Regulation of melanocyte pivotal transcription factor MITF by some other transcription factors

Molecular characterization of transcription factor CREB3L2 and CREB3L3 and their role in melanogenesis in Pacific oysters (Crassostrea gigas)

Colorful shells in mollusks are commonly attributable to the presence of biological pigments. In Pacific oysters, the inheritance patterns of several shell colors have been investigated, but little is known about the molecular mechanisms of melanogenesis and pigmentation. cAMP-response element binding proteins (CREB) are important transcription factors in the cAMP-mediated melanogenesis pathway. In this study, we characterized two CREB genes (CREB3L2 and CREB3L3) from Pacific oysters. Both of them contained a conserved DNA-binding and dimerization domain (a basic-leucine zipper domain). CREB3L2 and CREB3L3 were expressed highly in the mantle tissues and exhibited higher expression levels in the black-shell oyster than in the white. Masson-Fontana melanin staining and immunofluorescence analysis showed that the location of CREB3L2 protein was generally consistent with the distribution of melanin in oyster edge mantle. Dual-luciferase reporter assays revealed that CREB3L2 and CREB3L3 could activate the microphthalmia-associated transcription factor (MITF) promoter and this process was regulated by the level of cAMP. Additionally, we found that cAMP regulated melanogenic gene expression through the CREB-MITF-TYR axis. These results implied that CREB3L2 and CREB3L3 play important roles in melanin synthesis and pigmentation in Pacific oysters.

The relationship of MITF gene expression and promoter methylation with plumage colour in quail

1. This study focused on the relationship between MITF mRNA expression and plumage colour in quail and the effect of promoter methylation on the expression of MITF mRNA.2. The CDS region of MITF mRNA was cloned by RT-PCR, followed by DNA sequencing. The RT-qPCR method was used to analyse the expression levels of MITF mRNA in dorsal skin tissue in Korean quail and Beijing white quail. The promoter region of the MITF gene was cloned, and the CpG island was predicted by the CpGplot program. The methylation levels of the CpG island were analysed using BS-PCR technology.3. Quail MITF mRNA contains a 1,476 bp complete ORF, which encodes a 492 amino acid residue protein. The MITF protein has no signal peptide or transmembrane region. The expression of MITF mRNA in dorsal tissue of Korean quail was significantly higher than that in Beijing white quail (p < 0.01). Abundant cis-elements and a 346 bp CpG island were found in the promoter region of the MITF gene. The average methylation level of the CpG island was 22 (22%) in Korean quail, and 46 (30%) in Beijing white quail (p < 0.05).4. The hypermethylation of the MITF gene promoter region in Beijing white quail resulted in a decrease in expression level, which was related to white feather colour.

cAMP-Mediated CREM-MITF-TYR Axis Regulates Melanin Synthesis in Pacific Oysters

Colorful shells in bivalves are mostly caused by the presence of biological pigments, among which melanin is a key component in the formation of shell colours. Cyclic adenosine monophosphate (cAMP) is an important messenger in the regulation of pigmentation in some species. However, the role of cAMP in bivalve melanogenesis has not yet been reported. In this study, we performed in vitro and in vivo experiments to determine the role of cAMP in regulating melanogenesis in Pacific oysters. Besides, the function of cAMP-responsive element modulator (CREM) and the interactions between CREM and melanogenic genes were investigated. Our results showed that a high level of cAMP promotes the expression of melanogenic genes in Pacific oysters. CREM controls the expression of the MITF gene under cAMP regulation. In addition, CREM can regulate melanogenic gene expression, tyrosine metabolism, and melanin synthesis. These results indicate that cAMP plays an important role in the regulation of melanogenesis in Pacific oysters. CREM is a key transcription factor in the oyster melanin synthesis pathway, which plays a crucial role in oyster melanin synthesis through a cAMP-mediated CREM-MITF-TYR axis.

The whitening effect of cuscutin responsible for traditional use of Bergenia purpurascens

ETHNOPHARMACOLOGICAL RELEVANCE

The roots and rhizomes of Bergenia purpurascens (Hook. f. et Thomson) Engl., was used as a sunscreen to protect against ultraviolet rays in Tibet of China historically, but its skin whitening constituents and pharmacological effects of this plant remained unknown.

AIM OF THE STUDY

To investigate the anti-melanogenesis effect of B. purpurascens in vitro and in vivo, and then explore the preliminary mechanism.

MATERIALS AND METHODS

An ultraviolet B (UVB)-induced skin injury model of mice was used to verify the ameliorative effect of B. purpurascens extract (BPE) on ultraviolet damage. Then, alpha-melanocyte stimulating hormone (α-MSH)-induced murine melanoma cell line (B16F10) melanin generation model was further adopted to approval the effects of BPE and its bioactive compound, cuscutin, in vitro. Moreover, α-MSH stimulated melanogenesis model in zebrafish was employed to confirm the anti-pigmentation effect of cuscutin. Then, proteins expressions associated with melanin production were observed using western blotting assay to explore preliminary mechanism.

RESULTS

BPE inhibited UVB-induced mice injury and restored skin barrier function observably in vivo. BPE and cuscutin suppressed the overproduction of melanin in α-MSH induced B16F10 significantly, in which cuscutin exhibited better effect than well-known whitening agent α-arbutin at same 10 μg/mL concentration. Moreover, the pigmentation of zebrafish embryo was decreased by cuscutin. Finally, cuscutin showed significant downregulation of expressions of tyrosinase (TYR) and tyrosinase related protein-1 (TRP-1), TRP-2 and microphthalmia-associated transcription factor (MITF) in the melanogenic signaling pathway.

CONCLUSION

B. purpurascens extract and its major bioactive constituent, cuscutin, showed potent anti-melanogenesis and skin-whitening effect by targeting TYR and TRP-2 proteins for the first time, which supported its traditional use.

Human Mesenchymal Stem Cell-Derived Exosomes Promote the Proliferation and Melanogenesis of Primary Melanocytes by Attenuating the H2O2-Related Cytotoxicity in vitro

Background

Mesenchymal stem cell-derived exosomes (MSC-Exo) have therapeutic potential. However, the impact of MSC-Exo on the survival and melanogenesis of human primary melanocytes following H2O2-induced damage has not been clarified. We therefore investigated the effects of MSC-Exo on the H2O2-affected survival of human primary melanocytes and their proliferation, apoptosis, senescence, and melanogenesis in vitro.

Methods

MSC-Exo were prepared from human MSCs by sequential centrifugations and characterized by Transmission Electron Microscopy, Western blot and Nanoparticle Tracking Analysis. Human primary melanocytes were isolated and treated with different concentrations of MSC-Exo, followed by exposing to H2O2. Furthermore, the impact of pretreatment with MSC-Exo on the proliferation, apoptosis, senescence and melanogenesis of melanocytes were tested by CCK-8, flow cytometry, Western blot, L-Dopa staining, tyrosinase activity and RT-qPCR.

Results

Pretreatment with lower doses of MSC-Exo protected human primary melanocytes from the H2O2-triggered apoptosis, while pretreatment with higher doses of MSC-Exo enhanced the H2O2-induced melanocyte apoptosis. Compared with the untreated control, pretreatment with a lower dose (1 µg/mL) of MSC-Exo enhanced the proliferation of melanocytes, abrogated the H2O2-increased p53, p21, IL-1β, IL-6 and IL-8 expression and partially rescued the H2O2-decreased L-dopa staining reaction, tyrosinase activity, MITF and TRP1 expression in melanocytes.

Conclusion

Our findings indicate that treatment with a low dose of MSC-Exo promotes the proliferation and melanogenesis of human primary melanocytes by ameliorating the H2O2-induced apoptosis and senescence of melanocytes. MSC-Exo may be a promising therapeutic strategy of vitiligo.

