Activity Of Melanocytes Research Articles

DNA Methylation Analysis of the Gene CDKN2B in Gallus gallus (Chicken)

Methylation is an epigenetic modification of DNA affecting gene expression without changing the structure of nucleotides. It plays a crucial role in the embryonic and post-embryonic development of living organisms. Methylation level is tissue and species-specific and changes with age. The study was aimed at identifying the methylation of the CDKN2B gene situated at locus bar in Polbar chickens on the 6th and 18th day of embryonic development using the MSP (methylation-specific PCR) method. Methylation was not detected in the promoter region of gene CDKN2B on the 6th and 18th day of embryonic development. As one of the five genes responsible for melanine activity in melanocytes and highly active, it can contribute to the production of this pigment. The present research broadens the current knowledge of the chicken epigenome and the mechanism of autosexing in birds.

Effect of nuclear translocation of E2p45 related factor 2 on the biological activity of melanocytes

Objective To investigate the effect of nuclear translocation of E2p45 related factor 2 (Nrf2)on the biological activity of melanocytes.Methods Plasmid vectors containing wild-type nrf2 gene (pcDNA-nrf2) and nls-deleted nrf2 gene (pcDNA-nrf2△nls) were constructed.B10BR normal murine melanocytes were classified into three groups,i.e.,untransfected group,wild-type nrf2 group transfected with pcDNA-nrf2,and mutated nrf2 group transfected with pcDNA-nrf2△nls.Each of the above groups were further divided into three subgroups:control subgroup receiving no treatment,hydrogen peroxide (H2O2) subgroup treated with H2O2 of 200 μmol/L for 24 hours,and combined subgroup pretreated with tert-butyl hydroquinone (TBHQ) followed by treatment with H2O2 of 200 μmol/L for 24 hours.Subsequently,methyl thiazolyl tetrazolium (MTT) assay was performed to evaluate the proliferative activity of cells,dopa oxidation assay to determine tyrosinase activity,Transwell assay to estimate cell migration ability,Western blot to quantify the expressions of Nrf2 and his tag fusion protein.Results TBHQ significantly enhanced the nuclear expression of Nrf2 in B10BR cells transfected with pcDNA-nrf2 or pcDNA-nrf2△nls (both P ＜ 0.01).No significant difference was observed in tyrosinase activity between untreated wild-type nrf2 group,mutated nrf2 group,and untransfected group (P ＞ 0.05).There was a statistical decrease in tyrosinase activity in the two H2O2-treated transfected groups compared with the untreated transfected groups (both P ＜ 0.05),and the decrease was reversed by TBHQ pretreatment in the wildtype nrf2 group (P ＜ 0.05),but not in the mutated nrf2 group (P ＞ 0.05).Further more,the proliferative activity of B10BR cells experienced no obvious changes in the wild-type nrf2 group (P ＞ 0.05),but was significantly reduced in the untransfected group (P ＜ 0.05) and mutated nrf2 group (P ＜ 0.01) after the H2O2 treatment compared with the corresponding untreated groups.TBHQ could protect the pcDNA-nrf2-transfected B10BR cells,but not pcDNA-nrf2△nls-transfected B10BR cells,from H2O2-induced oxidative damage.Transwell assay showed no significant difference in migration ability among these nine groups (P ＞ 0.05).Conclusions Abnormal nuclear translocation of Nrf2 could affect antioxidant activity of,proliferative activity of and tyrosinase activity in melanocytes.TBHQ may enhance the tyrosinase activity in,proliferative activity and antioxidant activity of melanocytes via activating the nuclear expression of wild type Nrf2. Key words: Melanocytes; E2p45 related factor 2; Nuclear translocation; Monophenol monooxygenase

