Binding of canonical Wnt ligands to their receptor complexes occurs in ordered plasma membrane environments.

Erdinc Sezgin,Cathleen Teh,Christian Eggeling,Xue W Ng,Thorsten Wohland,Gilbert Weidinger,Kai Simons,Yagmur Azbazdar,Gunes Ozhan

doi:10.1111/febs.14139

Abstract

While the cytosolic events of Wnt/β‐catenin signaling (canonical Wnt signaling) pathway have been widely studied, only little is known about the molecular mechanisms involved in Wnt binding to its receptors at the plasma membrane. Here, we reveal the influence of the immediate plasma membrane environment on the canonical Wnt–receptor interaction. While the receptors are distributed both in ordered and disordered environments, Wnt binding to its receptors selectively occurs in more ordered membrane environments which appear to cointernalize with the Wnt‐receptor complex. Moreover, Wnt/β‐catenin signaling is significantly reduced when the membrane order is disturbed by specific inhibitors of certain lipids that prefer to localize at the ordered environments. Similarly, a reduction in Wnt signaling activity is observed in Niemann–Pick Type C disease cells where trafficking of ordered membrane lipid components to the plasma membrane is genetically impaired. We thus conclude that ordered plasma membrane environments are essential for binding of canonical Wnts to their receptor complexes and downstream signaling activity.

Highlights

Wnt/b-catenin signaling, referred to as the canonical Wnt pathway, plays pivotal roles in regulation of embryonic development, maintenance of tissue homeostasis and regeneration [1,2,3,4,5]
In the absence of an active canonical Wnt ligand, b-catenin is phosphorylated in the cytoplasm by a complex of proteins, the so-called destruction complex, which includes the serine–threonine kinases Glycogen synthase kinase 3 (Gsk3) and Casein kinase 1 (Ck1), the scaffold protein Axin and the tumor suppressor Adenomatous polyposis coli (APC), leading to proteasomal degradation of b-catenin and suppression of Wnt/b-catenin signaling [11]. b-Catenin signaling is triggered by the binding of a canonical Wnt ligand to a Frizzled (Fz) receptor and the coreceptor low-density lipoprotein receptor-related protein 6 (Lrp6) or its close relative Lrp5 [12]
To figure out the direct impact of membrane environment on canonical Wnt signaling, we first aimed to determine the localization of the ligand–receptor complex components of Wnt/b-catenin signaling within the plasma membrane of live HEK293T cells

Summary

Introduction

Wnt/b-catenin signaling, referred to as the canonical Wnt pathway, plays pivotal roles in regulation of embryonic development, maintenance of tissue homeostasis and regeneration [1,2,3,4,5]. Development of new therapeutic approaches for these diseases necessitates elucidation of the molecular mechanisms underlying fine-tuning of the pathway at various levels. This fine-tuning can be based on a variety of events including ligand–receptor complex formation, phosphorylation by kinases, adjustment of intracellular b-catenin levels, and tissuespecific modulator activities [7,8,9,10]. Wnt binding leads to the phosphorylation and endocytosis of Lrp5/6, which are both essential events for pathway activation [13,14,15] Another key determinant in pathway activation is the stability of cytoplasmic b-catenin. Lrp5/6 phosphorylation by Gsk and Ck1 leads to the recruitment of the cytoplasmic proteins, Disheveled (Dvl) and Axin, to the receptor complex, which in turn inhibits the destruction complex, allowing stabilized b-catenin to translocate into the nucleus and bind to the transcription factors of the lymphoid enhancer-binding factor (Lef) and T-cell factor (Tcf) family to activate target gene transcription [12,16]

Methods

Results

Conclusion