An unexpected role for keratin 10 end domains in susceptibility to skin cancer

Translation-Dependent Skin Hyperplasia Is Promoted by Type 1/17 Inflammation in Psoriasis

BACKGROUND

Psoriasis vulgaris (PV) is a chronic skin inflammatory disease and characterized by aberrant epidermal hyperplasia. The molecule eukaryotic initiation factor (eIF) 4E controls translation initiation of certain protein synthesis and determines cell cycle or differentiation fate.

OBJECTIVE

To determine the role of eIF4E in keratinocytes abnormal differentiation in the context of psoriasis.

METHODS

The expression of eIF4E in psoriatic skin lesions and normal skin from human subjects was examined by western blot and immunohistochemistry. In a murine model of psoriasis-like dermatitis that is induced by topical imiquimod, 4EGI-1 was used to inhibit eIF4E activities. To measure murine skin eIF4E and keratinocytes differentiation, immunofluorescence and western blot assays were conducted. Normal human epidermal keratinocytes (NHEK) were isolated, cultured, and stimulated with cytokines including TNF-α, IFN-γ, and IL-17A, respectively. Immunofluorescence and western blot were performed to test eIF4E and effect of 4EGI-1 in a co-culture system.

RESULTS

Compared with healthy controls, skin lesions from patients with PV exhibited a higher expression of eIF4E, which was positively correlated with the epidermal thickness. This expression pattern of eIF4E was replicated by the imiquimod-induced murine model. Skin hyperplasia and eIF4E activities in the murine model were attenuated by the administration of 4EGI-1. Both IFN-γ and IL-17A, rather than TNF-α, are sufficient to induce NHEK abnormal differentiation. This effect can be disrupted by 4EGI-1.

CONCLUSION

eIF4E plays a crucial role in keratinocytes abnormal differentiation driven by type 1/17 inflammation in the context of psoriasis. The initiation of abnormal translation provides an alternative treatment target for psoriasis.

The Potential Role of Exosomal Proteins in Prostate Cancer

Prostate cancer is the most prevalent malignant tumor in men across developed countries. Traditional diagnostic and therapeutic methods for this tumor have become increasingly difficult to adapt to today’s medical philosophy, thus compromising early detection, diagnosis, and treatment. Prospecting for new diagnostic markers and therapeutic targets has become a hot topic in today’s research. Notably, exosomes, small vesicles characterized by a phospholipid bilayer structure released by cells that is capable of delivering different types of cargo that target specific cells to regulate biological properties, have been extensively studied. Exosomes composition, coupled with their interactions with cells make them multifaceted regulators in cancer development. Numerous studies have described the role of prostate cancer-derived exosomal proteins in diagnosis and treatment of prostate cancer. However, so far, there is no relevant literature to systematically summarize its role in tumors, which brings obstacles to the later research of related proteins. In this review, we summarize exosomal proteins derived from prostate cancer from different sources and summarize their roles in tumor development and drug resistance.

Extracellular and Intracellular Skeletons: How Do They Involve in Apoptosis

Apoptosis plays a key role in removing abnormal or senescent cells, maintaining the overall health of the tissue, and coordinating individual development. Recently, it has been discovered that the intracellular cytoskeleton plays a role in the apoptotic process. In addition, the regulatory role of extracellular matrix (ECM) fibrous proteins, which can be considered as the extracellular skeleton, in the process of apoptosis is rarely summarized. In this review, we collect the latest knowledge about how fibrous proteins inside and outside cells regulate apoptosis. We describe how ECM fibrous proteins participate in the regulation of death receptor and mitochondrial pathways through various signaling cascades mediated by integrins. We then explore the molecular mechanisms by which intracellular intermediate filaments regulate cell apoptosis by regulating death receptors on the cell membrane surface. Similarly, we report on novel supporting functions of microtubules in the execution phase of apoptosis and discuss their formation mechanisms. Finally, we discuss that the polypeptide fragments formed by caspase degradation of ECM fibrous proteins and intracellular intermediate filament act as local regulatory signals to play different regulatory roles in apoptosis.

Keratins as an Inflammation Trigger Point in Epidermolysis Bullosa Simplex

Epidermolysis bullosa simplex (EBS) is a group of inherited keratinopathies that, in most cases, arise due to mutations in keratins and lead to intraepidermal ruptures. The cellular pathology of most EBS subtypes is associated with the fragility of the intermediate filament network, cytolysis of the basal layer of the epidermis, or attenuation of hemidesmosomal/desmosomal components. Mutations in keratins 5/14 or in other genes that encode associated proteins induce structural disarrangements of different strengths depending on their locations in the genes. Keratin aggregates display impaired dynamics of assembly and diminished solubility and appear to be the trigger for endoplasmic reticulum (ER) stress upon being phosphorylated by MAPKs. Global changes in cellular signaling mainly occur in cases of severe dominant EBS mutations. The spectrum of changes initiated by phosphorylation includes the inhibition of proteasome degradation, TNF-α signaling activation, deregulated proliferation, abnormal cell migration, and impaired adherence of keratinocytes. ER stress also leads to the release of proinflammatory danger-associated molecular pattern (DAMP) molecules, which enhance avalanche-like inflammation. Many instances of positive feedback in the course of cellular stress and the development of sterile inflammation led to systemic chronic inflammation in EBS. This highlights the role of keratin in the maintenance of epidermal and immune homeostasis.

