Tyrosinase Activity In Melanocytes Research Articles

Reduced Proliferative and Differentiative Activity of Mouse Pink-Eyed Dilution Melanoblasts is Related to Apoptosis

The mouse pink-eyed dilution (p) locus is known to control the melanin content, melanosome morphology, and tyrosinase activity in melanocytes. However, it is not well known whether the p allele is involved in regulating melanocyte proliferation, differentiation, and death. The aim of this study is to investigate in detail the role of the p allele in melanocyte proliferation, differentiation, and death using a cell culture system. The epidermal cell suspensions of the neonatal dorsal skin derived from wild type mice at the p locus (black, C57BL/10JHir-P/P) and their congenic mutant (pink-eyed dilution, C57BL/10JHir-p/p) were cultured with serum-free melanoblast-proliferation medium (MDMDF) and melanocyte-proliferation medium (MDMD). The proliferation and differentiation of p/p melanoblasts in MDMDF or MDMD were greatly inhibited compared with those of P/P melanoblasts and melanocytes. It is possible that apoptosis is related to the reduced proliferative and differentiative activity of p/p melanoblasts/melanocytes. The addition of apoptosis-inhibitors, such as caspase-9 inhibitor (C9I) and Bax-inhibiting peptide (BIP) into MDMDF or MDMD stimulated the proliferation and differentiation of p/p melanoblasts. In contrast, in P/P melanoblasts and melanocytes, C9I and BIP failed to stimulate their proliferation and differentiation. The number of apoptotic keratinocytes and melanoblasts/melanocytes in p/p mice was greater than in P/P mice. Moreover, expression of C9 and Bax in keratinocytes and melanoblasts/melanocytes in p/p mice was greater than in P/P mice. These results suggest that the increased apoptosis in keratinocytes and melanoblasts/melanocytes is related to the reduced proliferative and differentiative activity of p/p melanoblasts.

Effect of granulocyt e colony-stimulating factor and its receptor on the proliferation and tyrosinase activity of human melanocytes

Objective To measure the expression of granulocyte colony-stimulating factor receptor (G-CSFR) in human melanocytes and to evaluate the biologic effect of recombinant human granulocyte colony-stimulating factor (rhG-CSF) on human melanocytes.Methods Melanocytes were obtained from circumcision specimens of healthy males,and neutrophils were isolated from heparin-andcoagulated peripheral blood of healthy human followed by a primary culture.Then,the melanocytes in third passage were cultured with or without the presence of various concentrations (200,400,600,800 μg/L) of rhG-CSF for 72 hours.The growth and morphology of melanocytes were observed.Flow cytometry was performed to detect the expression of G-CSFR in untreated human melanocytes,neutrophils and erythroleukemia cells (HEL 92.1.7).Western blot and reverse transcription PCR (RT-PCR) were carried out to measure the expression of G-CSFR protein and mRNA respectively in the neutrophils,HEL 92.1.7 cells,treated or untreated human melanocytes.Methyl thiazolyl tetrazolium (MTT) assay was performed to evaluate the proliferation,and dopa-oxidation assay to estimate the tyrosinase activity,of treated melanocytes.Results The expression rate of G-CSFR was 76.81％ ± 10.70％ in human melanocytes,significantly higher than that in the HEL 92.1.7 cells (2.53％ ± 1.54％,P ＜ 0.01 ),but lower than that in the neutrophils (85.76％ ± 15.71％,P ＜ 0.05).Both G-CSFR protein and mRNA were expressed in melanocytes,and there was no significant differences in the expression level of G-CSFR protein and mRNA among melanocytes treated with different concentrations of rhG-CSF (both P ＞ 0.05).The expression levels of G-CSFR protein and mRNA in the melanecytes were significantly higher than those in the HEL 92.1.7 cells (both P ＜ 0.01 ),but lower than those in the neutrophils (P ＜ 0.05 or ＜ 0.01 ).rhG-CSF at 200-800 μg/L displayed a significantly promotive effect on the proliferation of melanocytes (P ＜ 0.01 or ＜ 0.05 ),and the effect was in a dose-dependent manner when rhG-CSF ranged from 200 to 600 μg/L (P ＜ 0.01 ).The rhG-CSF at 600 μg/L and 12-O-tetradecanoyl-phorbol-13-acetate (TPA) at 20 μg/L showed an equivalent effect on the proliferation of melanocytes (164.04％ ± 13.0％ vs.165.62％ ± 10.6％,P ＞ 0.05).However,rhG-CSF from 200 to 800 μg/L had no significant impact on the tyrosinase activity of melanocytes (all P ＞ 0.05 ).Conclusions G-CSFR is expressed in human melanocytes. rhG-CSF can promote the proliferation of cultured human melanocytes,but has no obvious influence on the tyrosinase activity of melanocytes. Key words: Melanocytes; Granulocyte colony-stimulating factor; Receptors, G-CSF

