Keratin and keratinization

Bridging Nature and Engineering: Protein-Derived Materials for Bio-Inspired Applications

The sophisticated, elegant protein-polymers designed by nature can serve as inspiration to redesign and biomanufacture protein-based materials using synthetic biology. Historically, petro-based polymeric materials have dominated industrial activities, consequently transforming our way of living. While this benefits humans, the fabrication and disposal of these materials causes environmental sustainability challenges. Fortunately, protein-based biopolymers can compete with and potentially surpass the performance of petro-based polymers because they can be biologically produced and degraded in an environmentally friendly fashion. This paper reviews four groups of protein-based polymers, including fibrous proteins (collagen, silk fibroin, fibrillin, and keratin), elastomeric proteins (elastin, resilin, and wheat glutenin), adhesive/matrix proteins (spongin and conchiolin), and cyanophycin. We discuss the connection between protein sequence, structure, function, and biomimetic applications. Protein engineering techniques, such as directed evolution and rational design, can be used to improve the functionality of natural protein-based materials. For example, the inclusion of specific protein domains, particularly those observed in structural proteins, such as silk and collagen, enables the creation of novel biomimetic materials with exceptional mechanical properties and adaptability. This review also discusses recent advancements in the production and application of new protein-based materials through the approach of synthetic biology combined biomimetics, providing insight for future research and development of cutting-edge bio-inspired products. Protein-based polymers that utilize nature's designs as a base, then modified by advancements at the intersection of biology and engineering, may provide mankind with more sustainable products.

OSBPL2 compound heterozygous variants cause dyschromatosis, ichthyosis, deafness and atopic disease syndrome

PURPOSE

In this study, we identified and diagnosed a novel inherited condition called Dyschromatosis, Ichthyosis, Deafness, and Atopic Disease (DIDA) syndrome. We present a series of studies to clarify the pathogenic variants and specific mechanism.

METHODS

Exome sequencing and Sanger sequencing was conducted in affected and unaffected family members. A variety of human and cell studies were performed to explore the pathogenic process of keratosis.

RESULTS

Our finding indicated that DIDA syndrome was caused by compound heterozygous variants in the oxysterol-binding protein-related protein 2 (OSBPL2) gene. Furthermore, our findings revealed a direct interaction between OSBPL2 and Phosphoinositide phospholipase C-beta-3 (PLCB3), a key player in hyperkeratosis. OSBPL2 effectively inhibits the ubiquitylation of PLCB3, thereby stabilizing PLCB3. Conversely, OSBPL2 variants lead to enhanced ubiquitination and subsequent degradation of PLCB3, leading to epidermal hyperkeratosis, characterized by aberrant proliferation and delayed terminal differentiation of keratinocytes.

CONCLUSIONS

Our study not only unveiled the association between OSBPL2 variants and the newly identified DIDA syndrome but also shed light on the underlying mechanism.

KRT17 from skin cells with high glucose stimulation promotes keratinocytes proliferation and migration

Impaired diabetic wound healing is an important issue in diabetic complications. Proliferation and migration of keratinocytes are major processes of skin wound repair after injury. However, hyperkeratosis can affect the speed of wound healing. Based on the results of preliminary experiments on increased KRT17 expression after high glucose stimulation of human skin tissue cells, a cell model of human immortalized keratinocyte (HaCaT) stimulation with different concentrations of KRT17 was established in vitro, and the promotion in cell proliferation and migration were discovered. KRT17 silencing promoted diabetic wound healing in the db/db diabetic wound model. Transcriptome sequencing (RNA-seq) was performed on HaCaT cells after KRT17 stimulation, and analysis showed significant enrichment in the PI3K-AKT signaling pathway, in which the regulation of cell c-MYB mRNA, a key molecule regulating cell proliferation and migration, was significantly upregulated. In vitro assays showed increased c-MYB expression and enhanced pAKT activity after HaCaT cell stimulation by KRT17. We speculate that KRT17 is upregulated under high glucose and promotes keratinocyte proliferation and migration caused hyperkeratosis, through the c-MYB/PI3K-AKT pathway, contributing to delayed wound healing.

Paleoproteomics

Paleoproteomics, the study of ancient proteins, is a rapidly growing field at the intersection of molecular biology, paleontology, archaeology, paleoecology, and history. Paleoproteomics research leverages the longevity and diversity of proteins to explore fundamental questions about the past. While its origins predate the characterization of DNA, it was only with the advent of soft ionization mass spectrometry that the study of ancient proteins became truly feasible. Technological gains over the past 20 years have allowed increasing opportunities to better understand preservation, degradation, and recovery of the rich bioarchive of ancient proteins found in the archaeological and paleontological records. Growing from a handful of studies in the 1990s on individual highly abundant ancient proteins, paleoproteomics today is an expanding field with diverse applications ranging from the taxonomic identification of highly fragmented bones and shells and the phylogenetic resolution of extinct species to the exploration of past cuisines from dental calculus and pottery food crusts and the characterization of past diseases. More broadly, these studies have opened new doors in understanding past human-animal interactions, the reconstruction of past environments and environmental changes, the expansion of the hominin fossil record through large scale screening of nondiagnostic bone fragments, and the phylogenetic resolution of the vertebrate fossil record. Even with these advances, much of the ancient proteomic record still remains unexplored. Here we provide an overview of the history of the field, a summary of the major methods and applications currently in use, and a critical evaluation of current challenges. We conclude by looking to the future, for which innovative solutions and emerging technology will play an important role in enabling us to access the still unexplored "dark" proteome, allowing for a fuller understanding of the role ancient proteins can play in the interpretation of the past.

