Cultures Of Human Melanocytes Research Articles

Curcumin Enhances the Anticancer Effects of Binimetinib on Melanoma Cells by Inducing Mitochondrial Dysfunction and Cell Apoptosis with Necroptosis.

Recent studies suggest that MEK1/2 inhibitors, including binimetinib, significantly improve malignant melanoma (MM) patient survival. Growing evidence suggests that phytochemicals, especially curcumin, can overcome drug resistance in cancer cells through a variety of mechanisms. This study aims to examine curcumin's efficacy in vitro combined with binimetinib in human MM cells. We used 2D monolayer and 3D spheroid human epidermal melanocyte culture models, HEMn-MP (human epidermal melanocytes, neonatal, moderately pigmented), and two human MM cell lines, G361 and SK-MEL-2, to evaluate cell viability, proliferation, migration, death, and reactive oxygen species (ROS) production following single therapy treatment, with either curcumin or binimetinib, or a combination of both. Compared to MM cells treated with single therapy, those with combination therapy showed significantly decreased cell viability and increased ROS production. We observed apoptosis following both single and combination therapies. However only those who had had combination therapy had necroptosis. Collectively, our data demonstrates that curcumin exerts significant synergistic anticancer effects on MM cells by inducing ROS and necroptosis when combined with binimetinib. Therefore, a strategy of adding curcumin to conventional anticancer agents holds promise for treating MM.

S-Palmitoylation of Tyrosinase at Cysteine500 Regulates Melanogenesis

Palmitoylation is a lipid modification involving the attachment of palmitic acid to a cysteine residue, thereby affecting protein function. We investigated the effect of palmitoylation of tyrosinase, the rate-limiting enzyme in melanin synthesis, using a human three-dimensional skin model system and melanocyte culture. The palmitoylation inhibitor, 2-bromopalmitate, increased melanin content and tyrosinase protein levels in melanogenic cells by suppressing tyrosinase degradation. The palmitoylation site was Cysteine500 in the C-terminal cytoplasmic tail of tyrosinase. The nonpalmitoylatable mutant, tyrosinase (C500A), was slowly degraded and less ubiquitinated than wild-type tyrosinase. Screening for the Asp-His-His-Cys (DHHC) family of proteins for tyrosinase palmitoylation suggested that DHHC2, 3, 7, and 15 are involved in tyrosinase palmitoylation. Knockdown of DHHC2, 3, or 15 increased tyrosinase protein levels and melanin content. Determination of their subcellular localization in primary melanocytes revealed that DHHC2, 3, and 15 were localized in the endoplasmic reticulum, Golgi apparatus, and/or melanosomes, whereas only DHHC2 was localized in the melanosomes. Immunoprecipitation showed that DHHC2 and DHHC3 predominantly bind to mature and immature tyrosinase, respectively. Taken together, tyrosinase palmitoylation at Cysteine500 by DHHC2, 3, and/or 15, especially DHHC2 in trans-Golgi apparatus and melanosomes and DHHC3 in the endoplasmic reticulum and cis-Golgi apparatus, regulate melanogenesis by modulating tyrosinase protein levels.

Differential Induction of Reactive Oxygen Species and Expression of Antioxidant Enzymes in Human Melanocytes Correlate with Melanin Content: Implications on the Response to Solar UV and Melanoma Susceptibility.

Constitutive pigmentation determines the response to sun exposure and the risk for melanoma, an oxidative stress–driven tumor. Using primary cultures of human melanocytes, we compared the effects of constitutive pigmentation on their antioxidant response to solar UV. The quantitation of eumelanin and pheomelanin showed that the eumelanin content and eumelanin to pheomelanin ratio correlated inversely with the basal levels of reactive oxygen species (ROS). Irradiation with 7 J/cm2 solar UV increased ROS generation without compromising melanocyte viability. Among the antioxidant enzymes tested, the basal levels of heme oxygenase-1 (HO-1) and the glutamate cysteine ligase catalytic subunit and modifier subunit (GCLC and GCLM) correlated directly with the eumelanin and total melanin contents. The levels of HO-1 and GCLM decreased at 6 h but increased at 24 h post–solar UV. Consistent with the GCLC and GCLM levels, the basal glutathione (GSH) content was significantly lower in light than in dark melanocytes. The expression of HMOX1, GCLC, GCLM, and CAT did not correlate with the melanin content and was reduced 3 h after solar UV irradiation, particularly in lightly pigmented melanocytes. Solar UV increased p53 and lipid peroxidation, which correlated inversely with the eumelanin and total melanin contents. These intrinsic differences between light and dark melanocytes should determine their antioxidant response and melanoma risk.