Istradefylline modulates purinergic enzymes and reduces malignancy-associated factors in B16F10 melanoma cells

ATP and adenosine exert pivotal roles in the development, maintenance, and metastatic spreading of melanoma. The action of such key melanoma tumor microenvironment (TME) constituents might be complementary or opposed, and their effects are not exclusive to immune cells but also to other host cells and tumor cells. The effects of ATP are controlled by the axis CD39/73, resulting in adenosine, the main actor in the TME, and A2A is the crucial mediator of its effects. We evaluated ATP and adenosine signaling through A2A on B16F10 melanoma cells using istradefylline (IST) (antiparkinsonian A2A antagonist) and caffeine (CAF) treatments after exposure to ATP and adenosine. Adenosine increased melanoma cell viability and proliferation in a concentration-dependent manner. ATP increases viability only as a substrate by CD39 to produce adenosine. Both IST and CAF are toxic to B16F10 cells, but only IST potentialized paclitaxel-induced cytotoxic effects, even decreasing its IC50 value. IST positively modulated CD39 and CD73 expression. CD39 activity was increased, and E-ADA was reduced, indicating that the melanoma cells promoted compensatory feedback in the production and maintenance of adenosine levels. A2A antagonism by IST reduced the factors associated with malignancy, like migration, adhesion, colony formation, and the capacity to produce melanin. Moreover, IST significantly increases nitric oxide (NO) production, which correlates to a decline in melanoma cell viability by apoptotic events. Altogether, our results suggest that adenosine signaling through A2A is essential for B16F10 cells, and its inhibition by IST causes compensatory purinergic enzymatic modulations. Furthermore, IST is a promising therapy that provides new ways to improve current melanoma treatments.

The potential role of ubiquitination and deubiquitination in melanogenesis

Melanogenesis is a critical biochemical process in which melanocytes produce melanin, a crucial element involved in the formation of coat colour in mammals. According to several earlier studies, melanocytes' post-translational modifications of proteins primarily control melanogenesis. Among the many post-translational changes that can affect melanin production, ubiquitination and deubiquitination can keep melanin production going by changing how proteins that are related to melanin are broken down or kept stable. Ubiquitination and deubiquitination maintain ubiquitin homeostasis, which is a highly dynamic process in balance under the action of E3 ubiquitin ligase and deubiquitinating enzymes. However, the regulatory mechanisms underlying ubiquitination and deubiquitination in melanogenesis are yet to be thoroughly investigated. As a result, there has been a growing focus on exploring the potential correlation between melanogenesis, ubiquitination and deubiquitination. This study discusses the mechanisms of ubiquitination and deubiquitination in the context of melanogenesis, a crucial process for enhancing mammalian coat coloration and addressing pigment-related diseases.

Green in situ immobilisation of gold nanoparticles on bacterial nanocellulose membranes using Tannic acid and its detection of Fe3

Oxidative stress is one of the factors that promote melanogenesis. Trivalent iron ions play a key role in regulating the iron-catalysed oxidative stress response. A novel SERS flexible membrane sensor based on tannic acid with good sensitivity and uniformity was prepared by green in situ reduction of gold nanoparticles on bacterial cellulose membrane（BCM）with a simple and highly selective method to detect Fe3+. Under alkaline conditions, Fe3+ is adsorbed on the BCM-TA@Au NPs flexible membrane by tannic acid (TA) through chelation, thus enabling the detection of Fe3+. Furthermore, this simple detection system has a wide linear detection range and high sensitivity to effortlessly evaluate Fe3+ at concentrations up to 10-7 M. More importantly, the proposed SERS flexible substrate performed well in determining Fe3+ concentrations in B16 melanocytes, providing new insights into the factors affecting the melanin synthesis pathway and providing a potential biomarker for melanoma treatment.

Creb2 involved in innate immunity by activating PpMitf-mediated melanogenesis in Pteria penguin

cAMP response element binding protein 2 (CREB2) acts as an intracellular transcriptional factor and regulates many physiological processes, including melanogenesis and melanocyte differentiation. In our previous research, the Creb2 gene has been characterized from Pteria penguin (P. penguin), but its role and regulatory mechanism in P. penguin are still unclear. In this study, first, the function of PpCreb2 in melanogenesis and innate immunity were identified. PpCreb2 silencing significantly decreased the tyrosinase activity and melanin content, indicating PpCreb2 played an important role in melanogenesis. Meanwhile, PpCreb2 silencing visibly suppressed the antibacterial activity of hemolymph supernatant, indicating that PpCreb2 was involved in innate immunity of P. penguin. Second, the PpCreb2 was confirmed to perform immune function by regulating the melanogenesis. The decreased melanin oxidation product due to PpCreb2 silencing triggered the declining of antibacterial activity of hemolymph supernatant, which then could be rescued by adding exogenous melanin oxidation products. Third, the regulation pathway of PpCreb2 involved in innate immunity was analyzed. The promoter sequence analysis of PpMitf discovered 5 conserved cAMP response element (CRE), which were specifically recognized by basic Leucine zipper domain (bZIP) of upstream activation transcription factor. The luciferase activities analysis showed that PpCreb2 could activate the CRE in PpMitf promoter via highly conserved bZIP domain and regulate the expression of PpMitf, which further regulated the PpTyr expression. Therefore, the results collectively demonstrated that PpCreb2 participated in innate immunity by activating PpMitf-mediated melanogenesis in P. penguin.

The ubiquitin-proteasome system in melanin metabolism

BACKGROUND

The ubiquitin-proteasome system (UPS) is a highly conserved way of regulating intracellular protein balance. UPS mediates proteolysis and disruption of variation or misfolding, while finely regulating proteins involved in differentiation and other biological processes.

AIMS

The aim of this review is to systematically introduce UPS as a key regulator of melanin metabolism.

METHODS

Systematic search and retrospective review were performed on the published data.

RESULTS

Melanocyte-inducing transcription factor (MITF) is a substrate of the ubiquitin ligase VCHL1 and acts as a transcription factor to regulate the expression of key enzymes in melanin synthesis such as tyrosinase (TYR). The rate-limiting enzyme TYR is modified by the ubiquitin ligase Hrd1 during melanosynthesis. Melanin itself is also regulated by multiple ubiquitin ligases including Fbp1 and Vhl. By regulating the ubiquitination modification to target each link of melanin synthesis, it plays an important role in correcting the disorder of melanin metabolism. A number of chemical agents have been proven to inhibit the activity of ubiquitin ligase.

CONCLUSIONS

Drugs targeting E3 ligase and deubiquitinating enzymes have great potential in the treatment of melanin metabolism disorders.

The Mechanisms of Fur Development and Color Formation in American Mink Revealed Using Comparative Transcriptomics

American mink fur is an important economic product, but the molecular mechanisms underlying its color formation and fur development remain unclear. We used RNA-seq to analyze the skin transcriptomes of young and adult mink with two different hair colors. The mink comprised black adults (AB), white adults (AW), black juveniles (TB), and white juveniles (TW) (three each). Through pair comparison and cross-screening among different subgroups, we found that 13 KRTAP genes and five signaling pathways (the JAK-STAT signaling pathway (cfa04630), signaling pathways regulating pluripotency of stem cells (cfa04550), ECM-receptor interaction (cfa04512), focal adhesion (cfa04510), and the Ras signaling pathway (cfa04014)) were related to mink fur development. We also found that members of a tyrosinase family (TYR, TYRP1, and TYRP2) are involved in mink hair color formation. The expression levels of TYR were higher in young black mink than in young white mink, but this phenomenon was not observed in adult mink. Our study found significant differences in adult and juvenile mink skin transcriptomes, which may shed light on the mechanisms of mink fur development. At the same time, the skin transcriptomes of black and white mink also showed differences, with the results varying by age, suggesting that the genes regulating hair color are active in early development rather than in adulthood. The results of this study provide molecular support in breeding for mink coat color and improving fur quality.

Bioassay-Guided Characterization, Antioxidant, Anti-Melanogenic and Anti-Photoaging Activities of Pueraria thunbergiana L. Leaf Extracts in Human Epidermal Keratinocytes (HaCaT) Cells

Although the roots and flowers of P. thunbergiana are known to have various physiologically active effects, studies on the anti-melanin production and anti-photoaging effects of its leaf extracts and cellular mechanisms are still lacking. In this study, we evaluated the possibility of using Pueraria thunbergiana leaves as a natural material for skin whitening and anti-aging-related functional cosmetics. The 30% ethyl alcohol (EtOH) extract from P. thunbergiana leaves was fractionated using n-hexane, ethyl acetate (EtOAc), butanol, and aqueous solution to measure their whitening, and anti-aging effects. The EtOAc fraction contained a high content of phenolic and flavonoids and showed higher 1,1-diphenyl-2-picryhydrazyl (DPPH) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) radical scavenging activities than the other fractions. It was also confirmed that the EtOAc fraction markedly inhibited α-melanocyte stimulating hormone (α-MSH)-induced melanogenesis in B16F10 melanoma cells. In addition, the EtOAc fraction showed a protective effect against ultraviolet B (UVB) in HaCaT cells and increased the collagen synthesis that was decreased due to UVB exposure. Matrix metalloproteinase-1 (MMP-1) activity and MMP-1 protein expression were reduced in human epidermal keratinocytes (HaCaT) cells. These results indicate that the EtOAc fraction has superior antioxidant activity, anti-melanogenesis, and anti-photoaging effects compared to the other fractions. Therefore, in this study, we confirmed the potential of P. thunbergiana leaf extract as a functional cosmetic ingredient, and it can be used as basic data for the physiological activity of P. thunbergiana leaf extracts.

