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Human skin is located at the outermost part of the body, and various cosmetics and chemicals that may come in contact with human skin need to be evaluated for their potential to cause irritation. Until recently, the Draize test was considered the standard method for skin irritation; however, this technique has disadvantages such as the need to sacrifice many rabbits and subjective scoring. Thus, to contribute to the development of an animal-free alternative skin irritation test, we investigated the cytotoxicity and inflammatory response to standard skin irritants in SV40 large T antigen-transformed human epidermal keratinocyte 2 cells (SV-HEK2 cells). In this study, we established an SV-HEK2 cell line immortalized by SV40 large T antigen (SV40 T) and characterized the inherent morphological and cytological properties. We next used 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) or neutral red uptake (NRU) assays of cell viability to investigate the optimal experimental conditions for determining SV-HEK2 cell viability after exposure to sodium dodecyl sulfate at 6.25 × 10 − 3 % to 1 × 10 − 1 % as a standard skin irritant. We then examined the viability of SV-HEK2 cells in response to five skin irritants (benzalkonium chloride, isopropanol, sodium dodecyl sulfate, Triton X-100 and Tween20) at 5 × 10 − 3 % to 1 × 10 − 1 % by MTT or NRU assay. Finally, we estimated the level of cytokines secretion in response to stimulation by skin irritants in SV-HEK2 cells. The results revealed that SV-HEK2 cells responded well to skin irritants in a concentration-dependent manner and that there was good correlation between irritant concentration and cytotoxicity (or cytokine secretion) when cells were exposed to skin irritants for 10 min at room temperature (RT) using an MTT assay. Overall, these findings suggest that SV-HEK2 cells could be a good alternative in vitro model for skin irritation tests. [ABSTRACT FROM AUTHOR]

Autophagy, one mechanism of programmed cell death, is fundamental to cellular homeostasis. Previous studies have identified autophagy as a novel mechanism by which cytokines control the immune response. However, its precise role in immune-related inflammatory skin diseases such as psoriasis remains unclear. Thus, this study explored the functional role of autophagy in psoriatic inflammation of epidermal keratinocytes. Strong light chain 3 immunoreactivity was observed in epidermal keratinocytes of both human psoriatic lesions and imiquimod-induced mice psoriatic model, and it was readily induced by polycytidylic acid (poly (I:C)), which stimulates Toll-like receptor 3 (TLR3), in human epidermal keratinocytes in vitro. Rapamycin-induced activation of autophagy significantly reduced poly (I:C)-induced inflammatory reaction, whereas, inhibition of autophagy by 3-methyladeine increased that. Our results indicate that the induction of autophagy may attenuate TLR3-mediated immune responses in human epidermal keratinocytes, thus providing novel insights into the mechanisms underlying the development of inflammatory skin diseases including psoriasis. [ABSTRACT FROM AUTHOR]

Kruppel-like factor 4 (KLF4) is a zinc-finger transcription factor that plays a role in terminal differentiation of epidermal keratinocytes. There are conflicting reports regarding the role of KLF4 in tumor development, with both the tumor suppressive and/or oncogenic properties depending on different conditions and cell types. In this study, we investigated the functional importance of KLF4 in cutaneous squamous cell carcinoma (SCC). Immunohistochemistry showed that KLF4 expression was relatively low in SCC lesion compared to normal epidermis. To examine the effects of KFL4, we transduced SCC lines (SCC12 and SCC13 cells) with the KLF4-expressing recombinant adenovirus. Overexpression of KLF4 significantly decreased cell proliferation and colony forming activity. In addition, overexpression of KLF4 markedly reduced invasive potential, along with the downregulation of epithelial-mesenchymal transition (EMT)-related molecules. In a mechanistic study, KLF4 inhibited SOX2, of which expression is critical for tumor initiation and growth of SCC. Further investigations indicated that SOX2 expression is induced by TGF-β/SMAD signaling, and that overexpression of KLF4 inhibited SMAD signaling via upregulation of SMAD7, an important inhibitory SMAD molecule. Based on these data, KLF4 plays a tumor suppressive role in cutaneous SCC cells. • Overexpression of KLF4 decreased the cell proliferation, colony forming activity, invasion and EMT potential in cutaneous SCC cells. • Overexpression of KLF4 decreased SOX2 level via inhibition of SMAD2 phosphorylation. • Overexpression of KLF4 inhibited SMAD signaling via upregualtion of SMAD7, an inhibitory SMAD molecule. [ABSTRACT FROM AUTHOR]

