Downregulation Of Microphthalmia-associated Transcription Factor Research Articles

AVS-1357 inhibits melanogenesis via prolonged ERK activation.

In this study, we demonstrated that a derivative of imidazole, AVS-1357, is a novel skin-whitening compound. AVS-1357 was found to significantly inhibit melanin production in a dose-dependent manner; however, it did not directly inhibit tyrosinase. Furthermore, we found that AVS-1357 induced prolonged activation of extracellular signal-regulated kinase (ERK) and Akt, while it downregulated microphthalmia-associated transcription factor (MITF) and tyrosinase. It has been reported that the activation of ERK and/or Akt is involved in melanogenesis. Therefore, we examined the effects of AVS-1357 on melanogenesis in the absence or presence of PD98059 (a specific inhibitor of the ERK pathway) and/or LY294002 (a specific inhibitor of the Akt pathway). PD98059 dramatically increased melanogenesis, whereas LY294002 had no effect. Furthermore, PD98059 attenuated AVS-1357 induced ERK activation, as well as the downregulation of MITF and tyrosinase. These findings suggest that the effects of AVS-1357 occur via downregulation of MITF and tyrosinase, which is caused by AVS-1357-induced prolonged ERK activation. Taken together, our results indicate that AVS-1357 has the potential as a new skin whitening agent.

Long‐term suppression of tyrosinase by terrein via tyrosinase degradation and its decreased expression

Previously, we reported that a fungal metabolite, terrein, decreases melanin synthesis via downregulation of microphthalmia-associated transcription factor (MITF). In the present study, we further investigated the long-term hypopigmenting action of terrein in a spontaneously immortalized mouse melanocyte cell line, Mel-Ab. Treatment with terrein at a concentration of 50 mum strongly decreased melanogenesis in a time-dependent manner. Interestingly, the decreased tyrosinase protein levels lasted for at least 7 days, even though the MITF protein levels were restored after 3 days of treatment. In accordance with the results of Western blot analyses, the tyrosinase mRNA levels were found to be continuously decreased for at least 7 days, even though recovery of the MITF mRNA levels began after 3 days of terrein treatment. Therefore, we evaluated tyrosinase downregulation to determine if it is caused by proteasomal degradation. We found that the reduction in tyrosinase levels that was induced by terrein was clearly recovered by MG-132, a proteasome inhibitor. Moreover, ubiquitination of tyrosinase increased following treatment with terrein in the presence of MG-132. Taken together, these results suggest that terrein decreases melanogenesis through ubiquitin-dependent proteasomal degradation as well as via decreased expression of its mRNA.

Effect of xanthohumol on melanogenesis in B16 melanoma cells

Xanthohumol (XH), the principal prenylflavonoid of the hop plant (Humulus lupulus L.), dose-dependently inhibited isobutylmethylxanthine (IBMX)-induced melanogenesis in B16 melanoma cells, with little cytotoxicity at the effective concentrations. Decreased melanin content was accompanied by reduced tyrosinase enzyme activity, protein and mRNA expression. The levels of tyrosinase-related protein 1 and 2 mRNAs were decreased by XH. XH also inhibited alpha-melanocyte stimulating hormone- or forskolin-induced increases in melanogenesis, suggesting an action on the cAMP-dependent melanogenic pathway. XH downregulated the protein and mRNA expression of microphthalmia-associated transcription factor (MITF), a master transcriptional regulator of key melanogenic enzymes. These results suggest that XH might act as a hypo-pigmenting agent through the downregulation of MITF in the cAMP-dependent melanogenic pathway.

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.

Sphingosylphosphorylcholine‐induced ERK activation inhibits melanin synthesis in human melanocytes

Sphingosylphosphorylcholine (SPC) is emerging as a potent signaling-lipid mediator. In this study, we investigated the effects of SPC on melanogenesis using cultured human melanocytes. Our results show that SPC significantly inhibits melanin synthesis in a concentration-dependent manner, and further that it reduces the activity of tyrosinase, the rate-limiting melanogenic enzyme. SPC treatment was also found to induce short-thick dendrites in human melanocytes, but not to reduce tyrosinase activity in a cell-free system, whereas kojic acid directly inhibited tyrosinase. These results suggest that SPC reduces pigmentation by indirectly regulating tyrosinase. In further experiments, SPC was found to downregulate microphthalmia-associated transcription factor (MITF) and tyrosinase, and Western blotting showed that SPC induces the activations of extracellular signal-regulated kinase (ERK) and 90 kDa ribosomal S6 kinase (RSK-1). Moreover, the specific ERK pathway inhibitor, PD98059, blocked the hypopigmentation effect of SPC, and abrogated the SPC-mediated downregulation of MITF. These results suggest that the ERK pathway is involved in the melanogenic signaling cascade, and that ERK activation by SPC reduces melanin synthesis via MITF downregulation.

