Tyrosinase related protein 1 (TRP1) functions as a DHICA oxidase in melanin biosynthesis

Additive Effect of a Combination of Artocarpus lakoocha and Glycyrrhiza glabra Extracts on Tyrosinase Inhibition in Melanoma B16 Cells

Artocarpus lakoocha (Al) and Glycyrrhiza glabra (Gg) extracts have been reported to show tyrosinase inhibitory activity and melanin pigment reduction. This is the first study to assess the combination of Al and Gg extracts in enhancing inhibition of tyrosinase and reduction of melanin pigments. Al and Gg extracted by maceration in 70% and 95% ethanol were analyzed for oxyresveratrol and glabridin using Ultra High Performance Liquid Chromatography. Extracts of Al and Gg singly and combinations of Al95 and Gg95 were tested for cytotoxicity, tyrosinase inhibitory activity, and reduction of melanin pigments in melanoma B16 cells. Al95 had higher antioxidant, tyrosinase inhibitory activity and reduced more melanin pigments in B16 cells compared to Al70, and exhibited higher levels of oxyresveratrol. Gg95 inhibited oxidative stress and mushroom tyrosinase better than Gg70, and exhibited higher levels of glabridin. Combinations of Al95 and Gg95 at various ratios (concentration of 0.1 mg/mL) were not cytotoxic to B16 cells. Interestingly, Al95 and Gg95 combined at a ratio 9:1 reduced melanin pigment up to 53% in B16 cells. This combination of Al95 and Gg95 extracts exhibited the additive effect of reducing melanin pigments by suppressing the expression of microphthalmia-associated transcription factor (MITF), tyrosinase (TYR) and tyrosinase-related protein-2 (TRP-2) in B16 cells. The combination of Al and Gg extracts could be developed as skin care products for hyperpigmentation treatment.

Chemical Reactivities of ortho-Quinones Produced in Living Organisms: Fate of Quinonoid Products Formed by Tyrosinase and Phenoloxidase Action on Phenols and Catechols

Tyrosinase catalyzes the oxidation of phenols and catechols (o-diphenols) to o-quinones. The reactivities of o-quinones thus generated are responsible for oxidative browning of plant products, sclerotization of insect cuticle, defense reaction in arthropods, tunichrome biochemistry in tunicates, production of mussel glue, and most importantly melanin biosynthesis in all organisms. These reactions also form a set of major reactions that are of nonenzymatic origin in nature. In this review, we summarized the chemical fates of o-quinones. Many of the reactions of o-quinones proceed extremely fast with a half-life of less than a second. As a result, the corresponding quinone production can only be detected through rapid scanning spectrophotometry. Michael-1,6-addition with thiols, intramolecular cyclization reaction with side chain amino groups, and the redox regeneration to original catechol represent some of the fast reactions exhibited by o-quinones, while, nucleophilic addition of carboxyl group, alcoholic group, and water are mostly slow reactions. A variety of catecholamines also exhibit side chain desaturation through tautomeric quinone methide formation. Therefore, quinone methide tautomers also play a pivotal role in the fate of numerous o-quinones. Armed with such wide and dangerous reactivity, o-quinones are capable of modifying the structure of important cellular components especially proteins and DNA and causing severe cytotoxicity and carcinogenic effects. The reactivities of different o-quinones involved in these processes along with special emphasis on mechanism of melanogenesis are discussed.

Melanogenic Inhibition and Toxicity Assessment of Flavokawain A and B on B16/F10 Melanoma Cells and Zebrafish (Danio rerio)

Excessive production of melanin implicates hyperpigmentation disorders. Flavokawain A (FLA) and flavokawain B (FLB) have been reported with anti-melanogenic activity, but their melanogenic inhibition and toxicity effects on the vertebrate model of zebrafish are still unknown. In the present study, cytotoxic as well as melanogenic effects of FLA and FLB on cellular melanin content and tyrosinase activity were evaluated in α-MSH-induced B16/F10 cells. Master regulator of microphthalmia-associated transcription factor (Mitf) and the other downstream melanogenic-related genes were verified via quantitative real time PCR (qPCR). Toxicity assessment and melanogenesis inhibition on zebrafish model was further observed. FLA and FLB significantly reduced the specific cellular melanin content by 4.3-fold and 9.6-fold decrement, respectively in α-MSH-induced B16/F10 cells. Concomitantly, FLA significantly reduced the specific cellular tyrosinase activity by 7-fold whilst FLB by 9-fold. The decrement of melanin production and tyrosinase activity were correlated with the mRNA suppression of Mitf which in turn down-regulate Tyr, Trp-1 and Trp-2. FLA and FLB exhibited non-toxic effects on the zebrafish model at 25 and 6.25 µM, respectively. Further experiments on the zebrafish model demonstrated successful phenotype-based depigmenting activity of FLA and FLB under induced melanogenesis. To sum up, our findings provide an important first key step for both of the chalcone derivatives to be further studied and developed as potent depigmenting agents.

Thymocid®, a Standardized Black Cumin (Nigella sativa) Seed Extract, Modulates Collagen Cross-Linking, Collagenase and Elastase Activities, and Melanogenesis in Murine B16F10 Melanoma Cells

Black cumin (Nigella sativa) seed extract has been shown to improve dermatological conditions, yet its beneficial effects for skin are not fully elucidated. Herein, Thymocid®, a chemically standardized black cumin seed extract, was investigated for its cosmeceutical potential including anti-aging properties associated with modulation of glycation, collagen cross-linking, and collagenase and elastase activities, as well as antimelanogenic effect in murine melanoma B16F10 cells. Thymocid® (50, 100, and 300 µg/mL) inhibited the formation of advanced glycation end-products (by 16.7-70.7%), collagen cross-linking (by 45.1-93.3%), collagenase activity (by 10.4-92.4%), and elastases activities (type I and III by 25.3-75.4% and 36.0-91.1%, respectively). In addition, Thymocid® (2.5-20 µg/mL) decreased melanin content in B16F10 cells by 42.5-61.6% and reduced cellular tyrosinase activity by 20.9% (at 20 µg/mL). Furthermore, Thymocid® (20 µg/mL for 72 h) markedly suppressed the mRNA expression levels of melanogenesis-related genes including microphthalmia-associated transcription factor (MITF), tyrosinase-related protein 1 (TYRP1), and TYRP2 to 78.9%, 0.3%, and 0.2%, respectively. Thymocid® (10 µg/mL) also suppressed the protein expression levels of MITF (by 15.2%) and TYRP1 (by 97.7%). Findings from this study support the anti-aging and antimelanogenic potential of Thymocid® as a bioactive cosmeceutical ingredient for skin care products.

