A novel three-dimensional cell culture method to analyze epidermal cell differentiation in vitro.

Studies of the epidermis have been carried out in various models, such as the monolayer culture in vitro model and three-dimensional (3D) skin models, that are spatially organized to display the architectural features seen in human skin. These models have furthered our understanding of epidermal cell biology and provided quite a few lines of evidence on proliferation, cellular metabolism, morphological status, and state of differentiation. In this chapter, we describe a novel method using epithelial cell aggregates embedded in a collagen gel, instead of individual cells, for building cell-cell and cell-matrix interactions. Analyzing cell behaviors during epidermal differentiation would be helpful. Our method would help to analyze a possible regulatory mechanism underlying epidermal differentiation.

Extracellular epimorphin modulates epidermal differentiation signals mediated by epidermal growth factor receptor.

BACKGROUND: The epidermal stratification/differentiation program is initiated in keratinocytes by a basement membrane-detachment cue and subsequently controlled by spatially and temporally regulated signaling molecules. The vital signals for the developmental behavior of the epidermis include those mediated by epidermal growth factor receptor (EGFR); however, regulatory elements responsible for activation have not yet been fully elucidated. OBJECTIVE: The objectives of this study were (1) to assess the effects of EGFR activation on epidermal differentiation, (2) to study the effects of epimorphin on the level of EGFR signaling degree dependent on matrix engagement, and (3) to address the impact of epimorphin modulation on EGFR-driven epidermal differentiation in a three-dimensional (3D) organotypic skin model. METHODS: We constructed skin-equivalent models with a well-stratified differentiated epidermis and utilized them to evaluate the epidermal behaviors. RESULTS: Extracellularly secreted epimorphin was identified as a strong candidate for signaling pathway involvement. In a 3D epidermis model, EGF stimulation was sufficient for epidermal stratification. However, overactivation of EGFR led to irregular multicellular arrangements with an abnormal differentiation profile, which appeared to be reorganized back to the normal epidermal phenotype by extracellular epimorphin. Extracellular epimorphin interestingly attenuated EGF-stimulated EGFR phosphorylation, cell growth, and migration in adherent cells. In contrast to the results of adhesion culture, extracellular epimorphin reinforced EGFR activation in suspended cells. CONCLUSIONS: These results demonstrate that epimorphin modulates the signaling pathways mediated by EGFR for epidermal tissue organization.

The impact of extracellular syntaxin4 on HaCaT keratinocyte behavior.

Syntaxin4 belongs to t-SNARE protein family and functions as a vesicular fusion mediator in the plasma membrane in a wide variety of cell types. This protein resembles another family member, epimorphin, a subpopulation of which has been shown to be secreted extracellularly in order to exert signaling functions. Here, we demonstrate the secretion of syntaxin4 via a non-classical pathway and its extracellular functions by using the functionally normal keratinocyte HaCaT. Extracellularly presented syntaxin4 appeared to elicit many cell responses similar to epimorphin with an important exception: it clearly facilitated keratinocyte cornification. The circularized peptide ST4n1 was synthesized from the putative functional core of syntaxin4 (a.a. 103-108), which is equivalent to the previously generated antagonist of epimorphin, and neutralized this contradictory effect. Intriguingly, an epimorphin mutant (EP4M) in which the functional core was replaced by that of syntaxin4 behaved like epimorphin, which was again antagonized by ST4n1. Electrophoresis-based analyses demonstrated the distinct structure of syntaxin4 compared to epimorphin or EP4M. These results revealed, for the first time, the extracellular role of syntaxin4 and shed light on the division of the extracellular effects exerted by epimorphin and syntaxin4 on keratinocyte cornification.

Epimorphin-derived peptide antagonists remedy epidermal parakeratosis triggered by unsaturated fatty acid.

