AMPK Phosphorylates ZDHHC13 to Increase MC1R Activity and Suppress Melanomagenesis

Inherited genetic variations in the melanocortin-1 receptor (MC1R) responsible for human red hair color (RHC) variants are associated with impaired DNA damage repair and increased melanoma risk. MC1R signaling is critically dependent on palmitoylation, primarily mediated by the protein acyltransferase zinc finger DHHC-type palmitoyltransferase 13 (ZDHHC13). A better understanding of how ZDHHC13 is physiologically activated could help identify approaches to prevent melanomagenesis in redheads. Here, we report that AMP-activated protein kinase (AMPK) phosphorylates ZDHHC13 at S208 to strengthen the interaction between ZDHHC13 and MC1R-RHC, leading to enhanced MC1R palmitoylation in redheads. Consequently, phosphorylation of ZDHHC13 by AMPK increased MC1R-RHC downstream signaling. AMPK activation and MC1R palmitoylation repressed UVB-induced transformation of human melanocytes in vitro and delayed melanomagenesis in vivo in C57BL/6J-MC1R-RHC mice. The importance of AMPK to MC1R signaling was validated in human melanomas where AMPK upregulation correlated with expression of factors downstream from MC1R signaling and with prolonged patient survival. These findings suggest AMPK activation as a promising strategy to reduce melanoma risk, especially for individuals with red hair.

SIGNIFICANCE

Phosphorylation of ZDHHC13 by AMPK at S208 promotes MC1R activation and suppresses melanocyte transformation, indicating activation of AMPK as a potential approach to prevent melanoma in people with red hair.

Antioxidant and anti-aging carbon quantum dots using tannic acid

Overexpression of collagenase, elastase, and tyrosinase is caused by external factors such as ultraviolet (UV) radiation and stress, resulting in wrinkle formation and freckles through the loss of skin elasticity and skin pigmentation. In this study, we developed novel carbon quantum dots (CQDs) with antioxidant and anti-aging properties using tannic acid as a carbon source through a simple microwave-assisted pyrolysis method. The synthesized tannic acid-derived CQDs (T-CQDs) showed bright blue fluorescence (QY = 28.2 ± 4.0%), exhibiting maximum emission at 430 nm under 350 nm excitation. Even though small amount of the T-CQDs (3μg ml^-1) was used, they exhibited excellent free radical scavenging ability (82.8 ± 4.3%). Also, the T-CQDs (10μg ml^-1) revealed remarkable inhibitory activity against skin aging-related collagenase (77.6 ± 4.8%), elastase (52.6 ± 1.0%), and tyrosinase (44.2 ± 1.3%), demonstrating their antioxidant and anti-aging effects. Furthermore, their antioxidant and anti-aging properties were superior to those of tannic acid, L-ascorbic acid, and quercetin used as positive controls. Finally, the T-CQDs effectively suppressed UV-induced reactive oxygen species generation by 30% at the cellular levels and showed high cell viability (99.7 ± 0.8%) even at 500μg ml^-1. These results demonstrate that the T-CQDs with superior antioxidant, anti-aging properties, and low cytotoxicity can be utilized as novel anti-aging materials in cosmetic and nanomedicine fields.

Capsaicin Inhibits the Expression of Melanogenic Proteins in Melanocyte via Activation of TRPV1 Channel: Identifying an Inhibitor of Skin Melanogenesis

Chili pepper belongs to the genus Capsicum of Solanaceae family. Capsaicin is the primary capsaicinoid in placenta and flesh of chili pepper fruit, which has been shown to have various pharmacological functions, including gastric protection, anti-inflammation, and obesity treatment. Here, we revealed that capsaicin as well as chilli extract was able to inhibit synthesis of melanin in melanocytes. In cultured melanocytes, the melanin content was reduced to 54 ± 6.55% and 42 ± 7.41% with p < 0.001 under treatment of 50 μM capsaicin for 24 and 72 h, respectively. In parallel, the protein levels of tyrosinase and tyrosinase-related protein-1 were reduced to 62 ± 8.35% and 48 ± 8.92% with p < 0.001. Such an inhibitory effect of capsaicin was mediated by activation of transient receptor potential vanilloid 1-induced phosphorylation of extracellular signal-regulated kinase. This resulted in a degradation of microphthalmia-associated transcription factor, leading to reduction of melanogenic enzymes and melanin. These results revealed that capsaicin could be an effective inhibitor for skin melanogenesis. Hence, chili pepper, as our daily food, has potential in dermatological application, and capsaicin should be considered as a safe agent in treating hyperpigmentation problems.

Advances in the Design of Genuine Human Tyrosinase Inhibitors for Targeting Melanogenesis and Related Pigmentations

Human tyrosinase (hsTYR) is the key enzyme ensuring the conversion of l-tyrosine to dopaquinone, thereby initiating melanin synthesis, i.e., melanogenesis. Although the protein has long been familiar, knowledge about its three-dimensional structure and efficient overexpression protocols emerged only recently. Consequently, for decades medicinal chemistry studies aiming at developing skin depigmenting agents relied almost exclusively on biological assays performed using mushroom tyrosinase (abTYR), producing a plethoric literature, often of little useful purpose. Indeed, several recent reports have pointed out spectacular differences in terms of interaction patterns and inhibition values between hsTYR and abTYR, including for widely used standard tyrosinase inhibitors. In this review, we summarize the last developments regarding the potential role of hsTYR in human pathologies, the advances in recombinant expression systems and structural data retrieving, and the pioneer generation of true hsTYR inhibitors. Finally, we present suggestions for the design of future inhibitors of this highly attractive target in pharmacology and dermocosmetics.

ERK1/2 Pathway Is Involved in the Enhancement of Fatty Acids from Phaeodactylum tricornutum Extract (PTE) on Hair Follicle Cell Proliferation

Extractions from Phaeodactylum tricornutum have been widely studied and evaluated to various biological effects. The aim of this study was to investigate the promotional effect of P. tricornutum extract (PTE) on the ERK1/2 signaling pathway involved in hair follicle cell proliferation. In order to illuminate the enhancement of PTE on hair growth by promoting proliferation of hair follicle cells, the activities of human hair follicle outer root sheath cell (HFORSC), human hair follicle germinal matrix cells (HFGMC), and hair epithelial melanocytes (HEM) were observed under PET treatment. Levels of keratins, PKCζ, ERK1/2, and p38 MAPK in hair follicle cells were determined by Western blotting to illustrate the mechanisms of PTE effects on hair growth. Analyzed by GC-MS, the main polyunsaturated fatty acids which were 9.43% of total fatty acids in PTE were linolenic acid, linoleic acid, eicosapentaenoic acid, and docosahexaenoic acid. Melanin content and tyrosinase activity in HEM were measured. The results showed that PTE exhibited remarkable enhancement on cell proliferation. Melanin production was inhibited by PTE treatment, while keratin-14, keratin-15, and keratin-17 levels on hair follicle cells were elevated at different concentrations. The promotions of ERK1/2 and p38 MAPK levels indicated that the ERK1/2 signaling pathway is involved in the proliferation of hair follicle cells. These results are the evidence that PTE potentially deserves further study as a new natural candidate for hair care applications.

