Human Epidermal Melanocytes Research Articles

P‐coumaric acid not only inhibits human tyrosinase activity in vitro but also melanogenesis in cells exposed to UVB

Tyrosinase (TYR) catalyzes rate-limiting steps of melanogenesis and thus its inhibitors are potentially useful as hypopigmenting agents. Recently, p-coumaric acid (p-CA) has been suggested to interfere with the pro-melanogenic actions of tyrosine due to its structural similarity with tyrosine (An SM et al., Br J Dermatol 2008. 159: 292). In this study, we compared the inhibitory effects of p-CA and two other well known TYR inhibitors used in cosmetics--arbutin and kojic acid--on the catalytic activities of mushroom, murine and human TYRs in vitro, using tyrosine and 3,4-dihydroxyphenylalanine (DOPA) as substrates. The results showed that p-CA is a weaker inhibitor of mushroom TYR but much stronger inhibitor of human or murine TYR in comparison with kojic acid and arbutin. In addition, p-CA inhibited human TYR at much lower concentrations than those required for the inhibition of murine or mushroom TYRs. Enzyme kinetics analysis indicated that p-CA is a mixed type (for tyrosine) or competitive inhibitor (for DOPA) of human TYR. Potent antimelanogenic effects of p-CA were observed in human epidermal melanocytes exposed to UVB. The present study demonstrated that p-CA is a potent and selective inhibitor of human TYR and is potentially useful as a hypopigmenting agent.

Mechanisms of melanogenesis inhibition by propafenone

Melanogenesis is a physiological process that results in the synthesis of melanin pigments, which play a crucial protective role against skin photocarcinogenesis. The present study was conducted to determine the inhibitory effects of propafenone on melanogenesis and to elucidate the molecular events involved in the inhibition of melanogenesis by propafenone. To accomplish this, several experiments were conducted using human epidermal melanocyte cells. The melanin content and cAMP production were evaluated, and western blots for proteins involved in melanogenesis were conducted. The melanin content was significantly inhibited by propafenone in a concentration-dependent manner. To clarify the mechanism of the depigmenting property of propafenone, we examined the involvement of propafenone in cAMP signaling. In the cAMP production assay, the intracellular cAMP level was reduced by propafenone. The level of microphthalmia-associated transcription factor (MITF) protein, the upstream transcription factor of tyrosinase, was also reduced by propafenone. In addition, propafenone inhibited the expression of tyrosinase, TRP-1, and TRP-2. Taken together, the results of our study show that propafenone inhibits melanogenesis by suppressing cAMP production, which is involved in the expression of melanogenesis-related proteins and suggests that propafenone may be an effective inhibitor of hyperpigmentation.

(−)-N-Formylanonaine from Michelia alba as a human tyrosinase inhibitor and antioxidant

Tyrosinase is the first and rate limiting enzyme in the synthesis of melanin pigments for coloring hair, skin, and eyes. As reported in this study, a natural product, (−)-N-formylanonaine isolated from the leaves of Michelia alba D.C. (Magnolianceae), was found to inhibit mushroom tyrosinase with an IC50 of 74.3μM and to have tyrosinase and melanin reducing activities in human epidermal melanocytes without apparent cytotoxicity to human cells, superior to the known tyrosinase inhibitors, such as kojic acid and 1-phenyl-2-thiourea (PTU). Based on homology modeling, the compound binds the active site by coordinating with two Cu2+ ions. In addition, the compound had antioxidation activities in tests for scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH), reducing power, and chelating metal ions. To our knowledge, this is the first study to reveal the bioactivities of (−)-N-formylanonaine from this plant species.

