Search

Wound healing is a response to injury that is initiated to reconstruct damaged tissue. In skin, reepithelialization involves both epithelial cells and fibroblasts and contributes to the reformation of a barrier between the external environment and internal milieu. Growth factors including epidermal growth factor (EGF) play important roles in promoting this process. In the present studies we employed CV-1 fibroblasts in a tissue culture model of reepithelialization to develop strategies for optimizing wound closure stimulated by EGF. We found that EGF enhanced cell motility within 6-8 h of EGF treatment in serum-free medium but wounds failed to close within 24 h. However, if medium on these cultures was exchanged for medium containing serum, ceils pretreated with EGF closed new scrape wounds more rapidly than did cells that were not pretreated. These results indicate that serum factors work in concert with EGF to coordinate cell motility for efficient wound closure. Indeed, EGF enhanced the rate of wound closure in the presence of serum, and this effect also persisted for at least 24 h after EGF was removed. This coordination of EGF-induced cell motility was accompanied by an increase in the transient phosphorylation of ERK1 and ERK2. The persistent effects of EGF were blocked by transient exposure to reversible inhibitors of transcription and translation, indicating that the expression of new proteins mediated this response. We propose that EGF-stimulated CV-1 fibrublast motility is coordinated by a serum component that induces cell-cell adhesive properties consistent with an epithelial phenotype, thereby enhancing the reepitheliafization process. [ABSTRACT FROM AUTHOR]

On binding to its receptor, epidermal growth factor (EGF) initiates a cascade of events leading to cell proliferation or differentiation. In addition, the EGF receptor itself is downregulated to attenuate mitogenic signaling. Downregulation occurs through trafficking of receptors to lysosomes, culminating in proteolytic destruction of both the receptor and ligand; however, endocytic sorting mechanisms that underlie lysosomal targeting remain obscure. The goal of this study was to explore one aspect of the molecular basis for ligandinduced lysosomal targeting and degradation of EGF receptors. In this study, we identify a tyrosine-leucine motif (954YLVI) that is essential for transit of ligand-receptor complexes to lysosomes. When this motif is mutated, HEK 293 cells expressing the mutant receptors demonstrate impaired lysosomal targeting and downregulation compared with wildtype receptors. 954YLVI is highly conserved among EGF receptors from various mammalian and invertebrate species and is critical for receptor downregulation. We propose that 954YLVI works in concert with at least two additional regions within the EGF receptor cytoplasmic domain that are essential for efficiently targeting ligand-receptor complexes to the lysosome. [ABSTRACT FROM AUTHOR]