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

Neutral pH and copper ions promote eumelanogenesis after the dopachrome stage

The diversity of pigmentation in the skin, hair, and eyes of humans has been largely attributed to the diversity of pH in melanosomes with acidic pH being proposed to suppress melanin production. Tyrosinase has an optimum pH of 7.4 and its activity is suppressed greatly at lower pH values. The first step of eumelanogenesis is the oxidation of tyrosine to dopachrome (DC) via dopaquinone. However, how eumelanogenesis is controlled by pH beyond this stage is not known. In this study, we examined the effects of pH (5.3-7.3) on the conversion of DC to 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and the subsequent oxidation of DHI and DHICA to form eumelanin. The effects of Cu(2+) ions on those reactions were also compared. The results indicate that an acidic pH greatly suppresses the late stages of eumelanogenesis and that Cu(2+) ions accelerate the conversion of DC to DHICA and its subsequent oxidation.

Activation of MITF by Argan Oil Leads to the Inhibition of the Tyrosinase and Dopachrome Tautomerase Expressions in B16 Murine Melanoma Cells

Argan (Argania spinosa L.) oil has been used for centuries in Morocco as cosmetic oil to maintain a fair complexion and to cure skin pimples and chicken pox pustules scars. Although it is popular, the scientific basis for its effect on the skin has not yet been established. Here, the melanogenesis regulatory effect of argan oil was evaluated using B16 murine melanoma cells. Results of melanin assay using B16 cells treated with different concentrations of argan oil showed a dose-dependent decrease in melanin content. Western blot results showed that the expression levels of tyrosinase (TYR), tyrosinase-related protein 1 (TRP1), and dopachrome tautomerase (DCT) proteins were decreased. In addition, there was an increase in the activation of MITF and ERK1/2. Real-time PCR results revealed a downregulation of Tyr, Trp1, Dct, and Mitf mRNA expressions. Argan oil treatment causes MITF phosphorylation which subsequently inhibited the transcription of melanogenic enzymes, TYR and DCT. The inhibitory effect of argan oil on melanin biosynthesis may be attributed to tocopherols as well as the synergistic effect of its components. The results of this study provide the scientific basis for the traditionally established benefits of argan oil and present its therapeutic potential against hyperpigmentation disorders.

Melanins and melanogenesis: methods, standards, protocols

Despite considerable advances in the past decade, melanin research still suffers from the lack of universally accepted and shared nomenclature, methodologies, and structural models. This paper stems from the joint efforts of chemists, biochemists, physicists, biologists, and physicians with recognized and consolidated expertise in the field of melanins and melanogenesis, who critically reviewed and experimentally revisited methods, standards, and protocols to provide for the first time a consensus set of recommended procedures to be adopted and shared by researchers involved in pigment cell research. The aim of the paper was to define an unprecedented frame of reference built on cutting-edge knowledge and state-of-the-art methodology, to enable reliable comparison of results among laboratories and new progress in the field based on standardized methods and shared information.

In silico screening and molecular dynamics simulation of disease-associated nsSNP in TYRP1 gene and its structural consequences in OCA3

Oculocutaneous albinism type III (OCA3), caused by mutations of TYRP1 gene, is an autosomal recessive disorder characterized by reduced biosynthesis of melanin pigment in the hair, skin, and eyes. The TYRP1 gene encodes a protein called tyrosinase-related protein-1 (Tyrp1). Tyrp1 is involved in maintaining the stability of tyrosinase protein and modulating its catalytic activity in eumelanin synthesis. Tyrp1 is also involved in maintenance of melanosome structure and affects melanocyte proliferation and cell death. In this work we implemented computational analysis to filter the most probable mutation that might be associated with OCA3. We found R326H and R356Q as most deleterious and disease associated by using PolyPhen 2.0, SIFT, PANTHER, I-mutant 3.0, PhD-SNP, SNP&GO, Pmut, and Mutpred tools. To understand the atomic arrangement in 3D space, the native and mutant (R326H and R356Q) structures were modelled. Finally the structural analyses of native and mutant Tyrp1 proteins were investigated using molecular dynamics simulation (MDS) approach. MDS results showed more flexibility in native Tyrp1 structure. Due to mutation in Tyrp1 protein, it became more rigid and might disturb the structural conformation and catalytic function of the structure and might also play a significant role in inducing OCA3. The results obtained from this study would facilitate wet-lab researches to develop a potent drug therapies against OCA3.

Coordinated regulation of chromatophore differentiation and melanogenesis during the ontogeny of skin pigmentation of Solea senegalensis (Kaup, 1858)

Abnormal pigmentation of Senegalese sole has been described as one problem facing the full exploitation of its commercial production. To improve our understanding of flatfish pigmentation of this commercially important species we have evaluated eleven genes related to two different processes of pigmentation: melanophore differentiation, and melanin production. The temporal distribution of gene expression peaks corresponds well with changes in pigmentation patterns and the intensity of skin melanization. Several gene ratios were also examined to put in perspective possible genetic markers for the different stages of normal pigmentation development. Further, the phenotypic changes that occur during morphogenesis correspond well with the main transitions in gene expression that occur. Given the dramatic phenotypic alterations which flatfish undergo, including the asymmetric coloration that occurs between the ocular and the blind side, and the synchrony of the two processes of morphogenesis and pigmentation ontogenesis, these species constitute an interesting model for the study of pigmentation. In this study we present a first approximation towards explaining the genetic mechanisms for regulating pigmentation ontogeny in Senegalese sole, Solea senegalensis.