BACKGROUND: Unsaturated fatty acid from accumulated sebum disrupts calcium influx in keratinocytes and triggers epidermal hyperplasia, leading to comedone formation in the skin. Oleic acid, a representative unsaturated fatty acid, has been shown to be a useful reagent to induce these cellular alternations, however, the detailed mechanism still remains to be elucidated. OBJECTIVES: This study aimed at the identification of the mediator of unsaturated fatty acid-caused epidermal hyperplasia so as to generate the effective therapeutic agents. METHODS: The downstream mediator of oleic acid-treatment was identified in the epidermal keratinocyte and the effect of its antagonistic peptides on the epidermal behaviors was investigated in culture and in vivo. RESULTS: In culture, treatment with oleic acid augmented extracellular secretion of epimorphin in HaCaT keratinocytes and prevented the epidermal terminal differentiation including programmed cell death and cornified envelope formation. The antagonistic peptide of epimorphin (EPn1: a circular compound composed of CGSIEQSC), which was newly generated in this study, restored normal keratinocyte behaviors. In hairless mice, topical application of oleic acid to the dorsal skin caused epidermal hyperplasia with decreased enucleation in the horny layer, which was dramatically hampered by the administration of EPn1. CONCLUSIONS: The effects of unsaturated fatty acid are attributed to the overstimulation of epimorphin signaling and suggest the epimorphin antagonist as a possible therapeutic agent for acne and hyperkeratotic skin disease.

Influence of neighbouring base sequences on the mutagenesis induced by 7,8-dihydro-8-oxoguanine in yeast.

We have analysed the influence of neighbouring base sequences on the mutagenesis induced by 7,8-dihydro-8-oxoguanine (8-oxoG or G(o)), a typical oxidative lesion of DNA, using the yeast oligonucleotide transformation technique. Two oligonucleotides, oligo-CCG(o) and oligo-CGG(o), each possessing a single 8-oxoG residue and represented by the sequences 5'-CCG(o)-3' and 5'-CGG(o)-3', respectively, were introduced into a chromosome of Saccharomyces cerevisiae and their mutagenic potentials were compared. In a wild-type strain, 8-oxoG showed very weak mutagenic potential in both cases. However, the lesion in 5'-CCG(o)-3' can cause efficient G-to-T transversion in a strain lacking the rad30 gene which encodes yeast DNA polymerase eta (Ypoleta). To explore the properties associated with this translesion synthesis (TLS), the same two oligonucleotides possessing an 8-oxoG were used as templates for a standing-start primer extension assay, and the nucleotide incorporation opposite 8-oxoG was investigated. We found that dATP incorporation opposite 8-oxoG with Ypoleta was low for both sequences. In particular, very low dATP incorporation was observed for the 5'-CCG(o)-3' sequence. These results account for the efficient inhibition of mutagenesis by Ypoleta. TLS plays an important role in one DNA sequence in terms of avoiding mutagenesis induced by 8-oxoG in yeast. In contrast, human yeast DNA polymerase eta showed higher dATP incorporation rates even with the 5'-CCG(o)-3' sequence.

Overexpression of extracellular epimorphin leads to impaired epidermal differentiation in HaCaT keratinocytes.

Epimorphin (also known as syntaxin2) is a stromal signaling factor that is temporally secreted via a non-classical route to regulate the morphogenesis of various epithelia, including skin epidermis. In this study, we show that epimorphin signaling also regulates the differentiation program in the keratinocyte. The extracellular presentation of this molecule is detectable predominantly in the dermal compartments of the skin and its secretion is increased by cell stress such as UVB irradiation, which generates an epimorphin signaling gradient in the epidermis. Artificial stimulation of functionally normal keratinocyte HaCaT cells with extracellular epimorphin triggered initiation of their differentiation program with a dramatic depression of metabolic turnover. Intriguingly, however, sustained epimorphin signaling appeared to severely attenuate the terminal cornification in the cells induced by calcium influx and anchorage-dependent anoikis. In the organotypic culture of HaCaT cells, overexpression of epimorphin impaired the successive differentiation program in the stratified epidermis-like structures; the cells underwent aberrant multicellular arrangement with a presentation of mid-differentiation markers throughout all the cell layers. These results demonstrate that inadequate epimorphin elicits an abnormal differentiation response in keratinocytes, and indicate a causal function of the epimorphin signaling gradient for the establishment of differentiated epidermal structure in the skin.