Transcript levels of keratin 1/5/6/14/15/16/17 as potential prognostic indicators in melanoma patients

Keratins (KRTs), the intermediate filament-forming proteins of epithelial cells, are extensively used as diagnostic biomarkers in cancers and associated with tumorigenesis and metastasis in multiple cancers. However, the diverse expression patterns and prognostic values of KRTs in melanoma have yet to be elucidated. In the current study, we examined the transcriptional and clinical data of KRTs in patients with melanoma from GEO, TCGA, ONCOMINE, GEPIA, cBioPortal, TIMER and TISIDB databases. We found that the mRNA levels of KRT1/2/5/6/8/10/14/15/16/17 were significantly differential expressed between primary melanoma and metastatic melanoma. The expression levels of KRT1/2/5/6/10/14/15/16/17 were correlated with advanced tumor stage. Survival analysis revealed that the high transcription levels of KRT1/5/6/14/15/16/17 were associated with low overall survival in melanoma patients. GSEA analysis indicated that the most involved hallmarks pathways were P53 pathway, KRAS signaling, estrogen response early and estrogen response late. Furthermore, we found some correlations among the expression of KRTs and the infiltration of immune cells. Our study may provide novel insights for the selection of prognostic biomarkers for melanoma.

Keratin expression by corneal and limbal stem cells during development

Keratins are the forming units of intermediate filaments (IF) that provide mechanical support, and formation of desmosomes between cells and hemi desmosomes with basement membranes for epithelium integrity. Keratin IF are polymers of obligate heterodimer consisting one type I keratin and one type II keratin molecules. There are 54 functional keratin genes in human genome, which are classified into three major groups, i.e., epithelial keratins, hair follicle cell-specific epithelial keratins and hair keratins. Their expression is cell type-specific and developmentally regulated. Corneal epithelium expresses a subgroup of keratins similar to those of epidermal epithelium. Limbal basal stem cells express K5/K14, and K8/K18 and K8/K19 IF suggesting that there probably are two populations of limbal stem cells (LSCs). In human, LSCs at limbal basal layer can directly stratify and differentiate to limbal suprabasal cells that express K3/K12 IF, or centripetally migrate then differentiate to corneal basal transient amplifying cells (TAC) that co-express both K3/K12 and K5/K14 prior to moving upward and assuming suprabasal cells phenotype of only K3/K12 expression that signifies corneal type epithelium differentiation. In rodent, the differentiated cornea epithelial cells express K5/K12 in lieu of K3/K12, because K3 allele exists as a pseudogene and does not encode a functional K3 protein. The basal corneal cells of new-born mice originate from surface ectoderm during embryonic development slowly commit to differentiation of becoming TAC co-expressing K5/K12 and K5/K14 IF. However, the centripetal migration may still occur at a slower rate in young mice, which is accelerated during wound healing. In this review, we will discuss and compare the cornea-specific keratins expression patterns between corneal and epidermal epithelial cells during mouse development, and between human and mouse during development and homeostasis in adult, and pathology caused by a mutation of keratins.

A novel multifunctional skin care formulation with a unique blend of antipollution, brightening and antiaging active complexes

BACKGROUND

High demand on anti-aging skin care encourage the improvement and development of more personalized formulations with additional benefits for general skin health and age associated skin signs. The skin aging physical and biological phenotypes manifest differently between diverse ethnic populations. A highly polluted environment can be viewed as an extrinsic factor accelerating the skin aging process.

AIM

To develop a unique formula with active complexes, having multifunctional effects for anti-pollution, brightening and anti-aging/barrier strengthening purposes with confirmed activities in vitro and ex vivo skin models, suitable for polluted skin.

METHODS

In vitro culture model with primary human skin cells, ex vivo studies with full-thickness human skin, melanocyte 3D coculture model, gene expression of epidermal and dermal genes, anti-glycation, proteasomal activity, melanin, and cytokine assays.

RESULTS

In vitro and ex vivo studies clearly demonstrated that diglucosyl gallic acid (active A) and the formulation complex inhibited pollution mediated MMP1 protein, CYP1A1 gene expression, and IL-6 protein secretion, while caprylic/capric triglyceride, diacetyl boldine (active B) had anti-melanogenic effect in in vitro primary melanocyte monoculture and 3D spheroid model. Another active compound, acetyl dipeptide 1 cetyl ester (active D), significantly upregulated epidermal barrier genes (Aquaporin 3 [AQP3], Filaggrin [FLG], caspase 14, and keratin 10) in human primary keratinocytes. Interestingly, both acetyl dipeptide 1 cetyl ester (active D) and niacinamide (active C) improved dermal gene expression (fibrillin-1, Collagen type 1 alpha 1, Decorin, Lysyl oxidase-like 1) and, moreover, had significant anti-glycant and proteasomal promoter activity in human primary fibroblasts.