Development of hMC1R Selective Small Agonists for Sunless Tanning and Prevention of Genotoxicity of UV in Melanocytes

Activation of the human melanocortin 1 receptor (hMC1R) expressed on melanocytes by α-melanocortin plays a central role in regulating human pigmentation and reducing the genotoxicity of UV by activating DNA repair and antioxidant defenses. For the development of a hMC1R-targeted photoprotection strategy, we designed tetra- and tripeptide agonists with modifications that provide the necessary lipophilicity and hMC1R selectivity to be effective drugs. These peptides proved to be superior to most of the existing analogs of the physiological tridecapeptide α-melanocortin because of their small size and high hMC1R selectivity. Testing on primary cultures of human melanocytes showed that these peptides are highly potent with prolonged stimulation of melanogenesis, enhanced repair of UV-induced DNA photoproducts, and reduced apoptosis. One of the tripeptides, designated as LK-514 (5), with a molecular weight of 660 Da, has unprecedented (>100,000) hMC1R selectivity when compared with the other melanocortin receptors hMC3R, hMC4R, and hMC5R, and increases pigmentation (sunless tanning) in a cultured, three-dimensional skin model. These new analogs should be efficacious in preventing skin cancer, including melanoma, and treatment of skin disorders, such as vitiligo and polymorphic light eruptions.

Influence of Fucoxanthin on Proliferative Activity of Human Melanocyte Culture.

We studied the effect of algae pigment fucoxanthin on proliferative activity of melanocyte culture from human skin. Fucoxanthin in high concentrations can be cytotoxic, which was confirmed by changes in melanocyte morphology and a decrease in their proliferative activity.

The PI3K pathway induced by αMSH exerts a negative feedback on melanogenesis and contributes to the release of pigment.

The melanocortin-1 receptor (MC1R) belongs to the family of the G protein-coupled receptor (GPCR). Activated GPCRs can promote the phosphoinositide 3-kinase (PI3K) pathway. Few studies deal with the role of the PI3K pathway activation in response to αMSH. On B16-F10 cell line, we investigated the αMSH-dependent modulation of pAKT/AKT, as a key element of the PI3K pathway after rapid and prolonged stimulation. We demonstrated that αMSH triggers a rapid modulation of AKT which culminates in an increase in its phosphorylation. We highlighted a comparable upregulation of pAKT after exposure to αMSH on primary cultures of normal human melanocytes (NHMs) expressing a wild-type MC1R. On B16-F10 cells, NHMs, and an ex vivo model of human skin biopsies, we explored the influence of PI3K/AKT signaling triggered by αMSH, focusing on the control of melanogenesis and pigment release. We showed that the αMSH-dependent PI3K/AKT pathway exerts a negative feedback on melanogenesis and promotes the extracellular release of pigment. We strengthened the role of the PI3K/AKT pathway triggered by αMSH in preserving redox equilibrium and genome integrity, highlighting its role in affecting cell survival.

Melanocyte Activation Mechanisms and Rational Therapeutic Treatments of Solar Lentigos

To characterize the pathobiology of solar lentigos (SLs), analyses by semiquantitative RT-PCR, Western blotting, and immunohistochemistry revealed the upregulated expression of endothelin (EDN)-1/endothelin B receptors (EDNBRs), stem cell factor (SCF)/c-KIT, and tumor necrosis factor (TNF)α in the lesional epidermis, which contrasted with the downregulated expression of interleukin (IL) 1α. These findings strongly support the hypothesis that previous repeated UVB exposure triggers keratinocytes to continuously produce TNFα. TNFα then stimulates the secretion of EDNs and the production of SCF in an autocrine fashion, leading to the continuous melanogenic activation of neighboring melanocytes, which causes SLs. A clinical study of 36 patients with SLs for six months treated with an M. Chamomilla extract with a potent ability to abrogate the EDN1-induced increase in DNA synthesis and melanization of human melanocytes in culture revealed a significant improvement in pigment scores and color differences expressed as L values. Another clinical study using a tyrosinase inhibitor L-ascorbate-2-phosphate 3 Na (ASP) demonstrated that L values of test lotion (6% APS)-treated skin significantly increased in SLs and in non-lesional skin with a significantly higher ΔL value in SLs when compared with non-lesional skin. The sum of these findings strongly suggests that combined topical treatment with EDN signaling blockers and tyrosinase inhibitors is a desirable therapeutic choice for SLs.