Involvement of Nurr-1/Nur77 in corticotropin-releasing factor/urocortin1-induced tyrosinase-related protein 1 gene transcription in human melanoma HMV-II cells

Recent molecular and biochemical analyses have revealed the presence of corticotropin-releasing factor (CRF) and urocortin (Ucn), together with their corresponding receptors in mammalian skin. The melanosomal enzyme tyrosinase-related protein 1 (TRP1) is involved in modulation of pigment production in response to stressors. Although CRF and Ucn are thought to have potent effects on the skin system, their possible roles and regulation have yet to be fully determined. This study aimed to explore the effects of CRF and Ucn on TRP1 gene expression using human melanoma HMV-II cells. The mRNA of CRF, Ucn1, Ucn2, and CRF receptor type 1 (CRF1 receptor) was detected in HMV-II cells. CRF and Ucn1 stimulated TRP1 gene transcription via the CRF1 receptor, and increased both Nurr-1 and Nur77 mRNA expression levels. Both CRF- and Ucn1-induced Nurr-1/Nur77 acted via a NGFI-B response element on the TRP1 promoter. The combination of Nurr-1/Nur77 and microphthalmia-associated transcription factor, a melanocyte-specific transcription factor gene induced by α-melanocyte-stimulating hormone, had additive effects on activation of TRP1 gene transcription. The findings suggest that in human melanoma HMV-II cells both CRF and Ucn1 regulate TRP1 gene expression via Nurr-1/Nur77 production, independent of pro-opiomelanocortin or α-melanocyte-stimulating hormone stimulation.

Inhibitory effects of Asterina pectinifera extracts on melanin biosynthesis through tyrosinase activity

The control of melanogenesis is an important strategy in the treatment of abnormal skin pigmentation for cosmetic purposes. The aim of the present study was to investigate the anti-melanogenic effect of Asterina pectinifera (A. pectinifera) extracts by cell-free mushroom tyrosinase assay, cellular tyrosinase assay, melanin content assay and the analysis of related protein expression in melan-a cells. A. pectinifera was extracted with 80% methanol (80-MAP) and further fractionated with hexane (He-AP) and ethyl acetate (EA-AP). In addition, the enzyme extract (En-AP) of A. pectinifera, to which protease was added, was processed. EA-AP and En-AP among A. pectinifera extracts showed strong inhibitory activity against the cell-free mushroom tyrosinase activity. EA-AP and En-AP induced significant inhibition of melanin production and cellular tyrosinase activity. In the action of EA-AP and En-AP on melanogenesis, they reduced the expression of melanogenic genes and proteins including tyrosinase, tyrosinase-related protein-1 (TRP-1) and dopachrome tautomerase (Dct). These results showed that EA-AP and En-AP inhibited melanogenesis by reducing tyrosinase activity and melanin production via subsequent downregulation of tyrosinase-related proteins. The overall results suggest that EA-AP and En-AP among A. pectinifera extracts may be promising candidates for the treatment of hyperpigmentation disorder and useful for self-tanning cosmetic products.

Up-regulation of melanin synthesis by the antidepressant fluoxetine

Fluoxetine, a member of the class of selective serotonin reuptake inhibitors, is a potent antidepressant commonly used in clinical practice. Here, we report that fluoxetine increases cellular tyrosinase (TYR) activity, enhances the protein levels of microphthalmia-associated transcription factor (MITF), TYR and tyrosinase-related protein-1 (TRP-1) and eventually leads to a dramatic increase in melanin production in both murine B16F10 melanoma cells and normal human melanocytes (NHMCs). In well-characterized C57BL/6 mouse models, systemic application of fluoxetine increased hair pigmentation by up-regulating hair follicular MITF, TYR, TRP-1 and tyrosinase-related protein-2 (TRP-2) protein levels. Using a serotonin 1A receptor (SR1A) antagonist and RNA interference (RNAi) technique, we revealed that SR1A appears to be one of the involved pathways in the fluoxetine-induced melanogenesis in B16F10 cells. These results suggest that fluoxetine may hold a significant therapeutic potential for treating skin hypopigmentation disorders, and SR1A may serve as a novel target in modulating melanogenesis.

Dual inhibition of γ-oryzanol on cellular melanogenesis: inhibition of tyrosinase activity and reduction of melanogenic gene expression by a protein kinase A-dependent mechanism

The in vitro effects on melanogenesis of γ-oryzanol (1), a rice bran-derived phytosterol, were investigated. The melanin content in B16F1 cells was significantly and dose-dependently reduced (-13% and -28% at 3 and 30 μM, respectively). Tyrosinase enzyme activity was inhibited by 1 both in a cell-free assay and when analyzed based on the measurement of cellular tyrosinase activity. Transcriptome analysis was performed to investigate the biological pathways altered by 1, and it was found that gene expression involving protein kinase A (PKA) signaling was markedly altered. Subsequent analyses revealed that 1 stimulation in B16 cells reduced cytosolic cAMP concentrations, PKA activity (-13% for cAMP levels and -40% for PKA activity), and phosphorylation of the cAMP-response element binding protein (-57%), which, in turn, downregulated the expression of microphthalmia-associated transcription factor (MITF; -59% for mRNA and -64% for protein), a key melanogenic gene transcription factor. Accordingly, tyrosinase-related protein 1 (TRP-1; -69% for mRNA and -82% for protein) and dopachrome tautomerase (-51% for mRNA and -92% for protein) in 1-stimulated B16F1 cells were also downregulated. These results suggest that 1 has dual inhibitory activities for cellular melanogenesis by inhibiting tyrosinase enzyme activity and reducing MITF and target genes in the PKA-dependent pathway.