CONCLUSION

Considering consumers need in heavily polluted areas, we developed a multipurpose formulation comprised of unique active complexes toward pollution, pollution induced inflammation, skin brightening, and antiaging concerns with beneficial results demonstrated by in vitro and ex vivo studies.

Novel K6-K14 keratin fusion enhances cancer stemness and aggressiveness in oral squamous cell carcinoma

Keratin intermediate filament (IF) is one component of cellular architectures, which provides necessary mechanical support to conquer environmental stresses. Recent findings reveal its involvement in mechano-transduction and the associated stem cell reprogramming, suggesting the possible roles in cancer development. Here, we report t(12;17)(q13.13;q21.2) chromosomal rearrangement as the most common fusion event in OSCC, resulting in a variety of inter-keratin fusions. Junction site mapping verified 9 in-frame K6-K14 variants, three of which were correlated with lymph node invasion, late tumor stages (T3/T4) and shorter disease-free survival times. When expressed in OSCC cells, those fusion variants disturbed wild-type K14 organization through direct interaction or aggregate formation, leading to perinuclear structure loss and nuclear deformation. Protein array analyses showed the ability of K6-K14 variant 7 (K6-K14/V7) to upregulate TGF-β and G-CSF signaling, which contributed to cell stemness, drug tolerance, and cell aggressiveness. Notably, K6-K14/V7-expressing cells easily adapted to a soft 3-D culture condition in vitro and formed larger, less differentiated tumors in vivo. In addition to the anti-mechanical-stress activity, our data uncover oncogenic functionality of novel keratin filaments caused by gene fusions during OSCC development.

Chitosan-Poly(caprolactone) Nanofibers for Skin Repair

Dermal wounds, both acute and chronic, represent a significant clinical challenge and therefore the development of novel biomaterial-based skin substitutes to promote skin repair is essential. Nanofibers have garnered attention as materials to promote skin regeneration due to the similarities in morphology and dimensionality between nanofibers and native extracellular matrix proteins, which are critical in guiding cutaneous wound healing. Electrospun chitosan-poly(caprolactone) (CPCL) nanofiber scaffolds, which combine the important intrinsic biological properties of chitosan and the mechanical integrity and stability of PCL, were evaluated as skin tissue engineering scaffolds using a mouse cutaneous excisional skin defect model. Gross assessment of wound size and measurement of defect recovery over time as well as histological evaluation of wound healing showed that CPCL nanofiber scaffolds increased wound healing rate and promoted more complete wound closure as compared with Tegaderm, a commercially available occlusive dressing. CPCL nanofiber scaffolds represent a biomimetic approach to skin repair by serving as an immediately available provisional matrix to promote wound closure. These nanofiber scaffolds may have significant potential as a skin substitute or as the basis for more complex skin tissue engineering constructs involving integration with biologics.

In silico predicted structural and functional insights of all missense mutations on 2B domain of K1/K10 causing genodermatoses

The K1 and K10 associated genodermatoses are characterized by clinical symptoms of mild to severe redness, blistering and hypertrophy of the skin. In this paper, we set out to computationally investigate the structural and functional effects of missense mutations on the 2B domain of K1/K10 heterodimer and its consequences in disease phenotype. We modeled the structure of the K1/K10 heterodimer based on crystal structures for the human homolog K5/K14 heterodimer, and identified that the missense mutations exert their effects on stability and assembly competence of the heterodimer by altering physico-chemical properties, interatomic interactions, and inter-residue atomic contacts. Comparative structural analysis between all the missense mutations and SNPs showed that the location and physico-chemical properties of the substituted amino acid are significantly correlated with phenotypic variations. In particular, we find evidence that a particular SNP (K10, p.E443K) is a pathogenic nsSNP which disrupts formation of the hydrophobic core and destabilizes the heterodimer through the loss of interatomic interactions. Our study is the first comprehensive report analyzing the mutations located on 2B domain of K1/K10 heterodimeric coiled-coil complex.

Multiple roles for keratin intermediate filaments in the regulation of epithelial barrier function and apico-basal polarity

As multicellular organisms evolved a family of cytoskeletal proteins, the keratins (types I and II) expressed in epithelial cells diversified in more than 20 genes in vertebrates. There is no question that keratin filaments confer mechanical stiffness to cells. However, such a number of genes can hardly be explained by evolutionary advantages in mechanical features. The use of transgenic mouse models has revealed unexpected functional relationships between keratin intermediate filaments and intracellular signaling. Accordingly, loss of keratins or mutations in keratins that cause or predispose to human diseases, result in increased sensitivity to apoptosis, regulation of innate immunity, permeabilization of tight junctions, and mistargeting of apical proteins in different epithelia. Precise mechanistic explanations for these phenomena are still lacking. However, immobilization of membrane or cytoplasmic proteins, including chaperones, on intermediate filaments (“scaffolding”) appear as common molecular mechanisms and may explain the need for so many different keratin genes in vertebrates.