Effects of heat treatment on the activity of cultured human melanocytes irradiated by ultraviolet B in vitro

Objective To investigate the effect of heat treatment combined with narrow band ultraviolet B (NB-UVB) on cultured normal human melanocytes in vitro.Methods Melanocytes were isolated from the foreskin of normal human,cullured in vitro,and irradiated with NB-UVB of different doses (20,30,50,70,90,120 and 180 mJ/cm2).Then,MTT assay was performed to evaluate the proliferation and activity of melanocytes to determine the optimal dose of UVB for the next experiment.Melanocytes were classified into 3 groups to be treated with heat at 42 ℃ for 1 hour (heat group),irradiated with UVB at 50 mJ/cm2 (UVB group),or irradiated with UVB at 50 mJ/cm2 followed by heat treatment at 42 ℃ for 1 hour (combination group),daily for 3 successive days; those receiving no treatment served as the control.After 24-hour culture following the last treatment,tyrosinase activity was evaluated with L-dopa as the substrate,melanin content was detected by NaOH assay,and cell cycle stages were determined by flow cytometry.Results NB-UVB irradiation decreased the viability of melanocytes in a dose-dependent manner,and the optimum dose of UVB was 50 mJ/cm2.The tyrosinase activity of melanocytes was 0.244 ± 0.018 and 0.310 ± 0.015 respectively in the UVB group and combination group,and increased by 3.8％ (P ＜ 0.05) and 31.9％ (P ＜ 0.05) respectively compared with the control group (0.235 ± 0.018); the melanin content was 0.201 ± 0.016 and 0.286 ± 0.019,respectively in the UVB group and combination group,and increased by 17.5％ (P ＜ 0.05 ) and 67.3％ (P ＜ 0.05) compared with the control group (0.171 ± 0.016).In comparison with the control group,the percentage of melanocytes in G1 phase was decreased by 23.94％ in the UVB group (P＜ 0.05) and 33.51％ in the combination group (P ＜ 0.05),while that in S phase and G2 phase increased by 15.35％ (P ＜ 0.05 ) and 11.93％ (P ＜ 0.05),respectively in the UVB group,and 17.76％ (P ＞ 0.05) and 16.08％ (P ＞ 0.05),respectively in the heat group.Conclusion Heat treatment and NB-UVB can synergistically enhance the tyrosinase activity and accelerate melanogenesis,proliferation and differentiation,of melanocytes. Key words: Heat; Ultraviolet rays; Melanocytes; Cell cycle

Dual inhibitions of lemon balm (Melissa officinalis) ethanolic extract on melanogenesis in B16-F1 murine melanocytes: Inhibition of tyrosinase activity and its gene expression

