Untangling Frizzled functions

Abstract

Wnt signaling is a complex network of cellular signals with multiple downstream pathways regulated by signaling complexes comprised of combinations of the 19 Wnt ligands, 10 Frizzled (FZD) receptors, various co‐receptors and Dishevelled (DVL) second messengers. Up until now, Wnt receptors have either been functionally defined as whole families or individually by how they affect specific disease states when they are dysregulated, but the specific roles each receptor plays in Wnt signaling and activating the various pathways have yet to be fully understood.CRISPR is a powerful tool that has allowed whole families of protein isomers to be knocked out. By using cellular models that have been modified by CRISPR/Cas9 and are missing key proteins in the Wnt signaling complex, we can determine their individual functions and redundancies.We have determined that a FZD is necessary but any of the individual receptors is sufficient for DVL phosphorylation. Additionally, we have found that some Wnt signals can be rescued by single receptors, or just part of a receptor, while others seem to require multiple FZDs. The expression of these receptors is crucial for not only regulation within the Wnt family of pathways, but we also discovered a new arm of crosstalk with mTOR signaling.Wnt signaling is known to play key roles in many aspects of development, but erroneous signaling can cause diseases such as cancer and osteoporosis. Current therapeutics act as a sledgehammer and target all Wnt signaling, which leads to many off‐target effects and unintended side‐effects. Since cell surface receptors are typically the easiest to therapeutically target, FZD receptors have considerable therapeutic potential. Understanding the roles of each FZD receptor will allow us to better target individual disease mechanisms.