Epidermal impermeable barriers in mouse and fly

Promising dawn in tumor microenvironment therapy: engineering oral bacteria

Despite decades of research, cancer continues to be a major global health concern. The human mouth appears to be a multiplicity of local environments communicating with other organs and causing diseases via microbes. Nowadays, the role of oral microbes in the development and progression of cancer has received increasing scrutiny. At the same time, bioengineering technology and nanotechnology is growing rapidly, in which the physiological activities of natural bacteria are modified to improve the therapeutic efficiency of cancers. These engineered bacteria were transformed to achieve directed genetic reprogramming, selective functional reorganization and precise control. In contrast to endotoxins produced by typical genetically modified bacteria, oral flora exhibits favorable biosafety characteristics. To outline the current cognitions upon oral microbes, engineered microbes and human cancers, related literatures were searched and reviewed based on the PubMed database. We focused on a number of oral microbes and related mechanisms associated with the tumor microenvironment, which involve in cancer occurrence and development. Whether engineering oral bacteria can be a possible application of cancer therapy is worth consideration. A deeper understanding of the relationship between engineered oral bacteria and cancer therapy may enhance our knowledge of tumor pathogenesis thus providing new insights and strategies for cancer prevention and treatment.

Grainyhead-like transcription factors: guardians of the skin barrier

There has been selective pressure to maintain a skin barrier since terrestrial animals evolved 360 million years ago. These animals acquired an unique integumentary system with a keratinized, stratified, squamous epithelium surface barrier. The barrier protects against dehydration and entry of microbes and toxins. The skin barrier centres on the stratum corneum layer of the epidermis and consists of cornified envelopes cemented by the intercorneocyte lipid matrix. Multiple components of the barrier undergo cross-linking by transglutaminase (TGM) enzymes, while keratins provide additional mechanical strength. Cellular tight junctions also are crucial for barrier integrity. The grainyhead-like (GRHL) transcription factors regulate the formation and maintenance of the integument in diverse species. GRHL3 is essential for formation of the skin barrier during embryonic development, whereas GRHL1 maintains the skin barrier postnatally. This is achieved by transactivation of Tgm1 and Tgm5, respectively. In addition to its barrier function, GRHL3 plays key roles in wound repair and as an epidermal tumour suppressor. In its former role, GRHL3 activates the planar cell polarity signalling pathway to mediate wound healing by providing directional migration cues. In squamous epithelium, GRHL3 regulates the balance between proliferation and differentiation, and its loss induces squamous cell carcinoma (SCC). In the skin, this is mediated through increased expression of MIR21, which reduces the expression levels of GRHL3 and its direct target, PTEN, leading to activation of the PI3K-AKT signalling pathway. These data position the GRHL family as master regulators of epidermal homeostasis across a vast gulf of evolutionary history.

Keratinocytes Isolated From Individual Cleft Lip/Palate Patients Display Variations in Their Differentiation Potential in vitro

To gain more understanding of the complex molecular processes underlying cleft lip/palate (CLP), we established a unique human cell bank, consisting of keratinocytes and corresponding fibroblasts from individual CLP patients as a new study tool. After their careful characterization, we used such patient-derived cell cultures as well as control keratinocytes for in vitro differentiation and proliferation assays. Foreskin-derived control cells as a group showed significant higher induction of the late differentiation markers Loricrin and Filaggrin than the group of CLP patients-derived keratinocytes. Additionally, we detected great variations between individual CLP keratinocyte cell cultures in regard to their potential to terminally differentiate as assessed by the induction of Loricrin and Filaggrin. Primary patient cell cultures that did not properly differentiate, exhibited high proliferation rates. Moreover, we could correlate the expression levels of transcription factor IRF6 to the ability of individual cell cultures to terminally differentiate. Using clinically relevant, patient-derived cells, our results suggest that some of the genetic predispositions causing CLP might also lead to deficiencies in keratinocyte differentiation manifested in in vitro assays.