Guggulsterone inhibits melanogenesis in B16 murine melanoma cells by downregulating tyrosinase expression

In the present study, we investigated the effect of guggulsterone on melanogenesis in B16 melanoma cells and elucidated its possible mechanism of action. The effects of guggulsterone on melanogenesis were determined by assaying melanin synthesis and cellular tyrosinase activity in B16/F10 mouse melanoma cells. Guggulsterone dose-dependently inhibited isobutylmethylxanthine (IBMX)-induced melanogenesis and cellular tyrosinase activity with no cytotoxicity. Decreased melanin biosynthesis was accompanied by the reduced expression of melanogenesis-related genes, such as tyrosinase, microphthalmia-associated transcription factor, tyrosinase-related protein (TRP)-1 and TRP-2. Guggulsterone also inhibited α-melanocyte stimulating hormone- or forskolin-induced increases in melanogenesis, suggesting an action on the cAMP-dependent melanogenic pathway. Co-incubation with chenodeoxycholic acid, a well-known farnesoid-X receptor agonist, did not affect IBMX-induced melanogenesis. These results suggest that guggulsterone exerts a melanogenic inhibitory effect through the downregulation of tyrosinase expression.

Molecular genetic studies and delineation of the oculocutaneous albinism phenotype in the Pakistani population

Background

Oculocutaneous albinism (OCA) is caused by a group of genetically heterogeneous inherited defects that result in the loss of pigmentation in the eyes, skin and hair. Mutations in the TYR, OCA2, TYRP1 and SLC45A2 genes have been shown to cause isolated OCA. No comprehensive analysis has been conducted to study the spectrum of OCA alleles prevailing in Pakistani albino populations.

Methods

We enrolled 40 large Pakistani families and screened them for OCA genes and a candidate gene, SLC24A5. Protein function effects were evaluated using in silico prediction algorithms and ex vivo studies in human melanocytes. The effects of splice-site mutations were determined using an exon-trapping assay.

Results

Screening of the TYR gene revealed four known (p.Arg299His, p.Pro406Leu, p.Gly419Arg, p.Arg278*) and three novel mutations (p.Pro21Leu, p.Cys35Arg, p.Tyr411His) in ten families. Ex vivo studies revealed the retention of an EGFP-tagged mutant (p.Pro21Leu, p.Cys35Arg or p.Tyr411His) tyrosinase in the endoplasmic reticulum (ER) at 37°C, but a significant fraction of p.Cys35Arg and p.Tyr411His left the ER in cells grown at a permissive temperature (31°C). Three novel (p.Asp486Tyr, p.Leu527Arg, c.1045-15 T > G) and two known mutations (p.Pro743Leu, p.Ala787Thr) of OCA2 were found in fourteen families. Exon-trapping assays with a construct containing a novel c.1045-15 T > G mutation revealed an error in splicing. No mutation in TYRP1, SLC45A2, and SLC24A5 was found in the remaining 16 families. Clinical evaluation of the families segregating either TYR or OCA2 mutations showed nystagmus, photophobia, and loss of pigmentation in the skin or hair follicles. Most of the affected individuals had grayish-blue colored eyes.

Conclusions

Our results show that ten and fourteen families harbored mutations in the TYR and OCA2 genes, respectively. Our findings, along with the results of previous studies, indicate that the p.Cys35Arg, p.Arg278* and p.Gly419Arg alleles of TYR and the p.Asp486Tyr and c.1045-15 T > G alleles of OCA2 are the most common causes of OCA in Pakistani families. To the best of our knowledge, this study represents the first documentation of OCA2 alleles in the Pakistani population. A significant proportion of our cohort did not have mutations in known OCA genes. Overall, our study contributes to the development of genetic testing protocols and genetic counseling for OCA in Pakistani families.

Microphthalmia-associated transcription factor modulates expression of NADPH oxidase type 4: a negative regulator of melanogenesis

How signaling via reactive oxygen species (ROS) influences skin pigmentation is unclear. We have investigated how NADPH oxidase-derived ROS modulates the expression of the key pigment "melanin" synthesizing enzymes in B16 mouse melanoma cells. A melanin inducer α-melanocyte-stimulating hormone (α-MSH) caused ROS generation that was inhibited by the NADPH oxidase inhibitor Diphenyleneiodonium (DPI) and was insensitive to antagonists of other ROS-producing enzyme systems including mitochondrial enzymes, cycloxygenase, and xanthine oxidase. NADPH oxidase 4 (Nox4) was found to be the most abundant isoform expressed in B16 cells, and its gene levels, as well as ROS generation, were enhanced by α-MSH. Interestingly, silencing Nox4 gene expression with Nox4 siRNA augmented melanin formation under basal conditions and after α-MSH stimulation, demonstrating that constitutive or stimulated Nox4-dependent ROS inhibits melanin formation. This process may be mediated by targeting the promoter region of a melanin synthesizing enzyme tyrosinase, because Nox4 siRNA enhanced tyrosinase promoter activity. Moreover, inhibition of tyrosinase mRNA expression in Nox4 siRNA-treated cells by blocking de novo mRNA and protein synthesis with actinomycin D and cycloheximide respectively indicates that Nox4 repression induces melanogenesis by increasing tyrosinase gene expression. We also found that α-MSH activated its downstream signal transducer microphthalmia-associated transcription factor (MITF) to stimulate Nox4 gene expression. We thus identified a novel mechanism by MITF signaling that in turn stimulates Nox4 to drive ROS generation, thereby repressing melanin synthesis. Such sequence of actions appears to act as an internal feedback mechanism to fine-tune melanin synthesis in response to exogenous challenges such as UV radiation.