Nucleotide incorporation against 7,8-dihydro-8-oxoguanine is influenced by neighboring base sequences in TLS DNA polymerase reaction.

7,8-Dihydro-8-oxoguanine (8-oxoG) is a well-known oxidative lesion in DNA and is related to carcinogenesis and ageing processes. Misincorporation of dATP opposite to 8-oxoG leads to G --> T transversion mutations. DNA sequence has been proved as an important factor influencing the replication and enzymatic repair of various types of damages. To explore the influence of sequence effect on the properties of translesion synthesis (TLS) polymerase bypass of 8-oxoG, oligonucleotides with an 8-oxoG in different sequence contexts were used. We conclude that the 5'-nearest base next to 8-oxoG has significant effects in the G --> T mutation by hpoleta.

Oligonucleotide transformation for the study of mutagenic specificities of DNA lesions in yeast.

We developed a method for the analyzing mutagenic potential of DNA damage based on the oligonucleotide transformation technique in yeast. Using this assay we have analyzed mutagenic specificities of various DNA lesions. In the present study, we analyzed the mutagenic properties of 2-hydroxyadenine and 5-hydroxycytosine in yeast. Oligonucleotides containing 2-hydroxyadenine or 5-hydroxycytosine were used for the transformation. The oligonucleotides showed transforming activities similar to unmodified oligonucleotides. This indicates that no repair systems were working on them. The sequencing data of the transformants showed that 5-hydroxycytosine and 2-hydroxyadenine are read mainly as cytosine and adenine. We will also discuss the mechanism of oligonucleotide transformation and its application to the mutagenesis study.

Preventive effects of phosphorylated ascorbate on ultraviolet-B induced apoptotic cell death and DNA strand cleavage through enrichment of intracellular vitamin C in skin epidermal keratinocytes.

Mortality of mouse keratinocytes Pam212 that were irradiated with ultraviolet-B (UVB) was shown to be repressed by pre-irradiated administration with L-ascorbic acid (Asc) or more markedly with Asc-2-O-phosphate (Asc2P), but not with dehydroascorbic acid (DehAsc) or Asc-2-O-alpha-glucoside (Asc2G), although not repressed by post-irradiated administration. The cytoprotection by Asc2P was restricted against UVB below 5-20 mJ/cm2, and exhibited markedly by administration for a period over 2 h, which may be caused by intracellular Asc that was accumulated via dephosphorylation of Asc2P and was increased, 6-24 h after, to levels above twice as abundant as those of Asc-administration. Pre-irradiated Asc2P-administration slightly repressed a DNA ladder-like electrophoretic pattern for UVB-irradiated keratinocytes, containing the histone-bound DNA fragments as shown by ELISA assay, and appreciably repressed the DNA-3'OH cleavage terminals as shown by terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) stain. Thus, prevention of UVB-induced cell death by Asc2P was shown to occur concurrently with inhibition of DNA cleavages and enrichment of intracellular Asc.

UVA-induced degradation of 8-hydroxyguanine in oligonucleotide and the effect on its activities in yeast oligonucleotide transformation assay.

UVA-induced conversion of 8-hydroxyguanine in oligonucleotides was studied. By irradiation with 334 nm UVA light, 8-hydroxyguanine was completely changed to unknown compounds. Monomeric nucleoside may be much less labile to UVA. Mutagenic specificities of 8-hydroxyguanine were investigated using yeast oligonucleotide mutation assay. UVA irradiation moderately reduced the activity of the oligonucleotides.