Arachidonic acid drives amoeboid transendothelial invasion through ligand independent activation of EphA2.

221 Background: We have previously shown that the omega-6 poly unsaturated fatty acid arachidonic acid is a potent stimulator of prostate epithelial transendothelial migration across the bone marrow endothelium and can completely restore the invasive stimulatory capacity of adipocyte depleted human bone marrow stroma. Arachidonic acid induces of EphA2 ligand independent signaling via pAkt with subsequent downstream activation of FAK and Src. Here we present further characterization of the arachidonic acid induced EphA2 pathway. Methods: Transendothelial migration of PC-3 cells across the bone marrow endothelial cell line BMEC was followed by time lapse microscopy and by SEM with or without amoeboid or mesenchymal inhibitors. Western blot analysis of the PC-3 cells or their lipid raft (LR) components post AA stimulation was conducted and signaling pathways validated by siRNA knockdown. Results: Initial studies demonstrated a requirement of PC-3 cells to undergo a mesenchymal to amoeboid switch for transendothelial migration towards bone marrow stroma. The mesenchymal to amoeboid switch was also induced by direct treatment with arachidonic acid as characterized by induction of the Rho/Rock pathway and phosphorylation of myosin light chain. Knockdown of EphA2 by siRNA blocked the induction of the mesenchymal to amoeboid switch and prevented transendothelial invasion. Conclusions: Malignant prostate epithelial cells undergo a switch from mesenchymal to amoeboid movement in response to arachidonic acid in order to cross the bone marrow endothelial barrier.