Endogenous lectin from terminally differentiated epidermal cells

Carbohydrate expression and modification during keratinocyte differentiation in normal human and reconstructed epidermis

Using fluorescein isothiocyanate (FITC)-labeled lectins we were able to demonstrate the presence of specific carbohydrate moieties in normal human and reconstructed epidermis. Evidence is provided that in both cases the strongly reduced lectin staining at the level of the stratum corneum is the result of a hindered accessibility of the lectins in this lipid-rich hydrophobic environment. Isolated corneocytes and purified cornified envelopes (CEs) exhibited clearly glycosylated structures reacting with distinct lectins. The presence of glycosidase activity, particularly in the upper layers of the epidermis characterized by an acidic environment (pH 5.5), indicates that modifications of the sugar residues might be important in epidermal homeostasis, barrier behavior and desquamation. Absent or strongly reduced glycosidase activity in the stratum corneum of reconstructed epidermis with an impaired pH gradient could be in part responsible for the reduced barrier function and the lack of desquamation in this model.

Skin as a route of exposure to protein allergens

Protein contact with skin is associated with a number of clinical conditions, including protein contact dermatitis and immunologic contact urticaria. This article reviews the clinical and other selected evidence that proteinaceous materials penetrate skin. It is concluded that whilst penetration of intact proteins through normal skin is extremely low and without consequence, any damage to the skin barrier may allow penetration. As a result, risk assessment for contact of protein with skin must take into account potential barrier impairment and thus the possibility of both the induction and the elicitation of allergic skin reactions.

Desquamin is an epidermal ribonuclease

Desquamin is a glycoprotein that we have isolated from the upper granular layer and the stratum corneum of human epidermis; it is not ordinarily expressed in submerged cultures, whose terminal differentiation stops short of formation of these layers. The exogenous addition of desquamin to human cultured keratinocytes extended their maturation, and hematoxylin staining indicated a loss of cell nuclei. For confirmation, cultured cells were lysed in situ, and the nuclei were incubated with desquamin for several days, then stained with hematoxylin. Damage to the nuclei was evident: the nuclear inclusions remained intact, while the surrounding basophilic nuclear matrix was degraded. Desquamin was then tested directly for nuclease activity. Ribonuclease activity was determined by incubating desquamin with human epidermal total RNA and monitoring the dose-dependent disappearance of the 28S and 18S ribosomal RNA bands in an agarose/formaldehyde gel. On RNA-containing zymogels, we confirmed the RNase activity to be specific to desquamin. Using synthetic RNA homopolymers, we found the active RNase domains to be limited to cytosine residues. On the contrary, DNA was not degraded by an analogous procedure, even after strand-separation by denaturation.

30-kDa trypsin-like proteases in the plantar stratum corneum

The casein digestible proteases in human plantar stratum corneum were determined to be about 75-kDa, 30-kDa and 25-kDa in molecular weight by zymography. The enzymatic activity of the 75-kDa and 25-kDa proteases was specifically inhibited by chymostatin, which is an inhibitor of chymotrypsin-like serine proteases, and the proteases around 30-kDa were inhibited by leupeptin, a trypsin-like serine protease inhibitor. The enzymatic activity of all these proteases was inhibited by aprotinin. The 30-kDa trypsin-like proteases were heat-stable; their enzymatic activity still remained even after heating at 100 degrees C for 60 minutes. Their optimal pH was around 9, and the activity was higher in the outer part of the stratum corneum than in the inner part.

Ultraviolet rays induced expression of lectins on the surface of a squamous carcinoma keratinocyte cell line

Human keratinocytic cells from squamous carcinoma (SCL-1) present, under resting conditions, relatively low amounts of endogenous lectins (sugar-binding proteins). Upon uv irradiation, they express on their cell surface large amounts of endogenous lectin molecules able to bind neoglycoproteins bearing either alpha-L-rhamnosyl or alpha-D-glucosyl residues. A similar binding specificity was found with normal human keratinocytes under the same culture conditions. At sunlike doses, uv.A (365 nm) was more efficient than uv.B (312 nm) in the expression of such receptors on the surface of SCL-1 cells. The increased presentation of lectins by SCL-1 cells was transient and reached a maximum 4 h after irradiation. Such a specific modulation of receptor expression upon uv irradiation might be biologically significant, considering the numerous intercellular recognition phenomena in skin biology. alpha-L-Rhamnose-specific receptor on SCL-1 could not be distinguished from alpha-D-glucose-specific receptor on the basis of neoglycoproteins binding, uptake, and related inhibitions. Lectin expression was mainly detected on the cell surface, and its overexpression due to uv rays required a de novo protein synthesis process.