Genome-wide identification, characterization, and expression analysis of keratin genes (KRTs) family in yak (Bos grunniens)

As the largest subgroup of intermediate filament proteins, keratins are divided into two types of subfamily. Currently, the molecular mechanism of keratins in several animals has been reported but is limited in yak. Here, 53 different kinds of keratins were identified in the yak genome, including 23 type I and 30 type II keratins. Bioinformatics analysis in this study revealed that multiple phosphorylation sites were identified among all the family members. And the subcellular localization of these proteins was predicted to be in the nucleus, cytoskeleton, and cytoplasm. All keratin family proteins were unstable and the scores of instability coefficient were higher than 40. Phylogenetic analysis showed that high consistency results of the sequence conservation and grouping were found in the genomes of yak, sheep, cattle, mouse, rat, and human. Based on the expression patterns obtained from the transcriptome data, keratin genes (KRTs) were grouped into five clusters, and results also showed that KRTs were highly activated in skin tissues during the hair cycle in yak. Among the five clusters, Cluster II contained the most KRTs, which was the main expression pattern of the yak hair follicle cycle, followed by Cluster III. These results indicated the transition period from telogen to anagen and catagen to telogen were highly dynamic in yak. Gene expression correlation analysis showed that KRTs exhibited a strong correlation (mainly positive correlation) throughout the hair follicle development cycle. And the identification of hub KRTs in specific modules related to hair follicle development in this study was performed using the Weight Gene Co-Expression Network Analysis (WGCNA). Specific modules that include KRTs were darkgreen (KRT40), darkgrey (KRT5), turquoise (KRT1, KRT2, KRT10), bisque4 (KRT4), thistle2 (KRT9, KRT39), and yellowgreen (KRT24). The interaction network showed that these genes were found to be related to the regulation of cell cycle, melanogenesis, hair follicle development, keratinocyte proliferation. Our study provides theoretical support for the study of the evolutionary relationship and molecular mechanism of keratin family in B. grunnien.

Engineering with keratin: A functional material and a source of bioinspiration

Keratin is a highly multifunctional biopolymer serving various roles in nature due to its diverse material properties, wide spectrum of structural designs, and impressive performance. Keratin-based materials are mechanically robust, thermally insulating, lightweight, capable of undergoing reversible adhesion through van der Waals forces, and exhibit structural coloration and hydrophobic surfaces. Thus, they have become templates for bioinspired designs and have even been applied as a functional material for biomedical applications and environmentally sustainable fiber-reinforced composites. This review aims to highlight keratin's remarkable capabilities as a biological component, a source of design inspiration, and an engineering material. We conclude with future directions for the exploration of keratinous materials.

Keratins and the plakin family cytolinker proteins control the length of epithelial microridge protrusions

Actin filaments and microtubules create diverse cellular protrusions, but intermediate filaments, the strongest and most stable cytoskeletal elements, are not known to directly participate in the formation of protrusions. Here we show that keratin intermediate filaments directly regulate the morphogenesis of microridges, elongated protrusions arranged in elaborate maze-like patterns on the surface of mucosal epithelial cells. We found that microridges on zebrafish skin cells contained both actin and keratin filaments. Keratin filaments stabilized microridges, and overexpressing keratins lengthened them. Envoplakin and periplakin, plakin family cytolinkers that bind F-actin and keratins, localized to microridges, and were required for their morphogenesis. Strikingly, plakin protein levels directly dictate microridge length. An actin-binding domain of periplakin was required to initiate microridge morphogenesis, whereas periplakin-keratin binding was required to elongate microridges. These findings separate microridge morphogenesis into distinct steps, expand our understanding of intermediate filament functions, and identify microridges as protrusions that integrate actin and intermediate filaments.

Immunohistochemical Studies of Cytokeratins and Differentiation Markers in Bovine Ocular Squamous Cell Carcinoma

Bovine Ocular Squamous Cell Carcinoma is considered the most common bovine tumour, causing significant economic losses, mainly by abattoir condemnations. To obtain a better insight into the genesis and neoplastic transformation, 19 samples collected at slaughter from Holstein Friesian cattle and diagnosed as Ocular Squamous Cell Carcinoma were studied. Tumours were histologically classified into three categories: poorly (26.3%), moderately (26.3%), and well differentiated (47.4%). Expression of keratins (MNF116 and LP34) and of cornified envelope precursors (involucrin and profilaggrin) was studied. Expression of MNF116 was observed in all carcinomas. LP34 immunostaining was seen in all but three carcinomas, one from each degree. Involucrin immunoreaction was observed in all but one poorly differentiated carcinoma. Profilaggrin was present in only two moderately differentiated carcinomas, in all but one well differentiated, and in all but one poorly differentiated. MNF116 is a useful marker to confirm the epithelial origin of the tumour and stain most neoplastic cells in these tumours. The expression of involucrin and LP34 demonstrates that, in all tumours, cells have reached the final program of differentiation, regardless of the grade. The expression of profilaggrin could indicate molecular changes during malignant transformation but their expression does not seem to be of diagnostic value.

Hereditary Palmoplantar Keratoderma: A Practical Approach to the Diagnosis

The ridged skin of the palms and soles has several unique features: (i) presence of dermatoglyphics created by alternating ridges and grooves forming a unique pattern, (ii) presence of the highest density of eccrine sweat glands and absence of pilosebaceous units, and (iii) differential expression of keratins compared to the glabrous skin. These features explain the preferential localization of palmoplantar keratoderma (PPK) and several of its characteristic clinical features. PPK develops as a compensatory hyperproliferation of the epidermis and excessive production of stratum corneum in response to altered cornification of the palmoplantar skin due to mutations in the genes encoding several of the proteins involved in it. PPK can manifest as diffuse, focal, striate, or punctate forms per se or as a feature of several dermatological or systemic diseases. There is a wide genetic and phenotypic heterogeneity in hereditary PPK, due to which reaching an accurate diagnosis only on the basis of clinical features may be sometimes challenging for the clinicians in the absence of molecular studies. Nevertheless, recognizing the clinical patterns of keratoderma, extent of involvement, degree of mutilation, and associated appendageal and systemic involvement may help in delineating different forms. Molecular studies, despite high cost, are imperative for accurate classification, recognizing clinical patterns in resource poor settings is important for appropriate diagnosis, genetic counseling, and management. This review intends to develop a practical approach for clinical diagnosis of different types of hereditary PPK with reasonable accuracy.

Barrier Function, Epidermal Differentiation, and Human β-Defensin 2 Expression in Tinea Corporis

Tinea corporis is a superficial mycotic infection resulting in substantial epidermal changes. We determined skin barrier function, epidermal differentiation, and human-beta-defensin 2 (hBD-2) protein expression in 10 patients with tinea corporis caused by Trichophyton rubrum (T. rubrum). We found disturbed skin barrier function as shown by a significant increase in transepidermal water loss (TEWL) and specific ultrastructural changes including disturbed formation of extracellular lipid bilayers, lamellar body extrusion, and deposit of clotted material at the stratum granulosum/stratum corneum interface. Epidermal proliferation in tinea increased several fold and accordingly, proliferation and inflammation-associated keratins K6, K16, and K17 were expressed. Expression of basal keratins K5 and K14 increased, whereas differentiation-associated K10 was reduced. Reduction of the cornified envelope proteins involucrin, loricrin, and the S100 protein filaggrin was also seen. Reduced filaggrin expression correlated with reduced skin hydration; protein breakdown products of filaggrin have been shown to be important for water binding. Surprisingly, we found pronounced epidermal protein expression of hBD-2, which may be related to disturbed epidermal differentiation and inflammation. hBD-2 showed a weak, although significant, antifungal activity against T. rubrum in the turbidimetric assay and the immunohistological staining was somewhat less pronounced in areas directly underneath fungal hyphae in the stratum corneum. Together, we describe profound changes in skin barrier structure and function, epidermal proliferation, and differentiation including pronounced protein expression of hBD-2 in tinea corporis.

