Claudin-1 is a p63 target gene with a crucial role in epithelial development

Cell-size-dependent regulation of Ezrin dictates epithelial resilience to stretch by countering myosin-II-mediated contractility

The epithelial adaptations to mechanical stress are facilitated by molecular and tissue-scale changes that include the strengthening of junctions, cytoskeletal reorganization, and cell-proliferation-mediated changes in tissue rheology. However, the role of cell size in controlling these properties remains underexplored. Our experiments in the zebrafish embryonic epidermis, guided by theoretical estimations, reveal a link between epithelial mechanics and cell size, demonstrating that an increase in cell size compromises the tissue fracture strength and compliance. We show that an increase in E-cadherin levels in the proliferation-deficient epidermis restores epidermal compliance but not the fracture strength, which is largely regulated by Ezrin-an apical membrane-cytoskeleton crosslinker. We show that Ezrin fortifies the epithelium in a cell-size-dependent manner by countering non-muscle myosin-II-mediated contractility. This work uncovers the importance of cell size maintenance in regulating the mechanical properties of the epithelium and fostering protection against future mechanical stresses.

The diet-microbiota axis: a key regulator of intestinal permeability in human health and disease

The intestinal barrier orchestrates selective permeability to nutrients and metabolites while excluding noxious stimuli. Recent scientific advances establishing a causal role for the gut microbiota in human health outcomes have generated a resurgent interest toward intestinal permeability. Considering the well-established role of the gut barrier in protection against foreign antigens, there is mounting evidence for a causal link between gut permeability and the microbiome in regulating human health. However, an understanding of the dynamic host-microbiota interactions that govern intestinal barrier functions remains poorly defined. Furthermore, the system-level mechanisms by which microbiome-targeted therapies, such as probiotics and prebiotics, simultaneously promote intestinal barrier function and host health remain an area of active investigation. This review summarizes the recent advances in understanding the dynamics of intestinal permeability in human health and its integration with gut microbiota. We further summarize mechanisms by which probiotics/prebiotics influence the gut microbiota and intestinal barrier functions.

The non-oral infection of larval Echinococcus granulosus induces immune and metabolic reprogramming in the colon of mice

Background

The intestinal tract serves as a critical regulator for nutrient absorption and overall health. However, its involvement in anti-parasitic infection and immunity has been largely neglected, especially when a parasite is not transmitted orally. The present study investigated the colonic histopathology and functional reprogramming in mice with intraperitoneal infection of the larval Echinococcus granulosus (E. granulosus).

Results

Compared with the control group, the E. granulosus-infected mice exhibited deteriorated secreted mucus, shortened length, decreased expression of tight junction proteins zonula occludens-1 (ZO-1), and occludin in the colon. Moreover, RNA sequencing was employed to characterize colonic gene expression after infection. In total, 3,019 differentially expressed genes (1,346 upregulated and 1,673 downregulated genes) were identified in the colon of infected mice. KEGG pathway and GO enrichment analysis revealed that differentially expressed genes involved in intestinal immune responses, infectious disease-associated pathways, metabolism, or focal adhesion were significantly enriched. Among these, 18 tight junction-relative genes, 44 immune response-associated genes, and 23 metabolic genes were annotated. Furthermore, mebendazole treatment could reverse the colonic histopathology induced by E. granulosus infection.

Conclusions

Intraperitoneal infection with E. granulosus induced the pathological changes and functional reprogramming in the colon of mice, and mebendazole administration alleviated above alternations, highlighting the significance of the colon as a protective barrier against parasitic infection. The findings provide a novel perspective on host-parasite interplay and propose intestine as a possible target for treating parasitic diseases that are not transmitted orally.

Inhibition of HDAC and Signal Transduction Pathways Induces Tight Junctions and Promotes Differentiation in p63-Positive Salivary Duct Adenocarcinoma

Simple Summary

The p53 family p63 gene is essential for the proliferation and differentiation of various epithelial cells, and it is overexpressed in some salivary gland neoplasia. Histone deacetylases (HDACs) are thought to play a crucial role in carcinogenesis, and HDAC inhibitors downregulate p63 expression in cancers. p63 is not only a diagnostic marker of salivary gland neoplasia, but it also promotes the malignancy. Inhibition of HDAC and signal transduction pathways inhibited cell proliferation and migration, induced tight junctions, and promoted differentiation in p63-positive salivary duct adenocarcinoma (SDC). It is, therefore, useful in therapy for p63-positive SDC cells.

Abstract

Background: The p53 family p63 is essential for the proliferation and differentiation of various epithelial basal cells. It is overexpressed in several cancers, including salivary gland neoplasia. Histone deacetylases (HDACs) are thought to play a crucial role in carcinogenesis, and HDAC inhibitors downregulate p63 expression in cancers. Methods: In the present study, to investigate the roles and regulation of p63 in salivary duct adenocarcinoma (SDC), human SDC cell line A253 was transfected with siRNA-p63 or treated with the HDAC inhibitors trichostatin A (TSA) and quisinostat (JNJ-26481585). Results: In a DNA array, the knockdown of p63 markedly induced mRNAs of the tight junction (TJ) proteins cingulin (CGN) and zonula occuludin-3 (ZO-3). The knockdown of p63 resulted in the recruitment of the TJ proteins, the angulin-1/lipolysis-stimulated lipoprotein receptor (LSR), occludin (OCLN), CGN, and ZO-3 at the membranes, preventing cell proliferation, and leading to increased cell metabolism. Treatment with HDAC inhibitors downregulated the expression of p63, induced TJ structures, recruited the TJ proteins, increased the epithelial barrier function, and prevented cell proliferation and migration. Conclusions: p63 is not only a diagnostic marker of salivary gland neoplasia, but it also promotes the malignancy. Inhibition of HDAC and signal transduction pathways is, therefore, useful in therapy for p63-positive SDC cells.

HDAC inhibitors suppress the proliferation, migration and invasiveness of human head and neck squamous cell carcinoma cells via p63‑mediated tight junction molecules and p21‑mediated growth arrest

In human head and neck squamous cell carcinoma (HNSCC), the invasion and metastatic properties of cancer cells are promoted by junctional adhesion molecule-A (JAM-A) and claudin-1; these are epithelial tight junction molecules regulated by histone deacetylases (HDACs) and transcription factor p63. HDAC expression is reportedly upregulated in HNSCC, and HDAC inhibitors suppress cancer cell proliferation by initiating proliferative arrest or apoptosis. However, little is known of the anti-cancer mechanisms of HDAC inhibitors in HNSCC. Thus, in the present study, the HNSCC Detroit 562 cell line and primary cultured HNSCC cells were treated with HDAC inhibitors to investigate their effects in HNSCC. Higher expression of p63, HDAC1, JAM-A and claudin-1 was observed in HNSCC tissues compared with the adjacent dysplastic regions. In Detroit 562 cells, treatment with trichostatin A (TSA), an inhibitor of HDAC1 and 6, downregulated the expression of p63, JAM-A and claudin-1, and upregulated that of acetylated tubulin; conversely, p63 knockdown resulted in the downregulation of JAM-A and claudin-1. Collectively, inhibiting HDAC suppressed the migration and invasiveness of cancer cells. In addition, treatment with TSA suppressed cancer cell proliferation via G₂/M arrest, as well as upregulating p21 and downregulating cyclin D1 expression. TSA also downregulated the expression of epidermal growth factor receptor (EGFR) and phospho-ERK1/2. p63 knockdown and treatment with an EGFR inhibitor induced G₁ arrest and downregulated EGFR and phospho-ERK1/2 levels, respectively. HDAC inhibition also suppressed the migration and invasiveness of primary cultured HNSCC cells. Collectively, the results of the present study indicate that HDAC inhibitors suppress the proliferation, migration and invasiveness of HNSCC by downregulating the p63-mediated tight junction molecules JAM-A and claudin-1, and inducing p63 or p21-mediated growth arrest.

