Fujimura Naoko, Vacik Tomas, Machon Ondrej, Vlcek Cestmir, Scalabrin Simone, Speth Martin, Diep Dzung, Krauss Stefan, Kozmik Zbynek
Institute of Molecular Genetics, Academy of Sciences of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech Republic.
J Biol Chem. 2007 Jan 12;282(2):1225-37. doi: 10.1074/jbc.M605851200. Epub 2006 Nov 6.
Wnt/beta-catenin signaling regulates many processes during vertebrate development. To study transcriptional targets of canonical Wnt signaling, we used the conditional Cre/loxP system in mouse to ectopically activate beta-catenin during central nervous system development. We show that the activation of Wnt/beta-catenin signaling in the embryonic mouse telencephalon results in the up-regulation of Sp5 gene, which encodes a member of the Sp1 transcription factor family. A proximal promoter of Sp5 gene is highly evolutionarily conserved and contains five TCF/LEF binding sites that mediate direct regulation of Sp5 expression by canonical Wnt signaling. We provide evidence that Sp5 works as a transcriptional repressor and has three independent repressor domains, called R1, R2, and R3, respectively. Furthermore, we show that the repression activity of R1 domain is mediated through direct interaction with a transcriptional corepressor mSin3a. Finally, our data strongly suggest that Sp5 has the same DNA binding specificity as Sp1 and represses Sp1 target genes such as p21. We conclude that Sp5 transcription factor mediates the downstream responses to Wnt/beta-catenin signaling by directly repressing Sp1 target genes.
Wnt/β-连环蛋白信号通路在脊椎动物发育过程中调控许多过程。为了研究经典Wnt信号通路的转录靶点，我们在小鼠中使用条件性Cre/loxP系统，在中枢神经系统发育过程中异位激活β-连环蛋白。我们发现，在胚胎小鼠端脑中激活Wnt/β-连环蛋白信号通路会导致Sp5基因上调，该基因编码Sp1转录因子家族的一个成员。Sp5基因的近端启动子在进化上高度保守，包含五个TCF/LEF结合位点，介导经典Wnt信号通路对Sp5表达的直接调控。我们提供的证据表明，Sp5作为一种转录抑制因子，分别具有三个独立的抑制结构域，称为R1、R2和R3。此外，我们发现R1结构域的抑制活性是通过与转录共抑制因子mSin3a直接相互作用介导的。最后，我们的数据强烈表明，Sp5与Sp1具有相同的DNA结合特异性，并抑制Sp1靶基因如p21。我们得出结论，Sp5转录因子通过直接抑制Sp1靶基因介导对Wnt/β-连环蛋白信号通路的下游反应。