Meta-analysis of GWA studies provides new insights on the genetic architecture of skin pigmentation in recently admixed populations

BackgroundAssociation studies in recently admixed populations are extremely useful to identify the genetic architecture of pigmentation, due to their high genotypic and phenotypic variation. However, to date only four Genome-Wide Association Studies (GWAS) have been carried out in these populations.ResultsWe present a GWAS of skin pigmentation in an admixed sample from Cuba (N = 762). Additionally, we conducted a meta-analysis including the Cuban sample, and admixed samples from Cape Verde, Puerto Rico and African-Americans from San Francisco. This meta-analysis is one of the largest efforts so far to characterize the genetic basis of skin pigmentation in admixed populations (N = 2,104). We identified five genome-wide significant regions in the meta-analysis, and explored if the markers observed in these regions are associated with the expression of relevant pigmentary genes in human melanocyte cultures. In three of the regions identified in the meta-analysis (SLC24A5, SLC45A2, and GRM5/TYR), the association seems to be driven by non-synonymous variants (rs1426654, rs16891982, and rs1042602, respectively). The rs16891982 polymorphism is strongly associated with the expression of the SLC45A2 gene. In the GRM5/TYR region, in addition to the rs1042602 non-synonymous SNP located on the TYR gene, variants located in the nearby GRM5 gene have an independent effect on pigmentation, possibly through regulation of gene expression of the TYR gene. We also replicated an association recently described near the MFSD12 gene on chromosome 19 (lead variant rs112332856). Additionally, our analyses support the presence of multiple signals in the OCA2/HERC2/APBA2 region on chromosome 15. A clear causal candidate is the HERC2 intronic variant rs12913832, which has a profound influence on OCA2 expression. This variant has pleiotropic effects on eye, hair, and skin pigmentation. However, conditional and haplotype-based analyses indicate the presence of other variants with independent effects on melanin levels in OCA2 and APBA2. Finally, a follow-up of genome-wide signals identified in a recent GWAS for tanning response indicates that there is a substantial overlap in the genetic factors influencing skin pigmentation and tanning response.ConclusionsOur meta-analysis of skin pigmentation GWAS in recently admixed populations provides new insights about the genetic architecture of this complex trait.

Adipose-Derived Stem Cell Coculturing Stimulates Integrin-Mediated Extracellular Matrix Adhesion of Melanocytes by Upregulating Growth Factors.

Coculture with adipose-derived stem cells (ADSCs) can stimulate proliferation and migration of melanocytes. To enhance outcomes of skin disorders caused by melanocyte loss or death, mixed transplantation with ADSCs has been suggested. However, role of cocultured ADSCs in proliferation and migration of melanocytes remains unclear. This study determined the effect of ADSCs on production of growth factors and expression levels of intergrins in primary culture of adult human melanocytes with or without ADSCs and in nude mice grafted with such melanocytes. Higher amounts of growth factors for melanocytes, such as bFGF and SCF were produced and released from ADSCs by coculturing with melanocytes. Relative levels of integrins β1, α5, and α6 as well as adhesion to fibronectin and laminin were increased in melanocytes cocultured with ADSCs. Such increases were inhibited by neutralization of bFGF or SCF. Relative levels of bFGF, SCF and integrins were increased in nude mice skin after grafting with melanocyte+ADSC cocultures. Collectively, these results indicate that ADSCs can stimulate proliferation and migration of melanocytes by increasing expression of integrins in melanocytes through upregulation of production/release of melanocyte growth factors such as bFGF and SCF.