β‐Catenin regulates melanocyte dendricity through the modulation of PKCζ and PKCδ

SummaryThe Wnt/β‐catenin signaling pathway is involved in the melanocyte differentiation and melanoma development. However, the effect of β‐catenin for dendrite formation has not been clearly elucidated yet in normal human epidermal melanocytes (NHEM). To investigate the effect of β‐catenin, we transduced NHEM with recombinant adenovirus expressing β‐catenin. Forced expression of β‐catenin led to the dramatic morphological changes of NHEM, including the reduction of dendrite length and enlargement of cell body. Concomitantly with, the protein levels for dendrite formation‐related molecules, such as Rac1 and Cdc42, were markedly decreased. In addition, phosphorylation of p38 MAPK was significantly reduced by β‐catenin, potentiating its inhibitory role for dendrite formation. Interestingly, overexpression of β‐catenin led to the increase of protein kinase C ζ (PKCζ) level, while protein kinase C δ (PKCδ) was decreased by β‐catenin, suggesting that those PKCs were β‐catenin‐downstream modulators in NHMC. When PKCζ was overexpressed, dendrites were shortened, with the reduced protein levels for Rac1 and Cdc42. In contrast, PKCδ overexpression led to the elongation of dendrites, with the increased levels for Rac1 and Cdc42. These results suggest that β‐catenin play an inhibitory role for dendrite formation through the modulation of PKCζ and PKCδ.

Prostaglandin-E2 is produced by adult human epidermal melanocytes in response to UVB in a melanogenesis-independent manner.

Excessive ultraviolet radiation (UVR) exposure induces erythema, mediated in part by prostaglandin-E2 (PGE2). While keratinocytes are a major PGE2 source, epidermal melanocytes (EM) also express PGE2-production machinery. It is unclear whether EM-produced PGE2 contributes to UVR-induced skin inflammation, and whether this is correlated with melanogenesis. Epidermal melanocytes were cultured from skin phototype-1 and -4 donors, followed by assessment of PGE2 production and melanogenesis. Epidermal melanocytes expressed cytoplasmic phospholipase-A2, cyclooxygenase-1, cytoplasmic prostaglandin-E synthase and microsomal prostaglandin-E synthase-1, -2. Epidermal melanocytes produced PGE2 under basal conditions, which increased further after arachidonic acid stimulation. Epidermal melanocytes expressed cyclooxygenase-2 (COX-2) mRNA and a selective COX-2 inhibitor (NS-398) reduced PGE2 production. Ultraviolet B-induced PGE2 production was positively correlated with skin phototype-1, despite variability between individual EM donors. By contrast, there was no correlation between PGE2 production by EM and their melanogenic status. Thus, EM may contribute to UVR-induced erythema, with role of donor skin phototype more important than their melanogenic status.

IGFBP7 Is Not Required for B-RAF-Induced Melanocyte Senescence

Induction of senescence permanently restricts cellular proliferation after oncogenic stimulation thereby acting as a potent barrier to tumor development. The relevant effector proteins may therefore be fundamental to cancer development. A recent study identified IGFBP7 as a secreted factor mediating melanocyte senescence induced by oncogenic B-RAF, which is found commonly in cutaneous nevi. In contrast to the previous report, we demonstrate that B-RAF signaling does not induce IGFBP7 expression, nor the expression of the IGFBP7 targets, BNIP3L, SMARCB1, or PEA15, in human melanocytes or fibroblasts. We also found no correlation between B-RAF mutational status and IGFBP7 protein expression levels in 22 melanoma cell lines, 90 melanomas, and 46 benign nevi. Furthermore, using a lentiviral silencing strategy we show that B-RAF induces senescence in melanocytes and fibroblasts, irrespective of the presence of IGFBP7. Therefore, we conclude that the secreted protein IGFBP7 is dispensable for B-RAF(V600E)-induced senescence in human melanocytes.