New insights into the prognosis of intraocular malignancy: Interventions for association mechanisms between cancer and diabetes

The intraocular malignancies, which mostly originate from the retina and uvea, exhibit a high incidence of blindness and even death. Uveal melanoma (UM) and retinoblastoma (RB) are the most common intraocular malignancies in adults and children, respectively. The high risks of distant metastases lead to an extremely poor prognosis. Nowadays, various epidemiological studies have demonstrated that diabetes is associated with the high incidence and mortality of cancers, such as liver cancer, pancreatic cancer, and bladder cancer. However, the mechanisms and interventions associated with diabetes and intraocular malignancies have not been reviewed. In this review, we have summarized the associated mechanisms between diabetes and intraocular malignancy. Diabetes mellitus is a chronic metabolic disease characterized by prolonged periods of hyperglycemia. Recent studies have reported that the abnormal glucose metabolism, insulin resistance, and the activation of the IGF/insulin-like growth factor-1 receptor (IGF-1R) signaling axis in diabetes contribute to the genesis, growth, proliferation, and metastases of intraocular malignancy. In addition, diabetic patients are more prone to suffer severe complications and poor prognosis after radiotherapy for intraocular malignancy. Based on the common pathogenesis shared by diabetes and intraocular malignancy, they may be related to interventions and treatments. Therefore, interventions targeting the abnormal glucose metabolism, insulin resistance, and IGF-1/IGF-1R signaling axis show therapeutic potentials to treat intraocular malignancy.

Altered expression of ferroptosis markers and iron metabolism reveals a potential role of ferroptosis in vitiligo

Oxidative stress is one of the triggering factors for vitiligo, which leads to melanocyte (MC) destruction in vitiligo lesions. Ferroptosis, which is characterized by iron-dependent increase in oxidative stress and lipid peroxidation, has been widely explored in numerous diseases, whereas whether ferroptosis plays a role in MC loss of vitiligo remains to be elucidated. Quantitative real-time PCR and western blot analysis were used to determine the expression of ferroptosis markers in vitiligo patients. Immunonephelometry and electrochemiluminescence were performed to analyze iron status. Reactive oxygen species (ROS), Fe²⁺ , and lipid ROS were assessed by flow cytometry. The expression of ferroptosis markers was significantly altered in the epidermis of vitiligo patients. Iron deficiency was revealed in the blood of patients. Erastin reduced cell viability and led to oxidative stress, iron overload as well as lipid peroxide accumulation in human epidermal MCs in vitro. Altered expression of ferroptosis markers and inhibition of melanin synthesis in MCs were induced by erastin, which was attenuated by N-acetyl-L-cysteine (NAC) pretreatment or post-treatment in vitro. In conclusion, ferroptosis might take place during the process of vitiligo. Erastin could induce ferroptosis in human epidermal MCs and NAC could protect MCs from ferroptosis in vitro.

Daphnetin inhibits α-MSH-induced melanogenesis via PKA and ERK signaling pathways in B16F10 melanoma cells

Daphnetin is a dehydroxylated derivative of coumarin isolated from Daphne species. However, the effect of daphnetin on melanogenesis has not been elucidated. This study aims to investigate the inhibitory effect of daphnetin on melanogenesis in α-melanocyte stimulating hormone (α-MSH)-treated B16F10 cells and its potential mechanism. Melanin content analysis and cellular tyrosinase activity assay showed that daphnetin inhibited melanin biosynthesis in α-MSH-treated B16F10 cells. Immunoblotting and qRT-PCR also indicated that daphnetin suppressed the expression of microphthalmia-associated transcription factor, a mastering transcription factor of melanogenesis and its downstream melanogenic enzymes including tyrosinase and tyrosinase-related proteins. Moreover, daphnetin downregulated the phosphorylation of PKA, ERK, MSK1, and CREB. Additionally, daphnetin inhibited melanin synthesis in UVB-irradiated HaCaT conditioned medium system suggesting that daphnetin has potential as an antipigmentation activity in a physiological skin condition. Our data propose that daphnetin inhibits melanogenesis via modulating both the PKA/CREB and the ERK/MSK1/CREB pathways.

Genome-wide association analysis reveal the genetic reasons affect melanin spot accumulation in beak skin of ducks

Background

Skin pigmentation is a broadly appearing phenomenon of most animals and humans in nature. Here we used a bird model to investigate why melanin spot deposits on the skin.

Results

Our result showed that growth age and the sunlight might induce melanin deposition in bird beak skin which was determined by genetic factors. GWAS helped us to identify two major loci affecting melanin deposition, located on chromosomes 13 and 25, respectively. The fine mapping works narrowed the candidate regions to 0.98 Mb and 1.0 Mb on chromosomes 13 and 25. The MITF and POU2F3 may be the causative genes and synergistically affect melanin deposition during duck beak skin. Furthermore, our data strongly demonstrated that the pathway of melanin metabolism contributes to melanin deposition on the skin.

Conclusions

We demonstrated that age and sunlight induce melanin deposition in bird beak skin, while heredity is fundamental. The MITF and POU2F3 likely played a synergistic effect on the regulation of melanin synthesis, and their mutations contribute to phenotypic differences in beak melanin deposition among individuals. It is pointed out that melanin deposition in the skin is related to the pathway of melanin metabolism, which provided insights into the molecular regulatory mechanisms and the genetic improvement of the melanin deposition in duck beak.

Fraxinol Stimulates Melanogenesis in B16F10 Mouse Melanoma Cells through CREB/MITF Signaling

Melanin pigment produced in melanocytes plays a protective role against ultraviolet radiation. Selective destruction of melanocytes causes chronic depigmentation conditions such as vitiligo, for which there are very few specific medical treatments. Here, we found that fraxinol, a natural coumarin from Fraxinus plants, effectively stimulated melanogenesis. Treatment of B16-F10 cells with fraxinol increased the melanin content and tyrosinase activity in a concentration-dependent manner without causing cytotoxicity. Additionally, fraxinol enhanced the mRNA expression of melanogenic enzymes such as tyrosinase, tyrosinase-related protein-1, and tyrosinase-related protein-2. Fraxinol also increased the expression of microphthalmia-associated transcription factor at both mRNA and protein levels. Fraxinol upregulated the phosphorylation of cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB). Furthermore, H89, a cAMP-dependent protein kinase A inhibitor, decreased fraxinol-induced CREB phosphorylation and microphthalmia-associated transcription factor expression and significantly attenuated the fraxinol-induced melanin content and intracellular tyrosinase activity. These results suggest that fraxinol enhances melanogenesis via a protein kinase A-mediated mechanism, which may be useful for developing potent melanogenesis stimulators.

Phylogenetic Analysis of Core Melanin Synthesis Genes Provides Novel Insights Into the Molecular Basis of Albinism in Fish

Melanin is the most prevalent pigment in animals. Its synthesis involves a series of functional genes. Particularly, teleosts have more copies of these genes related to the melanin synthesis than tetrapods. Despite the increasing number of available vertebrate genomes, a few systematically genomic studies were reported to identify and compare these core genes for the melanin synthesis. Here, we performed a comparative genomic analysis on several core genes, including tyrosinase genes (tyr, tyrp1, and tyrp2), premelanosome protein (pmel), microphthalmia-associated transcription factor (mitf), and solute carrier family 24 member 5 (slc24a5), based on 90 representative vertebrate genomes. Gene number and mutation identification suggest that loss-of-function mutations in these core genes may interact to generate an albinism phenotype. We found nonsense mutations in tyrp1a and pmelb of an albino golden-line barbel fish, in pmelb of an albino deep-sea snailfish (Pseudoliparis swirei), in slc24a5 of cave-restricted Mexican tetra (Astyanax mexicanus, cavefish population), and in mitf of a transparent icefish (Protosalanx hyalocranius). Convergent evolution may explain this phenomenon since nonsense mutations in these core genes for melanin synthesis have been identified across diverse albino fishes. These newly identified nonsense mutations and gene loss will provide molecular guidance for ornamental fish breeding, further enhancing our in-depth understanding of human skin coloration.