3D культура меланоцитов как тест-система и клеточная модель для изучения патологии меланогенеза

Функциональная активность меланоцитов обусловливает защитные свойства кожи против воздействия ультрафиолета, вызывающего фотостарение. Однако изучение меланоцитов in vivo затруднено тем, что необходимо использовать животные модели и трудоемкие методы анализа, а культивирование клеток в монослойной культуре in vitro сопряжено с потерей тканеспецифичных маркеров клеток. Данная работа посвящена получению и изучению сфероидов из меланоцитов, так как 3D культивирование меланоцитов в виде сфероидов может сохранить их фенотип и функциональность. Исследование проводили на первичной культуре меланоцитов кожи человека. Клетки культивировали в монослое в полной ростовой среде до 4 пассажа. Далее клетки помещали на агарозные планшеты с микролунками в посевной плотности 3,3 х 10 кл./мл. Анализ полученных сфероидов производили с помощью фотометрии, иммуноцитохимии и ПЦР в реальном времени. Было показано, что, при культивировании в монослое, к 4 пассажу снижалось количество синтезируемого меланина. Тогда как в 3D условиях меланоциты формировали компактные сфероиды, внутри которых в процессе культивирования не только сохранялся синтез, но и накапливался меланин. Была выявлена экспрессия специфических генов TYR и MCR1, и увеличивался синтез белков, участвующих в меланогенезе - gp100 и MITF. Таким образом, в данном исследовании было показано, что меланоциты in vitro способны формировать длительно живущие, жизнеспособные 3D структуры - сфероиды, с сохранением фенотипа и синтеза тканеспецифичных маркеров. Поэтому данные сфероиды могут быть успешно использованы как тест-системы для оценки эффективности препаратов, направленных на регуляцию уровня пигментации кожи. The functional activity of melanocytes determines protective properties of the skin against the effect of ultraviolet radiation, which causes photo-aging. However, studying melanocytes in vivo and in an in vitro monolayer culture is difficult because animal models and laborious analytical methods are required, and the culturing is associated with loss of tissue-specific cell markers. Since 3D cultivation of melanocytes in the form of spheroids can preserve their phenotype and functionality, this work focused on obtaining and studying melanocyte spheroids. The study was conducted using a primary culture of human skin melanocytes. Cells were cultured in a monolayer to the fourth passage. Then these cells were placed in agarose plates with microwells at the cell suspension concentration of 3.3 х 10 in vitro . These features make the melanocyte spheroids a convenient test-system for studying toxicity and efficiency of drugs targeted at regulation of skin pigmentation.

In vitro behavior and UV response of melanocytes derived from carriers of CDKN2A mutations and MC1R variants.

Coinheritance of germline mutation in cyclin-dependent kinase inhibitor 2A (CDKN2A) and loss-of-function (LOF) melanocortin 1 receptor (MC1R) variants is clinically associated with exaggerated risk for melanoma. To understand the combined impact of these mutations, we established and tested primary human melanocyte cultures from different CDKN2A mutation carriers, expressing either wild-type MC1R or MC1RLOF variant(s). These cultures expressed the CDKN2A product p16 (INK4A) and functional MC1R. Except for 32ins24 mutant melanocytes, the remaining cultures showed no detectable aberrations in proliferation or capacity for replicative senescence. Additionally, the latter cultures responded normally to ultraviolet radiation (UV) by cell cycle arrest, JNK, p38, and p53 activation, hydrogen peroxide generation, and repair of DNA photoproducts. We propose that malignant transformation of melanocytes expressing CDKN2A mutation and MC1RLOF allele(s) requires acquisition of somatic mutations facilitated by MC1R genotype or aberrant microenvironment due to CDKN2A mutation in keratinocytes and fibroblasts.

Abstract 491: Understanding the roles of miRNAs in melanoma susceptibility through miQTL study using miRNA transcriptomes from 106 individuals