Lactobacillus helveticus-Fermented Milk Whey Suppresses Melanin Production by Inhibiting Tyrosinase through Decreasing MITF Expression

Whey obtained from milk fermented by the Lactobacillus helveticus CM4 strain (LHMW) has been shown to improve skin barrier function and increase skin-moisturizing factors. In this study, we investigated the effects of LHMW on melanin production to explore the additional impacts of LHMW on the skin. We treated mouse B16 melanoma cells with α-melanocyte-stimulating hormone (α-MSH) alone or simultaneously with LHMW and measured the amount of melanin. The amount of melanin in B16 cells treated with α-MSH significantly increased by 2-fold compared with that in control cells, and tyrosinase activity was also elevated. Moreover, treatment with LHMW significantly suppressed the increase in melanin content and elevation of tyrosinase activity due to α-MSH. LHMW also suppressed the α-MSH-induced increased expression of tyrosinase, tyrosinase-related protein 1 (TRP1), and dopachrome tautomerase (DCT) at the protein and mRNA levels. Furthermore, the mRNA and protein microphthalmia-associated transcription factor (MITF) expression levels were significantly increased with treatment with α-MSH alone, which were also suppressed by LHMW addition. LHMW suppression of melanin production is suggested to involve inhibition of the expression of the tyrosinase gene family by lowering the MITF expression level. LHMW may have promise as a material for cosmetics with expected clinical application in humans.

Synthesis of Resorcinol Derivatives and their Effects on Melanin Production

Several resorcinol derivatives were synthesized and their effects on the survival rate of B16 murine melanoma cells, melanin production, and tyrosinase activity were investigated with an aim to evaluate their skin whitening effect. Twelve resorcinol derivatives were synthesized by esterification with three functional groups (L-ascorb-6-yl, ethyl, and glyceryl) linked via four alkyl chains of varying lengths (n = 2–5) at the 4-position. The structures of the 12 resorcinol derivatives were confirmed by Nuclear Magnetic Resonance (NMR). The derivatives were added to B16 murine melanoma cells and the melanin contents in the cells and culture medium were measured. To measure the tyrosinase activity, the substrate L-DOPA was added to a mushroom-derived tyrosinase solution, and the inhibition of the tyrosinase activity was determined. At 10 µM, the resorcinol derivatives did not affect the survival of the B16 murine melanoma cells, but the melanin content was reduced. At 1 µM, the derivatives significantly inhibited the tyrosinase activity in the mushroom-derived tyrosinase solution. A plot of the inhibitory effect on melanin production against the cLogP value for each resorcinol derivative indicated that the highest inhibition occurred at a cLogP value of approximately 2. Therefore, these resorcinol derivatives are expected to serve as effective skin whitening agents.

Melanogenesis-inhibitory activities of limonoids and tricyclic diterpenoids from Azadirachta indica

The chemical constituents of the roots and bark of Azadirachta indica were investigated, leading to the isolation of six tricyclic diterpenoids and four limonoids including a new compound, azadirachtin J (4). The structures were elucidated on the basis of NMR spectroscopic techniques, mass spectrometry as well as comparison with the literature. Furthermore, melanogenesis-inhibitory activities of the isolated compounds were evaluated. As a result, compounds 1-3 and 10 exhibited superior inhibitory activities against melanogenesis with no, or almost no, toxicity to the cells (86.5-105.1% cell viability). Western blot analysis showed that compounds 1 and 3 exhibited melanogenesis inhibitory activities in α-MSH-stimulated B16 melanoma cells due to, at least in part, inhibition of the expression of MITF, followed by a decrease in the expression of tyrosinase, TRP-1, and TRP-2. Compounds 1 and 3 exhibited tyrosinase inhibitory activities (IC₅₀ values of 44.86 μM and 69.85 μM respectively). Docking results confirm that the active inhibitors strongly interact with tyrosinase residues.

Tyrosinase-Targeting Gallacetophenone Inhibits Melanogenesis in Melanocytes and Human Skin-Equivalents

Demands for safe depigmentation compounds are constantly increasing in the pharmaceutical and cosmetic industry, since the numerous relevant compounds reported to date have shown undesirable side effects or low anti-melanogenic effects. In this study, we reported three novel inhibitors of tyrosinase, which is the key enzyme in melanogenesis, identified using docking-based high throughput virtual screening of an in-house natural compound library followed by mushroom tyrosinase inhibition assay. Of the three compounds, gallacetophenone showed high anti-melanogenic effect in both human epidermal melanocytes and a 3D human skin model, MelanoDerm. The inhibitory effect of gallacetophenone on tyrosinase was elucidated by computational molecular modeling at the atomic level. Binding of gallacetophenone to the active site of tyrosinase was found to be stabilized by hydrophobic interactions with His367, Ile368, and Val377; hydrogen bonding with Ser380 and a water molecule bridging the copper ions. Thus, our results strongly suggested gallacetophenone as an anti-melanogenic ingredient that inhibits tyrosinase.

Anti-melanogenic activity of methanolic extract from leaves of Sorbaria sorbifolia var. stellipila Max. on α-MSH-stimulated B16 melanoma 4A5 cells

Background

Melanin is a pigment, which is widely distributed in organisms. In humans, melanin pigments determine eye, hair, and skin color and protect the skin from damage by ultraviolet radiation; however, immoderate distribution of melanin in the skin causes discoloration. In the present study, we screened methanolic extracts from leaves of 47 plant species, most of which are native to East Asia, for the inhibitory activity against melanogenesis.

Methods

B16 melanoma 4A5 cells were used in all assays conducted in this study. Melanin content assay was performed using methanolic extracts from leaves of 47 plant species. Cytotoxicity of the extract from leaves of Sorbaria sorbifolia var. stellipila Max. (SME) was evaluated by WST-8 assay. Tyrosinase activity was determined using the lysate of α-MSH-stimulated B16 melanoma 4A5 cells and L-dopa as a colorimetric substrate. Melanogenic gene expression was determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

Results

SME showed the highest inhibitory activity among tested samples without cytotoxicity. SME exhibited the inhibition potency for the enzymatic activity of tyrosinase. In addition, qRT-PCR result displayed that SME downregulates the expression of melanogenic genes including tyrosinase, TRP-1, TRP-2, and the transcription factor MITF.

Conclusion

Overall results revealed that the extract from leaves of S. sorbifolia var. stellipila Max. has a potential to be used as a skin whitening agent.

RNA-seq profiling of skin in temperate and tropical cattle

Skin is a major thermoregulatory organ in the body controlling homeothermy, a critical function for climate adaptation. We compared genes expressed between tropical- and temperate-adapted cattle to better understand genes involved in climate adaptation and hence thermoregulation. We profiled the skin of representative tropical and temperate cattle using RNA-seq. A total of 214,754,759 reads were generated and assembled into 72,993,478 reads and were mapped to unique regions in the bovine genome. Gene coverage of unique regions of the reference genome showed that of 24,616 genes, only 13,130 genes (53.34%) displayed more than one count per million reads for at least two libraries and were considered suitable for downstream analyses. Our results revealed that of 255 genes expressed differentially, 98 genes were upregulated in tropically-adapted White Fulani (WF; Bos indicus) and 157 genes were down regulated in WF compared to Angus, AG (Bos taurus). Fifteen pathways were identified from the differential gene sets through gene ontology and pathway analyses. These include the significantly enriched melanin metabolic process, proteinaceous extracellular matrix, inflammatory response, defense response, calcium ion binding and response to wounding. Quantitative PCR was used to validate six representative genes which are associated with skin thermoregulation and epithelia dysfunction (mean correlation 0.92; p < 0.001). Our results contribute to identifying genes and understanding molecular mechanisms of skin thermoregulation that may influence strategic genomic selection in cattle to withstand climate adaptation, microbial invasion and mechanical damage.