Impact of Sunscreens on Preventing UVR-Induced Effects in Nevi

Sun damage is the most important environmental factor associated with malignant melanoma. To address the health threat, as well as the economic burden, primary prevention and early detection are crucial. To test the efficacy of a topical sunscreen in the prevention of UV-induced effects in nevi. Prospective study of nevi protected by sunscreen vs a physical barrier. Twenty-three nevi from 20 patients attending a referral hospital. Half of each nevus was protected by either a physical barrier or a sunscreen. Lesions were completely irradiated by a single dose of UV-B. In vivo examination before and 7 days after irradiation and histopathologic-immunopathologic evaluation after excision on the seventh day. The most frequent clinical changes after UV radiation were pigmentation, scaling, and erythema; the most frequent dermoscopic changes were increased globules/dots, blurred network, regression, and dotted vessels. Both physical barrier- and sunscreen-protected areas showed some degree of these changes. More than 30% (7) of nevi did not show any change on clinical examination, and 18% (4) had no dermoscopic change. Immunohistopathologic differences between the halves of each nevus were demonstrable even when in vivo examination detected nothing. Parakeratotic scale, increased number and activation of superficial melanocytes, and keratinocyte proliferation were the most remarkable features. The only difference between both barriers was more enhanced melanocytic activation and regression features in the sunscreen group. No phenotypic features were found to predict a specific UV-B response. Both physical barriers and sunscreens can partially prevent UV-B effects on nevi. Subclinical UV radiation effects, not always associated with visible changes, can develop even after protection. Sunscreens are not quite as effective as physical barriers in the prevention of inflammatory UV-B-induced effects.

Tobacco smoke–induced skin pigmentation is mediated by the aryl hydrocarbon receptor

It is widely recognized that tobacco smoke causes skin pigmentation. No studies, however, have directly evaluated the mechanisms of the changes in smoker's skin pigmentation. In this study, when cultured with water-soluble tobacco smoke extract, the human epidermal melanocytes grew to a large size and produced more melanins. We evaluated melanocyte activation by quantifying microphthalmia-associated transcription factor (MITF) expression by real-time polymerase chain reaction. MITF expression was significantly and dose-dependently increased by exposure to tobacco smoke extract. The Wnt/β-catenin signalling pathway seemed to mediate the tobacco smoke extract-induced melanocyte activation. Immunocytochemical studies revealed that the activated melanocytes actively expressed aryl hydrocarbon receptors (AhR) around the nuclear membrane. The tobacco smoke extract-induced MITF activation was inhibited by RNA silencing of the AhR. This study provides the evidence that tobacco smoke enhances pigmentation in vitro and that the increase in pigmentation may involve β-catenin- and AhR-mediated mechanisms inside human melanocytes.

A regulator of ubiquitin-proteasome activity, 2-hexyldecanol, suppresses melanin synthesis and the appearance of facial hyperpigmented spots

2-Hexyldecanol has long been used in skin-care products, but has not previously been reported as an active ingredient for skin benefits. To evaluate 2-hexyldecanol in in vitro and ex vivo systems and, if found to be active, progress it to topical clinical testing to determine effects on pigmentation in skin. 2-Hexyldecanol was tested in melanocyte cell culture systems (B16 mouse melanoma cells and normal human melanocytes) for its effect on proteolytic activity and melanin production, in the absence and presence of the proteasome-specific inhibitor, MG132. It was further tested in a human skin explant model for its effect on melanin production. Lastly, topically applied 2-hexyldecanol was evaluated for its effect on the appearance of facial pigmentation in an 8-week, randomized, double-blind, vehicle-controlled, split-face incomplete block design study in Chinese women. In submerged cell culture, 2-hexyldecanol upregulated proteolytic activity and decreased melanin synthesis. These effects were antagonized by the proteasome-specific inhibitor MG132. MG132, tested in the absence of 2-hexyldecanol, increased melanin production. In a human skin explant model, topical 2-hexyldecanol suppressed the production of melanin vs. a vehicle control. In a human clinical study in Chinese women (n = 110 observations per test material), a 2-hexyldecanol-containing formulation significantly reduced the appearance of facial hyperpigmented spots vs. its control. These data indicate that regulation of proteasome activity is a viable target for control of melanin production, that 2-hexyldecanol upregulates proteasomal activity in melanocytes, and that topical 2-hexyldecanol reduces the appearance of hyperpigmentation.

Comparison of Surgical Stripping; Erbium‐Doped:Yttrium, Aluminum, and Garnet Laser; and Carbon Dioxide Laser Techniques for Gingival Depigmentation: A Clinical and Histologic Study