Altered Morphology and Distribution of Cellular Junction Proteins in Non-Lesional Psoriatic Epidermis: An Insight into Disease Severity

BACKGROUND

Psoriasis affects 2.7% of the world's population. Keratinocyte proliferation outside the basal layer suggests alterations in cell-cell interactions in affected epidermis. Anomalous expression of proteins forming intercellular junctions has been reported in lesional skin of psoriatic patients. In contrast, little is known about possible alterations in psoriatic non-lesional skin.

METHODS

Ten clinically diagnosed psoriasis vulgaris patients and ten controls were studied. All patients were diagnosed with active but controlled psoriatic plates (PASI 3 to 5) and had not received any systemic treatment. The mean age was 43 years for patients and 43.5 years for controls. Four-mm2 skin samples were taken from lesional and non-lesional zones in patients and from abdomen in controls. Five-mum sections were examined for integrity and structural organization by fluorescent labeling of actin filaments and nuclei. Specific antibodies were utilized to localize occludin, E-cadherin, beta-catenin, and proliferation-specific keratins in sections and epidermal sheets. Samples were also processed for immunoblotting with occludin antibody.

RESULTS

Lesional and non-lesional psoriatic epidermis from all patients showed keratinocyte hyperproliferation, lack of rete ridges and dermal papillae in the dermal-epidermal junction in some areas. Proteins forming tight and adherens junctions in non-lesional skin keratinocytes from two patients who during the course of the study evolved to uncontrolled disease, showed similar alterations to those observed in lesional skin of all the patients. However, the occludin isoforms expressed were apparently the same in all samples.

CONCLUSIONS

Analysis of non-lesional skin in psoriatic patients diagnosed with controlled disease may provide clues about incipient structural abnormalities in the pathogenesis of psoriasis, providing an early diagnostic indicator for evolution to a generalized form of the disease.

Cytokeratins and dermatology

Cytokeratins are fibrous intermediate-filament protein polymers present in almost all animal cells. Their function is related to epithelium structural maintenance, protection from mechanical trauma, and possibly communication between adjacent cells or cytoplasm components. Today there are 20 known cytokeratins, classified according to their molecular weight and pH as type I or acidic (cytokeratins 9-20) and type II or neutral-basic (cytokeratins 1-8). Cytokeratins are always expressed in specific pairs for each type of tissue, composed of one unit of type I and one unit of type II. Primary structural defects of cytokeratins are associated with various keratinization impairments. Two of the better characterized defects are bullous epidermolysis and epidermolytic hyperkeratosis. Anti-cytokeratin monoclonal antibodies are being used for diagnostic purposes to characterize the origin of poorly differentiated tumors and metastatic solid tumors.

Preservation of phenotype in an organotypic cell culture model of a recessive keratinization defect of Norfolk terrier dogs

The purpose of this study is to reproduce in vitro a recessive keratinization defect of Norfolk terrier dogs characterized by a lack of keratin 10 (K10) production. Keratinocytes from skin biopsy samples of four normal dogs and two affected dogs were cultured organotypically with growth factor-supplemented media in order to stimulate cornification. The cultured epidermis from the normal dogs closely resembled the normal epidermis in vivo and cornified. The cultured epidermis from the affected dogs displayed many phenotypic alterations identified in skin biopsies from dogs with this heritable defect. Immunohistochemistry and immunoblotting showed a marked decrease in K10 from the cultures of the affected keratinocytes, compared to that in K10 from the cultures of the normal keratinocytes. Real-time reverse transcription polymerase chain reaction quantitation showed a 31-fold decrease in K10, a 1.75-fold increase in K1 and a 136-fold increase in K2e between the affected and the normal epidermis. Organotypic keratinocytes showed a 241-fold decrease in K10, a 31-fold decrease in K1 and a 1467-fold decrease in K2e between the affected and normal cultures. Although in vitro keratin expression did not precisely simulate in vivo, the morphology of the normal and the affected epidermis was largely preserved; thus, this culture system may provide an alternative to in vivo investigations for cutaneous research involving cornification.

Epidermal differentiation: the role of proteases and their inhibitors

Dermatological diseases range from minor cosmetic problems to life-threatening conditions, as seen in some severe disorders of keratinization and cornification. These disorders are commonly due to abnormal epidermal differentiation processes, which result in disturbed barrier function of human skin. Elucidation of the cellular differentiation programs that regulate the formation and homeostasis of the epidermis is therefore of great importance for the understanding and therapy of these disorders. Much of the barrier function of human epidermis against the environment is provided by the cornified cell envelope (CE), which is assembled by transglutaminase (TGase)-mediated cross-linking of several structural proteins and lipids during the terminal stages of normal keratinocyte differentiation. The major constituents of the stratum corneum and the current knowledge on the formation of the stratum corneum will be briefly reviewed here. The discovery of mutations that underlie several human diseases caused by genetic defects in the protein or lipid components of the CE, and recent analyses of mouse mutants with defects in the structural components of the CE, catalyzing enzymes, and lipid processing, have highlighted their essential function in establishing the epidermal barrier. In addition, recent findings have provided evidence that a disturbed protease-antiprotease balance could cause faulty differentiation processes in the epidermis and hair follicle. The importance of regulated proteolysis in epithelia is well demonstrated by the recent identification of the SPINK5 serine proteinase inhibitor as the defective gene in Netherton syndrome, cathepsin C mutations in Papillon-Lefevre syndrome, cathepsin L deficiency infurless mice, targeted ablation of the serine protease Matriptase/MTSP1, targeted ablation of the aspartate protease cathepsin D, and the phenotype of targeted epidermal overexpression of stratum corneum chymotryptic enzyme in mice. Notably, our recent findings on the role of cystatin M/E and legumain as a functional dyad in skin and hair follicle cornification, a paradigm example of the regulatory functions exerted by epidermal proteases, will be discussed.