Abstract microRNAs (miRNA) are important mediators of post-transcriptional gene regulation and play critical roles in tumorigenesis. In melanoma, miRNAs are involved in proliferation, migration, invasion and drug resistance modulating RAS/MAPK and MITF pathways and others. Melanoma arises in melanocytes, and understanding heritable regulation of miRNAs in primary melanocytes could enhance our knowledge of genes and pathways contributing to melanoma risk. While a handful of studies in limited tissue types have identified miRNA transcripts with expression levels that are correlated with common genotypes using an expression quantitative loci approach (miQTL), expression levels of miRNAs are highly tissue-specific, further correlating with tissue-specific mRNA expression. Given the lack of cell-type specific miQTL data, we established a miQTL dataset using primary cultures of human melanocytes from 106 newborn males mainly of European decent. To assess comprehensive miRNA transcript levels from these samples, we performed RNA sequencing of the small RNA population (single-end, stranded, 51bp). An average of 63M reads per sample were obtained, and subsequently processed following miRMaster pipeline (ccb-compute.cs.uni-saarland.de/mirmaster) to detect known and novel miRNAs. A total of 961 known and 1262 novel miRNA transcripts were expressed above the background noise (> 0.05 Read Per Million and >5 reads per transcript in >=10 samples). Genotypes of 106 individuals were also assessed by direct genotyping using Illumina OmniExpress arrays followed by imputation using Michigan Imputation Server to produce a total of 10,687,550 genotypes. Subsequent QTL analyses using FastQTL (fastqtl.sourceforge.net) and QTLtools (qtltools.github.io/qtltools) identified 33 known and 34 novel miRNA transcripts as cis-miQTLs (q-value < 0.05) and 2 known and 6 novel miRNAs as trans-miQTLs (FDR < 0.1), respectively. We also observed a subset of significant cis-miQTLs overlapping with marginally significant mRNA trans-eQTLs from the same RNA samples, suggesting miRNA-mediated trans regulation. Further identification of melanocyte-specific miQTLs and their target genes will provide better understanding of melanocyte-specific miRNA regulation network. To identify candidate melanoma susceptibility genes functioning through heritable miRNA expression, melanocyte miQTLs will also be overlaid with melanoma genome-wide association data. In addition to the results from these analyses, further analyses of differentially expressed miRNAs and target genes between our primary melanocytes and melanoma tumors (available through The Cancer Genome Atlas) will shed light on the altered gene networks in melanomagenesis that might have therapeutic relevance through miRNA-mediated intervention. Citation Format: Jiyeon Choi, Tongwu Zhang, Michael Kovacs, Mai Xu, Andrew Vu, NISC Comparative Sequencing Program, Stacie Loftus, William Pavan, Kevin Brown. Understanding the roles of miRNAs in melanoma susceptibility through miQTL study using miRNA transcriptomes from 106 individuals [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 491.

TNFSF14 inhibits melanogenesis via NF-kB signaling in melanocytes

Melanin synthesis in melanocytes is affected by various cytokines. Here, we reported for the first time that tumor necrosis factor superfamily member 14 (TNFSF14) inhibits melanogenesis in the primary culture of human epidermal melanocytes. TNFSF14 is known to bind to its receptors herpes virus entry mediator (HVEM) and lymphotoxin β receptor (LTβR) for signal transduction, but TNFSF14-induced hypopigmentation was independent of HVEM and LTβR in melanocytes. To explore signaling in melanocytes treated with TNFSF14, we performed RNA-seq and found that nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) signaling is activated by TNFSF14. Further, we observed that inhibition of NF-kB effectively blocks the hypopigmentation induced by TNFSF14. We conclude that TNFSF14 inhibits melanogenesis in melanocytes via NF-κB signaling and could be applied in the treatment of cutaneous pigment disorders.

The \u03b1-melanocyte stimulating hormone/peroxisome proliferator activated receptor-\u03b3 pathway down-regulates proliferation in melanoma cell lines