UP256 Inhibits Hyperpigmentation by Tyrosinase Expression/Dendrite Formation via Rho-Dependent Signaling and by Primary Cilium Formation in Melanocytes

Skin hyperpigmentation is generally characterized by increased synthesis and deposition of melanin in the skin. UP256, containing bakuchiol, is a well-known medication for acne vulgaris. Acne sometimes leaves dark spots on the skin, and we hypothesized that UP256 may be effective against hyperpigmentation-associated diseases. UP256 was treated for anti-melanogenesis and melanocyte dendrite formation in cultured normal human epidermal melanocytes as well as in the reconstituted skin and zebrafish models. Western blot analysis and glutathione S-transferase (GST)-pull down assays were used to evaluate the expression and interaction of enzymes related in melanin synthesis and transportation. The cellular tyrosinase activity and melanin content assay revealed that UP256 decreased melanin synthesis by regulating the expression of proteins related on melanogenesis including tyrosinase, TRP-1 and -2, and SOX9. UP256 also decreased dendrite formation in melanocytes via regulating the Rac/Cdc42/α-PAK signaling proteins, without cytotoxic effects. UP256 also inhibited ciliogenesis-dependent melanogenesis in normal human epidermal melanocytes. Furthermore, UP256 suppressed melanin contents in the zebrafish and the 3D human skin tissue model. All things taken together, UP256 inhibits melanin synthesis, dendrite formation, and primary cilium formation leading to the inhibition of melanogenesis.

Guanine Deaminase in Human Epidermal Keratinocytes Contributes to Skin Pigmentation

Epidermal keratinocytes are considered as the most important neighboring cells that modify melanogenesis. Our previous study used microarray to show that guanine deaminase (GDA) gene expression is highly increased in melasma lesions. Hence, we investigated the role of GDA in skin pigmentation. We examined GDA expression in post-inflammatory hyperpigmentation (PIH) lesions, diagnosed as Riehl’s melanosis. We further investigated the possible role of keratinocyte-derived GDA in melanogenesis by quantitative PCR, immunofluorescence staining, small interfering RNA-based GDA knockdown, and adenovirus-mediated GDA overexpression. We found higher GDA positivity in the hyperpigmentary lesional epidermis than in the perilesional epidermis. Both UVB irradiation and stem cell factor (SCF) plus endothelin-1 (ET-1) were used, which are well-known melanogenic stimuli upregulating GDA expression in both keratinocyte culture alone and keratinocyte and melanocyte coculture. GDA knockdown downregulated melanin content, while GDA overexpression promoted melanogenesis in the coculture. When melanocytes were treated with UVB-exposed keratinocyte-conditioned media, the melanin content was increased. Also, GDA knockdown lowered SCF and ET-1 expression levels in keratinocytes. GDA in epidermal keratinocytes may promote melanogenesis by upregulating SCF and ET-1, suggesting its role in skin hyperpigmentary disorders.

Chronic stress induces fur color change from dark to brown by decreasing follicle melanocytes and tyrosinase activity in female C57BL/6 mice

Increasing evidence suggests that stress may induce changes in hair color, with the underlying mechanism incompletely understood. In this study, female C57BL/6 mice subjected to electric foot shock combined with restraint stress were used to build chronic stress mouse model. The melanin contents and tyrosinase activity were measured in mouse skin and B16F10 melanoma cells. The enzyme-linked immunosorbent assay (ELISA) was used to determine the content of tumor necrosis factor α (TNF-α), interleukin- 1β (IL-1β) and interleukin-6 (IL-6) in the mouse skin. The content of nuclear factor κB (NFκB)/p65 subunit in mouse skins was valued by immunofluorescence staining. The results demonstrated that under chronic stress, the fur color turned from dark to brown in C57BL/6 mice due to the decrease of follicle melanocytes and tyrosinase activity in C57BL/6 mouse skin. Simultaneously, inflammatory responses in skins were detected as shown by increased NFκB activity and TNF-α expression in stressed mouse skin. In cultured B16F10 melanoma cells, TNF-α reduced the melanogenesis and tyrosinase activity in a dose-dependent manner. These findings indicate that chronic stress induces fur color change by decreasing follicle melanocytes and tyrosinase activity in female C57BL/6 mice, and TNF-α may play an important role in stress-induced hair color change.

Poria cocos Wolf extracts represses pigmentation in vitro and in vivo

In skin, melanocytes determine skin color using melanogenesis, which induces protective mechanism to oxidative stress and UV damage. However, when melanin is excessive produced by the various stimulus, the accumulated melanin induces hyperpigmentation disease such as melasma, freckles, Melanism ware induced. Therefore, it is implicated to finding potential agents for whitening to be used in cosmetic products. In our present study, we show that Poria cocos Wolf extracts decreased melanin synthesis in B16F10. And then this inhibition of melanogenesis was provoked by regulation of tyrosinase activity and tyrosinase and MITF expression. Moreover, Poria cocos Wolf extracts contained cream improved skin tone using increase of bright value. Overall, these results provide evidence to potential agent for whitening to be used in cosmetic products.

Cyclin-dependent kinase 5 regulates MAPK/ERK signaling in the skin of mice

Cyclin-dependent kinase 5 (CDK5) is a proline-directed serine/threonine kinase that has been shown to play important roles in many tissues except the nervous system. We previously reported that CDK5 showed differential expression in the transcriptome profiles of the skin of alpacas with different hair colors. To understand the functional role of CDK5 in hair color determination, we constructed CDK5-knockdown mice and identified the effect on the mitogen-activated protein kinase (MAPK) pathway in the mouse skin. Quantitative real-time polymerase chain reaction, co-immunoprecipitation, and western blotting were performed to analyze the effects of CDK5-knockdown on the MAPK pathway in mice. The results showed that MAP3K6 was inhibited by phosphorylated CDK5 through its activator CDK7. The decrease in MAP3K6 levels caused down-regulation of MEK1 and ERK expression, leading to the up-regulation of miR-143-3p, which targets MAP3K6 via Dicer. Taken together, our findings indicate that CDK5 functions in regulating the MAPK pathway. Given that MAP3K6 was inhibited in two directions, this mechanism can provide insight into the contributions of the MAPK/ERK pathway to the inhibition of melanin production.

Mutational activation of BRAF confers sensitivity to transforming growth factor beta inhibitors in human cancer cells

Recent data implicate elevated transforming growth factor-β (TGFβ) signalling in BRAF inhibitor drug-resistance mechanisms, but the potential for targeting TGFβ signalling in cases of advanced melanoma has not been investigated. We show that mutant BRAFV600E confers an intrinsic dependence on TGFβ/TGFβ receptor 1 (TGFBR1) signalling for clonogenicity of murine melanocytes. Pharmacological inhibition of the TGFBR1 blocked the clonogenicity of human mutant BRAF melanoma cells through SMAD4-independent inhibition of mitosis, and also inhibited metastasis in xenografted zebrafish. When investigating the therapeutic potential of combining inhibitors of mutant BRAF and TGFBR1, we noted that unexpectedly, low-dose PLX-4720 (a vemurafenib analogue) promoted proliferation of drug-naïve melanoma cells. Pharmacological or pharmacogenetic inhibition of TGFBR1 blocked growth promotion and phosphorylation of SRC, which is frequently associated with vemurafenib-resistance mechanisms. Importantly, vemurafenib-resistant patient derived cells retained sensitivity to TGFBR1 inhibition, suggesting that TGFBR1 could be targeted therapeutically to combat the development of vemurafenib drug-resistance.

Immunohistochemical expression of cyclooxygenase-2 (COX-2) in oral nevi and melanoma

BACKGROUND

Cyclooxygenase-2 (COX-2) catalyses the conversion of arachidonic acid to prostaglandin, and its overexpression has been demonstrated in different malignant tumors, including cutaneous melanoma. However, no data about the expression of this protein in oral melanocytic lesions are available to date. The aim of this study was to evaluate the immunohistochemical expression of COX-2 in oral nevi and melanomas, comparing the results with correspondent cutaneous lesions.

METHODS

COX-2 was evaluated by immunohistochemistry in 49 oral melanocytic lesions, including 36 intramucosal nevi and 13 primary oral melanomas, and in four cutaneous nevi and eight melanomas.

RESULTS

All cases of oral and cutaneous melanomas were positive for COX-2. On the other hand, all oral and cutaneous melanocytic nevi were negative.

