Induction of supermelanin synthesis and morphological changes in interspecific reconstituted cells and its reversal by tumor promoter

Chloramphenicol-resistant (CAPr) reconstituted cells and cybrids were isolated by fusion of karyoplasts (or intact cells) of mouse amelanotic melanoma B16 cells with cytoplasts of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) -deficient, CAPr rat myoblastic cells, L6TG.CAPr, and double selection in HAT medium containing CAP. Reconstituted cells or cybrids exhibited unique cellular arrangement, and about one third of the isolated clones expressed high tyrosinase activity and marked melanin synthesis, although the parental mouse cells expressed low tyrosinase activity and the parental rat cells did not express tyrosinase activity. These phenotypic changes have been stable for more than a year. The phenotypic reversions of these clonal cells were induced by treatment with a tumor promoter. There were changes in the morphology of the treated cells to that of the mouse B16 cells and extinction of tyrosinase activity and melanin synthesis in pigmented clonal cells. These phenotypic changes and reversions induced by a promoter were repeatedly reversible.     

The Expression of Tyrosinase,Tyrosinase-Related Proteins 1 and 2 (TRP1 and TRP2), the Silver Protein,and a Melanogenic Inhibitor in Human Melanoma Cells of Differing Melanogenic Activities

The expression of various melanogenic proteins, including tyrosinase, the tyrosinase-related proteins 1 (TRP1) and 2 (TRP2/DOPAchrome tautomerase), and the silver protein in human melanocytes was studied in six different human melanoma cell lines and compared to a mouse derived melanoma cell line. Analysis of the expression of tyrosinase, TRP1, TRP2, and the silver protein using flow cytometry revealed that in general there was a positive correlation between melanin formation and the expression of those melanogenic enzymes. Although several of the melanoma cell lines possessed significant activities of TRP2, the levels of DOPAchrome tautomerase in extracts of human cells were relatively low compared to those in murine melanocytes. Melanins derived from melanotic murine JB/MS cells, from melanotic human Ihara cells and HM-IY cells, from sepia melanin, and from C57BL/6 mouse hair were chemically analyzed. JB/MS cells, as well as Ihara cells and HM-TY cells, possessed significant amounts of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) derived melanins, this being dependent on the activity of TRP2. Kinetic HPLC assays showed that 5,6-dihydroxyindole (DHI) produced during melanogenesis was metabolized quickly to melanin in pigmented KHm-1/4 cells, whereas DHI was stable in amelanotic human SK-MEL-24 cells. A melanogenic inhibitor that has been purified from SK-MEL-24 cells that suppressed oxidation of DHI in the presence or absence of tyrosinase, but had no effect on DHICA oxidation. The sum of these results suggest that the expression of melanogenic enzymes as well as the activity of a melanogenic inhibitor are critical to the production of melanin synthesis in humans.     

Investigation of the Regulation of Pigmentation in α-Melanocyte-Stimulating Hormone Responsive and Unresponsive Cultured B16 Melanoma Cells

In vitro melanocyte-stimulating hormone (MSH) stimulates melanogenesis in some, but not all, melanocytes and melanoma cells. In an attempt to explain this variation in response to αMSH, we examined cyclic adenosine monophosphate (cAMP) accumulation, tyrosinase activity, and melanin production in primary (1°) murine B16 melanoma cells and in two B16 cell lines (B16 F1 and B16 F10) that are known to respond to αMSH. In vivo all three B16 melanoma cell types produced pigmented tumours. In vitro αMSH increased tyrosinase activity and melanin content in the F1 and F10 cells but not in the B16 1° cells. αMSH, however, increased cAMP production in all three cell types, confirming that the inability of B16 1° cells to produce melanin in response to αMSH is not due to a lack of αMSH receptors or cAMP response to αMSH. Further, we present evidence for a separate pathway of melanogenesis that is independent of cAMP as calmodulin antagonists, which do not elevate cAMP, increased tyrosinase activity, and melanin production in both 1° and F1 cells.     