BackgroundThe α-Melanocyte Stimulating Hormone (αMSH)/Melanocortin-1 receptor (MC1R) interaction promotes melanogenesis through the cAMP/PKA pathway. The direct induction of this pathway by Forskolin (FSK) is also known to enhance melanocyte proliferation. αMSH acts as a mitogenic agent in melanocytes and its effect on proliferation of melanoma cells is less known. We previously identified the αMSH/Peroxisome Proliferator Activated Receptor (PPARγ) pathway as a new pathway on the B16-F10 mouse melanoma cell line. αMSH induced the translocation of PPARγ into the nucleus as an active transcription factor. This effect was independent of the cAMP/PKA pathway and was mediated by the activation of the PI(4,5)P2/PLC pathway, a pathway which we have described to be triggered by the αMSH-dependent MC1R stimulation. Moreover, in the same study, preliminary experiments showed that mouse melanoma cells responded to αMSH by reducing proliferation and that PPARγ was involved in this effect. Due to its key role in the control of cell proliferation, PPARγ agonists are used in therapeutic models for different forms of cancer, including melanoma. The purpose of this study was: (a) to confirm the different proliferative behavior in response to αMSH in healthy and in melanoma condition; (b) to verify whether the cAMP/PKA pathway and the PLC/PPARγ pathway could exert an antagonistic function in the control of proliferation; (c) to deepen the knowledge of the molecular basis responsible for the down-proliferative response of melanoma cells after exposure to αMSH.MethodsWe employed B16-F10 cell line, a human melanoma cell line (Mel 13) and two primary cultures of human melanocytes (NHM 1 and NHM 2, respectively), all expressing a wild type MC1R and responding to the αMSH in terms of pigmentation. We evaluated cell proliferation through: a) cell counting, b) cell cycle analysis c) protein expression of proliferation modulators (p27, p21, cyclin D1 and cyclin E).ResultsThe αMSH acted as a mitogenic agent in primary cultures of human melanocytes, whereas it determined a slow down of proliferation in melanoma cell lines. FSK, as an inducer of the cAMP/PKA pathway, reproduced the αMSH mediated effect on proliferation in NHMs but it did not mimic the αMSH effect on proliferation in B16-F10 and Mel 13 melanoma cell lines. Meanwhile, 3 M3-FBS (3 M3), as an inducer of PI(4,5)P2/PLC pathway, reproduced the αMSH proliferative effect. Further experiments, treating melanoma cell lines with αMSH in the presence/absence of GW9662, as an inhibitor of PPARγ, confirmed the key role of this transcription factor in decreasing cell proliferation in response to the hormone exposure.ConclusionsIn both melanoma cell lines, αMSH determined the reduction of proliferation through the PI(4,5)P2/PLC pathway, employing PPARγ as an effector element. These evidence could offer perspectives for new therapeutic approaches for melanoma.

608 Targeting the MC1R by selective tetra- and tripeptide analogs of α-Melanocortin for melanoma prevention

Our goal is to develop a topical formulation of small peptide analogs of α-Melanocortin (α-melanocyte stimulating hormone; α-MSH) that are highly selective for the melanocortin 1 receptor (MC1R) for prevention of photodamage in human melanocytes (HM) and ultimately melanoma. The MC1R is a melanoma susceptibility gene, and its loss-of-function variants result in red hair phenotype, reduced tanning and DNA repair capacity, and increased melanoma risk. Activation of the MC1R by its physiological agonist α-MSH stimulates eumelanin synthesis and proliferation, enhances the repair of UV-induced DNA damage and inhibits apoptosis of HM. We have designed short peptide analogs of the physiological tridecapeptide α-MSH exhibiting full MC1R agonism and excellent MC1R selectivity. Modifications of the His-D-Phe-Arg-Trp, or His-D-Phe-Arg sequence of α-MSH combined with terminal modifications resulted in stable small molecules with logD favorable for skin penetration. The tetrapeptides LK 184 and LK 467, and the tripeptide LK 514 were tested on primary cultures of HM and cultured skin substitutes (CSS). Dose-response experiments revealed that LK 184 and LK 467 were 100 fold more potent, while LK 514 was slightly less (≤10 fold) potent than α-MSH in stimulating cAMP formation and the activity of tyrosinase, the rate-limiting enzyme for melanin synthesis, in HM. The three peptides enhanced the repair of UV-induced DNA damage in HM. Treatment of CSS with LK 184 and LK 467 at 100 nM, or LK 514 at -5 μM for 10-15 days significantly increased pigmentation in the absence of UV exposure, and increased repair of UV-induced DNA photoproducts in melanocytes and the epidermis in the CSS or intact human skin. Prolonged treatment with these peptides had no effect on melanocyte number or histology of CSS. Given that increased pigmentation and DNA repair protect against photocarcinogenesis, we are continuing with preclinical testing of these peptides to determine their safety and efficacy as topical agents for sunless tanning and prevention of photodamage and melanoma.

A Comparison Between Phorbol 12 Myristate 13 Acetate and Phorbol 12, 13 Dibutyrate in Human Melanocyte Culture.