Isoform-Specific Roles of Mutant p63 in Human Diseases

Simple Summary

The protein p63 belongs to the family of the p53 tumor suppressor. Mouse models have, however, shown that it is not a classical tumor suppressor but instead involved in developmental processes. Mutations in the p63 gene cause several developmental defects in human patients characterized by limb deformation, cleft lip/palate, and ectodermal dysplasia due to p63’s role as a master regulator of epidermal development. In addition, p63 plays a key role as a quality control factor in oocytes and p63 mutations can result either in compromised genetic quality control or premature cell death of all oocytes.

Abstract

The p63 gene encodes a master regulator of epidermal commitment, development, and differentiation. Heterozygous mutations in the DNA binding domain cause Ectrodactyly, Ectodermal Dysplasia, characterized by limb deformation, cleft lip/palate, and ectodermal dysplasia while mutations in in the C-terminal domain of the α-isoform cause Ankyloblepharon-Ectodermal defects-Cleft lip/palate (AEC) syndrome, a life-threatening disorder characterized by skin fragility, severe, long-lasting skin erosions, and cleft lip/palate. The molecular disease mechanisms of these syndromes have recently become elucidated and have enhanced our understanding of the role of p63 in epidermal development. Here we review the molecular cause and functional consequences of these p63-mutations for skin development and discuss the consequences of p63 mutations for female fertility.

Transcriptional and signalling regulation of skin epithelial stem cells in homeostasis, wounds and cancer

The epidermis and skin appendages are maintained by their resident epithelial stem cells, which undergo long-term self-renewal and multilineage differentiation. Upon injury, stem cells are activated to mediate re-epithelialization and restore tissue function. During this process, they often mount lineage plasticity and expand their fates in response to damage signals. Stem cell function is tightly controlled by transcription machineries and signalling transductions, many of which derail in degenerative, inflammatory and malignant dermatologic diseases. Here, by describing both well-characterized and newly emerged pathways, we discuss the transcriptional and signalling mechanisms governing skin epithelial homeostasis, wound repair and squamous cancer. Throughout, we highlight common themes underscoring epithelial stem cell plasticity and tissue-level crosstalk in the context of skin physiology and pathology.

Partial Epithelial-Mesenchymal Transition Was Observed Under p63 Expression in Acquired Middle Ear Cholesteatoma and Congenital Cholesteatoma

INTRODUCTION

Partial epithelial-mesenchymal transition (p-EMT) is a process by which epithelial cells partially lose their intercellular adhesion and change to obtain migration ability. The transcription factor p63 regulates the expression of cadherin family and induces epithelial cell proliferation. In this study, we hypothesized that p-EMT under p63 expression may be a key factor in epithelial cell growth in middle ear cholesteatoma.

METHODS

Specimens were surgically excised from patients with congenital cholesteatoma (CC) (n = 48), acquired middle ear cholesteatoma (AC) (n = 120), and normal skin tissue (n = 34). We analyzed immunohistochemically for the EMT marker (N-cadherin), adherence junction marker (E-cadherin), and tight junction marker (claudin-1, claudin-4, occludin). We also examined the labeling index (LI) of p63 and Proliferating cell nuclear antigen (PCNA) (late S phase marker), and Snail expression as a mobility marker.

RESULTS

The expression of p63 (CC 51.0 ± 7.4%, AC 50.0 ± 5.9%) was significantly higher in the thickened epithelium of CC and AC compared with normal skin tissue (p < 0.0001). The loss of E-cadherin was observed (CC 50.0%, AC 55.8%) but the expression patterns in the tight junction were almost normal. N-cadherin was partially detected in the basal and upper layer of epithelium in CC and AC. In contrast to that of normal skin tissue, the LI of PCNA was significantly higher in AC (p < 0.0001). The positive rate of Snail was significantly higher in CC (p < 0.0001).

CONCLUSION

This study indicates that p-EMT via the p63 signaling pathway might plays an essential role in epithelial growth in AC and CC formation, although tight junction formation and terminal differentiation were not affected in those processes.

Effects of prostaglandin E2 on gap junction protein alpha 1 in the rat epididymis

Gap junctions are responsible for intercellular communication. In the adult mammalian epididymis, gap junction protein alpha 1 (GJA1) is localized between basal and either principal or clear cells. GJA1 levels and localization change during the differentiation of basal cells. The present objective was to determine the role of basal cells and prostaglandin E2 (PGE2) on GJA1 in the rat epididymis. Prior to basal cell differentiation, GJA1 is colocalized with TJP1 at the apical lateral margins between adjacent epithelial cells. When basal cells are present, GJA1 becomes associated between basal and principal cells, where it is primarily immunolocalized until adulthood. Basal cells express TP63, differentiate from epithelial cells, and produce prostaglandin-endoperoxide synthase 1 by 21 days of age. Prior to day 21, GJA1and TP63 are not strongly associated at the apical region. However, by day 28, TP63-positive basal cells migrate to the base of the epithelium, and also express GJA1. To assess effects of PGE2 on GJA1, rat caput epididymal (RCE) cells were exposed to PGE2 (50 μM) for 3 h. PGE2 increased levels of Gja1 mRNA in RCE cells, while levels of Gjb1, Gjb2, Gjb4, and GjB5 were unaltered. Furthermore, PGE2 increased protein levels of GJA1, phospho-GJA1, phospho-AKT, CTNNB1, and phospho-CTNNB1. Total AKT and the tight junction protein claudin1 were also not altered by PGE2. Data suggest that development of the epididymal epithelium and differentiation of epididymal basal cells regulate the targeting of GJA1, and that this appears to be mediated by PGE2.

Molecular Mechanisms of p63-Mediated Squamous Cancer Pathogenesis

The p63 gene is a member of the p53/p63/p73 family of transcription factors and plays a critical role in development and homeostasis of squamous epithelium. p63 is transcribed as multiple isoforms; ΔNp63α, the predominant p63 isoform in stratified squamous epithelium, is localized to the basal cells and is overexpressed in squamous cell cancers of multiple organ sites, including skin, head and neck, and lung. Further, p63 is considered a stem cell marker, and within the epidermis, ΔNp63α directs lineage commitment. ΔNp63α has been implicated in numerous processes of skin biology that impact normal epidermal homeostasis and can contribute to squamous cancer pathogenesis by supporting proliferation and survival with roles in blocking terminal differentiation, apoptosis, and senescence, and influencing adhesion and migration. ΔNp63α overexpression may also influence the tissue microenvironment through remodeling of the extracellular matrix and vasculature, as well as by enhancing cytokine and chemokine secretion to recruit pro-inflammatory infiltrate. This review focuses on the role of ΔNp63α in normal epidermal biology and how dysregulation can contribute to cutaneous squamous cancer development, drawing from knowledge also gained by squamous cancers from other organ sites that share p63 overexpression as a defining feature.

