Distinct Effects of Wntless on WNT1 and WNT3A Signaling: A Difference in Binding Affinity
Benjamin Lee
Department of Biology
Faculty Supervisor: Laura (Kai) Burrus
In developing embryos, cell-cell communication regulates proliferation, specification, and differentiation. Ligands, such as the Wnt family of proteins, are required to transmit information between cells. Wnts are translated, lipid-modified, and escorted to the cell membrane by Wntless (WLS). Wnts are then transported to receiving cells where they bind to Frizzled receptors triggering a cascade of reactions resulting in the transcription of downstream genes. However, the mechanism underlying Wnt transport remains unclear. Our research has shown that co-expression of WLS with WNT1 redistributes WNT1 from the ER to the cell membrane, induces new filopodia, and augments WNT1 signaling in HEK293T cells, thus suggesting a role for filopodia in signaling. As WLS is required for the biological activity of all lipid-modified Wnts in drosophila, we hypothesized that WLS would have similar effects on the ability of WNT3A, which is functionally redundant with WNT1, to redistribute WNT3A, induce new filopodia, and augment signaling. Consistent with our hypothesis, WLS redistributed WNT3A and induced new filopodia. However, WLS augmented WNT1 signaling far greater than for WNT3A, leading us to predict that WLS binds WNT1 with a higher affinity than WNT3A, and through a co-immunoprecipitation, we found that WLS binds WNT1 more than WNT3A. Our results suggest that WLS interacts with both WNT1 and WNT3A and promotes the subcellular redistribution of both ligands and the induction of new filopodia by both ligands but has a stronger affinity for WNT1. This stronger affinity may explain the more robust effect of WLS on WNT1 signaling than WNT3A.