cDNA cloning and characterization of sciellin, a LIM domain protein of the keratinocyte cornified envelope

The Tilapia Cyst Tissue Enclosing the Proliferating Myxobolus bejeranoi Parasite Exhibits Cornified Structure and Immune Barrier Function

Myxozoa, a unique group of obligate endoparasites within the phylum Cnidaria, can cause emerging diseases in wild and cultured fish populations. Recently, the myxozoan Myxobolus bejeranoi has been identified as a prevalent pathogen infecting the gills of cultured hybrid tilapia, leading to systemic immune suppression and considerable mortality. Here, we employed a proteomic approach to examine the impact of M. bejeranoi infection on fish gills, focusing on the structure of the granulomata, or cyst, formed around the proliferating parasite to prevent its spread to surrounding tissue. Enrichment analysis showed increased immune response and oxidative stress in infected gill tissue, most markedly in the cyst's wall. The intense immune reaction included a consortium of endopeptidase inhibitors, potentially combating the myxozoan arsenal of secreted proteases. Analysis of the cyst's proteome and histology staining indicated that keratin intermediate filaments contribute to its structural rigidity. Moreover, we uncovered skin-specific proteins, including a grainyhead-like transcription factor and a teleost-specific S100 calcium-binding protein that may play a role in epithelial morphogenesis and cysts formation. These findings deepen our understanding of the proteomic elements that grant the cyst its distinctive nature at the critical interface between the fish host and myxozoan parasite.

Predicting Proteolysis in Complex Proteomes Using Deep Learning

Both protease- and reactive oxygen species (ROS)-mediated proteolysis are thought to be key effectors of tissue remodeling. We have previously shown that comparison of amino acid composition can predict the differential susceptibilities of proteins to photo-oxidation. However, predicting protein susceptibility to endogenous proteases remains challenging. Here, we aim to develop bioinformatics tools to (i) predict cleavage site locations (and hence putative protein susceptibilities) and (ii) compare the predicted vulnerabilities of skin proteins to protease- and ROS-mediated proteolysis. The first goal of this study was to experimentally evaluate the ability of existing protease cleavage site prediction models (PROSPER and DeepCleave) to identify experimentally determined MMP9 cleavage sites in two purified proteins and in a complex human dermal fibroblast-derived extracellular matrix (ECM) proteome. We subsequently developed deep bidirectional recurrent neural network (BRNN) models to predict cleavage sites for 14 tissue proteases. The predictions of the new models were tested against experimental datasets and combined with amino acid composition analysis (to predict ultraviolet radiation (UVR)/ROS susceptibility) in a new web app: the Manchester proteome susceptibility calculator (MPSC). The BRNN models performed better in predicting cleavage sites in native dermal ECM proteins than existing models (DeepCleave and PROSPER), and application of MPSC to the skin proteome suggests that: compared with the elastic fiber network, fibrillar collagens may be susceptible primarily to protease-mediated proteolysis. We also identify additional putative targets of oxidative damage (dermatopontin, fibulins and defensins) and protease action (laminins and nidogen). MPSC has the potential to identify potential targets of proteolysis in disparate tissues and disease states.

A Single-Cell Atlas of the Human Healthy Airways

Rationale: The respiratory tract constitutes an elaborate line of defense that is based on a unique cellular ecosystem.Objectives: We aimed to investigate cell population distributions and transcriptional changes along the airways by using single-cell RNA profiling.Methods: We have explored the cellular heterogeneity of the human airway epithelium in 10 healthy living volunteers by single-cell RNA profiling. A total of 77,969 cells were collected at 35 distinct locations, from the nose to the 12th division of the airway tree.Measurements and Main Results: The resulting atlas is composed of a high percentage of epithelial cells (89.1%) but also immune (6.2%) and stromal (4.7%) cells with distinct cellular proportions in different regions of the airways. It reveals differential gene expression between identical cell types (suprabasal, secretory, and multiciliated cells) from the nose (MUC4, PI3, SIX3) and tracheobronchial (SCGB1A1, TFF3) airways. By contrast, cell-type-specific gene expression is stable across all tracheobronchial samples. Our atlas improves the description of ionocytes, pulmonary neuroendocrine cells, and brush cells and identifies a related population of NREP-positive cells. We also report the association of KRT13 with dividing cells that are reminiscent of previously described mouse "hillock" cells and with squamous cells expressing SCEL and SPRR1A/B.Conclusions: Robust characterization of a single-cell cohort in healthy airways establishes a valuable resource for future investigations. The precise description of the continuum existing from the nasal epithelium to successive divisions of the airways and the stable gene expression profile of these regions better defines conditions under which relevant tracheobronchial proxies of human respiratory diseases can be developed.

Role of Sciellin in gallbladder cancer proliferation and formation of neutrophil extracellular traps

Apart from primary tumor development and metastasis, cancer-associated thrombosis is the second cause of cancer death in solid tumor malignancy. However, the mechanistic insight into the development of gallbladder cancer (GBC) and cancer-associated thrombosis remains unclear. This study aimed to investigate the mechanistic role of Sciellin (SCEL) in GBC cell proliferation and the development of venous thromboembolism. The expression level of SCEL was determined by immunohistochemical staining. Roles of SCEL in gallbladder cancer cell were determined by molecular and cell biology methods. SCEL was markedly upregulated in GBC and associated with advanced TNM stages and a poor prognosis. Furthermore, SCEL interacted with EGFR and stabilized EGFR expression that activates downstream PI3K and Akt pathway, leading to cell proliferation. In addition, SCEL induces tumor cell IL-8 production that stimulates the formation of neutrophil extracellular traps (NETs), accelerating thromboembolism. In xenografts, SCEL-expressing GBCs developed larger tumors and thrombosis compared with control cells. The present results indicate that SCEL promotes GBC cell proliferation and induces NET-associated thrombosis, thus serving as a potential therapeutic target.