Gingival melanin depigmentation procedures are commonly associated with recurrence of pigmentation, which starts with migration of melanocytes from the adjacent free gingiva. The extent and rate of recurrence varies according to the treatment modalities used and duration of follow-up. The aim of this study is to compare the surgical stripping; carbon dioxide (CO2); and erbium-doped:yttrium, aluminum, and garnet (Er:YAG) laser techniques for gingival depigmentation and to evaluate their effect on histologic changes in melanocyte activity and clinical repigmentation. In this study, 140 sites from 35 patients with bilateral melanin hyperpigmentation were treated with surgical stripping (two sites per patient), "epithelial-peel" (CO2 laser, 2 to 4 W, continuous wave),and "brushstroke" (Er:YAG laser, 180 mJ, 10 Hz, long pulse) techniques. Surgical microscope monitoring was performed intraoperatively. Patient preference and perception of pain, change in Dummett oral pigmentation index (DOPI), Hedin index, and change in area of pigmentation from baseline to 6 months postoperatively were recorded. Twenty samples each from the three treatment modalities were selected for histologic analysis using hematoxylin and eosin and dihydroxyphenylalanine oxidase special stains. At the 6-month postoperative visit, 15 of 70 (21.4%) and three of 20 (15%) of the surgical-treated; 10 of 35 (28.6%) and six of 20 (30%) of the Er:YAG-laser-treated; and eight of 35 (22.8%) and four of 20 (20%) of the CO2-laser-treated sites showed clinical and histologic repigmentation, respectively. Paired t test, analysis of variance, and χ(2) tests were used for statistical analyses. P values for comparison of microscopic evaluation, change in DOPI, Hedin index, and area of pigmentation were 0.001, which were statistically significant. Comparison for patient preference and pain indices gave statistically significant values for Er:YAG laser depigmentation (P = 0.001). Clinical repigmentation after gingival depigmentation is an outcome of histologic changes in the melanocyte activity and density of the melanin pigments. Surgical stripping for gingival depigmentation remains the gold standard; however, Er:YAG laser and CO2 lasers can be effectively used but with distinct differences.

Paracrine cytokine mechanisms underlying the hyperpigmentation of seborrheic keratosis in covered skin areas

We previously reported that increased expression of the endothelin (EDN)1/EDNB receptor (EDNBR) as well as the stem cell factor (SCF)/SCF receptor (c-KIT) linkages is mainly responsible for the activation of melanocytes in the epidermal hyperpigmentation of ultraviolet (UV)-B melanosis and lentigo senilis (LS). In this study, we characterized seborrheic keratosis (SK) to examine the paracrine cytokine mechanism(s) involved in its epidermal hyperpigmentation by reverse transcription polymerase chain reaction, immunohistochemistry and western blotting analyses. In contrast to our previous study which showed the upregulated expression of EDN1 and EDNBR at the transcriptional and translational levels in the epidermis of SK, we observed unexpectedly that the cytokine SCF and its receptor c-KIT are not upregulated, but are downregulated at both the gene and protein levels. We established SK cell lines to examine whether SK basaloid cells are less sensitive to SCF-inducible stimulation than are normal human keratinocytes (NHK). Comparison of the stimulatory effects of interleukin (IL)-1α or tumor necrosis factor (TNF)-α on SCF production between SK cells and NHK demonstrated that SK cells do not respond to IL-1α or TNF-α to stimulate production of SCF, whereas a significant stimulation of SCF is elicited by those same cytokines in NHK. These finding underscore a role of phenotypic changes in melanogenic cytokine production in the epidermis between SK and LS/UV-B melanosis.

Antioxidant and Antityrosinase Activity of Cissus quadrangularis Extract

The effects of Cissus quadrangularis Linn. extract on antioxidation and tyrosinase inhibition were investigated. The extract showed anti-oxidative activity with an IC50 value of 522.0 μg/mL, and inhibitory effects on tyrosinase activity and melanin production in B16 melanocytes in a dose-dependent manner (100-2000 μg/mL). This study suggests that this species contains anti-tyrosinase components.

Abstract 1516: Melanocyte activation by UVR-induced calprotectin.