Inhibition of melanogenesis by the extract from Agaricus blazei without affecting iNOS gene expression

Tyrosinase is a key enzyme in melanin synthesis. Owing to enlargement of availability of edible types of mushrooms in food medicines, we investigated effects of Agaricus blazei (ABE) on tyrosinase activity using l-tyrosine and l-3, 4-dihydroxyphenylalanine (l-DOPA) as the substrate in normal human epidermal melanocytes (NHEM). ABE inhibited tyrosinase activity similar to arbutin and Vitamin C as two whitening agents in a dose dependent manner. In agreement with this, treatment of the cells with ABE (3–100 μg/ml) reduced melanin content up to 57% of the control in NHEM. In addition, production of nitric oxide (NO) which has the ability of inducing tyrosinase activity in melanocytes was also suppressed by ABE treatment. Furthermore, ABE inhibited NO production in lipopolysaccharides (LPS)-stimulated RAW264.7 macrophages, in a dose dependent manner but without affecting iNOS mRNA expression indicated by reverse transcription-PCR (RT-PCR) technique. These findings suggest that ABE inhibits melanin production via partial inhibition of tyrosinase activity and NO production. This hypopigmenting effect of water soluble Agaricus blazei extract could be useful for the treatment of some skin disorders.

Lipocalin-type prostaglandin D synthase as a regulator of the retinoic acid signalling in melanocytes

Lipocalin-type prostaglandin D synthase (L-PGDS) catalyses the formation of prostaglandin D(2) (PGD(2)) and also functions as a transporter for lipophilic ligands, including all-trans retinoic acid (RA). Here, we show that human epidermal melanocytes produce and secrete L-PGDS and PGD(2) in culture medium, whereas L-PGDS is not expressed in human melanoma cell lines, HMV-II, SK-MEL-28, 624 mel and G361. Treatment with RA (1 or 10 microM) for 4 days decreased the proliferation of melanocytes (30% decrease), but not melanoma cells. We therefore isolated L-PGDS-expressing cell lines from 624 mel cells. Treatment with RA decreased the proliferation of L-PGDS-expressing cells by 20%, but not mock-transfected cell lines lacking L-PGDS expression. RA induced expression of a cyclin-dependent kinase inhibitor p21(Cip1) in L-PGDS-expressing cells, but not mock-transfected cells. Moreover, RA increased the transient expression of a reporter gene carrying the RA-responsive elements in L-PGDS-expressing cell lines (at least 5-fold activation), compared to the 2-fold activation in mock-transfected cell lines, suggesting that L-PGDS may increase the sensitivity to RA. Lastly, the knockdown of L-PGDS expression by RNA interference was associated with the restoration of the RA-mediated decrease in proliferation of human and mouse melanocytes. In conclusion, L-PGDS may fine-tune the RA signalling in melanocytes.

Abstract 1891: Tanshinone IIA is a novel agent for melanoma prevention and therapy

Abstract Background: Tanshinone IIA (TIIA) is a non-toxic natural compound isolated from traditional Chinese herb, Salvia Miltiorrhiza that has been used for prevention and therapy of a wide array of diseases such as vascular diseases and cancers in other countries. It has been documented outside the United States that TIIA has the biological functions of being pro-differentiation, anti-oxidant, anti-inflammation, anti-carcinogenesis and anti-tumor. However, TIIA has not been studied for melanoma prevention and therapy up to date. Methods: Purified standard substance of TIIA has been use for this pilot study. Human adult epidermal melanocyte HEMa-LP and primary human melanoma cell MEL526 were used. Western blot, flow cytometry, ELISA and immunofluorescence techniques were employed to probe the biomarkers interested pre and post treatment of TIIA. Results: TIIA inhibited MEL526 proliferation and induced MEL526 apoptosis at 20 µM that is below far away from TIIA plasma therapeutic concentrations in vivo. TIIA inhibited MEL526 cell motility at concentrations of 2.5µM or 5µM. TIIA (1.25 µM, 2.5 µM and 5 µM) prevented melanocyte epigenetic transdifferentiation to malignant melanoma cell induced by MEL526 conditioned cell culture medium, while TIIA is not toxic to normal melanocytes at those concentrations. TIIA induced transformed-HEMa-LP cell apoptosis at the above concentrations addressed. TIIA consistently down-regulated, at various ratios of drug concentration/cell density, the expression of melanoma stem cell biomarker CD133, and the expression of chondroitin sulfate proteoglycan 4 that is associated positively with melanocytic malignant transformation/progression and melanoma stem cell biomarker expression. STAT5-mediated up-regulation of Foxp3 has been documented in regulatory T cell differentiation and function, but not in melanocyte; and the higher expression level of STAT5a predicts the lower degree of atypia of nevi. In this study it was fund that TIIA increased the expression of STAT5a in MEL526 while the expression of Foxp3, a cancer suppressor gene, was up-regulated. TIIA inhibited the activation EFGR, which activation promotes carcinogenesis and progression of skin cancers. It was not found that TIIA regulated other biomarkers tested such as HLA Class I and B7H1 antigens. In addition, it was found that TIIA promoted human PBMC to produce IFNγ. Conclusion: TIIA is a potential novel agent used for melanoma prevention and therapy. However, further studies of TIIA are needed to prove the biological function and mechanisms in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1891.