The Proteins Interacting with Prmt5 in Medaka (Oryzias latipes) Identified by Yeast Two-Hybridization

BACKGROUND

Prmt5 plays major role in regulation of gene expression, RNA processing, cell growth and differentiation, signal transduction, germ cell development, etc., in mammals. Prmt5 is also related to cancer. Knowing the proteins interacting with Prmt5 is important to understand Prmt5's function in cells. Although there have been reports on proteins binding with Prmt5 in mammals, the partner proteins of Prmt5 in fish are still unclear.

OBJECTIVES

The objective was to obtain proteins that bind with Prmt5 in medaka, a model fish.

METHODS

Yeast two hybridization was adopted to achieve the objective. Medaka Prmt5 was used as a bait to fish the prey, binding proteins in a cDNA library of medaka. Co-immunoprecipitation and in silicon analysis were performed to study the interaction of medaka Mep50 and Prmt5.

RESULTS

Eight proteins were identified to bind with Prmt5 from 69 preliminary positive colonies. The binding proteins are methylosome protein 50 (Mep50), apolipoprotein A-I-like (Apo-AI), PR domain containing protein 1a with zinc fingers (Prdm1a), Prdm1b, T-cell immunoglobulin mucin family member 3 (Tim-3), phosphoribosylaminoimidazole carboxylase and phosphoribosylaminoimidazolesuccinocarboxamide synthase (Paics), NADH dehydrogenase subunit 4 (ND4) and sciellin (Scl). Co-immunoprecipitation confirmed the interaction of medaka Prmt5 and Mep50. Predicted structures of medaka Prtm5 and Mep50 are similar to that of human PRMT5 and MEP50.

CONCLUSION

Medaka Mep50, Prdm1a, Prdm1b, Apo-AI, Tim-3, Paics, ND4, and Scl bind with Prmt5.

Identification of ROBO1/2 and SCEL as candidate genes in Kallmann syndrome with emerging bioinformatic analysis

Kallmann syndrome (KS) is a congenital hypogonadotropic hypogonadism that coincides with anosmia or hyposmia. Although this rare genetic disease has a very low incidence, it harbors a complicated genetic heterogeneity, which indicates X-linked, autosomal, and oligogenic inheritance of puberty, sexuality, reproductivity, and olfactory defects. There has been limited elucidation of molecular etiologies completed to date. Here, a chromosome reciprocal translocation (46, XX, t (3; 13) (p13; q22)) was identified in a 27-year-old Chinese female diagnosed with KS. Genome sequencing found an intronic breakpoint of SCEL in chromosome 13 and an intergenic breakpoint between ROBO1 and ROBO2 in chromosome 3. This translocation resulted in the reduced expression levels of these genes. An array-CGH test captured no abnormal genomic copy numbers of clinical significance. The basic features of all known KS-related genes were also reviewed and analyzed for their roles in KS onset with bioinformatic methods. Signal pathway and gene enrichment analysis of KS-related genes suggested that these genes have integrated functions in neuronal migration and differentiation. An interesting chromosome locational pattern of KS-related genes was also discovered. This study provided constructive clues for further investigations into the molecular etiology of KS.

Transcriptional Analysis Shows a Robust Host Response to Toxoplasma gondii during Early and Late Chronic Infection in Both Male and Female Mice

The long-term host effects caused by the protozoan parasite Toxoplasma gondii are poorly understood. High-throughput RNA sequencing analysis previously determined that the host response in the brain was greater and more complex at 28 days than at 10 days postinfection. Here, we analyzed the host transcriptional profile of age- and sex-matched mice during very early (21 days), early (28 days), mid (3 months), and late (6 months) chronic infection. We found that a majority of the host genes which increase in abundance at day 21 postinfection are still increased at 6 months postinfection for both male and female mice. While most of the differentially expressed genes were similar between sexes, females had far fewer genes that were significantly less abundant, which may have led to the slightly increased cyst burden in males. Transcripts for C-X-C motif chemokine ligand 13 and a C-C motif chemokine receptor 2 (CCR2) were significantly higher in females than in males during infection. As T. gondii chronic infection and profilin (PRF) confer resistance to Listeria monocytogenes infection in a CCR2-dependent manner, the differences in CCR2 expression led us to retest the protection of PRF in both sexes. Male mice were nearly as effective as female mice at reducing the bacterial burden either with a chronic infection or when treated with PRF. These data show that most of the host genes differentially expressed in response to T. gondii infection are similar between males and females. While differences in transcript abundance exist between the sexes, the infection phenotypes tested here did not show significant differences.

White Matter is the Predilection Site of Late-Delayed Radiation-Induced Brain Injury in Non-Human Primates