Abstract Melanoma is the most common cause of skin cancer death, although it accounts for only 5% of all skin cancers. Epidemiologic and clinical observations have shown that the ultraviolet (UVR) component of sunlight is the most important etiologic factor in melanoma; however, the precise mechanisms by which UVR drives melanomagenesis are unknown. Mutations in oncogenes and tumor suppressor genes have been identified in melanomas, but most of these are not the UVR signature mutations found in non-melanoma skin cancers. This suggests an indirect role for UVR in melanomagenesis, likely as a tumor promoter. UVR is a potent inducer of keratinocyte-derived paracrine and melanocyte/melanoma cell-derived autocrine factors that profoundly affect melanocyte/melanoma cell gene expression and behavior. Many of these mediators are also potent proinflammatory signals that create an inflammatory environment with additional effects on untransformed and transformed melanocytes. We have identified calprotectin, a secreted heterodimer of S100A8 and A9, as one of these mediators. UVR exposure induces S100A8 and A9 transcription in and calprotectin release from human keratinocytes and melanocytes. Human melanocytes and melanoma cells constitutively express TLR4, one of the receptors for calprotectin. Treatment of human melanocytes and melanoma cells with exogenous calprotectin enhances their proliferation, migration, and invasiveness. UVR-induced calprotectin secretion by melanocytes/melanoma cells and surrounding keratinocytes activates melanocytes/melanoma cells and may thus promote melanomagenesis. Citation Format: Kristine von Maltzan, Stephanie H. Shirley, Donna F. Kusewitt. Melanocyte activation by UVR-induced calprotectin. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1516. doi:10.1158/1538-7445.AM2013-1516

The melanocyte photosensory system in the human skin

The pigment cells form the largest population of neural crest cells to migrate into the epidermis and hair follicle along each dermatomic area from the neural folds. The melanopsin system responsible for photoentrainment, was isolated from the photosensitive dermal melanophores of frogs Xenopus laevis responding to light. Melanocytes form a photoresponsive network which reads the environmental seasonal variations in the light cycles in the same manner. The present work was undertaken to study the organization of this system by: I. Experimental assessment of photoresponse and II. Evidence of an organized system of photoreception in the skin. Melanocytes, in whole skin organ cultures and epidermal strips, from margin of vitiligo in G2 phase show prominent dendricity, and express pigment, biogenic amines and hormones on UV exposure. The photoresponse depends on the photosensitive enzymes NAT/HIOMT and dopaoxidase. Melanocytes interact with adjacent keratinocytes, dermal capillaries, and nerve endings. The melanocyte network reads the diurnal and seasonal photophase by the melatonin/serotonin switch like the pineal. Sleep disorders and winter depression are corrected by phototherapy utilising this mechanism. Melanocytes showing photoactivity, aplasia, hypoplasia and hyperplasia, and interactive keratinocytes occupy the trigeminal, brachial and lumbosacral dermatomes, zones of high embryonic induction, forming an ectodermal placodal system. Melanin units and hair follicles serve as photoreceptors. Migration of active melanocytes to defined areas is evident in pigment patterns in guinea pigs. This study identifies defined photoreceptor melanocyte/epidermal domains which read the seasonal photophase and control the sleep waking cycle in response to the environmental light. I. Whole skin organ cultures, and epidermal strips from margin of vitiligo in G2 phase are exposed to UV and IR to study sequential and dose response of marginal melanocytes, using histochemistry, immunohistochemistry to assess pigment, biogenic amines and hormones on UV exposure. II. Dermatomic Distributions: Detailed maps of melanocyte photoresponse in 356 biopsies, lesions in 297 vitiligo, 100 melanosis, 165 melanomas 142 leprosy and 442 basal cell/keratinocytes lesions were assessed for patterns of dermatomic distribution. Embryonal melanocyte migration along dermatomes was assessed in 285 guinea pigs from an inbred colony having black, brown and white patches.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-2-158) contains supplementary material, which is available to authorized users.

Putative role of HIF transcriptional activity in melanocytes and melanoma biology

Hypoxia-inducible factor-1α (HIF-1α) is a highly oxygen sensitive bHLH protein that is part of the heterodimeric HIF-1 transcription factor. Under hypoxic stress, HIF-1 activity is induced to control expression of multiple downstream target genes, including vascular endothelial growth factor (VEGF). The normal epidermis exists in a constant mild hypoxic microenvironment and constitutively expresses HIF-1α and HIF-2α. Expression of HIF-1α and/or HIF-2α has been suggested to correlate with the increased malignant potential of melanocytes, therefore, failures of melanoma therapies may be partially linked to high HIF activity. Notably, melanomas that have the V600E BRAF mutation exhibit increased HIF-1α expression. We have utilized a bioinformatics approach to identify putative hypoxia response elements (HREs) in a set of genes known to participate in the process of melanogenesis (includingTRPM1, SLC45A2, HRAS, C-KIT, PMEL and CRH). While some of the mechanistic links between these genes and the HIF pathway have been previously explored, others await further investigation. Although agents targeting HIF activity have been proposed as novel treatment modalities for melanoma, there are currently no clinical trials in progress to test their efficacy in melanoma.