Tissue regeneration and the epididymal stem cell

BACKGROUND

In most pseudostratified epithelia, basal cells represent a multipotent adult stem cell population. These cells generally remain in a quiescent state, until they are stimulated to respond to tissue damage by initiating epithelial regeneration. In the epididymis, cell proliferation occurs at a relatively slow rate under normal physiological conditions. Epididymal basal cells have been shown to share common properties with multipotent adult stem cells. The development of organoids from stem cells represents a novel approach for understanding cellular differentiation and characterization of stem cells.

OBJECTIVE

To review the literature on tissue regeneration in the epididymis and demonstrate the presence of an epididymal stem cell population.

METHODS

PubMed database was searched for studies reporting on cell proliferation, regeneration, and stem cells in the epididymis. Three-dimensional cell culture of epididymal cells was used to determine whether these can develop into organoids in a similar fashion to stem cells from other tissues.

RESULTS

The epididymal epithelium can rapidly regenerate following orchidectomy or efferent duct ligation, in order to maintain epithelial integrity. Studies have isolated a highly purified fraction of rat epididymal basal cells and reported that these cells displayed properties similar to those of multipotent adult stem cells. In two-dimensional cell culture conditions, these cells differentiated into cells which expressed connexin 26, a marker of columnar cells, and cytokeratin 8. Furthermore, three-dimensional cell culture of epididymal cells resulted in the formation of organoids, a phenomenon associated with the proliferation and differentiation of stem cells in vitro.

CONCLUSIONS

The rapid proliferation and tissue regeneration of the epididymal epithelium to preserve its integrity following tissue damage as well as the ability of cells to differentiate into organoids in vitro support the notion of a resident progenitor/stem cell population in the adult epididymis.

Tight Junction barriers in human hair follicles - role of claudin-1

Barrier function of hair follicles (HFs) is of great interest because they might be an entry port for allergens/pathogens, but could on the other hand be used for drug delivery or vaccination. Therefore we investigated tight junction (TJ) barrier function in human HFs. We show that there is a TJ barrier in the outermost living layer bordering to the environment from the infundibulum to the lower central part and between Henle’s and Huxles layer of anagen HFs. In club hair typical for catagen and telogen HFs a TJ barrier is found surrounding the club. This demonstrates that there is a continuous TJ barrier along interfollicular epidermis and HFs in different phases of HF cycle. However, interestingly, in cell culture experiments we can show that barrier is less tight in HF keratinocytes compared to interfollicular keratinocytes. Knock-down of the TJ protein claudin-1, which we demonstrate here to be less expressed in HFs of lesional atopic dermatitis skin, results in impaired barrier function, decreased proliferation and increased apoptosis of hair keratinocytes. This is in line with a hair growth phenotype in claudin-1 deficient patients (NISCH syndrome) and corresponding knock-out mice and indicates an important role of claudin-1 in HF barrier function and growth.

Cellular junctions in the epididymis, a critical parameter for understanding male reproductive toxicology

Epididymal sperm maturation is a critical aspect of male reproduction in which sperm acquire motility and the ability to fertilize an ovum. Sperm maturation is dependent on the creation of a specific environment that changes along the epididymis and which enables the maturation process. The blood-epididymis barrier creates a unique luminal micro-environment, different from blood, by limiting paracellular transport and forcing receptor-mediated transport of macromolecules across the epididymal epithelium. Direct cellular communication between cells allows coordinated function of the epithelium. A limited number of studies have directly examined the effects of toxicants on junctional proteins and barrier function in the epididymis. Effects on the integrity of the blood-epididymis barrier have resulted in decreased fertility and, in some cases, the development of sperm granulomas. Studies have shown that in addition to tight junctions, proteins implicated in the maintenance of adherens junctions and gap junctions alter epididymal functions. This review will provide an overview of the types and roles of cellular junctions in the epididymis, and how these are targeted by different toxicants.

The histone acetyltransferase inhibitor Nir regulates epidermis development

In addition to its function as an inhibitor of histone acetyltransferases, Nir (Noc2l) binds to p53 and TAp63 to regulate their activity. Here, we show that epidermis-specific ablation of Nir impairs epidermal stratification and barrier function, resulting in perinatal lethality. Nir-deficient epidermis lacks appendages and remains single layered during embryogenesis. Cell proliferation is inhibited, whereas apoptosis and p53 acetylation are increased, indicating that Nir is controlling cell proliferation by limiting p53 acetylation. Transcriptome analysis revealed that Nir regulates the expression of essential factors in epidermis development, such as keratins, integrins and laminins. Furthermore, Nir binds to and controls the expression of p63 and limits H3K18ac at the p63 promoter. Corroborating the stratification defects, asymmetric cell divisions were virtually absent in Nir-deficient mice, suggesting that Nir is required for correct mitotic spindle orientation. In summary, our data define Nir as a key regulator of skin development.

Transcription Factor CTIP1/ BCL11A Regulates Epidermal Differentiation and Lipid Metabolism During Skin Development

The epidermal permeability barrier (EPB) prevents organisms from dehydration and infection. The transcriptional regulation of EPB development is poorly understood. We demonstrate here that transcription factor COUP-TF-interacting protein 1 (CTIP1/BCL11A; hereafter CTIP1) is highly expressed in the developing murine epidermis. Germline deletion of Ctip1 (Ctip1^−/−) results in EPB defects accompanied by compromised epidermal differentiation, drastic reduction in profilaggrin processing, reduced lamellar bodies in granular layers and significantly altered lipid composition. Transcriptional profiling of Ctip1^−/− embryonic skin identified altered expression of genes encoding lipid-metabolism enzymes, skin barrier-associated transcription factors and junctional proteins. CTIP1 was observed to interact with genomic elements within the regulatory region of the gene encoding the differentiation-associated gene, Fos-related antigen2 (Fosl2) and lipid-metabolism-related gene, Fatty acid elongase 4 (Elvol4), and the expression of both was altered in Ctip1^−/− mice. CTIP1 appears to play a role in EPB establishment of via direct or indirect regulation of a subset of genes encoding proteins involved in epidermal differentiation and lipid metabolism. These results identify potential, CTIP1-regulated avenues for treatment of skin disorders involving EBP defects.