Abstract Skin color is determined by the melanin pigments that are produced in melanocytes then transferred to surrounding keratinocytes. Despite the growing number of commercial products claiming the pigmentation-regulatory effects, there is still a demand for the development of new materials that are safe and more efficacious. We tried to screen the pigmentation-regulatory materials using a commercially available drugs, and found that nilotinib could induce pigmentation in melanoma cells. When HM3KO melanoma cells were treated with nilotinib, melanin content was increased together with increase of tyrosinase activity. Nilotinib increased the expression of pigmentation-related genes such as MITF, tyrosinase and TRP1. Consistent with these results, the protein level for MITF, tyrosinase, and TRP1 was significantly increased by nilotinib. To delineate the action mechanism of nilotinib, we investigated the effects of nilotinib on intracellular signaling. As a result, nilotinib decreased the phosphorylation of AKT, while increased the phosphorylation of CREB. The pretreatment of PKA inhibitor H89 markedly blocked the nilotinib-induced phosphorylation of CREB. In accordance with, pretreatment of H89 significantly inhibited the nilotinib-induced pigmentation, indicating that nilotinib induces pigmentation via the activation of PKA signaling. Together, our data suggest that nilotinib can be developed for the treatment of hypopigmentary disorder such as vitiligo. Highlights • The nilotinib induced the pigmentation of HM3KO melanoma cells. • The nilotinib decreased the phosphorylation of AKT, while increased the phosphorylation of CREB. • The inhibition of PKA signaling abrogated nilotinib-induced pigmentation. [ABSTRACT FROM AUTHOR]

Eccrine sweat glands regulate body temperature by secreting water and electrolytes. In humans, eccrine sweat glands are ubiquitous in the skin, except in the lips and external genitalia. In mice, eccrine sweat glands are present only in the paw pad. Brn2 is a protein belonging to a large family of transcription factors. A few studies have examined Brn2 in melanoma cells and epidermal keratinocytes. This study investigated changes in the skin in the K5-Brn2 transgenic mouse, which overexpresses Brn2 and contains the keratin 5 promotor. Interestingly, the volume of eccrine sweat glands was reduced markedly in the K5-Brn2 transgenic mouse compared with the wild-type, while the expression of aquaporin 5, important molecule in sweat secretion, was increased in each sweat gland cell, probably to compensate for the reduction in gland development. However, sweating response to a pilocarpine injection in the hind paw was significantly decreased in the K5-Brn2 transgenic mouse compared with the wild-type. The paw epidermis was thicker in the K5-Brn2 transgenic mouse compared with the wild-type. Taken together, eccrine sweat gland development and sweat secretion were suppressed markedly in the K5-Brn2 transgenic mouse. These results may be associated with dominant development of the epidermis by Brn2 overexpression in the paw skin. [ABSTRACT FROM AUTHOR]

Adiponectin plays important roles in metabolic function, inflammation and multiple biological activities in various tissues. However, evidence for adiponectin signaling in sebaceous glands is lacking, and its role remains to be clarified. This study investigated the role of adiponectin in lipid production in sebaceous glands in an experimental study of human sebocytes. We demonstrated that human sebaceous glands in vivo and sebocytes in vitro express adiponectin receptor and that adiponectin increased cell proliferation. Moreover, based on a lipogenesis study using Oil Red O, Nile red staining and thin layer chromatography, adiponectin strongly upregulated lipid production in sebocytes. In three-dimensional culture of sebocytes, lipid synthesis was markedly enhanced in sebocytes treated with adiponectin. This study suggested that adiponectin plays a significant role in human sebaceous gland biology. Adiponectin signaling is a promising target in the clinical management of barrier disorders in which sebum production is decreased, such as in atopic dermatitis and aged skin. [ABSTRACT FROM AUTHOR]

Psoriasis is a common skin disease, of which pathogenesis involves the increase of inflammatory reaction in epidermal cells. In an attempt to find therapeutics for psoriasis, we found that cucurbitacin B has an inhibitory potential on imiquimod-induced inflammation of keratinocytes. Cucurbitacin B significantly inhibited imiquimod-induced expression of crucial psoriatic cytokines, such as IL-8 and CCL20, via down-regulation of NF-κB and STAT3 signaling pathway in human keratinocytes. In addition, keratinocyte proliferation was markedly inhibited by cucurbitacin B. The potential beneficial effect of cucurbitacin B on psoriasis was further validated in imiquimod-induced psoriasiform dermatitis of experimental animal. Topical application of cucurbitacin B resulted in significant reduction of epidermal hyperplasia and inflammatory cytokines production, and ameliorated the psoriatic symptom. Taken together, these results suggest that cucurbitacin B may be a potential candidate for the treatment of psoriasis. [ABSTRACT FROM AUTHOR]

