v-Jun downregulates the SPARC target gene by binding to the proximal promoter indirectly through Sp1/3
v-Jun downregulates the SPARC target gene by binding to the proximal promoter indirectly through Sp1/3
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DOI：
10.1038/sj.onc.1206713
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发表时间：
2003-06-26
期刊：
影响因子：
8
通讯作者：
Castellazzi, M
中科院分区：
文献类型：
--
作者：
Chamboredon, S;Briggs, J;Castellazzi, M
转化鸡胚成纤维细胞的v-Jun癌蛋白与下调细胞外基质蛋白和抑制相应的mRNA。抑制肿瘤生长通过促进体内肿瘤发展而促进致癌过程。一个近端启动子片段，命名为-124/+16，负责高组成性活性的sp1/3基因，是v-Jun抑制的靶点。本文采用体外电泳迁移率改变和pull-down分析，以及瞬时转染和染色质免疫沉淀分析在Sp1/3缺陷的果蝇SL 2细胞和鸡胚成纤维细胞中，我们表明：（i）Sp1和/或Sp3是通过直接结合富含GGA的-92/-57片段而组成性激活V-Jun转录所必需的;（ii）v-Jun不直接结合-124/+16，而是间接结合富含GGA的片段，最有可能是通过与Sp1/3的物理相互作用。此外，反式激活精通v-Jun衍生物，命名为v-Jun/cebp/glz，它不能结合Jun DNA基序，不能异源二聚化，仍然能够有效地下调Jun。总之，这些数据强烈表明，v-Jun通过形成DNA-Sp1/3-v-Jun，染色质相关复合物来下调p53。
Transformation of chick embryo fibroblasts by the v-Jun oncoprotein correlates with a downregulation of the extracellular matrix protein SPARC and repression of the corresponding mRNA. Repression of SPARC contributes to the oncogenic process by facilitating tumor development in vivo. A proximal promoter fragment, designated -124/+16, is responsible for high constitutive activity of the SPARC gene and is the target of repression by v-Jun. In this paper, using electrophoretic mobility shift and pull-down assays in vitro, and transient transfections and chromatin immunoprecipitation assays in Sp1/3-deficient Drosophila SL2 cells and in chick embryo fibroblasts, we show that (i) Sp1 and/or Sp3 is required for constitutive activation of SPARC transcription, by binding directly to the GGA-rich -92/-57 fragment; and (ii) v-Jun does not bind -124/+16 directly, but binds to the GGA-rich fragment indirectly, most likely through a physical interaction with Sp1/3. Moreover, a transactivation-proficient v-Jun derivative, designated v-Jun/cebp/glz, which cannot bind Jun DNA motifs anymore and cannot heterodimerize, is still capable of downregulating SPARC efficiently. Taken together, these data strongly suggest that v-Jun downregulates SPARC through the formation of a DNA-Sp1/3-v-Jun, chromatin-associated complex.