Characterisation of the peanut lectin-binding glycoproteins of human epidermal keratinocytes.
We have previously shown that peanut lectin (PNA) binding is a useful marker of keratinocyte terminal differentiation and have identified two PNA-binding glycoproteins with electrophoretic mobilities of approximately 250 kDa and 110 kDa [11]. We now report that in epidermis and stratified cultures of keratinocytes the binding patterns of PNA and the sialic acid-specific lectin Limax flavus agglutinin (LFA) are complementary, with LFA showing specificity for cells in the basal layer. LFA bound to the 250-kDa glycoprotein immunoprecipitated with an antiserum raised against the PNA-binding glycoproteins (anti PNA-gp), but not to the 110-kDa glycoprotein; it also bound additional high-molecular-weight material. These data suggest that the 250-kDa glycoprotein is expressed in the basal layer in a form with terminal sialic acid residues and suprabasally in a form with terminal galactose. LFA and anti-PNA-gp stained all cells in a range of cultured epithelial lines tested, whereas PNA stained only cells that had lost contact with the culture substratum, raising the possibility that loss of sialic acid residues is associated with stratification. Anti PNA-gp recognized glycoproteins of differing mobilities in these lines. Anti PNA-gp also stained epithelial cells in all tissues tested. In keratinocytes the PNA-binding glycoproteins were localised to the cell surface by immunoelectron microscopy; they were abundant on the microvilli and absent from desmosomal junctions. In conclusion, we have obtained further information about the nature of the PNA-binding glycoproteins in keratinocytes and related glycoproteins in other epithelial cell types.