New insights into the evolution of metazoan tyrosinase gene family

Tyrosinases, widely distributed among animals, plants and fungi, are involved in the biosynthesis of melanin, a pigment that has been exploited, in the course of evolution, to serve different functions. We conducted a deep evolutionary analysis of tyrosinase family amongst metazoa, thanks to the availability of new sequenced genomes, assessing that tyrosinases (tyr) represent a distinctive feature of all the organisms included in our study and, interestingly, they show an independent expansion in most of the analyzed phyla. Tyrosinase-related proteins (tyrp), which derive from tyr but show distinct key residues in the catalytic domain, constitute an invention of chordate lineage. In addition we here reported a detailed study of the expression territories of the ascidian Ciona intestinalis tyr and tyrps. Furthermore, we put efforts in the identification of the regulatory sequences responsible for their expression in pigment cell lineage. Collectively, the results reported here enlarge our knowledge about the tyrosinase gene family as valuable resource for understanding the genetic components involved in pigment cells evolution and development.

Mechanism of Mitf inhibition and morphological differentiation effects of hirsein A on B16 melanoma cells revealed by DNA microarray

BACKGROUND

We have previously reported that hirsein A inhibits melanogenesis in B16 melanoma cells by downregulating the Mitf gene expression.

OBJECTIVE

In this study, microarray was employed to determine the transcriptional response of B16 cells to hirsein A (HA) treatment and to find out the mechanism underlying Mitf downregulation.

METHODS

DNA microarray, spotted with 265 genes for melanogenesis and signal transduction, was performed using the total RNA isolated from B16 cells treated with HA. Validation of the results was done using real-time PCR. In addition, real-time PCR using primers for Mda-7 gene and F-actin staining were performed. Transfection experiments were performed to knockdown the expression of the Mc1r gene to evaluate its role in the cell morphological change observed.

RESULTS

As expected, the expressions of the Mitf-regulated melanosome transport genes and the Mc1r gene were downregulated. Furthermore, the expressions of the MAPK pathway intermediates were either up- or downregulated. Genes associated with cell differentiation, such as Gadd45b, were upregulated and prompted us to determine the expression of the Il-24 (Mda-7) gene using real-time PCR. There was an increase in the Mda-7 mRNA expression in B16 and HMV-II melanoma cells, and in human melanocytes. To better visualize the cell morphology, F-actin staining was performed and the results showed an increase in the dendrite outgrowth in HA-treated cells. Silencing the Mc1r gene did not cause a change in the B16 cell morphology observed in cells treated with HA.

CONCLUSION

This study demonstrated that HA downregulates Mitf gene expression by regulating the expressions of the MAPK signaling pathway intermediates. In addition, the inhibited Mc1r gene expression also contributed to the overall Mitf downregulation but does not play a role in the observed change in B16 cell morphology. HA surprisingly can regulate genes associated with differentiating cells (Mda-7) suggesting a role for HA in the melanoma cell differentiation induction. While the exact molecular mechanism by which HA promotes cell differentiation remain to be determined, it is clear that HA can downregulate Mitf expression and promote cell differentiation and has the potential to be used in the development of therapy for melanoma.

Evidence for baseline retinal pigment epithelium pathology in the Trp1-Cre mouse

The increasing popularity of the Cre/loxP recombination system has led to the generation of numerous transgenic mouse lines in which Cre recombinase is expressed under the control of organ- or cell-specific promoters. Alterations in retinal pigment epithelium (RPE), a multifunctional cell monolayer that separates the retinal photoreceptors from the choroid, are prevalent in the pathogenesis of a number of ocular disorders, including age-related macular degeneration. To date, six transgenic mouse lines have been developed that target Cre to the RPE under the control of various gene promoters. However, multiple lines of evidence indicate that high levels of Cre expression can be toxic to mammalian cells. In this study, we report that in the Trp1-Cre mouse, a commonly used transgenic Cre strain for RPE gene function studies, Cre recombinase expression alone leads to RPE dysfunction and concomitant disorganization of RPE layer morphology, large areas of RPE atrophy, retinal photoreceptor dysfunction, and microglial cell activation in the affected areas. The phenotype described herein is similar to previously published reports of conditional gene knockouts that used the Trp1-Cre mouse, suggesting that Cre toxicity alone could account for some of the reported phenotypes and highlighting the importance of the inclusion of Cre-expressing mice as controls in conditional gene targeting studies.

Mechanism of pigmentation by minocycline in murine B16 melanoma cells

Long-term treatment with minocycline is known to induce pigmentation or discoloration in tissues but how remains unclear. We investigated the mechanism of pigmentation using B16 melanoma cells. First, we confirmed that intracellular melanin levels increased on minocycline treatment. Then, using the reverse transcriptase-polymerase chain reaction (RT-PCR), we found the expression of mRNA of tyrosinase, tyrosinase-related protein (TRP)-1 and TRP-2, to also be significantly increased by treatment with minocycline at 5 µg/ml for 72 h. These results suggest that the minocycline-induced stimulation of melanogenesis occurs at the transcriptional level. Western-blotting revealed slight phosphorylation of extracellular signal-regulated kinase (ERK) 30-60 min after the minocycline treatment. The mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitor U0126 and the p38 inhibitor SB203580 were used to examine the signaling pathway associated with the mRNA expression of tyrosinase, TRP-1, or TRP-2 when B16 melanoma cells were treated with minocycline. The SB203580 inhibited the mRNA expression of tyrosinase and TRP-1, suggesting the minocycline-induced melanogensis occurred via a p38 signaling pathway.

