This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Corneal epithelial wound healing and homeostasis is regulated by Epidermal Growth Factor Receptor (EGFR) activity. Stimulation of the EGFR in corneal epithelial cells induces the three cellular changes associated with corneal epithelial wound healing: cell migration, proliferation, and stratification. Inhibition of ligand-stimulated EGFR activation, either through small molecule inhibitors or blocking antibodies, results in a decrease in all three cellular changes as well as impaired wound healing. Despite evidence that the EGFR is necessary and sufficient for corneal epithelial homeostasis and wound healing, EGF has limited therapeutic utility. We hypothesize that desensitization of the EGFR limits the therapeutic use of EGF ligands. Desensitization occurs through internalization of the ligand:receptor complex via clathrin-coated vesicles into the cell. This complex traffics through the endocytic pathway through early and late endosomes and culminates with the lysosomal degradation of the complex. We have identified transforming growth factor-alpha (TGF-alpha) as a ligand that alters the itinerary of endocytic trafficking of the ligand:receptor complex. Treatment with TGF-alpha promotes internalization of the ligand:receptor complex, but rather than targeting it to the lysosome, promotes receptor recycling to the plasma membrane. As a result, the EGFR can signal for longer. The physiological consequence of enhanced signaling is an increase in corneal epithelial cell migration. Since it is not clear if the increase in cell migration is due to the duration of EGFR signaling or the spatial placement of signaling, future studies will disrupt endocytic trafficking at discrete endocytic stages with the goal of making this distinction.
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