3,4,5-Tri-O-Caffeoylquinic Acid Promoted Hair Pigmentation Through β-Catenin and Its Target Genes

The hair follicle undergoes a regular cycle composed of three phases: anagen, catagen, and telogen. The life of follicular melanocytes is totally linked to the hair cycle; and during anagen or the growth phase, the melanocytes are active and produce the melanin responsible of hair shaft pigmentation. Various signaling pathways regulate the hair growth cycle and, therefore, the pigmentation; we distinguish the Wnt/β-catenin signaling pathway as it plays a major role in the development, growth, and proliferation of the melanocytes and the activation of melanogenesis enzymes and the related transcription factor. In this study, 3,4,5-tri-O-caffeoylquinic acid (TCQA), a caffeoylquinic acid derivative, stimulated the pigmentation in C3H mouse hair follicle, in human melanocytes, and B16F10 melanoma cells. An enhancement in pigmentation associated genes was observed upon TCQA treatment in vivo and in vitro. Interestingly, the expression of β-catenin was remarkably upregulated in mouse treated skin and in pigment cell lines. Moreover, TCQA upregulated CTNNB1 expression after inhibition in human melanocytes. Taken together, this study suggests that TCQA triggered β-catenin activation to enhance the pigmentation during the anagen phase of the hair cycle.

The effect of antioxidant and whitening action on Plantago asiatica L. leaf ethanol extract for health care

BACKGROUND

The Plantago asiatica L. is easy to cultivate and has been used as a folk remedy since ancient times because of various pharmacological actions such as anti-inflammation and antioxidation. It also contains a variety of flavonoids such as aucubin, which is thought to be excellent for whitening, antioxidant and anti-inflammatory action.

OBJECTIVE

We investigated the effect of P. asiatica L. leaf ethanol extracts containing various active ingredients on antioxidative, anti-inflammation and whitening action and investigated its potential as a health care material. P. asiatica L. has been widely used in folk remedies.

RESULTS

The cell toxicity test using RAW264.7 cells showed a high cell survival rate of over 75%, thus demonstrating the safety of the sample. In order to study the antioxidant activity of P. asiatica L. leaf ethanol extracts, we studied a sample which showed radical scavenging activity in a dose-dependent manner. To observe the antioxidant activity at the cell level, RAW 264.7 cells were used and inhibition of ROS production was measured. The ROS production was suppressed in a dose-dependent manner and the scavenging activity was stronger than the sample's own radical scavenging ability. To observe the anti-inflammatory effect of P. asiatica L. leaf ethanol extracts, inhibition of NO generation was observed using LPS-induced RAW 264.7 cells. NO generation was inhibited in a dose-dependent manner and was strongly inhibited by 31% at 100 μg/mL. In vitro, L-DOPA and L-tyrosine were used to inhibit tyrosinase action in a dose-dependent manner. The concentration of melanin at 1, 10, and 100 μg/mL was suppressed in B16 F10 melanin cells supplemented with α-MSH in the cells, and the inhibition was suppressed to 29% at 100 μg/mL. In the B16 F10 melanin cell stimulated with MSH, the P. asiatica L. leaf ethanol extracts inhibited melanin formation in a dose-dependent manner.

CONCLUSION

P. asiatica L. leaf ethanol extracts are expected to be developed as whitening cosmeceutical ingredients and as health care ingredients with antioxidant and anti-inflammatory properties.

Challenging the concept that eumelanin is the polymorphic brown banded pigment in Cepaea nemoralis

The common grove snail Cepaea nemoralis displays a stable pigmentation polymorphism in its shell that has held the attention of scientists for decades. While the details of the molecular mechanisms that generate and maintain this diversity remain elusive, it has long been employed as a model system to address questions related to ecology, population genetics and evolution. In order to contribute to the ongoing efforts to identify the genes that generate this polymorphism we have tested the long-standing assumption that melanin is the pigment that comprises the dark-brown bands. Surprisingly, using a newly established analytical chemical method, we find no evidence that eumelanin is differentially distributed within the shells of C. nemoralis. Furthermore, genes known to be responsible for melanin deposition in other metazoans are not differentially expressed within the shell-forming mantle tissue of C. nemoralis. These results have implications for the continuing search for the supergene that generates the various pigmentation morphotypes.

Phenylthiourea Binding to Human Tyrosinase-Related Protein 1

Tyrosinase-related protein 1 (TYRP1) is one of the three human melanogenic enzymes involved in the biosynthesis of melanin, a pigment responsible for the color of the skin, hair, and eyes. It shares high sequence identity with tyrosinase, but has two zinc ions in its active site rather than two copper ions as in tyrosinase. Typical tyrosinase inhibitors do not directly coordinate to the zinc ions of TYRP1. Here, we show, from an X-ray crystal structure determination, that phenylthiourea, a highly potent tyrosinase inhibitor, does neither coordinate the active site zinc ions, but binds differently from other structurally characterized TYRP1-inhibitor complexes. Its aromatic ring is directed outwards from the active site, apparently as a result from the absence of polar oxygen substituents that can take the position of water molecules bound in the active site. The compound binds via hydrophobic interactions, thereby blocking substrate access to the active site.

Protein Stability and Functional Characterization of Intra-Melanosomal Domain of Human Recombinant Tyrosinase-Related Protein 1

Pigmentation is the result of a complex process by which the biopolymer melanin is synthesized and packed into melanosomes of melanocytes. Various types of oculocutaneous albinism (OCA), a series of autosomal recessive disorders, are associated with reduced pigmentation in the skin, eyes, and hair due to genetic mutations of proteins involved in melanogenesis. Human tyrosinase (Tyr) and tyrosinase-related protein 1 (Tyrp1) drives the enzymatic process of pigment bio-polymerization. However, within the melanogenic pathway, Tyrp1 has catalytic functions not clearly defined and distinct from Tyr. Here, we characterize the biochemical and biophysical properties of recombinant human Tyrp1. For this purpose, we purified and analyzed the intra-melanosomal domain (Tyrp1tr) for protein stability and enzymatic function in conditions mimicking the environment within melanosomes and the endoplasmic reticulum. The study suggests that Tyrp1tr is a monomeric molecule at ambient temperatures and below (<25 °C). At higher temperatures, >31 °C, higher protein aggregates form with a concurrent decrease of monomers in solution. Also, Tyrp1tr diphenol oxidase activity at pH 5.5 rises as both the pre-incubation temperature and the higher molecular weight protein aggregates formation increases. The enhanced protein activity is consistent with the volume exclusion change caused by protein aggregates.

Transcriptome analysis provides insight into the role of the melanin pathway in two differently pigmented strains of the turtle Pelodiscus sinensis

Pelodiscus sinensis is the most common turtle species raised in East and Southeast Asia. The Japanese strain and the Qingxi black strain are important aquatic breeds of P. sinensis in China with unique characteristics in terms of production performance and appearance, including skin color. In this study, melanin content measure and histological analysis on skin samples of these two strains were carried out to compare their color characteristics. The results showed that Qingxi black turtles clearly have a greater ability to deposit melanin than the Japanese strain especially in the abdomen. Then, de novo transcriptome assembly and differential expression profiling analyses on the ventral skin from the two strains were performed to identify the genes responsible for the differences in skin color using the Illumina RNA-Seq system with three biological replicates. A total of 19,331 annotated unigenes were found by aligning to the reference genome of P. sinensis using TopHat v2.0.12. Differential expression analysis revealed that 670 genes were expressed differently, including 185 upregulated genes and 485 downregulated genes in Qingxi black strain using the DESeq R package (|log2FoldChange| ≥ 1, padj < 0.05). Sixteen differentially expressed genes (DEGs), which were randomly selected, were confirmed by quantitative real-time PCR (qRT-PCR). GO and KEGG analyses revealed four DEGs (agouti signaling protein, frizzled family receptor 1, phospholipase C, and protein kinase C) were related to melanogenesis pathway. Gene expression levels of the four DEGs as well as three genes from the tyrosinase gene family were measured by qRT-PCR. The results indicated that agouti signaling protein, tyrosinase-related protein, and dopachrome tautomerase could be the main genes responsible for the difference in abdominal skin color between the two turtle strains. This study provided valuable information for further analysis of the melanogenesis mechanisms in different varieties of P. sinensis.