Kinetics of 5alpha-cholestan-3beta-yl N-(2-naphthyl)carbamate/n-alkane organogel formation and its influence on the fibrillar networks

The kinetics and mode of nucleation and growth of fibers by 5alpha-cholestan-3beta-yl N-(2-naphthyl)carbamate (CNC), a low-molecular-mass organogelator (LMOG), in n-octane and n-dodecane have been investigated as their sols were transformed isothermally to organogels. The kinetics has been followed in detail by circular dichroism, fluorescence, small-angle neutron scattering, and rheological methods. When treated according to Avrami theory, kinetic data from the four methods are self-consistent and describe a gelation process involving one-dimensional growth and "instantaneous nucleation". As expected from this growth model, polarized optical micrographs of the self-assembled fibrillar networks (SAFINs) show fibrous aggregates. However, their size and appearance change abruptly from spherulitic to rodlike as temperature is increased. This morphological change is attended by corresponding excursions in static and kinetic CD, fluorescence and rheological data. Furthermore, the rheological measurements reveal an unusual linear increase in viscoelastic moduli in the initial stages of self-assembly. Each of the methods employed becomes sensitive to changes of the system at different stages of the transformation from single molecules of the LMOG to their eventual SAFINs. This study also provides a methodology for investigating aggregation phenomena of some other self-assembling systems, including those of biological and physiological importance.

Avances biomoleculares en los trastornos epidérmicos hereditarios

In recent years, the genes responsible for many hereditary skin diseases have been discovered. These genes encode different proteins that participate in the terminal differentiation of the epidermis, so their alteration or absence causes a keratinization disorder and/or an increase in skin fragility. Thanks to genetic analyses, we have been able to understand the physiopathology of numerous genodermatoses and we have become closer to diagnosing many others. In the not-too-distant future, biomolecular techniques may foreseeably help us prevent and treat these processes, which include skin diseases as serious as epidermolysis bullosa or epidermolytic hyperkeratosis. In this article, we will study the most recent biomolecular findings referring to keratinization and epidermal disorders, mentioning the altered genes and/ or the defective proteins that cause them.

Engraftment of umbilical cord epithelial cells in athymic mice: in an attempt to improve reconstructed skin equivalents used as epithelial composite

BACKGROUND

The umbilical cord (UC) is composed of connective tissue called Wharton Jelly, covered by a simple epithelium believed to derive from amniotic membrane epithelium. In previous studies, we observed that the umbilical cord epithelium (UCE) in situ displayed stratified epithelial structures, in some areas that expressed cytokeratins and differentiation markers as characteristic of keratinocytes under airlifted condition in vitro, UCE cells grown on collagen gel displayed more keratinocytes characteristics.

OBJECTIVE

To study the ability of UCE cells to undergo terminal differentiation when grown in the most proper environment.

METHODS

UCE cells were seeded onto the surface of a fibroblast-populated collagen gel then grafted onto the back of nude mice and examined using immunohistochemical techniques and by transmission electron microscope (TEM).

RESULTS

Post-grafted UCE cells formed a stratified epithelial structure similar to that formed by keratinocytes. Although immunohistochemical staining of UCE cells in skin grafts showed a similar pattern to that seen with the keratinocyte controls, UCE cells maintained many of their own intrinsic characteristics, such as stronger expression of mucous membrane cytokeratins and expression of simple epithelial cytokeratin. Notably, with longer transplant periods, expression of keratinocyte characteristics in UCE cells increased while expression of simple epithelial properties decreased. We observed formation of a complete basement membrane, which had not been achieved using an in vitro model.

CONCLUSIONS

Grafted UCE cells in an animal model maintain their own intrinsic characteristics, but display the stratified morphogenesis, terminal differentiation and ultrastructures similar to those seen in keratinocytes.

A Heritable Keratinization Defect of the Superficial Epidermis in Norfolk Terriers

Although well-characterized in man, abnormal cornification secondary to heritable superficial keratin defects is rarely reported in animals. This report describes a mild cornification defect in seven related Norfolk terrier dogs. Lesions were present at birth and pedigree analysis suggested an autosomal recessive mode of inheritance. The affected dogs had hyperpigmented skin with scaling following mild trauma. The lesions were generalized but most prominent in the glabrous skin of the axillary and inguinal regions-areas where the epidermis is not protected by hair and is subject to frequent trauma. The most striking histological change was vacuolation in the upper epidermis, which often resulted in epidermolysis and blister formation. All of the affected dogs showed similar gross and histological changes. Ultrastructural changes included abnormal keratin filament clumping, prominent clear spaces in the cytoplasm of suprabasal keratinocytes, and abnormal keratohyaline granules. Immunohistochemical labelling for keratin 10 demonstrated a lack of expression in the superficial epidermis of affected dogs. All of the morphological changes noted in the Norfolk terriers were consistent with a mild form of a heritable defect in superficial keratin synthesis.

Acitretin treatment in (pre)malignant skin disorders of renal transplant recipients: histologic and immunohistochemical effects

BACKGROUND

The incidence of (pre)malignant skin lesions after renal transplantation is high. Acitretin treatment appears to decrease the number of new squamous cell carcinomas and ameliorates the aspect and reduces the number of actinic keratoses. However, no histologic and immunohistochemical studies have been performed to further substantiate these observations.

METHODS

In 33 renal transplant recipients, biopsies were taken before and after 3 months of treatment with acitretin in doses up to 0.4 mg/kg/day. Histologic and immunohistochemical parameters for dysplasia, epidermal thickness, proliferation, differentiation, apoptosis, and dermal inflammation were analyzed.

RESULTS

Following acitretin treatment, a significant reduction in epidermal thickness (P =.002) and a significant increase in normal differentiation parameter K10 (P =.02) was observed. Epidermal proliferation did not change, nor did apoptosis, inflammation, keratinocytic epidermal neoplasia score, or transglutaminase staining. At baseline, in 8 actinic keratoses, a single cell expression pattern of K13 and/or K19 was found. This was associated with high levels of parameters indicative of high-risk lesions (P <.05). After acitretin treatment, an increase in K13 (P =.006) and K19 (P =.05) was found, together with a change in expression towards a focal or band-like staining pattern.

CONCLUSION

Acitretin improves the aspect of actinic keratoses via alteration of keratinization, resulting in peeling of the stratum corneum. No significant change in proliferation was found, which may explain the rapid recurrence of actinic keratoses seen after cessation of acitretin treatment.

Detection of nonmelanoma skin cancer micrometastases in lymph nodes by using reverse transcriptase-polymerase chain reaction for keratin 19 mRNA

BACKGROUND

A new sensitive method for the detection of skin cancer micrometastases in lymph nodes is based on amplification of keratin 19 (K19) mRNA by reverse transcriptase-polymerase chain reaction (RT-PCR).