The effects of wild type and UV-irradiated lemon balm (Melissa officinalis) ethanolic extracts (MOE and UMOE) on melanogenesis in vitro were examined. UMOE showed potent antioxidant activity and significantly inhibited the mushroom and melanocyte tyrosinase activity, and lowered cellular melanin content by 49% at 200 μg/mL in B16-F1 melanocytes. The key gene and protein expression of tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 were reduced (−73% for TRP-1 protein at 200 μg/mL UMOE, p<0.05). MOE showed similar results to a slightly lesser degree. We found that myo-inositol, a major compound in lemon balm extracts, significantly reduced cellular melanin synthesis and its effect was greater than arbutin at 1 mM. These suggest that both MOE and UMOE have anti-melanogenic role by both direct inhibition of tyrosinase and down-regulation of gene expressions in melanogenesis. UV-irradiation slightly improved the anti-melanogenic activities. UMOE may be useful as natural anti-melanogenic biomaterials for functional foods and cosmetics.

Effects of hyaluronic acid on biological activity of melanocytes

Objective To observe the effect of hyaluronic acid on the proliferation of and tyrosinase activity in melanocytes.Methods Normal primary human melanocytes were isolated from infant foreskin tissue and cultured.Different concentrations(0 to 10 g/L)of hyaluronic acid wero added to the culture medium immediately or 8 hours after the inoculation of melanocytes.MTT assay was performed to detect the proliferation of melanocytes,and tyrosinase activity was determined to evaluate the effect of hyaluronic acid on the melanin synthesis by melanocytes.Results The proliferation level (absorbance at 490 am,A490)of melanocytes was 0.14±0.02,0.37±0.08,0.45±0.11,0.49±0.07,0.55±0.12,0.52±0.11,0.49±0.07,0.39±0.05,0.19±0.03 and 0.01 4-0.01 when treated with hyaluronic acid of 0,0.008,0.016,0.313,0.625,1.250,2.500,5.000,7.500 and 10.000 g/L,respectively.The hyaluronic acid of 0.08 to 5 g/L markedly accelerated the proliferation of melanocytes,while that of 10 g/L inhibited their proliferation.The tyrosinase activity in melanocytes was promoted by hyaluronie acid of 0.2 to 5 g/L,but suppressed by that of 10 g/L.The proliferation of melanocytes treated with hyaluronic acid immediately after the inoculation was more rapid than that treated with hyaluronic acid 8 hours after the inoculation.Conclusion The hyaluronic acid of 0.2 to 5 g/L can enhance the proliferation of and tyrosinase activity in melanocytes. Key words: Vitiligo; Melanocyte; Hyaluronic acid

The mouse pink‐eyed dilution allele of the P‐gene greatly inhibits eumelanin but not pheomelanin synthesis

The mouse pink-eyed dilution (p) locus is known to control eumelanin synthesis, melanosome morphology, and tyrosinase activity in melanocytes. However, it has not been fully determined whether the mutant allele, p affects pheomelanin synthesis. Effects of the p allele on eumelanin and phemelanin synthesis were investigated by chemical analysis of dorsal hairs of 5-week-old mice obtained from the F(2) generations (black, pink-eyed black, recessive yellow, pink-eyed recessive yellow, agouti, and pink-eyed agouti) between C57BL/10JHir (B10)-congenic pink-eyed black mice (B10-p/p) and recessive yellow (B10-Mc1r(e)/Mc1r(e)) or agouti (B10-A/A) mice. The eumelanin content was dramatically (>20-fold) decreased in pink-eyed black and pink-eyed agouti mice, whereas the pheomelanin content did not decrease in pink-eyed black, pink-eyed recessive yellow, or pink-eyed agouti mice compared to the corresponding P/- mice. These results suggest that the pink-eyed dilution allele greatly inhibits eumelanin synthesis, but not pheomelanin synthesis.

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.

Antidyslipidaemic activity of Glycyrrhiza glabra in high fructose diet induced dsyslipidaemic Syrian golden hamsters.