Ichthyosis with confetti: clinics, molecular genetics and management

Ichthyosis with confetti (IWC) is an autosomal dominant congenital ichthyosis also known as ichthyosis variegata or congenital reticular ichthyosiform erythroderma. It manifests at birth with generalized ichthyosiform erythroderma or with a collodion baby picture. The erythrodermic and ichthyotic phenotype persists during life and its severity may modify. However, the hallmark of the disease is the appearance, in childhood or later in life, of healthy skin confetti-like spots, which increase in number and size with time. IWC is a very rare genodermatosis, with a prevalence <1/1,000,000 and only 40 cases reported worldwide. The most important associated clinical features include ear deformities, mammillae hypoplasia, palmoplantar keratoderma, hypertrichosis and ectropion. IWC is due to dominant negative mutations in the KRT10 and KRT1 genes, encoding for keratins 10 and keratin 1, respectively. In this context, healthy skin confetti-like spots represent “repaired” skin due to independent events of reversion of keratin gene mutations via mitotic recombination. In most cases, IWC clinical suspicion is delayed until the detection of white skin spots. Clinical features, which may represent hint to the diagnosis of IWC even before appearance of confetti-like spots, include ear and mammillae hypoplasia, the progressive development of hypertrichosis and, in some patients, of adherent verrucous plaques of hyperkeratosis. Altogether the histopathological finding of keratinocyte vacuolization and the nuclear staining for keratin 10 and keratin 1 by immunofluorescence are pathognomonic. Nevertheless, mutational analysis of KRT10 or KRT1 genes is at present the gold standard to confirm the diagnosis. IWC has to be differentiated mainly from congenital ichthyosiform erythroderma. Differential diagnosis also includes syndromic ichthyoses, in particular Netherton syndrome, and the keratinopathic ichthyoses. Most of reported IWC cases are sporadic, but familial cases with autosomal dominant mode of inheritance have been also described. Therefore, knowledge of the mutation is the only way to properly counsel the couples. No specific and satisfactory therapy is currently available for IWC. Like for other congenital ichthyoses, topical treatments (mainly emollients and keratolytics) are symptomatic and offer only temporary relief. Among systemic treatments, retinoids, in particular acitretin, improve disease symptoms in most patients. Although at present there is no curative therapy for ichthyoses, treatments have improved considerably over the years and the best therapy for each patient is always the result of both physician and patient efforts.

Mutations Affecting Keratin 10 Surface-Exposed Residues Highlight the Structural Basis of Phenotypic Variation in Epidermolytic Ichthyosis

Epidermolytic ichthyosis (EI) due to KRT10 mutations is a rare, typically autosomal dominant, disorder characterized by generalized erythema and cutaneous blistering at birth followed by hyperkeratosis and less frequent blistering later in life. We identified two KRT10 mutations p.Q434del and p.R441P in subjects presenting with a mild EI phenotype. Both occur within the mutational "hot spot" of the keratin 10 (K10) 2B rod domain, adjacent to severe EI-associated mutations. p.Q434del and p.R441P formed collapsed K10 fibers rather than aggregates characteristic of severe EI KRT10 mutations such as p.R156C. Upon differentiation, keratinocytes from p.Q434del showed significantly lower apoptosis (P-value<0.01) compared with p.R156C as assessed by the TUNEL assay. Conversely, the mitotic index of the p.Q434del epidermis was significantly higher compared with that of p.R156C (P-value<0.01) as estimated by the Ki67 assay. Structural basis of EI phenotype variation was investigated by homology-based modeling of wild-type and mutant K1-K10 dimers. Both mild EI mutations were found to affect the surface-exposed residues of the K10 alpha helix coiled-coil and caused localized disorganization of the K1-K10 heterodimer. In contrast, adjacent severe EI mutations disrupt key intermolecular dimer interactions. Our findings provide structural insights into phenotypic variation in EI due to KRT10 mutations.

Beyond expectations: novel insights into epidermal keratin function and regulation

The epidermis is a stratified epithelium that relies on its cytoskeleton and cell junctions to protect the body against mechanical injury, dehydration, and infections. Keratin intermediate filament proteins are involved in many of these functions by forming cell-specific cytoskeletal scaffolds crucial for the maintenance of cell and tissue integrity. In response to various stresses, the expression and organization of keratins are altered at transcriptional and posttranslational levels to restore tissue homeostasis. Failure to restore tissue homeostasis in the presence of keratin gene mutations results in acute and chronic skin disorders for which currently no rational therapies are available. Here, we review the recent progress on the role of keratins in cytoarchitecture, adhesion, signaling, and inflammation. By focusing on epidermal keratins, we illustrate the contribution of keratin isotypes to differentiated epithelial functions.