The role of transcriptional factor p63 in regulation of epithelial barrier and ciliogenesis of human nasal epithelial cells

Disruption of nasal epithelial tight junctions (TJs) and ciliary dysfunction are found in patients with chronic rhinosinusitis (CRS) and nasal polyps (NPs), along with an increase of p63-positive basal cells and histone deacetylase (HDAC) activity. To investigate these mechanisms, primary cultures of HNECs transfected with human telomerase reverse transcriptase (hTERT-HNECs) were transfected with siRNAs of TAp63 and ΔNp63, treated with the NF-kB inhibitor curucumin and inhibitors of HDACs, and infected with respiratory syncytial virus (RSV). In TERT-HNECs, knockdown of p63 by siRNAs of TAp63 and ΔNp63, induced claudin-1 and -4 with Sp1 activity and enhanced barrier and fence functions. The knockdown of p63 enhanced the number of microvilli with the presence of cilia-like structures. Treatment with curcumin and inhibitors of HDACs, or infection with RSV prevented expression of p63 with an increase of claudin-4 and the number of microvilli. The knockdown or downregulation of p63 inhibited phospho-p38MAPK, and the p38MAPK inhibitor downregulated p63 and upregulated the barrier function. Thus, epithelial barrier and ciliogenesis of nasal epithelium are regulated in a p63-negative manner in normal and upper airway diseases. Understanding of the regulation of p63/p38 MAPK/NF-κB may be important in the therapy for airway allergy and its drug delivery system.

ΔNp63α and microRNAs: leveraging the epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is a cellular reprogramming mechanism that is an underlying cause of cancer metastasis. Recent investigations have uncovered an intricate network of regulation involving the TGFβ, Wnt, and Notch signaling pathways and small regulatory RNA species called microRNAs (miRNAs). The activity of a transcription factor vital to the maintenance of epithelial stemness, ΔNp63α, has been shown to modulate the activity of these EMT pathways to either repress or promote EMT. Furthermore, ΔNp63α is a known regulator of miRNA, including those directly involved in EMT. This review discusses the evidence of ΔNp63α as a master regulator of EMT components and miRNA, highlighting the need for a deeper understanding of its role in EMT. This expanded knowledge may provide a basis for new developments in the diagnosis and treatment of metastatic cancer.

FGF8, c-Abl and p300 participate in a pathway that controls stability and function of the ΔNp63α protein

The p63 transcription factor, homolog to the p53 tumor suppressor gene, plays a crucial role in epidermal and limb development, as its mutations are associated to human congenital syndromes characterized by skin, craniofacial and limb defects. While limb and skin-specific p63 transcriptional targets are being discovered, little is known of the post-translation modifications controlling ΔNp63α functions. Here we show that the p300 acetyl-transferase physically interacts in vivo with ΔNp63α and catalyzes its acetylation on lysine 193 (K193) inducing ΔNp63α stabilization and activating specific transcriptional functions. Furthermore we show that Fibroblast Growth Factor-8 (FGF8), a morphogenetic signaling molecule essential for embryonic limb development, increases the binding of ΔNp63α to the tyrosine kinase c-Abl as well as the levels of ΔNp63α acetylation. Notably, the natural mutant ΔNp63α-K193E, associated to the Split-Hand/Foot Malformation-IV syndrome, cannot be acetylated by this pathway. This mutant ΔNp63α protein displays promoter-specific loss of DNA binding activity and consequent altered expression of development-associated ΔNp63α target genes. Our results link FGF8, c-Abl and p300 in a regulatory pathway that controls ΔNp63α protein stability and transcriptional activity. Hence, limb malformation-causing p63 mutations, such as the K193E mutation, are likely to result in aberrant limb development via the combined action of altered protein stability and altered promoter occupancy.

HIF-dependent regulation of claudin-1 is central to intestinal epithelial tight junction integrity

This study demonstrates a critical link between hypoxia-inducible factor (HIF) and claudin-1 (CLDN1). HIF1β-deficient intestinal epithelial cells develop abnormal tight junction (TJ) structure and have striking barrier defects. CLDN1 is an HIF target gene, and overexpression of CLDN1 in HIF1β-deficient cells restores TJ structure and function.

Intestinal epithelial cells (IECs) are exposed to profound fluctuations in oxygen tension and have evolved adaptive transcriptional responses to a low-oxygen environment. These adaptations are mediated primarily through the hypoxia-inducible factor (HIF) complex. Given the central role of the IEC in barrier function, we sought to determine whether HIF influenced epithelial tight junction (TJ) structure and function. Initial studies revealed that short hairpin RNA–mediated depletion of the HIF1β in T84 cells resulted in profound defects in barrier and nonuniform, undulating TJ morphology. Global HIF1α chromatin immunoprecipitation (ChIP) analysis identified claudin-1 (CLDN1) as a prominent HIF target gene. Analysis of HIF1β-deficient IEC revealed significantly reduced levels of CLDN1. Overexpression of CLDN1 in HIF1β-deficient cells resulted in resolution of morphological abnormalities and restoration of barrier function. ChIP and site-directed mutagenesis revealed prominent hypoxia response elements in the CLDN1 promoter region. Subsequent in vivo analysis revealed the importance of HIF-mediated CLDN1 expression during experimental colitis. These results identify a critical link between HIF and specific tight junction function, providing important insight into mechanisms of HIF-regulated epithelial homeostasis.

Gene regulatory mechanisms orchestrated by p63 in epithelial development and related disorders

The transcription factor p63 belongs to the p53 family and is a key regulator in epithelial commitment and development. Mutations in p63 give rise to several epithelial related disorders with defects in skin, limb and orofacial structures. Since the discovery of p63, efforts have been made to identify its target genes using individual gene approaches and to understand p63 function in normal epithelial development and related diseases. Recent genome-wide approaches have identified tens of thousands of potential p63-regulated target genes and regulatory elements, and reshaped the concept of gene regulation orchestrated by p63. These data also provide insights into p63-related disease mechanisms. In this review, we discuss the regulatory role of p63 in normal and diseased epithelial development in light of these novel findings. We also propose future perspectives for dissecting the molecular mechanism of p63-mediated epithelial development and related disorders as well as for potential therapeutic strategies.

Epidermal cell junctions and their regulation by p63 in health and disease

As the outermost tissue of the body, the epidermis is the first physical barrier for any pressure, stress or trauma. Several specialized cell-matrix and cell-cell adhesion structures, together with an intracellular network of dedicated intermediate filaments, are required to confer critical resilience to mechanical stress. The transcription factor p63 is a master regulator of gene expression in the epidermis and in other stratified epithelia. It has been extensively demonstrated that p63 positively controls a large number of tissue-specific genes, including those encoding a large fraction of tissue-restricted cell adhesion molecules. Consistent with p63 functions in cell adhesion and in epidermal differentiation, heterozygous mutations clustered mainly in the p63 C-terminus are causative of AEC syndrome, an autosomal dominant disorder characterized by cleft palate, ankyloblepharon and ectodermal dysplasia associated with severe skin erosions, bleeding and infections. The molecular basis of skin erosions in AEC patients is not fully understood, although defects in desmosomes and in other cell junctions are likely to be involved. Here, we provide an extensive review of the different epidermal cell junctions that cooperate to withstand mechanical stress and on the mechanisms by which p63 regulates gene expression of their components in healthy skin and in AEC syndrome. Collectively, advancement in understanding the molecular mechanisms by which epidermal cell junctions precisely exert their functions and how p63 orchestrates their coordinated expression, will ultimately lead to insight into developing future strategies for the treatment of AEC syndrome and more in generally for diseases that share an overlapping phenotype.