Epigenetic regulation of melanogenesis

Melanogenesis is a complex process in which melanin is synthesized in melanocytes and transported to keratinocytes, which involves multiple genes and signaling pathways. Epigenetics refers to the potential genetic changes that affect gene expression without involving changes in the original sequence of DNA nucleotides. DNA methylation regulates the expression of key genes such as tyrosinase (TYR), tyrosinase-related protein 1 (TYRP1), dopachrome tautomerase (DCT) and microphthalmia-associated transcription factor (MITF), as well as paracrine factors such as stem cell factor (SCF) and endothelin-1 (ET-1) in melanogenesis. Potential DNA methylation sites are present in the genes of melanogenesis-related signaling pathways such as "Wnt", "PI3K/Akt/CREB" and "MAPK". H3K27 acetylation is abundant in melanogenesis-related genes. Both the upstream activation and downstream regulation of MITF depend on histone acetyltransferase CBP/p300, and pH-induced H3K27 acetylation may be the amplifying mechanism of MITF's effect. HDAC1 and HDAC10 catalyze histone deacetylation of melanogenesis-related gene promoters. Chromatin remodelers SWI/SNF complex and ISWI complex use the energy of ATP hydrolysis to rearrange nucleosomes, while their active subunits BRG1, BRM and BPTF, act as activators and cofactors of MITF. MicroRNAs (miRNAs) can directly target a large number of melanogenesis-related genes, while long noncoding RNAs (lncRNAs) and circular RNAs (circRNAs) regulate melanogenesis in a variety of ways. Interactions exist among the epigenetic mechanisms of melanogenesis. For example, the methyl CpG binding domain protein 2 (MeCP2) links DNA methylation, histone deacetylation, and histone methylation. Epigenetic-based therapy provides novel opportunities for treating dermatoses that are caused by pigmentation disturbances. This review summarizes the epigenetic regulation mechanisms of melanogenesis, and examines the pathogenesis and treatment of epigenetics in pigmentation disorders.

Sperm-Specific Glycolysis Enzyme Glyceraldehyde-3-Phosphate Dehydrogenase Regulated by Transcription Factor SOX10 to Promote Uveal Melanoma Tumorigenesis

Melanoma cells exhibit increased aerobic glycolysis, which represents a major biochemical alteration associated with malignant transformation; thus, glycolytic enzymes could be exploited to selectively target cancer cells in cancer therapy. Sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDHS) switches glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate by coupling with the reduction of NAD+ to NADH. Here, we demonstrated that GAPDHS displays significantly higher expression in uveal melanoma (UM) than in normal controls. Functionally, the knockdown of GAPDHS in UM cell lines hindered glycolysis by decreasing glucose uptake, lactate production, adenosine triphosphate (ATP) generation, cell growth and proliferation; conversely, overexpression of GAPDHS promoted glycolysis, cell growth and proliferation. Furthermore, we identified that SOX10 knockdown reduced the activation of GAPDHS, leading to an attenuated malignant phenotype, and that SOX10 overexpression promoted the activation of GAPDHS, leading to an enhanced malignant phenotype. Mechanistically, SOX10 exerted its function by binding to the promoter of GAPDHS to regulate its expression. Importantly, SOX10 abrogation suppressed in vivo tumor growth and proliferation. Collectively, the results reveal that GAPDHS, which is regulated by SOX10, controls glycolysis and contributes to UM tumorigenesis, highlighting its potential as a therapeutic target.

Oenothera laciniata Hill Extracts Exhibits Antioxidant Effects and Attenuates Melanogenesis in B16-F10 Cells via Downregulating CREB/MITF/Tyrosinase and Upregulating p-ERK and p-JNK

Oenothera laciniata Hill is a perennial herb traditionally used to alleviate inflammatory complications. This study investigated the antioxidant and anti-melanogenic activities of O. laciniata. The methanolic extract (OLM) of O. laciniata and its different fractions, including ethyl acetate (OLEF), n-butanol (OLBF), and water (OLWF) fractions, were prepared. Antioxidant activities were evaluated by total phenolic content, the radical-scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH^•), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS^+•), and superoxide anion (O2^−•), reducing capacity, and metal chelating ability. OLM and its fractions exhibited potent antioxidant activity in these in vitro assays, with a correlation between radical-scavenging activity and total phenolic content. OLM and its fractions inhibited the mushroom tyrosinase activity superior to the reference control, ascorbic acid. In B16-F10 melanoma cells, OLM and its fractions significantly decreased melanin production and tyrosinase activity. Mechanistic investigations revealed that OLM and its fractions inhibited tyrosinase and TRP-2 expressions via downregulating MITF and phosphorylated CREB and differentially inducing ERK or JNK phosphorylation. Additionally, OLM and its fractions caused no significant cytotoxicity towards B16-F10 or skin fibroblast cells at concentrations used in these cellular assays. These findings demonstrated the potential of O. laciniata extracts as the ideal skin protective agent with dual antioxidant and anti-melanogenic activities.

Monodactylous Longitudinal Melanonychia: A Sign of Bowen's Disease in Skin of Color

Introduction

Monodactylous longitudinal melanonychia (LM) may represent both benign and malignant dermatologic disorders. However, squamous cell carcinoma in situ (SCCis) is not commonly considered in this setting.

Case Presentation

In this report, we present 2 cases of SCCis of the nail matrix in patients with skin of color who presented with monodactylous LM involving the lateral aspect of the nail.

Conclusion

These cases suggest that SCCis should be included in the differential diagnosis for monodactylous LM, especially when involving the lateral nail plate in darker skin.

SOX10 is as specific as S100 protein in detecting metastases of melanoma in lymph nodes and is recommended for sentinel lymph node assessment

BACKGROUND

Sentinel lymph node (SLN) biopsy remains crucial for melanoma staging. The European Organisation for Research and Treatment of Cancer Melanoma Group recommends performing immunohistochemical stainings for reproducible identification of melanoma metastases. S100 protein (pS100) is a commonly used melanocytic antigen because of its high sensitivity in spite of relatively low specificity. SRY-related HMG-box 10 protein (SOX10) is a transcription factor characterising neural crest-derived cells. It is uniformly expressed mostly in the nuclei of melanocytes, neural, and myoepithelial cells. Pathologists sometimes prefer SOX10 as a melanoma marker, but it has not yet been investigated on a large-scale to confirm that it is reliable and recommendable for routine SLN evaluation.

METHODS

Four hundred one treatment-naïve lymph node (LN) metastatic melanomas were included in high-density tissue microarrays and were assessed for the presence of SOX10 and pS100 by immunohistochemistry. The slides were digitalised, shared and evaluated by a panel of experienced melanoma pathologists.

RESULTS

The vast majority of melanomas were double-positive for pS100 and SOX10 (93.2%); a small percentage of the cases (3.9%) were double-negative melanomas. Discordance between the two markers was observed: 1.9% pS100(-)/SOX10(+) and 0.75% pS100(+)/SOX10(-). SOX10 was not expressed by immune cell types in the LN, resulting in a less controversial interpretation of the staining.

CONCLUSIONS

SOX10 is as equally specific as pS100 for the detection of melanoma metastases in LNs. The interpretation of SOX10 staining is highly reproducible among different centres and different pathologists because of the absence of staining of immune cells.

Genome and Transcriptome Sequencing of casper and roy Zebrafish Mutants Provides Novel Genetic Clues for Iridophore Loss

casper has been a widely used transparent mutant of zebrafish. It possesses a combined loss of reflective iridophores and light-absorbing melanophores, which gives rise to its almost transparent trunk throughout larval and adult stages. Nevertheless, genomic causal mutations of this transparent phenotype are poorly defined. To identify the potential genetic basis of this fascinating morphological phenotype, we constructed genome maps by performing genome sequencing of 28 zebrafish individuals including wild-type AB strain, roy orbison (roy), and casper mutants. A total of 4.3 million high-quality and high-confidence homozygous single nucleotide polymorphisms (SNPs) were detected in the present study. We also identified a 6.0-Mb linkage disequilibrium block specifically in both roy and casper that was composed of 39 functional genes, of which the mpv17 gene was potentially involved in the regulation of iridophore formation and maintenance. This is the first report of high-confidence genomic mutations in the mpv17 gene of roy and casper that potentially leads to defective splicing as one major molecular clue for the iridophore loss. Additionally, comparative transcriptomic analyses of skin tissues from the AB, roy and casper groups revealed detailed transcriptional changes of several core genes that may be involved in melanophore and iridophore degeneration. In summary, our updated genome and transcriptome sequencing of the casper and roy mutants provides novel genetic clues for the iridophore loss. These new genomic variation maps will offer a solid genetic basis for expanding the zebrafish mutant database and in-depth investigation into pigmentation of animals.