Proteomic analysis of mature adipocytes from obese patients in relation to aging

Obesity and aging are interrelated conditions that both cause changes in adipocyte metabolism and affect the distribution of fat in both subcutaneous and visceral depots. In addition, both weight gain and aging can lead to similar clinical outcomes such as insulin resistance, cardiovascular disease, type 2 diabetes mellitus, atherosclerosis and stroke. Our objective was to examine the changes in protein expression within the subcutaneous adipose tissue of obese patients, matched for BMI, in relation to age. Mature adipocytes were isolated from liposuction samples of abdominal subcutaneous adipose tissue collected from both young (26.2±4.3 (mean age±SD); n=7) and old (52.2±4.7 (mean age±SD); n=7) obese individuals. Total protein extracts were then compared by two-dimensional difference in gel electrophoresis (2D DIGE). Thirty differentially expressed protein spots (ANOVA test, p≤0.05; fold-change ≥1.8) were detected, of which, 15 were identified by MALDI-TOF mass spectrometry. These were comprised of a total of thirteen unique protein sequences. Nine proteins were more abundant in the adipocytes isolated from old vs. young individuals. These proteins included prohibitin 1, protein disulphide isomerase A3, beta actin, profilin, aldo-ketoreductase 1 C2, alpha crystallin B and the annexins A1, A5 and A6. Four other proteins were less abundant in the adipocytes from old, obese subjects and these included keratin type 2 cytoskeletal 1, keratin type 2 cytoskeletal 10 and hemoglobins A and B. The differentially abundant proteins were investigated by Ingenuity Pathway Analysis (IPA) to reveal their associations with known biological functions. This analysis identified signal transducer and activator of transcription 3 as the central molecule in the connectivity map and the apoptotic pathway as the pathway with the highest score. Differences in the abundances of several proteins were confirmed by immunoblotting: i.e., prohibitin 1, protein disulphide isomerase A3, beta actin, profilin and signal transducer and activator of transcription 3 proteins. In conclusion, proteomic analysis of subcutaneous adipose tissue reveals differences in the abundance of proteins in adipocytes isolated from young vs. old individuals. These differentially abundant proteins are involved in the regulation of apoptosis, cellular senescence and inflammatory response. All these are common pathologic events in both obesity and aging.

Gene expression profile in white alpaca (Vicugna pacos) skin

A cDNA library from white alpaca (Vicugna pacos) skin was constructed using SMART technology to investigate the global gene expression profile in alpaca skin and identify genes associated with physiology of alpaca skin and pigmentation. A total of 5359 high-quality EST (expressed sequence tag) sequences were generated by sequencing random cDNA clones from the library. Clustering analysis of sequences revealed a total of 3504 unique sequences including 739 contigs (assembled from 2594 ESTs) and 2765 singletons. BLAST analysis against GenBank nr database resulted in 1287 significant hits (E-value < 10(-10)), of which 863 were annotated through gene ontology analysis. Transcripts for genes related to fleece quality, growth and coat color (e.g. collagen types I and III, troponin C2 and secreted protein acidic and rich in cysteine) were abundantly present in the library. Other genes, such as keratin family genes known to be involved in melanosome protein production, were also identified in the library. Members (KRT10, 14 and 15) of this gene family are evolutionarily conserved as revealed by a cross-species comparative analysis. This collection of ESTs provides a valuable resource for future research to understand the network of gene expression linked to physiology of alpaca skin and development of pigmentation.

Defining keratin protein function in skin epithelia: epidermolysis bullosa simplex and its aftermath

Epidermolysis bullosa simplex (EBS) is a rare genetic condition typified by superficial bullous lesions following incident frictional trauma to the skin. Most cases of EBS are due to dominantly acting mutations in keratin 14 (K14) or K5, the type I and II intermediate filament (IF) proteins that copolymerize to form a pancytoplasmic network of 10 nm filaments in basal keratinocytes of epidermis and related epithelia. Defects in K5-K14 filament network architecture cause basal keratinocytes to become fragile, and account for their rupture upon exposure to mechanical trauma. The discovery of the etiology and pathophysiology of EBS was intimately linked to the quest for an understanding of the properties and function of keratin filaments in skin epithelia. Since then, continued cross-fertilization between basic science efforts and clinical endeavors has highlighted several additional functional roles for keratin proteins in the skin, suggested new avenues for effective therapies for keratin-based diseases, and expanded our understanding of the remarkable properties of the skin as an organ system.