Ethnic and mouse strain differences in central corneal thickness and association with pigmentation phenotype

The cornea is a transparent structure that permits the refraction of light into the eye. Evidence from a range of studies indicates that central corneal thickness (CCT) is strongly genetically determined. Support for a genetic component comes from data showing significant variation in CCT between different human ethnic groups. Interestingly, these studies also appear to show that skin pigmentation may influence CCT. To validate these observations, we undertook the first analysis of CCT in an oculocutaneous albinism (OCA) and Ugandan cohort, populations with distinct skin pigmentation phenotypes. There was a significant difference in the mean CCT of the OCA, Ugandan and Australian-Caucasian cohorts (Ugandan: 517.3±37 µm; Caucasian: 539.7±32.8 µm, OCA: 563.3±37.2 µm; p<0.001). A meta-analysis of 53 studies investigating the CCT of different ethnic groups was then performed and demonstrated that darker skin pigmentation is associated with a thinner CCT (p<0.001). To further verify these observations, we measured CCT in 13 different inbred mouse strains and found a significant difference between the albino and pigmented strains (p = 0.008). Specific mutations within the melanin synthesis pathway were then investigated in mice for an association with CCT. Significant differences between mutant and wild type strains were seen with the nonagouti (p<0.001), myosin VA (p<0.001), tyrosinase (p = 0.025) and tyrosinase related protein (p = 0.001) genes. These findings provide support for our hypothesis that pigmentation is associated with CCT and identifies pigment-related genes as candidates for developmental determination of a non-pigmented structure.

Activation of p38 MAPK pathway contributes to the melanogenic property of apigenin in B16 cells

We investigated the involvement of MAPK pathways in the melanogenic effect of apigenin in B16 cells. Apigenin treatment for 48 h dose (5-20 μm)-dependently up-regulated protein expression levels of microphthalmia-associated transcription factor (MITF) and melanogenic enzymes including tyrosinase, tyrosinase-related protein-1 (TRP-1) and TRP-2 and enhanced the phosphorylation of p38 MAPK, without affecting the phosphorylation of JNK or ERK MAPK. Treatment with 10 μm apigenin time (6-48 h)-dependently elevated the protein expressions of p-p38, MITF and melanogenic enzymes. Moreover, PD169316, a selective inhibitor of p38 kinase, suppressed the stimulatory effects of apigenin on tyrosinase activity and melanin synthesis, which were accompanied by decreased MITF protein expression. In conclusion, apigenin increased melanogenesis in B16 cells, at least in part, by activating the p38 MAPK pathway. The novel findings of this study shed light on the molecular mechanisms underlying the melanogenic activity of apigenin and suggest that apigenin/its derivatives may be potentially used for treating hypopigmentation disorders.

Human hair melanins: what we have learned and have not learned from mouse coat color pigmentation

Hair pigmentation is one of the most conspicuous phenotypes in humans. Melanocytes produce two distinct types of melanin pigment: brown to black, indolic eumelanin and yellow to reddish brown, sulfur-containing pheomelanin. Biochemically, the precursor tyrosine and the key enzyme tyrosinase and the tyrosinase-related proteins are involved in eumelanogenesis, while only the additional presence of cysteine is necessary for pheomelanogenesis. Other important proteins involved in melanogenesis include P protein, MATP protein, α-MSH, agouti signaling protein (ASIP), MC1R (the receptor for MSH and ASIP), and SLC7A11, a cystine transporter. Many studies have examined the effects of loss-of-function mutations of those proteins on mouse coat color pigmentation. In contrast, much less is known regarding the effects of mutations of the corresponding proteins on human hair pigmentation except for MC1R polymorphisms that lead to pheomelanogenesis. This perspective will discuss what we have/have not learned from mouse coat color pigmentation, with special emphasis on the significant roles of pH and the level of cysteine in melanosomes in controlling melanogenesis. Based on these data, a hypothesis is proposed to explain the diversity of human hair pigmentation.

Colours of domestication

During the last decade, coat colouration in mammals has been investigated in numerous studies. Most of these studies addressing the genetics of coat colouration were on domesticated animals. In contrast to their wild ancestors, domesticated species are often characterized by a huge allelic variability of coat-colour-associated genes. This variability results from artificial selection accepting negative pleiotropic effects linked with certain coat-colour variants. Recent studies demonstrate that this selection for coat-colour phenotypes started at the beginning of domestication. Although to date more than 300 genetic loci and more than 150 identified coat-colour-associated genes have been discovered, which influence pigmentation in various ways, the genetic pathways influencing coat colouration are still only poorly described. On the one hand, similar coat colourations observed in different species can be the product of a few conserved genes. On the other hand, different genes can be responsible for highly similar coat colourations in different individuals of a species or in different species. Therefore, any phenotypic classification of coat colouration blurs underlying differences in the genetic basis of colour variants. In this review we focus on (i) the underlying causes that have resulted in the observed increase of colour variation in domesticated animals compared to their wild ancestors, and (ii) the current state of knowledge with regard to the molecular mechanisms of colouration, with a special emphasis on when and where the different coat-colour-associated genes act.

Inhibitory effects of Hoelen extract on melanogenesis in B16/F1 melanoma cells

Melanin synthesis is regulated by melanogenic proteins, such as tyrosinase, tyrosinase-related protein 1 (TRP-1) and TRP-2. The effects of Hoelen extract on melanogenesis were investigated in B16Fl murine melanoma cells. Specifically, tyrosinase activity, cell viability and melanin content were assayed, and western blotting and RT-PCR for tyrosinase, TRP-1 and TRP-2 conducted. The results show that Hoelen significantly inhibited melanin synthesis through inhibition of TRP-2 expression, while it did not affect tyrosinase activity or its expression. Taken together, RT-PCR results showed that the depigmentation effect of Hoelen may be due to inhibition of TRP-2 gene transcription. These results suggest that Hoelen may be a useful inhibitor for the attenuation of melanogenesis and hyperpigmentation in skin cells.