Liquiritin and Liquiritigenin Induce Melanogenesis via Enhancement of p38 and PKA Signaling Pathways

Background: Liquiritin (LQ) and its aglycone, liquiritigenin (LQG), are major flavonoids in licorice root (Glycyrrhiza spp.). Our preliminary screening identified LQ and LQG, which promote melanin synthesis in the melanoma cells. In this study, we investigated the molecular mechanism of melanin synthesis activated by LQ and LQG. Methods: Murine (B16-F1) and human (HMVII) melanoma cell lines were treated with LQ or LQG. After incubation, melanin contents, intracellular tyrosinase activity, and cell viability were evaluated. Protein levels were determined using Western blotting. Results: LQ and LQG activated melanin synthesis and intracellular tyrosinase activity. The induction of melanin and intracellular tyrosinase activity by LQG was higher than that by LQ. LQ and LQG induced the expression of tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2. LQ and LQG also enhanced microphthalmia-associated transcription factor (MITF) expression, and cyclic AMP-responsive element-binding protein (CREB) phosphorylation. The phosphorylation of p38 and extracellular signal-regulated kinase (ERK), but not Akt, was significantly increased by LQ or LQG. Furthermore, LQ- or LQG-mediated melanin synthesis was partially blocked by p38 inhibitor (SB203580) and protein kinase A (PKA) inhibitor (H-89); however, ERK kinase (MEK) inhibitor (U0126) and phosphatidylinositol-3-kinase (PI3K) inhibitor (LY294002) had no effect. Conclusions: The results suggest that LQ and LQG enhance melanin synthesis by upregulating the expression of melanogenic enzymes, which were activated by p38 and PKA signaling pathways, leading to MITF expression and CREB phosphorylation.

Fargesin inhibits melanin synthesis in murine malignant and immortalized melanocytes by regulating PKA/CREB and P38/MAPK signaling pathways

BACKGROUND

Fargesin is commonly used in the treatment of allergic rhinitis, inflammation, sinusitis and headache.

OBJECTIVE

The aim of the study is to investigate a new function of fargesin against melanin production and its underlying molecular mechanism.

METHODS

B16F10 mouse melanoma cells, Melan-a and human epidermal melanocytes were treated with different concentrations of fargesin for the indicated time. The extracellular and cellular melanin content was detected by spectrometry at 490 nm and 405 nm, respectively. RT-qPCR and Western blot analysis were used to exam the expression of melanogenic enzymes and the activities of PKA/CREB and p38 MAPK pathway components. Zebrafish was used as an in vivo model for studying the function of fargesin in regulating melanogenesis.

RESULTS

Fargesin effectively inhibited melanin production at moderate dose in mouse B16F10 melanoma cells, normal melanocyte cell lines and zebrafish. The expression of microphthalmia-associated transcription factor (MITF), its downstream melanogenic enzymes and tyrosinase activity were also strongly reduced by fargesin. Moreover, the increase of melanin production induced by UVB and forskolin could be fully reversed by fargesin treatment. Fargesin also effectively inhibited the activation of PKA/CREB and p38 MAPK as well as their interactions, which in turn is responsible for the expression of MITF and melanogenic enzymes.

CONCLUSIONS

These results show that fargesin can function as an anti-melanogenic agent, at least in part, by inhibiting PKA/CREB and p38/MAPK signaling pathways. Therefore, fargesin and its derivatives may potentially be used for preventing hyperpigmentation disorders in the future.

Effects of penthiopyrad on the development and behaviour of zebrafish in early-life stages

The agricultural use of succinate dehydrogenase inhibitor (SDHI) fungicides has increased dramatically in the US and Europe. As the SDHI fungicides, boscalid, flutolanil and thifluzamide had been reported to induce a series of toxic effects on zebrafish. However, the toxic effects of penthiopyrad on zebrafish have not been reported yet. This study aimed to assess the acute toxicity of penthiopyrad to zebrafish in early-life stages and investigate behavioural response of larvae and the effects on lipid metabolism and pigmentation under sub-lethal exposure of penthiopyrad. Based on results of the acute toxicity tests of zebrafish embryo and larvae, penthiopyrad had an acute toxicity to early-life stages of zebrafish and induced a series of deformities during development. Based on the results of sub-lethal exposure for 8 days, penthiopyrad resulted in significant decreases in swimming velocity, acceleration speed, distance moved and inactive time of larvae at 0.3, 0.6 and 1.2 mg/L. Penthiopyrad induced the disorders of lipid metabolism via affecting fatty acid synthesis and β-oxidation, in accordance with remarkable changes in the content of triglycerides and cholesterol and the expression of key genes (hmgcrα, pparα1, srebf1, cyp51 and acca1) at 1.2 mg/L. In addition, the disorder of melanin synthesis and distribution was caused by penthiopyrad in larvae in accordance with changes in body colour and related gene expression at 8 dpe.

Tissue-Specific Actions of Pax6 on Proliferation and Differentiation Balance in Developing Forebrain Are Foxg1 Dependent

Differences in the growth and maturation of diverse forebrain tissues depend on region-specific transcriptional regulation. Individual transcription factors act simultaneously in multiple regions that develop very differently, raising questions about the extent to which their actions vary regionally. We found that the transcription factor Pax6 affects the transcriptomes and the balance between proliferation and differentiation in opposite directions in the diencephalon versus cerebral cortex. We tested several possible mechanisms to explain Pax6's tissue-specific actions and found that the presence of the transcription factor Foxg1 in the cortex but not in the diencephalon was most influential. We found that Foxg1 is responsible for many of the differences in cell cycle gene expression between the diencephalon and cortex and, in cortex lacking Foxg1, Pax6's action on the balance of proliferation versus differentiation becomes diencephalon like. Our findings reveal a mechanism for generating regional forebrain diversity in which one transcription factor completely reverses the actions of another.

Intracellular Signaling Mechanisms Involved in the Biological Effects of the Xanthophyll Carotenoid Astaxanthin to Prevent the Photo-aging of the Skin in a Reactive Oxygen Species Depletion-independent Manner: The Key Role of Mitogen and Stress-activated Protein Kinase 1

In the first review, we summarized the biological effects of the xanthophyll carotenoid astaxanthin (AX) to prevent UV-induced cutaneous inflammation, abnormal keratinization, pigmentation, and wrinkling in a manner independent of the depletion of reactive oxygen species. In this manuscript, we review what is known about the intracellular signaling mechanisms that are involved in those effects in keratinocytes and in melanocytes. Our research has characterized the intracellular stress signaling mechanism(s) that are involved in the up-regulated expression of genes encoding cyclooxygenase (COX2), interleukin (IL)-8, granulocyte macrophage colony stimulatory factor (GM-CSF), and transglutaminase (TGase)1 in UVB-exposed keratinocytes as well as in the stimulated transcription and/or translation of melanogenic factors, including microphthalmia-associated transcription factor (MITF), in stem cell factor (SCF)-treated melanocytes. The results reveal that while the expression of COX2, IL-8, GM-CSF, and TGase1 stimulated by UVB is due to effects primarily via the NFκB pathway, that stimulation can be abrogated by specifically interrupting the p38/MSK1/NFκBp65Ser276 axis. Further, the stimulation of melanogenesis by SCF can be inhibited by disrupting the phosphorylation of MSK1 via the p38, MSK1, CREB, and MITF axis. The sum of these findings provides new evidence for the interruption of ROS depletion independent-signaling by antioxidants.

