In B16 melanoma cells, the inhibition of melanogenesis by TPA results from PKC activation and diminution of microphthalmia binding to the M-box of the tyrosinase promoter
In B16 melanoma cells, the inhibition of melanogenesis by TPA results from PKC activation and diminution of microphthalmia binding to the M-box of the tyrosinase promoter
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DOI：
10.1038/sj.onc.1201685
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发表时间：
1998-04-02
期刊：
影响因子：
8
通讯作者：
Ballotti, R
中科院分区：
文献类型：
--
作者：
Bertolotto, C;Bille, K;Ballotti, R
在B16黑色素瘤细胞中，cAMP诱导的黑色素生成被促进肿瘤的佛波酯TPA抑制，然而，PKC激活或耗竭在TPA抑制黑色素生成中的作用仍然存在争议。在本报告中，使用特定的PKC抑制剂，证明PKC抑制不会损害cAMP诱导的黑色素合成和酪氨酸酶表达。此外，TPA对黑色素生成的抑制是由于TPA的减少所致。酪氨酸酶启动子转录活性，并且这种效应是通过 PKC α 的组成型活性形式的过表达来模拟的。这些发现清楚地表明 PKC 激活是 TPA 抑制黑色素合成的原因。进行了其他实验以阐明 TPA 抑制酪氨酸酶基因转录的机制。酪氨酸酶启动子中的缺失和突变表明 TPA 作用于参与组织特异性表达和调节的 M-box。酪氨酸酶基因的 cAMP，我们发现 TPA 降低了小眼（一种碱性螺旋-环-螺旋转录因子）与 M-box 的结合。由于小眼症强烈刺激启动子的转录活性，我们认为TPA通过PKC激活，减少小眼症与酪氨酸酶启动子M-box的结合，从而导致酪氨酸酶表达减少和黑素生成抑制。
In B16 melanoma cells, cAMP-induced melanogenesis is inhibited by the tumor promoting phorbol ester, TPA, However, the role of PKC activation or depletion in the inhibition of melanogenesis by TPA remains controversial, In this report, using specific PKC inhibitors, ne demonstrated that PKC inhibition does not impair cAMP-induced melanin synthesis and tyrosinase expression, Further, the inhibition of melanogenesis by TPA results from a decrease of the tyrosinase promoter transcriptional activity and this effect is mimicked by over-expression of a constitutively active form of PKC alpha, These findings clearly demonstrate that PKC activation accounts for the inhibition of melanin synthesis by TPA, Additional experiments were undertaken to elucidate the mechanism by which TPA inhibits the tyrosinase gene transcription, Deletions and mutation in the tyrosinase promoter showed that TPA acts on a M-box which is involved in tissue-specific expression and regulation ba cAMP of the tyrosinase gene, We showed that TPA decreases the binding of microphthalmia, a basic helix-loop-helix transcription factor, to the M-box. Since microphthalmia, strongly stimulates the transcriptional activity of the promoter we propose that TPA, through PKC activation, decreases microphthalmia binding to the M-box of the tyrosinase promoter, thereby leading to a reduced tyrosinase expression and melanogenesis inhibition.