OBJECTIVES

To compare results of RT-PCR with those of histological examination in terms of the detection rate of skin cancer micrometastases.

METHODS

Twenty-six lymph nodes obtained from 13 patients with squamous cell carcinoma (SCC), eccrine porocarcinoma and Paget's disease were investigated by histological examination (haematoxylin and eosin sections) and RT-PCR. RT-PCR was performed on extracted RNA by using K19 primer pairs. RT-PCR products were visualized by ethidium bromide staining and confirmed by non-radioactive hybridization with K19-specific probes.

RESULTS

All of 10 histologically positive lymph nodes yielded the expected 460-bp band. Of the 16 histologically negative lymph nodes, one (6%) was found by RT-PCR to express K19 mRNA, indicating the presence of micrometastases which could not be detected by histological examination. A serial dilution study using RNA extracted from SCC cells mixed with RNA extracted from normal lymph node cells showed a detection sensitivity of K19 RT-PCR of 10-5 micro g cancer cell RNA in 1 micro g lymph node RNA. Nested RT-PCR showed a detection sensitivity of one tumour cell in 106 lymphocytes.

CONCLUSIONS

These results demonstrate the usefulness of K19 RT-PCR for the detection of skin cancer micrometastases in lymph nodes.

Sinonasal undifferentiated carcinoma, nasopharyngeal-type undifferentiated carcinoma, and keratinizing and nonkeratinizing squamous cell carcinoma express different cytokeratin patterns

Sinonasal undifferentiated carcinoma (SNUC) is a highly aggressive malignant neoplasm that is often difficult to distinguish from other poorly differentiated carcinomas arising in the sinonasal tract. To search for a differential cytokeratin (CK) expression that could be useful for diagnostic purposes, we compared the expression of a large panel of CKs in a series of 6 SNUCs, 10 poorly differentiated squamous cell carcinomas (SCCs), 10 nonkeratinizing squamous cell carcinomas (NKSCCs), and 5 nasopharyngeal-type undifferentiated carcinomas (NPTCs). SCC, NKSCC, and NPTC frequently showed immunoreactivity for CK5/CK6, CK8, CK13, and CK19. In addition, SCC and NKSCC expressed CK14, which was not detected in NPTC, and SCC expressed CK7 (60% of cases) and CK4 (30% of cases), which were absent in NKSCC and NPTC. Three NKSCCs were associated with a Schneiderian papilloma, and the results of the immunostaining were similar in the two components, with the exception of CK4 and CK7, which were expressed by the papilloma and not by the carcinoma. In contrast to other carcinomas, SNUC was characterized by the exclusive expression of CKs of simple epithelia, such as CK8 (100% of cases), CK7 (50% of cases), and CK19 (50% of cases). Thus, there are significant differences in the pattern of CK expression between SNUC, SCC, NKSCC, and NPTC, which could be of diagnostic aid. Moreover, these findings support the hypothesis that SNUC is a separate entity from SCC and NPTC of the sinonasal tract.

Microscopic and immunohistochemical analysis of the skin changes of free forearm flaps in intraoral reconstruction

In the literature, few studies based on clinical and histological evaluation analyze skin structural changes after transplantation to the oral cavity. Ten patients affected by squamous cell carcinoma of the oral cavity who were reconstructed with a free forearm flap were included in the current study to analyze skin alterations. The authors performed a histological and ultrastructural evaluation of skin samples from the free forearm flap before transplantation and 18 months after intraoral reconstruction. They analyzed cytokeratin and involucrin distribution, which represent markers of maturation and differentiation of epithelia. The aim of this study was to demonstrate whether skin "mucosalization" occurs. They found that the skin undergoes some morphological changes induced by the intraoral environment. Cytokeratin and involucrin distribution is mostly unchanged. This aspect is in favor of skin structure preservation. Thus, they found that "mucosalization" of the skin is not evident after 18 months.

The prefabricated scapula flap consists of syngeneic bone, connective tissue, and a self-assembled epithelial coating

The reconstruction of maxillary defects is a challenge in plastic surgery. The so-called prefabricated scapula flap consists of syngeneic bone covered with syngeneic dermis and is used to reconstruct maxillary defects. After placing these flaps into the oral cavity, they are reepithelialized within a short time period, raising the question of the cellular origin of the "neomucosa." We therefore obtained sequential biopsy samples of the prefabricated flap and of the flap after being placed into the oral cavity and analyzed the keratin expression profile of epithelial cells. We expected that after placing the prefabricated flap into the oral cavity, keratinocytes from adnexal structures of the dermal component of the graft would migrate onto the surface and reepithelialize the flap. Unexpectedly, reepithelialization occurred earlier. The flap had acquired a mucosa-like epithelium at the interface between the Gore-Tex coating and the dermis while still being positioned within the scapular region. The keratin expression profile of this epithelium was very similar to that of mucosal epithelium. Thus, the prefabricated scapula flap not only consisted of bone covered with connective tissue, but was also covered with epithelial cells derived from adnexal structures of the dermal graft. This seems to be the reason for the rapid restoration of an intact mucosa and the excellent outcome achieved with this surgical technique.

Olmsted syndrome

Olmsted syndrome is an uncommon inherited disorder of keratinization that presents mutilating palmoplantar keratoderma, perioral hyperkeratosis, leukokeratosis and alopecia. We report a case of this rare syndrome diagnosed in a 48-year-old woman and confirms the existence of a generalized abnormality in keratin expression. Immunoreactivity in our case suggests an abnormal expression of keratins 5 and 14 similar to the observed in other hyperproliferative disorders.