Potent anti-tumor effects of a dual specific oncolytic adenovirus expressing apoptin in vitro and in vivo

BackgroundOncolytic virotherapy is an attractive drug platform of cancer gene therapy, but efficacy and specificity are important prerequisites for success of such strategies. Previous studies determined that Apoptin is a p53 independent, bcl-2 insensitive apoptotic protein with the ability to specifically induce apoptosis in tumor cells. Here, we generated a conditional replication-competent adenovirus (CRCA), designated Ad-hTERT-E1a-Apoptin, and investigated the effectiveness of the CRCA a gene therapy agent for further clinical trials.ResultsThe observation that infection with Ad-hTERT-E1a-Apoptin significantly inhibited growth of the melanoma cells, protecting normal human epidermal melanocytes from growth inhibition confirmed cancer cell selective adenoviral replication, growth inhibition, and apoptosis induction of this therapeutic approach. The in vivo assays performed by using C57BL/6 mice containing established primary or metastatic tumors expanded the in vitro studies. When treated with Ad-hTERT-E1a-Apoptin, the subcutaneous primary tumor volume reduction was not only observed in intratumoral injection group but in systemic delivery mice. In the lung metastasis model, Ad-hTERT-E1a-Apoptin effectively suppressed pulmonary metastatic lesions. Furthermore, treatment of primary and metastatic models with Ad-hTERT-E1a-Apoptin increased mice survival.ConclusionsThese data further reinforce the previously research showing that an adenovirus expressing Apoptin is more effective and advocate the potential applications of Ad-hTERT-E1a-Apoptin in the treatment of neoplastic diseases in future clinical trials.

Comparison of Antioxydant Defenses in Human Epidermal Melanocytes and Keratinocytes Suggests that Pigment Cells are Adapted to Oxidative Stress Induced by Melanin Related Compounds

Comparison of Antioxydant Defenses in Human Epidermal Melanocytes and Keratinocytes Suggests that Pigment Cells are Adapted to Oxidative Stress Induced by Melanin Related Compounds

A new steroidal 5,7-diene derivative, 3β-hydroxyandrosta-5,7-diene-17β-carboxylic acid, shows potent anti-proliferative activity