Glucosamine abrogates the stem cell factor + endothelin-1-induced stimulation of melanogenesis via a deficiency in MITF expression due to the proteolytic degradation of CREB in human melanocytes

We have already reported that glucosamine (GlcN) distinctly abrogates the pigmentation of human epidermal equivalents stimulated by stem cell factor + endothelin-1 (SE). In this study, we characterized the molecular mechanism involved in the anti-melanogenic effects of GlcN using normal human melanocytes (NHMs) in culture. The SE-stimulated gene (12 h) and protein (24 h) expression levels of melanocyte-specific proteins (at the indicated times post-stimulation) were significantly abrogated by pretreatment with GlcN for 72 h. Western blotting analysis of the phosphorylation of intracellular signaling molecules in the MAPK pathway revealed that despite the significantly decreased level of total CREB protein at all times post-stimulation, the SE-stimulated phosphorylation of ERK, CREB and MITF is not attenuated at 15 min post-stimulation in GlcN-treated NHMs. However, the SE-stimulated protein expression level of total MITF at 2 and 6 h post-stimulation was significantly abrogated by 72 h pretreatment with GlcN. Consistently, pretreatment with GlcN for 72 h abrogated the stimulated gene and protein expression levels of MITF at 1 h and 2 h post-stimulation, respectively. Analysis of gene and protein expression levels also demonstrated that pretreatment with GlcN for 72 h significantly reduced the protein levels of CREB and MITF without affecting their gene expression levels prior to the SE stimulation. Silencing with a CREB siRNA distinctly abrogated the SE-stimulated expression of MITF (at 2 h post-stimulation) and melanocyte-specific proteins (at 24 h post-stimulation). Similarly, transfection of MITF siRNA markedly abrogated the SE-stimulated expression of MITF protein and melanocyte-specific proteins at 2 and 24 h post-stimulation, respectively. Finally, the decreased levels of CREB and MITF proteins induced by 72 h pretreatment with GlcN were abrogated by the co-addition of the proteosomal degradation inhibitor MG132. These findings suggest that the anti-melanogenic effect elicited by GlcN is mediated via the decreased expression of MITF which results from the attenuated transcriptional activity of CREB due to proteolytic degradation.

(2E,5E)-2,5-Bis(3-hydroxy-4-methoxybenzylidene) cyclopentanone Exerts Anti-Melanogenesis and Anti-Wrinkle Activities in B16F10 Melanoma and Hs27 Fibroblast Cells

Ultraviolet (UV) radiation exposure is the primary cause of extrinsic skin aging, which results in skin hyperpigmentation and wrinkling. In this study, we investigated the whitening effect of (2E,5E)-2,5-bis(3-hydroxy-4-methoxybenzylidene)cyclopentanone (BHCP) on B16F10 melanoma and its anti-wrinkle activity on Hs27 fibroblasts cells. BHCP was found to potently inhibit tyrosinase, with 50% inhibition concentration (IC₅₀) values of 1.10 µM and 8.18 µM for monophenolase (l-tyrosine) and diphenolase (l-DOPA), and the enzyme kinetics study revealed that BHCP is a competitive-type tyrosinase inhibitor. Furthermore, BHCP significantly inhibited melanin content and cellular tyrosinase activity, and downregulated the levels of microphthalmia-associated transcription factor (MITF), phosphorylated levels of cAMP response element-binding (CREB) protein, and tyrosinase in α-melanocyte stimulating hormone (α-MSH)-induced B16F10 melanoma cells. Moreover, BHCP inhibited the phosphorylation of p65 and expression of matrix metalloproteinases (MMP-1, MMP-9, MMP-12, and MMP-13) in Hs27 fibroblasts stimulated with UV radiation. Therefore, our results demonstrate that BHCP may be a good candidate for the development of therapeutic agents for diseases associated with hyperpigmentation and wrinkling.

Beyond MITF: Multiple transcription factors directly regulate the cellular phenotype in melanocytes and melanoma

MITF governs multiple steps in the development of melanocytes, including specification from neural crest, growth, survival, and terminal differentiation. In addition, the level of MITF activity determines the phenotype adopted by melanoma cells, whether invasive, proliferative, or differentiated. However, MITF does not act alone. Here, we review literature on the transcription factors that co-regulate MITF-dependent genes. ChIP-seq studies have indicated that the transcription factors SOX10, YY1, and TFAP2A co-occupy subsets of regulatory elements bound by MITF in melanocytes. Analyses at single loci also support roles for LEF1, RB1, IRF4, and PAX3 acting in combination with MITF, while sequence motif analyses suggest that additional transcription factors colocalize with MITF at many melanocyte-specific regulatory elements. However, the precise biochemical functions of each of these MITF collaborators and their contributions to gene expression remain to be elucidated. Analogous to the transcriptional networks in morphogen-patterned tissues during embryogenesis, we anticipate that the level of MITF activity is controlled not only by the concentration of activated MITF, but also by additional transcription factors that either quantitatively or qualitatively influence the expression of MITF-target genes.

Effects of Extremely Low Frequency Electromagnetic Fields on Melanogenesis through p-ERK and p-SAPK/JNK Pathways in Human Melanocytes

This study evaluated frequency-dependent effects of extremely low frequency electromagnetic fields (ELF-EMFs) on melanogenesis by melanocytes in vitro. Melanocytes were exposed to 2 mT EMFs at 30-75 Hz for 3 days before melanogenesis was examined. Exposure to ELF-EMFs at 50 and 60 Hz induced melanogenic maturation without cell damage, without changing cell proliferation and mitochondrial activity. Melanin content and tyrosinase activity of cells exposed to 50 Hz were higher than in controls, and mRNA expression of tyrosinase-related protein-2 was elevated relative to controls at 50 Hz. Phosphorylated cyclic adenosine monophosphate response element-binding protein (p-CREB) levels were higher than controls in cells exposed to ELF-EMFs at 50-75 Hz. Immunohistochemical staining showed that melanocyte-specific markers (HMB45, Melan-A) were strongly expressed in cells exposed to EMFs at 50 and 60 Hz compared to controls. Thus, exposure to ELF-EMFs at 50 Hz could stimulate melanogenesis in melanocytes, through activation of p-CREB and p-p38 and inhibition of phosphorylated extracellular signal-regulated protein kinase and phosphorylated stress-activated protein kinase/c-Jun N-terminal kinase. The results may form the basis of an appropriate anti-gray hair treatment or be applied in a therapeutic device for inducing repigmentation in the skin of vitiligo patients.

Prunus mume extract exerts antioxidant activities and suppressive effect of melanogenesis under the stimulation by alpha-melanocyte stimulating hormone in B16-F10 melanoma cells

In the current study, we examined the antioxidant and skin-whitening properties of Prunus mume extract (PME). The ability of PME to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals was investigated in vitro. At a concentration of 1000 μg/mL, PME neutralized >45% free radical activity. Cell viability assessment with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that at concentrations <1500 μg/mL, PME does not exert cytotoxic effects on murine B16 melanoma (B16) cells. Morphological analysis disclosed that melanin production is inhibited in B16 cells treated with 250 nM α-melanocyte-stimulating hormone (α-MSH) and PME. We conclude that fruit extracts of P. mume exert a skin-whitening effect by inhibiting melanin production via regulation of melanogenesis-associated protein expression in melanocytes.

Anti-melanogenic activity of phytosphingosine via the modulation of the microphthalmia-associated transcription factor signaling pathway

BACKGROUND

Microphthalmia-associated transcription factor (MITF) suppresses the expression of enzymes controlling the production of melanin. Phytosphingosine is a well-known cosmetic agent, but its anti-melanogenic activity and mechanism of action remain unclear.

OBJECTIVE

This study was designed to investigate the effects of phytosphingosine on melanin synthesis and elucidate the plausible mechanism of actions in vitro and ex vivo systems.

METHODS

Melanin content, cell viability, tyrosinase activity, p-CREB DNA binding activity, and the protein gene expression levels of the enzymes and proteins involved in melanogenesis were measured with the treatment of phytosphingosine.

RESULTS

Phytosphingosine inhibits melanin synthesis in cultured melan-a cells and a reconstructed human skin model. One possible mechanism of the anti-melanogenic activity of phytosphingosine appears to be associated with the modulation of MITF, which suppresses the expression of tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2. Further analysis revealed that phytosphingosine suppressed paired box 3 and SRY-related HMG-box 10, critical transcription factors of MITF. Phytosphingosine also effectively downregulated the protein levels of β-catenin and the phospho-cAMP response element binding protein, an upstream regulatory factor of MITF. These results are closely related to the suppression of MITF gene expression. In addition, treatment with phytosphingosine for over 12h, which is a relatively long period of time, did not directly suppress these MITF transcriptional factors. Instead, phytosphingosine induced ERK activation, which led to MITF phosphorylation, followed by its degradation. Therefore, the downregulation of MITF protein levels by phytosphingosine with a long time exposure is in part associated with MITF protein degradation through the MAPK kinase activation pathway.

CONCLUSION

The modulation of MITF by phytosphingosine is closely related with the signaling pathways, such as the suppression of the MITF gene expression and the degradation of the MITF protein, depending on the duration of treatment time. These results suggest that phytosphingosine might serve as an effective melanogenesis inhibitor in melanocytes via the regulation of the MITF signaling pathways.