Proliferation and differentiation of the keratinocytes in hyperplastic epidermis overlying dermatofibroma: immunohistochemical characterization

Epidermal changes overlying dermatofibromas (DFs) have been described as ranging from psoriasiform simple hyperplasia to basaloid hyperplasia sometimes morphologically indistinguishable from superficial basal cell carcinoma (BCC). To characterize epidermal hyperplasia overlying DFs and to determine its association with the disease process, we examined 30 cases of DF showing hyperplastic epidermis. We used nine immunohistochemical markers associated with keratinocyte proliferation or differentiation. In DFs, the dermal metallothionein (MT) expression and immunophenotypic changes with regard to epidermal differentiation varied depending on the stage of lesional evolution of the DFs. Immunostaining for epidermal growth factor receptor (EGFR), MT, and keratin 6 (K6) increased in simple hyperplastic epidermis (SHE) overlying DFs (n = 11), whereas it gradually diminished in basaloid hyperplastic epidermis (BHE) overlying DFs (n = 19). In SHE, there was a significant increase in K14 expression. Among 19 BHE cases, 12 showed premature expression of involucrin and delayed appearance of K1 along with aberrant expression of K14. Conversely, the remaining 7 BHE cases showed a pattern of involucrin and K1 similar to that of normal skin coinciding with decreased or absent dermal MT expression. Loricrin and filaggrin expression in all DFs was the same as that of normal skin. Based on the sparse positivity of Ki-67 in the hyperplastic epidermis overlying DFs, we found that the biologic ability of BHE and SHE was not apparent in the hyperproliferative state observed in psoriasis and BCC. These results suggest that the dermal fibrohistiocytic process may trigger the induction of SHE overlying DFs by an unknown mechanism and then mediate both the abnormal keratinocyte differentiation and the transformation of SHE to BHE through the evolution of the dermal lesions.

Soluble scute proteins of healthy and ill desert tortoises (Gopherus agassizii)

OBJECTIVES

To characterize protein composition of shell scute of desert tortoises and to determine whether detectable differences could be used to identify healthy tortoises from tortoises with certain illnesses.

ANIMALS

20 desert tortoises.

PROCEDURES

Complete postmortem examinations were performed on all tortoises. Plastron scute proteins were solubilized, scute proteins were separated by use of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and proteins were analyzed, using densitometry. Two-dimensional immobilized pH gradient-PAGE (2D IPG-PAGE) and immunoblot analysis, using polyclonal antisera to chicken-feather beta keratin and to alligator-scale beta keratin, were conducted on representative samples. The 14-kd proteins were analyzed for amino acid composition.

RESULTS

The SDS-PAGE and densitometry revealed 7 distinct bands, each with a mean relative protein concentration of > 1 %, ranging from 8 to 47 kd, and a major protein component of approximately 14 kd that constituted up to 75% of the scute protein. The 2D IPG-PAGE revealed additional distinct 62- and 68-kd protein bands. On immunoblot analysis, the 14-, 32-, and 45-kd proteins reacted with both antisera. The 14-kd proteins had an amino acid composition similar to that of chicken beta keratins. There was a substantial difference in the percentage of the major 14-kd proteins from scute of ill tortoises with normal appearing shells, compared with 14-kd proteins of healthy tortoises.

CONCLUSIONS AND CLINICAL RELEVANCE

The major protein components of shell scute of desert tortoises have amino acid composition and antigenic features of beta keratins. Scute protein composition may be altered in tortoises with certain systemic illnesses.

Cable-piliated Burkholderia cepacia binds to cytokeratin 13 of epithelial cells

Although the Burkholderia cepacia complex consists of several genomovars, one highly transmissible strain of B. cepacia has been isolated from the sputa of cystic fibrosis (CF) patients throughout the United Kingdom and Canada. This strain expresses surface cable (Cbl) pili and is thought to be the major strain associated with the fatal "cepacia syndrome." In the present report we characterize the specific 55-kDa buccal epithelial cell (BEC) protein that binds cable pilus-positive B. cepacia. N-terminal sequences of CNBr-generated internal peptides identified the protein as cytokeratin 13 (CK13). Western blots of BEC extracts probed with a specific monoclonal antibody to CK13 confirmed the identification. Mixed epidermal cytokeratins (which contain CK13), cytokeratin extract from BEC (which consists essentially of CK13 and CK4), and a polyclonal antibody to mixed cytokeratins inhibited B. cepacia binding to CK13 blots and to normal human bronchial epithelial (NHBE) cells. Preabsorption of the antikeratin antibody with the BEC cytokeratin fraction reversed the inhibitory effect of the antibody. A cytokeratin mixture lacking CK13 was ineffective as an inhibitor of binding. Colocalization of CK13 and B. cepacia by confocal microscopy demonstrated that intact nonpermeabilized NHBE cells express small amounts of surface CK13 and bind Cbl-positive B. cepacia in the same location. Binding to intact NHBE cells was dependent on bacterial concentration and was saturable, whereas a Cbl-negative isolate exhibited negligible binding. These findings raise the possibility that surface-accessible CK13 in respiratory epithelia may be a biologically relevant target for the binding of cable piliated B. cepacia.

Intrinsic regulation of differentiation markers in human epidermis, hard palate and buccal mucosa

Different epithelia show extensive variation in differentiation. Epidermis and epithelium from the hard palate are both typical examples of orthokeratinized epithelia whereas buccal mucosa is an example of a non-keratinized epithelium. Each of these tissues can be distinguished morphologically and also by the expression of a number of structural proteins. Tissue explants derived from epidermis, hard palate or buccal mucosa were cultured at the air-liquid interface on collagen gels containing human dermal fibroblasts. Reconstructed epithelia that retained many of the morphological and immunohistochemical characteristics of the original tissue were formed. Cultures derived from epidermis and the hard palate both had a well-defined stratum basale, stratum spinosum, stratum granulosum and stratum corneum whereas cultures derived from buccal mucosa had no stratum granulosum or corneum and the cells retained their nuclei. Significantly more living cell layers were observed in both types of epithelia obtained from the mouth than in epidermis. The specific localization of proliferation and differentiation markers (Ki67, loricrin, involucrin, SPRR2, SPRR3 and keratin 10) closely resembled that of the tissue from which the cultures were derived. As identical three-dimensional culture models were used here, it is concluded that the differences observed between these epithelia were due to intrinsic properties of the keratinocytes.

Keratin 9 mutations in the coil 1A region in epidermolytic palmoplantar keratoderma

The palmoplantar keratodermas (PPK) are a heterogeneous group of conditions, most frequently inherited in autosomal dominant fashion. A few are well-documented autosomal recessive disorders; other are acquired in association with certain metabolic disorders and malignancies. Recently different point mutations of the keratin 9 (K9) gene have been identified in unrelated families with epidermolytic palmoplantar keratoderma (EPPK). We investigated two unrelated Hungarian families with EPPK. In one, a mutation consisting of a G-->A transversion at nucleotide position 551, which changes codon arginine to glutamine at codon 162 (R162Q), was found. In the other, we observed a novel mutation at nucleotide position 571, which changes codon 169 lysine (AAG) into the amber stop codon (TAG) (K169X). Each found mutation is present in the highly conserved coil 1A region of the rod domain. In the case of a stop codon type of mutation, it is questionable whether it really results in a clinical phenotype, but segregation analysis revealed cosegregation of the PPK phenotype with the mutant allele.