CONCLUSION

COX-2 is highly positive in oral melanomas and negative in oral nevi and might represent a useful marker to distinguish melanocytic lesions of the oral cavity.

Characterization and expression of soluble guanylate cyclase in skins and melanocytes of sheep

The study reported the characterization of soluble guanylate cyclase (sGC) with the size of CDS of 1860bp, encoding a protein of 620 amino acids and containing several conserved functional domains including HNOB, HNOBA, and CHD. Quantitative real time PCR analysis of sGC showed that the expression of sGC mRNA is higher (∼5 fold) in white sheep skin relative to black sheep skin with significant difference (P<0.01). Using a rabbit polyclonal anti-sGC antibody, an immune reactive band corresponding to sheep sGC protein was detected in the skin samples by Western blotting analysis, and the expression of sGC protein was significantly higher in white sheep skin compared to black sheep skin (P<0.01). Immunohistochemical analysis revealed that sGC protein was localized in cytoplasm and intercellular substance of upper hair papilla in hair follicles of white sheep skin, but the protein was localized in cytoplasm and intercellular substance of lower hair bulb and outer root sheath cells in hair follicles of black sheep skin. The immunocytochemical analysis revealed that sGC was expressed in melanocytes in vitro of sheep skin. Over expression of sGC in melanocytes resulted in decreased expression of key melanogenic genes including microphthalmia transcription factor (MITF), tyrosinase (TYR), tyrosinase related protein 1(TYRTP1), and tyrosinase related protein 2(TYRP2) both at mRNA and protein level. Moreover, the melanocytes was capable of producing cGMP and cAMP. The observed differential expression and localization of sGC in sheep skins and melanocytes and the capability of producing cGMP and cAMP, which suggested a potential role for this gene in hair color regulation.

Melanoma growth and progression after ultraviolet a irradiation: impact of lysosomal exocytosis and cathepsin proteases

Ultraviolet (UV) irradiation is a risk factor for development of malignant melanoma. UVA-induced lysosomal exocytosis and subsequent cell growth enhancement was studied in malignant melanoma cell lines and human skin melanocytes. UVA irradiation caused plasma membrane damage that was rapidly repaired by calcium-dependent lysosomal exocytosis. Lysosomal content was released into the culture medium directly after irradiation and such conditioned media stimulated the growth of non-irradiated cell cultures. By comparing melanocytes and melanoma cells, it was found that only the melanoma cells spontaneously secreted cathepsins into the surrounding medium. Melanoma cells from a primary tumour showed pronounced invasion ability, which was prevented by addition of inhibitors of cathepsins B, D and L. Proliferation was reduced by cathepsin L inhibition in all melanoma cell lines, but did not affect melano-cyte growth. In conclusion, UVA-induced release of cathepsins outside cells may be an important factor that promotes melanoma growth and progression.

Discovery of Potent Cysteine-Containing Dipeptide Inhibitors against Tyrosinase: A Comprehensive Investigation of 20 × 20 Dipeptides in Inhibiting Dopachrome Formation

Tyrosinase is an essential copper-containing enzyme required for melanin synthesis. The overproduction and abnormal accumulation of melanin cause hyperpigmentation and neurodegenerative diseases. Thus, tyrosinase is promising for use in medicine and cosmetics. Our previous study identified a natural product, A5, resembling the structure of the dipeptide WY and apparently inhibiting tyrosinase. Here, we comprehensively estimated the inhibitory capability of 20 × 20 dipeptides against mushroom tyrosinase. We found that cysteine-containing dipeptides, directly blocking the active site of tyrosinase, are highly potent in inhibition; in particular, N-terminal cysteine-containing dipeptides markedly outperform the C-terminal-containing ones. The cysteine-containing dipeptides, CE, CS, CY, and CW, show comparative bioactivities, and tyrosine-containing dipeptides are substrate-like inhibitors. The dipeptide PD attenuates 16.5% melanin content without any significant cytotoxicity. This study reveals the functional role of cysteine residue positional preference and the selectivity of specific amino acids in cysteine-containing dipeptides against tyrosinase, aiding in developing skin-whitening products.

Interferon-gamma Inhibits Melanogenesis and Induces Apoptosis in Melanocytes: A Pivotal Role of CD8+ Cytotoxic T Lymphocytes in Vitiligo

Increased expression of the cytokine interferon (IFN)-γ plays a pivotal role in vitiligo-induced depigmentation. However, the major source of IFN-γ in vitiligo patients and the mechanisms underlying melanocyte destruction are unknown. In this study, a large number of skin infiltrating IFN-γ+ cells and CD8+ T cells were detected in progressive vitiligo. Among the peripheral blood mononuclear cells (PBMCs) of vitiligo patients, CD8+ cytotoxic T lymphocytes (CTLs) that express IFN-γ exhibited significant expansion, which suggests that activated CTLs are the main source of increased IFN-γ in progressive vitiligo. An in vitro analysis demonstrated that IFN-γ inhibits melanogenesis in primary cultured human melanocytes by altering melanogenic enzyme mRNA expression and, more importantly, that IFN-γ directly induces melanocyte apoptosis. Our data indicate that vitiligo pathophysiology may be linked to globally activated CD8+ CTL subpopulations, which produce increased IFN-γ and induce melanocyte dysfunction and apoptosis.

IMPACT OF GENTAMICIN ON ANTIOXIDANT ENZYMES ACTIVITY IN HEMn-DP CELLS

Aminoglycoside antibiotics, including gentamicin, are widely used clinically in treatment of bacterial infections. Unfortunately, their side effects, especially nephrotoxicity and ototoxicity remain a problem. It is known that aminoglycoside antibiotics bind well to melanin biopolymer, but the relation between their affinity to melanin and ototoxicity is not well documented. The aim of this work was to examine the impact of gentamicin on antioxidant enzymes activity in cultured dark pigmented normal human melanocytes (HEMn-DP). The WST-1 assay was used to detect gentamicin cytotoxic effect. The analyzed antibiotic induced concentration-dependent loss in melanocytes viability. The value of EC50 was found to be 7.5 mM. Significant changes in the cellular antioxidant enzymes: SOD, CAT and GPx were stated in melanocytes exposed to gentamicin, what may indicate the depletion of antioxidant defense system. It is concluded, that the results obtained in vitro may explain a potential role of melanocytes and melanin in the causative mechanisms of aminoglycosides ototoxic effects in vivo.

Melatonin and its metabolites accumulate in the human epidermis in vivo and inhibit proliferation and tyrosinase activity in epidermal melanocytes in vitro

Melatonin and its metabolites including 6-hydroxymelatonin (6(OH)M), N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK) and 5-methoxytryptamine (5MT) are endogenously produced in human epidermis. This production depends on race, gender and age. The highest melatonin levels are in African-Americans. In each racial group they are highest in young African-Americans [30-50 years old (yo)], old Caucasians (60-90 yo) and Caucasian females. AFMK levels are the highest in African-Americans, while 6(OH)M and 5MT levels are similar in all groups. Testing of their phenotypic effects in normal human melanocytes show that melatonin and its metabolites (10(-5) M) inhibit tyrosinase activity and cell growth, and inhibit DNA synthesis in a dose dependent manner with 10(-9) M being the lowest effective concentration. In melanoma cells, they inhibited cell growth but had no effect on melanogenesis, except for 5MT which enhanced L-tyrosine induced melanogenesis. In conclusion, melatonin and its metabolites [6(OH)M, AFMK and 5MT] are produced endogenously in human epidermis and can affect melanocyte and melanoma behavior.

[Human caspase-14 expression in malignant melanoma and its significance]

OBJECTIVE

To detect the caspase-14 expression in malignant melanoma cells and tumor tissues and its effect on tumor resistance to drug.