The Cloning and Characterization of Chick Tyrosinase from a Novel Embryonic cDNA Library

Very little is known about the genes involved in the regulation of avian skin and feather pigmentation. In mammals, two gene families have been identified as being important for the regulation of melanin biosynthesis. To isolate the avian equivalents of these families, we have generated an embryonic chick melanocyte cDNA library. Neural crest cells from 500 black chick embryos were cultured under conditions supportive of melanocyte differentiation and proliferation. A cDNA library was constructed and screened with a mouse tyrosinase cDNA probe. Nineteen clones were obtained, seven of which cross-hybridized to a mouse tyrosinase cDNA on Southern blots. The longest of these clones, B8.3 (1.9 kb), was sequenced and found to share 99.7% nucleotide and 99.8% amino acid sequence homology to a reported chick tyrosinase cDNA. Both Northern blot analysis andin situhybridization demonstrated that clone B8.3 was expressed in the retinal pigment epithelium of chick embryos. Our results suggest therefore that the cDNA library described here may allow the cloning of novel melanogenic genes.     

Tyrosinase inhibitory effect and inhibitory mechanism of tiliroside from raspberry

Tiliroside was found to inhibit both monophenolase and diphenolase activity of mushroom tyrosinase. The lag time of tyrosine oxidation catalyzed by mushroom tyrosinase was obviously lengthened; 0.337?mM of tiliroside resulted in the lag time extension from 46.7?s to 435.1?s. A kinetic analysis shown that tiliroside was a competitive inhibitor for monophenolase and diphenolase with K_i values of 0.052?mM and 0.26?mM, respectively. Furthermore, tiliroside showed 34.5% (p?<?0.05) inhibition of intracellular tyrosinase activity and 54.1% (p?<?0.05) inhibition of melanin production with low cytotoxicity on B16 mouse melanoma cells at 0.168?mM. In contrast, arbutin displayed 9.1% inhibition of cellular tyrosinase activity and 29.5% inhibition of melanin production at the same concentration. These results suggested that tiliroside was a potent tyrosinase inhibitor and might be used as a skin-whitening agent and pigmentation medicine.     

Progressive Effects of Phloridzin on Melanogenesis in B16 Mouse Melanoma Cells

When we studied the effects of polyphenols from apple fruits on melanogenesis in B16 mouse melanoma cell lines, phloridzin had dose-dependent progressive effects on melanogenesis between 10 and 500 μg/ml without inhibiting cell growth. At a concentration of 500 μg/ml, phloridzin increased the melanin content in the cells to 181% of that in control cells. In contrast, phloretin, the aglycon of phloridzin, did not activate melanogenesis in the cells and was cytotoxic at a concentration of 5 μg/ml. Phloridzin increased the activity of tyrosinase to 223% of that in control cells. Furthermore, phloridzin inhibited the activity of protein kinase C (PKC), which is recognized to regulate tyrosinase activity. The inhibition of PKC activity continued for 120min from the addition of phloridzin. Therefore, we estimated that the activation of melanogenesis by phloridzin resulted from the increase of tyrosinase activity caused by the inhibition of PKC activity.     

Regulation of Melanogenesis Induced by 5-Methoxypsoralen Without Ultraviolet Light in Murine Melanoma Cells

Melanogenesis in melanoma cells can be enhanced by psoralens in the absence of UV light. Melanin biosynthesis is regulated by a number of melanocyte-specific proteins, including tyrosinase, DOPAchrome tautomerase (DCT), and tyrosinase-related protein-1 (TRP-1, gp75). To get more insight on the molecular mechanisms involved in psoralens-induced melanogenesis, we determined tyrosinase and DCT activities as well as mRNA and protein levels of tyrosinase, DCT, and TRP-1 in S91 mouse melanoma cells treated by 5-MOP. High concentration of 5-MOP (5 × 10^-5 M) induced a time-dependent increase of tyrosinase activity and melanin content, which was correlated to an increase of both mRNA and protein levels of tyrosinase. These results demonstrate that the 5-MOP stimulation of melanogenesis is related to increased tyrosinase synthesis. In addition, 5-MOP stimulated TRP-1 synthesis and induced a dose-dependent decrease of DCT activity without any modification in the expression of the protein. We explored then the signalling pathways involved in 5-MOP-induced melanogenesis and, particularly, the role of cyclic AMP and protein kinase C (PKC). A small stimulation of cyclic AMP production was observed in presence of 5-MOP. Furthermore, 1-oleoyl-2-acetylglycerol (OAG), a PKC activator, potentiated the 5-MOP stimulation of tyrosinase activity, while calphostin, a specific PKC inhibitor, inhibited the 5-MOP induction of tyrosinase activity. Phorbol-myristate acetate (PMA), described as a strong activator of PKC, inhibited also the effect of 5-MOP when used at long term. Taken together, these results demonstrate that in murine melanoma cells 5-MOP stimulates melanogenesis by increasing activity and synthesis of tyrosinase. Tyrosinase and TRP-1 expression are coordinately regulated by 5-MOP Furthermore, a negative correlation between melanogenesis and DCT activity was observed under 5-MOP stimulation. At least, PKA and PKC systems appear to play an important role in the melanogenic effect of 5-MOP.     