Granular parakeratosis - a unique acquired disorder of keratinization

Axillary granular parakeratosis is a recently described condition presenting with erythematous hyperkeratotic papules and plaques. We report on nine women and one man with eruptions not only localized to the axillae. Biopsy specimens were investigated by histology, immunohistochemistry, electron microscopy, immuno-electron microscopy, and in situ hybridization. In general, the epidermis was hyperplastic and showed a well preserved stratum granulosum. In the upper dermis a discrete perivascular CD4+ T-cell infiltrate was found, CD1+ dendritic cells were absent from the epidermis. The distribution pattern of the epidermal keratins (keratin 5/14, 1/10) and the expression of involucrin was regular. The horny layer was excessively thickened and parakeratotic. The nuclear remnants showed marginal chromatin condensation and were reactive for the nick-end labeling technique using TdT-mediated dUTP-biotin. The corneocytes were characteristically replete with basophilic granules which showed both ultrastructural features of keratohyalin granules and immunoreactivity for filaggrin. Loricrin was expressed irregularly in small L-granules. Granular parakeratotic cells revealed regular development of a cornified envelope while cell membranes and desmosomes remained undegraded. In conclusion, our studies on granular parakeratosis suggest a basic defect in processing of profilaggrin to filaggrin that results in a failure to degrade keratohyalin granules and to aggregate keratin filaments during cornification. Associated abnormalities of the cell surface structures and dysregulation of cornified envelope components may account for the retention hyperkeratosis. Further studies are necessary to clarify the etiology of this unique, acquired disorder of keratinization that localizes to intertriginous areas and body folds.

Unique inflammatory features noted in intraorally transferred skin flaps: correlation with Candida albicans infection

OBJECTIVE

The purpose of this study was to evaluate how well intraorally transferred skin flaps endure their new surroundings.

STUDY DESIGN

Biopsy specimens were taken from 20 patients who had undergone microsurgical reconstruction and as pretransferred skin from 5 of these patients at the time of surgery. The study used immunohistochemistry for immunocompetent cells, differentiation markers for the epidermis and desmosomal proteins, and immunoelectron microscopy for desmosomal protein, in addition to routine histologic examination, including Sudan IV, periodic acid Schiff, and Grocott stains. We also measured the thickness of the epidermis and stratum corneum. Oral swabs from the skin flaps were examined for the presence of yeasts, particularly Candida albicans, by means of a culture method.

RESULTS

According to the results of periodic acid-Schiff and Grocott staining, 20 cases were divided into 2 groups: fungal element-positive cases (n = 15) and fungal element-negative cases (n = 5). All swabs from the former were positive for Candida albicans. In these fungus-positive cases, histopathologic evaluation revealed marked diminution of stratum corneum and pronounced epidermal hyperplasia. Immunohistochemistry demonstrated the dermal infiltration of numerous immunocompetent cells-CD4+, CD8+, CD20+, CD68+, neutrophil elastase+, and HLA-DR+ cells-and the scarce infiltration of IgA+ and IgG+ cells. There were scattered CD1a+, CD4+, CD8+, and HLA-DR+ cells and elastase+ neutrophils in the epidermis. Expression of cytokeratin subtypes (10, 14, 16, and 19), involucrin, and tenascin showed the characteristic features of epidermal proliferation. Enumeration of Ki-67+ keratinocytes showed an increase, indicating epidermal proliferation. Expression of desmoglein 1 and desmocollin 1 in the epidermal keratinocytes was decreased in comparison with that in the pretransferred skin. Immunoelectron microscopy for desmoglein 1 confirmed the reduced immunoreactive deposits along the desmosomal plaques. In the fungus-negative cases, all such changes were a great deal milder.

CONCLUSIONS

Taken together, our results demonstrate that most intraorally transferred flaps are affected by an inflammatory process that is induced by the influence of the wet oral environment. They present psoriasiform tissue reactions characterized by epidermal hyperproliferation that are mostly due to Candida albicans infection.

Identification of novel and known mutations in the genes for keratin 5 and 14 in Danish patients with epidermolysis bullosa simplex: correlation between genotype and phenotype

Epidermolysis bullosa simplex (EBS) is a group of autosomal dominant inherited skin diseases caused by mutations in either the keratin 5 (K5) or the keratin 14 (K14) genes and characterized by development of intraepidermal skin blisters. The three major subtypes of EBS are Weber-Cockayne, Koebner, and Dowling-Meara, of which the Dowling-Meara form is the most severe. We have investigated five large Danish families with EBS and two sporadic patients with the Dowling-Meara form of EBS. In the sporadic Dowling-Meara EBS patients, a novel K14 mutation (N123S) and a previously published K5 mutation (N176S) were identified, respectively. A novel K14 mutation (K116N) was found in three seemingly unrelated families, whereas another family harbored a different novel K14 mutation (L143P). The last family harbored a novel K5 mutation (L325P). The identified mutations were not present in more than 100 normal chromosomes. Six polymorphisms were identified in the K14 gene and their frequencies were determined in normal controls. These polymorphisms were used to show that the K14 K116N mutation was located in chromosomes with the same haplotype in all three families, suggesting a common ancestor. We observed a strict genotype-phenotype correlation in the investigated patients as the same mutation always resulted in a similar phenotype in all individuals with the mutation, but our results also show that it is not possible to predict the EBS phenotype merely by the location (i.e., head, rod, or linker domains) of a mutation. The nature of the amino acid substitution must also be taken into account.

Expression of epidermal keratins and the cornified envelope protein involucrin is influenced by permeability barrier disruption

In previous studies we have shown that experimental permeability barrier disruption leads to an increase in epidermal lipid and DNA synthesis. Here we investigate whether barrier disruption also influences keratins and cornified envelope proteins as major structural keratinocyte proteins. Cutaneous barrier disruption was achieved in hairless mouse skin by treatments with acetone +/- occlusion, sodium dodecyl sulfate, or tape-stripping. As a chronic model for barrier disruption, we used essential fatty acid deficient mice. Epidermal keratins were determined by one- and two-dimensional gel electrophoresis, immunoblots, and anti-keratin antibodies in biopsy samples. In addition, the expression of the cornified envelope proteins loricrin and involucrin after barrier disruption was determined by specific antibodies in human skin. Acute as well as chronic barrier disruption resulted in the induction of the expression of keratins K6, K16, and K17. Occlusion after acute disruption led to a slight reduction of keratin K6 and K16 expression. Expression of basal keratins K5 and K14 was reduced after both methods of barrier disruption. Suprabasal keratin K10 expression was increased after acute barrier disruption and K1 as well as K10 expression was increased after chronic barrier disruption. Loricrin expression in mouse and in human skin was unchanged after barrier disruption. In contrast, involucrin expression, which was restricted to the granular and upper spinous layers in normal human skin, showed an extension to the lower spinous layers 24 h after acetone treatment. In summary, our results document that acute or chronic barrier disruption leads to expression of keratins K6, K16, and K17 and to a premature expression of involucrin. We suggest that the coordinated regulation of lipid, DNA, keratin, and involucrin synthesis is critical for epidermal permeability barrier function.