Effect of fatty acids on melanogenesis and tumor cell growth in melanoma cells

Fatty acids have various physiological effects on melanoma. For example, palmitic acid (PA) increases melanin levels; linoleic acid and DHA decrease melanin levels; and DHA suppresses tumor growth. In this study, we focused on the relationship between the structure of fatty acids and their physiological effects in melanoma to examine the likely mechanisms of action. We showed that saturated fatty acids and PUFAs display opposing effects on melanin content in melanoma cells. Likewise, PA and EPA have opposing effects in terms of actin polymerization. Our findings suggest that PA and EPA change melanin content in melanoma to alter melanosome trafficking by modulating actin polymerization. Here, we also examined the mechanism of the anti-tumor effect of DHA. We found that DHA interacts with receptor for activated C kinase 1 and represses melanoma cell proliferation by suppressing protein kinase C signaling. Our results suggest a new mechanism to explain the physiological effects of fatty acids.

Micro RNAs upregulated in Vitiligo skin play an important role in its aetiopathogenesis by altering TRP1 expression and keratinocyte-melanocytes cross-talk

Translation of genes is regulated by many factors including microRNAs (miRNAs). miRNA profiling of lesional and non-lesional epidermal RNA from 18 vitiligo patients revealed significant upregulation of 29 miRNAs in the lesional epidermis, of which 6 miRNAs were transfected in normal human epidermal keratinocytes (NHEKs) to study their downstream effects using quantitative proteomics. Many proteins involved in oxidative stress, Vesicle trafficking, Cellular apoptosis, Mitochondrial proteins and Keratins were regulated after miRNA transfections in the keratinocytes. However, tyrosinase related protein-1 (TRP1/TYRP1), a melanogenesis protein, was consistently downregulated in NHEKs by all the six miRNAs tested, which was quite intriguing. TRP1 was also downregulated in lesional epidermis compared with non-lesional epidermis. Since melanocytes synthesize and transfer melanosomes to the surrounding keratinocytes, we hypothesized that downregulation of TRP1 in NHEKs may have a role in melanosome transfer, which was confirmed by our co-culture experiments. Downregulation of TRP1 in keratinocytes negatively affected the melanosome transfer from melanocytes to keratinocytes resulting in melanin accumulation which may be leading to melanin induced cytotoxicity in melanocytes. Regulation of key processes involved in aetiopathogenesis of vitiligo along with TRP1 suggests that miRNAs act in an integrated manner which may be detrimental for the loss of melanocytes in vitiligo.

A New Tyrosinase Inhibitor from the Red Alga Symphyocladia latiuscula (Harvey) Yamada (Rhodomelaceae)

A marine red alga, Symphyocladia latiuscula (Harvey) Yamada (Rhodomelaceae), is a rich source of bromophenols with a wide array of biological activities. This study investigates the anti-tyrosinase activity of the alga. Moderate activity was demonstrated by the methanol extract of S. latiuscula, and subsequent column chromatography identified three bromophenols: 2,3,6-tribromo-4,5-dihydroxybenzyl methyl alcohol (1), 2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether (2), and bis-(2,3,6-tribromo-4,5-dihydroxybenzyl methyl ether) (3). Bromophenols 1 and 3 exhibited potent competitive tyrosinase inhibitory activity against l-tyrosine substrates, with IC₅₀ values of 10.78 ± 0.19 and 2.92 ± 0.04 μM, respectively. Against substrate l-3,4-dihydroxyphenylalanine (l-DOPA), compounds 1 and 3 demonstrated moderate activity, while 2 showed no observable effect. The experimental data were verified by a molecular docking study that found catalytic hydrogen and halogen interactions were responsible for the activity. In addition, compounds 1 and 3 exhibited dose-dependent inhibitory effects in melanin and intracellular tyrosinase levels in α-melanocyte-stimulating hormone (α-MSH)-induced B16F10 melanoma cells. Compounds 3 and 1 were the most effective tyrosinase inhibitors. In addition, increasing the bromine group number increased the mushroom tyrosinase inhibitory activity.

Minimal Efficacy of Nitisinone Treatment in a Novel Mouse Model of Oculocutaneous Albinism, Type 3

Purpose

Oral nitisinone has been shown to increase fur and ocular pigmentation in a mouse model of oculocutaneous albinism (OCA) due to hypomorphic mutations in tyrosinase (TYR), OCA1B. This study determines if nitisinone can improve ocular and/or fur pigmentation in a mouse model of OCA type 3 (OCA3), caused by mutation of the tyrosinase-related protein 1 (Tyrp1) gene.

Methods

Mice homozygous for a null allele in the Tyrp1 gene (C57BL/6J-Tyrp1 b-J/J) were treated with 8 mg/kg nitisinone or vehicle every other day by oral gavage. Changes in fur and ocular melanin pigmentation were monitored. Mature ocular melanosome number and size were quantified in pigmented ocular structures by electron microscopy.

Results

C57BL/6J-Tyrp1 b-J/J mice carry a novel c.403T>A; 404delG mutation in Tyrp1, predicted to result in premature truncation of the TYRP1 protein. Nitisinone treatment resulted in an approximately 7-fold increase in plasma tyrosine concentrations without overt toxicity. After 1 month of treatment, no change in the color of fur or pigmented ocular structures was observed. The distribution of melanosome cross-sectional area was unchanged in ocular tissues. There was no significant difference in the number of pigmented melanosomes in the RPE/choroid of nitisinone-treated and control groups. However, there was a significant difference in the number of pigmented melanosomes in the iris.

Conclusions

Treatment of a mouse model of OCA3 with oral nitisinone did not have a favorable clinical effect on melanin production and minimally affected the number of pigmented melanosomes in the iris stroma. As such, treatment of OCA3 patients with nitisinone is unlikely to be therapeutic.

