Upregulation of EphA2 during in vivo and in vitro renal ischemia-reperfusion injury: role of Src kinases

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury in both native kidneys and renal allografts. Disruption of the actin cytoskeleton is a key event with multiple repercussions on cell adhesion and function during IRI. However, receptors involved in regulating cytoskeletal repair following injury have not been identified. In an in vivo model of renal IRI, we used multiprobe RNase protection assay to examine the expression of Eph receptor tyrosine kinases, key regulators of actin dynamics in embryonic development. We found that one receptor in particular, EphA2, was strongly upregulated in the kidney following IRI. Ephrins, the cell-bound ligands of Eph receptors, were also strongly expressed. In cultured renal tubular cells, diverse injurious stimuli mimicking IRI also resulted in upregulation of EphA2 protein expression. Upregulation of EphA2 was inhibited by the Src kinase inhibitor PP2. Conversely, overexpression of Src kinases strongly enhanced the expression of endogenous EphA2 as well as the activity of a human EphA2 promoter construct. Activation of the Erk pathway was necessary, but not sufficient for full induction of EphA2 upreglation by Src kinases. Stimulation of renal tubular epithelial cells with the EphA2 ligand ephrin-A1 caused tyrosine phosphorylation of endogenous EphA2, paxillin, and an unidentified similar to 65-kDa protein and resulted in increased cortical F-actin staining. In summary, under in vitro conditions mimicking IRI, EphA2 expression is strongly upregulated through a Src kinase-dependent pathway. Interactions between upregulated EphA2 and its ephrin ligands may provide critical cell contact-dependent, bidirectional cues for cytoskeletal repair in renal IRI.