Involvement of phospholipase D1 in melanogenesis of mouse B16 melanoma cells

In response to alpha-melanocyte-stimulating hormone (alpha-MSH) or cAMP-elevating agents (forskolin and isobutylmethylxanthine), mouse B16 melanoma cells underwent differentiation characterized by increased melanin biosynthesis. However, the mechanism(s) underlying the regulation of melanogenesis during differentiation has not yet been clearly understood. Phospholipase D (PLD) has been reported to be involved in differentiation. This enzyme cleaves phosphatidylcholine upon stimulation with stimuli to generate phosphatidic acid. In the current study, the involvement of PLD in the regulation of melanogenesis characteristic of differentiation was examined using mouse B16 melanoma cells. Treatment of B16 cells with alpha-MSH was found to cause marked decreases in the PLD1 activity concurrent with its reduced protein level. Moreover, treatment of exogenous bacterial PLD also inhibited alpha-MSH-induced melanogenesis. To further investigate the role of PLD1 in the regulation of melanogenesis, we examined the effects of overexpression of PLD1 on melanogenesis in B16 melanoma cells. The B16 cells overexpressing PLD were prepared by transfection with the vector containing the cDNA encoding PLD1. The melanin contents in PLD1-overexpressing cells (B16/PLD1) were observed to be lower compared with those in the vector control cells (B16/Vec), concomitant with the decreases in both activity and protein level of tyrosinase, a key regulatory enzyme in melanogenesis. Moreover, overexpression of PLD1 resulted in a marked inhibition of melanogenesis induced by alpha-MSH. The inhibition of melanogenesis was well correlated with the decrease in the tyrosinase activity associated with its expression. These results indicated that PLD1 negatively regulated the melanogenic signaling by modulating the expression of tyrosinase in mouse B16 melanoma cells.     

Transglutaminase participates in the blockade of neurotransmitter release by tetanus toxin: evidence for a novel biological function

The aim of this study was to collect evidences on the role of transglutaminase (TG, E.C.2.3.2.13) in the antineoplastic properties exerted by nimesulide (NMS), a non-steroidal anti-inflammatory drug, on murine B16-F10 melanoma cells. Treatment of melanoma cells with nimesulide produces a considerable reduction of cell proliferation, paralleled by a remarkable decrease of the intracellular concentration of polyamines spermidine and spermine. NMS treatment induces cancer cell differentiation, likely through the observed enhancement of TG and tyrosinase activities and increase of melanin production, well known markers of melanocyte differentiation. The overall results highlight the possibility that nimesulide acts as antineoplastic agent likely through the induction of intracellular TG activity.     

Keratinocyte-derived Laminin-332 Protein Promotes Melanin Synthesis via Regulation of Tyrosine Uptake

Melanocytes, which produce the pigment melanin, are known to be closely regulated by neighboring keratinocytes. However, how keratinocytes regulate melanin production is unclear. Here we report that melanin production in melanoma cells (B16F10 and MNT-1) was increased markedly on a keratinocyte-derived extracellular matrix compared with a melanoma cell-derived extracellular matrix. siRNA-mediated reduction of keratinocyte-derived laminin-332 expression decreased melanin synthesis in melanoma cells, and laminin-332, but not fibronectin, enhanced melanin content and α-melanocyte-stimulating hormone-regulated melanin production in melanoma cells. Similar effects were observed in human melanocytes. Interestingly, however, laminin-332 did not affect the expression or activity of tyrosinase. Instead, laminin-332 promoted the uptake of extracellular tyrosine and, subsequently, increased intracellular levels of tyrosine in both melanocytes and melanoma cells. Taken together, these data strongly suggest that keratinocyte-derived laminin-332 contributes to melanin production by regulating tyrosine uptake.     