Tyrosinase related protein 1 (TYRP1/gp75) in human cutaneous melanoma

Melanoma prognosis is based on specific pathological features at the primary lesion. In metastatic patients, the extent of lymph node involvement is also an important prognosis indicator. Many progression markers both in tissues and serum, including circulating tumor cells, have been studied and new molecular markers are awaited from high-throughput screenings to discriminate between clinical stages and predict disease progression. The present review focuses on human tyrosinase related protein 1 also known as gp75 glycoprotein (Tyrp1/gp75), a melanosomal protein involved in the pigmentary machinery of the melanocyte and often used as differentiation marker, with a special emphasis on its emerging roles in the malignant melanocyte and melanoma progression.

Spectral analysis by XANES reveals that GPNMB influences the chemical composition of intact melanosomes

GPNMB is a unique melanosomal protein. Unlike many melanosomal proteins, GPNMB has not been associated with any forms of albinism, and it is unclear whether GPNMB has any direct influence on melanosomes. Here, melanosomes from congenic strains of C57BL/6J mice mutant for Gpnmb are compared to strain-matched controls using standard transmission electron microscopy and synchrotron-based X-ray absorption near-edge structure analysis (XANES). Whereas electron microscopy did not detect any ultrastructural changes in melanosomes lacking functional GPNMB, XANES uncovered multiple spectral phenotypes. These results directly demonstrate that GPNMB influences the chemical composition of melanosomes and more broadly illustrate the potential for using genetic approaches in combination with nano-imaging technologies to study organelle biology.

Update on the regulation of mammalian melanocyte function and skin pigmentation

Melanogenesis is the unique process of producing pigmented biopolymers that are sequestered within melanosomes, which provides color to the skin, hair and eyes of animals and, in the case of human skin, also protects the underlying tissues from UV damage. We review the current understanding of melanogenesis, focusing on factors important to the biochemistry of pigment synthesis, the biogenesis of melanosomes, signaling pathways and factors that regulate melanogenesis, intramelanosomal pH, transport and transfer of melanosomes, and pigmentary disorders related to the dysfunction of melanosome-related proteins. Although it has been known for some time that many of the factors that affect melanogenesis are derived from keratinocytes, fibroblasts, endothelial cells, hormones, inflammatory cells and nerves, a number of new factors that are involved in that regulation have recently been reported, such as factors that regulate melanosome pH and ion transport.

The melanogenesis and mechanisms of skin-lightening agents--existing and new approaches

Skin-lightening products are commercially available for cosmetic purposes to obtain lighter skin complexion. Clinically, they are also used for treatment of hyperpigmentary disorders such as melasma, café au lait spot and solar lentigo. All of these target naturally melanin production, and many of the commonly used agents are known as competitive inhibitors of tyrosinase, one of the key enzymes in melanogenesis. In this review, we present an overview of commonly used skin-whitening ingredients that are commercialized, but we also hypothesize on other mechanisms that could be important targets to control skin pigmentation such as for example regulation of the adrenergic and glutaminergic signalling and also control of tetrahydrobiopterins in the human skin.

Flavonoids, apigenin and icariin exert potent melanogenic activities in murine B16 melanoma cells

We aimed to screen for melanogenic agents among 35 botanical compounds. The compounds were first assessed with regard to their effects on tyrosinase activity in B16 cells. At 100 μM, 13 compounds showed tyrosinase activity-enhancing effects, ranging from 2.6 to 372.8% activation. Five of them showed more than 50% enhancement and were further tested for their EC(50) values. Compared with 8-Methoxypsoralen, an effective tyrosinase activator with an EC(50) of 7.26 μM, 3 compounds exhibited smaller EC(50) values (apigenin, 0.45 μM; hyperosid, 0.92 μM; and icariin, 1.01 μM for enhancing tyrosinase activity). The 3 compounds significantly increased cellular melanin contents without affecting cell proliferation. Compared with 8-Methoxypsoralen (EC(50), 35.94 μM for stimulating pigmentation), apigenin (EC(50), 17.46 μM) and icariin (EC(50), 32.77 μM) showed better melanogenic activity, while hyperosid (EC(50), 70.4 μM) was less potent. Western blot analysis demonstrated that the 3 compounds could differentially increase the expression levels of tyrosinase, and tyrosinase-related proteins 1 and 2. Together these data suggest that apigenin and icariin exert potent melanogenic activities through, at least in part, upregulating the protein expression levels of melanogenic enzymes in B16 cells. Thus, further investigations are merited to ascertain their potential application in treating hypopigmentation disorders.

Involvement of p38 MAPK signaling pathway in the anti-melanogenic effect of San-bai-tang, a Chinese herbal formula, in B16 cells

AIM OF THE STUDY

San-bai-tang (SBT), a Chinese herbal formula, is traditionally used as a skin whitener in China. In our previous screening assays, SBT was identified as an effective tyrosinase inhibitor. In this study, we aim to investigate the anti-melanogenic effect and mechanisms of SBT in B16 cells.

MATERIALS AND METHODS

Cell viability was examined by the MTT assay. Cellular tyrosinase activity and melanin content were determined using spectrophotographic methods. Protein expression was analyzed by immunoblotting.

RESULTS

SBT inhibited tyrosinase activity with an IC(50) of 215.6 ± 10.3 μg/ml, and decreased cellular melanin content with an IC(50) of 254.8 ± 14.5 μg/ml at 48 h. MTT assay demonstrated that 48-h SBT (50-400 μg/ml) treatment did not show obvious cytotoxicity. Immunoblot analysis showed that SBT (100, 200 or 400 μg/ml) treatment for 48 h down-regulated the expression levels of phosphorylated-p38, MITF, tyrosinase, TRP-1 and TRP-2 in a dose-dependent manner.

CONCLUSIONS

SBT inhibited melanogenesis in B16 cells, and suppression of p38 MAPK signaling pathway contributed to the anti-melanogenic effect of SBT by down-regulating the expression of MITF and melanogenic enzymes. These novel findings demonstrated the anti-melanogenic effect and mechanisms of SBT, and provide pharmacological basis for the traditional use of SBT.