Fractionated whole-brain irradiation for the treatment of intracranial neoplasia causes progressive neurodegeneration and neuroinflammation. The long-term consequences of single-fraction high-dose irradiation to the brain are unknown. To assess the late effects of brain irradiation we compared transcriptomic gene expression profiles from nonhuman primates (NHP; rhesus macaques Macaca mulatta) receiving single-fraction total-body irradiation (TBI; n = 5, 6.75-8.05 Gy, 6-9 years prior to necropsy) to those receiving fractionated whole-brain irradiation (fWBI; n = 5, 40 Gy, 8 × 5 Gy fractions; 12 months prior to necropsy) and control comparators (n = 5). Gene expression profiles from the dorsolateral prefrontal cortex (DLPFC), hippocampus (HC) and deep white matter (WM; centrum semiovale) were compared. Stratified analyses by treatment and region revealed that radiation-induced transcriptomic alterations were most prominent in animals receiving fWBI, and primarily affected white matter in both TBI and fWBI groups. Unsupervised canonical and ontologic analysis revealed that TBI or fWBI animals demonstrated shared patterns of injury, including white matter neuroinflammation, increased expression of complement factors and T-cell activation. Both irradiated groups also showed evidence of impaired glutamatergic neurotransmission and signal transduction within white matter, but not within the dorsolateral prefrontal cortex or hippocampus. Signaling pathways and structural elements involved in extracellular matrix (ECM) deposition and remodeling were noted within the white matter of animals receiving fWBI, but not of those receiving TBI. These findings indicate that those animals receiving TBI are susceptible to neurological injury similar to that observed after fWBI, and these changes persist for years postirradiation. Transcriptomic profiling reaffirmed that macrophage/microglial-mediated neuroinflammation is present in radiation-induced brain injury (RIBI), and our data provide novel evidence that the complement system may contribute to the pathogenesis of RIBI. Finally, these data challenge the assumption that the hippocampus is the predilection site of injury in RIBI, and indicate that impaired glutamatergic neurotransmission may occur in white matter injury.

Sciellin mediates mesenchymal-to-epithelial transition in colorectal cancer hepatic metastasis

Hepatic metastasis is the major cause of mortality in colorectal cancer (CRC) patients. Using proteomic analysis, we found sciellin (SCEL) to be specifically expressed in hepatic metastatic CRC cell lines. SCEL knockdown increased CRC cell migration and invasion, while overexpression had the opposite effect. SCEL knockdown also caused cancer cells to form more invasive structures within 3D cultures, increased the mesenchymal marker vimentin, and attenuated the epithelial marker E-cadherin. SCEL increased WNT signaling by activating β-catenin and its downstream target c-myc, and activated mesenchymal-to-epithelial transition (MET) through a SCEL-β-catenin-E-cadherin axis. SCEL showed higher expression in late stage primary CRC than in its hepatic metastatic counterpart. SCEL expression is dynamically modulated by TGF-β1 and hypoxia, revealing a plastic MET mechanism for tumor colonization. Intrahepatic injection in immunodeficient mice revealed that SCEL is necessary for metastatic CRC tumor growth in the liver. These results demonstrate that SCEL is a MET inducer dynamically regulated through the metastasis process. They suggest SCEL may be a useful therapeutic target for preventing or eliminating CRC hepatic metastasis.

Sciellin is a marker for papillary renal cell tumours

There are no adequate immunohistochemical markers for papillary renal cell tumours. The aim of this study was to establish a gene expression profile of papillary renal cell tumours using an expression microarray approach. Through hierarchical clustering and significant analysis of microarrays, we have selected the best 13 genes and analysed their expression by real-time polymerase chain reaction (RT-PCR). Of these genes, we selected SCEL as potential marker of interest. Immunohistochemical staining of tissue microarrays containing all major types of kidney cancers revealed positive staining for sciellin in 87 of 114 papillary renal cell tumours and in 13 of 19 precursor lesions. No other renal tumour types were positive for sciellin. Our study indicates that although not all tumours express sciellin, its expression may help to confirm the diagnosis papillary renal cell tumour.

A murine model of Denys-Drash syndrome reveals novel transcriptional targets of WT1 in podocytes

The Wilms tumor-suppressor gene WT1, a key player in renal development, also has a crucial role in maintenance of the glomerulus in the mature kidney. However, molecular pathways orchestrated by WT1 in podocytes, where it is highly expressed, remain unknown. Their defects are thought to modify the cross-talk between podocytes and other glomerular cells and ultimately lead to glomerular sclerosis, as observed in diffuse mesangial sclerosis (DMS) a nephropathy associated with WT1 mutations. To identify podocyte WT1 targets, we generated a novel DMS mouse line, performed gene expression profiling in isolated glomeruli and identified excellent candidates that may modify podocyte differentiation and growth factor signaling in glomeruli. Scel, encoding sciellin, a protein of the cornified envelope in the skin, and Sulf1, encoding a 6-O endosulfatase, are shown to be expressed in wild-type podocytes and to be strongly down-regulated in mutants. Co-expression of Wt1, Scel and Sulf1 was also found in a mesonephric cell line, and siRNA-mediated knockdown of WT1 decreased Scel and Sulf1 mRNAs and proteins. By ChIP we show that Scel and Sulf1 are direct WT1 targets. Cyp26a1, encoding an enzyme involved in the degradation of retinoic acid, is shown to be up-regulated in mutant podocytes. Cyp26a1 may play a role in the development of glomerular lesions but does not seem to be regulated by WT1. These results provide novel clues in our understanding of normal glomerular function and early events involved in glomerulosclerosis.

Biomechanical stress induces novel arterial intima-enriched genes: implications for vascular adaptation to stress

BACKGROUND

The arterial vasculature is subjected to considerably greater biomechanical stress than the venous circulation. This is reflected in the difference in morphology between large arteries and veins, however little is known about the molecular differences that arise as a consequence of biomechanical stress. Previously, we identified a group of arterial intima-enriched (AIE) genes: sciellin, periplakin, SPRR3, envoplakin, galectin 7, and plakoglobin that are functionally related in that they contribute to the stress properties of stratified epithelium. We sought to test our hypothesis that these genes were regulated by biomechanical stress in vascular smooth muscle cells (VSMCs).

METHODS

Immunofluorescence was employed to determine the expression of the AIE genes in saphenous vein coronary artery bypass grafts. Furthermore, we used a model of cyclic stress to determine if the AIE genes were regulated by biomechanical stress in VSMCs in vitro.

RESULTS

Sciellin and periplakin were upregulated in saphenous vein coronary artery bypass grafts after arterialization, but were absent in non-arterialized saphenous veins. Sciellin, SPRR3, and periplakin transcripts were all upregulated (4.67-, 4.95-, 2.77-fold, respectively) by prolonged exposure to cyclic strain (24-72 h), but not at earlier time points.