Metabotropic glutamate receptor 6 signaling enhances TRPM1 calcium channel function and increases melanin content in human melanocytes

Mutations in TRPM1, a calcium channel expressed in retinal bipolar cells and epidermal melanocytes, cause complete congenital stationary night blindness with no discernible skin phenotype. In the retina, TRPM1 activity is negatively coupled to metabotropic glutamate receptor 6 (mGluR6) signaling through Gαo and TRPM1 mutations result in the loss of responsiveness of TRPM1 to mGluR6 signaling. Here, we show that human melanocytes express mGluR6, and treatment of melanocytes with L-AP4, a type III mGluR-selective agonist, enhances Ca(2+) uptake. Knockdown of TRPM1 or mGluR6 by shRNA abolished L-AP4-induced Ca(2+) influx and TRPM1 currents, showing that TRPM1 activity in melanocytes is positively coupled to mGluR6 signaling. Gαo protein is absent in melanocytes. However, forced expression of Gαo restored negative coupling of TRPM1 to mGluR6 signaling, but treatment with pertussis toxin, an inhibitor of Gi /Go proteins, did not affect basal or mGluR6-induced Ca(2+) uptake. Additionally, chronic stimulation of mGluR6 altered melanocyte morphology and increased melanin content. These data suggest differences in coupling of TRPM1 function to mGluR6 signaling explain different cellular responses to glutamate in the retina and the skin.

Photoprotective and antioxidant effects of Rhubarb: inhibitory action on tyrosinase and tyrosine kinase activities and TNF-α, IL-1α and α-MSH production in human melanocytes

BackgroundExposure to ultraviolet (UV) radiation causes various forms of acute and chronic skin damage, including immunosuppression, inflammation, premature aging and photodamage. Furthermore, it induces the generation of reactive oxygen species, produces proinflammatory cytokines and melanocyte-stimulating hormone (MSH) and increases tyrosinase activity. The aim of this study was to evaluate the potential photoprotective effects of Rheum rhaponticum L. rhizome extract on human UV-stimulated melanocytes.MethodsThe effects of Rheum rhaponticum rhizome extract on tyrosine kinase activity, and on interleukin-1α (IL-1α), tumour necrosis factor α (TNF-α), and α-MSH production in human epidermal melanocytes were evaluated under UV-stimulated and non-stimulated conditions. Antioxidant activity was evaluated by lipid peroxidation and 1,1-dyphenyl-2-picryl-hydrazyl (DPPH) assays, while anti-tyrosinase activity was evaluated by the mushroom tyrosinase method.ResultsRheum rhaponticum L. rhizome extract showed in vitro antioxidant properties against lipid peroxidation, free radical scavenging and anti-tyrosinase activities, and inhibited the production of IL-1α, TNF-α, α-MSH, and tyrosine kinase activity in melanocytes subjected to UV radiation.ConclusionsThese results support the inclusion of Rheum rhaponticum L. rhizome extract into cosmetic, sunscreen and skin care products for the prevention or reduction of photodamage.

Endothelin‐1 is a transcriptional target of p53 in epidermal keratinocytes and regulates ultraviolet‐induced melanocyte homeostasis

Keratinocytes contribute to melanocyte activity by influencing their microenvironment, in part, through secretion of paracrine factors. Here, we discovered that p53 directly regulates Edn1 expression in epidermal keratinocytes and controls UV-induced melanocyte homeostasis. Selective ablation of endothelin-1 (EDN1) in murine epidermis (EDN1(ep-/-) ) does not alter melanocyte homeostasis in newborn skin but decreases dermal melanocytes in adult skin. Results showed that keratinocytic EDN1 in a non-cell autonomous manner controls melanocyte proliferation, migration, DNA damage, and apoptosis after ultraviolet B (UVB) irradiation. Expression of other keratinocyte-derived paracrine factors did not compensate for the loss of EDN1. Topical treatment with EDN1 receptor (EDNRB) antagonist BQ788 abrogated UV-induced melanocyte activation and recapitulated the phenotype seen in EDN1(ep-/-) mice. Altogether, the present studies establish an essential role of EDN1 in epidermal keratinocytes to mediate UV-induced melanocyte homeostasis in vivo.