METHODS

The mRNA and protein level of caspase-14 in 4 melanoma cell lines (A375, A875, M14, and SK-Mel-1) and the melanocytes, was detected by reverse transcription PCR (RT-PCR) and Western blotting. Caspase-14 expression in 34 malignant melanoma tumor tissues and 10 dermal nevus tissues was determined by in situ hybridization and immunohistochemistry.

RESULTS

Caspase-14 expression was seen in melanoma cells and melanocytes. It was higher in melanoma-associated antigen 1 recognized by T cells (MART-1) positive cells than in MART-1 negative cells. The cells expressing the lower caspase-14 were more sensitive to the treatment with either chemotherapy drugs camptothecin and cisplatin or radiotherapy than the ones expressing the higher caspase-14 (P<0.01). Caspase-14 expression was observed in 70% dermal nevus, as well as 97% in malignant melanoma tissues, and the difference between them was statistically significant (P<0.05).

CONCLUSION

Caspase-14 is expressed in tissues and cells of malignant melanoma. Our data indicated that the expression level of caspase-14 affected the drug sensitivity of melanoma.

Fatty acid synthase inhibitors induce apoptosis in non-tumorigenic melan-a cells associated with inhibition of mitochondrial respiration

The metabolic enzyme fatty acid synthase (FASN) is responsible for the endogenous synthesis of palmitate, a saturated long-chain fatty acid. In contrast to most normal tissues, a variety of human cancers overexpress FASN. One such cancer is cutaneous melanoma, in which the level of FASN expression is associated with tumor invasion and poor prognosis. We previously reported that two FASN inhibitors, cerulenin and orlistat, induce apoptosis in B16-F10 mouse melanoma cells via the intrinsic apoptosis pathway. Here, we investigated the effects of these inhibitors on non-tumorigenic melan-a cells. Cerulenin and orlistat treatments were found to induce apoptosis and decrease cell proliferation, in addition to inducing the release of mitochondrial cytochrome c and activating caspases-9 and -3. Transfection with FASN siRNA did not result in apoptosis. Mass spectrometry analysis demonstrated that treatment with the FASN inhibitors did not alter either the mitochondrial free fatty acid content or composition. This result suggests that cerulenin- and orlistat-induced apoptosis events are independent of FASN inhibition. Analysis of the energy-linked functions of melan-a mitochondria demonstrated the inhibition of respiration, followed by a significant decrease in mitochondrial membrane potential (ΔΨm) and the stimulation of superoxide anion generation. The inhibition of NADH-linked substrate oxidation was approximately 40% and 61% for cerulenin and orlistat treatments, respectively, and the inhibition of succinate oxidation was approximately 46% and 52%, respectively. In contrast, no significant inhibition occurred when respiration was supported by the complex IV substrate N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). The protection conferred by the free radical scavenger N-acetyl-cysteine indicates that the FASN inhibitors induced apoptosis through an oxidative stress-associated mechanism. In combination, the present results demonstrate that cerulenin and orlistat induce apoptosis in non-tumorigenic cells via mitochondrial dysfunction, independent of FASN inhibition.

Targeted BRAF inhibition impacts survival in melanoma patients with high levels of Wnt/β-catenin signaling

Unprecedented clinical responses have been reported in advanced stage metastatic melanoma patients treated with targeted inhibitors of constitutively activated mutant BRAF, which is present in approximately half of all melanomas. We and others have previously observed an association of elevated nuclear β-catenin with improved survival in molecularly-unselected melanoma patients. This study sought to determine whether levels of Wnt/β-catenin signaling in melanoma tumors prior to treatment might predict patient responses to BRAF inhibitors (BRAFi). We performed automated quantification of β-catenin immunohistochemical expression in pretreatment BRAF-mutant tumors from 32 BRAFi-treated melanoma patients. Unexpectedly, patients with higher nuclear β-catenin in their tumors did not exhibit the survival advantage previously observed in molecularly-unselected melanoma patients who did not receive BRAFi. In cultured melanoma cells treated with long-term BRAFi, activation of Wnt/β-catenin signaling is markedly inhibited, coinciding with a loss of the enhancement of BRAFi-induced apoptosis by WNT3A observed in BRAFi-naïve cells. Together, these observations suggest that long-term treatment with BRAFi can impact the interaction between BRAF/MAPK and Wnt/β-catenin signaling to affect patient outcomes. Studies with larger patient cohorts are required to determine whether nuclear β-catenin expression correlates with clinical responses to BRAFi and to specific mechanisms of acquired resistance to BRAFi. Understanding these pathway interactions will be necessary to facilitate efforts to individualize therapies for melanoma patients.

Cystathionase mediates senescence evasion in melanocytes and melanoma cells

The development of malignant melanoma is a highly complex process, which is still poorly understood. A majority of human melanomas are found to express a few oncogenic proteins, such as mutant RAS and BRAF variants. However, these oncogenes are also found in nevi, and it is now a well-accepted fact that their expression alone leads to senescence. This renders the understanding of senescence escape mechanisms an important point to understand tumor development. Here, we approached the question of senescence evasion by expressing the transcription factor v-myc myelocytomatosis viral oncogene homolog (c-MYC), which is known to act synergistically with many oncogenes, in melanocytes. We observed that MYC drives the evasion of reactive-oxygen stress-induced melanocyte senescence, caused by activated receptor tyrosine kinase signaling. Conversely, MIZ1, the growth suppressing interaction partner of MYC, is involved in mediating melanocyte senescence. Both, MYC overexpression and Miz1 knockdown led to a strong reduction of endogenous reactive-oxygen species (ROS), DNA damage and senescence. We identified the cystathionase (CTH) gene product as mediator of the ROS-related MYC and MIZ1 effects. Blocking CTH enzymatic activity in MYC-overexpressing and Miz1 knockdown cells increased intracellular stress and senescence. Importantly, pharmacological inhibition of CTH in human melanoma cells also reconstituted senescence in the majority of cell lines, and CTH knockdown reduced tumorigenic effects such as proliferation, H2O2 resistance and soft agar growth. Thus, we identified CTH as new MYC target gene with an important function in senescence evasion.

Inhibition of melanin content by Punicalagins in the super fruit pomegranate (Punica granatum)

Current efforts to develop effective skin lightening products through the inhibition of melanin production have focused on compounds that inhibit the function and activity of tyrosinase, the rate-limiting enzyme in the melanin biosynthesis pathway. Synthetic tyrosinase inhibitors, such as hydroquinone, kojic acid, and arbutin, have been reported to cause skin irritation or acute dermatitis, raising concerns about the safety of these compounds. As a result, there is a need for safe natural ingredients that show effective skin lightening. In this report, we have identified a natural ingredient, pomegranate fruit extract, that inhibits melanin production in melanocytes and shows potential for use as a cosmetic skin lightening agent. In addition, we have identified a polyphenolic compound, punicalagins, as the active melanin inhibitor in pomegranate fruit extract based on its capacity to directly inhibit melanin production.

Octaphlorethol A isolated from Ishige foliacea inhibits α-MSH-stimulated induced melanogenesis via ERK pathway in B16F10 melanoma cells

In this study, the potent skin-whitening effects of Octaphlorethol A (OPA) isolated from Ishige foliacea was investigated through inhibitory effect of melanin synthesis and tyrosinase activity in alpha-melanocyte stimulating hormone (α-MSH) induced B16F10 melanoma cells. OPA markedly inhibited melanin synthesis and tyrosinase activity in a concentration-dependent manner. We also found that OPA decreased microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein-1 and -2 (TRP-1 and TRP-2) protein expressions. Moreover, OPA reduces p38 MAPK protein levels and activates extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinases (JNKs) protein expressions in B16F10 cells. A specific ERK inhibitor PD98059 significantly blocks OPA-inhibited melanin synthesis and tyrosinase activity, whereas a p38MAP and JNK inhibitor had no effect. These findings provide evidence demonstrating that the anti-melanogenic effect of OPA is mediated through the activation of ERK signal pathway in B16F10 cells. These results indicate that OPA has the potential to be used as a melanogenesis inhibitor in the food and cosmetics industry.