CONCLUSIONS

These findings suggest a novel role for several human AIE genes in the VSMC response to arterialization and extended cyclic strain.

SUMMARY

Biomechanical stress has long been implicated in vascular pathologies. We report the novel finding of a group of genes, previously studied in stratified epithelium, that were regulated by prolonged cyclic stress in vascular smooth muscle cells. This may have important implications to vascular disease.

Characterization of keratins and associated proteins involved in the corneification of crocodilian epidermis

Crocodilian keratinocytes accumulate keratin and form a corneous cell envelope of which the composition is poorly known. The present immunological study characterizes the molecular weight, isoelectric point (pI) and the protein pattern of alpha- and beta-keratins in the epidermis of crocodilians. Some acidic alpha-keratins of 47-68 kDa are present. Cross-reactive bands for loricrin (70, 66, 55 kDa), sciellin (66, 55-57 kDa), and filaggrin-AE2-positive keratins (67, 55 kDa) are detected while caveolin is absent. These proteins may participate in the formation of the cornified cell membranes, especially in hinge regions among scales. Beta-keratins of 17-20 kDa and of prevalent basic pI (7.0-8.4) are also present. Acidic beta-keratins of 10-16 kDa are scarce and may represent altered forms of the original basic proteins. Crocodilian beta-keratins are not recognized by a lizard beta-keratin antibody (A68B), and by a turtle beta-keratin antibody (A685). This result indicates that these antibodies recognize specific epitopes in different reptiles. Conversely, crocodilian beta-keratins cross-react with the Beta-universal antibody indicating they share a specific 20 amino acid epitope with avian beta-keratins. Although crocodilian beta-keratins are larger proteins than those present in birds our results indicate presence of shared epitopes between avian and crocodilian beta-keratins which give good indication for the future determination of the sequence of these proteins.

Molecular analysis of anoikis resistance in oral cavity squamous cell carcinoma

Oral cavity squamous cell carcinoma (OSCC) is one of the leading causes of cancer deaths worldwide and most of these deaths result from local-regional recurrence and metastases. Evasion of apoptosis is an important hallmark of cancer development and progression, and previous studies have shown that evasion of anoikis, or detachment-induced apoptosis, correlates with a more aggressive phenotype of carcinoma cells in OSCC. To elucidate the cytogenetic and molecular characteristics of anoikis resistance, we generated several cell lines and clones that displayed this cellular phenotype. To test the hypothesis that chromosomal alterations may underlie this phenotypic transformation, we used karyotype analysis to observe changes in the chromosomal structure of anoikis-sensitive and anoikis-resistant cell lines. We further hypothesized that a unique pattern of gene expression was induced by cell-detachment of anoikis-resistant cell lines, and cDNA microarray analysis was performed using a panel of anoikis-resistant oral cancer cell lines grown under attached and detached growth conditions. We identified S100P, KLK6 and CTNNAL1 as genes whose expression levels were differentially regulated in the anoikis-resistant cell lines compared to the anoikis-sensitive cells under detached conditions. These results were verified using real-time RT-PCR. The anoikis-resistant phenotype of squamous cell carcinoma has a distinct genetic expression pattern that is marked by chromosomal alterations that may contribute to differential expression of genes involved in diverse cellular functions. Therapies targeting these potential mediators of anoikis resistance may prove to be beneficial in the treatment of metastatic squamous cell carcinoma.

Skin structure and cornification proteins in the soft-shelled turtle Trionyx spiniferus

In contrast to most chelonians, the fully aquatic soft-shelled turtles have a smooth, unscaled, and pliable shell. The skin of the shell, tail, limbs, and neck of juveniles of Trionyx spiniferus has been studied by ultrastructural, immunocytochemical, and immunoblotting methods. The epidermis of the carapace and plastron has a thick corneous layer composed of alpha-corneocytes surrounded by a cornified cell envelope. The softer epidermis is similar to that of the shell but the epidermis and corneous layer are much thinner. Pre-corneous cells in both soft and shell epidermis are rich in vesicles produced in the Golgi apparatus and smooth endoplasmic vesicles, and contain numerous dense-core mucus-like and vesicular (lamellar) bodies. Secreted material is present among corneocytes where it probably forms an extensive intercellular lipid-mucus waterproof barrier. The dermis is very thick and composed of several layers of collagen bundles that form a plywood-patterned dermis. This dermis constitutes a strong mechanical barrier that compensates for the low content in beta-keratin, and lack of cornified scutes and dermal bones. The growth of the shell mainly occurs along the lateral margins. Immunocytochemistry reveals the presence of some beta-keratin in soft and shell epidermis, and this is confirmed by immunoblotting where bands at 18 and 32-35 kDa are present. Other proteins of the cornified cell envelope (loricrin and sciellin) or associated to lipid trafficking (caveolin-1) are also detected by immunoblotting. Loricrin positive bands at 24 and 57 kDa are present while bands cross-reactive for sciellin are seen at 45 and 53 kDa. Caveolin-1 positive bands are seen at 21-22 kDa. The presence of these proteins indicates that the epidermis is both coriaceous and waterproof. These results suggest that the shell of Trionyx is tough enough to be as mechanically efficient as the hard shell of the other turtles. At the same time, a soft shell is lighter, its shape is more easily controlled by muscles, and it allows a more controlled closure and retraction of limbs and neck inside the shell. Thus, the shell makes the animal more streamlined for swimming.