Unique amino acid signatures that are evolutionarily conserved distinguish simple-type, epidermal and hair keratins

Keratins (Ks) consist of central α-helical rod domains that are flanked by non-α-helical head and tail domains. The cellular abundance of keratins, coupled with their selective cell expression patterns, suggests that they diversified to fulfill tissue-specific functions although the primary structure differences between them have not been comprehensively compared. We analyzed keratin sequences from many species: K1, K2, K5, K9, K10, K14 were studied as representatives of epidermal keratins, and compared with K7, K8, K18, K19, K20 and K31, K35, K81, K85, K86, which represent simple-type (single-layered or glandular) epithelial and hair keratins, respectively. We show that keratin domains have striking differences in their amino acids. There are many cysteines in hair keratins but only a small number in epidermal keratins and rare or none in simple-type keratins. The heads and/or tails of epidermal keratins are glycine and phenylalanine rich but alanine poor, whereas parallel domains of hair keratins are abundant in prolines, and those of simple-type epithelial keratins are enriched in acidic and/or basic residues. The observed differences between simple-type, epidermal and hair keratins are highly conserved throughout evolution. Cysteines and histidines, which are infrequent keratin amino acids, are involved in de novo mutations that are markedly overrepresented in keratins. Hence, keratins have evolutionarily conserved and domain-selectively enriched amino acids including glycine and phenylalanine (epidermal), cysteine and proline (hair), and basic and acidic (simple-type epithelial), which reflect unique functions related to structural flexibility, rigidity and solubility, respectively. Our findings also support the importance of human keratin 'mutation hotspot' residues and their wild-type counterparts.

Loss of Desmocollin 3 in skin tumor development and progression

Desmocollin 3 (DSC3) is a desmosomal cadherin that is required for maintaining cell adhesion in the epidermis as demonstrated by the intra-epidermal blistering observed in Dsc3 null skin. Recently, it has been suggested that deregulated expression of DSC3 occurs in certain human tumor types. It is not clear whether DSC3 plays a role in the development or progression of cancers arising in stratified epithelia such as the epidermis. To address this issue, we generated a mouse model in which Dsc3 expression is ablated in K-Ras oncogene-induced skin tumors. Our results demonstrate that loss of Dsc3 leads to an increase in K-Ras-induced skin tumors. We hypothesize that acantholysis-induced epidermal hyperplasia in the Dsc3 null epidermis facilitates Ras-induced tumor development. Further, we demonstrate that spontaneous loss of DSC3 expression is a common occurrence during human and mouse skin tumor progression. This loss occurs in tumor cells invading the dermis. Interestingly, other desmosomal proteins are still expressed in tumor cells that lack DSC3, suggesting a specific function of DSC3 loss in tumor progression. While loss of DSC3 on the skin surface leads to epidermal blistering, it does not appear to induce loss of cell-cell adhesion in tumor cells invading the dermis, most likely due to a protection of these cells within the dermis from mechanical stress. We thus hypothesize that DSC3 can contribute to the progression of tumors both by cell adhesion-dependent (skin surface) and likely by cell adhesion-independent (invading tumor cells) mechanisms.

Structural changes in the skin of hairless mice following exposure to sulfur mustard correlate with inflammation and DNA damage

Sulfur mustard (SM, bis(2-chloroethyl)sulfide) is a bifunctional alkylating agent that causes dermal inflammation, edema and blistering. To investigate the pathogenesis of SM-induced injury, we used a vapor cup model which provides an occlusive environment in which SM is in constant contact with the skin. The dorsal skin of SKH-1 hairless mice was exposed to saturated SM vapor or air control. Histopathological changes, inflammatory markers and DNA damage were analyzed 1-14 days later. After 1 day, SM caused epidermal thinning, stratum corneum shedding, basal cell karyolysis, hemorrhage and macrophage and neutrophil accumulation in the dermis. Cleaved caspase-3 and phosphorylated histone 2A.X (phospho-H2A.X), markers of apoptosis and DNA damage, respectively, were increased whereas proliferating cell nuclear antigen (PCNA) was down-regulated after SM exposure. By 3 days, epithelial cell hypertrophy, edema, parakeratosis and loss of epidermal structures were noted. Enzymes generating pro-inflammatory mediators including myeloperoxidase and cyclooxygenase-2 were upregulated. After 7 days, keratin-10, a differentiation marker, was evident in the stratum corneum. This was associated with an underlying eschar, as neoepidermis began to migrate at the wound edges. Trichrome staining revealed increased collagen deposition in the dermis. PCNA expression in the epidermis was correlated with hyperplasia, hyperkeratosis, and parakeratosis. By 14 days, there was epidermal regeneration with extensive hyperplasia, and reduced expression of cleaved caspase-3, cyclooxygenase-2 and phospho-H2A.X. These findings are consistent with the pathophysiology of SM-induced skin injury in humans suggesting that the hairless mouse can be used to investigate the dermatoxicity of vesicants and the potential efficacy of countermeasures.

