Brown Foundation Institute of Molecular Medicine, Texas Therapeutics Institute, University of Texas Health Science Center at Houston, Houston, Texas, USA.
Mol Cell Biol. 2012 Jun;32(11):2054-64. doi: 10.1128/MCB.00272-12. Epub 2012 Apr 2.
LGR5, a seven-transmembrane domain receptor of the rhodopsin family, is a Wnt target gene and a bona fide marker of adult stem cells in the gastrointestinal tract and hair follicle bulge. Recently, we and others demonstrated that LGR5 and its homologues function as receptors of the R-spondin family of stem cell factors to potentiate Wnt/β-catenin signaling. However, the mechanism of how LGR5 enhances the signaling output remains unclear. Here we report that following costimulation with the ligands R-spondin1 and Wnt3a, LGR5 interacts and forms a supercomplex with the Wnt coreceptors LRP6 and Fzd5 which is rapidly internalized and then degraded. Internalization of LGR5 is mediated through a dynamin- and clathrin-dependent pathway. Inhibition of this endocytic process has no effect on LGR5 signaling. Deletion of the C-terminal tail of LGR5 maintains its ability to interact with LRP6, yet this LGR5 mutant exhibits increased signaling activity and a decreased rate of endocytosis in response to R-spondin1 compared to the wild-type receptor. This study provides direct evidence that LGR5 becomes part of the Wnt signaling complex at the membrane level to enhance Wnt/β-catenin signaling. However, internalization of LGR5 does not appear to be essential for potentiating the canonical Wnt signaling pathway.
LGR5 是七次跨膜结构域的视紫红质家族受体，是 Wnt 的靶基因，也是胃肠道和毛囊隆突中成年干细胞的真正标志物。最近，我们和其他人证明，LGR5 及其同源物作为干细胞因子 R 分泌蛋白家族的受体发挥作用，增强 Wnt/β-catenin 信号。然而，LGR5 增强信号输出的机制尚不清楚。在这里，我们报告说，在与配体 R 分泌蛋白 1 和 Wnt3a 共刺激后，LGR5 与 Wnt 核心受体 LRP6 和 Fzd5 相互作用并形成超复合物，该复合物迅速内化并随后降解。LGR5 的内化是通过网格蛋白和动力蛋白依赖性途径介导的。抑制这个内吞过程对 LGR5 信号没有影响。LGR5 的 C 端尾部缺失保持其与 LRP6 相互作用的能力，但与野生型受体相比，这种 LGR5 突变体在响应 R 分泌蛋白 1 时表现出增加的信号活性和降低的内化率。这项研究提供了直接的证据，表明 LGR5 在膜水平上成为 Wnt 信号复合物的一部分，以增强 Wnt/β-catenin 信号。然而，LGR5 的内化似乎不是增强经典 Wnt 信号通路所必需的。
