The Key Laboratory for Human Disease Gene Study of Sichuan Province and the Department of Laboratory Medicine, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, China.
Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan, China.
EMBO Rep. 2023 Jun 5;24(6):e55873. doi: 10.15252/embr.202255873. Epub 2023 Mar 30.
The membrane-tethered protease Tiki antagonizes Wnt3a signaling by cleaving and inactivating Wnt3a in Wnt-producing cells. Tiki also functions in Wnt-receiving cells to antagonize Wnt signaling by an unknown mechanism. Here, we demonstrate that Tiki inhibition of Wnt signaling at the cell surface requires Frizzled (FZD) receptors. Tiki associates with the Wnt-FZD complex and cleaves the N-terminus of Wnt3a or Wnt5a, preventing the Wnt-FZD complex from recruiting and activating the coreceptor LRP6 or ROR1/2 without affecting Wnt-FZD complex stability. Intriguingly, we demonstrate that the N-terminus of Wnt3a is required for Wnt3a binding to LRP6 and activating β-catenin signaling, while the N-terminus of Wnt5a is dispensable for recruiting and phosphorylating ROR1/2. Both Tiki enzymatic activity and its association with the Wnt-FZD complex contribute to its inhibitory function on Wnt5a. Our study uncovers the mechanism by which Tiki antagonizes Wnt signaling at the cell surface and reveals a negative role of FZDs in Wnt signaling by acting as Tiki cofactors. Our findings also reveal an unexpected role of the Wnt3a N-terminus in the engagement of the coreceptor LRP6.
膜锚定蛋白酶 Tiki 通过切割和使 Wnt 产生细胞中的 Wnt3a 失活来拮抗 Wnt3a 信号。Tiki 还通过未知机制在 Wnt 接收细胞中发挥作用，拮抗 Wnt 信号。在这里，我们证明 Tiki 在细胞表面抑制 Wnt 信号需要 Frizzled（FZD）受体。Tiki 与 Wnt-FZD 复合物结合并切割 Wnt3a 或 Wnt5a 的 N 端，阻止 Wnt-FZD 复合物招募和激活核心受体 LRP6 或 ROR1/2，而不影响 Wnt-FZD 复合物的稳定性。有趣的是，我们证明 Wnt3a 的 N 端对于 Wnt3a 与 LRP6 的结合和激活 β-catenin 信号是必需的，而 Wnt5a 的 N 端对于招募和磷酸化 ROR1/2 是可有可无的。Tiki 的酶活性及其与 Wnt-FZD 复合物的结合都有助于其对 Wnt5a 的抑制作用。我们的研究揭示了 Tiki 在细胞表面拮抗 Wnt 信号的机制，并揭示了 FZDs 通过作为 Tiki 辅助因子在 Wnt 信号中的负调控作用。我们的发现还揭示了 Wnt3a N 端在与核心受体 LRP6 结合中的意外作用。