Premature graying of hair

Premature graying is an important cause of low self-esteem, often interfering with socio-cultural adjustment. The onset and progression of graying or canities correlate very closely with chronological aging, and occur in varying degrees in all individuals eventually, regardless of gender or race. Premature canities may occur alone as an autosomal dominant condition or in association with various autoimmune or premature aging syndromes. It needs to be differentiated from various genetic hypomelanotic hair disorders. Reduction in melanogenically active melanocytes in the hair bulb of gray anagen hair follicles with resultant pigment loss is central to the pathogenesis of graying. Defective melanosomal transfers to cortical keratinocytes and melanin incontinence due to melanocyte degeneration are also believed to contribute to this. The white color of canities is an optical effect; the reflection of incident light masks the intrinsic pale yellow color of hair keratin. Full range of color from normal to white can be seen both along individual hair and from hair to hair, and admixture of pigmented and white hair is believed to give the appearance of gray. Graying of hair is usually progressive and permanent, but there are occasional reports of spontaneous repigmentation of gray hair. Studies evaluating the association of canities with osteopenia and cardiovascular disease have revealed mixed results. Despite the extensive molecular research being carried out to understand the pathogenesis of canities, there is paucity of effective evidence-based treatment options. Reports of repigmentation of previously white hair following certain inflammatory processes and use of drugs have suggested the possibility of cytokine-induced recruitment of outer sheath melanocytes to the hair bulb and rekindled the hope for finding an effective drug for treatment of premature canities. In the end, camouflage techniques using hair colorants are outlined.

Effects of lactic acid bacteria-fermented soy milk on melanogenesis in B16F0 melanocytes

In our previous studies, soy milk fermented with lactic acid bacteria (LAB) was found to improve the nutritional and bioactivity values of consumed foods. In this study, we used soy milk fermented with LAB strains to evaluate the effects of LAB-fermented soy milk on melanogenesis. It was found that β-glucosidase-producing LAB strains exhibited a higher degree of β-glucosidase activity and significantly higher aglycone isoflavone content (p<0.05). The extracts from Lactobacillus plantarum TWK10 (TWK10)-fermented soy milk inhibited mushroom tyrosinase activity and melanin production in B16F0 melanocytes more strongly compared to non-fermented and other LAB strains-fermented soy milk. TWK10-fermented soy milk also suppressed the activity and expression of tyrosinase, microphthalmia-associated transcription factor (MITF), and p38 mitogen-activated protein kinase (MAPK). Extracellular regulated kinase activation and MITF degradation were not affected by this pathway. Thus, TWK10-fermented soy milk inhibits melanogenesis by suppressing tyrosinase activity and expression through the positive regulator, MITF, and p38 MAPK inactivation. These results may be used to develop health foods and cosmetics, and to increase the range of applications of traditional agricultural products.

Interleukin-18 augments growth ability of primary human melanocytes by PTEN inactivation through the AKT/NF-κB pathway

Normal human skin relies on melanocytes to provide photoprotection and thermoregulation by producing melanin. The growth and behavior of melanocytes are controlled by many factors. Interleukin-18 (IL-18) is expressed in both immune and non-immune cells and participates in the adjustment of multitude cellular functions. Nonetheless, the regulative roles of IL-18 in melanogenesis and growth of melanocytes have not been explored. The present study was conducted to investigate the effects of IL-18 on melanocytes and elucidate the underlying mechanisms. We proved that IL-18 increased the tyrosinase activity and melanin content in normal human foreskin-derived epidermal melanocytes (NHEM). Treatment with IL-18 (20ng/ml) enhanced the expression of c-Kit, microphtalmia-associated transcription factor (MITF) and its downstream tyrosinase-related protein 1 (TRP-1), and TRP-2. In addition, IL-18 induced NHEM migration at concentration of 20ng/ml. These results indicated a promotive action of IL-18 on melanogenesis in NHEM. Our data revealed that IL-18 stimulated ERK1/2 and NF-κB activation, improved p-Akt, p70 S6K and anti-apoptotic Bcl-2 levels, and deactivated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in NHEM. Besides, IL-18 increased level of PTEN phosphorylation to protect NHEM from damage induced by H2O2. These results in vitro showed the accommodation of IL-18 in melanocytes growth. Therefore, we suggested an important regulating action of IL-18 to melanogenesis and cell growth ability of skin melanocytes.

