Date Published: February 22, 2019
Publisher: Public Library of Science
Author(s): Naushad Moti, Jia Yu, Gaelle Boncompain, Franck Perez, David M. Virshup, Yi Li.
Wnts are a family of secreted palmitoleated glycoproteins that play key roles in cell to cell communication during development and regulate stem cell compartments in adults. Wnt receptors, downstream signaling cascades and target pathways have been extensively studied while less is known about how Wnts are secreted and move from producing cells to receiving cells. We used the synchronization system called Retention Using Selective Hook (RUSH) to study Wnt trafficking from endoplasmic reticulum to Golgi and then to plasma membrane and filopodia in real time. Inhibition of porcupine (PORCN) or knockout of Wntless (WLS) blocked Wnt exit from the ER. Wnt-containing vesicles paused at sub-cortical regions of the plasma membrane before exiting the cell. Wnt-containing vesicles were associated with filopodia extending to adjacent cells. These data visualize and confirm the role of WLS and PORCN in ER exit of Wnts and support the role of filopodia in Wnt signaling.
Wnt proteins are secreted morphogens that play an important role in a variety of biological processes ranging from embryonic development, proliferation, differentiation, adult tissue homeostasis and cancers [1–3]. Wnts bind to cell surface receptors to activate diverse signaling pathways, the best-studied of which leads to the stabilization of β-catenin and the activation of target gene expression. Less is known about how Wnts travel from one cell to engage receptors on neighboring cells [4–6].
Cell-to-cell communication is a vital step in the regulation of growth, development and homeostasis via secretory proteins. Understanding the mechanism underlying the transmission of signals through tissues is of profound interest and requires robust assays for their study. We show here that the quantitative and real-time RUSH system is well suited to study the production and movement of biologically active fluorescent-tagged Wnt proteins from the time of their initial synthesis to their movement to the cell surface . The RUSH system also demonstrated Wnt-containing vesicles travelling via filopodia to neighboring cells, a phenomenon previously described in Drosophila and zebrafish but not to our knowledge in human cells.