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K.L. Carraway, W.M. Lomako, C.A. Carrraway, J. Lomako; A Role for Sialomucin Muc4 in Desquamation of Cultivated Rat Corneal Epithelium . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1340.
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Purpose: To study expression of Muc4 and its interaction with ErbB2 in the process of rat corneal epithelium desquamation. Methods: The corneal epithelium was cultivated as described in accompanying poster. Expression of Muc4 and growth factor receptors was monitored by Western blots or by immunofluorescence using specific antibodies. Immunoprecipitation-immunoblot analysis was used for detection of Muc4-ErbB2 receptor complexes. Desquamated cells were collected from the medium by centrifugation. Apoptosis in epithelial layers and in desquamated cells was determined by annexin V- propidium iodide and TUNEL techniques. Serum starved cultures (24 h) were treated overnight with epidermal growth factor or for 5 minutes with neuregulin. After treatment Muc4 expression and ErbB2 phosphorylation were examined. Results: Muc4 acts as a potent anti-cell adhesive. Its transmembrane subunit, ASGP-2, acts as intermembrane ligand for ErbB2 tyrosine kinase receptor, and is expressed in abundant amount in cultivated corneal rat epithelium, as is ErbB2. Immunofluorescence and immunoprecipitation studies indicated that the proteins colocalized and associated in a complex in cultivated rat corneal epithelium. Treatment with neuregulin increased significantly phosphorylation of ErbB2 in the complex. Muc4 was predominantly membrane bound, but secreted and intracellular soluble forms were also present. Electron microscopy and immunofluorescence studies revealed cells committed to desquamation. These cells and those already desquamated were rich in microvilli and expressed significant amount of the membrane-bound form of Muc4; they were not apoptotic. EGF inhibited desquamation and promoted secretion of Muc4. Conclusions: Desquamation of cultivated corneal epithelium is an internally programmed process and coincides with high expression of membrane bound sialomucin Muc4. This process may be regulated through growth factor receptors.
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