Two Ancient Gene Families Are Critical for Maintenance of the Mammalian Skin Barrier in Postnatal Life

The skin barrier is critical for mammalian survival in the terrestrial environment, affording protection against fluid loss, microbes, toxins, and UV exposure. Many genes indispensable for barrier formation in the embryo have been identified, but loss of these genes in adult mice does not induce barrier regression. We describe a complex regulatory network centered on two ancient gene families, the grainyhead-like (Grhl) transcription factors and the protein cross-linking enzymes (tissue transglutaminases [Tgms]), which are essential for skin permeability barrier maintenance in adult mice. Embryonic deletion of Grhl3 induces loss of Tgm1 expression, which disrupts the cornified envelope, thus preventing permeability barrier formation leading to neonatal death. However, gene deletion of Grhl3 in adult mice does not disrupt the preformed barrier, with cornified envelope integrity maintained by Grhl1 and Tgm5, which are up-regulated in response to postnatal loss of Grhl3. Concomitant deletion of both Grhl factors in adult mice induced loss of Tgm1 and Tgm5 expression, perturbation of the cornified envelope, and complete permeability barrier regression that was incompatible with life. These findings define the molecular safeguards for barrier function that accompany the transition from intrauterine to terrestrial life.

Identification of a Novel Proto-oncogenic Network in Head and Neck Squamous Cell Carcinoma

BACKGROUND

The developmental transcription factor Grainyhead-like 3 (GRHL3) plays a critical tumor suppressor role in the mammalian epidermis through direct regulation of PTEN and the PI3K/AKT/mTOR signaling pathway. GRHL3 is highly expressed in all tissues derived from the surface ectoderm, including the oral cavity, raising a question about its potential role in suppression of head and neck squamous cell carcinoma (HNSCC).

METHODS

We explored the tumor suppressor role of Grhl3 in HNSCC using a conditional knockout (Grhl3 (∆/-) /K14Cre (+) ) mouse line (n = 26) exposed to an oral chemical carcinogen. We defined the proto-oncogenic pathway activated in the HNSCC derived from these mice and assessed it in primary human HNSCC samples, normal oral epithelial cell lines carrying shRNA to GRHL3, and human HNSCC cell lines. Data were analyzed with two-sided chi square and Student's t tests.

RESULTS

Deletion of Grhl3 in oral epithelium in mice did not perturb PTEN/PI3K/AKT/mTOR signaling, but instead evoked loss of GSK3B expression, resulting in stabilization and accumulation of c-MYC and aggressive HNSCC. This molecular signature was also evident in a subset of primary human HNSCC and HNSCC cell lines. Loss of Gsk3b in mice, independent of Grhl3, predisposed to chemical-induced HNSCC. Restoration of GSK3B expression blocked proliferation of normal oral epithelial cell lines carrying shRNA to GRHL3 (cell no., Day 8: Scramble ctl, 616±21.8 x 10(3) vs GRHL3-kd, 1194±44 X 10(3), P < .001; GRHL3-kd vs GRHL3-kd + GSK3B, 800±98.84 X 10(3), P = .003) and human HNSCC cells.

CONCLUSIONS

We defined a novel molecular signature in mammalian HNSCC, suggesting new treatment strategies targeting the GRHL3/GSK3B/c-MYC proto-oncogenic network.

The epidermis of grhl3-null mice displays altered lipid processing and cellular hyperproliferation

The presence of an impermeable surface barrier is an essential homeostatic mechanism in almost all living organisms. We have recently described a novel gene that is critical for the developmental instruction and repair of the integument in mammals. This gene, Grainy head-like 3 (Grhl3) is a member of a large family of transcription factors that are homologs of the Drosophila developmental gene grainy head (grh). Mice lacking Grhl3 fail to form an adequate skin barrier, and die at birth due to dehydration. These animals are also unable to repair the epidermis, exhibiting failed wound healing in both fetal and adult stages of development. These defects are due, in part, to diminished expression of a Grhl3 target gene, Transglutaminase 1 (TGase 1), which encodes a key enzyme involved in cross-linking of epidermal structural proteins and lipids into the cornified envelope (CE). Remarkably, the Drosophila grh gene plays an analogous role, regulating enzymes involved in the generation of quinones, which are essential for cross-linking structural components of the fly epidermis. In an extension of our initial analyses, we focus this report on additional defects observed in the Grhl3-null epidermis, namely defective extra-cellular lipid processing, altered lamellar lipid architecture and cellular hyperproliferation. These abnormalities suggest that Grhl3 plays diverse mechanistic roles in maintaining homeostasis in the skin.

