CHARACTERIZATION OF AN 80-KD MEMBRANE GLYCOPROTEIN (GP80) OF HUMAN KERATINOCYTES - A MARKER FOR COMMITMENT TO TERMINAL DIFFERENTIATION IN-VIVO AND IN-VITRO

We have characterized an 80-kD cell-surface glycoprotein (gp80) identi fied by monoclonal antibody BT 15, the expression of which is closely associated with a commitment to terminal squamous or follicular differ entiation of keratinocytes in normal adult and fetal human epidermis, Maximum expression was found in the suprabasal layers, but basal cells located at the epidermal sulci were also clearly positive, in contras t to the virtually negative basal cells at the epidermal ridges, This protein was also present in benign hyperproliferative disorders of the epidermis (i.e., common warts, keratoacanthoma, psoriasis, and seborr hoic keratoses) with monoclonal antibody BT 15 preferentially staining suprabasal cells and some basal cells at the epidermal sulci. Gp80 wa s completely lacking in most basal cell carcinomas; the only exception s were two cases of partially cornifying tumors that were strongly sta ined around keratotic pearls, In squamous cell carcinomas, gp80 was ex pressed in keratinized areas of the tumors. In organotypic keratinocyt e cultures that resemble the in vivo situation, gp80 was strongly expr essed in the suprabasal layers, However, unlike known markers for term inal differentiation, gp80 was weakly expressed by basal cells, Synthe sis rates of gp80 were high in keratinocyte cell suspensions freshly p repared from skin, and decreased in primary cultures and first and sec ond subcultures (ratio 10:4:2:1), Elevated concentrations of the Ca+that increased stratification of cultured keratinocytes resulted in a two- to threefold increase of gp80 synthesis, Gp80 was not synthesized at detectable levels by the immortal keratinocyte cell line HaCaT; ho wever, it was expressed in HaCaT cultures treated with mitomycin C, in dicating an association with cessation of growth, Pulse-chase experime nts revealed that gp80 is synthesized from a 55-kD precursor molecule, the maturation of which was prevented by treating cells with tunicamy cin, Glycosidase digestion of BT 15 immunoprecipitates from untreated cells indicated that the predominant post-translational modification o f the protein is N-linked glycosylation, Our data indicate that gp80 i s a glycoprotein that is expressed by growth-arrested human keratinocy tes or as part of the terminal differentiation program.