Human stratum corneum lipids have a distorted orthorhombic packing at the surface of cohesive failure

The cohesive strength of the stratum corneum is determined by its unique molecular composition and structural architecture. Whereas the structure responsible for corneocyte cohesion has been visualized at the microscopic level, the structure of the intercellular domain has not been characterized at the molecular level. In this report, new insight into the molecular architecture of the stratum corneum has been provided by atomic force microscopy and x-ray photoelectron spectroscopy. The surface layer of human stratum corneum was stripped, yielding the characteristic polygonal corneocytes shown by scanning electron microscopy as well as low resolution atomic force microscopy. With atomic force microscopy, the resolution was increased to allow imaging of the molecular architecture of the stratum corneum. With the high resolution image, a repetitive pattern characteristic of lipids in an ordered state was visualized. The lattice appeared to be orthorhombic where the lattice distances were about 5.5 and 9 angstroms, and the lattice angle was close to 90 degrees. The atomic composition of the superficial layers was 82% carbon, 16.5% oxygen, and 1.4% nitrogen as determined by x-ray photoelectron spectroscopy. The high nitrogen content compared to the calculated stratum corneum lipid composition and measured model lipid composition suggests that proteins were detected. In summary, although proteins are present, the fracture plane of the stratum corneum is largely composed of lipids that appear to have a distorted orthorhombic packing.

Cohesion and desquamation of epidermal stratum corneum

This article attempts to provide a comprehensive review on the roles of various classes of molecules in the cohesion and desquamation of the stratum corneum. In the first part of this monograph we review the field of epidermal differentiation in vivo and vitro, describing the expression and functions of a number of key structural molecules that characterize the process. In the second part we emphasize terminal differentiation and the biogenesis of the stratum corneum. The stratum corneum is a cell layer unique to fully differentiated squamous epithelia such as skin. While it is a dead stratum, it nevertheless is in a homeostatic process of continual shedding and renewal in synchrony with basal cell replication. It is also a degradative layer containing many proteinases and glycosidases in which a variety of intracellular and intercellular macromolecules are degraded. We highlight the molecules localized within the intercorneal matrix that are most likely to play a role in cohesion and desquamation, including: glycoproteins, lipids and enzymes. Because it is difficult to study the stratum corneum and desquamation in the native tissue, we discuss a number of model systems that have been used. The stratum corneum can be dispersed into single squames in different ways; these include mechanical dispersion as well as agents such as detergents and enzymes. The solubilized molecules and the structures remaining can then be studied as to their specific roles in desquamation. Using this approach it is possible to reconstitute multilayered structures that resemble a real stratum corneum. We have shown that glycoproteins play a key role in squame reaggregation and that this process can be modulated with amino sugars in a lectin-like fashion. Cohesion and desquamation can also be studied in tissue culture. Depending on the culture system, the extent of terminal differentiation and squame accumulation varies. Yet desquamation does not normally occur. It can be induced however by the inclusion of exogenous agents such as IFN-gamma which are found in the native epidermis but are absent in vitro. Modulation of desquamation by other exogenous agents is likely to yield further knowledge of how shedding occurs in vivo. Insight has also come from studies of scaling skin disorders. The glycoprotein and lipid profiles are altered in the stratum corneum in many diseases of aberrant terminal differentiation. A number of abnormalities in the levels of cytokines and growth factors have also been reported in the lesional tissue of such diseases.(ABSTRACT TRUNCATED AT 400 WORDS)

Interferon-gamma modulates terminal differentiation and the expression of desquamin in cultured keratinocytes

Interferon (IFN)-gamma has been shown to modulate cell differentiation and the expression of cell surface molecules of cultured human keratinocytes; it also induces cell shedding. We have previously described the properties of desquamin, a cell surface adhesion molecule from the stratum corneum. We report here on the impact of IFN-gamma on the expression of desquamin. We document the related morphological changes in terminal differentiation. We cultured human keratinocytes in three different culture systems: in serum-free medium at low Ca2+ (0.1 mM), at high Ca2+ (1.5 mM), and at high Ca2+ with 10% serum. IFN-gamma (100 U/ml) was added to each culture system after overnight incubation. In all cases, IFN-gamma induced an altered phenotype, as shown by phase contrast and electron microscopy. We exposed cultured cells to antibodies to the desquamins (glycoproteins from the stratum corneum). Immunoflurescent localization and Western blotting showed that the desquamins were expressed only under culture conditions where both serum and IFN-gamma were present. The induction of desquamin expression by IFN-gamma coupled with an increase in cell shedding, suggests that we have developed a suitable culture system for the study of desquamation in vitro.

Identification of late differentiation antigens of human cornified epithelia, expressed in re-organized desmosomes and bound to cross-linked envelope

Little is known about the process leading to desquamation in cornified epithelia. We describe late differentiation antigens (Ag) specific for human cornified squamous epithelia, defined by two murine monoclonal antibodies (MoAb), G36-19 and B17-21, produced after immunization with plantar stratum corneum (SC). Histologically, in epidermis both Ag are cytoplasmic in the lower stratum granulosum (SG), become pericellular in the upper SG, and progressively disappear in the lower SC. In contrast, they persist up to the desquamating corneocytes in the palmoplantar epidermis and hard palate epithelium, as well as in the three cornified epithelial components of the inner root sheath (IRS) of the hair follicle (HF). Cytologically, both Ag are expressed as surface spots only on rough corneocytes. They are largely preserved on cross-linked envelopes (CLE) of the fragile type. Ultrastructurally, both Ag appear in keratinosome-like cytoplasmic vesicles in the upper stratum spinosum (SS) and the SG keratinocytes, then are found in both the regular and reorganizing desmosomes of the SG keratinocytes, and lastly in the corneocyte-specific reorganized desmosomes we propose to name corneodesmosomes. On CLE, the Ag are located on fibrils gathered over the external side of the envelope. Immunochemically, the G36-19--defined epitope is sequential and shared by five non-cytokeratin protein antigens of molecular weight 33.5, 36.5, 40, 49, and 52 kD, the higher molecular weight polypeptides being possibly precursors of the 33.5-kD protein. In contrast, the B17-21 epitope, unaccessible by immunoblotting, is probably conformational. In long-term cultured keratinocytes, the Ag are only expressed when epidermal sheets are morphologically differentiated. The expression is enhanced in the absence of fetal calf serum (FCS) and of epidermal growth factor (EGF). G36-19 and B17-21 Ag participate in a corneodesmosome-CLE superstructure that is probably involved in corneocyte cohesiveness and partly responsible for the mechanical resistance of the SC. These Ag are relevant markers for studying desmosomal maturation during epidermal differentiation and desquamation.

Carbohydrate-binding specificity of calcyclin and its expression in human tissues and leukemic cells

Binding of biotinylated fetuin in a solid-phase assay served as activity assay for purification of calcyclin, the product of a cell growth-related cDNA with homologies to Ca(2+)-binding proteins. Asialofetuin failed to bind to calcyclin, emphasizing the importance of sialic acids. Binding of fetuin was most effectively reduced by N-glycolylneuraminic acid within a panel of mostly negatively charged sugars. Bovine submaxillary mucin and the ganglioside GM1, but not asialo-GM1, proved more effective than neoglycoproteins, carrying negatively charged carbohydrate moieties. Extension of N-acetyl-neuraminic acid to its lactosyl derivative increased its inhibitory potency. Among charge-free carbohydrate residues, only N-acetylglucosamine, lactose, and mannose, but not fucose, melibiose, or N-acetylgalactosamine affected fetuin binding, substantiating the inherent selectivity. Chemical modification with group-specific reagents revealed that lysine and arginine residues appear to be involved in ligand binding that is optimal in the presence of Ca2+, but not Zn2+ and stable up to 1 m NaCl. Biotinylation of calcyclin by modification of carboxyl groups facilitated performance of solid-phase assays with calcyclin in solution, yielding similar results with (neo)glycoproteins in relation to assays with immobilized calcyclin, thereby excluding an impact of binding to nitrocellulose on calcyclin's specificity. Subcellular fractionation disclosed the presence of fetuin-binding activity in all fractions, the specific activity decreasing from the nuclear to the particulate cytoplasmic fraction and the cytoplasmic supernatant. Affinity-purified antibodies were employed to detect high levels of calcyclin expression in acute lymphoblastic, myelogenous, and monocytic leukemia cell lines, but not in myeloma or lymphoblastoid cells. In comparison, most cells were nearly devoid of an O-acetylsialic acid-specific protein that is more abundant in various tissue types than calcyclin.