Cytochemical, biochemical and molecular aspects of the process of keratinization in the epidermis of reptilian scales

The characteristics of scaled skin of reptiles is one of their main features that distinguish them from the other amniotes, birds and mammals. The different scale patterns observed in extant reptiles result from a long evolutive history that allowed each species to adapt to its specific environment. The present review deals with comparative aspects of epidermal keratinization in reptiles, chelonians (turtles and tortoises), lepidosaurian (lizards, snakes, sphenodontids), archosaurians (crocodilians). Initially the morphology and cytology of reptilian scales is outlined to show the diversity in the epidermis among different groups. The structural proteins (alpha-keratins and associated proteins), and enzymes utilized to form the corneous layer of the epidermis are presented. Aside cytokeratins (alpha-keratins), used for making the cytoskeleton, reptilian alpha-keratinocytes produce interkeratin (matrix) and corneous cell envelope proteins. Keratin bundles and degraded cell organelles constitute most of the corneous material of alpha-keratinocytes. Matrix, histidine-rich and sulfur-rich proteins are produced in the soft epidermis and accumulated in the cornified cell envelope. Main emphasis is given to the composition and to the evolution of the hard keratins (beta-keratins). Beta-keratins constitute the hard corneous material of scales. These small proteins are synthesized in beta-keratinocytes and are accumulated into small packets that rapidly merge into a compact corneous material and form densely cornified layers. Beta-keratins are smaller proteins (8-20 kDa) in comparison to alpha-keratins (40-70 kDa), and this size may determine their dense packing in corneocytes. Both glycine-sulfur-rich and glycine-proline-rich proteins have been so far sequenced in the corneous material of scales in few reptilian species. The latter keratins possess C- and N-amino terminal amino acid regions with sequence homology with those of mammalian hard keratins. Also, reptilian beta-keratins possess a central core with homology with avian scale/feather keratins. Multiple genes code for these proteins and their discovery and sequentiation is presently an active field of research. These initial findings however suggest that ancient reptiles already possessed some common genes that have later diversified to produce the specific keratin-associated proteins in their descendants: extant reptiles, birds and mammals. The evolution of these small proteins in lepidosaurians, chelonians and archosaurians represent the next step to understand the evolution of cornification in reptiles and derived amniotes (birds and mammals).

Distribution and characterization of proteins associated with cornification in the epidermis of gecko lizard

The distribution and molecular weight of epidermal proteins of gecko lizards have been studied by ultrastructural, autoradiographic, and immunological methods. Setae of the climbing digital pads are cross-reactive to antibodies directed against a chick scutate scale beta-keratin but not against feather beta-keratin. Cross-reactivity for mammalian loricrin, sciellin, filaggrin, and transglutaminase are present in alpha-keratogenic layers of gecko epidermis. Alpha-keratins have a molecular weight in the range 40-58 kDa. Loricrin cross-reactive bands have molecular weights of 42, 50, and 58 kDa. Bands for filaggrin-like protein are found at 35 and 42 kDa, bands for sciellin are found at 40-45 and 50-55 kDa, and bands for transglutaminase are seen at 48-50 and 60 kDa. The specific role of these proteins remains to be elucidated. After injection of tritiated histidine, the tracer is incorporated into keratin and in setae. Tritiated proline labels the developing setae of the oberhautchen and beta layers, and proline-labeled proteins (beta-keratins) of 10-14, 16-18, 22-24 and 32-35 kDa are extracted from the epidermis. In whole epidermal extract (that includes the epidermis with corneous layer and the setae of digital pads), beta-keratins of low-molecular weight (10, 14-16, and 18-19 kDa) are prevalent over those at higher molecular weight (34 and 38 kDa). In contrast, in shed epidermis of body scales (made of corneous layer only while setae were not collected), higher molecular weight beta-keratins are present (25-27 and 30-34 kDa). This suggests that a proportion of the small beta-keratins present in the epidermis of geckos derive from the differentiating beta layer of scales and from the setae of digital pads. Neither small nor large beta-keratins of gecko epidermis cross-react with an antibody specifically directed against the feather beta-keratin of 10-12 kDa. This result shows that the 10 and 14-16 kDa beta-keratins of gecko (lepidosaurian) have a different composition than the 10-12 kDa beta-keratin of feather (archosaurian). It is suggested that the smaller beta-keratins in both lineages of sauropsids were selected during evolution in order to build elongated bundles of keratin filaments to make elongated cells. Larger beta-keratins in reptilian scales produce keratin aggregations with no orientation, used for mechanical protection.

Targeted deletion of the sciellin gene resulted in normal development and maturation

Sciellin, together with other precursor proteins, was cross-linked by transglutaminase 1 to form the cornified envelope, an essential component of the physical barrier of the epidermis and stratified squamous epithelia. To more fully understand the function of sciellin in cornified envelope formation, we generated sciellin null mice. The mice appeared normal in their development and maturation and there were no structural features that distinguished them from littermate controls. Isolated cornified envelopes appeared normal in structure and were not more fragile to mechanical stress. There was no evidence of decreased barrier function or altered expression of other cornified envelope components. Transgenic mice expressing the repeat domain appeared to have a normal phenotype, like the null, and did not alter endogenous sciellin expression. We conclude that sciellin null mice had no structural anomalies and the transgenic mice did not act as a dominant-negative mutation.

Mammalian transglutaminases. Identification of substrates as a key to physiological function and physiopathological relevance

Transglutaminases form a large family of intracellular and extracellular enzymes that catalyse the Ca2+-dependent post-translational modification of proteins. Despite significant advances in our understanding of the biological role of most mammalian transglutaminase isoforms, recent findings suggest new scenarios, most notably for the ubiquitous tissue transglutaminase. It is becoming apparent that some transglutaminases, normally expressed at low levels in many tissue types, are activated and/or overexpressed in a variety of diseases, thereby resulting in enhanced concentrations of cross-linked proteins. As applies to all enzymes that exert their metabolic function by modifying the properties of target proteins, the identification and characterization of the modified proteins will cast light on the functions of transglutaminases and their involvement in human diseases. In this paper we review data on the properties of mammalian transglutaminases, particularly as regards their protein substrates and the relevance of transglutaminase-catalysed reactions in physiological and disease conditions.