Application of a combined sulphorhodamine B and melanin assay to the evaluation of Chinese medicines and their constituent compounds for hyperpigmentation treatment

AIM OF THE STUDY

To investigate the efficacy of traditional Chinese medicine (TCM) in the treatment of hyperpigmentation problems, extracts of herbs selected based on traditional Chinese medical literature were screened.

MATERIALS AND METHODS

Forty extracts were extracted from 10 selected herbs using hexane, dichloromethane, methanol and water. They were then screened using melan-a cells, an immortalized non-tumorigenic mouse melanocyte cell line. Sulphorhodamine B (SRB) assay and measurement of melanin production were performed to examine the effects of the extracts as well as some natural compounds from these herbs on melanogenesis in the melan-a cells.

RESULTS

The hexane and dichloromethane extracts of Angelica sinensis exhibited strong hypopigmentary effects.

CONCLUSIONS

Natural compounds occurring in this herb were also investigated. Among them 4-ethylresorcinol, 4-ethylphenol and 1-tetradecanol demonstrated positive effects in attenuating melanin synthesis in the cultured cells.

Rab7 is a critical mediator in vesicular transport of tyrosinase-related protein 1 in melanocytes

How melanosomal proteins such as enzymic proteins (tyrosinase and tyrosinase-related proteins, Tyrps) and structural protein (gp100) are transported from Golgi to melanosomal compartments is not yet fully understood. A number of small GTPases have been found to be associated with melanosomes and we have identified one of them, Rab7, a regulator of vesicular transport, organelle motility, phospholipid signaling and cytosolic degradative machinery, as being involved in the transport of Tyrp1 from Golgi to stage I melanosomes. This study further characterizes the role of Rab7 as a regulator of differential sorting of melanosomal proteins in this process. Murine melanocytes were transiently transfected with a plasmid encoding either wild-type (Rab7WT), constitutively active (Rab7Q67L) or dominant-negative (Rab7N125I and Rab7T22N) Rab7. Through immunocytostaining and confocal laser scanning microscopy, we quantitatively compared the bio-distribution of melanosomal proteins between Rab7WT-expressing cells and mutant Rab7-expressing cells. We also characterized their differential elimination from melanosomal compartments by Rab7 by utilizing a proteasome inhibitor, MG132. Our findings indicate that Rab7 plays an important role in differential sorting of tyrosinase, Tyrp1 and gp100 in early melanogenesis cascade, and that it is more specifically involved with Tyrp1 than tyrosinase and gp100 in the trafficking from Golgi to melanosomes and the specific exit from the degradative process.

Inhibitory effects of 2-amino-3H-phenoxazin-3-one on the melanogenesis of murine B16 melanoma cell line

Hyperpigmentations are a serious concern addressed by both the medical community and the cosmetic industry through the development of agents that block melanin biosynthesis. In this study, we found that 2-amino-3H-phenoxazin-3-one (APO), isolated from extracts of the edible mushroom Agaricus bisporus Imbach, exhibited potent inhibitory effects on melanogenesis in B16 cells, a murine melanoma cell line. APO inhibited melanin biosynthesis at 1,000 times lower concentrations (IC(50)=1.31+/-0.08 microM) than kojic acid (IC(50)=1.31+/-0.13 mM), without causing cellular toxicity. APO did not directly inhibit the enzyme activity of tyrosinase, the rate-limiting melanogenic enzyme. Further study showed that APO inhibited the protein expression of tyrosinase and microphthalmia-associated transcription factor (MITF), a melanogenic transcription factor that regulates the expression of tyrosinase. These results suggest that APO is a promising depigmenting agent with both therapeutic and cosmetic value in preventing melanogenesis.

Spectrum of candidate gene mutations associated with Indian familial oculocutaneous and ocular albinism

PURPOSE

Albinism is a group of genetic disorders, showing a broad spectrum of different phenotypes. The purpose of this study was to screen known candidate genes for oculocutaneous albinism (OCA) and ocular albinism (OA) mutations in Indian patients.

METHODS

Blood samples were collected from 23 probands and 13 affected family members from 23 genetically unrelated Indian families (22 diagnosed as OCA and 1 diagnosed as OA) and analyzed by bidirectional DNA sequencing of the classic OCA genes--tyrosinase (TYR, or oculocutaneous albinism IA), pink eyed dilution (P; or oculocutaneous albinism II (OCA2]), tyrosinase-related protein 1 (TYRP1), solute carrier family 45, member 2 (SLC45A2; or membrane-associated transporter protein [MATP])--and the OA1 gene, G protein-coupled receptor 143 (GPR143).

RESULTS

Three missense mutations, c. 715 C>T (R239W), c. 896 G>A (R299H), c.1255 G>A (G419R), and one termination c. 832 C>T (R278X), were identified in TYR, as well as one novel mutation, c.1453 G>A (G485R) in P. One novel single nucleotide polymorphism (SNP) was identified in both TYR and P; few reported SNPs were identified. The G>A base substitution caused relatively conservative amino acid changes, which altered glycine to arginine residues within the topological domain. The novel OCA2 mutation was not present in 100 control samples. This study identified two probands carrying mutations alone, 16 probands carrying SNPs alone, 4 probands carrying both mutations and SNPs and only one proband carrying neither mutations nor SNPs.

CONCLUSIONS

Although sequence analysis was performed with all five candidate genes, only four (17.39%) of the 23 probands showed mutations in TYR and 2 probands (8.69%) showed an unreported novel mutation in P. Genetic counseling for phenotypical diagnosis and genetic mutation screening of these genes will help to minimize the incidence of OCA and OA in future generations.