Use of tyrosine hydroxylase RNAi to study Megoura viciae (Hemiptera: Aphididae) sequestration of its host's l-DOPA for body melanism

Melanism in insects is important for their physical protection, immunoreactions, and sclerotization. The vetch aphid, Megoura viciae (Buckton), has relatively strong tanning in its prothorax, head, antennae, cornicles, and legs. It was hypothesized that M. viciae may sequester the high level of l-DOPA in its host Vicia faba to help in its melanization process for ecological adaptation. To confirm this hypothesis, the amount of l-DOPA in M. viciae was modified and quantified. We first generated a Trifolium repens (clover, low l-DOPA containing) host to cut off the extra l-DOPA intake by M. viciae. The rate-limiting tyrosine hydroxylase gene of M. viciae (MV-TH) was then cloned and analyzed. To further reduce the l-DOPA level in the insect, RNAi was used to downregulate the transcriptional level of MV-TH. Our results confirmed that M. viciae could indeed sequester l-DOPA in its body, and its ample storage of this amino acid could be the reason for the strong tanning of its body. M. viciae reared on T. repens could upregulate its MV-TH to enhance l-DOPA biosynthesis and thus maintain a high level of l-DOPA. The MV-TH repression by RNAi lasted for about 3 days, successfully decreasing the l-DOPA level. Aside from a slight decrease in exuvia tanning, no other obvious change in body appearance was detected in the RNAi-treated insect. Although M. viciae can obtain most of its l-DOPA directly from its original host, its internal l-DOPA synthetase is still functional, especially when extra l-DOPA is removed from the diet. This capability to enhance its shield ensures the ecological adaptation of this insect.

Src inhibition induces melanogenesis in human G361 cells

The Src kinase family (SKF) includes non-receptor tyrosine kinases that interact with many cellular cytosolic, nuclear and membrane proteins, and is involved in the progression of cellular transformation and oncogenic activity. However, there is little to no evidence on the effect of SKF or its inhibitors on melanogenesis. Therefore, the present study investigated whether C-terminal Src kinase inhibition can induce melanogenesis and examined the associated signaling pathways and mRNA expression of melanogenic proteins. First, whether stimulators of melanogenesis, such as ultraviolet B and α-melanocyte-stimulating hormone, can dephosphorylate Src protein was evaluated, and the results revealed that SU6656 and PP2 inhibited the phosphorylation of Src in G361 cells. Src inhibition by these chemical inhibitors induced melanogenesis in G361 cells and upregulated the mRNA expression levels of melanogenesis-associated genes encoding microphthalmia-associated transcription factor, tyrosinase-related protein 1 (TRP1), TRP2, and tyrosinase. In addition, Src inhibition by small interfering RNA induced melanogenesis and upregulated the mRNA expression levels of melanogenesis-associated genes. As the p38 mitogen-activated protein kinase (MAPK) and cyclic adenosine monophosphate response element binding (CREB) pathways serve key roles in melanogenesis, the present study further examined whether Src mediates melanogenesis via these pathways. As expected, Src inhibition via SU6656 or PP2 administration induced the phosphorylation of p38 or CREB, as determined by western blotting analysis, and increased the levels of phosphorylated p38 or CREB, as determined by immunofluorescence staining. In addition, the induced pigmentation and melanin content of G361 cells by Src inhibitors was significantly inhibited by p38 or CREB inhibitors. Taken together, these data indicate that Src is associated with melanogenesis, and Src inhibition induces melanogenesis via the MAPK and CREB pathways in G361 cells.

Melanosomes: Biogenesis, Properties, and Evolution of an Ancient Organelle

Melanosomes are organelles that produce and store melanin, a widespread biological pigment with a unique suite of properties including high refractive index, semiconducting capabilities, material stiffness, and high fossilization potential. They are involved in numerous critical biological functions in organisms across the tree of life. Individual components such as melanin chemistry and melanosome development have recently been addressed, but a broad synthesis is needed. Here, we review the hierarchical structure, development, functions, and evolution of melanosomes. We highlight variation in melanin chemistry and melanosome morphology and how these may relate to function. For example, we review what is known of the chemical differences between different melanin types (eumelanin, pheomelanin, allomelanin) and whether/how melanosome morphology relates to chemistry and color. We integrate the distribution of melanin across living organisms with what is known from the fossil record and produce hypotheses on its evolution. We suggest that melanin was present in life forms early in evolutionary history and that melanosomes evolved at the origin of organelles. Throughout, we discuss the (sometimes gaping) holes in our knowledge and suggest areas that need particular attention as we move forward in our understanding of these still-mysterious organelles and the materials that they contain.

Leathesia difformis Extract Inhibits α-MSH-Induced Melanogenesis in B16F10 Cells via Down-Regulation of CREB Signaling Pathway

Leathesia difformis (L.) Areschoug (L. difformis) is a species of littoral brown algae of the class Phaeophyceae. Only a few studies on the apoptotic, antiviral, and antioxidant properties of L. difformis have been reported, and its inhibitory effect on melanin synthesis has not been studied. The aim of this study was to investigate the anti-melanogenic effect of L. difformis extract on α-melanocyte-stimulating hormone (α-MSH)-induced B16F10 melanocytes and its mechanism of action. L. difformis was extracted using 80% ethanol (LDE) and then fractioned between ethyl acetate (LDE-EA) and water (LDE-A). Our data demonstrated that LDE-EA significantly inhibited melanin level and cellular tyrosinase activity in α-MSH-stimulated B16 cells. In addition, the expression of genes associated with melanin synthesis, such as microphthalmia-associated transcription factor (Mitf), tyrosinase (Tyr), tyrosinase-related protein-1 (Trp-1), dopachrome tautomerase (Dct), and melanocortin 1 receptor (Mc1r) was down-regulated by LDE-EA treatment. Moreover, LDE-EA decreased p-CREB levels, which suggests that the inhibition of the cAMP/PKA/CREB pathways may be involved in the anti-melanogenic effect of LDE-EA. Thus, this study revealed that LDE-EA is an effective inhibitor of hyperpigmentation through inhibition of CREB pathways and may be considered as a potential therapeutic agent for hyperpigmentation disorders.

Feather follicles transcriptome profiles in Bashang long-tailed chickens with different plumage colors

Despite the rich variety in plumage color found in nature, genetic studies on how feather follicles affect pigmentation are often limited to animals that have black and white pigment. To test how gene expression influences plumage color, transcriptomes of chicken feather follicles with white, black, hemp, reed catkins, silvery grey, and landscape plumage colors were generated using Illumina sequencing. We generated six RNA-Seq libraries with over 25 million paired-end clean reads per library with percentage of paired-end clean reads ranging from 96.73 to 96.98%. 78% of the reads mapped to the chicken genome, and approximately 70% of the reads were mapped to exons and 6% mapped to introns. Transcriptomes of feather follicles producing hemp and land plumage were similar, but these two showed moderate differences compared with gray and reed colored plumage. The black and white follicle transcriptomes were most divergent from the other colors. We identified several candidate genes, including GPNMB, PMEL, TYRP1, GPR143, OCA2, SOX10, SLC45A2, KRT75, and TYR. All of these genes are known to induce pigment formation in mice. White feathers result from the lack of pigment formation, and our results suggest that the white chickens due to the recessive insertion mutation of TYR. The formation of black area size and color depth may be due to the expression levels of GPNMB, PMEL, TYRP1, GPR143, OCA2, SOX10, SLC45A2, KRT75, and TYR. The GO analysis of the differentially expressed genes (DEGs) revealed that DEGs in our transcriptome analysis were enriched in cytoskeleton and cell structure related pathways. The black plumage transcriptome showed significant differences in melanogenesis, tyrosine metabolism, and riboflavin metabolism compared with transcriptomes of other plumage colors. The transcriptome profiles of the different chicken plumage colors provide a valuable resource to understand how gene expression influences plumage color, and will be an important resource for identifying candidate genes in breeding programs.

