Structural insights into Wnt/β-catenin signaling regulation by LGR4, R-spondin, and ZNRF3

Area of Science:

• Structural Biology
• Molecular Biology
• Cell Signaling

Background:

• Leucine-rich repeat-containing G protein-coupled receptor 4 (LGR4) is vital for Wnt/β-catenin signaling, organ development, and carcinogenesis.
• LGR4 and its ligand R-spondin (RSPO) enhance Wnt signaling by recruiting and clearing the suppressor Zinc and Ring Finger 3 (ZNRF3).
• The precise mechanisms of LGR4-RSPO-ZNRF3 interaction remain largely unelucidated.

Purpose of the Study:

• To determine the structural basis of LGR4-RSPO2-ZNRF3 complex formation.
• To elucidate the mechanism by which LGR4 and RSPO2 potentiate Wnt/β-catenin signaling.
• To provide a foundation for therapeutic strategies targeting the LGR4-RSPO2-ZNRF3 pathway.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was employed to resolve the structures of human LGR4, LGR4-RSPO2, and the LGR4-RSPO2-ZNRF3 complex.
• Analysis of conformational changes in LGR4 upon RSPO2 binding.
• Characterization of the stoichiometry and architecture of the ternary complex.

Main Results:

• LGR4 exhibits minimal conformational changes in its extracellular and transmembrane domains upon RSPO2 binding.
• The LGR4, RSPO2, and ZNRF3 proteins assemble into a precise 2:2:2 stoichiometry, forming a central ZNRF3 dimer.
• This specific ternary complex formation explains how LGR4 and RSPO2 enhance Wnt signaling by sequestering and inactivating ZNRF3.

Conclusions:

• The study provides the first structural evidence for the LGR4-RSPO2-ZNRF3 complex, revealing a unique 2:2:2 architecture.
• This structural understanding clarifies the mechanism of Wnt/β-catenin signaling potentiation via LGR4 and RSPO2.
• The findings offer potential avenues for developing novel therapeutics targeting cancer and developmental disorders associated with this pathway.