Epican, a heparan/chondroitin sulfate proteoglycan form of CD44, mediates cell-cell adhesion

Epican is a heparan/chondroitin sulfate proteoglycan form of CD44 and is expressed on the surface of keratinocytes from the basal layer to the granular layer of the epidermis. To analyze the adhesive properties of epican apart from the influence of other adhesive molecules found on keratinocytes, mouse L cell fibroblasts were transfected with CD44Epican cDNA. The epican expressed on the surface of transfected L cells was predominantly a heparan or chondroitin sulfate proteoglycan. The CD44Epican-transfected L cells acquired: (a) a selfaggregating phenotype that required hyaluronan but was calcium-independent; and (b) a new capacity to adhere to keratinocytes, a property that was blocked by an antiepican antibody. Both aggregation and adhesion of CD44Epican-transfected cells were completely prevented by pretreatment with hyaluronidase, but were totally restored by the addition of exogenous hyaluronan. Aggregation of transfected L cells was minimally influenced by other glycosaminoglycans, but adhesion of transfected L cells to keratinocytes was substantially inhibited by heparin. The ability of epican to mediate adhesion between keratinocytes was evaluated in a newly developed adhesion assay. In the presence of 0.03 mM calcium, a monoclonal antibody against epican inhibited keratinocyte adhesion to keratinocyte monolayers by 80%. These data demonstrate that epican causes adhesion and aggregation in the transfected L cell model system, that the adhesive function of epican is hyaluronan-dependent, and that epican could have an adhesive function in intact epidermis.