The root of Glycyrrhiza glabra is a traditional medicine used mainly for the treatment of peptic ulcer, hepatitis C, pulmonary and skin diseases, although clinical and experimental studies suggest that it has several other useful pharmacological properties such as antiinflammatory, antiviral, antimicrobial, antioxidative, anticancer activities, immunomodulatory, hepatoprotective and cardioprotective effects. Glycyrrhizinic acid, a major component of licorice, has antiulcer effect by raising the local concentration of prostaglandins that promote mucous secretion and cell proliferation in the stomach. Glycyrrhizin shows hepatoprotective effect by preventing changes in cell membrane permeability, inhibiting phospholipase A(2) (PLA(2)) and increasing survival rate of hepatocytes. Glabridin has effect in melanogenesis and inflammation by inhibiting the tyrosinase activity of melanocytes. α-glycyhrritinic acid exhibits anti-inflammatory activity by inhibiting glucocorticoid metabolism. In present study ethanolic (95%) extract of root of Glycyrrhiza glabra and its fractions were investigated for its antidyslipidaemic activity on HFD induced dyslipidaemic hamsters. Ethanolic extract and its ethyl acetate soluble, water soluble and hexane soluble fractions decreased serum level of total cholesterol by 25.9, 38.0, 39.0 and 26.3%, respectively. On the other hand ethanolic extract, ethyl acetate soluble, water soluble and hexane soluble fraction increased the serum HDL-cholesterol level by 14.8, 34.3, 27.3 and 17.2%, respectively. Ethanolic extract, ethyl acetate fraction, aqueous fraction and hexane fraction decreased triglyceride level by 31.3, 37.2, 41.2 and 28.9%, respectively. The reduction in LDL-cholesterol level by ethanolic extract, ethyl acetate soluble fraction and water soluble fraction were 43.9, 31.0, 33.4 and 24.6%, respectively.

Skin-Lightening Effect of a Polyphenol Extract from Acerola (Malpighia emarginataDC.) Fruit on UV-Induced Pigmentation

To investigate the physiological functions of polyphenols from acerola (Malpighia emarginata DC.) fruit, the effects on melanogenesis were studied. The crude polyphenol concentrated extract from acerola (C-AP) was used to examine the skin-lightening effect on brownish guinea pigs which had been subjected to controlled UVB irradiation. The results show that C-AP significantly lightened the UVB-irradiated skin pigmentation. Furthermore, treatment with C-AP reduced the content of melanin in B16 melanoma cells, suggesting that the in vivo skin-lightening effect of C-AP was due to the suppression of melanin biosynthesis in melanocytes. In addition, we found that C-AP could effectively inhibit mushroom tyrosinase activity, the main constituents responsible for this effect being thought to be such anthocyanins as cyanidin-3-alpha-O-rhamnoside (C3R) and pelargonidin-3-alpha-O-rhamnoside (P3R). This result indicates that the skin-lightening effect of C-AP can be partly attributed to the suppression of melanogenesis through the inhibition of tyrosinase activity in melanocytes. An oral ingestion of C-AP may therefore be efficacious for reducing UVB-induced hyper-pigmentation by inhibiting the tyrosinase in melanocytes.

Post-Transcriptional Regulation of Melanin Biosynthetic Enzymes by cAMP and Resveratrol in Human Melanocytes

Upregulation of microphthalmia-associated transcription factor (MITF) expression has been proposed to mediate melanogenesis stimulated by cAMP, whereas downregulation of MITF has been suggested to underlie the depigmentary effects of resveratrol, a promising chemotherapeutic found in red wine. We have assessed the contribution of MITF to pigmentation regulation by treating primary cultures of normal human melanocytes with the adenylate cyclase activator forskolin and/or resveratrol, then quantifying mRNA and protein levels for MITF, tyrosinase, tyrosinase-related protein-1, and dopachrome tautomerase (DCT). The inhibition of tyrosinase activity by resveratrol was not due to alterations in MITF, but instead was explained by both direct tyrosinase inhibition and a post-transcriptional effect that reduced the amount of fully processed tyrosinase. Glycosidase digestion revealed that the basis for the tyrosinase decrease was the retention of an immature form in the ER and subsequent loss of the mature, Golgi-processed enzyme. Elevation of intracellular cAMP by forskolin markedly increased protein levels for MITF, tyrosinase and DCT, however there was no concomitant increase in tyrosinase or DCT mRNA. This indicated that elevated levels of MITF were not sufficient to promote transcription of these melanogenic genes and that the increase in their protein abundance appeared to be predominantly mediated through post-transcriptional processing events.