p63-dependent and independent mechanisms of nectin-1 and nectin-4 regulation in the epidermis

Nectins are immunoglobulin-like cell adhesion molecules mainly localized in adherens junctions. The transcription factor p63 is a master regulator of gene expression in stratified epithelia and controls several molecular processes. As mutations in the Pvrl1 and Pvrl4 genes encoding for nectins cause genetic disorders with phenotypes similar to p63-related syndromes, we investigated whether these proteins might be under p63 transcriptional control. Here, we show that in p63-null skin, Pvrl1 gene expression is strongly reduced, whereas Pvrl4 expression is unaffected. In human and mouse primary keratinocytes p63 depletion leads to a specific downregulation of the Pvrl1 gene. Consistent with a direct regulation, chromatin immunoprecipitation experiments (ChIP) indicate that p63 binds to two conserved intronic Pvrl1 enhancer regions. Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder, caused by mutations in p63 gene, mainly characterized by skin fragility. To test whether nectins may be affected in AEC syndrome, their expression was measured in keratinocytes obtained from patients with AEC or from a conditional mouse model for AEC syndrome. Pvrl1 expression was reduced in AEC keratinocytes, consistent with impaired p63 function. Surprisingly, Pvrl4 expression was similarly affected, in parallel with decreased expression of the transcription factor Irf6. Consistent with the well-characterized role of Irf6 in keratinocyte differentiation and its strong downregulation in AEC syndrome, Irf6 depletion caused reduced expression of Pvrl4 in wild-type keratinocytes. Taken together, our results indicate that Pvrl1 is a bona fide target gene of the transcription factor p63, whereas Pvrl4 regulation is linked to epidermal differentiation and is under Irf6 control.

The blood-epididymis barrier and inflammation

The blood-epididymis barrier (BEB) is a critical structure for male fertility. It enables the development of a specific luminal environment that allows spermatozoa to acquire both the ability to swim and fertilize an ovum. The presence of tight junctions and specific cellular transporters can regulate the composition of the epididymal lumen to favor proper sperm maturation. The BEB is also at the interface between the immune system and sperm. Not only does the BEB protect maturing spermatozoa from the immune system, it is also influenced by cytokines released during inflammation, which can result in the loss of barrier function. Such a loss is associated with an immune response, decreased sperm functions, and appears to be a contributing factor to post-testicular male infertility. Alterations in the BEB may be responsible for the formation of inflammatory conditions such as sperm granulomas. The present review summarizes current knowledge on the morphological, physiological and pathological components associated with the BEB, the role of immune function on the regulation of the BEB, and how disturbance of these factors can result in inflammatory lesions of the epididymis.

21-Benzylidene digoxin: a proapoptotic cardenolide of cancer cells that up-regulates Na,K-ATPase and epithelial tight junctions

Cardiotonic steroids are used to treat heart failure and arrhythmia and have promising anticancer effects. The prototypic cardiotonic steroid ouabain may also be a hormone that modulates epithelial cell adhesion. Cardiotonic steroids consist of a steroid nucleus and a lactone ring, and their biological effects depend on the binding to their receptor, Na,K-ATPase, through which, they inhibit Na+ and K+ ion transport and activate of several intracellular signaling pathways. In this study, we added a styrene group to the lactone ring of the cardiotonic steroid digoxin, to obtain 21-benzylidene digoxin (21-BD), and investigated the effects of this synthetic cardiotonic steroid in different cell models. Molecular modeling indicates that 21-BD binds to its target Na,K-ATPase with low affinity, adopting a different pharmacophoric conformation when bound to its receptor than digoxin. Accordingly, 21-DB, at relatively high µM amounts inhibits the activity of Na,K-ATPase α1, but not α2 and α3 isoforms. In addition, 21-BD targets other proteins outside the Na,K-ATPase, inhibiting the multidrug exporter Pdr5p. When used on whole cells at low µM concentrations, 21-BD produces several effects, including: 1) up-regulation of Na,K-ATPase expression and activity in HeLa and RKO cancer cells, which is not found for digoxin, 2) cell specific changes in cell viability, reducing it in HeLa and RKO cancer cells, but increasing it in normal epithelial MDCK cells, which is different from the response to digoxin, and 3) changes in cell-cell interaction, altering the molecular composition of tight junctions and elevating transepithelial electrical resistance of MDCK monolayers, an effect previously found for ouabain. These results indicate that modification of the lactone ring of digoxin provides new properties to the compound, and shows that the structural change introduced could be used for the design of cardiotonic steroid with novel functions.

Integrating animal models and in vitro tissue models to elucidate the role of desmosomal proteins in diseases

Desmosomes are intercellular junctions that provide tissues with structural stability. These junctions might also act as signaling centers that transmit environmental clues to the cell, thereby affecting cell differentiation, migration, and proliferation. The importance of desmosomes is underscored by devastating skin and heart diseases caused by mutations in desmosomal genes. Recent observations suggest that abnormal desmosomal protein expression might indirectly contribute to skin disorders previously not linked to these proteins. For example, it has been postulated that reduced desmosomal protein expression occurs in patients affected by Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome (AEC), a skin fragility disorder caused by mutations in the transcription factor TP63. Currently, it is not clear how these changes in desmosomal gene expression contribute to AEC. We will discuss new approaches that combine in vitro and in vivo models to elucidate the role of desmosomal gene deregulation in human skin diseases such as AEC.

Modeling AEC-New approaches to study rare genetic disorders

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome is a rare monogenetic disorder that is characterized by severe abnormalities in ectoderm-derived tissues, such as skin and its appendages. A major cause of morbidity among affected infants is severe and chronic skin erosions. Currently, supportive care is the only available treatment option for AEC patients. Mutations in TP63, a gene that encodes key regulators of epidermal development, are the genetic cause of AEC. However, it is currently not clear how mutations in TP63 lead to the various defects seen in the patients' skin. In this review, we will discuss current knowledge of the AEC disease mechanism obtained by studying patient tissue and genetically engineered mouse models designed to mimic aspects of the disorder. We will then focus on new approaches to model AEC, including the use of patient cells and stem cell technology to replicate the disease in a human tissue culture model. The latter approach will advance our understanding of the disease and will allow for the development of new in vitro systems to identify drugs for the treatment of skin erosions in AEC patients. Further, the use of stem cell technology, in particular induced pluripotent stem cells (iPSC), will enable researchers to develop new therapeutic approaches to treat the disease using the patient's own cells (autologous keratinocyte transplantation) after correction of the disease-causing mutations.

p63 and Brg1 control developmentally regulated higher-order chromatin remodelling at the epidermal differentiation complex locus in epidermal progenitor cells