Imiquimod is known to exert its effects through Toll-like receptor 7 (TLR7) and/or TLR8, resulting in expression of proinflammatory cytokines and chemokines. Keratinocytes have not been reported to constitutively express TLR7 and TLR8, and the action of imiquimod is thought to be mediated by the adenine receptor, not TLR7 or TLR8. In this study, we revealed the expression of TLR7 in keratinocytes after calcium-induced differentiation. After addition of calcium to cultured keratinocytes, the immunological responses induced by imiquimod, such as activation of NF-κB and induction of TNF-α and IL-8, were more rapid and stronger. In addition, imiquimod induced the expression TLR7, and acted synergistically with calcium to induce proinflammatory cytokines. We confirmed that the responses induced by imiquimod were significantly inhibited by microRNAs suppressing TLR7 expression. These results suggest that TLR7 expressed in keratinocytes play key roles in the activation of NF-κB signaling by imiquimod, and that their modulation in keratinocytes could provide therapeutic potential for many inflammatory skin diseases. [ABSTRACT FROM AUTHOR]

Abstract: S100A8 and S100A9 are members of the S100A8 protein family that exist as homodimers and heterodimers in neutrophils, monocytes, and macrophages. Recent studies have shown the pivotal roles of S100A8 and S100A9 in the propagation of inflammation and keratinocyte proliferation in psoriasis. We found significant up-regulation of S100A8 and S100A9 secretion from keratinocytes in psoriatic lesions. To mimic the in vivo secretory conditions of S100A8 and S100A9 from psoriatic epidermal keratinocytes, we used the culture medium (CM) of S100A8 and S100A8/A9 adenovirus-transduced keratinocytes to investigate the functions of S100A8 and S100A9. We detected increased levels of various pro-inflammatory cytokines in the CM, including IL-8 and TNF-α, which are involved in aggravating psoriatic skin lesions, and IL-6 and members of the CXCL family of pro-angiogenic cytokines. The CM increased immune cell migration and increased angiogenesis in human umbilical vein endothelial cells. In conclusion, we found that the upregulated production of S100A8 and S100A9 by psoriatic epidermal keratinocytes activated adjacent keratinocytes to produce several cytokines. Moreover, S100A8 and S100A9 themselves function as pro-angiogenic and chemotactic factors, generating a psoriatic milieu in skin. [Copyright &y& Elsevier]

Abstract: Background: Ionizing radiation is used to treat many of cancers, however, it also produces unwanted side effect on normal tissues, such as radiodermatitis. We previously established an animal model for radiodermatitis, and found that X-ray irradiation induced the expression of ID3 in hairless mouse skin by cDNA microarray. Objective: The aim of this study is to investigate the functional role of ID3 in X-ray irradiated keratinocytes. Methods: Immunohistochemistry, RT-PCR and Western blot were performed to demonstrate the ID3 induction by X-ray irradiation. HaCaT keratinocytes were transduced with the recombinant adenovirus expressing HA-ID3, and then effects on apoptosis were analyzed. Results: X-ray irradiation increased markedly the ID3 protein level in epidermis of mouse skin. X-ray irradiation also induced the expression of ID3 in HaCaT keratinocytes cultured in vitro, at both mRNA and protein levels. When ID3 was overexpressed by recombinant adenovirus, apoptosis of keratinocytes were induced even in the absence of X-ray irradiation. Furthermore, overexpression of ID3 sensitized X-ray-induced apoptosis. Interestingly, X-ray irradiation significantly reduced the endogenous β-catenin level, which was related with induction of apoptosis. Similarly, overexpression of ID3 led to remarkable reduction in β-catenin level. Conclusion: These results suggest that ID3 plays a role as an apoptosis inducer in response to X-ray irradiation via the regulation of endogenous β-catenin level. [ABSTRACT FROM AUTHOR]

Abstract: Paired-like homeodomain transcription factor 2 (PITX2) has been implicated as one of the genes responsible for Rieger syndrome. It has been also shown to play a central role during development. In this study, we investigated the functional role of PITX2 in keratinocyte differentiation. RT–PCR analysis showed that PITX2c isoform was predominantly expressed in a differentiation-dependent manner. Consistent with, immunohistochemical staining showed that PITX2 expression was increased in the upper layer of epidermis. When PITX2c was overexpressed in cultured keratinocytes by a recombinant adenovirus, the differentiation markers such as involucrin and loricrin were significantly increased at both mRNA and protein levels. In addition, PITX2c overexpression led to the decrease of cell growth, concomitantly with the upregulation of cell cycle-related genes p21. To investigate the effect of PITX2c in vivo, we microinjected PITX2c expression vector into zebrafish embryo. Interestingly, overexpression of PITX2c in zebrafish embryo led to the formation of horn-like structure and thickening of epidermis, together with the increase of keratin 8 (K8) expression. These results suggest that PITX2c has a role in proliferation and differentiation of epidermal keratinocytes. [ABSTRACT FROM AUTHOR]