Melanocyte culture is an integral part of the studies of skin biology and cosmetic applications. After the introduction of selective medium for the culture of human melanocyte using Phorbol 12-myristate13-acetate (PMA) in 1982, a lot of methods of culturing were tried but till date PMA is a preferred mitogen because of its cost effectiveness compared to growth factors. We have tried to preliminarily evaluate the efficacy of another phorbol ester, Phorbol 12, 13-dibutyrate (PDBu) in melanocyte culture because of its less hydrophobic nature compared to PMA. This property minimizes the trace amount of mitogen in cell culture after washing off and hence does not interfere in other biological assays. To evaluate the differences in the melanocyte survival rate, morphology and mitotic index when grown in media supplemented with PMA and PDBu. Foreskins were collected from children undergoing circumcision. Epidermal cells were isolated from foreskin and cultured using PMA and PDBu. Melanocytes in culture were monitored for the better establishment and documented. In proliferative assay, melanocytes were treated with PMA and PDBu for 24, 48 and 72 hours and proliferation was measured using 3-(4,5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay method. When cultured, melanocytes acquired proliferative status and bipolar morphology quicker in PDBu medium than in PMA medium. Keratinocytes survived as contamination in PMA medium whereas PDBu medium had minimal keratinocytes. MTT assay showed that PDBu has higher proliferative induction capacity than PMA. In even lower concentration of PDBu in medium, melanocytes survived till 72 hours without significant cell loss in compared to PMA medium. PDBu can be a valuable replacement for PMA in human melanocyte culture. Higher proliferation induction, unfavourable to keratinocyte survival and less hydrophobicity make PDBu a promising alternative for quicker establishment of pure human melanocyte cultures especially in cosmetic in vitro experimental dermatology.

Modulation of Melanogenesis by Heme Oxygenase-1 via p53 in Normal Human Melanocytes.

As a key regulator of melanogenesis, p53 controls microphthalmia-associated transcription factor (MITF) and tyrosinase expression. The anti-oxidant enzyme heme oxygenase-1 (HO-1) is induced by various forms of cellular stress and diverse oxidative stimuli. However, few studies have examined the role of HO-1 in melanogenesis. Therefore, the aim of this study was to determine the role of HO-1 in melanogenesis and the mechanism underlying this relationship. Cultures of normal human melanocytes were treated with the HO-1 inducer cobalt protoporphyrin (CoPP) or the HO-1 inhibitor zinc protoporphyrin (ZnPP). We then measured the melanin content of the cells. Additional analyses consisted of Western blotting and RT-PCR. The results showed that the cellular melanin content was increased by CoPP and decreased by ZnPP. The Western blot and RT-PCR analyses showed that CoPP increased p53, MITF and tyrosinase levels, and ZnPP reduced all of them. The knockdown of p53 by siRNA transfection was followed by large decreases in the expression levels of p53, MITF and tyrosinase at 3 h of transfection. The presence of CoPP or ZnPP had no significant increased or decreased effects on MITF and tyrosinase levels from 15 h in the siRNA transfectants. Our results suggest that HO-1 modulates melanogenesis in human melanocytes via a p53-dependent pathway.

Hesperetin induces melanin production in adult human epidermal melanocytes

One of the major sources of flavonoids for humans are citrus fruits, hesperidin being the predominant flavonoid. Hesperetin (HSP), the aglycon of hesperidin, has been reported to provide health benefits such as antioxidant, anti-inflammatory and anticarcinogenic effects. However, the effect of HSP on skin pigmentation is not clear. Some authors have found that HSP induces melanogenesis in murine B16-F10 melanoma cells, which, if extrapolated to in vivo conditions, might protect skin against photodamage. Since the effect of HSP on normal melanocytes could be different to that observed on melanoma cells, the described effect of HSP on murine melanoma cells has been compared to the effect obtained using normal human melanocytes. HSP concentrations of 25 and 50 µM induced melanin synthesis and tyrosinase activity in human melanocytes in a concentration-dependent manner. Compared to control melanocytes, 25 µM HSP increased melanin production and tyrosinase activity 1.4-fold (p < 0.01) and 1.1-fold (p < 0.01), respectively, and the corresponding increases in the case of 50 µM HSP were 1.9-fold (p < 0.001) and 1.3-fold (p < 0.001). Therefore, HSP could be considered a valuable photoprotective substance if its capacity to increase melanin production in human melanocyte cultures could be reproduced on human skin.