Grainy head and its target genes in epithelial morphogenesis and wound healing

The Grainy head (Grh) family of transcription factors is characterized by a unique DNA-binding domain that binds to a conserved consensus sequence. Nematodes and flies have a single grh gene, whereas mice and humans have evolved three genes encoding Grainy head-like (Grhl) factors. We review the biological function of Grh in different animals and the mechanisms modulating its activity. grh and grhl genes play a remarkably conserved role in epithelial organ development and extracellular barrier repair after tissue damage. Recent studies in flies and vertebrates suggest that Grh factors may be primary determinants of cell adhesion and epithelial tissue formation. Grh proteins can dimerize and act as activators or repressors in different developmental contexts. In flies, tissue-specific, alternative splicing generates different Grh isoforms with different DNA-binding specificities and functions. Grh activity is also modulated by receptor tyrosine kinases: it is phosphorylated by extracellular signal regulated kinase, and this phosphorylation is selectively required for epidermal barrier repair. Two mechanisms have been proposed to explain the repressive function of Grh on target gene transcription. First, Grh can target the Polycomb silencing complex to specific response elements. Second, it can directly compete for DNA binding with transcriptional activators. Understanding the molecular mechanisms of gene regulation by Grh factors is likely to elucidate phylogenetically conserved mechanisms of epithelial cell morphogenesis and regeneration upon tissue damage.

Targeting of the tumor suppressor GRHL3 by a miR-21-dependent proto-oncogenic network results in PTEN loss and tumorigenesis

Despite its prevalence, the molecular basis of squamous cell carcinoma (SCC) remains poorly understood. Here, we identify the developmental transcription factor Grhl3 as a potent tumor suppressor of SCC in mice, and demonstrate that targeting of Grhl3 by a miR-21-dependent proto-oncogenic network underpins SCC in humans. Deletion of Grhl3 in adult epidermis evokes loss of expression of PTEN, a direct GRHL3 target, resulting in aggressive SCC induced by activation of PI3K/AKT/mTOR signaling. Restoration of Pten expression completely abrogates SCC formation. Reduced levels of GRHL3 and PTEN are evident in human skin, and head and neck SCC, associated with increased expression of miR-21, which targets both tumor suppressors. Our data define the GRHL3-PTEN axis as a critical tumor suppressor pathway in SCC.

Essential role of Duox in stabilization of Drosophila wing

NADPH oxidase produces reactive oxygen species (ROS). Drosophila melanogaster has two homologs of NADPH oxidase, dNox and dDuox, with functions that remain unclear in vivo. To clarify these functions, two independent transgenic fly lines expressing dsRNA targeted for different portions of dDuox mRNA were used. In both flies, en-GAL4> UAS-dDuoxIR(976-1145) and en-GAL4> UAS-dDuoxIR(370-518), in which dDuox was knocked down selectively in the posterior area of the wing disc, the posterior compartment of the adult wings became paler and more fragile with wing veins that were indistinct by comparison with the anterior one. Fluorescence staining of the en-GAL4> UAS-dDuoxIR(976-1145) adult wings revealed that the ROS concentration in the posterior compartment was significantly lower than that in the anterior compartment. Moreover, in these flies, the posterior compartment of the wing imaginal disc showed a greater number of apoptotic cells detected by immunostaining with anti-cleaved caspase-3 antibody than those in the anterior compartment. Respective knockdown of tyrosine hydroxylase or dopa-decarboxylase showed paler wing blades in the posterior compartment similar to the phenotype of dDuox-knockdown files. Along with this observation, analysis of the catecholic and dityrosine components in the wings of adult flies proved that dDuox plays important roles in the stabilization of the cuticle structure of the wings via tyrosine cross-linking, the sclerotization and melanization processes possibly through ROS production. These dDuox-knockdown fly lines would be useful tools for further studying dDuox functions during the development of Drosophila.