Chemical Constituents of the Seed Cake of Camellia oleifera and Their Antioxidant and Antimelanogenic Activities

There is a growing interest in the exploitation of agricultural byproducts. This study explored the potential beneficial health effects from the main biowaste, tea seed pomace of Camellia oleifera Abel (Theaceae), produced when tea seed is processed. Eighteen compounds were isolated from the 70% EtOH extract of the seed cake of C. oleifera. Their structures were determined by ESI-MS, ¹ H- and ¹³ C-NMR together with literature data. All fractions and compounds were evaluated for the antioxidant and melanogenesis inhibitory activities. As the result, AcOEt fraction has the best in vitro antioxidant and antimelanogenesis activities, compounds 7 - 12 and 15 showed remarkable antioxidant activity, compounds 4, 6, 8, and 15 - 17 exhibited superior inhibitory activities against melanogenesis. Furthermore, tyrosinase inhibitory activity assay suggested that compound 8 could suppress melanogenesis by inhibiting the expression of tyrosinase.

The Late Stages of Melanogenesis: Exploring the Chemical Facets and the Application Opportunities

In the last decade, the late stages of melanin biosynthesis involving the oxidative polymerization of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) have been extensively investigated. Most of the information derived from a biomimetic approach in which the oxidation of melanogenic indoles was carried out under conditions mimicking those occurring in the biological environment. Characterization of the early oligomers allowed for drawing a structural picture of DHI and DHICA melanins, providing also an interpretative basis for the different properties exhibited by these pigments, e.g., the chromophore and the antioxidant ability. The improved knowledge has opened new perspectives toward the exploitation of the unique chemistry of melanins and its precursors in cosmetic and health care applications. A noticeable example is the development of an innovative hair dyeing system that is based on the marked ease of DHI to give rise to black melanin on air oxidation under slightly alkaline conditions. The advantage of this method for a step-wise coverage of gray hair with a natural shade pigmentation on repeated treatment with a DHI-based formulation with respect to traditional dyes is presented. A variant of DHICA melanin combining solubility in water-miscible organic solvents, an intense chromophore in the UltraViolet-A UV-A region, and a marked antioxidant potency was evaluated as an ingredient for cosmetic formulations.

Improved antimelanogenesis and antioxidant effects of polysaccharide from Cuscuta chinensis Lam seeds after enzymatic hydrolysis

Cuscuta chinensis polysaccharide (CPS) was extracted using hot water and enzymatically hydrolyzed C. chinensis polysaccharide (ECPS) was produced by the mannase enzymatic hydrolysis process. The purpose of this research was to investigate the antimelanogenic activity of ECPS and CPS in B16F10 melanoma cells. The in vitro antioxidant activity was assessed by their ferric iron reducing power and DPPH free radical scavenging activities. The molecular mass distribution of polysaccharides was determined using SEC-MALLS-RI. CPS was successfully enzymatically degraded using mannase and the weighted average molecular weights of CPS and ECPS were 434.6 kDa and 211.7 kDa. The results of biological activity assays suggested that the enzymatically hydrolyzed polysaccharide had superior antimelanogenic activity and antioxidant effect than the original polysaccharide. ECPS exhibited antimelanogenic activity by down-regulating the expression of tyrosinase, MITF, and TRP-1 without cytotoxic effects in B16F10 melanoma cells. In conclusion, ECPS have the potential to become a skin whitening product.

Three new cardiac glycosides obtained from the roots of Streblus asper Lour. and their cytotoxic and melanogenesis-inhibitory activities

Three new cardiac glycosides strophanthidin-3-O-α-l-rhamnopyranosyl-(1→4)-6-deoxy-β-d-allopyranoside (1), 5βH-16β-acetylkamaloside (2), and mansonin-19-carboxylic acid (3) along with seven known steroids including five cardiac glycosides were isolated from the methanol extracts of Streblus asper Lour. roots. The structures of these compounds were established by spectroscopic analyses. The cytotoxicities of crude extracts and all the isolated compounds were evaluated against four human cancer cell lines (HL60, A549, AZ521, and SKBR3). Furthermore, the selective index (SI) of each compound was measured by the ratio of cytotoxic effect on a normal cell line (WI38) to the cytotoxic effect on cancer cell line (A549). The results suggested that cardiac glycosides (2, 4, and 6-8) exhibited significant cytotoxicities with IC50 values from 0.01 to 3.77 μM as well as high selective index for WI38/A549 (SI 1.50-24.26), and they displayed superior selectivities when compared with the reference cisplatin (SI 1.09). Preliminary structure-activity relationships (SARs) were also discussed regarding the type of C-10 group in the cardiac glycosides being a crucial factor in determining the cytotoxic activities and regarding the sugar moieties having much less of an active role than the type of C-10 group. In addition, the melanogenesis-inhibitory abilities of these compounds were also evaluated. Cardiac glycosides (3 and 6-8) displayed moderate inhibition effects on melanogenesis with melanin content (MC) of 26.22-74.90% at a concentration of 100 μM, thus showing high cell viability (CV: 77.94-111.70%) compared with that of the reference arbutin (MC: 82.50% and CV: 107.60%). Furthermore, western blot analysis of melanogenesis-related proteins suggested that 3 could inhibit melanogenesis by suppressing the protein expressions of TRP-2 and tyrosinase.

Inhibitors of Melanogenesis: An Updated Review

Melanins are pigment molecules that determine the skin, eye, and hair color of the human subject to its amount, quality, and distribution. Melanocytes synthesize melanin and provide epidermal protection from various stimuli, such as harmful ultraviolet radiation, through the complex process called melanogenesis. However, serious dermatological problems occur when there is excessive production of melanin in different parts of the human body. These include freckles, melasma, senile lentigo, pigmented acne scars, and cancer. Therefore, controlling the production of melanin is an important approach for the treatment of pigmentation related disorderes. In this Perspective, we focus on the inhibitors of melanogenesis that directly/indirectly target a key enzyme tyrosinase as well as its associated signaling pathways.

Anti-melanogenesis effect of dehydroglyasperin C through the downregulation of MITF via the reduction of intracellular cAMP and acceleration of ERK activation in B16F1 melanoma cells

BACKGROUND

In mammals, UV radiation induces melanin synthesis in melanocyte for protecting their skin through the stimulation of α-melanocyte stimulating hormone (α-MSH) from keratinocytes. In this study, the inhibitory effects of dehydroglyasperin C (DGC), an useful component of Glycyrrhiza uralensis (G. uralensis), was investigated on melanogenesis induced by α-melanocyte stimulating hormone (α-MSH) and its mechanisms.

METHODS

Melanogenesis suppression effect of DGC on α-MSH induced B16F1 melanoma cells. The cell viability was measured by MTT assay. Expression and phosphorylation of melanogeic protein were conducted using western blot. cAMP acceleration was measured by cAMP immunoassay kit. To investigate whitening mechanism, we used ERK inhibitor (PD98059).

RESULTS

DGC decreased intra cellular tyrosinase (TYR) activity and expression of melanin synthesis related proteins (TYR and TRP-1) in a dose-dependent manner on α-MSH induced melanogenesis. In addition, DGC induced the downregulation of MITF (melanocyte-specific transcription factor) through suppression of cAMP-CREB pathway. Also, phosphorylation of extracellular signal regulated kinase (ERK) decreased MITF by DGC treatment.