Hermansky–Pudlak HPS1/pale ear Gene Regulates Epidermal and Dermal Melanocyte Development

The pale ear (ep) mouse strain is a model for the Hermansky-Pudlak syndrome type 1 (HPS-1), an autosomal recessive disorder causing pigmentary dilution, visual disturbances, bleeding diatheses, pulmonary fibrosis, and granulomatous colitis. The ep mice have a coat color very similar to the black-colored parental strain, C57BL/6. However, the ears and tails of ep mice are significantly hypopigmented compared with the control animals, suggesting that the gene mutation in ep mice reveals a differential regulation of melanocyte function in dorsal back skin melanocytes versus tail or ear skin. In this study, we analyzed the mutant phenotype in detail and determined that in the tail, the defective gene causes delayed onset of interfollicular epidermal melanocyte tyrosinase activity, decreased numbers of melanocytes in the interfollicular epidermis and dermis, and severe immaturity of tail epidermal melanosomes, findings not observed in dorsal back follicular melanocytes. These results highlight differences between follicular and interfollicular melanocyte biology and demonstrate that defects in the ep protein not only affect melanosome biogenesis, but also play a developmental role in determining interfollicular epidermal and dermal melanocyte function. The implications of these findings for the mechanisms governing physiologic variation in human pigmentation and for the pathogenesis of vitiligo are discussed.

Inhibition of Melanogenesis by Selina-4(14),7(11)-dien-8-one Isolated from Atractylodis Rhizoma Alba

To develop effective skin-lightening agents, we tested medicinal herbal extracts for their melanogenic-inhibitory activities. We isolated a sesquiterpenoid compound from the extract of Atractylodis Rhizoma Alba using the bioactivity-guided fractionation and identified it as selina-4(14),7(11)-dien-8-one (compound 1) with spectroscopic methods. Compound 1 dramatically reduced melanin synthesis of melan-a cells without any apparent cytotoxicity. Compound 1 did not inhibit cell-free tyrosinase activity but decreased tyrosinase activity in melanocytes. These effects were attributed to reduced expression of melanogenic enzymes such as tyrosinase, tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2). These results suggest that compound 1 may be an effective skin-lightening agent that regulates expression of melanogenic enzymes.

Correlation between age and the secretions of melanocyte-stimulating cytokines in cultured keratinocytes and fibroblasts

