Molecular changes in the cell surface of differentiating epidermal keratinocytes

The specific binding of lectins to the cell surfaces in particular epidermal strata indicates that oligosaccharide moieties of the glycoconjugates on the cell membrane are altered as the keratinocyte differentiates. The disappearance of binding by the Bandeiraea simplicifolia isolectin I-B4 (BS I-B4) and the appearance of binding by the Ulex europeus agglutinin I (UEA), which occur as the basal cell moves up into the spinous layer of the cutaneous epidermis of the newborn rat, could result from (a) redistribution of existing glycoconjugates in the cell membrane, (b) hydrolysis of galactosyl residues exposing fucosyl binding sites, or (c) addition of fucosyl residues to pre-existing oligosaccharides with specificity for the galactoside. Isolation of glycoproteins from the cell membrane using lectin-affinity column chromatography on Sepharose-4B showed a decrease in the amount of protein which bound to the BS I-B4 and an increase in the protein with affinity for the UEA as the ratio of spinous to basal cells increased in the population of cells from which the glycoproteins were obtained. These data indicate the existence of two different classes of glycoproteins on the surfaces of cells in the lower epidermis and argue against a redistribution of glycoconjugates as the explanation for the selective binding of specific lectins observed in tissue sections. Exposure of sections of skin to alpha-galactosidase completely eliminated the binding of fluorescein isothiocyanate-labeled (FITC) BS I-B4 in the lower epidermis but did not result in additional binding of UEA. Exposure to fucosidase eliminated binding by UEA and increased the binding of BS I-B4 in the spinous layer.(ABSTRACT TRUNCATED AT 250 WORDS)