The new steroidal 5,7-diene, 3β-hydroxyandrosta-5,7-diene-17β-carboxylic acid (17-COOH-7DA), was synthesized from 21-acetoxypregnenolone, with the oxidative cleavage of the side chain being dependent on the presence of oxygen. In human epidermal (HaCaT) keratinocytes, 17-COOH-7DA inhibited proliferation in a dose-dependent manner, starting at a dose as low as 10 −11 M. This inhibition was accompanied by decreased expression of epidermal growth factor receptor, bcl2 and cyclin E2 mRNAs and by increased expression of involucrin mRNA. Inhibition of proliferation was associated with slowing of the cell cycle in G1/G0 phases but not with cell death. 17-COOH-7DA was significantly more potent than pregnenolone, 17-COOH-pregnenolone, 17-COOCH 3-7DA and calcitriol. 17-COOH-7DA also inhibited proliferation of normal human epidermal melanocytes and human and hamster melanoma lines, however, with lower potency than for keratinocytes. In normal human dermal fibroblasts 17-COOH-7DA stimulated proliferation in serum-free media but inhibited it in the presence of 5% serum. 17-COOH-7DA inhibited cell colony formation of human and hamster melanoma cells, and induced monocyte-like differentiation of human HL60 leukemia cells. Thus, the new steroidal 5,7-diene, 17-COOH-7DA, can serve as an inhibitor of proliferation of normal keratinocytes and normal and malignant melanocytes, as a condition-dependent regulator of fibroblast proliferation and a stimulator of leukemia cell differentiation.

Date Seed Oil Inhibits Hydrogen Peroxide-Induced Oxidative Stress in Normal Human Epidermal Melanocytes

The administration of antioxidants has been shown to enhance repair and healing processes in cutaneous tissue. Date seed oil (DSO) extract, which might be a potential source of natural antioxidants such as phenols and tocopherols, has been reported to be beneficial in the reduction of chemically induced oxidative stress in normal human skin. In this study, we investigated the protective effects of DSO against hydrogen peroxide (H(2)O(2))-induced oxidative stress in terms of lipid peroxidation, depletion of such endogenous antioxidant defense enzymes as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) using normal human epidermal melanocytes (NHEM). The results showed that DSO, endowed with a radical scavenging ability, decreased oxidative injury by inhibition of damage caused by H(2)O(2). Treatment of NHEM with DSO inhibited H(2)O(2)-induced lipid peroxidation. In addition, the extract inhibited H(2)O(2)-induced depletion of antioxidant defense components, such as SOD, CAT, and GPx. Our findings demonstrate that DSO is an efficient extract able to prevent melanocytes oxidative damage induced by H(2)O(2) exposure. Thus it may be a potential promising candidate, as a chemopreventive agent, in the development of melanocyte-related pathologies like vitiligo and melanoma.

Cultured human melanocytes express functional Toll-like receptors 2–4, 7 and 9

Toll-like receptors (TLRs) recognize pathogen-associated molecular patterns (PAMPs), which have been evolutionarily conserved in microbes. Human melanocytes are not simply pigment-producing cells but also have the phagocytic capacity and can produce pro-inflammatory mediators. However, the mechanisms of recognition of microbes by melanocytes have not yet been fully established. We investigated the TLRs 1-10 expression profile in human epidermal melanocytes and assessed their functions after triggering by their specific ligands. TLRs mRNA expression was determined by RT-PCR, and the TLR protein expression was measured by flow cytometry and immunofluorescence assays. After stimulation with various TLR ligands, the production of inflammatory cytokine IL-8 and IL-6 was measured by ELISA and the mRNA for chemokine CCL2, CCL3 and CCL5 was analyzed by real-time PCR. Phosphorylation of IkappaBalpha in TLR ligands-triggered melanocytes was determined by Western blot and the nucleus translocation of NF-kappaBp65 was analyzed by immunofluorescence. Human melanocytes constitutively expressed TLRs 1-4, 6, 7 and 9 mRNA. Ample amounts of TLRs 2-4, 7 and 9 were confirmed at protein level. Stimulation of melanocytes with TLRs ligands resulted in the release of cytokines (IL-8 and IL-6) and the mRNA accumulation of chemokines (CCL2, CCL3 and CCL5). Triggering of TLRs in melanocytes resulted in the up-regulation of phosphorylated IkappaBalpha and in the nucleus translocation of NF-kappaBp65. Present study indicates human melanocytes express a panel of functional TLRs. The ligation of TLRs can turn these cells into active players of the skin innate immunity.