Localization and Characterization of Specific Cornification Proteins in Avian Epidermis

Little is known about proteins involved in the formation of the stratum corneum in the avian apteric epidermis. The present immunocytochemical, autoradiographic and electrophoretic study shows that antibodies against characteristic proteins of mammalian cornification (alpha-keratins, loricrin, sciellin, filaggrin, transglutaminase) recognize avian epidermal proteins. This suggests the presence of avian protein with epitopes common to related mammalian proteins. These proteins may also be involved in the formation of the cornified core and cell envelope of mature avian corneocytes. The immunoblotting study suggests that protein bands, cross-reactive for antibodies against loricrin (45, 52-57 kDa), sciellin (54, 84 kDa), filaggrin (32, 38, 45-48 kDa), and transglutaminase (40, 50, 58 kDa), are present in the avian epidermis. Immunocytochemistry shows that immunoreactivity for the above proteins is localized in the transitional and lowermost corneous layer of apteric epidermis. Their epitopes are rapidly masked/altered in cornifying cells and are no longer detectable in mature corneocytes. In scaled epidermis a thick layer made of beta-keratins of 14-18, 20-22, and 33 kDa is formed. Only in feathered epidermis (not in scale epidermis), an antifeather chicken beta-keratin antibody recognized a protein band at 8-12 kDa. This small beta-keratin is probably suitable for the formation of long, axial filaments in elongated barb, barbule and calamus cells. Conversely, the larger beta-keratins in scales are irregularly deposited forming flat plates. Tritiated histidine coupled to autoradiography show an absence of both keratohyalin and histidine-rich proteins in adult feathered and scaled epidermis. Most of the labeling appears in proteins within the range of beta- and alpha-keratins. These data on apteric epidermis support the hypothesis of an evolution of the apteric and interfollicular epidermis from the expansion of hinge regions of protoavian archosaurians.

Immuno-Cross reactivity of transglutaminase and cornification marker proteins in the epidermis of vertebrates suggests common processes of soft cornification across species

In differentiating mammalian keratinocytes proteins are linked to the plasma membrane by epidermal transglutaminases through N-epsilon-(gamma-glutamyl)-lysine isopeptide bonds to form the cornified cell envelope. The presence of transglutaminases and their protein substrates in the epidermis of nonmammalian vertebrates is not known. The present study analyses the presence and localization of the above proteins in the epidermis using immuno-cross reactivity across different classes of amniotes. After immunoblotting, some protein bands appear labelled for loricrin, sciellin, and transglutaminase in most species. These proteins are scarce to absent in the epidermis of aquatic species (goldfish and newt) where a stratum corneum is absent or very thin. The molecular weight of transglutaminase immunoreactive bands generally varies between 40 to 62 kDa, with the most represented bands at 52-57 kDa in most species. The more intense loricrin- and sciellin-immunoreactive bands are seen at 50-55-62 kDa, but are weak or absent in aquatic vertebrates. Loricrine-like immunoreactivity is present in the epidermis where alpha-(soft)-keratinization occurs. Isopeptide bonds are mainly associated to bands in the range of 50-62 kDa. In vertebrates where hard-keratin is expressed (the beta-keratin corneous layer of sauropsids and in feathers) or in hair cortex of mammals, no loricrin-like, transglutaminase-, and isopeptide-bond-immunoreactivities are seen. Immunoblotting however shows loricrin-, sciellin-, and trasnsglutaminase-positive bands in the corneous layers containing beta-keratin. Histologically, the epidermis of most amniotes shows variable transglutaminase immunoreactivity, but isopeptide-bond and sciellin immunoreactivities are weak or undetactable in most species. The limitations of immunohistochemical methods are discussed and compared with results from immunoblotting. In reptilian epidermis transglutaminase is mainly localized in 0.15-0.3 microm dense granules or diffuse in transitional alpha-keratogenic cells. In beta-keratogenic cells few small dense granules show a weak immunolabeling. Transglutaminase is present in nuclei of terminal differentiating alpha- and beta-keratinocytes, as in those of mature inner and outer root sheath. The present study suggests that keratinization based on loricrin, sciellin and transglutaminase was probably present in the stratum corneoum of basic amniotes in the Carboniferous. These proteins were mainly maintained in alpha-keratogenic layers of amniotes but decreased in beta-keratogenic layers of sauropsids (reptiles and birds). The study suggests that similar proteins for the formation of the cornified cell envelope are present in alpha-keratinocytes across vertebrates but not in beta-keratinocytes.

Differentiation of the epidermis in turtle: an immunocytochemical, autoradiographic and electrophoretic analysis

