Direct Ubiquitination of β-Catenin by Siah-1 and Regulation by the Exchange Factor TBL1
Direct Ubiquitination of β-Catenin by Siah-1 and Regulation by the Exchange Factor TBL1
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DOI：
10.1074/jbc.m109.049411
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发表时间：
2010-04-30
影响因子：
4.8
通讯作者：
Chazin, Walter J.
中科院分区：
文献类型：
--
作者：
Dimitrova, Yoana N.;Li, Jiong;Chazin, Walter J.
beta-Catenin 是 Wnt 信号通路的关键组成部分，作为 Wnt 靶基因的转录共激活因子。在紫外线诱导的 DNA 损伤后，β-连环蛋白被一种独特的 p53 诱导的 SCF 样复合物 (SCF(TBL1)) 募集进行多泛素化和随后的蛋白酶体降解，该复合物由 Siah-1、Siah-1 相互作用蛋白 (SIP)、Skp1、转导蛋白 β 样 1 (TBL1) 和腺瘤性息肉病大肠杆菌 (APC) 组成。鉴于所涉及的各种因素的复杂性以及非磷酸化β-连环蛋白底物泛素化的新颖性，我们在体外和细胞中研究了Siah-1介导的β-连环蛋白泛素化。针对每种 SCF(TBL1) 蛋白开发了过表达和纯化方案，从而能够使用体外泛素化测定对 β-连环蛋白泛素化进行系统分析。这项研究表明，仅 Siah-1 就能够多泛素化 β-连环蛋白。此外，TBL1 还显示出在体外保护 β-catenin 免受 Siah-1 泛素化以及细胞中 Siah-1 靶向蛋白酶体降解的作用。 Siah-1 和 TBL1 被发现与 β-catenin 的相同犰狳重复结构域结合，表明 β-catenin 的多泛素化受到 Wnt 信号传导过程中 Siah-1 和 TBL1 之间竞争的调节。
beta-Catenin is a key component of the Wnt signaling pathway that functions as a transcriptional co-activator of Wnt target genes. Upon UV-induced DNA damage, beta-catenin is recruited for polyubiquitination and subsequent proteasomal degradation by a unique, p53-induced SCF-like complex (SCF(TBL1)), comprised of Siah-1, Siah-1-interacting protein (SIP), Skp1, transducin beta-like 1 (TBL1), and adenomatous polyposis coli (APC). Given the complexity of the various factors involved and the novelty of ubiquitination of the non-phosphorylated beta-catenin substrate, we have investigated Siah-1-mediated ubiquitination of beta-catenin in vitro and in cells. Overexpression and purification protocols were developed for each of the SCF(TBL1) proteins, enabling a systematic analysis of beta-catenin ubiquitination using an in vitro ubiquitination assay. This study revealed that Siah-1 alone was able to polyubiquitinate beta-catenin. In addition, TBL1 was shown to play a role in protecting beta-catenin from Siah-1 ubiquitination in vitro and from Siah-1-targeted proteasomal degradation in cells. Siah-1 and TBL1 were found to bind to the same armadillo repeat domain of beta-catenin, suggesting that polyubiquitination of beta-catenin is regulated by competition between Siah-1 and TBL1 during Wnt signaling.