Cripto localizes Nodal at the limiting membrane of early endosomes

Area of Science:

• Cell biology
• Molecular signaling
• Protein interactions

Background:

• Cripto is a GPI-anchored co-receptor for Nodal and TGF-beta family ligands.
• It possesses EGF-like and CFC domains involved in ligand and receptor binding.
• The precise mechanism of Cripto in modulating Nodal activity remained unclear.

Purpose of the Study:

• To investigate the role of Cripto in Nodal localization and signaling.
• To elucidate the specific domains and residues of Cripto involved in Nodal interaction and trafficking.
• To understand how Cripto influences Nodal activity at the endosomal level.

Main Methods:

• Site-directed mutagenesis of Cripto protein.
• Analysis of Nodal binding and co-localization with Cripto in endosomes.
• Cellular assays to assess Nodal signaling pathway activation.

Main Results:

• The EGF-like motif of Cripto is not essential for Nodal binding.
• Specific residues (Phe78, