Comparative studies of keratins isolated from psoriasis and atopic dermatitis

Notch signaling may be involved in the abnormal differentiation of epidermal keratinocytes in psoriasis

Localization of each keratin isoform differs among epidermal layers. Proliferating basal cells synthesize keratin 14 (K14) and suprabasal cells express keratin 10 (K10) in normal skin. Notch signaling is essential for keratinocyte differentiation. Notch1 is expressed in all epidermal layers, Notch2 in the basal cell layer and Notch3 in basal cell and spinous cell layers in normal epidermis. It has been poorly elucidated how localization and expression levels of Notch molecules are related to epidermal molecular markers K10 and K14 in psoriatic skin with abnormal differentiation of epidermal tissue. This study aimed to investigate the relationship between abnormal differentiation of epidermal cells in psoriatic skin and expression of Notch molecules. We investigated keratins (K14 and K10) and Notches (1, 2, 3 and 4) using immunohistochemistry in psoriatic skin (n=30) and normal skin (n=10). In normal skin, K14 and K10 were discretely observed in the basal cell layer and suprabasal layer, respectively. In psoriatic skin, K14 was expressed in the pan epidermal layer while it and K10 were co-expressed in some middle suprabasal layer cells. Notch1, 2, 3, and 4 localized in all epidermal layers in normal skin. In psoriatic skin, Notch1, 2, and 4 mainly localized in suprabasilar layers and Notch3 is lacalized in pan epidermal, suprabasilar, and basilar layers. Protein and mRNA of Notch1, 2, and 3 isoforms decreased in psoriatic epidermis compared with normal epidermis. These data suggest that decrements in these Notch molecules might cause aberrant expression of K10 and K14 leading to anomalous differentiation of the epidermis in psoriatic lesions.

New drugs in the treatment of psoriasis

Psoriasis is one of the most common skin disorders affecting approximately 2% of the population; the disease is recurrent and can be very debilitating. The cause of psoriasis is unknown, although it appears to be an autoimmune disease with a genetic component to its aetiology. Past topical treatments such as emollients, coal tar and dithranol have been messy, cosmetically unacceptable or of low efficacy, while older systemic therapies have suffered from significant side effects. Newer drugs with better therapeutic indexes and new antiproliferative/immunomodulatory therapies based on an increased understanding of the origins of psoriasis have brought us closer to the goal of safely and efficaciously treating the disease. This review will cover the newest topical and systemic drugs currently in use, in clinical trials or preclinical development.

Keratin expression in cutaneous lichen planus

The characteristic expression of keratins by keratinocytes is well documented. A typical 'hyperproliferative' profile of epidermal keratin expression occurs in psoriasis, wound healing and warts. This study analyses keratin expression in cutaneous lichen planus to determine abnormalities of differentiation occurring in this inflammatory disorder. Using a panel of monoclonal antibodies 28 samples (20 patients) were studied. The results showed that squamous differentiation was unaffected, with keratins K1 and K10 being expressed normally for the site sampled. The main abnormalities included extension of reactivity of the basal cell marker, LH8, into the suprabasal compartment. Keratin K17, usually restricted to adnexal structures, was variably expressed in the basal and suprabasal layers of the interfollicular epithelium of affected epidermis. Keratins K6 and K16, found suprabasally in hyperproliferative states, were detected both basally and suprabasally in all diseased samples. The keratin profile in lichen planus is analogous to the wound healing response. Suprabasal keratin K17 is found in psoriasis, wound healing and viral warts so the changes in keratin K17 may reflect hyperproliferative changes. It is likely that the changes in epidermal keratin expression are due to up-regulation of specific keratin genes by the production of cytokines and inflammatory mediators from the lymphocytic infiltrate typical of lichen planus.

Keratinocyte differentiation in psoriatic scalp: morphology and expression of epithelial keratins

The morphology of hair follicles was examined in psoriatic scalp biopsies and compared with normal scalp. In scalp psoriasis the lower outer root sheath and hair matrix were not affected by the psoriatic changes, although there was an irregular expansion in the proximal lower outer root sheath. This area has been characterized, by the presence of keratin K19-containing cells, as the putative stem cell region. In addition, marked shrinkage of the sebaceous glands was seen in the psoriatic scalp, as previously reported. A panel of monospecific monoclonal antibodies to individual epithelial keratins was used to analyse scalp specimens immunohistochemically. Keratin expression in scalp was generally unaffected by psoriasis, except for widespread expression of suprabasal keratins K16 and K17 in suprabasal interfollicular psoriatic scalp epidermis. Simple epithelial keratins K8 and K18 were not found in follicular epithelium from either normal or psoriatic scalp, using multiple monospecific antibodies. This study shows that keratin K17 is induced suprabasally during epidermal hyperproliferation, and cannot therefore be considered a hair follicle-specific keratin.

Response of psoriasis to a new topical retinoid, AGN 190168

BACKGROUND

Oral retinoids have been widely used in psoriasis, but topical forms have been ineffective or irritating.

OBJECTIVE

Our purpose was to determine the clinical and molecular effects of a new topical retinoid, AGN 190168, on psoriasis.

METHODS

Seven patients with psoriasis were treated for 2 weeks with topical retinoid and 2 weeks with vehicle. Two control subjects with psoriasis were treated for 2 weeks with vehicle alone. Biopsy specimens from normal skin as well as from untreated and treated psoriatic lesions were compared by immunohistochemical analysis. Differentiation and inflammatory markers were studied.

RESULTS

Clinical improvement was seen in all seven patients after 2 weeks of treatment. Improvement was still present, but not significant, after 2 additional weeks of vehicle application. Histologic examination showed a return to a more normal morphology in four of seven biopsy specimens, which correlated with filaggrin expression. There was a diminution in the precocious expression of keratinocyte transglutaminase, keratin 16, and involucrin, as well as a decrease in epidermal growth factor receptor and in the number of cells expressing intercellular adhesion molecule type 1 and HLA-DR.

CONCLUSION

Clinical and histologic improvements were seen in psoriasis in association with the topical application of AGN 190168 at 2 weeks, including decreased inflammation and restoration of normal epidermal differentiation. Small patient numbers and the possibility that the changes were related to clinical improvement alone and not the topical agent preclude definitive conclusions.

Normal psoriatic epidermis expression of hyperproliferation-associated keratins

Keratin expression in lesional, marginal and uninvolved psoriatic epidermis was analysed by one- and two-dimensional gel electrophoresis and immunoblotting. Keratins K1, K5, K6, K10, K14, and K16 were identified in lesional epidermis. Keratins K6 and K16 were found in all epidermis probes of uninvolved skin, but never occurred in normal epidermis of control skin samples. By means of laser-densitometric evaluation of one-dimensional gels a downregulation of K1 and K10 and an upregulation of K6 and K16 was found in psoriatic epidermis. Unexpectedly, the level of K5 was considerably lower and the level of K14 considerably higher in lesional skin than in normal epidermis. These results demonstrate that not only basal keratinocytes in lesional epidermis but also suprabasal keratinocytes in uninvolved psoriatic epidermis express an altered differentiation pattern. The latter phenomenon could be very important in understanding the development of the so-called "Köbner effect" in psoriatic epidermis.

Effect of retinoids on hyperproliferation-associated keratins K6 and K16 in cultured human keratinocytes: a quantitative analysis

The keratin patterns of human epidermal keratinocytes cultured on a 3T3-feeder layer in the presence of 10(-8) M non-aromatic (all-trans retinoic acid and 13-cis retinoic acid) and polyaromatic (arotinoid, arotinoid-sulfone, and free arotinoic-acid) retinoids were analyzed by high resolution one- and two-dimensional gel electrophoresis and immunoblotting. Laser densitometric evaluation of one-dimensional gels allowed to quantitate the changes within the keratin patterns and revealed an increase in the expression of keratins K13, K15, and K19 as induced by both non-aromatic and polyaromatic retinoids, except for the parent compound arotinoid. This would then indicate that such keratinocytes are pursuing a more embryonic type of differentiation. In evaluating the data for the hyperproliferation-associated keratins K6 and K16 we noticed an unexpected result: except for all-trans retinoic acid, these two keratins showed opposite responses. As compared to control cultures, the amount of K6 did generally increase, while K16 was reduced, with arotinoid acid being the most effective retinoid. The apparently uncoupled expression of K6 and K16 appeared also to be concentration dependent when 13-cis retinoic acid at concentrations of 10(-9), 10(-8), and 10(-7) M was analyzed. Considering the overall antiproliferative potency of retinoids, we therefore conclude that K16 alone, rather than the pair K6/K16, should be regarded as a proliferation-related keratin and as such may be used as a sensitive marker to evaluate keratinocyte proliferation.

Unusual patterns of keratin expression in the overlying epidermis of patients with dermatofibromas: biochemical alterations in the epidermis as a consequence of dermal tumors

Dermatofibromas are frequently associated with acanthosis of the overlying epidermis. Using monospecific antisera and cRNA probes, we have examined the pattern of expression of keratin and keratin mRNA in the affected epidermis of patients with these dermal tumors. Our studies reveal several abnormalities in keratin expression within the thickened areas of overlying epidermis. In two of 15 patients, we detected K6 and K16, keratins which are frequently associated with epidermal diseases of hyperproliferation but are not present in normal epidermis. In both cases, K6 and K16 were found in suprabasal layers, similar to that seen for psoriasis and squamous cell carcinomas. Expression of K6 and K16 in skin samples from patients with dermatofibromas seemed to be dependent upon how near was the tumor to the overlying epidermis, and possibly upon the degree of cellularity within the tumor mass. A second aberration in keratin expression, and one which did not appear to be linked to K6/K16 expression, was the altered expression of the basal epidermal keratin K14. Expression of this keratin and its mRNA was variable, often extending into multiple suprabasal layers and including both basal-like and squamous-like cells. In contrast to the expression of K6/K16, aberrant expression of K14 was a relatively frequent event, occurring in greater than 70% of the dermatofibroma skin samples examined. These observations provide the first biochemical evidence in support of previous morphologic studies, indicating that alterations in epidermal differentiation can occur as a consequence of dermal skin tumors.

Increased membrane-associated transglutaminase activity in psoriasis

Terminal differentiation of human skin involves the formation of an insoluble cross-linked protein envelope (CLE), which functions as an external barrier. To characterize terminal differentiation in the skin disease psoriasis, we have measured 1) membrane-associated transglutaminase (mTGase) activity, the rate limiting enzyme in the formation of CLE, and 2) the number of CLE in biopsies from normal and psoriatic skin. mTGase activity was increased 5-fold (p less than 0.0001) in psoriatic versus normal skin. Kinetic analysis revealed that the increased activity was due to an elevation in the Vmax of the enzyme. In addition, the number of CLE was 10-fold greater in psoriatic compared to normal skin. The increase in mTGase and CLE in psoriasis is in contrast to the decrease in other markers of terminal differentiation in skin, such as synthesis of specific intermediate filaments, observed in this disease.

The use of retinoic acid to probe the relation between hyperproliferation-associated keratins and cell proliferation in normal and malignant epidermal cells

When cells from normal human epidermis and from the human squamous cell carcinoma line SCC-13 were seeded on floating rafts of collagen and fibroblasts, they stratified and underwent terminal differentiation. Although the program of differentiation in SCC-13 cells was morphologically abnormal, the cultures resembled normal epidermal raft cultures by expressing the terminal differentiation-specific keratins, K1/K10, and by restricting their proliferative capacity to the basal-like cells of the population. In addition, the differentiating cells of both normal and SCC-13 raft cultures expressed keratins K6 and K16, which are not normally expressed in epidermis, but are synthesized suprabasally during wound-healing and in various epidermal diseases associated with hyperproliferation. While the behavior of normal and SCC-13 rafts was quite similar when they were cultured over normal medium, significant biochemical differences began to emerge when the cultures were exposed to retinoic acid. Most notably, while the SCC-13 cultures still stratified extensively, they showed a marked inhibition of both abnormal (K6/K16) and normal (K1/K10) differentiation-associated keratins, concomitantly with an overall disappearance of differentiated phenotype. Surprisingly, the reduction in K6/K16 in retinoid-treated SCC-13 cultures was not accompanied by a decrease in cell proliferation. Using immunohistochemistry combined with [3H]thymidine labeling, we demonstrate that while the expression of K6 and K16 are often associated with hyperproliferation, these keratins are only produced in the nondividing, differentiating populations of proliferating cultures. Moreover, since their expression can be suppressed without a corresponding decrease in proliferation, the expression of these keratins cannot be essential to the nature of the hyperproliferative epidermal cell.

An elevated level of autoantibodies against 48- to 50-kd keratins in the serum of patients with psoriasis

Studies on the anti-keratin intermediate filament autoantibodies (anti-KIF-Abs) in sera from psoriasis (Pso) patients were performed by immunoblotting and enzyme-linked immunosorbent assay (ELISA). According to their reactivities against keratin subunits (50, 56.5, 58, and 63-68 kd), sera were divided into four groups. However, no significant differences in these reactive patterns were found between healthy volunteers and Pso patients. In the second experiment, anti-KIF-Abs in sera from Pso patients, pustulosis palmaris et plantaris (PPP) patients, atopic dermatitis (AD) patients, systemic lupus erythematosus (SLE) patients, and healthy volunteers were determined by ELISA, using as substrate keratins purified from normal human stratum corneum and 48- and 50-kd keratins purified from psoriatic stratum corneum. The serum titers of anti-KIF-Abs against 48- and 50-kd keratins in Pso patients were significantly higher than those in PPP patients, AD patients, SLE patients, or healthy volunteers. The elevated titers of anti-KIF-Abs against the 48- and 50-kd keratins in sera of Pso patients showed a significant decrease with improvement of psoriatic lesions. The above results suggest that anti-KIF-Abs against 48- and 50-kd keratins in sera of Pso patients have some relevance to the severity of the disease and can be used as a marker for the evaluation of the disease activity of psoriasis.

Use of monospecific antisera and cRNA probes to localize the major changes in keratin expression during normal and abnormal epidermal differentiation

We report here the isolation and characterization of three antisera, each of which is specific for a single keratin from one of the three different pairs (K1/K10, K14/K5, K16/K6) that are differentially expressed in normal human epidermis and in epidermal diseases of hyperproliferation. We have used these antisera in conjunction with monospecific cRNA probes for epidermal keratin mRNAs to investigate pathways of differentiation in human epidermis and epidermal diseases in vivo and in epidermal cells cultured from normal skin and from squamous cell carcinomas in vitro. Specifically, our results suggest that: (a) the basal-specific keratin mRNAs are down-regulated upon commitment to terminal differentiation, but their encoded proteins are stable, and can be detected throughout the spinous layers; (b) the hyperproliferation-associated keratin mRNAs are expressed at a low level throughout normal epidermis when their encoded proteins are not expressed, but are synthesized at high levels in the suprabasal layers of hyperproliferating epidermis, coincident with the induced expression of the hyperproliferation-associated keratins in these cells; and (c) concomitantly with the induction of the hyperproliferation-associated keratins in the suprabasal layers of the epidermis is the down-regulation of the expression of the terminal differentiation-specific keratins. These data have important implications for our understanding of normal epidermal differentiation and the deviations from this process in the course of epidermal diseases of hyperproliferation.

Ultrastructure of psoriatic epidermis

The ultrastructure of human affected and unaffected psoriatic epidermis was studied in skin biopsies from 5 patients and 3 normal controls. Transmission electron microscopic investigations revealed abnormalities in all cell layers of the affected epidermis. Common to psoriatic keratinocytes from affected epidermis was the reduction of tonofilaments. The essential ultrastructural changes were located in the stratum granulosum and stratum corneum. Thus, absence of the fusion between the keratohyalin granules and the tonofilaments was found in stratum granulosum. The keratinocytes of the stratum corneum showed a large accumulation of ribosomes and vesicles resembling lipid vesicles.

Abnormal sequence of expression of differentiation markers in psoriatic epidermis: inversion of two steps in the differentiation program?

This immunohistologic study was undertaken to compare epidermal differentiation in normal and psoriatic skin. Although basal cells retain a normal phenotype in this disease, suprabasal layers exhibit abnormal sets of differentiation markers. The 67-kD keratin and Bd5 antigen, which are found in normal epidermis immediately above the basal layer, appear several layers higher in involved psoriatic epidermis. On the contrary, KF2 antigen, which is found in the upper spinous layers of normal epidermis, appears more precociously in psoriatic epidermis. Paradoxically, in this disease characterized by the absence of a granular layer, some markers specific for this layer in normal skin, such as involucrin and transglutaminase, appear in lower skin cell layers, while other granular markers, such as filaggrin, are either absent or found in the parakeratotic scales. These results point out the existence in psoriasis of a suprabasal cell population characterized by a set of markers that are never coexpressed in normal epidermis. The existence of this abnormal population of cells can be explained as the result of the inversion of two steps in the differentiation program. Thus, instead of an inability to express a given differentiation marker, psoriasis seems to be characterized by an abnormal sequence of expression of these markers.

Distribution pattern of psoriatic keratoblasts: computer-assisted image-analysis for combined evaluation of DNA synthesis and expression of 67 kD keratin polypeptides in the epidermis of stable plaques of psoriasis

Psoriatic epidermis is characterized by increased DNA synthesis and disturbed differentiation. Even though these processes are closely associated, most investigations do not give insight into temporal/spatial relationships between both events. We previously developed a double labeling method for the simultaneous demonstration of the germinative and differentiated epidermal compartments in normal human skin by using tritium-labeled thymidine ([3H] Thd) incorporation and immunoperoxidase staining of 67 kD keratin polypeptides. In this paper we report the results of combined evaluation of these compartments in stable plaques of psoriasis. Scanning of skin sections with an automatic image analyzer allows objective quantification of areas of total epidermis, 67 kD+ differentiated epidermis and numbers of [3H] Thdr+ nuclei. Our data indicate that the 67 kD- undifferentiated psoriatic epidermis is expanded. Increased numbers of [3H] Thd+ basal and suprabasal psoriatic keratinocytes are present and most of them (97.9%) pertain to the 67 kD- compartment. Keratin identification in scales taken from the same sites showed a variable but distinct decrease of 67 kD keratin polypeptides. Hence, the hyperplastic epidermis of stable plaques of psoriasis is characterized by the presence of increased numbers of [3H] Thd+ cells, which primarily belong to the undifferentiated (67 kD-) basal and suprabasal compartments, especially in the lowermost parts of the elongated interpapillary rete ridges. These changes are associated with a relative decrease of synthesis of 67 kD polypeptides and the presence in the scales of keratins that confer a characteristic hyperproliferative epidermal keratin pattern to the psoriatic plaque.

Assemblies of psoriatic keratin and their relation to normal intermediate filament structures

Protein extracts from normal human epidermis reassemble in vitro into 8-10 nm diameter filaments characteristic of intermediate filaments, whereas extracts from psoriatic epidermal scales reassemble, under identical conditions, into a variety of paracrystalline bundles. Optical diffraction and image analysis of these paracrystalline bundles reveal an axial repeat of 16.5 nm, which subdivides into three bands of 5.5 nm, and a lateral spacing of 5.1 nm. This information, together with available sequence studies of intermediate filaments and biochemical data, suggests that the subunit of psoriatic keratin is made up essentially from the coiled-coil alpha-helical rod domain of the normal keratin subunits, whereas the random coil domains are missing or greatly reduced in size.

Psoriasis: maintenance of an intact monolayer basal cell differentiation compartment in spite of hyperproliferation

Frozen sections of punch biopsies from normal epidermis and psoriatic involved and uninvolved epidermis have been examined immunocytochemically using a panel of anti-keratin monoclonal antibodies with various specificities in the skin. Since psoriasis is thought to involve hyperproliferative expansion of the basal compartment from one to about three cell layers in thickness, the samples were screened with antibodies to intermediate filament determinants associated with basal cells, suprabasal cells and hyperproliferating keratinocyte-derived cell lines, respectively. The basal-suprabasal division was observed to be intact, with only one layer of basal cells demarcated by the specific antibodies used under all circumstances. This suggests that (a) psoriatic "basal cell hyperproliferation' may not specifically involve the basal cell compartment containing the stem cells, but rather a population of amplifying transit cells which are predominantly suprabasal, and that (b) while keratinocyte differentiation begins as the cells lose contact with the basal lamina, the first stages at least of differentiation are not dependent on the loss of the capacity to divide.

Electron microscopy and image processing applied to the study of protein structure and protein-protein interactions

We review the application of electron microscopy and image processing at the molecular level to an ever increasing range of biological specimens. Although recent advances have been due in part to development of more sophisticated instrumentation and/or processing algorithms, widespread application of the well-known techniques of image enhancement and structure reconstruction has depended on new strategies of in vitro crystallization and polymerization, some of which are outlined here. We also discuss the use of stoichiometric labeling and/or "cocrystallization" in identifying the different subunits in multisubunit complexes and in studying protein-protein interactions.

Monoclonal antibody analysis of keratin expression in epidermal diseases: a 48- and 56-kdalton keratin as molecular markers for hyperproliferative keratinocytes

The polypeptide composition of epidermal keratin varies in disease. To better understand the biological meaning of these variations, we have analyzed keratins from a number of human epidermal diseases by the immunoblot technique using AE1 and AE3 monoclonal antikeratin antibodies. The results reveal a continuous spectrum of keratin expression ranging from one closely resembling the normal in vivo pattern to one almost identical to cultured epidermal keratinocytes. Specifically, a 50-kilodalton (kd) (AE1-positive) and a 58-kd (AE3-positive) keratin are present in all diseases, supporting the concept that they represent "permanent" markers for keratinocytes. A 56.5-kd (AE1) and a 65-67-kd (AE3) keratin, previously shown to be markers for keratinization, are expressed only by lesions retaining a keratinized morphology. A 48-kd (AE1) and a 56-kd (AE3) keratin are present in all hyperproliferative (para- or nonkeratinized) disorders, but not in normal abdominal epidermis or in ichthyosis vulgaris which is a nonhyperproliferative disease. These two keratins have previously been found in various nonepidermal keratinocytes undergoing hyperproliferation, suggesting that these keratins are not epidermis-specific and may represent markers for hyperproliferative keratinocytes in general. In various epidermal diseases, there is a reciprocal expression of the (keratin) markers for hyperproliferation and keratinization, supporting the mutual exclusiveness of the two cellular events. Moreover, our results indicate that, as far as keratin expression is concerned, cultured human epidermal cells resemble and thus may be regarded as a model for epidermal hyperplasia. Finally, the apparent lack of any major, disease-specific keratin changes in the epidermal disorders studied so far implies that keratin abnormalities probably represent the consequence, rather than the cause, of these diseases.

The fibrillar substructure of keratin filaments unraveled

We show that intermediate-sized filaments reconstituted from human epidermal keratins appear unraveled in the presence of phosphate ions. In such unraveling filaments, up to four "4.5-nm protofibrils" can be distinguished, which are helically twisted around each other in a right-handed sense. Lowering the pH of phosphate-containing preparations causes the unraveling filaments to further dissociate into "2-nm protofilaments." In addition, we find that reconstitution of keratin extracts in the presence of small amounts of trypsin yields paracrystalline arrays of 4.5-nm protofibrils with a prominent 5.4-nm axial repeat. Limited proteolysis of intact filaments immobilized on an electron microscope grid also unveils the presence of 4.5-nm protofibrils within the filament with the same 5.4-nm axial repeat. These results, together with other published data, are consistent with a 10-nm filament model based on three distinct levels of helical organization: (a) the 2-nm protofilament, consisting of multi-chain extended alpha-helical segments coiled around each other; (b) the 4.5-nm protofibril, being a multi-stranded helix of protofilaments; and (c) the 10-nm filament, being a four-stranded helix of protofibrils.

The ichthyoses--pathogenesis and prenatal diagnosis: a review of recent advances

Disturbances in the process of normal cornification leading to pathologic scaling provide the pathophysiologic basis for the ichthyoses. These disturbances may result from either abnormalities in protein metabolism (keratinization) (i.e., the "bricks") or in lipid metabolism (i.e., the "mortar") (Fig. 1). The evidence linking the various ichthyoses to defects in protein or lipid metabolism have been reviewed. It is likely that future advances will lead not only to a more complete understanding of the pathogenesis of these disorders, but also will shed significant light on the normal stratum corneum functions of barrier formation and desquamation, as well as lead the way to more rational and effective therapies. In recent years, prenatal diagnosis has been successfully performed in several of the ichthyoses. It is likely that improvements in our ability to prenatally diagnose those disorders will advance hand-in-hand with further progress in unraveling their underlying causes.

Keratin polypeptide profile in psoriatic epidermis normalized by treatment with etretinate (aromatic retinoid Ro 10-9359)

The variations in the expression of epidermal keratins occurring during retinoid therapy were studied in patients with psoriasis before and during oral administration of etretinate (aromatic retinoid Ro 10-9359) and compared with normal epidermis. Sodium dodecyl sulfate polyacrylamide gel electrophoresis densitometric readings were performed on keratins extracted from epidermal cells obtained through trypsinization of skin specimens. Epidermal cells were also tested by immunofluorescence (IF) for the presence of BMZ antigens as markers of basal cells and for the presence of TK and KP (67 K, 63 K, and 55 K) with sera with antibodies against BMZ antigens and specific antisera for TK and KP. In psoriasis-involved epidermis, SDS-PAGE anaLysis showed lower amounts of 67 K and increased amounts of 63 K and 55 K, as compared with normal epidermis. Low proportions of cells expressing by IF the 67 K and the 63 K were also noted, with a defective expression of these two KP by suprabasal keratinocytes in psoriasis-involved epidermis. During etretinate administration, a return toward the normal electrophoretic pattern and a correction of the defective cellular expression of these two KP were obtained parallel with clinical improvement. These findings indicate the presence in involved psoriatic epidermis of a population of suprabasal keratinocytes that do not express the high-molecular-weight KP and show a normalization of the relative proportions of the KP with etretinate.

Epidermolytic hyperkeratosis: ultrastructure and biochemistry of skin and amniotic fluid cells from two affected fetuses and a newborn infant

Skin biopsy samples and amniotic fluid cells obtained in utero from two fetuses at risk for epidermolytic hyperkeratosis were examined by light and electron microscopy. Both fetuses were affected; the second was carried to term. Epidermal extracts were prepared from blisters of the newborn for analysis of keratin and filaggrin proteins. Abnormal clumps of keratin filaments were present in all layers of the prekeratinized fetal epidermis except the periderm and stratum germinativum. A significant population of amniotic fluid cells also contained the filament aggregations. Prenatal diagnosis of the disease should be possible using cells obtained at amniocentesis, thus avoiding fetal skin biopsy. Biochemical studies showed abnormalities in keratin and filaggrin proteins. The structural alterations in the tissue might be a consequence of altered interaction between these two abnormal epidermal proteins.

Characterization of keratin polypeptides of normal and psoriatic horny cells

Keratin was extracted from normal human horny cells of the leg, calluses of the sole, and psoriatic scales. After dissociation in sodium dodecyl sulfate the polypeptides were separated by Laemmli's gel electrophoresis method and their molecular weights and relative amounts determined. Normal horny cells contained 3 polypeptide chains of Mr 67K, 59K, and 57K, while those of callus contained 9 polypeptides of Mr 67K, 66K, 63K, 62K, 58K, 54K, 52K, 48K, and 45K. In both cases all keratin polypeptides participated in filament reassembly in vitro and were recovered from the filaments. In psoriatic scale keratin, 7 prominent polypeptides were detected having Mr 67K, 59K, 57K, 50K, 48K, 42K, and 40K. The 67K polypeptide could not be recovered from reassembled filaments. Ultrastructural studies revealed that these filaments are imperfect and readily aggregate into thick fibrils. These observations indicate that there are significant differences in composition of keratin of normal horny cells, calluses, and psoriatic scales.

Comparison of prekeratin and keratin polypeptides in normal and psoriatic human epidermis

High-resolution electrophoresis has been used to extend previous observations on the polypeptide composition of keratins in psoriatic epidermis. We have compared psoriatic scale keratins with normal and with scale extracts from several different epidermal disorders. Uninvolved psoriatic epidermis contained prekeratin and keratin of normal profile (68, 60, 58, 52 kDa and 66, 58, 55 kDa, respectively). Prekeratin from involved psoriatic epidermis showed a variable quantitative reduction in the 68-kDa polypeptide and an altered expression of smaller polypeptides (Mr 40 000-55 000). Keratin from the psoriatic lesion was abnormal and appeared 'prekeratin-like'. Keratin from the involved stratum corneum of patients with seborrhoeic eczema. Darier's disease and common dandruff were also similar to prekeratin, but that from ichthyosis and toxic epidermal necrolysis was normal. These results suggest that psoriatic keratinocytes have a defective but variable expression of prekeratin polypeptides. Furthermore, the differentiation-linked modification of prekeratin to keratin is defective in psoriasis, a phenomenon found in other hyperkeratotic epidermal disorders.