The majority of skin changes associated with ageing are caused by photoageing and reflect cumulative sun exposure. Although the actinic damage plays a major role in skin pigmentation, it is also important to examine the effects of chronological cellular ageing on the pigmentation. The chief cellular components of the skin other than melanocytes are keratinocytes and fibroblasts, and the influences of age-related changes in those cells on skin pigmentation have not been elucidated. To clarify the effects of cellular ageing of keratinocytes and fibroblasts on age-related skin pigmentation. Using ELISA analysis, we measured the level of melanogenic cytokines secreted by cultured keratinocytes and fibroblasts derived from skin of various chronological ages. We also compared the cytokine secretion by cultured keratinocytes between the second and fifth cultures. There was no correlation between age and hepatocyte growth factor (HGF), stem cell factor (SCF), and basic fibroblast growth factor (bFGF) secretion by fibroblasts. On the other hand, a significant positive correlation existed between age and interleukin ((IL)-1alpha secretion (R2=0.50, P=0.002), and a relatively weak correlation existed between age and endothelin-1 (ET-1) secretion (R2=0.17, P=0.051, not significant). The IL-1alpha secretion by keratinocytes was significantly increased in the fifth cultures compared with the second cultures (P<0.005). These findings suggest that IL-1alpha secretion increases as cells grow older, and the increased secretion of IL-1alpha by aged keratinocytes may stimulate HGF production in dermal fibroblasts paracrinely and ET-1 production in keratinocytes autocrinely, which stimulates melanocyte proliferation and induces an increase of tyrosinase activity in melanocytes. Because IL-1alpha is a primary mediator that responds to inflammation and injury, the transcription of genes involved in skin inflammation may be persistently induced in the aged skin. Thus the increased secretion of IL-1alpha by aged keratinocytes in the aged skin may play a role in the accentuated cutaneous pigmentation and other skin ageing.

N-Terminal Fatty Acylated His-dPhe-Arg-Trp-NH2Tetrapeptides: Influence of Fatty Acid Chain Length on Potency and Selectivity at the Mouse Melanocortin Receptors and Human Melanocytes

The melanocortin system is involved in the regulation of a diverse number of physiologically important pathways including pigmentation, feeding behavior, weight and energy homeostasis, inflammation, and sexual function. All the endogenous melanocortin agonist ligands possess the conserved His-Phe-Arg-Trp tetrapeptide sequence that is postulated to be important for melanocortin receptor molecular recognition and stimulation. Previous studies by our laboratory resulted in the discovery that increasing alkyl chain length at the N-terminal "capping" region of the His-dPhe-Arg-Trp-NH(2) tetrapeptide resulted in a 100-fold increased melanocortin receptor agonist potency. This study was undertaken to systematically evaluate the pharmacological effects of increasing N-capping alkyl chain length of the CH(3)(CH(2))(n)CO-His-dPhe-Arg-Trp-NH(2) (n = 6-16) tetrapeptide template. Twelve analogues were synthesized and pharmacologically characterized at the mouse melanocortin receptors MC1R and MC3R-MC5R and human melanocytes known to express the MC1R. These peptides demonstrated melanocortin receptor selectivity profiles different from those of previously published tetrapeptides. The most notable results of enhanced ligand potency (20- to 200-fold) and receptor selectivity were observed at the MC1R. Tetrapeptides that possessed greater than nine alkyl groups were superior to alpha-MSH in terms of the stimulation of human melanocyte tyrosinase activity. Additionally, the n-pentadecanoyl derivative had a residual effect on tyrosinase activity that existed for at least 4 days after the peptide was removed from the human melanocyte culture medium. These data demonstrate the utility, potency, and residual effect of melanocortin tetrapeptides by adding N-terminal fatty acid moieties.

Tyrosinase Induction in Normal Human Cultured Melanocytes by Endothelin-1

Since endothelin was found to be expressed epithelium as well as vascular enothelium, the functional regulation of various cells with endothelin have been actively investigated. Especially, it is suggested that endothelin may influence pigmentation and depigmentation, which are mediated by melanocytes. In the present study, we investigated the regulation of melanocyte functions and tyrosinase expression by endothelin from the aspects of tyrosinase protein expression and enzyme activity. The influence of endothelins on melanocyte functions was fundamentally assessed. Melanocytes showed a dose-dependent increase in cell proliferation with the addition of endothelin-1. When the confluence melanocytes were cultured with endothelin-1 for 72 hours, the tyrosinase activity in melanocytes was significantly decreased dose-dependently. In contrast, there was no significant change with endothelin-3. However, the tyrosinase protein expression of melanocytes was significantly increased by endothelin-1 dose-dependently, but endothelin-3 had no effect. Either the suppression of tyrosinase activity or the tyrosinase expression was regulated by endothelin-A receptor antagonists (e.g. BQ123). From these observations, endothelin-1-induced tyrosinase was considered to be mediated by endothelin-A receptors. In actuality, however, the reason for the decrease in the specific activity of tyrosinase remains unknown, and our results suggest that another mechanism underlying the activation of tyrosinase is present in addition to the inductive action of endothelin-1 on tyrosinase.