Chromatin structural states and their remodelling, including higher-order chromatin folding and three-dimensional (3D) genome organisation, play an important role in the control of gene expression. The role of 3D genome organisation in the control and execution of lineage-specific transcription programmes during the development and differentiation of multipotent stem cells into specialised cell types remains poorly understood. Here, we show that substantial remodelling of the higher-order chromatin structure of the epidermal differentiation complex (EDC), a keratinocyte lineage-specific gene locus on mouse chromosome 3, occurs during epidermal morphogenesis. During epidermal development, the locus relocates away from the nuclear periphery towards the nuclear interior into a compartment enriched in SC35-positive nuclear speckles. Relocation of the EDC locus occurs prior to the full activation of EDC genes involved in controlling terminal keratinocyte differentiation and is a lineage-specific, developmentally regulated event controlled by transcription factor p63, a master regulator of epidermal development. We also show that, in epidermal progenitor cells, p63 directly regulates the expression of the ATP-dependent chromatin remodeller Brg1, which binds to distinct domains within the EDC and is required for relocation of the EDC towards the nuclear interior. Furthermore, Brg1 also regulates gene expression within the EDC locus during epidermal morphogenesis. Thus, p63 and its direct target Brg1 play an essential role in remodelling the higher-order chromatin structure of the EDC and in the specific positioning of this locus within the landscape of the 3D nuclear space, as required for the efficient expression of EDC genes in epidermal progenitor cells during skin development.

DLX5, FGF8 and the Pin1 isomerase control ΔNp63α protein stability during limb development: a regulatory loop at the basis of the SHFM and EEC congenital malformations

Ectrodactyly, or Split-Hand/Foot Malformation (SHFM), is a congenital condition characterized by the loss of central rays of hands and feet. The p63 and the DLX5;DLX6 transcription factors, expressed in the embryonic limb buds and ectoderm, are disease genes for these conditions. Mutations of p63 also cause the ectodermal dysplasia–ectrodactyly–cleft lip/palate (EEC) syndrome, comprising SHFM. Ectrodactyly is linked to defects of the apical ectodermal ridge (AER) of the developing limb buds. FGF8 is the key signaling molecule in this process, able to direct proximo-distal growth and patterning of the skeletal primordial of the limbs. In the limb buds of both p63 and Dlx5;Dlx6 murine models of SHFM, the AER is poorly stratified and FGF8 expression is severely reduced. We show here that the FGF8 locus is a downstream target of DLX5 and that FGF8 counteracts Pin1–ΔNp63α interaction. In vivo, lack of Pin1 leads to accumulation of the p63 protein in the embryonic limbs and ectoderm. We show also that ΔNp63α protein stability is negatively regulated by the interaction with the prolyl-isomerase Pin1, via proteasome-mediated degradation; p63 mutant proteins associated with SHFM or EEC syndromes are resistant to Pin1 action. Thus, DLX5, p63, Pin1 and FGF8 participate to the same time- and location-restricted regulatory loop essential for AER stratification, hence for normal patterning and skeletal morphogenesis of the limb buds. These results shed new light on the molecular mechanisms at the basis of the SHFM and EEC limb malformations.

Tight junction protein claudin-1 is differentially expressed in craniopharyngioma subtypes and indicates invasive tumor growth

BACKGROUND

Claudins are tight junction proteins expressed in epithelial tissues that play important roles in cell polarity and adhesion. Altered distribution of claudin-1(CLDN1) affects cell mobility and tumor invasiveness. Craniopharyngiomas (CPs) represent epithelial tumors of the sellar region, consisting of adamantinomatous (adaCP) and papillary (papCP) variants. Their tendency to infiltrate surrounding brain structures complicates successful surgery. Reliable markers are required to predict tumor behavior and to establish individualized treatment protocols.

METHODS

We describe the distribution pattern of CLDN1 in a large cohort of 66 adaCPs, 21 papCPs, and 24 Rathke`s cleft cyst (RCC) cases using immunohistochemistry. CLDN1 mRNA levels were analyzed with qRT-PCR in 33 CP samples. The impact on the migration potential was studied in primary adaCP cell cultures (n = 11) treated with small interfering RNA (siRNA) for CLDN1. Furthermore, CLDN1 distribution patterns and expression levels were compared between invasive (n = 16) and noninvasive (n = 17) tumor groups.

RESULTS

PapCPs and RCCs exhibited a distinct homogenous and membranous expression pattern, whereas CLDN1 immunoreactivity appeared weaker and more heterogeneous in adaCPs. In the latter cases, whirl-like cell clusters showed complete absence of CLDN1. mRNA analysis confirmed reduced CLDN1 levels in adaCPs versus papCPs. Interestingly, invasive tumors exhibited significantly lower CLDN1 expression compared with noninvasive counterparts regardless of CP subtype. Accordingly, siRNA treatment for CLDN1 altered tumor cell migration in vitro.

CONCLUSION

CLDN1 represents a novel marker in the differential diagnosis of CP variants and RCCs. Low CLDN1 expression levels correlate with an invasive CP growth pattern and may serve as a prognostic marker.

Role of SH2-containing tyrosine phosphatase Shp2 in mouse corneal epithelial stratification

PURPOSE

Shp2 protein tyrosine phosphatase mediates a wide variety of receptor tyrosine kinases (RTK) cell signaling. Herein, we investigate the role of Shp2 in corneal morphogenesis and homeostasis.

METHODS

Shp2 was conditionally knocked out (Shp2(cko)) in Krt14-rtTA;tet-O-Cre;Shp2(f/f) triple transgenic mice administrated with doxycycline (Dox) from postnatal day 1 (P1) to P10, P15, and P25, respectively. In addition, corneal epithelial debridement was performed in adult (P42) mice treated with or without Dox for 8 days (from P42-P50). Mouse eyes were then subjected to histology and immunohistochemistry.

RESULTS

Shp2(cko) revealed impaired stratification of conjunctival and corneal epithelia during morphogenesis. Likewise, Shp2(cko) failed to restore epithelial stratification after a corneal epithelial wound in adult Shp2(cko). At the cellular level, the ratio of proliferating cell nuclear antigen (PCNA-positive)/total basal cells remained unchanged, but cells in G2/M (survivin-positive) phase was significantly increased in Shp2(cko) as compared with those in the control littermate. Interestingly, deltaN-p63 (ΔNp63) expression and the asymmetric division of the basal cells were coincidentally dampened in Shp2(cko). Transmission electron microscopic study showed that desmosome and hemidesmosome densities were reduced in the corneal epithelium of Shp2(cko). Immunohistochemistry also demonstrated that expression of E-cadherin/β-catenin junction and laminin-β1 was extensively downregulated in Shp2(cko). On the other hand, corneal epithelium lacking Shp2 remained positive for K14, Pax-6, and keratin 12 (K12), suggesting that Shp2 was dispensable for the corneal epithelial-type differentiation.

CONCLUSIONS

These data argued that Shp2 deficiency predominantly impacted p63-dependent cell division and cell adhesive ability, which resulted in the impairment of stratification during corneal epithelial development and wound healing.

