PI4K2β/AP-1-based TGN-endosomal sorting regulates Wnt signaling.

Area of Science:

• Cell Biology
• Molecular Biology
• Developmental Biology

Background:

• Endosomal membrane traffic is vital for cellular functions, including signaling and development.
• Adaptor protein 1 (AP-1) regulates sorting between endosomes and the trans-Golgi network (TGN), requiring phosphatidylinositol 4-phosphate [PI(4)P].
• The precise PI4 kinase isozymes generating this PI(4)P pool and the role of TGN/endosomal sorting in Wnt-receiving cells are unknown.

Purpose of the Study:

• To identify the PI4 kinase isozyme involved in AP-1 recruitment and TGN/endosomal sorting.
• To investigate the role of TGN/endosomal sorting in Wnt signaling.
• To elucidate the mechanism by which PI4K2β regulates Wnt signaling.

Main Methods:

• Interaction studies between PI4K2β and AP-1.
• Zebrafish embryo depletion experiments for PI4K2β and AP-1.
• Wnt signaling pathway analysis and gene expression studies.
• Analysis of Frizzled (Fz) receptor endosomal recycling.

Main Results:

• PI4-kinase type 2β (PI4K2β) was identified as a regulator of TGN/endosomal sorting and Wnt signaling.
• PI4K2β and AP-1 directly interact and are essential for efficient endosome-TGN sorting.
• Depletion of PI4K2β or AP-1 in zebrafish embryos resulted in defective Wnt signaling and lack of pectoral fins.
• PI4K2β binds Dishevelled (Dvl), regulates Fz receptor recycling, and influences Wnt target gene expression.

Conclusions:

• PI4K2β and AP-1 form a complex that couples phosphoinositide metabolism to AP-1-mediated sorting.
• This complex plays a conserved role in regulating Wnt signaling through endosomal sorting and receptor recycling.
• PI4K2β is a critical regulator of Wnt signaling, impacting developmental processes like pectoral fin formation.