Suppression of melanogenesis by induction of endogenous intracellular metallothionein in human melanocytes.

Nitric oxide (NO) is a potent intercellular mediator of melanogenesis, whereas metallothionein (MT) is an inducible intracellular antioxidant that has been reported to scavenge NO. We investigated the existence and induction of MT in melanocytes, and its inhibitory effect on NO-induced melanogenesis. The expression of MT was detected in melanocytes, however, at a lower level than in keratinocytes, and its induction was possible by the addition of zinc chloride. Further, an NO-stimulated increase of tyrosinase activity in melanocytes was remarkably suppressed, when MT was induced prior to NO stimulation. Melanogenesis was also suppressed, when dexamethasone was used to induce MT. However, an NO-stimulated increase of tyrosinase expression was not suppressed at the gene and protein level, when MT was induced in melanocytes. The same suppressive effect of melanogenesis was also observed, when alpha-melanocyte-stimulating hormone or endothelin-1 was used as a stimulator. Because these results implied a mechanism other than NO scavenging to explain the suppressive effect of MT induction on melanogenesis, the direct inhibition of tyrosinase by MT was examined. Melanosome fractions were prepared from melanocytes, whose melanogenesis was suppressed by the induction of MT. Tyrosinase suppression was observed in the melanosome fractions, which was neutralized by the addition of anti-MT antibody. These results suggest that MT induction may be effective to suppress melanogenesis stimulated by NO as well as other melanogens, and these suppressive effects might be due to a direct inhibition of tyrosinase activity in melanosome and not a scavenging effect of NO.

The effect of antisense tyrosinase-related protein 1 on melanocytes and malignant melanoma cells.

Tyrosinase-related proteins (TRPs) include tyrosinase, TRP-1 and TRP-2. The functions of tyrosinase and TRP-2 have been determined, but the biological role of TRP-1 is still controversial and is not well known in humans. To study further the biological role of the human TRP-1 gene in melanocytes and melanoma cells. TRP-1 cDNA was subcloned into eukaryotic expression vector pcDNA3.1 in the reverse direction, and antisense recombinant vector was transfected into melanocytes and a melanoma cell line using Lipofectamine 2000. Positive cells were selected by geneticin. TRP-1 mRNA level was measured by reverse transcription-polymerase chain reaction (RT-PCR), and TRP-1 protein level by Western blot. Cell cycles were determined by flow cytometry, and the activity of tyrosinase was evaluated by L-DOPA reaction. Light microscopy, electron microscopy and flow cytometry were used to observe cell morphology and apoptosis. For in vivo assays, the antitumour activity of antisense TRP-1 against the malignant melanoma (MM) cell line, Libr, was evaluated in an animal-tumour model of subcutaneous tumours. Positive transfected cells steadily expressed TRP-1 antisense RNA. RT-PCR and Western blot showed a low level of TRP-1 mRNA and TRP-1 protein, respectively. Cell cycles were blocked in the G1 stage, and the activity of tyrosinase decreased significantly (P < 0.01). Light and electron microscopy showed abnormal cell morphology, and apoptosis was detected. The neoplasia activity of antisense TRP-1-transfected MM cells was significantly lower than that of MM cells (P < 0.01). TRP-1 plays an important role in the proliferation, morphology and tyrosinase activity of melanocytes and melanoma cells.

Molecular responses to photogenotoxic stress induced by the antibiotic lomefloxacin in human skin cells: from DNA damage to apoptosis.