UVB-stimulated TNFα release from human melanocyte and melanoma cells is mediated by p38 MAPK

Ultraviolet (UV) radiation activates cell signaling pathways in melanocytes. As a result of altered signaling pathways and UV-induced cellular damage, melanocytes can undergo oncogenesis and develop into melanomas. In this study, we investigated the effect of UV-radiation on p38 MAPK (mitogen-activated protein kinase), JNK and NFκB pathways to determine which plays a major role in stimulating TNFα secretion in human HEM (melanocytes) and MM96L (melanoma) cells. MM96L cells exhibited 3.5-fold higher p38 activity than HEM cells at 5 min following UVA + B radiation and 1.6-fold higher JNK activity at 15–30 min following UVB+A radiation, while NFκB was minimally activated in both cells. Irradiated HEM cells had the greatest fold of TNFα secretion (UVB: 109-fold, UVA + B: 103-fold & UVB+A: 130-fold) when co-exposed to IL1α. The p38 inhibitor, SB202190, inhibited TNFα release by 93% from UVB-irradiated HEM cells. In the UVB-irradiated MM96L cells, both SB202190 and sulfasalazine (NFκB inhibitor) inhibited TNFα release by 52%. Although, anisomycin was a p38 MAPK activator, it inhibited TNFα release in UV-irradiated cells. This suggests that UV-mediated TNFα release may occur via different p38 pathway intermediates compared to those stimulated by anisomycin. As such, further studies into the functional role p38 MAPK plays in regulating TNFα release in UV-irradiated melanocyte-derived cells are warranted.

Transplantation of melanocytes obtained from the skin ameliorates apomorphine-induced abnormal behavior in rodent hemi-parkinsonian models

Tyrosinase, which catalyzes both the hydroxylation of tyrosine and consequent oxidation of L-DOPA to form melanin in melanocytes, is also expressed in the brain, and oxidizes L-DOPA and dopamine. Replacement of dopamine synthesis by tyrosinase was reported in tyrosine hydroxylase null mice. To examine the potential benefits of autograft cell transplantation for patients with Parkinson’s disease, tyrosinase-producing cells including melanocytes, were transplanted into the striatum of hemi-parkinsonian model rats or mice lesioned with 6-hydroxydopamine. Marked improvement in apomorphine-induced rotation was noted at day 40 after intrastriatal melanoma cell transplantation. Transplantation of tyrosinase cDNA-transfected hepatoma cells, which constitutively produce L-DOPA, resulted in marked amelioration of the asymmetric apomorphine-induced rotation in hemi-parkinsonian mice and the effect was present up to 2 months. Moreover, parkinsonian mice transplanted with melanocytes from the back skin of black newborn mice, but not from albino mice, showed marked improvement in the apomorphine-induced rotation behavior up to 3 months after the transplantation. Dopamine-positive signals were seen around the surviving transplants in these experiments. Taken together with previous studies showing dopamine synthesis and metabolism by tyrosinase, these results highlight therapeutic potential of intrastriatal autograft cell transplantation of melanocytes in patients with Parkinson’s disease.

In vitro melanogenesis inhibitory effects of N-feruloyldopamine

Tyrosinase is the rate-limiting enzyme in the melanogenesis process. It remains the most efficient way to downregulate melanin production and improve unsightly pigmentary disorders. The aim of our investigations was to find a structurally characterized molecule with better efficacy than existing molecules without cell toxicity. We focused our investigations on compounds that could act as substrate-mimicking inhibitors of tyrosinase and identified N-feruloyldopamine as the best candidate. In vitro, N-feruloyldopamine inhibited human tyrosinase with higher efficacy than the reference inhibitor arbutin without cell toxicity at least up to 100 μM as measured in cultured normal human epidermal melanocytes (NHEMs). Moreover, the inhibition appeared to be specific to mammalian tyrosinases as shown by a very poor inhibition of mushroom tyrosinase, but a significant decrease of total melanin in B16-F10 cells. The antioxidant capacity assessed using DPPH (1,1-diphenyl-2-picrylhydrazyl) assay was comparable to that of vitamin C and finally, N-feruloyldopamine exerted a significant inhibition of Pmel17 gene expression when used at 100 μM on cultured NHEM. Taken together, these results suggest that N-feruloyldopamine is a serious candidate for in vivo application as complexion-brightening ingredient.

Inhibitory effects of geranic acid derivatives on melanin biosynthesis

The effects of geranic acid and its structurally related derivatives (geraniol, citronellic acid, and citronellol) on cell viability and melanin biosynthesis in Melan-a cells were evaluated in this study. Among them, geranic acid evidenced the strongest inhibitory activity on melanin production, coupled with low cell toxicity. Treatment with 500 μM of this compound resulted in a reduction in melanin content of 35.4% as compared to the live cell percentage (91.7%). Moreover, geranic acid also inhibited tyrosinase activity and intracellular tyrosinase expression in a dose-dependent manner. These results show that geranic acid may function as a skin depigmenting agent via the inhibition of tyrosinase activity and expression within melanocytes.

DeoxyArbutin and its derivatives inhibit tyrosinase activity and melanin synthesis without inducing reactive oxygen species or apoptosis

Safety is a major concern in developing commercial skin-lightening agents. Here, we report the modulating effects of deoxyArbutin (dA) and its second-generation derivatives - deoxyFuran (dF), 2-fluorodeoxyArbutin (fdA), and thiodeoxyArbutin (tdA) - on tyrosinase, and consequently, on melanization. Results demonstrate that dA and its derivatives inhibit tyrosine hydroxylase and dopa oxidase activity of tyrosinase. The inhibition is dose-dependent, thereby inhibiting melanin synthesis in intact melanocytes, when used at concentrations that retain 95% viability of the treated cells in culture. Herein we demonstrate that dA, and its second-generation derivatives dF, fdA, and tdA, exhibit dose-dependent reductions in melanocyte cell number, primarily due to inhibition of proliferation rather than initiation of apoptosis as exemplified by hydroquinone (HQ), ie, cytostatic as opposed to cytotoxic. Human and murine melanocytes with functional mutations in either tyrosinase or tyrosinase-related protein 1 (Tyrp1) are less sensitive to the cytostatic effects of dA and its derivatives. Minimal amounts of reactive oxygen species (ROS) were generated upon treatment with dA and its derivatives, in contrast to a dramatic amount of ROS induced by HQ. This increase in ROS subsequently induced the expression of the endogenous antioxidant catalase in treated melanocytes. Treatment with exogenous antioxidants provided protection for melanocytes treated with HQ, but not dA and its derivatives, suggesting that HQ exerts more oxidative stress. These studies demonstrate that dA and its derivatives are relatively safe tyrosinase inhibitors for skin lightening or for ameliorating hyperpigmented lesions.

Melanoblasts on the move: Rac1 sets the pace

Cell migration is fundamental to development and many cell types have a migratory phase during embryonic development when tissues and body structures are forming. Cancer metastasis is in many ways thought to be analogous to embryonic development. Some of the mechanisms that tumor cells use to hijack the adult body are thought to derive from their abilities to reactivate embryonic signaling and motility pathways and thus enhance their growth and motility. Melanomas are notorious for their ability to become highly invasive and metastatic if not removed early. While adult melanin producing cells, melanocytes, have limited mobility, melanoblasts are highly motile cells that move through the dermis and epidermis during embryogenesis and could serve as a useful paradigm for some aspects of melanoma invasion and metastasis. Recent findings from our laboratory using ex-vivo imaging of mouse melanoblast migration in the epidermis provide the first insights into the role of Rac1 in developing mouse melanoblasts in vivo. Melanoblasts do not move as a collective group, or use an invasive or blebbing mode of migration as revealed by other in vivo systems, but rather they extend short and long dynamic pseudopodia and squeeze between epidermal keratinocytes using myosin motors. Melanoblasts can initiate short actin-based protrusions independently of Rac1. Rac1 is required to control the rate of formation of long actin-based protrusions for effective translocation in skin. Our results reveal a novel mode of in vivo migration controlled by Rac1 that is important for normal development and likely in melanoma.