The unique and cooperative roles of the Grainy head-like transcription factors in epidermal development reflect unexpected target gene specificity

The Grainy head-like 3 (Grhl3) gene encodes a transcription factor that plays essential roles in epidermal morphogenesis during embryonic development, with deficient mice exhibiting failed skin barrier formation, defective wound repair, and loss of eyelid fusion. Despite sharing significant sequence homology, overlapping expression patterns, and an identical core consensus DNA binding site, the other members of the Grhl family (Grhl1 and -2) fail to compensate for the loss of Grhl3 in these processes. Here, we have employed diverse genetic models, coupled with biochemical studies, to define the inter-relationships of the Grhl factors in epidermal development. We show that Grhl1 and Grhl3 have evolved complete functional independence, as evidenced by a lack of genetic interactions in embryos carrying combinations of targeted alleles of these genes. In contrast, compound heterozygous Grhl2/Grhl3 embryos displayed failed wound repair, and loss of a single Grhl2 allele in Grhl3-null embryos results in fully penetrant eyes open at birth. Expression of Grhl2 from the Grhl3 locus in homozygous knock-in mice corrects the wound repair defect, but these embryos still display a complete failure of skin barrier formation. This functional dissociation is due to unexpected differences in target gene specificity, as both GRHL2 and GRHL3 bind to and regulate expression of the wound repair gene Rho GEF 19, but regulation of the barrier forming gene, Transglutaminase 1 (TGase1), is unique to GRHL3. Our findings define the mechanisms underpinning the unique and cooperative roles of the Grhl genes in epidermal development.

Cuticle laccase of the silkworm, Bombyx mori: purification, gene identification and presence of its inactive precursor in the cuticle

Laccase is a multi-copper enzyme found in variety of organisms including plants, fungi and bacteria. In insects, laccase is thought to play an important role in cuticle sclerotization with its ability to catalyze the oxidation of phenolic compounds to their corresponding quinones. From the newly ecdysed pupae of the silkworm, Bombyx mori, we purified a dimer form of cuticular laccase with 70-kDa polypeptides. Mass spectrometric analysis of the tryptic fragments and cDNA sequence analysis revealed that the gene for the purified laccase (BmLaccase2) is an ortholog of laccase2, one of the multiple laccase genes found in insect genomes. BmLaccase2 is highly expressed in the epidermis prior to ecdysis, suggesting that the BmLaccase2 protein accumulates before ecdysis. However, the cuticle of newly ecdysed pupa does not have laccase activity, and the activity only becomes detectable several hours after ecdysis. These data suggest that cuticle laccase is synthesized as an inactive precursor, which is later activated after ecdysis. We also found that urea-solubilized cuticle protein extract contains an inactive form of laccase that can be activated by trypsin treatment.

Developmental and evolutionary basis for drought tolerance of the Anopheles gambiae embryo

During the evolution of the Diptera there is a dramatic modification of the embryonic ectoderm, whereby mosquitoes contain separate amnion and serosa lineages while higher flies such as Drosophila melanogaster contain a single amnioserosa. Whole-genome transcriptome assays were performed with isolated serosa from Anopheles gambiae embryos. These assays identified a large number of genes implicated in the production of the larval cuticle. In D. melanogaster, these genes are activated just once during embryogenesis, during late stages where they are used for the production of the larval cuticle. Evidence is presented that the serosal cells secrete a dedicated serosal cuticle, which protects A. gambiae embryos from desiccation. Detailed temporal microarray assays of mosquito gene expression profiles revealed that the cuticular genes display biphasic expression during A. gambiae embryogenesis, first in the serosa of early embryos and then again during late stages as seen in D. melanogaster. We discuss how evolutionary modifications in the well-defined dorsal-ventral patterning network led to the wholesale deployment of the cuticle biosynthesis pathway in early embryos of A. gambiae.

Scab formation and wound healing of plant tissue by soldier aphid

In the social aphid Nipponaphis monzeni, a unique gall-repairing behaviour has been known: when a hole is made on the gall, many soldier nymphs discharge body fluid on the breach, which promptly solidifies and plugs the hole. Here, we experimentally investigated the subsequent fate of repaired galls and their inhabitants. Irrespective of natural repair by soldier nymphs or artificial repair with adhesive, repaired galls survived significantly better than non-repaired galls. Within a month after repair, the plant tissue around the hole proliferated and sealed up the hole. Many soldier nymphs were localized at the hole area and extermination of inhabiting aphids by insecticides aborted the gall regeneration, indicating that the gall regeneration requires inhabiting aphids, wherein soldier nymphs are likely to play a major role. This study provides an unprecedented case of scab formation and wound healing, which occurs at an animal-plant interface: scab derived from insect body fluid promptly plugs damaged plant tissue and subsequently the insects actively stimulate regeneration of the plant tissue, whereby the compromised plant tissue recovers. We suggest that the novel system may have evolved in the aphid lineage through enhancement and recruitment of the pre-existing capabilities of haemolymph coagulation and gall formation.