Evaluation of the inhibition of mushroom tyrosinase and cellular tyrosinase activities of oxyresveratrol: comparison with mulberroside A

The inhibitory effects of oxyresveratrol, the aglycone of mulberroside A, on mushroom and cellular tyrosinase activities and melanin synthesis were evaluated. Mulberroside A and oxyresveratrol showed inhibitory activity against mushroom tyrosinase, with oxyresveratrol demonstrating a greater inhibitory effect than that of mulberroside A. Oxyresveratrol and mulberroside A strongly inhibited melanin production in Streptomyces bikiniensis and exhibited dose-dependent inhibition of tyrosinase activity and inhibition of melanin synthesis in B16F10 melanoma cells. However, the compounds exhibited nearly similar inhibitory effects on the activity of cellular tyrosinase and melanin synthesis in murine melanocytes. The inhibition of melanin synthesis by mulberroside A and oxyresveratrol was involved in suppressing the expression level of melanogenic enzymes, tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). These results indicate that the inhibition rate of mushroom tyrosinase might not provide an accurate estimate of the inhibition rate of melanin synthesis in melanocytes.     

Pigment-cell-specific genes from fibroblasts are transactivated after chromosomal transfer into melanoma cells.

Human and mouse fibroblast chromosomes carrying tyrosinase or b-locus genes were introduced, by microcell hybridization, into pigmented Syrian hamster melanoma cells, and the microcell hybrids were tested for transactivation of the fibroblast tyrosinase and b-locus genes. By using species-specific PCR amplification to distinguish fibroblast and melanoma cDNAs, it was demonstrated that the previously silent fibroblast tyrosinase and b-locus genes were transactivated following chromosomal transfer into pigmented melanoma cells. However, transactivation of the mouse fibroblast tyrosinase gene was unstable in microcell hybrid subclones and possibly dependent on a second fibroblast locus that could have segregated in the subclones. This second locus was not necessary for transactivation of the fibroblast b-locus gene, thus demonstrating noncoordinate transactivation of fibroblast tyrosinase and b-locus genes. Transactivation of the fibroblast tyrosinase gene in microcell hybrids apparently is dependent on the absence of a putative fibroblast extinguisher locus for tyrosinase gene expression, which presumably is responsible for the extinction of pigmentation in hybrids between karyotypically complete fibroblasts and melanoma cells.     

Investigation of the regulation of pigmentation in alpha-melanocyte-stimulating hormone responsive and unresponsive cultured B16 melanoma cells

In vitro melanocyte-stimulating hormone (MSH) stimulates melanogenesis in some, but not all, melanocytes and melanoma cells. In an attempt to explain this variation in response to alpha MSH, we examined cyclic adenosine monophosphate (cAMP) accumulation, tyrosinase activity, and melanin production in primary (1 degree) murine B16 melanoma cells and in two B16 cell lines (B16 F1 and B16 F10) that are known to respond to alpha MSH. In vivo all three B16 melanoma cell types produced pigmented tumours. In vitro alpha MSH increased tyrosinase activity and melanin content in the F1 and F10 cells but not in the B16 1 degree cells. alpha MSH, however, increased cAMP production in all three cell types, confirming that the inability of B16 1 degree cells to produce melanin in response to alpha MSH is not due to a lack of alpha MSH receptors or cAMP response to alpha MSH. Further, we present evidence for a separate pathway of melanogenesis that is independent of cAMP as calmodulin antagonists, which do not elevate cAMP, increased tyrosinase activity, and melanin production in both 1 degree and F1 cells.     

Evaluation of the inhibition of mushroom tyrosinase and cellular tyrosinase activities of oxyresveratrol: comparison with mulberroside A

The inhibitory effects of oxyresveratrol, the aglycone of mulberroside A, on mushroom and cellular tyrosinase activities and melanin synthesis were evaluated. Mulberroside A and oxyresveratrol showed inhibitory activity against mushroom tyrosinase, with oxyresveratrol demonstrating a greater inhibitory effect than that of mulberroside A. Oxyresveratrol and mulberroside A strongly inhibited melanin production in Streptomyces bikiniensis and exhibited dose-dependent inhibition of tyrosinase activity and inhibition of melanin synthesis in B16F10 melanoma cells. However, the compounds exhibited nearly similar inhibitory effects on the activity of cellular tyrosinase and melanin synthesis in murine melanocytes. The inhibition of melanin synthesis by mulberroside A and oxyresveratrol was involved in suppressing the expression level of melanogenic enzymes, tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). These results indicate that the inhibition rate of mushroom tyrosinase might not provide an accurate estimate of the inhibition rate of melanin synthesis in melanocytes.