Functional analysis of residues on Profilin1 that are modulated by Wnt signaling

Abstract

The non-canonical Wnt signaling pathway regulates the actin cytoskeleton controlling cell migration, cell polarity, and cell survival. The protein Profilin1 is a downstream effector of the non-canonical Wnt pathway and directly binds to actin to facilitate cytoskeleton rearrangement. Profilin1 binds to monomeric actin and brings it to the FH1 (Formin Homology 1) domain of Daam1. The neighboring FH2 (Formin Homology 2) domain nucleates actin and caps the growing end of the completed actin filament. It is currently unknown which amino acids on Profilin1 facilitate binding to Daam1 and actin in non-canonical Wnt signaling. In this study, I identified two residues on the Xenopus protein Profilin1- Tyrosine 131 and Serine 135- that play a role in non-canonical Wnt signaling. In this study, I was able to show that non-canonical Wnt signaling leads to the phosphorylation of Tyrosine 131. Mutating Tyrosine 131 to Alanine (Tyr131Ala) causes a cytokinesis defect preventing gastrulation in Xenopus embryos. Additionally, overexpression of PFN1-Tyr131Ala prevents Wnt5a-mediated actin fiber formation and increases multinucleation in HeLa cells. Mutating Serine 135 to Alanine (PFN1-Ser135Ala) lowers the binding affinity of Profilin1 to the FH1 domain of Daam1 but does not affect cytokinesis. The evidence presented in this study suggests that Tyr131 regulates gastrulation, while Ser135 plays a role in modulating binding of Profilin1 to Daam1. Further research into the molecular mechanism of regulation of Tyr131 and Ser135 in non-canonical Wnt signaling would be a major step in uncovering the mechanism of actin polymerization and a better understanding of cell signaling during vertebrate gastrulation.