesion to the substrat