Terrein: a new melanogenesis inhibitor and its mechanism

Terrein is a bioactive fungal metabolite whose effects are almost unknown. In this study, we found for the first time that terrein has a strong hypopigmentary effect in a spontaneously immortalized mouse melanocyte cell line, Mel-Ab. Treatment of Mel-Ab cells with terrein (10-100 microM) for 4 days significantly reduced melanin levels in a dose-dependent manner. In addition, terrein at the same concentration also reduced tyrosinase activity. We then investigated whether terrein influences the extracellular signal-regulated protein kinase (ERK) pathway and the expression of microphthalmia-associated transcription factor (MITF), which is required for tyrosinase expression. Terrein was found to induce sustained ERK activation and MITF down-regulation, and luciferase assays showed that terrein inhibits MITF promoter activity in a dose-dependent manner. To elucidate the correlation between ERK pathway activation and a decreased MITF transcriptional level, PD98059, a specific inhibitor of the ERK pathway, was applied before terrein treatment and found to abrogate the terrein-induced MITF attenuation. Terrein also reduced the tyrosinase protein level for at least 72 h. These results suggest that terrein reduces melanin synthesis by reducing tyrosinase production via ERK activation, and that this is followed by MITF down-regulation.

Transforming growth factor-$beta;1 decreases melanin synthesis via delayed extracellular signal-regulated kinase activation

Transforming growth factor-β1 (TGF-β1) plays a pivotal role in cell proliferation, differentiation, and apoptosis. In this study, we investigated the effects of TGF-β1 on melanogenesis using a spontaneously immortalized mouse melanocyte cell line, Mel-Ab. Our results show that TGF-β1 significantly inhibits melanin synthesis in a concentration-dependent manner and that it reduces the activity of tyrosinase, the rate-limiting melanogenic enzyme. We also found that TGF-β1 reduces microphthalmia-associated transcription factor (MITF) promoter activity and decreased MITF, tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2 protein production. In addition, TGF-β1 was found to induce a delay in the activation of extracellular signal-regulated kinase (ERK) at 6 h, whereas many growth factors activate ERK transiently in minutes. Moreover, the specific ERK pathway inhibitor, PD98059 blocked the hypopigmenting effects induced by TGF-β1. PD98059 was also found to abrogate the TGF-β1-mediated down-regulation of MITF, tyrosinase, TRP-1, and TRP-2 production. These results suggest that the ERK pathway may be involved in the melanogenic signaling cascade, and that delayed ERK activation by TGF-β1 contributes to reduced melanin synthesis via MITF down-regulation.

Transforming growth factor-β1 decreases melanin synthesis via delayed extracellular signal-regulated kinase activation

Transforming growth factor-β1 (TGF-β1) plays a pivotal role in cell proliferation, differentiation, and apoptosis. In this study, we investigated the effects of TGF-β1 on melanogenesis using a spontaneously immortalized mouse melanocyte cell line, Mel-Ab. Our results show that TGF-β1 significantly inhibits melanin synthesis in a concentration-dependent manner and that it reduces the activity of tyrosinase, the rate-limiting melanogenic enzyme. We also found that TGF-β1 reduces microphthalmia-associated transcription factor (MITF) promoter activity and decreased MITF, tyrosinase, tyrosinase-related protein-1 (TRP-1), and TRP-2 protein production. In addition, TGF-β1 was found to induce a delay in the activation of extracellular signal-regulated kinase (ERK) at 6 h, whereas many growth factors activate ERK transiently in minutes. Moreover, the specific ERK pathway inhibitor, PD98059 blocked the hypopigmenting effects induced by TGF-β1. PD98059 was also found to abrogate the TGF-β1-mediated down-regulation of MITF, tyrosinase, TRP-1, and TRP-2 production. These results suggest that the ERK pathway may be involved in the melanogenic signaling cascade, and that delayed ERK activation by TGF-β1 contributes to reduced melanin synthesis via MITF down-regulation.

Effects of lysophosphatidic acid on melanogenesis

In this study, we investigated the effects of lysophosphatidic acid (LPA) on melanogenesis in Mel-Ab cells. We found that LPA significantly attenuates melanin synthesis, and reduces the activity of tyrosinase, the rate-limiting melanogenic enzyme. Interestingly, LPA was also found to induce the activation of a 90 kDa ribosomal S6 kinase (RSK-1), which is known to phosphorylate microphthalmia-associated transcription factor (MITF) at serine 409. Though it has been previously reported that the phosphorylation of MITF is followed by the degradation of MITF, we found that LPA significantly inhibited MITF promoter activity, and that this reduced MITF and tyrosinase protein production. Our results indicate that LPA contributes to reduced melanin synthesis via the down-regulation of MITF.