Proteins involved in the process of cornification of turtle epidermis are not well known. The present immunocytochemical, electrophoretic and autoradiographic study reports on the localization patterns and molecular weights of keratins, which are cornification proteins, and of tritiated histidine in turtle epidermis. Alpha-keratins with a molecular weight of 40-62 kDa are present in the epidermis. Beta-keratin is mainly detectable in the stratum corneum of the carapace and plastron, but is rarely present or even absent in the corneous layer of limb, tail and neck epidermis. After electrophoresis and immunoblotting with an antibody against chicken scale beta-keratin, bands at 15-17, 22-24, and 36-38 kDa appeared. This antibody recognized weaker bands at 38-40 and 58-60 kDa in the soft epidermis. After reduction and carboxymethylation of proteins extracted from carapace and plastron, but not of proteins from the soft epidermis, protein bands at 15-17 and 35-37 kDa were found when using the anti-beta 1-keratin antibody. Loricrin-, filaggrin-, sciellin-, and transglutaminase-like immunostaining was detectable only in the transitional and lowermost corneous layers of the soft epidermis. Vesicular bodies in the transitional layer were immunolabeled by the anti-loricrin antibody, and weakly by the anti-filaggrin and anti-transglutaminase antibodies. In immunoblots, the anti-loricrin antibody reacted with a major band at 50-54 kDa in both carapace-plastron and soft epidermis. The anti-sciellin antibody detected major bands at 38-40 and 50 kDa in hard epidermis, and at 50 and 54-56 kDa in soft epidermis. Filaggrin-like immunostained bands were observed at 50-55 and 62-64 kDa. This immunostaining was probably due to a common epitope in filaggrin and some keratins. Histidine was evenly incorporated in the epidermis, and the ultrastructural study showed random labeling, often associated with keratin bundles of alpha and beta-keratinocytes. Histidine-labeled protein bands were not found in the carapace-plastron. In the soft epidermis, weakly labeled bands at 15-20, 25, and 45-60 kDa were found occasionally. The latter bands probably represented neo-synthesized keratins as was also indicated by the ultrastructural autoradiographic analysis. In conclusion, our study suggests that proteins with epitopes that they have in common with cornification proteins of mammalian epidermis are also present in the epidermis of turtle.

Ratio of immature cornified envelopes does not correlate with parakeratosis in inflammatory skin disorders

We have previously established a non-invasive method to evaluate the maturity of cornified envelopes (CEs), and have reported the appearance of immature CEs in the stratum corneum (SC) with poor barrier function, such as the SC of the face. The purpose of the present study was to evaluate CEs in inflammatory skin disorders, and to clarify the relationship between the appearance of the immature CEs and parakeratosis, which is often used as a marker for defective keratinization in inflammatory skin disorders. Cornified envelopes in the outermost SC of involved areas of psoriasis vulgaris (PV) and atopic dermatitis (AD) were strikingly heterogeneous, and consisted of immature CEs stained with anti-involucrin and mature CEs stained with Nile red, whereas CEs of the uninvolved areas were relatively homogeneous, exhibiting mature phenotype. The ratio of immature CEs was significantly higher in the involved areas of PV and AD than that in the corresponding uninvolved areas, suggesting that defective CE maturation may, at least in part, account for the inflammatory disorders. Simultaneous evaluation of CE maturity and parakeratosis was carried out by a combination of involucrin immunostaining and nuclear staining of detergent-dissociated corneocytes. In the involved area of PV, four types of corneocytes in regard to the combination of involucrin staining and nuclear remnant were observed, while both immature CEs and parakeratosis were more often detected in the involved areas of PV than in the uninvolved areas or the upper arm of healthy subjects as a normal control. Thus, corneocytes with involucrin-positive immature CEs were not always associated with parakeratosis at the cellular level. In the involved areas of PV, the ratio of immature CEs and that of parakeratosis were heterogeneous, depending on the cases, and no correlation between the ratios was observed. Inter-individual and intraindividual variations in CE maturity were also suggested by the heterogeneous localization of involucrin in the psoriatic epidermis as examined by immunohistochemistry. In addition, in the face of healthy subjects, four types of corneocytes were similarly detected, and the ratio of immature CEs was significantly higher than that of parakeratosis. These results obviously suggest that the maturation of CEs and disappearance of nuclei are differentially regulated in the epidermis.

Differential gene expression profile of human tonsil high endothelial cells: implications for lymphocyte trafficking

Lymphocyte recirculation is dependent on the interactions of adhesion and signaling molecules expressed on lymphocytes and their partners on high endothelial cells (HEC). Many of the events in this process have yet to be molecularly characterized. To identify novel HEC-specific proteins with potential function in the recruitment cascade, we sequenced a normalized human tonsil HEC cDNA library (generated from an inflamed tonsil) from which lymphocyte and human umbilical vein endothelial cell cDNAs had been subtracted. One-thousand forty-nine sequences were analyzed. All but three mapped to known cDNAs or genomic DNAs. The two most abundant transcripts encoded alpha2-macroglobulin and hevin. The next-abundant transcripts encoded several other protease inhibitors, making this protein class the most prominent in HEC. Several endothelial-specific transcripts were also identified, including those encoding E-selectin, vascular cell adhesion molecule-1, vascular endothelial-junctional adhesion molecule, and platelet-endothelial cell adhesion molecule-1. The library contains a great diversity of transcripts, and studies of the encoded proteins will provide further insight into the complex biology of these specialized endothelial cells.

Keratinocyte Differentiation Is Regulated by the Rho and ROCK Signaling Pathway

The epidermis comprises multiple layers of specialized epithelial cells called keratinocytes. As cells are lost from the outermost epidermal layers, they are replaced through terminal differentiation, in which keratinocytes of the basal layer cease proliferating, migrate upwards, and eventually reach the outermost cornified layers. Normal homeostasis of the epidermis requires that the balance between proliferation and differentiation be tightly regulated. The GTP binding protein RhoA plays a fundamental role in the regulation of the actin cytoskeleton and in the adhesion events that are critically important to normal tissue homeostasis. Two central mediators of the signals from RhoA are the ROCK serine/threonine kinases ROCK-I and ROCK-II. We have analyzed ROCK's role in the regulation of epidermal keratinocyte function by using a pharmacological inhibitor and expressing conditionally active or inactive forms of ROCK-II in primary human keratinocytes. We report that blocking ROCK function results in inhibition of keratinocyte terminal differentiation and an increase in cell proliferation. In contrast, activation of ROCK-II in keratinocytes results in cell cycle arrest and an increase in the expression of a number of genes associated with terminal differentiation. Thus, these results indicate that ROCK plays a critical role in regulating the balance between proliferation and differentiation in human keratinocytes.