Abstract: Background: Plasminogen activator inhibitor-2 (PAI-2) is an enzyme inhibitor which is involved in various biological processes including cell differentiation, tissue regrowth and regeneration. Although PAI-2 has been originally isolated as an extracellular inhibitor of urokinase plasminogen activator (uPA), recent studies indicate that PAI-2 has other intracellular effects in keratinocyte, such as the component of cornified envelope. Objective: The aim of this study is to investigate the expression and functional role of PAI-2 during the keratinocyte differentiation. Methods: We transduced keratinocytes with adenovirus harboring the expression cassette for PAI-2, then examined the effect on keratinocytes differentiation. Results: When cultured epidermal keratinocytes were treated with 1.2mM calcium, PAI-2 expression was increased time-dependently at both mRNA and protein levels. The calcium-induced PAI-2 expression was abolished by treatment with p38 MAPK inhibitor, while overexpression of MKK6 led to the increase of PAI-2 expression. When PAI-2 was overexpressed by adenoviral transduction, the expression of keratinocyte differentiation markers such as involucrin, keratin 10 and loricrin was markedly increased. Concomitantly, overexpression of PAI-2 resulted in the retardation of cell growth, with the increase of Rb and p53. Conclusion: These results suggest that PAI-2 has a role for promoting the differentiation of epidermal keratinocytes. [Copyright &y& Elsevier]

Abstract: Terminal differentiation of skin keratinocytes is a vertically directed multi-step process that is tightly controlled by the sequential expression of a variety of genes. We previously investigated the gene expression profile and found that many of differentiation-related genes expressed in a temporally regulated manner. In this study, we attempted to find the hub-molecules and their intracellular signaling networks during keratinocyte differentiation using in silico analysis of data obtained from previous studies. We used protein–protein interaction prediction software called PSIMAP, and drew a hypothetical signaling network. We chose one candidate hub-molecule SHC1 that were predicted to link EGFR and MAPK signal, and then evaluated the protein–protein interactions experimentally. As predicted, SHC1 bound to the MEK1 in an EGF-regulated manner. Furthermore, SHC1 bound to the MEK1 and p38 MAPK in a keratinocyte differentiation dependent manner. These results demonstrate that in silico protein–protein interaction prediction system can be used to efficiently and cost-effectively select the experimental candidates. [Copyright &y& Elsevier]

Summary: Background: Ionizing radiation is used to treat a lot of cancers, however, it also produced unwanted side effect on normal tissues, such as radiodermatitis. We previously established an animal model for radiodermatitis, and identified many of radiation-induced genes by cDNA microarray. Of the candidates, we chose S100A8 gene for a further study. Objective: The aim of this study is to investigate the functional role of S100A8 in X-ray irradiated keratinocytes. Methods: RT-PCR and immunohistochemistry were performed to demonstrate the S100A8 induction by X-ray irradiation. HaCaT keratinocytes were transduced with the recombinant adenovirus expressing GFP-S100A8, and then effects on cell cycle and apoptosis were analyzed using flow cytometry and Western blot. Results: X-ray irradiation markedly induced S100A8 expression in the hyperplastic epidermis of mouse. Overexpression of S100A8 by adenoviral transduction led to the enhancement of cell proliferation in the absence and/or presence of X-ray irradiation, as compared with Ad/GFP control group. Furthermore, overexpression of S100A8 significantly protected the X-ray-induced apoptosis. Conclusion: These results suggest that S100A8 have an anti-apoptotic role in X-ray irradiated keratinocytes. [Copyright &y& Elsevier]

Seo E-Y, Lee W-H, Piao Y-J, Kim K-H, Lee K-M, Ahn K-S, Yang J-M, Seo Y-J, Kim CD, Park J-K, Lee J-H. Identification of calcium-inducible genes in primary keratinocytes using suppression-subtractive hybridization. Terminal differentiation in epidermal keratinocytes involves major biochemical changes including the expression of many new differentiation-specific genes. To further understand this process, we performed suppression-subtractive hybridization of keratinocytes cultured under high-calcium condition, known to induce differentiation in vitro. We randomly isolated 300 clones representing 90 different genes. By reverse Northern blot analyses, 20 different genes were found to be overexpressed, of which 13 were confirmed as differentially expressed genes during keratinocyte differentiation by Northern blot analysis. Of those, five genes, transglutaminase 1, keratin 6, interleukin-1 receptor antagonist, kallikrein 7, and heat shock protein 27, are known to be up-regulated during epidermal differentiation. Six genes, ferritin-L chain, ribosomal protein S6, tumor-associated calcium signal transducer 2, neuroendocrine secretory protein 55, phosphoserine aminotransferase, and neutrophil gelatinase-associated lipocalin, heretofore were not known to be up-regulated during keratinocyte differentiation. We also identified two novel genes. One of these maps to chromosome 1q21 of the epidermal differentiation complex, and its expression level was strongly increased in differentiating keratinocytes. These differentially expressed genes may provide significant opportunities for further understanding of the epidermal keratinocyte differentiation. [ABSTRACT FROM AUTHOR]