title: Expression of distinct desmocollin isoforms in human epidermis.
abstract: Previous evidence suggested the presence of two distinct desmocollin isoforms in human epidermis. These isoforms have now been distinguished at the protein level using monoclonal and polyclonal antibodies against N-terminal fragments of desmosomal glycoprotein (DG) IV/V isolated from plantar callus and antibodies against a fusion protein containing the extracellular domain of DGII/III. Immune blotting of glycoprotein fractions from whole epidermis, plantar callus, psoriatic scales and cultured keratinocytes showed that intact DGIV/V and its proteolytic fragments consistently migrated faster than DGII/III during SDS-PAGE. The apparent Mr difference between the two isoforms was in the range 2-5 kD. DGIV/V was the predominant species in epidermal tissue but was much less prominent in cultured cells by immune-blotting and immune precipitation. This is consistent with the differentiation-related expression of desmocollins revealed by immunofluorescence. DGIV/V was strongly expressed in the upper spinous/granular layer of the epidermis whereas DGII/III was more prominent in the basal layers of the tissue. The DGIV/V monoclonal (LH50) recognized an N-terminal, Ca(++)-sensitive epitope, because its staining of unfixed epidermal tissue was markedly influenced by Ca++ levels. Ca++ inhibition was observed at concentrations as low as 50 microM, suggesting its possible physiologic significance. Ca++ inhibition of LH50 binding was also observed in an enzyme-linked immunosorbent assay system using denatured glycoproteins although higher concentrations were required. It remains to be seen whether direct effects of Ca++ on desmocollin conformation are involved in the regulation of keratinization by extracellular Ca++.
authors.affiliation: Dermatology Research Centre, Harrow, London, U.K.
authors.forename: I A
authors.initials: IA
authors.lastname: King
authors.forename: A
authors.initials: A
authors.lastname: Tabiowo
authors.forename: P
authors.initials: P
authors.lastname: Purkis
authors.forename: I
authors.initials: I
authors.lastname: Leigh
authors.forename: A I
authors.initials: AI
authors.lastname: Magee
mesh_terms: D000911:Antibodies, Monoclonal / Q000187:drug effects; D002146:Bony Callus / Q000473:pathology; D002118:Calcium / Q000032:analysis / Q000494:pharmacology; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000032:analysis*; D051187:Desmocollins; D051180:Desmoplakins; D003896:Desmosomes / Q000737:chemistry; D004817:Epidermis / Q000737:chemistry; D006801:Humans; D015151:Immunoblotting; D007536:Isomerism; D015603:Keratinocytes / Q000166:cytology; D008297:Male; D011565:Psoriasis / Q000473:pathology; D012867:Skin / Q000737:chemistry*; D013194:Staining and Labeling
chemical_list: D000911:Antibodies, Monoclonal; D003598:Cytoskeletal Proteins; D051187:Desmocollins; D051180:Desmoplakins; D002118:Calcium