Negative regulation of Caenorhabditis elegans epidermal damage responses by death-associated protein kinase

Wounding of epidermal layers triggers multiple coordinated responses to damage. We show here that the Caenorhabditis elegans ortholog of the tumor suppressor death-associated protein kinase, dapk-1, acts as a previously undescribed negative regulator of barrier repair and innate immune responses to wounding. Loss of DAPK-1 function results in constitutive formation of scar-like structures in the cuticle, and up-regulation of innate immune responses to damage. Overexpression of DAPK-1 represses innate immune responses to needle wounding. Up-regulation of innate immune responses in dapk-1 requires the TIR-1/p38 signal transduction pathway; loss of function in this pathway synergizes with dapk-1 to drastically reduce adult lifespan. Our results reveal a previously undescribed function for the DAPK tumor suppressor family in regulation of epithelial damage responses.

Wounding sheets of epithelial cells activates the epidermal growth factor receptor through distinct short- and long-range mechanisms

Wounding epithelia induces activation of the epidermal growth factor receptor (EGFR), which is absolutely required for induction of motility. ATP is released from cells after wounding; it binds to purinergic receptors on the cell surface, and the EGFR is subsequently activated. Exogenous ATP activates phospholipase D, and we show here that ATP activates the EGFR through the phospholipase D2 isoform. The EGFR is activated in cells far (>0.3 cm) from wounds, which is mediated by diffusion of extracellular ATP because activation at a distance from wounds is abrogated by eliminating ATP in the medium with apyrase. In sharp contrast, activation of the EGFR near wounds is not sensitive to apyrase. Time-lapse microscopy revealed that cells exhibit increased motilities near edges of wounds; this increase in motility is not sensitive to apyrase, and apyrase does not detectably inhibit healing of wounds in epithelial sheets. This novel ATP/PLD2-independent pathway activates the EGFR by a transactivation process through ligand release, and it involves signaling by a member of the Src family of kinases. We conclude that wounding activates two distinct signaling pathways that induce EGFR activation and promote healing of wounds in epithelial cells. One pathway signals at a distance from wounds through release of ATP, and another pathway acts locally and is independent on ATP signaling.

Perturbed desmosomal cadherin expression in grainy head-like 1-null mice

In Drosophila, the grainy head (grh) gene plays a range of key developmental roles through the regulation of members of the cadherin gene family. We now report that mice lacking the grh homologue grainy head-like 1 (Grhl1) exhibit hair and skin phenotypes consistent with a reduction in expression of the genes encoding the desmosomal cadherin, desmoglein 1 (Dsg1). Grhl1-null mice show an initial delay in coat growth, and older mice exhibit hair loss as a result of poor anchoring of the hair shaft in the follicle. The mice also develop palmoplantar keratoderma, analogous to humans with DSG1 mutations. Sequence analysis, DNA binding, and chromatin immunoprecipitation experiments demonstrate that the human and mouse Dsg1 promoters are direct targets of GRHL1. Ultrastructural analysis reveals reduced numbers of abnormal desmosomes in the interfollicular epidermis. These findings establish GRHL1 as an important regulator of the Dsg1 genes in the context of hair anchorage and epidermal differentiation, and suggest that cadherin family genes are key targets of the grainy head-like genes across 700 million years of evolution.

Spatial and temporal expression of POF1B, a gene expressed in epithelia

Mammalian epithelia possess specialized cellular components that provide an impermeable barrier between two different environments. In particular, in the skin, mitotically dividing cells undergo a programmed set of morphological and biochemical changes leading to the establishment of the epidermal permeability barrier (EPB) to prevent escape of moisture and entrance of toxic molecules. Many different skin proteins are involved in the process but not all have been identified. We report here the results of the expression studies of a novel gene, highly and specifically expressed in the granular layer of the epidermis and in the epithelia of the oro-pharyngeal and gastro-intestinal tracts. Our data show that during mouse development Pof1b expression is activated in the external layers of the epidermis just prior to formation of the EPB.