The Expression of Vitamin D-Upregulated Protein 1 in Skin and its Interaction with Sciellin in Cultured Keratinocytes

Sciellin, a precursor of the cornified envelope, contains a LIM domain that is known to function as a protein interaction module. In this study we used the yeast two-hybrid system to find proteins interacting with sciellin and identified vitamin D-upregulated protein 1 (VDUP1). This protein had not been reported in skin, but was shown in a number of cells to interact with reduced thioredoxin and regulate its function. Using an affinity VDUP1 column and an extract of cultured keratinocytes it was shown that VDUP1 and sciellin interacted. By immunohistochemistry VDUP1 was localized to the basal layer of normal human epidermis and the inner and outer root sheaths but not the matrix of the hair follicle. In the proliferative epidermis of psoriasis, VDUP1 was most highly expressed in the upper epidermal layers. In cultured keratinocytes, VDUP1 and sciellin were more highly expressed in cells undergoing differentiation. Colocalization of the proteins could be demonstrated by immunohistochemistry in parts of the follicle, psoriatic epidermis, and cultured keratinocytes. Our results suggested that VDUP1 could have a unique role in epidermis regulating the conversion of postmitotic cells to differentiating ones.

Suprabasin, a novel epidermal differentiation marker and potential cornified envelope precursor

The suprabasin gene is a novel gene expressed in mouse and human differentiating keratinocytes. We identified a partial cDNA encoding suprabasin using a suppression subtractive hybridization method between the proliferative basal and differentiating suprabasal populations of the mouse epidermis. A 3' gene-specific probe hybridized to transcripts of 0.7- and 2.2-kb pairs on Northern blots with specific detection in differentiated keratinocytes of stratified epithelia. The mouse gene was mapped to chromosome 7 by fluorescence in situ hybridization. This region is syntenic to human chromosome band 19q13.1, which contained the only region in the data bases with homology to the mouse suprabasin sequence. During embryonic mouse development, suprabasin mRNA was detected at day 15.5, coinciding with epidermal stratification. Suprabasin was detected in the suprabasal layers of the epithelia in the tongue, stomach, and epidermis. Differentiation of cultured primary epidermal keratinocytes with 0.12 mm Ca(2+) or 12-O-tetradecanoylphorbol-13-acetate treatment resulted in the induction of suprabasin. The 2.2-kb cDNA transcript encodes a protein of 72 kDa with a predicted isoelectric point of 6.85. The translated sequence has an amino-terminal domain, a central domain composed of repeats rich in glycine and alanine, and a carboxyl-terminal domain. The alternatively spliced 0.7-kb transcript encodes a smaller protein that shares the NH(2)- and COOH-terminal regions but lacks the repeat domain region. Cross-linking experiments indicate that suprabasin is a substrate for transglutaminase 2 and 3 activity. Altogether, these results indicate that the suprabasin protein potentially plays a role in the process of epidermal differentiation.

Identification of immature cornified envelopes in the barrier-impaired epidermis by characterization of their hydrophobicity and antigenicities of the components

Cornified envelopes (CEs), rigid and insoluble structures in the stratum corneum, which are assembled by crosslinking of several precursor proteins by transglutaminases, provide a hydrophobic foundation for barrier function; omega-hydroxyceramides are covalently attached to the outer surface of CE components, and onto this hydrophobic assembly, lamellar layers of intercellular lipids are organized. Morphologically irregular, fragile CEs are found in the deep layer of the stratum corneum or in certain disorders, such as psoriasis, whereas most CEs from healthy subjects are rigid and polygonal. We have established a staining method to characterize such fragile CEs as immature and less hydrophobic CEs, and employed it to examine regional differences in the properties of CEs, especially in relation to the barrier function of the skin. CEs from the outermost stratum corneum of the trunk and extremities of healthy subjects were relatively uniform in morphology with larger shape, and were homogeneous in hydrophobicity as judged from the use of an environment-sensitive fluorescent dye, Nile red. However, CEs from the face were strikingly heterogeneous, and consisted of both rigid and fragile CEs. Rigid CEs were Nile red-positive and little stained by anti-involucrin. In contrast, fragile CEs were Nile red-negative but strongly stained with anti-involucrin, as detected by indirect immunofluorescence. Thus, CEs from the face were stained with Nile red or involucrin in a mutually exclusive manner. Fragile CEs were stained with antibodies against other CE components, including loricrin, envoplakin, filaggrin, and isopeptides. Such fragile, involucrin-positive CEs were detected not only in the face, but also in the deep layer of the stratum corneum of the arm. In addition, experimental barrier disruption resulted in the appearance of involucrin-positive CEs in the outermost stratum corneum. These results suggest that involucrin-positive, fragile CEs are immature and less hydrophobic, and that their occurrence is closely related to impairment of the barrier function of the skin.

Gene characterization of sciellin (SCEL) and protein localization in vertebrate epithelia displaying barrier properties

Sciellin is a precursor of the cornified envelope of mammalian stratified epithelia characterized by a central core of nonidentical repeats. We characterized the genomic structure of human sciellin and showed that each homologous repeat was encoded by one exon. We also characterized mouse sciellin and showed that mouse sciellin and human sciellin (HGMW-approved symbol SCEL) share a similar gene organization and protein expression pattern. This one exon/one repeat organization is unique among other cornified envelope precursors characterized by homologous repeats. We identified an alternatively spliced isoform of human sciellin, absent in mouse, characterized by an additional repeat at the beginning of the core domain. During embryonic development, the accumulation of sciellin transcript and the accumulation of sciellin protein in the epidermis correlated with the activation of markers of terminal differentiation in epidermis. Mouse sciellin was also identified in simple epithelia with barrier properties, lending further support to its importance in epithelial function.