Claudins 1, 2, 3, 4, 5 and 7 in solar keratosis and squamocellular carcinoma of the skin

Claudins are tight junction proteins regulating the paracellular permeability of cell layers. We investigated the expression of claudins 1, 2, 3, 4, 5 and 7 in a sample set consisting of a total of 93 cases representing normal skin, actinic keratoses and squamous cell carcinomas of the skin. There were several changes found in claudin expression. Claudin 1 appeared to be progressively decreased in solar keratosis and skin squamous cell carcinomas compared to normal skin while expression of claudin 2 was increased. With claudins 3 and 5 occasional immunoreactivity was found in squamous cell carcinomas. Claudins 4 and 7 were variably expressed in skin neoplasia compared to normal skin. According to the results expression of claudins 1 and 2 change in parallel with the severity of the epidermal preneoplastic and neoplastic lesions thus probably influencing the disturbed epithelial polarity characteristic of these lesions. Claudin 1 under- and claudin 2 overexpression also lead to a leakier epithelial barrier function of the skin with a resulting damage to skin epithelial resistance. Other claudins investigated in this study did not show progressive changes even though occasional overexpression of them was found in skin squamous cell carcinoma.

Trichostatin-A modulates claudin-1 mRNA stability through the modulation of Hu antigen R and tristetraprolin in colon cancer cells

Expression of claudin-1, a tight junction protein, is highly upregulated in colon cancer. We have reported that claudin-1 expression in colon cancer cells is epigenetically regulated as histone deacetylase (HDAC) inhibitors decrease claudin-1 messenger RNA (mRNA) stability and thus expression. In this regard, our data suggested a role of the 3'-untranslated region (UTR) in the regulation of HDAC-dependent regulation of claudin-1 mRNA stability. In the current study, we demonstrate, based on our continued investigation, that the ELAV-like RNA-binding proteins (RBPs), human antigen R (HuR) and tristetraprolin (TTP) associate with the 3'-UTR of claudin-1 mRNA to modulate the latter's stability. Ribonomic and site-directed mutagenesis approaches were used to confirm the binding of HuR and TTP to the 3'-UTR of claudin-1. We further confirmed their roles in the stabilization of claudin-1 mRNA, under conditions of HDAC inhibition. In summary, we report that HuR and TTP are the critical regulators of the posttranscriptional regulation of claudin-1 expression in colon cancer cells. We also demonstrate that inhibition of HDACs by trichostatin treatment decreased the binding of HuR while increasing the binding of TTP to the 3'-UTR of claudin-1. Additionally, we provide data showing transcriptional regulation of claudin-1 expression, through the regulation of transcription factor Sp1. Taken together, we demonstrate epigenetic regulation of claudin-1 expression in colon cancer cells at the transcriptional and posttranscriptional levels.

Phospho-ΔNp63α regulates AQP3, ALOX12B, CASP14 and CLDN1 expression through transcription and microRNA modulation

Cisplatin-induced and ATM-phosphorylated (p)-ΔNp63α regulates the expression of epidermal differentiation and skin barrier regulators (AQP3, CASP14, ALOX12B, and CLDN1) in squamous cell carcinoma (SCC) cells by dual transcriptional and post-transcriptional mechanisms. We found that p-ΔNp63α bound to target gene promoters, and regulated the activity of the tested promoters in vitro. P-ΔNp63α was shown to upregulate miR-185-5p and downregulate let7-5p, which subsequently modulated AQP3, CASP14, ALOX12B and CLDN1 through their respective 3'-untranslated regions. The introduction of miR-185-5p into resistant SCC-11M cells, which are unable to phosphorylate ΔNp63α, render these cells more sensitive to cisplatin treatment. Further studies of the AQP3, CASP14, ALOX12B, and CLDN1 contributions to chemoresistance may assist in developing novel microRNA-based therapies for human SCC.

Rab3Gap1 mediates exocytosis of Claudin-1 and tight junction formation during epidermal barrier acquisition

Epidermal barrier acquisition during late murine gestation is accompanied by an increase in Akt kinase activity and cJun dephosphorlyation. The latter is directed by the Ppp2r2a regulatory subunit of the Pp2a phosphatase. This was accompanied by a change of Claudin-1 localisation to the cell surface and interaction between Occludin and Claudin-1 which are thought to be required for tight junction formation.

The aim of this study was to determine the nature of the barrier defect caused by the loss of AKT/Ppp2r2a function. There was a paracellular barrier defect in rat epidermal keratinocytes expressing a Ppp2r2a siRNA. In Ppp2r2a knockdown cells, Claudin-1 was located to the cytoplasm and its expression was increased. Inhibiting cJun phosphorylation restored barrier function and plasma membrane localisation of Claudin-1. Expression of the Rab3 GTPase activating protein, Rab3Gap1, was restored in Ppp2r2a siRNA cells when cJun phosphorylation was inhibited. During normal mouse epidermal development, Claudin-1 plasma membrane localisation and Rab3Gap1 cell surface expression were co-incident with Akt activation in mouse epidermis, strongly suggesting a role of Rab3Gap1 in epidermal barrier acquisition. Supporting this hypothesis, siRNA knockdown of Rab3Gap1 prevented plasma membrane Claudin-1 expression and the formation of a barrier competent epithelium. Replacing Rab3Gap1 in Ppp2r2a knockdown cells was sufficient to rescue Claudin-1 transport to the cell surface. Therefore these data suggest Rab3Gap1 mediated exocytosis of Claudin-1 is an important component of epidermal barrier acquisition during epidermal development.

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Barrier acquisition correlates with Ppp2r2a and cell surface Claudin-1 expression.

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Ppp2r2a knockdown results in a paracellular barrier defect.

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Ppp2r2a knockdown prevents cell-surface claudin-1 expression in a c-Jun dependent fashion.

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Barrier rescue by inhibition of c-Jun phosphorylation involves exocytosis and Rab3Gap1.

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Rab3Gap1 is induced during barrier acquisition and is necessary for cell surface claudin-1.

APR-246/PRIMA-1(MET) rescues epidermal differentiation in skin keratinocytes derived from EEC syndrome patients with p63 mutations

p53 and p63 share extensive sequence and structure homology. p53 is frequently mutated in cancer, whereas mutations in p63 cause developmental disorders manifested in ectodermal dysplasia, limb defects, and orofacial clefting. We have established primary adult skin keratinocytes from ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome patients with p63 mutations as an in vitro human model to study the disease mechanism in the skin of EEC patients. We show that these patient keratinocytes cultured either in submerged 2D cultures or in 3D skin equivalents have impaired epidermal differentiation and stratification. Treatment of these patient keratinocytes with the mutant p53-targeting compound APR-246/PRIMA-1(MET) (p53 reactivation and induction of massive apoptosis) that has been successfully tested in a phase I/II clinical trial in cancer patients partially but consistently rescued morphological features and gene expression during epidermal stratification in both 2D and 3D models. This rescue coincides with restoration of p63 target-gene expression. Our data show that EEC patient keratinocytes with p63 mutations can be used for characterization of the abnormal molecular circuitry in patient skin and may open possibilities for the design of novel pharmacological treatment strategies for patients with mutant p63-associated developmental abnormalities.