Inhibition of glycoprotein synthesis in the endoplasmic reticulum as a novel anticancer mechanism of (-)-epigallocatechin-3-gallate

(-)-Epigallocatechin-3-gallate (EGCG) has been found to trigger the unfolded protein response (UPR) likely due to the inhibition of glucosidase II, a key enzyme of glycoprotein processing and quality control in the endoplasmic reticulum (ER). These findings strongly suggest that EGCG interferes with glycoprotein maturation and sorting in the ER. This hypothesis was tested in SK-Mel28 human melanoma cells by assessing the effect of EGCG and deoxynojirimycin (DNJ) on the synthesis of two endogenous glycoproteins. Both tyrosinase and vascular endothelial growth factor (VEGF) protein levels were remarkably reduced despite unaltered mRNA expression in EGCG- or DNJ-treated cells compared to control. The hindrance of tyrosinase and VEGF protein synthesis could be prevented by proteasome inhibitor, lactacystine. Collectively, our results support that glucosidase II inhibitor EGCG interferes with protein processing and quality control in the ER, which diverts tyrosinase, VEGF, and likely other glycoproteins towards proteasomal degradation. This mechanism provides a novel therapeutic approach in dermatology and might play an important role in the antitumor effect or hepatotoxicity of EGCG.

Partially purified components of Nardostachys chinensis suppress melanin synthesis through ERK and Akt signaling pathway with cAMP down-regulation in B16F10 cells

Ethnopharmacological relevance Nardostachys chinensis has been used in folk medicine to treat melasma and lentigines in Korea. We investigated the inhibitory activities of Nardostachys chinensis in melanogenesis and its related signaling pathway.

MATERIALS AND METHODS

Bioassay-guided fractionation of Nardostachys chinensis using solvent partitioning and purification with octadecylsilane open-column chromatography resulted in partial purification. The active 20% methanol chromatographic fraction from the ethyl acetate layer (PPNC) was used to investigate melanogenesis by melanin synthesis, tyrosinase activity assay, cAMP assay, Western blot and flow cytometric analyses in B16F10 mouse melanoma cells.

RESULTS

PPNC markedly inhibits melanin synthesis and tyrosinase activity in a concentration-dependent manner. We also found that PPNC decreases microphthalmia-associated transcription factor (MITF), tyrosinase, tyrosinase-related protein (TRP)-1, and dopachrome tautomerase (Dct) protein expressions and MITF and tyrosinase mRNA levels. Moreover, PPNC reduces intracellular cAMP levels and activates mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K)/Akt expression in B16F10 cells. The specific MEK/ERK inhibitor PD98059 and PI3K/Akt inhibitor LY294002, block the PPNC-induced hypopigmentation effect, and abrogate the PPNC-suppressed expression of melanogenic proteins such as MITF, tyrosinase, TRP-1, and Dct. Using flow cytometry, we elucidated whether PPNC directly induces ERK phosphorylation at the level of an intact single cell. PPNC shows marked expression of phosphorylated ERK in live B16F10 cells and abrogates PPNC-induced phosphorylated ERK by PD98059 treatment.

CONCLUSIONS

PPNC stimulates MEK/ERK phosphorylation and PI3K/Akt signaling with suppressing cAMP levels and subsequently stimulating MITF and TRPs down-regulation, resulting in melanin synthesis suppression.

Inhibitory effects of Sargassum polycystum on tyrosinase activity and melanin formation in B16F10 murine melanoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Sargassum polycystum, a type of brown seaweed, has been used for the treatment of skin-related disorders in traditional medicine.

AIM OF THE STUDY

The aim of the present study is to investigate the antimelanogenesis effect of Sargassum polycystum extracts by cell-free mushroom tyrosinase assay followed by cell viability assay, cellular tyrosinase assay and melanin content assay using B16F10 murine melanoma cells.

MATERIALS AND METHODS

Sargassum polycystum was extracted with 95% ethanol and further fractionated with hexane, ethyl acetate and water. The ethanolic crude extract and its fractionated extracts were tested for their potential to act as antimelanogenesis or skin-whitening agents by their abilities to inhibit tyrosinase activity in the cell-free mushroom tyrosinase assay and cellular tyrosinase derived from melanin-forming B16F10 murine melanoma cells. The tyrosinase inhibitory activity was correlated to the inhibition of melanin production in α-MSH-stimulated and unstimulated B16F10 cells.

RESULTS

Sargassum polycystum ethanolic extract and its fractions had little or no inhibitory effect on mushroom tyrosinase activity. However, when tested on cellular tyrosinase, the ethanolic extract and its non-polar fraction, hexane fraction (SPHF), showed significant inhibition of cellular tyrosinase activity. In parallel to its cellular tyrosinase inhibitory activity, SPHF was also able to inhibit basal and α-MSH-stimulated melanin production in B16F10 cells.

CONCLUSIONS

Our findings showed that (i) cellular tyrosinase assay is more reliable than mushroom tyrosinase assay in the initial testing of potential antimelanogenesis agents and, (ii) SPHF inhibited melanogenesis by inhibiting cellular tyrosinase activity. SPHF may be useful for treating hyperpigmentation and as a skin-whitening agent in cosmetics industry.

Mast cells in melanocytic skin lesions. An immunohistochemical and quantitative study

The mast cells participate in inflammation and possibly in carcinogenesis. The aim of the study was to study mast cells in melanocytic lesions. The material consisted of 24 pigmented nevi, 18 dysplastic nevi and 19 melanomas. The sections were stained immunohistochemically for tryptase and chymase. Positive cells were counted inside the lesions and at the interface between the lesion and dermis. The mean intralesional tryptase+ count was 15.75 for nevi, 21.78 for dysplastic nevi, and 8.07 for melanomas. The chymase+ intralesional count was 14.89 for nevi, 21.88 for dysplastic nevi, and 11.34 for melanomas. The tryptase+ perilesional count was 16.89 for nevi, 15.93 for dysplastic nevi, and 15.71 for melanomas. The chymase+ perilesional count was 16.52 for nevi, 16.16 for dysplastic nevi, and 14.77 for melanomas. The tryptase/chymase intralesional ratio was 0.93 for nevi, 1.05 for dysplastic nevi, and 1.67 for melanomas. The tryptase/chymase perilesional ratio was 1.02 for nevi, 1.09 for dysplastic nevi, and 1.00 for melanomas. The differences between intralesional mast cells, both tryptase+ and chymase+, were statistically significant. The intralesional tryptase+ count showed an inverse correlation to age (R = -0.42); this correlation was the strongest in melanomas. The results obtained in our study suggest a possible correlation between mast cells and the pathogenesis of cutaneous melanoma.

The phosphatidyl inositol 3-kinase pathway is central to the pathogenesis of Kit-activated melanoma

Mouse Kit L575P, the ortholog of human KIT L576P, a common KIT mutation found in human melanoma was expressed in an immortalized but non-transformed mouse Ink4a-Arf-deficient melanocyte cell line. The resultant Ink4a-Arf-deficient Kit L575P-expressing melanocytes exhibited increased proliferation, the ability to grow in soft agar, and increased migration. When these cells were injected subcutaneously into NOD/SCID/gamma(c) mice, melanomas arose in 5 of 7 (71%) mice. One of seven mice (14%) injected with these cells developed metastatic disease. Evaluation of signal transduction pathways downstream of constitutively activated Kit L575P revealed striking activation of the phosphatidyl inositol 3-kinase (PI3K) pathway. Inhibition of the PI3K pathway pharmacologically or genetically abolished the transformation phenotypes gained by the L575P single mutant. These studies validate this Kit L575P-activated model of melanoma and establish the PI3K pathway as a dominant signaling pathway downstream of Kit in melanoma.