CONCLUSION

Therefore, DGC could be used as a whitening ingredient in skin and clinical usage against hyperpigmentation.

On the Metal Cofactor in the Tyrosinase Family

The production of pigment in mammalian melanocytes requires the contribution of at least three melanogenic enzymes, tyrosinase and two other accessory enzymes called the tyrosinase-related proteins (Trp1 and Trp2), which regulate the type and amount of melanin. The last two proteins are paralogues to tyrosinase, and they appeared late in evolution by triplication of the tyrosinase gene. Tyrosinase is a copper-enzyme, and Trp2 is a zinc-enzyme. Trp1 has been more elusive, and the direct identification of its metal cofactor has never been achieved. However, due to its enzymatic activity and similarities with tyrosinase, it has been assumed as a copper-enzyme. Recently, recombinant human tyrosinase and Trp1 have been expressed in enough amounts to achieve for the first time their crystallization. Unexpectedly, it has been found that Trp1 contains a couple of Zn(II) at the active site. This review discusses data about the metal cofactor of tyrosinase and Trps. It points out differences in the studied models, and it proposes some possible points accounting for the apparent discrepancies currently appearing. Moreover, some proposals about the possible flexibility of the tyrosinase family to uptake copper or zinc are discussed.

Enzymatic browning in avocado (Persea americana) revisited: History, advances, and future perspectives

Considering nearly 80 years of research regarding one of the enzymes responsible for catalyzing the formation of pigments in higher animals, plants, fungi and bacteria, this review will focus on collecting and categorizing the existing information about polyphenol oxidase (PPO) in fruits, with particular emphasis on the information in relation to avocado, which is one of the hardiest species in terms of inactivation, has documented dual activity (EC 1.14.18.1/EC 1.10.3.1), and represents one of the oldest challenges for food science research and fruit processors. It is expected that this review will contribute to the further development of the field by highlighting the questions that have arisen during the characterization of PPO, the progress that has been made and the questions that remain today, in addition to new methodologies that are being applied to study this system. Holistic methodologies offer unexplored potential for advancing our understanding of the complex phenomena that govern PPO activity in fruits, because these methodologies will enable the characterization of this family of enzymes in all of its complexity. Subsequently, it will be possible to develop better techniques for controlling enzymatic browning in this valuable fruit.

Novel tyrosinase inhibitors from liquid culture of Neolentinus lepideus

Tyrosinase is the key enzyme that controls melanin formation in the human skin. We performed a screening of 96 extracts of mushroom cultures and fruiting bodies for examining their inhibitory activity against mushroom tyrosinase. The ethyl acetate extracts of culture filtrate of Neolentinus lepideus exhibited the strongest inhibitory activity. The active compounds 1 and 2 were purified by repeated chromatographic separations from the extract. On the basis of spectroscopic analyses, 1 and 2 were identified to be 1,3-dihydroisobenzofuran-4,5,7-triol and 5-methoxy-1,3-dihydroisobenzofuran-4,7-diol, respectively. Lineweaver-Burk plot of the enzyme reaction in the presence of 1 indicated that 1 was a potent competitive inhibitor. The respective IC₅₀ values of 1 and 2 were 173 and 263 μg/mL. Compound 1 at 15 μg/mL suppressed melanin accumulation stimulated by α-MSH in the murine melanoma B16 cells, as well as the induced accumulation of both tyrosinase transcript and protein without inhibiting cell proliferation.

Evaluation of Antioxidant and Anti-Melanogenic Activity of Different Extracts of Aerial Parts of N. Sintenisii in Murine Melanoma B16F10 Cells

Nepeta (Lamiaceae) is an important genus with beneficial medicinal properties. N. sintenisii Bornm. has been used in folk medicine of Iran to cure various diseases. We investigated the anti-melanogenesis effects of n-hexane, MeOH, CH₂Cl₂, n-BuOH, EtOAc, and H₂O extracts isolated from the plant in B16 melanoma cells. Various assays including cytotoxicity, mushroom tyrosinase inhibition, inhibition of cellular tyrosinase, melanin content, the amount of reactive oxygen species and western blotting were done to assess the plant activities on melanogenesis inhibition. All extracts of N. sintenisii could significantly reduce both tyrosinase activity and the cellular melanin content. Reactive oxygen species were also significantly decreased following the treatment of cell with n-BuOH and EtOAc extracts with no cytotoxicity. The plant significantly decreased the amount of microphthalmia-associated transcription factor proteins. Collectively, N. sintenisii inhibited melanin synthesis and tyrosinase activity in B16 melanoma cells with no cytotoxic effects. Hence, it might merit further investigations for elucidation of anti-hyperpigmentation agents.

Structure and Function of Human Tyrosinase and Tyrosinase-Related Proteins

Melanin is the main pigment responsible for the color of human skin, hair and eye. Its biosynthesis requires three melanogenic enzymes, tyrosinase (TYR), and the tyrosinase-related proteins TYRP1 and TYRP2. The difficulty of isolating pure and homogeneous proteins from endogenous sources has hampered their study, and resulted in many contradictory findings regarding their physiological functions. In this review, we summarize recent advances on the structure and function of TYR and TYRPs by virtue of the crystal structure of human TYRP1, which is the first available structure of a mammalian melanogenic enzyme. This structure, combined with tyrosinase structures from other lower eukaryotes and mutagenesis studies of key active site residues, sheds light on the mechanism of TYR and TYRPs. Furthermore, a TYRP1-based homology model of TYR provides a high-quality platform to map and analyze albinism-related mutations, as well as the design of specific antimelanogenic compounds. Finally, we provide perspectives for future structure/function studies of TYR and TYRPs.

Melanogenesis-Inhibitory and Cytotoxic Activities of Chemical Constituents from the Leaves of Sauropus androgynus L. Merr. (Euphorbiaceae)

A new steroid, 20-hydroxyisofucosterol (stigmasta-5,24(28)-diene-3β,20β-diol) (7), along with six known compounds 1 - 6 were isolated from the MeOH extract of the leaves of Sauropus androgynus L. Merr. (Euphorbiaceae). The structure of new steroid was determined by HR-APCI-MS and various NMR techniques in combination with literature data. Subsequently, their anti-inflammatory, cytotoxic activities against five human cell lines, as well as inhibitory activities against the α-MSH induced melanogenesis on the B16 cell line were evaluated. As the results, steroid compounds, 6 and 7 exhibited moderate cytotoxic to HL60, AZ521, SKBR3, and A549 tumor cell lines (IC₅₀ 26.9 - 45.1 μm) with high tumor selectivity for A549 relative to WI38 cell lines (SI 2.6 and 3.0, resp.). And, flavonoid compounds, 4 and 5 exhibited superior inhibitory activities against melanogenesis (67.0 - 94.7% melanin content), even with no or low toxicity to the cells (90.1 - 99.6% cell viability) at the concentrations from 10 to 100 μm. Furthermore, Western blot analysis suggested that compound 5 could inhibit melanogenesis by suppressing the protein expressions of MITF, TRP-1, TRP-2, and tyrosinase.

