BACKGROUND Microphthalmia-associated transcription factor (MITF) is regulated by expression and/or degradation pathway, controlling to the expression of melanogenic enzymes for melanin synthesis. Methyl-2-acetylamino-3-(4-hydroxyl-3,5-dimethoxybenzoylthio)propanoate (MAHDP) is reported to anti-melanogenesis effect but its mechanism remain unclear. OBJECTIVE To investigate the effects of MAHDP on melanogenesis and elucidate its mechanism. METHODS Tyrosinase activity, melanogenic proteins and gene expression levels were measured with MAHDP treatment in B16F1 cells, human melanocytes, reconstructed skin and clinical trial. RESULTS MAHDP attenuated melanin production in α-MSH (melanocyte stimulating hormone) stimulated-B16F1 cells. MAHDP decreased the expression of tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). But, MADPH did not affect the phosphorylation of p38 MAPK, JNK and AKT, which are associated with the regulation of MITF expression. These results suggest that MITF downstream is regulated not transcriptionally but translationally. Treatment of MG132 (a proteasomal degradation inhibitor) almost abolished the decrease of MITF protein levels by MAHDP. Phosphorylation and ubiquitination of MITF for proteasomal degradation were increased by treatment of MAHDP. Treatment of PD98059 (an ERK phosphorylation inhibitor) abrogated ERK phosphorylation, downregulation of MITF and tyrosinase as well as the decrease of melanin contents by MAHDP. Therefore, the degradation of MITF proteins by MAHDP is regulated to the ERK signaling. Finally, MAHDP improved the pigmentation in human epidermal melanocytes, a UVB-irradiated the reconstructed skin model and clinical trial without cytotoxicity and skin irritation. CONCLUSION These results clearly demonstrate that MAHDP suppresses the expression of melanogenic enzymes through ERK phosphorylation-mediated MITF proteasomal degradation, and suggest that MAHDP may be efficient as a therapeutic agent for hyperpigmentation.

中文翻译：

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Mmethyl-2-乙酰氨基-3-(4-羟基-3,5-二甲氧基苯甲酰硫基)丙酸酯通过 ERK 信号通路介导的 MITF 蛋白酶体降解抑制黑素生成。


背景技术小眼相关转录因子(MITF)通过表达和/或降解途径调节，控制黑色素合成的黑色素生成酶的表达。据报道，2-乙酰氨基-3-(4-羟基-3,5-二甲氧基苯甲酰硫基)丙酸甲酯(MAHDP)具有抗黑素生成作用，但其机制仍不清楚。目的探讨MAHDP对黑色素生成的影响并阐明其机制。方法 用 MAHDP 处理 B16F1 细胞、人黑素细胞、重建皮肤和临床试验，测量酪氨酸酶活性、黑素生成蛋白和基因表达水平。结果 MAHDP 减弱了 α-MSH（黑素细胞刺激激素）刺激的 B16F1 细胞中黑色素的产生。 MAHDP 降低酪氨酸酶、酪氨酸酶相关蛋白 1 (TRP-1) 和酪氨酸酶相关蛋白 2 (TRP-2) 的表达。但是，MADPH不影响p38 MAPK、JNK和AKT的磷酸化，这些磷酸化与MITF表达的调节有关。这些结果表明 MITF 下游不是转录调节而是翻译调节。 MG132（一种蛋白酶体降解抑制剂）的治疗几乎消除了 MAHDP 导致的 MITF 蛋白水平的降低。 MAHDP 处理增加了 MITF 的磷酸化和泛素化以促进蛋白酶体降解。 PD98059（一种 ERK 磷酸化抑制剂）的治疗消除了 ERK 磷酸化、MITF 和酪氨酸酶的下调以及 MAHDP 导致的黑色素含量的减少。因此，MAHDP 对 MITF 蛋白的降解受 ERK 信号传导的调节。最后，MAHDP改善了人表皮黑色素细胞的色素沉着，UVB照射重建的皮肤模型并进行临床试验，无细胞毒性和皮肤刺激。 结论 这些结果清楚地表明，MAHDP 通过 ERK 磷酸化介导的 MITF 蛋白酶体降解来抑制黑色素生成酶的表达，并表明 MAHDP 可能是有效的色素沉着过度治疗剂。