WLS-dependent secretion of WNT3A requires Ser209 acylation and vacuolar acidification

Area of Science:

• Cell Biology
• Developmental Biology
• Biochemistry

Background:

• Wnt proteins are essential secreted signaling molecules regulating cell development and proliferation.
• The precise mechanisms governing Wnt secretion and the roles of accessory factors remain incompletely understood.
• Wnt secretion involves post-translational modifications and interactions with specific carrier proteins like Wntless (WLS).

Purpose of the Study:

• To investigate the role of vacuolar acidification in Wnt secretion.
• To identify small molecules that modulate Wnt secretion.
• To elucidate the mechanism by which Wntless (WLS) facilitates Wnt release.

Main Methods:

• Conducted a small molecule screen to identify inhibitors of Wnt secretion.
• Utilized cultured human cells and Xenopus embryos for in vitro and in vivo studies.
• Employed biochemical assays to analyze Wnt-WLS complex formation and Wnt modification.
• Performed computational modeling to predict WLS structure and function.

Main Results:

• Inhibitors of vacuolar acidification, including V-ATPase inhibitors, potently blocked Wnt secretion and Wnt/β-catenin signaling.
• Disruption of vacuolar pH gradients impaired Wnt-regulated developmental processes in Xenopus embryos.
• Wntless (WLS) binds to Wnt proteins, requiring PORCN-dependent lipid modification of Wnt.
• Inhibition of vacuolar acidification led to the accumulation of the Wnt-WLS complex, suggesting a role in Wnt release from WLS.

Conclusions:

• Vacuolar acidification is essential for the efficient secretion of Wnt proteins.
• The Wntless (WLS) protein likely binds Wnts via a lipid-binding domain, and vacuolar acidification is required for releasing modified Wnts from WLS.
• These findings reveal a novel regulatory step in Wnt secretion, impacting developmental signaling pathways.