Refined Characterization of Corneodesmosin Proteolysis during Terminal Differentiation of Human Epidermis and Its Relationship to Desquamation* Received for publication, January 10, 2001, and in revised form, February 16, 2001 Published, JBC Papers in Press, February 16, 2001, DOI 10.1074/jbc.M100201200 Michel Simon‡, Nathalie Jonca‡§, Marina Guerrin‡, Marek Haftek¶, Dominique Bernard, Ce ´ cile Caubet‡**, Torbjo ¨ rn Egelrud‡‡, Rainer Schmidt, and Guy Serre‡§§ From the ‡Department of Biology and Pathology of the Cell, INSERM Contrat Jeune Formation 96 – 02, Toulouse-Purpan School of Medicine, University of Toulouse III (Institut Fe ´de ´ratif de Recherche 30, INSERM-CNRS-Universite ´ P. Sabatier- Centre Hospitalier Universitaire), 31073 Toulouse, France, ¶INSERM U346/CNRS “Human Skin and Immunity”, 69437 Lyon, France, L’Ore ´al, Life Science Research, Centre Charles Zviak, 92583 Clichy, France, and the ‡‡Department of Dermatology, University Hospital, S-901 85 Umea ˚ , Sweden Corneodesmosin is a putative adhesion glycoprotein lo- cated in the extracellular part of the desmosomes in the upper layers of the epidermis. Synthesized by granular ke- ratinocytes as a 52–56-kDa protein, corneodesmosin is pro- gressively proteolysed during corneocyte maturation. This processing is a prerequisite for desquamation. Two glycine- and serine-rich domains of the protein might take on the conformation of adhesive secondary structures similar to glycine loops. Corneodesmosin proteolysis was further character- ized. Deglycosylation experiments and reactivity with lectins demonstrated that the corneodesmosin carbohy- drate moiety does not prevent the proteolysis. Immuno- blotting, immunohistochemistry, and immunoelectron microscopy experiments using affinity-purified anti- peptide antibodies raised to four of the five structural domains of corneodesmosin and a monoclonal antibody against its fifth central domain showed that the first step in corneodesmosin processing is the cleavage of its extremities and probably occurs before its incorpora- tion into desmosomes. Then the glycine loop-related do- mains are cleaved, first the N-terminal and then part of the C-terminal domain. At the epidermis surface, the multistep proteolytic cleavage leaves intact only the central domain, which was detected on exfoliated cor- neocytes and probably lacks adhesive properties. Im- portantly, corneodesmosin was demonstrated to be a preferred substrate of two serine proteases involved in desquamation, the stratum corneum tryptic and chy- motryptic enzymes. Keratinocytes constitute the major cellular population in epidermis, where they proliferate in the innermost basal layer. During their transit through the spinous and granular layers toward the skin surface, keratinocytes express a specific pro- gram of terminal differentiation that culminates in the forma- tion of corneocytes (1, 2). These dead “mummified” cells accu- mulate and form the outermost cornified layer of epidermis or stratum corneum, (SC) 1 , which plays a critical role in the physical protection of the body. To maintain a constant SC thickness, as observed in normal epidermis, the contin- uous generation of corneocytes is balanced by cell shedding at the external surface in the tightly regulated process of desquamation (3). Cohesion of the SC is largely dependent on modified desmo- somes or corneodesmosomes. In fact, at the transition between the granular layer and the SC, profound changes are observed in desmosome morphology. The cytoplasmic plaque, which pro- vides anchorage for cytokeratin intermediate filaments, is no longer visible, and a homogeneous electron-dense plug occurs instead of the characteristic symmetrical tri-lamellar structure of the extracellular core (4 –9). Corneodesmosome degradation is of major importance in the desquamation process (6 –9). In xerosis and various hyperkeratotic states, including psoriasis, accumulation of scales is observed, and the number of cor- neodesmosomes persisting over the corneocyte surface in the upper SC is greatly increased (10 –13). Several serine pro- teases, including the stratum corneum chymotryptic enzyme (SCCE) and the stratum corneum tryptic enzyme (SCTE), are thought to be involved in corneodesmosome proteolysis (14 – 18). SCCE and SCTE belong to the kallikrein family, a subfam- ily of serine proteases whose genes are located in a single locus at 19q13.3–13.4 (19). At a molecular level, the two major adhesive transmembrane components of corneodesmosomes are desmoglein 1 (Dsg1) and desmocollin 1 (Dsc1) (20, 35). Desmogleins and desmocollins are glycoproteins belonging to the family of cadherins, calcium- dependent cell adhesion molecules. Each desmosomal cadherin is known to exist in three different isoforms encoded by three different genes. Their expression is tissue-specific and differ- entiation-dependent, Dsg1 and Dsc1 being expressed in the uppermost layers of the epidermis (for a review see (21)). We identified another protein, corneodesmosin (Cdsn), lo- cated in the corneodesmosome core (9). Cdsn is synthesized in the upper spinous and/or lower granular layers in the form of a 52–56-kDa phosphorylated basic glycoprotein. It is ex- * This study was supported in part by grants from the Universite ´ Paul Sabatier-Toulouse III, from L’Ore ´al (Paris, France) and from IN- SERM. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. § Supported by a postdoctoral fellowship from the Socie ´te ´ de Secours des Amis des Sciences and from the Singer Polignac Foundation. ** Recipient of a grant from the French Ministry of Research and Technology. §§ To whom correspondence should be addressed: Laboratoire de Biologie Cellulaire et Cytologie, CHU Purpan, Place du Dr Baylac, 31059 Toulouse Cedex, France. Tel.: 33-5-61-77-23-95; Fax: 33-5-61-77- 76-20; E-mail: serre.g@chu-toulouse.fr. 1 The abbreviations used are: SC, stratum corneum; SCCE, stratum corneum chymotryptic enzyme; SCTE, stratum corneum tryptic en- zyme; Dsc, desmocollin; Dsg, desmoglein; Cdsn, corneodesmosin; MoAb, monoclonal antibody; PAGE, polyacrylamide gel electrophoresis. THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 276, No. 23, Issue of June 8, pp. 20292–20299, 2001 © 2001 by The American Society for Biochemistry and Molecular Biology, Inc. Printed in U.S.A. This paper is available on line at http://www.jbc.org 20292 by guest on June 11, 2020 http://www.jbc.org/ Downloaded from