Mixture of fibroblasts and adipose tissue-derived stem cells can improve epidermal morphogenesis of tissue-engineered skin

Many studies demonstrate that the type of adjacent mesenchymal cells can affect epidermal morphogenesis of bilayered tissue-engineered skin. However, whether a mixture of different mesenchymal cell types can improve epidermal morphogenesis of bioengineered skin remains unknown. In this study, keratinocytes, dermal fibroblasts and adipose tissue-derived stem cells (ADSCs) were isolated and purified from human skin and subcutaneous fat. Conditioned medium generated from a mixture of dermal fibroblasts and ADSCs at the ratio of 1:1 was superior to that from fibroblasts or ADSCs alone in promoting keratinocyte proliferation, as indicated by MTT assay. Furthermore, ELISA results showed that the cytokine levels of human hepatocyte growth factor and keratinocyte growth factor (also known as FGF7) in the mixed fibroblasts/ADSC group were higher than those in the ADSC or dermal fibroblasts group. To examine the potential roles of mixed fibroblasts and ADSCs on epidermal morphogenesis, a three-dimensional tissue engineered skin system was applied. Histological analyses demonstrated that keratinocytes proliferated extensively over the mixture of fibroblasts and ADSCs, and formed a thick epidermal layer with well-differentiated structures. Keratin 10 (epidermal differentiation marker) was expressed in the suprabasal layer of bilayered tissue-engineered skin in the mixed fibroblasts and ADSCs group. Desmosomes and hemidesmosomes were detected in the newly formed epidermis by transmission electron microscopy analysis. Together, these findings revealed for the first time that a mixture of fibroblasts and ADSCs in bilayered tissue-engineered skin can improve epidermal morphogenesis.

Mitotic recombination in patients with ichthyosis causes reversion of dominant mutations in KRT10

Somatic loss of wild-type alleles can produce disease traits such as neoplasia. Conversely, somatic loss of disease-causing mutations can revert phenotypes; however, these events are infrequently observed. Here we show that ichthyosis with confetti, a severe, sporadic skin disease in humans, is associated with thousands of revertant clones of normal skin that arise from loss of heterozygosity on chromosome 17q via mitotic recombination. This allowed us to map and identify disease-causing mutations in the gene encoding keratin 10 (KRT10); all result in frameshifts into the same alternative reading frame, producing an arginine-rich C-terminal peptide that redirects keratin 10 from the cytokeratin filament network to the nucleolus. The high frequency of somatic reversion in ichthyosis with confetti suggests that revertant stem cell clones are under strong positive selection and/or that the rate of mitotic recombination is elevated in individuals with this disorder.

Implications of pannexin 1 and pannexin 3 for keratinocyte differentiation

Pannexin (Panx) 1 and Panx3 are integral membrane proteins that share some sequence homology with the innexin family of invertebrate gap junctions. They are expressed in mammalian skin. Pannexins have been reported to form functional mechanosensitive single-membrane channels, but their importance in regulating cellular function is poorly understood. In this study, Panx1 and Panx3 were detected in the epidermis of 13.5 day embryonic mice. Compared with newborn mice, there was less Panx1 expression in both thin and thick murine skin, whereas Panx3 expression was unchanged. To investigate the role of pannexins in keratinocyte differentiation, we employed rat epidermal keratinocytes (REKs) that have the capacity to differentiate into organotypic epidermis, and engineered them to overexpress Panx1, Panx1-GFP or Panx3. The expression of Panx1 or Panx3 resulted in the increased ability of REKs to take up dye, suggesting that cell-surface channels were formed. Compared with monolayer REKs, endogenous Panx1 levels remained unchanged, whereas the 70 kDa immunoreactive species of Panx3 was greatly increased in the organotypic epidermis. In monolayer cultures, ectopic Panx1 and Panx1-GFP localized to the plasma membrane, whereas Panx3 displayed both intracellular and plasma-membrane profiles. Although both pannexins reduced cell proliferation, only Panx1 disrupted the architecture of the organotypic epidermis and markedly dysregulated cytokeratin 14 expression and localization. Furthermore, ectopic expression of only Panx1 reduced the vital layer thickness of the organotypic epidermis. In summary, Panx1 and Panx3 are coexpressed in the mammalian epidermis, and the regulation of Panx1 plays a key role in keratinocyte differentiation.

ERK2 dependent signaling contributes to wound healing after a partial-thickness burn

Burn healing is a complex physiological process involving multiple cell activities, such as cell proliferation, migration and differentiation. Although extracellular signal-regulated kinases (ERK) have a pivotal role in regulating a variety of cellular responses, little is known about the individual functions of ERK isoform for healing in vivo. This study investigated the role of ERK2 in burn healing. To assess this, Erk2(+/-) mice generated by gene targeting were used. The resultant mice exhibited significant delay in re-epithelization of partial-thickness burns in the skin in comparison to wild-type. An in vitro proliferation assay revealed that keratinocytes from Erk2(+/-) mice grew significantly slower than those prepared from wild-type. These results highlight the importance of ERK2 in the process of burn healing.