Cholesterol regulates melanogenesis in human epidermal melanocytes and melanoma cells

Cholesterol is important for membrane stability and is the key substrate for the synthesis of steroid hormones and vitamin D. Furthermore, it is a major component of the lipid barrier in the stratum corneum of the human epidermis. Considering that steroid hormone synthesis is taking place in epidermal melanocytes, we tested whether downstream oestrogen receptor/cAMP signalling via MITF/tyrosine hydroxylase/tyrosinase/pigmentation could be possibly modulated by cholesterol. For this purpose, we utilized human primary melanocyte cell cultures and human melanoma cells with different pigmentation capacity applying immunofluorescence, RT-PCR, Western blotting and determination of melanin content. Our in situ and in vitro results demonstrated that melanocytes can synthesize cholesterol via HMG-CoA reductase and transport cholesterol via LDL/Apo-B100/LDLR. Moreover, we show that cholesterol increases melanogenesis in these cells and in human melanoma cells of intermediate pigmentation (FM55) in a time- and dose-dependent manner. Cellular cholesterol levels in melanoma cells with different pigmentation patterns, epidermal melanocytes and keratinocytes do not differ except in the amelanotic (FM3) melanoma cell line. This result is in agreement with decreasing cholesterol content versus increasing pigmentation in melanosomes. Cholesterol induces cAMP in a biphasic manner i.e. after 30 min and later after 6 and 24 h, meanwhile protein expression of oestrogen receptor beta, CREB, MITF, tyrosine hydroxylase and tyrosinase is induced after 72 h. Taken together, we show that human epidermal melanocytes have the capacity of cholesterol signalling via LDL/Apo-B100/LDL receptor and that cholesterol under in vitro conditions increases melanogenesis.

Calcium homeostasis in human melanocytes: role of transient receptor potential melastatin 1 (TRPM1) and its regulation by ultraviolet light

Transient receptor potential melastatin (TRPM) is a subfamily of ion channels that are involved in sensing taste, ambient temperature, low pH, osmolarity, and chemical ligands. Melastatin 1/TRPM1, the founding member, was originally identified as melanoma metastasis suppressor based on its expression in normal pigment cells in the skin and the eye but not in aggressive, metastasis-competent melanomas. The role of TRPM1 and its regulation in normal melanocytes and in melanoma progression is not understood. Here, we studied the relationship of TRPM1 expression to growth and differentiation of human epidermal melanocytes. TRPM1 expression and intracellular Ca(2+) levels are significantly lower in rapidly proliferating melanocytes compared to the slow growing, differentiated melanocytes. We show that lentiviral short hairpin RNA (shRNA)-mediated knockdown of TRPM1 results in reduced intracellular Ca(2+) and decreased Ca(2+) uptake suggesting a role for TRPM1 in Ca(2+) homeostasis in melanocytes. TRPM1 knockdown also resulted in a decrease in tyrosinase activity and intracellular melanin pigment. Expression of the tumor suppressor p53 by transfection or induction of endogenous p53 by ultraviolet B radiation caused repression of TRPM1 expression accompanied by decrease in mobilization of intracellular Ca(2+) and uptake of extracellular Ca(2+). These data suggest a role for TRPM1-mediated Ca(2+) homeostasis, which is also regulated by ultraviolet B, in melanogenesis.