RhCSF3 accelerates the proliferation of human melanocytes in culture through binding CSF3R and the expression of CSF3R transcripts.

Melanogenic paracrine and autocrine cytokine networks have recently been discovered in vitro between melanocytes and other types of skin cells. Granulocyte colony-stimulating factor receptor (CSF3R) controls the survival, proliferation and differentiation of many kinds of cells, including neutrophils. To understand the function of CSF3R and recombinant human granulocyte colony-stimulating factor (rhCSF3) on melanocyte proliferation, this study compared the expression of CSF3R and the effects of rhCSF3 in primary human melanocytes, neutrophils and HEL 92.1.7 cells. The results show that CSF3R is localized in the cytoplasm and on cell membranes of melanocytes and neutrophils. The percentage of CSF3R(+) melanocytes was higher than CSF3R(+) HEL 92.1.7 cells, but was lower than CSF3R(+) neutrophils. Both CSF3R mRNA and CSF3R protein levels in melanocytes were higher than in HEL 92.1.7 cells, but were lower than in neutrophils. Treatment with rhCSF3 increased the proliferation of human melanocytes, but not their tyrosinase activity. Transcripts of CSF3R in human melanocytes, M14, A375 melanoma and A431 squamous cell carcinoma cells were also detected. Expression of the CSF3R V3 transcript was lower in melanocytes than in M14, A375 melanoma and A431 squamous cell carcinoma cells. In conclusion, rhCSF3 can promote melanocyte proliferation through CSF3R without affecting tyrosinase activity.

Cell fate regulated by nuclear factor-κB- and activator protein-1-dependent signalling in human melanocytes exposed to ultraviolet A and ultraviolet B.

SummaryBackgroundUltraviolet (UV) radiation constitutes an important risk factor for malignant melanoma, but the wavelength responsible for the initiation of this disease is not fully elucidated. Solar UV induces multiple signalling pathways that are critical for initiation of apoptotic cell death as a cellular defence against malignant transformation.ObjectivesTo evaluate the involvement of the transcription factors nuclear factor (NF)-κB and activator protein (AP)-1 in the signalling pathways induced by UVA or UVB irradiation in human melanocytes.MethodsPrimary cultures of normal human melanocytes were irradiated with UVA or UVB, and the concomitant DNA damage and redox alterations were monitored. The resulting activation of the NF-κB and AP-1 signalling pathways and subsequent apoptosis were studied.ResultsUVB irradiation causes DNA damage detected as formation of cyclobutane pyrimidine dimers, while UVA induces increased levels of 8-hydroxydeoxyguanosine and lipid peroxidation. UVA and UVB initiate phosphorylation of c-Jun N-terminal protein kinase and extracellular signal-regulated kinase, and the apoptosis signalling pathways converge into a common mechanism. Downregulation of c-Jun suppresses AP-1-mediated signalling and prevents apoptosis upstream of lysosomal and mitochondrial membrane permeabilization, whereas inhibition of NF-κB by SN50 increases apoptosis.ConclusionsWe conclude that AP-1 induces proapoptotic signalling, whereas NF-κB is a key antiapoptotic/prosurvival factor in both UVA- and UVB-induced cellular damage in human melanocytes, which might in turn impact melanoma development and progression.What's already known about this topic? Melanocytes are the target cells of ultraviolet (UV) irradiation, and the cells from which melanoma originates. The mitogen-activated protein kinase signalling pathway is important for regulation of UV-induced cellular responses. Previous studies have strongly implicated the transcription factors activator protein (AP)-1 and nuclear factor (NF)-κB as mediators of the UV response in other cell types. What does this study add? The present study identifies NF-κB as an antiapoptotic/prosurvival factor and shows that AP-1 stimulates proapoptotic signalling during both UVA- and UVB-induced apoptosis in human melanocytes. An improved understanding of cellular responses in UV-exposed melanocytes is essential to understanding and preventing the formation of melanoma, and might provide an opportunity to identify apoptotic regulators.