Cdk5 regulates activation and localization of Src during corneal epithelial wound closure

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Abstract
Recent studies have shown that Cdk5, a member of the cyclin-dependent-kinase family, regulates adhesion and migration in a mouse corneal epithelial cell line. Here, we extend these findings to corneal wound healing in vivo and examine the mechanism linking Cdk5 to cytoskeletal reorganization and migration. Cdk5 was overexpressed in the corneal epithelium of transgenic mice under control of the ALDH3 promoter. Elevated Cdk5 expression retarded corneal debridement wound closure in these animals and suppressed remodeling of the actin cytoskeleton. Conversely, the Cdk5 inhibitor, olomoucine, accelerated debridement wound healing in organ cultured eyes of normal mice, caused migrating cells to separate from the epithelial cell sheet, and increased the level of activated Src(pY416) along the wound edge. To explore the relationship between Cdk5 and Src in greater detail, we examined scratch-wounded cultures of corneal epithelial cells. Src was activated in cells along the wound edge and blocking this activation with the Src kinase inhibitor, PP1, inhibited wound closure by 85%. Inhibiting Cdk5 activity with olomoucine or a dominant negative construct, Cdk5T33, increased the concentration of Src(pY416), shifted its subcellular localization to the cell periphery and enhanced wound closure. Cdk5(pY15), an activated form of Cdk5, also appeared along the wound edge. Inhibiting Src activity with PP1 blocked the appearance of Cdk5(pY15), suggesting that Cdk5 phosphorylation is Src dependent. Cdk5 and Src co-immunoprecipitated from scratch-wounded cultures, demonstrating that both kinases are part of an intracellular protein complex. These findings indicate that Cdk5 exerts its effects on cell migration during corneal epithelial wound healing by regulating the activation and localization of Src.