Mechanisms of silver_nanoparticles induced hypopigmentation in embryonic zebrafish

Silver_nanoparticles (AgNPs) have been reported to inhibit specification of erythroid cells and to induce spinal cord deformities and cardiac arrhythmia in vertebrates, but have not been implicated in development of neural crest (NC) and pigment cells in an in vivo model yet. In current study, down-regulated expressions of NC genes pax7 and foxd3, melanophore genes mitfa and dct, and xanthophore gene gch2 in AgNPs-exposed embryos were revealed by microarray, qRT-PCR and whole-mount in situ hybridization (WISH). Then, the down-regulated expressions of melanophore genes mitfa and dct but not xanthophore gene gch2 in AgNPs-exposed embryos were found to be recovered by melanogenesis agonists palmitic acid and dibutyryl cyclic AMP (dbcAMP). Finally, Ag⁺ chelating and AgNPs coating compound l-cysteine was found to neutralize AgNPs-induced hypopigmentation in AgNPs-exposed embryos, and to recover the down-regulated expressions of both dct and gch2 to nearly normal level in embryos, suggesting that AgNPs-releasing Ag⁺ might mediate their biological effects on zebrafish pigmentation mostly. This study was firstly to unveil that AgNPs might specifically act up-stream of mitfa and pax7 genes to suppress specification and differentiation of melanophore and xanthophore lineages respectively by their releasing Ag⁺ during vertebrate embryogenesis.

TFAP2 paralogs regulate melanocyte differentiation in parallel with MITF

Mutations in the gene encoding transcription factor TFAP2A result in pigmentation anomalies in model organisms and premature hair graying in humans. However, the pleiotropic functions of TFAP2A and its redundantly-acting paralogs have made the precise contribution of TFAP2-type activity to melanocyte differentiation unclear. Defining this contribution may help to explain why TFAP2A expression is reduced in advanced-stage melanoma compared to benign nevi. To identify genes with TFAP2A-dependent expression in melanocytes, we profile zebrafish tissue and mouse melanocytes deficient in Tfap2a, and find that expression of a small subset of genes underlying pigmentation phenotypes is TFAP2A-dependent, including Dct, Mc1r, Mlph, and Pmel. We then conduct TFAP2A ChIP-seq in mouse and human melanocytes and find that a much larger subset of pigmentation genes is associated with active regulatory elements bound by TFAP2A. These elements are also frequently bound by MITF, which is considered the "master regulator" of melanocyte development. For example, the promoter of TRPM1 is bound by both TFAP2A and MITF, and we show that the activity of a minimal TRPM1 promoter is lost upon deletion of the TFAP2A binding sites. However, the expression of Trpm1 is not TFAP2A-dependent, implying that additional TFAP2 paralogs function redundantly to drive melanocyte differentiation, which is consistent with previous results from zebrafish. Paralogs Tfap2a and Tfap2b are both expressed in mouse melanocytes, and we show that mouse embryos with Wnt1-Cre-mediated deletion of Tfap2a and Tfap2b in the neural crest almost completely lack melanocytes but retain neural crest-derived sensory ganglia. These results suggest that TFAP2 paralogs, like MITF, are also necessary for induction of the melanocyte lineage. Finally, we observe a genetic interaction between tfap2a and mitfa in zebrafish, but find that artificially elevating expression of tfap2a does not increase levels of melanin in mitfa hypomorphic or loss-of-function mutants. Collectively, these results show that TFAP2 paralogs, operating alongside lineage-specific transcription factors such as MITF, directly regulate effectors of terminal differentiation in melanocytes. In addition, they suggest that TFAP2A activity, like MITF activity, has the potential to modulate the phenotype of melanoma cells.

Vitiligo blood transcriptomics provides new insights into disease mechanisms and identifies potential novel therapeutic targets

BACKGROUND

Significant gaps remain regarding the pathomechanisms underlying the autoimmune response in vitiligo (VL), where the loss of self-tolerance leads to the targeted killing of melanocytes. Specifically, there is incomplete information regarding alterations in the systemic environment that are relevant to the disease state.

METHODS

We undertook a genome-wide profiling approach to examine gene expression in the peripheral blood of VL patients and healthy controls in the context of our previously published VL-skin gene expression profile. We used several in silico bioinformatics-based analyses to provide new insights into disease mechanisms and suggest novel targets for future therapy.

RESULTS

Unsupervised clustering methods of the VL-blood dataset demonstrate a "disease-state"-specific set of co-expressed genes. Ontology enrichment analysis of 99 differentially expressed genes (DEGs) uncovers a down-regulated immune/inflammatory response, B-Cell antigen receptor (BCR) pathways, apoptosis and catabolic processes in VL-blood. There is evidence for both type I and II interferon (IFN) playing a role in VL pathogenesis. We used interactome analysis to identify several key blood associated transcriptional factors (TFs) from within (STAT1, STAT6 and NF-kB), as well as "hidden" (CREB1, MYC, IRF4, IRF1, and TP53) from the dataset that potentially affect disease pathogenesis. The TFs overlap with our reported lesional-skin transcriptional circuitry, underscoring their potential importance to the disease. We also identify a shared VL-blood and -skin transcriptional "hot spot" that maps to chromosome 6, and includes three VL-blood dysregulated genes (PSMB8, PSMB9 and TAP1) described as potential VL-associated genetic susceptibility loci. Finally, we provide bioinformatics-based support for prioritizing dysregulated genes in VL-blood or skin as potential therapeutic targets.

CONCLUSIONS

We examined the VL-blood transcriptome in context with our (previously published) VL-skin transcriptional profile to address a major gap in knowledge regarding the systemic changes underlying skin-specific manifestation of vitiligo. Several transcriptional "hot spots" observed in both environments offer prioritized targets for identifying disease risk genes. Finally, within the transcriptional framework of VL, we identify five novel molecules (STAT1, PRKCD, PTPN6, MYC and FGFR2) that lend themselves to being targeted by drugs for future potential VL-therapy.

In Silico Analysis of Gene Expression Network Components Underlying Pigmentation Phenotypes in the Python Identified Evolutionarily Conserved Clusters of Transcription Factor Binding Sites

Color variation provides the opportunity to investigate the genetic basis of evolution and selection. Reptiles are less studied than mammals. Comparative genomics approaches allow for knowledge gained in one species to be leveraged for use in another species. We describe a comparative vertebrate analysis of conserved regulatory modules in pythons aimed at assessing bioinformatics evidence that transcription factors important in mammalian pigmentation phenotypes may also be important in python pigmentation phenotypes. We identified 23 python orthologs of mammalian genes associated with variation in coat color phenotypes for which we assessed the extent of pairwise protein sequence identity between pythons and mouse, dog, horse, cow, chicken, anole lizard, and garter snake. We next identified a set of melanocyte/pigment associated transcription factors (CREB, FOXD3, LEF-1, MITF, POU3F2, and USF-1) that exhibit relatively conserved sequence similarity within their DNA binding regions across species based on orthologous alignments across multiple species. Finally, we identified 27 evolutionarily conserved clusters of transcription factor binding sites within ~200-nucleotide intervals of the 1500-nucleotide upstream regions of AIM1, DCT, MC1R, MITF, MLANA, OA1, PMEL, RAB27A, and TYR from Python bivittatus. Our results provide insight into pigment phenotypes in pythons.

Microphthalmia-associated transcription factor expression levels in melanoma cells contribute to cell invasion and proliferation

Microphthalmia-associated transcription factor (MITF) is a nodal point in melanoma transcriptional network that regulates dozens of genes with critical functions in cell differentiation, proliferation and survival. Highly variable MITF expression levels exist in tumor cell subpopulations conferring marked heterogeneity and plasticity in the tumor tissue. A model has been postulated whereby lower MITF levels favour cell invasion and suppress proliferation, whereas high levels stimulate differentiation and proliferation. Additionally, MITF is considered to be a prosurvival gene and a lineage addiction oncogene in melanoma. Herein, we review how MITF expression may affect the melanoma phenotype with consequences on the survival, invasion and metastasis of melanoma cells, and we discuss the research challenges.