The neural guidance receptor Plexin C1 delays melanoma progression

Plexin C1 is a type I transmembrane receptor with intrinsic R-Ras GTPase activity, which regulates cytoskeletal remodeling and adhesion in normal human melanocytes. Melanocytes are pigment-producing cells of the epidermis, precursors for melanoma, and express high levels of Plexin C1, which is lost in melanoma in vitro and in vivo. To determine if Plexin C1 is a tumor suppressor for melanoma, we introduced Plexin C1 into a primary human melanoma cell line, and phenotypes including migration, apoptosis, proliferation and tumor growth in mice were analyzed. Complimentary studies in which Plexin C1 was silenced in human melanocytes were performed. Plexin C1 significantly inhibited migration and proliferation in melanoma, whereas in melanocytes, loss of Plexin C1 increased migration and proliferation. In mouse xenografts, Plexin C1 delayed tumor growth of melanoma at early time points, but tumors eventually escaped the suppressive effects of Plexin C1, due to Plexin C1-dependent activation of the pro-survival protein Akt. R-Ras activation stimulates melanoma migration. Plexin C1 lowered R-Ras activity in melanoma and melanocytes, consistent with inhibitory effects of Plexin C1 on migration of melanocytes and melanoma. To determine if R-Ras is expressed in melanocytic lesions in vivo, staining of tissue microarrays of nevi and melanoma were performed. R-Ras expression was highly limited in melanocytic lesions, being essentially confined to primary melanoma, and almost completely absent in nevi and metastatic melanoma. These data suggest that loss of Plexin C1 in melanoma may promote early steps in melanoma progression through suppression of migration and proliferation, but pro-survival effects of Plexin C1 ultimately abrogate the tumor suppressive effects of Plexin C1. In primary melanoma, loss of Plexin C1 may function in early steps of melanoma progression by releasing inhibition of R-Ras activation, and stimulating migration.

Reduced Proliferative and Differentiative Activity of Mouse Pink-Eyed Dilution Melanoblasts is Related to Apoptosis

The mouse pink-eyed dilution (p) locus is known to control the melanin content, melanosome morphology, and tyrosinase activity in melanocytes. However, it is not well known whether the p allele is involved in regulating melanocyte proliferation, differentiation, and death. The aim of this study is to investigate in detail the role of the p allele in melanocyte proliferation, differentiation, and death using a cell culture system. The epidermal cell suspensions of the neonatal dorsal skin derived from wild type mice at the p locus (black, C57BL/10JHir-P/P) and their congenic mutant (pink-eyed dilution, C57BL/10JHir-p/p) were cultured with serum-free melanoblast-proliferation medium (MDMDF) and melanocyte-proliferation medium (MDMD). The proliferation and differentiation of p/p melanoblasts in MDMDF or MDMD were greatly inhibited compared with those of P/P melanoblasts and melanocytes. It is possible that apoptosis is related to the reduced proliferative and differentiative activity of p/p melanoblasts/melanocytes. The addition of apoptosis-inhibitors, such as caspase-9 inhibitor (C9I) and Bax-inhibiting peptide (BIP) into MDMDF or MDMD stimulated the proliferation and differentiation of p/p melanoblasts. In contrast, in P/P melanoblasts and melanocytes, C9I and BIP failed to stimulate their proliferation and differentiation. The number of apoptotic keratinocytes and melanoblasts/melanocytes in p/p mice was greater than in P/P mice. Moreover, expression of C9 and Bax in keratinocytes and melanoblasts/melanocytes in p/p mice was greater than in P/P mice. These results suggest that the increased apoptosis in keratinocytes and melanoblasts/melanocytes is related to the reduced proliferative and differentiative activity of p/p melanoblasts.

Melasma: the imbalance between epidermal barrier and melanin barrier

Melasma is an acquired skin disease characterized by facial hyperpigmentation of unclear pathogenesis.This paper describes the changes of epidermal barrier,melanin barrier and dermal blood vessels in melasma.On this basis,the pathogenesis of melasma is speculated to be associated with ultraviolet,cosmetics,contraceptives and other adverse stimuli,which cause epidermal barrier dysfunction,lead to a compensatory increase in melanocyte activity and melanin barrier followed by the occurrence of diseases characterized by skin pigmentation.Moreover,dermal telangiectasis is induced and vascular endothelial growth factor expression is enhanced,which accelerate skin pigmentation accordingly. Key words: Chloasma; Epidermal barrier; Melanocytes