Differential Expression of the Antioxidant Repair Enzyme Methionine Sulfoxide Reductase (MSRA and MSRB) in Human Skin

Recently, the antioxidant repair enzymes methionine-S-sulfoxide reductase A (MSRA) and methionine-R-sulfoxide reductase B (MSRB) were described in human epidermal keratinocytes and melanocytes. Methionine sulfoxide reductases (MSRs) are thought to protect against reactive oxygen species-induced oxidative damage in many organs, including the most environmentally exposed organ, human skin. We sought to examine the expression and distribution of this enzyme family (MSRA, MSRB1, MSRB2, and MSRB3) within the various compartments of healthy and diseased human skin. Expression was assessed using polyclonal MSR antibodies and immunohistochemical staining of human skin biopsies from various anatomical sites. Remarkably, MSRA expression was not only found in the epidermis as previously described but also in hair follicles and eccrine glands and was most pronounced in sebaceous glands. Furthermore, MSRB2 expression was found in melanocytes while MSRB1 and MSRB3 were both expressed within vascular endothelial cells. In conclusion, MSR enzymes are differentially expressed in human skin. Thus, modulation of MSR repair antioxidants may have implications for cutaneous aging and carcinogenesis.

The ‘melanocyte-keratin’ mystery revisited: neither normal human epidermal nor hair follicle melanocytes express keratin 16 or keratin 6in situ

Keratin family proteins are generally accepted as being restricted to epithelial cells. However, several studies have challenged this paradigm by reporting, for example, that melanoma cells can express keratins and that normal human epidermal melanocytes, which derive from the neural crest, express keratin 16 (K16) in situ. We wished to confirm or refute that K16 and/or its intermediate filament partner, keratin 6 (K6), are expressed in normal human epidermal and/or hair follicle melanocytes in situ. Cryosections of normal human scalp skin were subjected to highly sensitive double immunohistochemistry with specific antibodies against K16 or K6 and against the melanocyte-specific marker NKI/beteb (gp100). Immunoreactivity (IR) was visualized by conventional light microscopy and confocal fluorescence microscopy. Despite the use of different, high-sensitivity immunostaining methods, stringent positive and negative controls, and monospecific, well-characterized antikeratin antibodies, we could detect neither K16 nor K6 IR within intraepidermal or intrafollicular pigment cells of normal human scalp skin. Instead, NKI/beteb+ cells were found to be intimately embedded in foci of K16+ and/or K6+ keratinocytes, which might create the illusion of keratin expression by these cells. Human epidermal or hair follicle melanocytes do not express K16 and/or K6 while residing in their natural habitat.

Loss of Class III β-Tubulin Induced by Histone Deacetylation Is Associated with Chemosensitivity to Paclitaxel in Malignant Melanoma Cells

Overexpression of class III beta-tubulin (TUBB3) is an important mechanism of taxane resistance. Using 7 melanoma cell lines, 2 normal neonatal human epidermal melanocyte (NHEM) cultures, and 49 primary melanomas, we investigated TUBB3 expression, its relationship to chemosensitivity to taxane derivatives, and the epigenetic mechanism controlling TUBB3 gene expression. Normal melanocytes in vitro and in vivo strongly expressed TUBB3 protein. NHEMs exhibited marked chemoresistance to paclitaxel-induced apoptosis. A subset (10 of 49, 20%) of primary malignant melanomas was TUBB3 negative. The incidence of TUBB3-negative melanomas increased with stage of progression. TUBB3 protein expression varied among cell lines; one (HMV-I) of the seven cell lines exhibited an extremely low endogenous level. TUBB3 protein expression correlated well with chemosensitivity to paclitaxel-induced apoptosis (P<0.05). Treatment with a histone deacetylase (HDAC) inhibitor restored TUBB3 expression in HMV-I. Chromatin immunoprecipitation assays revealed that histones H3 and H4 were hypoacetylated at the TUBB3 gene in HMV-I as compared with a TUBB3-overexpressing cell type (HMV-II). Treatment with the HDAC inhibitor induced gain of histone acetylation only in HMV-I. These results suggest that loss of TUBB3 protein may be induced by histone deacetylation in a subset of malignant melanomas, and may be associated with chemosensitivity to taxane.

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 μM) and the IC 50 value for suppression of cellular tyrosinase activity was estimated as 85.0 μM. 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.