Photo-unstable chemicals sometimes behave as phototoxins in skin, inducing untoward clinical side-effects when exposed to sunlight. Some drugs, such as psoralens or fluoroquinolones, can damage genomic DNA, thus increasing the risk of photocarcinogenesis. Here, lomefloxacin, an antibiotic from the fluoroquinolone family known to be involved in skin tumor development in photoexposed mice, was studied using normal human skin cells in culture: fibroblasts, keratinocytes, and Caucasian melanocytes. When treated cells were exposed to simulated solar ultraviolet A (320-400 nm), lomefloxacin induced damage such as strand breaks and pyrimidine dimers in genomic DNA. Lomefloxacin also triggered various stress responses: heme-oxygenase-1 expression in fibroblasts, changes in p53 status as shown by the accumulation of p53 and p21 proteins or the induction of MDM2 and GADD45 genes, and stimulation of melanogenesis by increasing the tyrosinase activity in melanocytes. Lomefloxacin could also lead to apoptosis in keratinocytes exposed to ultraviolet A: caspase-3 was activated and FAS-L gene was induced. Moreover, keratinocytes were shown to be the most sensitive cell type to lomefloxacin phototoxic effects, in spite of the well-established effectiveness of their antioxidant equipment. These data show that the phototoxicity of a given drug can be driven by different mechanisms and that its biologic impact varies according to cell type.

The inhibitory effect of androgen and sex-hormone-binding globulin on the intracellular cAMP level and tyrosinase activity of normal human melanocytes.

The effect of androgens on human melanocytes has not been well clarified. We studied the effects of androgens on normal human melanocytes in the presence or absence of sex-hormone-binding globulin (SHBG), which complexes with those hormones. Immunohistochemically, testosterone and SHBG co-localized on the cell membrane. Androgens such as testosterone, 5alpha-dihydrotestosterone, and methyltrienolone (R1881, a potent synthetic androgen), reduced intracellular cAMP levels after treatment with SHBG, but hydrocortisone had no effect. We also found that testosterone and R1881 slightly suppressed tyrosinase activity in melanocytes when treated with SHBG, although they had no effect on the expression of tyrosinase at the transcriptional or translational level, as measured by semi-quantitative reverse transcriptase-polymerase chain reaction and by Western blot analysis, respectively. Our results suggest that androgens may modulate tyrosinase activity at the posttranslational level through the cell membrane signaling pathway.

Electron microscopic DOPA reaction test for oculocutaneous albinism.

Oculocutaneous albinism (OCA) is an autosomal recessive disorder in which the biosynthesis of melanin is reduced or absent in skin, hair and eyes. Tyrosinase-related OCA (OCA1) is caused by mutations in the tyrosinase gene. Tyrosinase-negative OCA (OCA1A) is the most severe phenotype in which tyrosinase catalytic activity is completely lost, resulting in no mature melanin pigment. Yellow OCA (OCA1B) varies from very little pigment associated with whitish-blond hair to nearly normal pigment with dark-blond hair and skin. We determined the tyrosinase activity in melanocytes by the electron microscopic dihydroxyphenylalanine (EM-DOPA) reaction test using skin samples and analyzed tyrosinase gene mutations in nine Japanese patients with OCA. In 18 alleles of nine patients, the OCA1A-associated mutations, P310insC, R77Q and R278X, were found in seven, three and one alleles, respectively. Five patients who had these mutations in both alleles showed white hair, blue eyes and white skin and demonstrated no tyrosinase activity by the EM-DOPA reaction test. Three patients who had no tyrosinase gene mutation showed tyrosinase activity and heterogeneous clinical features. One patient in whom only an R77Q OCA1A mutation was found in one allele demonstrated a reduced tyrosinase activity, indicating OCA1B. This patient had white hair at birth, but it had turned blond by the age of 1 year. These results indicate that the EM-DOPA reaction test provides clear information on the status of tyrosinase activity which is essential for the identification of the disease subtype which in turn is important for the prognosis of patients with OCA.