Investigating Frizzled7-driven regulation of Vangl1 in Wnt/PCP signaling in breast cancer

Wnt/Planar Cell Polarity (Wnt/PCP) signaling is a non-canonical developmental pathway reactivated during tumorigenesis in many cancers, where it promotes tumor aggressiveness and correlates with poor prognosis (Hatakeyama et al., 2014). Vangl1, a transmembrane scaffolding protein specific to Wnt/PCP signaling, is an important site for assembly of protein complexes which drive cytoskeletal rearrangement at the leading edge of migratory cells, thereby supporting metastasis (Dreyer et al., 2023). Vangl1 interacts with the Wnt/PCP transmembrane receptor Frizzled7 both intercellularly-to promote polarity and establish epithelial organization-and intracellularly-to drive localized signaling events that promote migration. However, the regulatory relationship between Vangl1 and Frizzled7 is not fully understood.We recently found that Vangl1 undergoes a Frizzled7-dependent post-translational modification, evident from a mobility shift on SDS-PAGE upon Frizzled7 overexpression. Biochemical assays revealed this is a phosphorylation event that: (1) requires Vangl1's C-terminal PDZ-binding motif, (2) occurs independently of Wnt5a (the presumed Wnt/PCP ligand), and (3) persists despite mutation of two candidate phosphorylation sites-leaving the true sites undetermined.To identify key players and investigate functional consequences of this phosphorylation event, we performed Vangl1 immunoprecipitation-mass spectrometry (IP-MS) with and without Frizzled7 expression. The results identified several Vangl1 interactors, both known and novel, whose binding is altered by Frizzled7. These findings suggest that Frizzled7 may regulate Vangl1 function through phosphorylation-dependent modulation of its protein interactions and provide a foundation for future studies on how these interactions influence cancer cell migration and metastatic behavior.