Exploratory Research Center on Life and Living Systems (ExCELLS), National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki, Aichi, 444-8787, Japan.
National Institute for Basic Biology, National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji-cho, Okazaki, Aichi, 444-8787, Japan.
Commun Biol. 2024 Mar 1;7(1):254. doi: 10.1038/s42003-024-05881-8.
Wnt proteins are thought to be transported in several ways in the extracellular space. For instance, they are known to be carried by exosomes and by Wnt-carrier proteins, such as sFRP proteins. However, little is known about whether and/or how these two transport systems are related. Here, we show that adding sFRP1 or sFRP2, but not sFRP3 or sFRP4, to culture medium containing Wnt3a or Wnt5a increases re-secretion of exosome-loaded Wnt proteins from cells. This effect of sFRP2 is counteracted by heparinase, which removes sugar chains on heparan sulfate proteoglycans (HSPGs), but is independent of LRP5/6, Wnt co-receptors essential for Wnt signaling. Wnt3a and Wnt5a specifically dimerize with sFRP2 in culture supernatant. Furthermore, a Wnt3a mutant defective in heterodimerization with sFRP2 impairs the ability to increase exosome-mediated Wnt3a re-secretion. Based on these results, we propose that Wnt heterodimerization with its carrier protein, sFRP2, enhances Wnt accumulation at sugar chains on HSPGs on the cell surface, leading to increased endocytosis and exosome-mediated Wnt re-secretion. Our results suggest that the range of action of Wnt ligands is controlled by coordination of different transport systems.
Wnt 蛋白被认为以多种方式在细胞外空间中运输。例如，已知它们被外泌体和 Wnt 载体蛋白（如 sFRP 蛋白）携带。然而，对于这两种运输系统是否以及如何相关知之甚少。在这里，我们表明，在含有 Wnt3a 或 Wnt5a 的培养基中添加 sFRP1 或 sFRP2，但不添加 sFRP3 或 sFRP4，会增加细胞重新分泌含有外泌体的 Wnt 蛋白。sFRP2 的这种作用被肝素酶抵消，肝素酶去除硫酸乙酰肝素蛋白聚糖（HSPGs）上的糖链，但不依赖于 LRP5/6，LRP5/6 是 Wnt 信号所必需的 Wnt 共受体。Wnt3a 和 Wnt5a 在培养上清液中与 sFRP2 特异性二聚化。此外，Wnt3a 突变体与 sFRP2 异二聚化缺陷会损害增加外泌体介导的 Wnt3a 再分泌的能力。基于这些结果，我们提出 Wnt 与其载体蛋白 sFRP2 的异二聚化增强了 Wnt 在 HSPG 上糖链上的积累，导致内吞作用增加和外泌体介导的 Wnt 再分泌。我们的结果表明，Wnt 配体的作用范围受不同运输系统协调的控制。
