Murisier Fabien, Guichard Sabrina, Beermann Friedrich
Swiss Institute for Experimental Cancer Research (ISREC), National Center of Competence in Research (NCCR) Molecular Oncology, Chemin des Boveresses 155, 1066 Epalinges, Switzerland.
Pigment Cell Res. 2007 Jun;20(3):173-84. doi: 10.1111/j.1600-0749.2007.00368.x.
The terminal differentiation of melanocytes is associated with the transcriptional activation of genes responsible for pigment production such as tyrosinase. Pigment cell-specific transcription factors, such as Mitf, as well as specific proximal and distal regulatory elements (DRE) are implicated in the tight control of tyrosinase expression during development and adulthood. Proper tyrosinase expression in melanocytes depends upon the presence of a DRE that is located at -15 kb and provides enhancer activity via a central element termed core-enhancer. In this report, we show that the transcription factors Sox10, Mitf and USF-1 are able to activate the core-enhancer in luciferase reporter assays. Comparative sequence analysis identified evolutionarily motifs resembling Sox10 binding sites that were required for full enhancer activity in melanoma cells and in tyrosinase::lacZ transgenic mice. Sox10 was able to bind the DRE in vitro and mutation of the conserved motifs abolished the enhancer transactivation mediated by Sox10. In addition, two highly conserved CAGCTG E-box motifs were identified that were also required for enhancer activity and for transactivation by Mitf. The results suggest that Sox10 directly, and Mitf, most likely indirectly, activate the tyrosinase enhancer, underlining the contribution of Sox10 to tyrosinase gene regulation in melanocytes.
黑素细胞的终末分化与负责色素生成的基因（如酪氨酸酶）的转录激活相关。色素细胞特异性转录因子，如小眼畸形相关转录因子（Mitf），以及特定的近端和远端调控元件（DRE），参与了发育和成年期酪氨酸酶表达的严格调控。黑素细胞中酪氨酸酶的正常表达取决于一个位于-15 kb处的DRE的存在，该DRE通过一个称为核心增强子的中心元件提供增强子活性。在本报告中，我们表明转录因子Sox10、Mitf和USF-1能够在荧光素酶报告基因检测中激活核心增强子。比较序列分析确定了在黑素瘤细胞和酪氨酸酶::lacZ转基因小鼠中，与Sox10结合位点相似的、对完全增强子活性所必需的进化基序。Sox10能够在体外结合DRE，保守基序的突变消除了Sox10介导的增强子反式激活。此外，还鉴定出两个高度保守的CAGCTG E盒基序，它们也是增强子活性和Mitf反式激活所必需的。结果表明，Sox10直接激活，而Mitf很可能间接激活酪氨酸酶增强子，强调了Sox10对黑素细胞中酪氨酸酶基因调控的作用。