Comparison of the antimelanogenic effects of p-coumaric acid and its methyl ester and their skin permeabilities

BACKGROUND

p-Coumaric acid (PCA) inhibits human tyrosinase (TYR) activity and melanin synthesis in human epidermal melanocytes.

OBJECTIVE

The purpose of the current study was to examine the potential of PCA and its hydrophobic derivative, methyl p-coumarate (MPC), as hypopigmenting agents for topical use.

METHODS

PCA and MPC were comparatively tested against in vitro human TYR enzyme activity and cellular melanin synthesis in human epidermal melanocytes. Permeation studies were undertaken using an artificial lipophilic membrane and an excised porcine skin. In vivo hypopigmenting efficacy was assessed on the skin of melanin-possessing hairless mice exposed to UVB.

RESULTS

Although PCA was a stronger inhibitor than MPC against TYR activity in vitro, the former inhibited cellular melanin synthesis less effectively than the latter. A non-cell based permeability assay indicated that PCA was practically impermeable through the lipophilic barrier while MPC was highly permeable. In contrast, an ex vivo skin permeation study demonstrated that topically applied PCA in the form of a cream can diffuse into the aqueous medium underneath the skin. No MPC was released from a MPC cream but PCA was released instead as a bio-converted product. Topical application of PCA cream attenuated the UVB-induced erythema formation and pigmentation in mice models, more effectively compared with MPC cream.

CONCLUSION

PCA may be useful as an active ingredient for topical applications for a hypopigmenting effect. MPC has potential as a hypopigmenting agent but requires rather invasive methods for its delivery to the target cells.

Active constituents from Sophora japonica exhibiting cellular tyrosinase inhibition in human epidermal melanocytes

AIM OF THE STUDY

There is greater consumer awareness of plant-based skin-care products. Sophora japonica L. (Fabaceae) has been used traditionally as a hemostatic agent and also has skin-care and whitening benefits. The effect of the isolated active compounds of Sophora japonica L. (Fabaceae) that inhibits tyrosinase activity in human epidermal melanocytes (HEMn) was examined.

MATERIALS AND METHODS

We used the mushroom tyrosinase inhibitory assay to isolate active constituents from the extracts. The structures of these constituents were characterized by physical and spectroscopic analyses. Cellular tyrosinase kinetics were analyzed and showed by Lineweaver-Burk plot.

RESULTS

A new compound, N-feruloyl-N'-cis-feruloyl-putrescine (8), together with four flavonoids and three putrescine derivatives were obtained after assay-guided isolation of S. japonica. In HEMn, compound 8 was minimally cytotoxic (cell viability >90% at 100 microM) and the IC(50) value for suppression of cellular tyrosinase activity was estimated as 85.0 microM. Zymography analysis demonstrated the compound's concentration-dependent effects and the kinetic analysis indicated the compound's mixed-inhibitory action.

CONCLUSIONS

We concluded that the new compound 8 is the most potent component of S. japonica yet discovered. Its pigment inhibition activity may be exploitable cosmetically.

Prostaglandin induces the expression of matrix metalloproteinase-1 in ciliary melanocytes

BACKGROUND

Latanoprost, a prostaglandin F2alpha analog, has been shown to be an effective intraocular pressure lowering agent which acts by inducing ciliary muscle cells to synthesise matrix metalloproteinases. However, the response of ciliary melanocytes to latanoprost has never been reported. This research has investigated the ability of latanoprost to induce matrix metalloproteinase-1 expression in human ciliary melanocytes, and thereby advance the understanding of the mechanism of PGF(2alpha) in decreasing intraocular pressure.

METHODS

In vitro human ciliary melanocytes were treated for 48 hours with five different concentrations of latanoprost (100, 150, 200, 500, and 1000 nmol/L). Ciliary melanocytes treated with 0.01% ethanol (vehicle) were used as a control. The expression of matrix metalloproteinase-1 in ciliary melanocytes was determined by Western blotting and immunofluorescent staining.

RESULTS

Western blotting showed that the expression of matrix metalloproteinase-1 in ciliary melanocytes was induced by latanoprost, and the level of expression was dependent on the concentration of latanoprost in the culture medium. Immunofluorescent staining showed that matrix metalloproteinase-1 was confined to the ciliary melanocyte cytoplasm.

CONCLUSIONS

Latanoprost induced the expression of matrix metalloproteinase-1 in human ciliary melanocytes in a dose-dependent manner. Ciliary melanocytes, as well as ciliary muscle cells, may also play an important role in uveoscleral outflow modulation.

Minocycline protects melanocytes against H2O2-induced cell death via JNK and p38 MAPK pathways

Vitiligo is an acquired and progressive disorder manifested by the selective destruction of melanocytes in the skin. An extremely high level of hydrogen peroxide (H2O2) in plasma as well as in lesional skin has been reported in vitiligo patients. High H2O2 level has been suggested to be responsible for the disappearance of melanocytes in vitiligo. JNK and p38 MAPK are strongly induced by oxidative stress and related to neuron loss in neurodegenerative disorders. Minocycline, an antibiotic possessing antioxidant activity, is capable of attenuating oxidative stress-induced neurotoxicity. To investigate whether minocycline rescues melanocytes from H2O2-induced apoptosis, cultured mouse melanocytes (B10BR) were treated with H2O2 in the presence or absence of minocycline. Our data showed that H2O2 decreases cell viability in a concentration-dependent manner which is attenuated by minocycline. Also, H2O2 treatment activates JNK and p38 MAPK, and executive caspase 3 in B10BR cells. Minocycline significantly inhibits H2O2-induced activation of JNK, p38 MAPK and caspase 3. Collectively, we concluded that minocycline protects melanocytes against H2O2-induced apoptosis in vitro. Its protective effect is associated with the inhibition of JNK and p38 MAPK. Our findings suggest that minocycline, a clinically well-tolerated, safe antibiotic, may be used to prevent melanocyte loss in the early stage of vitiligo.

A plaidoyer for cutaneous enzymology: our view of some important unanswered questions on the contributions of selected key enzymes to epidermal homeostasis

This review highlights the importance of enzymology, a field of great neglect in current cutaneous biology research. It was therefore the aim by using selected examples of epidermal enzymes and their action including some open questions to demonstrate the importance of this area. Clearly a thorough understanding of basic knowledge in this field is needed which in turn offers a plethora of innovative research projects for a curious mind. Moreover, in order to gain the closest understanding to the truth instead of generating esoteric results, emphasis is put forward on a holistic view utilizing a combination of modern and sometimes old methods to get the answer. Last but not least the bench work is only useful for the welfare of our patients if we can apply our basic knowledge.

Glycolipid-dependent sorting of melanosomal from lysosomal membrane proteins by lumenal determinants

Melanosomes are lysosome-related organelles that coexist with lysosomes in mammalian pigment cells. Melanosomal and lysosomal membrane proteins share similar sorting signals in their cytoplasmic tail, raising the question how they are segregated. We show that in control melanocytes, the melanosomal enzymes tyrosinase-related protein 1 (Tyrp1) and tyrosinase follow an intracellular Golgi to melanosome pathway, whereas in the absence of glycosphingolipids, they are observed to pass over the cell surface. Unexpectedly, the lysosome-associated membrane protein 1 (LAMP-1) and 2 behaved exactly opposite: they were found to travel through the cell surface in control melanocytes but followed an intracellular pathway in the absence of glycosphingolipids. Chimeric proteins having the cytoplasmic tail of Tyrp1 or tyrosinase were transported like lysosomal proteins, whereas a LAMP-1 construct containing the lumenal domain of Tyrp1 localized to melanosomes. In conclusion, the lumenal domain contains sorting information that guides Tyrp1 and probably tyrosinase to melanosomes by an intracellular route that excludes lysosomal proteins and requires glucosylceramide.

