Golan Tamar, Yaniv Abraham, Bafico Anna, Liu Guizhong, Gazit Arnona
Department of Human Microbiology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel.
J Biol Chem. 2004 Apr 9;279(15):14879-88. doi: 10.1074/jbc.M306421200. Epub 2004 Jan 27.
Previously we have cloned the human Frizzled 1 (HFz1) and shown that it transmits the Wnt-3a-induced canonical pathway. We also cloned the human Frizzled 6 (HFz6) and show in the present study that, as opposed to HFz1, HFz6 did not activate the canonical Wnt pathway following exposure to various Wnts, whether belonging to the Wnt-1 or to the Wnt-5a group. Moreover we show that HFz6 repressed Wnt-3a-induced canonical signaling when co-expressed with HFz1. HFz6 repressed the canonical Wnt cascade activated also by various Wnt signaling intracellular mediators such as Dishevelled-1, a stabilized beta-catenin(S33Y) mutant, and LiCl-mediated repression of glycogen synthase kinase-3beta activity. Removal of HFz6 N'- or C'-terminal sequences abolished HFz6 repressive activity. As the HFz6 repressive effect was not associated with a decrease in the level of beta-catenin, it is suggested that HFz6 does not affect beta-catenin stabilization, implying that HFz6 transmits a repressive signaling that cross-talks with and inhibits the canonical Wnt pathway downstream of beta-catenin destruction complex. HFz6 did not affect the level of nuclear T-cell factor 4 (TCF4) nor did it affect beta-catenin.TCF4 complex formation. However, electrophoretic mobility shift assays indicated that HFz6 repressed the binding of TCF/lymphoid enhancer factor transcription factors to target DNA. Moreover we present data suggesting that HFz6 activates the transforming growth factor-beta-activated kinase-NEMO-like kinase pathway that blocks TCF/lymphoid enhancer factor binding to target promoters, thereby inhibiting the ability of beta-catenin to activate transcription of Wnt target genes.
此前我们已克隆出人类卷曲蛋白1（HFz1），并表明它能传递Wnt-3a诱导的经典信号通路。我们还克隆了人类卷曲蛋白6（HFz6），且在本研究中发现，与HFz1不同，HFz6在暴露于各种Wnt（无论是属于Wnt-1组还是Wnt-5a组）后并未激活经典Wnt信号通路。此外，我们发现当与HFz1共表达时，HFz6会抑制Wnt-3a诱导的经典信号传导。HFz6还能抑制由各种Wnt信号细胞内介质激活的经典Wnt级联反应，如Dishevelled-1、稳定的β-连环蛋白（S33Y）突变体以及LiCl介导的糖原合酶激酶-3β活性的抑制。去除HFz6的N端或C端序列会消除HFz6的抑制活性。由于HFz6的抑制作用与β-连环蛋白水平的降低无关，因此表明HFz6不影响β-连环蛋白的稳定性，这意味着HFz6传递了一种抑制性信号，该信号与β-连环蛋白破坏复合体下游的经典Wnt信号通路相互作用并抑制它。HFz6不影响核内T细胞因子4（TCF4）的水平，也不影响β-连环蛋白与TCF4复合体的形成。然而，电泳迁移率变动分析表明，HFz6抑制了TCF/淋巴细胞增强因子转录因子与靶DNA的结合。此外，我们提供的数据表明，HFz6激活了转化生长因子-β激活激酶-NEMO样激酶信号通路，该通路阻断了TCF/淋巴细胞增强因子与靶启动子的结合，从而抑制了β-连环蛋白激活Wnt靶基因转录的能力。