The limited difference between keratin patterns of squamous cell carcinomas and adenocarcinomas is explicable by both cell lineage and state of differentiation of tumour cells

AIM

To study the differentiation of epithelial tissues within their histological context, and to identify hypothetically, on the basis of keratin pattern, the putative tissue origin of a (metastatic) carcinoma.

METHODS

Using well characterised monoclonal antibodies against individual keratins 7, 8, 18, and 19, which are predominantly found in columnar epithelia, and keratins 4, 10, 13, and 14, predominantly expressed in (non)-keratinising squamous epithelia, the keratin patterns for a series of 45 squamous cell carcinomas and 44 adenocarcinomas originating from various epithelial tissues were characterised.

RESULTS

The predominant keratins in all adenocarcinomas proved to be 8, 18, and 19. In addition, these keratins were also abundantly present in squamous cell carcinomas of the lung, cervix, and rectum and, to a lesser extent, of the larynx, oesophagus, and tongue, but not in those of the vulva and skin. Keratins 4, 10, 13, and 14 were present in almost all squamous cell carcinomas, but also focally in some of the adenocarcinomas studied.

CONCLUSIONS

There is a limited differential expression of distinctive keratin filaments between squamous cell carcinomas and adenocarcinomas. Apparently, squamous cell carcinomas that originate from columnar epithelium by squamous metaplasia gain the keratins of squamous cells but retain the keratins of columnar epithelial cells. However, the simultaneous expression of two of three squamous keratins (4, 10, and 13) identifies a squamous cell carcinoma, and thus might be useful in solving differential diagnostic problems.

The major inherited disorders of cornification. New advances in pathogenesis

This article provides a synopsis of the major (most common) inherited disorders of cornification. It also reviews the recent advances that have been made for each disorder and their practical applications.

Expression pattern of human hair keratin basic 1 (hHb1) in hair follicle and pilomatricoma

Using in situ hybridization, human hair keratin basic 1 (hHb1) gene expression was investigated in human normal scalp. hHb1 transcripts were specifically detected in the cortical cells of hair shaft but neither in the outer and inner root sheaths, nor in the hair cuticle or the medulla. hHb1 expression was detected strongly in cortical cells located from the beginning of the keratogenous zone up to the isthmus. These data specify the localization of hHb1 expression. Furthermore, neoplasms with follicular differentiation, including trichoblastoma, trichoepithelioma, pilomatricoma, pilar carcinoma and basal-cell carcinoma, were analysed for hHb1 gene expression. One of the 4 pilomatricoma specimens examined exhibited a very high level of hHb1 transcripts. Interestingly, this labeling was specifically associated to a transitional cell layer en route to trichocytic differentiation, providing evidence that in pilomatricoma, epithelial germ cells can differentiate towards hair shaft keratinocytes before evolving in ghost cells.

Ultrastructural differentiation of epidermolysis bullosa subtypes and porphyria cutanea tarda

Identifying subtypes of epidermolysis bullosa clinically, particularly at the time of disease onset, can be extremely difficult. In this investigation samples of intact skin from cases of epidermolysis bullosa and porphyria cutanea tarda were examined ultrastructurally and compared with normal tissue. The histological composition of the blister roof and floor surfaces was also evaluated. Three of the ten epidermolysis bullosa subtypes examined revealed specific features. Distinctive, circumscribed, clumped tonofilament bodies were present in basal keratinocytes from epidermolysis bullosa herpetiformis Dowling-Meara. Blister formation in epidermolysis bullosa simplex generalisata gravis occurred immediately above the dermo-epidermal junction aspect of stratum basale cells and thick (30 nm diameter), cross-striated anchoring fibrils were absent in epidermolysis bullosa dystrophica generalisata gravis. Features relating to the lamina densa of the dermo-epidermal junction, dermal capillaries and blister composition were distinctive, but not confined to a particular epidermolysis bullosa subtype or porphyria cutanea tarda.

Differentiation-associated localization of small proline-rich protein in normal and diseased human skin

The expression of SPRR (small proline-rich protein) was investigated in normal human skin and in diseased skin from patients with psoriasis, squamous cell carcinoma, basal cell epithelioma, naevus pigmentosus, ichthyosis vulgaris and several inflammatory skin diseases, by immunohistochemical staining. A polyclonal antibody was raised against a synthetic peptide for a C-terminal common region for SPRR1 and SPRR3. In immunoblot analysis, a positive band of 18 kDa was detected, which showed the presence of SPRR1 in human epidermal keratinocytes. In normal epidermis, positive staining for SPRR was observed in keratinocytes in the granular layer and the uppermost or two spinous cell layers, with no staining of the other spinous or basal layers. The staining was obvious at the cell periphery, weak at the cytoplasm, and absent in the nucleus. Staining was observed in several outer layers of the follicular infundibulum to the isthmus. No staining was detected in the inner root sheath of the hair follicles, hair matrix, sebaceous gland, eccrine gland, eccrine duct, melanocytes, Langerhans cells or fibroblasts. The arrectores pilorum, striated muscles, muscle layers of vessels, and myoepithelia of eccrine gland, were weakly stained. In psoriatic skin, stained keratinocytes were distributed in the spinous cell layers except for the basal layer. In ichthyosis vulgaris, SPRR was barely expressed in the uppermost living cell layers of the epidermis. In epidermolytic hyperkeratosis, degenerated squamous cells widely expressed SPRR. In Darier's disease, dyskeratotic cells were clearly stained. In squamous cell carcinoma, staining was observed in keratotic cells around horny pearls. In basal cell epithelioma, naevus pigmentosus, and malignant melanoma, the tumour cells or naevus cells were not stained. The distribution of SPRR was similar to that of involucrin in normal and several diseased skin, except for ichthyosis vulgaris. We conclude that SPRR is expressed in close association with epidermal differentiation in normal skin and skin diseases. The alteration of the expression of the proteins correlated to terminal differentiation, and differs from disease to disease.