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B. P. Ceresa, J. L. McClintock, D. U. Stone; Choice of Ligand Forecasts the Spatial and Temporal Regulation the Epidermal Growth Factor Receptor in Corneal Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6373.
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The epidermal growth factor receptor (EGFR) is a cell surface receptor tyrosine kinase that plays a critical role in the homeostasis and healing of the corneal epithelium. Signaling by the EGFR is negatively regulated by endocytosis. This study examines the effect of naturally produced EGFR ligands on the regulation of receptor activity in corneal epithelial cells. Specifically, we examined how each ligand affected the rate and extent of EGFR degradation and the route of endocytic trafficking. These findings will help predict which ligands are most suitable for promoting corneal epithelial wound healing.
Immortalized and primary human corneal epithelial cells were treated with amphiregulin, betacellulin, heparin binding-EGF (HB-EGF), epidermal growth factor (EGF), and transforming growth factor-alpha (TGF-alpha) at a range of ligand concentrations. In addition, these same cell lines were incubated with ligands for varying amounts of time. Cells were monitored for the rate of EGFR degradation, localization, and phosphorylation.
All of the tested ligands were able to mediate EGFR endocytosis as determined by indirect immunofluorescence. Treatment with betacellulin, EGF, or HB-EGF resulted in degradation of the EGFR within 2-6 hours, whereas, treatment with TGF-alpha resulted in substantially less EGFR degradation. When the subcellular location of the EGFR was examined following ligand stimulation, TGF-alpha stimulated cells promoted receptor recycling, whereas other ligands promoted receptor degradation.
Here we show that the choice of ligand can provide the necessary spatial and temporal regulation the EGFR activity to maximize its biological and pharmacological activity. Our data indicate that ligand-mediated degradation of the EGFR can be avoided by stimulating the receptor with TGF-alpha, but not other ligands. By avoiding the desensitization process, TGF-alpha has an enhanced potential to increase the extent of EGFR-mediated corneal epithelial wound healing.
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