Elevated oxidative membrane damage associated with genetic modifiers of Lyst-mutant phenotypes

LYST is a large cytosolic protein that influences the biogenesis of lysosome-related organelles, and mutation of the encoding gene, LYST, can cause Chediak-Higashi syndrome. Recently, Lyst-mutant mice were recognized to also exhibit an iris disease resembling exfoliation syndrome, a common cause of glaucoma in humans. Here, Lyst-mutant iris phenotypes were used in a search for genes that influence Lyst pathways. In a candidate gene–driven approach, albino Lyst-mutant mice homozygous for a mutation in Tyr, whose product is key to melanin synthesis within melanosomes, exhibited complete rescue of Lyst-mutant iris phenotypes. In a genetic background–driven approach using a DBA/2J strain of congenic mice, an interval containing Tyrp1 enhanced Lyst-dependent iris phenotypes. Thus, both experimental approaches implicated the melanosome, an organelle that is a potential source of oxidative stress, as contributing to the disease phenotype. Confirming an association with oxidative damage, Lyst mutation resulted in genetic context–sensitive changes in iris lipid hydroperoxide levels, being lowest in albino and highest in DBA/2J mice. Surprisingly, the DBA/2J genetic background also exposed a late-onset neurodegenerative phenotype involving cerebellar Purkinje-cell degeneration. These results identify an association between oxidative damage to lipid membranes and the severity of Lyst-mutant phenotypes, revealing a new mechanism that contributes to pathophysiology involving LYST.

LYST is a poorly understood protein involved in hereditary disease. Mutations in the encoding gene cause Chediak-Higashi syndrome, a rare lethal disease affecting multiple tissues of the body. Mutations in Lyst also recapitulate features of exfoliation syndrome, a common disease affecting the anterior chamber of the eye. Unfortunately, the Lyst gene is quite large, rendering it difficult to study by many molecular and cellular approaches. Here, we use a genetic approach in mice to identify additional genetic pathways which might modify, or prevent, the ill consequences associated with Lyst mutation. Our experiments demonstrate that Lyst mutation results in elevated levels of oxidative damage to lipid membranes. These results identify a previously unrecognized consequence of Lyst mutation and a modifiable pathway of potential clinical relevance in humans. Ultimately, knowledge of these events will contribute to the design of new therapeutic strategies allowing a similar alleviation of disease in humans.

Saponified evening primrose oil reduces melanogenesis in B16 melanoma cells and reduces UV-induced skin pigmentation in humans

This study was conducted to determine whether saponified evening primrose oil (sap-EPO) has the potential for use as a whitening agent and to investigate its underlying mechanisms of action. In B16 melanoma cells, sap-EPO dose-dependently inhibited isobutylmethylxanthine-induced melanogenesis with no cytotoxicity. This decrease in melanin production was correlated with reduced enzyme activity and decreased mRNA and protein levels of tyrosinase. The mRNA levels of tyrosinase-related proteins 1 and 2 decreased in response to treatment with sap-EPO, indicating that it regulated tyrosinase at the transcriptional level. Expression of microphthalmia-associated transcription factor was also decreased by sap-EPO as evidenced by decreased mRNA and protein levels. Additionally, topical application of sap-EPO resulted in efficient whitening of UVB-induced hyperpigmentation of human skin. Taken together, these results suggest that sap-EPO has the potential for use as a cosmetic whitening agent.

The Efficacy and Safety of 4-n-butylresorcinol 0.1% Cream for the Treatment of Melasma: A Randomized Controlled Split-face Trial

BACKGROUND

Melasma is a common acquired symmetrical hypermelanosis that occurs on sun-exposed areas, and it is frequently observed among women. Various treatment modalities have been tried, but none are completely satisfactory. 4-n-butylresorcinol, which is a resorcinol derivative that has an inhibitory effect on both tyrosinase and tyrosinase-related protein-1, was introduced in 1995 and it has received increasing attention as a new hypopigmenting agent. However, the hypopigmenting effect of 4-n-butylresorcinol in human subjects has only been shown in a few studies.

OBJECTIVE

The aim of this study was to investigate the hypopigmenting efficacy and safety of 4-n-butylresorcinol 0.1% cream for the treatment of melasma.

METHODS

Twenty patients with melasma were enrolled to this randomized, double-blind, vehicle-controlled, split-face comparative study. The patients were instructed to apply 4-n-butylresorcinol 0.1% cream or vehicle to each side of the face twice daily for 8 weeks. Mexameter measurements were performed along with photography at baseline, 4 weeks and 8 weeks. Adverse events were observed and recorded throughout the study.

RESULTS

All the patients completed the study. Mexameter measurements demonstrated that the melanin index of the treated side showed a significant decrease when compared with that of the vehicle-treated side after 4 weeks (p=0.006) and after 8 weeks (p<0.0005). All the adverse reactions were mild and transient.

CONCLUSION

4-n-butylresorcinol 0.1% cream showed rapid efficacy and it was well tolerated when used for the treatment of melasma.

Evaluation of anti-pigmentary effect of synthetic sulfonylamino chalcone

The 4'-(p-toluenesulfonylamino)-4-hydroxychalcone (TSAHC), which bears inhibitory chemotypes for both alpha-glucosidase and tyrosinase, was evaluated for tyrosinase activity and depigmenting ability relative to compounds designed to only target tyrosianse activity. TSAHC emerged to be a competitive reversible inhibitor of mushroom tyrosinase. More importantly, it was also able to return the melanin content of alpha-melanocyte stimulated by alpha-MSH to base levels unlike other inhibitors that only targeted tyrosinase. The Western blot for expression levels of proteins involved in melanogenesis showed that TSAHC significantly decreased three main tyrosinase related protein in melanin biosynthesis, tyrosinase, TRP-1 and TRP-2.