Genetic background modulates gene expression profile induced by skin irradiation in ptch1 mice

PURPOSE

Ptch1 germ-line mutations in mice predispose to radiation-induced basal cell carcinoma of the skin, with tumor incidence modulated by the genetic background. Here, we examined the possible mechanisms underlying skin response to radiation in F1 progeny of Ptch1(neo67/+) mice crossed with either skin tumor-susceptible (Car-S) or -resistant (Car-R) mice and X-irradiated (3 Gy) at 2 days of age or left untreated.

METHODS AND MATERIALS

We conducted a gene expression profile analysis in mRNA samples extracted from the skin of irradiated or control mice, using Affymetrix whole mouse genome expression array. Confirmation of the results was done using real-time reverse-transcriptase polymerase chain reaction.

RESULTS

Analysis of the gene expression profile of normal skin of F1 mice at 4 weeks of age revealed a similar basal profile in the nonirradiated mice, but alterations in levels of 71 transcripts in irradiated Ptch1(neo67/+) mice of the Car-R cross and modulation of only eight genes in irradiated Ptch1(neo67/+) mice of the Car-S cross.

CONCLUSIONS

These results indicate that neonatal irradiation causes a persistent change in the gene expression profile of the skin. The tendency of mice genetically resistant to skin tumorigenesis to show a more complex pattern of transcriptional response to radiation than do genetically susceptible mice suggests a role for this response in genetic resistance to basal cell tumorigenesis.

Loss of desmocollin 3 in mice leads to epidermal blistering

Desmocollin 3 (DSC3) belongs to a subfamily of cadherins and is a major component of desmosomes in keratinocytes of stratified epithelia, such as the epidermis. Based on its amino acid sequence homology to classical cadherins, such as E-cadherin, it has been postulated that DSC3 functions as a cell-adhesion molecule. To test this hypothesis, we assessed the function of DSC3 in the development and maintenance of stratified epithelia, in particular the epidermis and hair follicles. Using a conditional null allele, we show that loss of Dsc3 function in the epidermis causes impaired cell-cell adhesion, leading to intra-epidermal blistering and telogen hair loss. Furthermore, the lesions in Dsc3-null skin resemble those observed in individuals with pemphigus vulgaris (PV), indicating that impaired Dsc3 function could be a potential cause of PV-like inherited or acquired skin blistering diseases.

Genetically engineered mouse models for skin research: taking the next step

Genetically engineered mouse models are invaluable to investigators in nearly all areas of biomedical research. The use of genetically engineered mice has allowed researchers to explore fundamental functions of genes in a mammal that shares substantial similarities with human physiology and pathology. Genetically engineered mice are often used as animal models of human diseases that are vital tools in investigating disease development and in developing and testing novel therapies. Gene targeting in embryonic stem cells allows endogenous genes to be specifically altered. As knowledge regarding precise genetic abnormalities underlying a variety of dermatological conditions continues to emerge, the ability to introduce corresponding alterations in endogenous gene loci in mice, often at a single base pair level, has become essential for detailed studies of these genetic diseases. In this review, we provide examples of mouse models harboring modified endogenous gene(s), generated using the technique commonly referred to as the "knock-in" approach, to exemplify the important and sometimes superior role of this methodology in dermatological research.

Dual roles of intermediate filaments in apoptosis

New roles have emerged recently for intermediate filaments (IFs), namely in modulating cell adhesion and growth, and providing resistance to various forms of stress and to apoptosis. In this context, we first summarize findings on the IF association with the cell response to mechanical stress and growth stimulation, in light of growth-related signaling events that are relevant to death-receptor engagement. We then address the molecular mechanisms by which IFs can provide cell resistance to apoptosis initiated by death-receptor stimulation and to necrosis triggered by excessive oxidative stress. In the same way, we examine IF involvement, along with cytolinker participation, in sequential caspase-mediated protein cleavages that are part of the overall cell death execution, particularly those that generate new functional IF protein fragments and uncover neoantigen markers. Finally, we report on the usefulness of these markers as diagnostic tools for disease-related aspects of apoptosis in humans. Clearly, the data accumulated in recent years provide new and significant insights into the multiple functions of IFs, particularly their dual roles in cell response to apoptotic insults.

Structural and regulatory functions of keratins

The diversity of epithelial functions is reflected by the expression of distinct keratin pairs that are responsible to protect epithelial cells against mechanical stress and to act as signaling platforms. The keratin cytoskeleton integrates these functions by forming a supracellular scaffold that connects at desmosomal cell-cell adhesions. Multiple human diseases and murine knockouts in which the integrity of this system is destroyed testify to its importance as a mechanical stabilizer in certain epithelia. Yet, surprisingly little is known about the precise mechanisms responsible for assembly and disease pathology. In addition to these structural aspects of keratin function, experimental evidence accumulating in recent years has led to a much more complex view of the keratin cytoskeleton. Distinct keratins emerge as highly dynamic scaffolds in different settings and contribute to cell size determination, translation control, proliferation, cell type-specific organelle transport, malignant transformation and various stress responses. All of these properties are controlled by highly complex patterns of phosphorylation and molecular associations.