GP37 is different from filaggrin

The identity of two differentiation markers of human epidermis, filaggrin and a Concanavalin A (Con-A) reactive glycoprotein of 37 kD, has been studied. Human epidermis was extracted in Nonidet P-40 buffer, and the soluble proteins were separated by two-dimensional electrophoresis. Con-A reactive glycoproteins were identified by incubating gels with iodinated lectin followed by autoradiography. Identical, parallel gels were electrophoretically transferred to nitrocellulose paper and filaggrin-related molecules labeled by the specific monoclonal antibody AKH1. We found that the 37-kD Con-A reactive component was resolved by two-dimensional gel electrophoresis into several glycoproteins and that the lectin Con-A does not bind to filaggrin. Under these conditions, the anti-GP37 serum failed to identify any component. However, when applied to human keratinocyte culture extract, AKH1 and the anti-GP37 serum reacted in a similar way. These data show 1) that the 37-kD band is not homogeneous but contains distinct markers of differentiation (filaggrin and Con-A reactive glycoproteins) and 2) that the GP37 antibody's specificity is for the filaggrin precursor.

Cell shedding from human plantar skin in vitro: evidence that two different types of protein structures are degraded by a chymotrypsin-like enzyme

A recently described endogenous proteolytic process in pieces of human plantar stratum corneum incubated in vitro has been further studied. This process leads to a decrease in cohesion between the cells that had been facing outwards in vivo. Using two methods, that differed with respect to efficiency, to detach surface cells with decreased cohesion, the process could be divided into two steps. The first step took place irrespective of the presence of ethylenediaminetetraacetate (EDTA) and led to a moderate decrease in cohesion between surface cells. The second step occurred only in the presence of EDTA and advanced to a point where the surface cells could be separated from the remaining cohesive tissue pieces by simple agitation. Both degradation steps could be inhibited by aprotinin and chymostatin but not by leupeptin. Zinc sulfate inhibited the first step. The results indicate that there are two different types of protein structures being degraded during the process of cell shedding in vitro. A chymotrypsin-like enzyme may be involved in the process.

Effect of gamma-interferon on lectin-binding glycoproteins in cultured human keratinocytes

We report the effect of exposure of human keratinocyte cultures to human recombinant gamma-interferon (g-IFN) on the expression of glycoproteins. Concanavalia ensiformis agglutinin (Con-A), and Arachis hypogaea agglutinin (PNA) were used to investigate expression of glycoproteins. NP-40 extracts from cultures grown with or without 100 U/ml g-IFN were analyzed by incubation of SDS-polyacrylamide gels with 125I-labeled lectins. Comparison of Con-A binding glycoprotein profiles showed both qualitative and quantitative changes related to the effect of g-IFN. Differences were also apparent after labeling of the gels with PNA. A limited number of components were labeled, with most of the reactivity falling within a couple of diffuse bands with high molecular weight (300 to 360 kDa). These components were strongly labeled in extracts from cells grown in the presence of g-IFN, but weakly reactive in control cultures. Neuraminidase treatment unmasked a 205 kDa PNA binding molecule only when cells were cultured in the absence of g-IFN. These changes are interpreted in terms of increased keratinocyte differentiation induced by g-IFN and demonstrate that glycoproteins bearing carbohydrate residues available to lectins Con-A and PNA have to be taken into account to better understand the complex action of this lymphokine. In inflammatory lesions, such changes in the glycoproteins of keratinocytes expressing HLA-DR antigens remain to be explored.

Interaction between corneocytes and stratum corneum lipid liposomes in vitro

Small unilamellar vesicles were made from a mixture of epidermal ceramides (45%), cholesterol (35%), free fatty acids (15%) and cholesteryl sulfate (5%). Isolated corneocytes prepared from pig epidermis were added to the liposomes and the interaction between corneocytes and liposomes was studied by (1) thin-section electron microscopy and (2) monitoring the release of aqueous contents of the vesicles by following the fluorescence intensity of carboxyfluorescein entrapped in the vesicles. The vesicles adsorbed readily onto the corneocytes and slowly transformed into lamellar sheets. Enhanced fluorescence intensity indicated a corneocyte-induced membrane fusion process that resulted in the release of aqueous contents of the vesicles. The results suggest a cohesive role for the corneocyte cell envelope, which consists of a monomolecular layer of lipids covalently bound to the outside of a cross-linked protein envelope. This may be one of the major factors in the reassembly of extruded membranous disks into lamellar sheets which occurs during the final stages of epidermal differentiation.

Identification of a cell cycle-dependent gene product as a sialic acid-binding protein

A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein.

Purification of proteins from polyacrylamide gels, free of detergent or dye

A two step procedure recovers proteins from sodium dodecyl sulfate polyacrylamide gels. The proteins are eluted by electrophoretic dialysis. The eluent is then passed through an Amberlite CG-400 anion-exchange resin. The recovery of protein is nearly total. The recovered proteins have no detectable sodium dodecyl sulfate contamination. With gels that have been stained with Coomassie Brilliant Blue R, the procedure recovers the proteins free of the dye. We have used this procedure successfully during the purification of epidermal glycoproteins.