p63 control of desmosome gene expression and adhesion is compromised in AEC syndrome

Ankyloblepharon, ectodermal defects, cleft lip/palate (AEC) syndrome is a rare autosomal dominant disorder caused by mutations in the p63 gene, essential for embryonic development of stratified epithelia. The most severe cutaneous manifestation of this disorder is the long-lasting skin fragility associated with severe skin erosions after birth. Using a knock-in mouse model for AEC syndrome, we found that skin fragility was associated with microscopic blistering between the basal and suprabasal compartments of the epidermis and reduced desmosomal contacts. Expression of desmosomal cadherins and desmoplakin was strongly reduced in AEC mutant keratinocytes and in newborn epidermis. A similar impairment in desmosome gene expression was observed in human keratinocytes isolated from AEC patients, in p63-depleted keratinocytes and in p63 null embryonic skin, indicating that p63 mutations causative of AEC syndrome have a dominant-negative effect on the wild-type p63 protein. Among the desmosomal components, desmocollin 3, desmoplakin and desmoglein 1 were the most significantly reduced by mutant p63 both at the RNA and protein levels. Chromatin immunoprecipitation experiments and transactivation assays revealed that p63 controls these genes at the transcriptional level. Consistent with reduced desmosome function, AEC mutant and p63-deficient keratinocytes had an impaired ability to withstand mechanical stress, which was alleviated by epidermal growth factor receptor inhibitors known to stabilize desmosomes. Our study reveals that p63 is a crucial regulator of a subset of desmosomal genes and that this function is impaired in AEC syndrome. Reduced mechanical strength resulting from p63 mutations can be alleviated pharmacologically by increasing desmosome adhesion with possible therapeutic implications.

Mutations in AEC syndrome skin reveal a role for p63 in basement membrane adhesion, skin barrier integrity and hair follicle biology

BACKGROUND

AEC (ankyloblepharon-ectodermal defects-clefting) syndrome is an autosomal dominant ectodermal dysplasia disorder caused by mutations in the transcription factor p63. Clinically, the skin is dry and often fragile; other features can include partial eyelid fusion (ankyloblepharon), hypodontia, orofacial clefting, sparse hair or alopecia, and nail dystrophy.

OBJECTIVES

To investigate how p63 gene mutations affect gene and protein expression in AEC syndrome skin.

METHODS

We performed microarray analysis on samples of intact and eroded AEC syndrome skin compared with control skin. Changes were verified by quantitative real-time reverse transcription-polymerase chain reaction and, for basal keratinocyte-associated genes, by immunohistochemistry and analysis of microdissected skin.

RESULTS

We identified significant upregulation of six genes and downregulation of 69 genes in AEC syndrome skin, with the main changes in genes implicated in epidermal adhesion, skin barrier formation and hair follicle biology. There was reduced expression of genes encoding the basement membrane proteins FRAS1 and collagen VII, as well as the skin barrier-associated small proline-rich proteins 1A and 4, late cornified envelope protein 5A, hornerin, and lipid transporters including ALOX15B. Reduced expression of the hair-associated keratins 25, 27, 31, 33B, 34, 35, 81 and 85 was also noted. We also confirmed similar alterations in gene expression for 26 of the 75 genes in eroded AEC scalp skin.

CONCLUSIONS

This study identifies specific changes in skin structural biology and signalling pathways that result from mutant p63 and provides new molecular insight into the AEC syndrome phenotype.

Analysis of large phenotypic variability of EEC and SHFM4 syndromes caused by K193E mutation of the TP63 gene

EEC (ectrodactyly, ectodermal dysplasia, clefting; OMIM 604292) is an autosomal dominant developmental disorder resulting mainly from pathogenic mutations of the DNA-binding domain (DBD) of the TP63 gene. In this study, we showed that K193E mutation in nine affected individuals of a four-generation kindred with a large degree of phenotypic variability causes four different syndromes or TP63-related disorders: EEC, Ectrodactyly-ectodermal dysplasia (EE), isolated ectodermal dysplasia, and isolated Split Hand/Foot Malformation type 4 (SHFM4). Genotype-phenotype and DBD structural modeling analysis showed that the K193-located loop L2-A is associated with R280 through hydrogen bonding interactions, while R280 mutations also often cause large phenotypic variability of EEC and SHFM4. Thus, we speculate that K193 and several other DBD mutation-associated syndromes may share similar pathogenic mechanisms, particularly in the case of the same mutation with different phenotypes. Our study and others also suggest that the phenotypic variability of EEC is attributed, at least partially, to genetic and/or epigenetic modifiers.

Mutant p63 causes defective expansion of ectodermal progenitor cells and impaired FGF signalling in AEC syndrome

Ankyloblepharon-ectodermal defects-cleft lip/palate (AEC) syndrome, which is characterized by cleft palate and severe defects of the skin, is an autosomal dominant disorder caused by mutations in the gene encoding transcription factor p63. Here, we report the generation of a knock-in mouse model for AEC syndrome (p63(+/L514F) ) that recapitulates the human disorder. The AEC mutation exerts a selective dominant-negative function on wild-type p63 by affecting progenitor cell expansion during ectodermal development leading to a defective epidermal stem cell compartment. These phenotypes are associated with impairment of fibroblast growth factor (FGF) signalling resulting from reduced expression of Fgfr2 and Fgfr3, direct p63 target genes. In parallel, a defective stem cell compartment is observed in humans affected by AEC syndrome and in Fgfr2b(-/-) mice. Restoring Fgfr2b expression in p63(+/L514F) epithelial cells by treatment with FGF7 reactivates downstream mitogen-activated protein kinase signalling and cell proliferation. These findings establish a functional link between FGF signalling and p63 in the expansion of epithelial progenitor cells and provide mechanistic insights into the pathogenesis of AEC syndrome.

Microarray analysis reveals increased expression of ΔNp63α in seborrhoeic keratosis

BACKGROUND

Seborrhoeic keratoses (SKs) are very common benign epidermal lesions without malignant potential. Ultraviolet radiation, old age and viruses are well-known risk factors for disease development. However, the pathomechanisms of SK are not fully understood.

OBJECTIVES

To detect and characterize the genes that are involved in the pathogenesis of SK.

METHODS

We performed a gene expression study using paired lesional and nonlesional skin samples from patients with SK.

RESULTS

We identified and validated 19 differentially expressed genes in SK. Of these 19 genes, we focused on p63 transcription factor, which plays a pivotal role in epidermal development by regulating its transcriptional programme. We found by immunofluorescence that the expression of ΔNp63α, the most abundantly expressed p63 isoform, was significantly increased in SK as compared with normal skin. Moreover, siRNA-mediated knockdown of ΔNp63 led to the downregulation of 11 genes, including a member of the tensin family TNS4. Chromatin immunoprecipitation assay revealed that TNS4 was a target gene of p63.

CONCLUSIONS

We identified upregulated genes in SK using genome-wide cDNA microarray and elucidated the functional contribution of p63 to the disease transcriptome by gene-silencing assay. Taken together, these data may provide a novel insight into the molecular basis of these benign skin lesions.