Ablation of epidermal RXRα in cooperation with activated CDK4 and oncogenic NRAS generates spontaneous and acute neonatal UVB induced malignant metastatic melanomas

BACKGROUND

Understanding the underlying molecular mechanisms involved in the formation of cutaneous malignant melanoma is critical for improved diagnosis and treatment. Keratinocytic nuclear receptor Retinoid X Receptor α (RXRα) has a protective role against melanomagenesis and is involved in the regulation of keratinocyte and melanocyte homeostasis subsequent acute ultraviolet (UV) irradiation.

METHODS

We generated a trigenic mouse model system (RXRα ep-/- | Tyr-NRAS Q61K | CDK4 R24C/R24C ) harboring an epidermal knockout of Retinoid X Receptor α (RXRα ep-/- ), combined with oncogenic NRAS Q61K (constitutively active RAS) and activated CDK4 R24C/R24C (constitutively active CDK4). Those mice were subjected to a single neonatal dose of UVB treatment and the role of RXR α was evaluated by characterizing the molecular and cellular changes that took place in the untreated and UVB treated trigenic RXRα ep-/- mice compared to the control mice with functional RXRα.

RESULTS

Here we report that the trigenic mice develops spontaneous melanoma and exposure to a single neonatal UVB treatment reduces the tumor latency in those mice compared to control mice with functional RXRα. Melanomas from the trigenic RXRα ep-/- mice are substantial in size, show increased proliferation, exhibit increased expression of malignant melanoma markers and exhibit enhanced vascularization. Altered expression of several biomarkers including increased expression of activated AKT, p21 and cyclin D1 and reduced expression of pro-apoptotic marker BAX was observed in the tumor adjacent normal (TAN) skin of acute ultraviolet B treated trigenic RXRα ep-/- mice. Interestingly, we observed a significant increase in p21 and Cyclin D1 in the TAN skin of un-irradiated trigenic RXRα ep-/- mice, suggesting that those changes might be consequences of loss of functional RXRα in the melanoma microenvironment. Loss of RXRα in the epidermal keratinocytes in combination with oncogenic NRAS Q61K and CDK4 R24C/R24C mutations in trigenic mice led to significant melanoma invasion into the draining lymph nodes as compared to controls with functional RXRα.

CONCLUSIONS

Our study demonstrates the protective role of keratinocytic RxRα in (1) suppressing spontaneous and acute UVB-induced melanoma, and (2) preventing progression of the melanoma to malignancy in the presence of driver mutations like activated CDK4 R24C/R24C and oncogenic NRAS Q61K .

Human Adipose Mesenchymal Cells Inhibit Melanocyte Differentiation and the Pigmentation of Human Skin via Increased Expression of TGF-β1

There is accumulating evidence that interactions between epidermal melanocytes and stromal cells play an important role in the regulation of skin pigmentation. In this study we established a pigmented dermo-epidermal skin model, melDESS, of human origin to investigate the effects of distinct stromal cells on melanogenesis. melDESS is a complex, clinically relevant skin equivalent composed of an epidermis containing both melanocytes and keratinocytes. Its dermal compartment consists either of adipose tissue-derived stromal cells, dermal fibroblasts (Fbs), or a mixture of both cell types. These skin substitutes were transplanted for 5 weeks on the backs of immuno-incompetent rats and analyzed. Gene expression and Western blot analyses showed a significantly higher expression of transforming growth factor-β1 by adipose tissue-derived stromal cells compared with dermal Fbs. In addition, we showed that melanocytes responded to the increased levels of transforming growth factor-β1 by down-regulating the expression of key melanogenic enzymes such as tyrosinase. This caused decreased melanin synthesis and, consequently, greatly reduced pigmentation of melDESS. The conclusions are of utmost clinical relevance, namely that adipose tissue-derived stromal cells derived from the hypodermis fail to appropriately interact with epidermal melanocytes, thus preventing the sustainable restoration of the patient's native skin color in bioengineered skin grafts.

Evolutionary loss of melanogenesis in the tunicate Molgula occulta

BACKGROUND

Analyzing close species with diverse developmental modes is instrumental for investigating the evolutionary significance of physiological, anatomical and behavioral features at a molecular level. Many examples of trait loss are known in metazoan populations living in dark environments. Tunicates are the closest living relatives of vertebrates and typically present a lifecycle with distinct motile larval and sessile adult stages. The nervous system of the motile larva contains melanized cells associated with geotactic and light-sensing organs. It has been suggested that these are homologous to vertebrate neural crest-derived melanocytes. Probably due to ecological adaptation to distinct habitats, several species of tunicates in the Molgulidae family have tailless (anural) larvae that fail to develop sensory organ-associated melanocytes. Here we studied the evolution of Tyrosinase family genes, indispensible for melanogenesis, in the anural, unpigmented Molgula occulta and in the tailed, pigmented Molgula oculata by using phylogenetic, developmental and molecular approaches.

RESULTS

We performed an evolutionary reconstruction of the tunicate Tyrosinase gene family: in particular, we found that M. oculata possesses genes predicted to encode one Tyrosinase (Tyr) and three Tyrosinase-related proteins (Tyrps) while M. occulta has only Tyr and Tyrp.a pseudogenes that are not likely to encode functional proteins. Analysis of Tyr sequences from various M. occulta individuals indicates that different alleles independently acquired frameshifting short indels and/or larger mobile genetic element insertions, resulting in pseudogenization of the Tyr locus. In M. oculata, Tyr is expressed in presumptive pigment cell precursors as in the model tunicate Ciona robusta. Furthermore, a M. oculata Tyr reporter gene construct was active in the pigment cell precursors of C. robusta embryos, hinting at conservation of the regulatory network underlying Tyr expression in tunicates. In contrast, we did not observe any expression of the Tyr pseudogene in M. occulta embryos. Similarly, M. occulta Tyr allele expression was not rescued in pigmented interspecific M. occulta × M. oculata hybrid embryos, suggesting deleterious mutations also to its cis-regulatory sequences. However, in situ hybridization for transcripts from the M. occulta Tyrp.a pseudogene revealed its expression in vestigial pigment cell precursors in this species.

CONCLUSIONS

We reveal a complex evolutionary history of the melanogenesis pathway in tunicates, characterized by distinct gene duplication and loss events. Our expression and molecular data support a tight correlation between pseudogenization of Tyrosinase family members and the absence of pigmentation in the immotile larvae of M. occulta. These results suggest that relaxation of purifying selection has resulted in the loss of sensory organ-associated melanocytes and core genes in the melanogenesis biosynthetic pathway in M. occulta.

Structure of Human Tyrosinase Related Protein 1 Reveals a Binuclear Zinc Active Site Important for Melanogenesis

Tyrosinase‐related protein 1 (TYRP1) is one of three tyrosinase‐like glycoenzymes in human melanocytes that are key to the production of melanin, the compound responsible for the pigmentation of skin, eye, and hair. Difficulties with producing these enzymes in pure form have hampered the understanding of their activity and the effect of mutations that cause albinism and pigmentation disorders. Herein we show that the typical tyrosinase‐like subdomain of TYRP1 contains two zinc ions in the active site instead of copper ions as found in tyrosinases, which explains why TYRP1 does not exhibit tyrosinase redox activity. In addition, the structures reveal for the first time that the Cys‐rich subdomain, which is unique to vertebrate melanogenic proteins, has an epidermal growth factor‐like fold and is tightly associated with the tyrosinase subdomain. Our structures suggest that most albinism‐related mutations of TYRP1 affect its stability or activity.