Regulation of melanogenesis--controversies and new concepts

Despite many efforts, regulation of skin and hair pigmentation is still not fully understood. This article focuses mainly on controversial aspects in pigment cell biology which have emerged over the last decade. The central role of tyrosinase as the key enzyme in initiation of melanogenesis has been closely associated with the 6BH4 dependent phenylalanine hydroxylase (PAH) and tyrosine hydroxylase isoform I (THI) providing evidence for an old concept of the three enzyme theory in the initiation of the pigmentation process. In this context, it is noteworthy that intracellular L-phenylalanine uptake and turnover to L-tyrosine via PAH is vital for substrate supply of THI and tyrosinase. While PAH acts in the cytosol of melanocytes, THI and tyrosinase are sitting side by side in the melanosomal membrane. THI at low pH provides L-3,4-hydroxyphenylalanine L-DOPA which in turn is required for activation of met-tyrosinase. After an intramelanosomal pH change, possibly by the p-protein, has taken place, tyrosinase is subject to control by 6/7BH4 and the proopiomelanocortin (POMC) peptides alpha-MSH melanocyte stimulating hormone and beta-MSH in a receptor independent manner. cAMP is required for the activation of microphthalmia-associated transcription factor to induce expression of tyrosinase, for transcription of THI and for activation of PAH. The redundancy of the cAMP signal is discussed. Finally, we propose a novel mechanism involving H2O2 in the regulation of tyrosinase via p53 through transcription of hepatocyte nuclear factor 1alpha which in turn can also affect the POMC response.

Leukocyte tyrosine kinase functions in pigment cell development

A fundamental problem in developmental biology concerns how multipotent precursors choose specific fates. Neural crest cells (NCCs) are multipotent, yet the mechanisms driving specific fate choices remain incompletely understood. Sox10 is required for specification of neural cells and melanocytes from NCCs. Like sox10 mutants, zebrafish shady mutants lack iridophores; we have proposed that sox10 and shady are required for iridophore specification from NCCs. We show using diverse approaches that shady encodes zebrafish leukocyte tyrosine kinase (Ltk). Cell transplantation studies show that Ltk acts cell-autonomously within the iridophore lineage. Consistent with this, ltk is expressed in a subset of NCCs, before becoming restricted to the iridophore lineage. Marker analysis reveals a primary defect in iridophore specification in ltk mutants. We saw no evidence for a fate-shift of neural crest cells into other pigment cell fates and some NCCs were subsequently lost by apoptosis. These features are also characteristic of the neural crest cell phenotype in sox10 mutants, leading us to examine iridophores in sox10 mutants. As expected, sox10 mutants largely lacked iridophore markers at late stages. In addition, sox10 mutants unexpectedly showed more ltk-expressing cells than wild-type siblings. These cells remained in a premigratory position and expressed sox10 but not the earliest neural crest markers and may represent multipotent, but partially-restricted, progenitors. In summary, we have discovered a novel signalling pathway in NCC development and demonstrate fate specification of iridophores as the first identified role for Ltk.

Stem and other multipotent cells generate diverse cell-types, but our understanding of how they make these decisions, which is important for their therapeutic use, is incomplete. Neural crest cells are an important class of multipotent cells and generate multiple stem cell types. We have looked at how pigment cells are made from the neural crest in the zebrafish. The silver shine familiar in so many fish is due to specialised mirror-like pigment cells, called iridophores. We show that these cells are missing in zebrafish shady mutants. We identify the shady gene as encoding a cell signalling receptor, leukocyte tyrosine kinase (Ltk), that has recently been associated with human auto-immune disease. We show that in zebrafish this gene is most likely required to make iridophores from neural crest cells. Thus, we identify a novel pathway required for diversification of these multipotent cells. Our work defines the first role for Ltk in a vertebrate. It provides a mutant resource that will allow us to discover the full breadth of roles for this important gene. Furthermore, the loss of iridophores forms a simple visual screen for inhibition of LTK function and might well have implications in drug discovery.

The secreted metalloprotease ADAMTS20 is required for melanoblast survival

ADAMTS20 (Adisintegrin-like and metalloprotease domain with thrombospondin type-1 motifs) is a member of a family of secreted metalloproteases that can process a variety of extracellular matrix (ECM) components and secreted molecules. Adamts20 mutations in belted (bt) mice cause white spotting of the dorsal and ventral torso, indicative of defective neural crest (NC)-derived melanoblast development. The expression pattern of Adamts20 in dermal mesenchymal cells adjacent to migrating melanoblasts led us to initially propose that Adamts20 regulated melanoblast migration. However, using a Dct-LacZ transgene to track melanoblast development, we determined that melanoblasts were distributed normally in whole mount E12.5 bt/bt embryos, but were specifically reduced in the trunk of E13.5 bt/bt embryos due to a seven-fold higher rate of apoptosis. The melanoblast defect was exacerbated in newborn skin and embryos from bt/bt animals that were also haploinsufficient for Adamts9, a close homolog of Adamts20, indicating that these metalloproteases functionally overlap in melanoblast development. We identified two potential mechanisms by which Adamts20 may regulate melanoblast survival. First, skin explant cultures demonstrated that Adamts20 was required for melanoblasts to respond to soluble Kit ligand (sKitl). In support of this requirement, bt/bt;Kit(tm1Alf)/+ and bt/bt;Kitl(Sl)/+ mice exhibited synergistically increased spotting. Second, ADAMTS20 cleaved the aggregating proteoglycan versican in vitro and was necessary for versican processing in vivo, raising the possibility that versican can participate in melanoblast development. These findings reveal previously unrecognized roles for Adamts proteases in cell survival and in mediating Kit signaling during melanoblast colonization of the skin. Our results have implications not only for understanding mechanisms of NC-derived melanoblast development but also provide insights on novel biological functions of secreted metalloproteases.

Anemonin is a natural bioactive compound that can regulate tyrosinase-related proteins and mRNA in human melanocytes

BACKGROUND

Melanin is the pigment responsible for skin color. Melanin synthesis occurs with the participation of the tyrosinase (TYR) family of proteins including TYR, tyrosinase-related protein 1 (TRP1), and tyrosinase-related protein 2(TRP2/DCT).

OBJECTIVE

The effect of a newly isolated natural compound that inhibits hyperpigmentation on the regulation of the TYR family of proteins was examined.

METHODS

The natural compound, anemonin, was isolated from Clematis crassifolia Benth and was used to inhibit cellular TYR activity; it was found to have a low cytotoxicity (cell viability > 80%) in human melanocytes.

RESULTS

In human melanocytes, anemonin showed both time- and dose-dependent inhibition (IC(50) 43.5 microM) of TYR. Western blot analysis and immunocytochemical staining revealed that expression of TYR, TRP1, and TRP2 was decreased in anemonin-treated melanocytes. Additionally, reverse transcription and quantitative real-time polymerase chain reaction analyses revealed that expression of mRNAs for MITF, TYR, TYRP1, and TYRP2 was also suppressed by anemonin.

CONCLUSION

The natural compound, anemonin, an active compound of C. crassifolia, inhibits pigmentation synthesis in human melanocytes. Anemonin inhibits melanin synthesis by inhibiting the transcription of the genes encoding MITF, TYR, TRP1, and TRP2. This natural compound may be a candidate for cosmetic use.