Inhibition of oncogenic BRAF activity by indole-3-carbinol disrupts microphthalmia-associated transcription factor expression and arrests melanoma cell proliferation

Indole-3-carbinol (I3C), an anti-cancer phytochemical derived from cruciferous vegetables, strongly inhibited proliferation and down-regulated protein levels of the melanocyte master regulator micropthalmia-associated transcription factor (MITF-M) in oncogenic BRAF-V600E expressing melanoma cells in culture as well as in vivo in tumor xenografted athymic nude mice. In contrast, wild type BRAF-expressing melanoma cells remained relatively insensitive to I3C anti-proliferative signaling. In BRAF-V600E-expressing melanoma cells, I3C treatment inhibited phosphorylation of MEK and ERK/MAPK, the down stream effectors of BRAF. The I3C anti-proliferative arrest was concomitant with the down-regulation of MITF-M transcripts and promoter activity, loss of endogenous BRN-2 binding to the MITF-M promoter, and was strongly attenuated by expression of exogenous MITF-M. Importantly, in vitro kinase assays using immunoprecipitated BRAF-V600E and wild type BRAF demonstrated that I3C selectively inhibited the enzymatic activity of the oncogenic BRAF-V600E but not of the wild type protein. In silico modeling predicted an I3C interaction site in the BRAF-V600E protomer distinct from where the clinically used BRAF-V600E inhibitor Vemurafenib binds to BRAF-V600E. Consistent with this prediction, combinations of I3C and Vemurafenib more potently inhibited melanoma cell proliferation and reduced MITF-M levels in BRAF-V600E expressing melanoma cells compared to the effects of each compound alone. Thus, our results demonstrate that oncogenic BRAF-V600E is a new cellular target of I3C that implicate this indolecarbinol compound as a potential candidate for novel single or combination therapies for melanoma. © 2016 Wiley Periodicals, Inc.

CD271 is an imperfect marker for melanoma initiating cells

Understanding the molecular and cellular processes underlying melanoma plasticity and heterogeneity is of paramount importance to improve the efficiency of current treatment and to overcome resistance to chemotherapy drugs. The notion of plasticity and heterogeneity implies the existence of melanoma cell populations with different phenotypic and tumorigenic properties.

Using melanoma cell lines and melanoma cells freshly isolated from patient biopsies, we investigated the relationship between ABCB5+, CD271+ and low-MITF, expressing populations that were reported to display melanoma initiating cell properties. Here, we showed that ABCB5+ and CD271+ populations poorly overlap. However, we found that the CD271+ population is enriched in low-MITF cells and expresses a higher level of stemness genes, such as OCT4, NANOG and NES. These features could explain the increased tumorigenicity of the CD271+ cells. The rapid conversion of CD271+ to CD271− cells in vitro demonstrates the plasticity ability of melanoma cells. Finally, we observed that the transient slow-growing population contains only CD271+ cells that are highly tumorigenic. However, the fast growing/CD271+ population exhibits a poor tumorigenic ability. Taking together, our data show that CD271 is an imperfect marker for melanoma initiating cells, but may be useful to identify melanoma cells with an increased stemness and tumorigenic potential.

UVB Stimulates the Expression of Endothelin B Receptor in Human Melanocytes via a Sequential Activation of the p38/MSK1/CREB/MITF Pathway Which Can Be Interrupted by a French Maritime Pine Bark Extract through a Direct Inactivation of MSK1

Melanogenesis is the physiological process by which melanin is synthesized to protect the skin from UV damage. While paracrine interactions between keratinocytes and melanocytes are crucial for regulating epidermal pigmentation, the endothelin (EDN)-endothelin B-receptor (EDNRB) interaction is one of the key linkages. In this study, we found that a single exposure of normal human melanocytes (NHMs) with UVB stimulates the expression of EDNRB and its upstream transcription factor microphthalmia-associated transcription factor (MITF) at the transcriptional and translational levels. That stimulation can be abrogated by post-irradiation treatment with a French maritime pine bark extract (PBE). UVB stimulated the phosphorylation of p38 and c-jun N-terminal kinase (JNK), but not ERK, followed by the increased phosphorylation of MSK1 and CREB. The post-irradiation treatment with PBE did not affect the increased phosphorylation of p38 and JNK, but distinctly abrogated the phosphorylation of MSK1 and CREB. Post-irradiation treatment with the MSK1 inhibitor H89 significantly down-regulated the increased gene expression of MITF and EDNRB in UVB-exposed NHMs. Our findings indicate for the first time that the increased expression of MITF that leads to the up-regulation of melanocyte-specific proteins in UVB-exposed NHMs is mediated via activation of the p38/MSK1/CREB pathway but not the ERK/RSK/CREB pathway. The mode of action by PBE demonstrates that interrupting MSK1 activation is a new target for antioxidants including PBE which can serve as anti-pigmenting agents in a reactive oxygen species-depletion-independent manner.

The peripheral clock regulates human pigmentation

Although the regulation of pigmentation is well characterized, it remains unclear whether cell-autonomous controls regulate the cyclic on-off switching of pigmentation in the hair follicle (HF). As human HFs and epidermal melanocytes express clock genes and proteins, and given that core clock genes (PER1, BMAL1) modulate human HF cycling, we investigated whether peripheral clock activity influences human HF pigmentation. We found that silencing BMAL1 or PER1 in human HFs increased HF melanin content. Furthermore, tyrosinase expression and activity, as well as TYRP1 and TYRP2 mRNA levels, gp100 protein expression, melanocyte dendricity, and the number gp100+ HF melanocytes, were all significantly increased in BMAL1 and/or PER1-silenced HFs. BMAL1 or PER1 silencing also increased epidermal melanin content, gp100 protein expression, and tyrosinase activity in human skin. These effects reflect direct modulation of melanocytes, as BMAL1 and/or PER1 silencing in isolated melanocytes increased tyrosinase activity and TYRP1/2 expression. Mechanistically, BMAL1 knockdown reduces PER1 transcription, and PER1 silencing induces phosphorylation of the master regulator of melanogenesis, microphthalmia-associated transcription factor, thus stimulating human melanogenesis and melanocyte activity in situ and in vitro. Therefore, the molecular clock operates as a cell-autonomous modulator of human pigmentation and may be targeted for future therapeutic strategies.

Astaxanthin and withaferin A block paracrine cytokine interactions between UVB-exposed human keratinocytes and human melanocytes via the attenuation of endothelin-1 secretion and its downstream intracellular signaling

BACKGROUND

Paracrine interactions between keratinocytes and melanocytes via cytokines play an essential role in regulating pigmentation in epidermal hyperpigmentary disorders. There is an urgent need for a human epidermal model in which melanogenic paracrine interactions between UVB-exposed keratinocytes and melanocytes can be precisely evaluated because human epidermal equivalents consisting of multilayered keratinocytes and melanocytes have significant limitations in this respect.

OBJECTIVE

To resolve this challenge, we established a co-culture system with cell inserts using human keratinocytes and human melanocytes that serves as an appropriate new model for UVB-induced hyperpigmentation. Using that new model, we examined the blocking effects of two natural chemicals, astaxanthin and withaferin A, on paracrine cytokine interactions between UVB-exposed keratinocytes and melanocytes and characterized their mechanisms of action.

METHODS AND RESULTS

RT-PCR analysis showed that co-culture of human keratinocytes that had been exposed to UVB significantly stimulated human melanocytes to increase their expression of genes encoding microphthalmia-associated transcription factor, tyrosinase and tyrosinase-related protein 1. The catalytic activity of tyrosinase was also increased. ELISA assays revealed that UVB significantly increased the secretion of interleukin-1α, interleukin-6/8, granulocyte macrophage stimulatory factor and endothelin-1 but not α-melanocyte stimulating hormone. The addition of an endothelin-1 neutralizing antibody significantly abrogated the increase of tyrosinase activity. Post-irradiation treatment with astaxanthin or withaferin A significantly abolished the up-regulation of tyrosinase activity induced by UVB. Treatment with astaxanthin or withaferin A significantly reduced the increased levels of interleukin-1α, interleukin-6/8, granulocyte macrophage stimulatory factor and endothelin-1. Withaferin A but not astaxanthin also significantly abrogated the endothelin-1-stimulated activity of tyrosinase in melanocytes. Western blot analysis of intracellular signaling factors revealed that withaferin A but not astaxanthin significantly abolished the endothelin-1-stimulated phosphorylation of Raf-1, MEK, ERK, MITF and CREB in human melanocytes.

CONCLUSIONS

These results demonstrate that this co-culture system is an appropriate model to characterize melanogenic paracrine interactions and that astaxanthin and withaferin A serve as potent inhibitors of those interactions. Their effects are caused not only by down-regulating the increased secretion of an intrinsic melanogenic cytokine, endothelin-1, by UVB-exposed human keratinocytes, but also by interrupting the endothelin-1-triggered downstream intracellular signaling between protein kinase C and Raf-1 in human melanocytes (only for withaferin A).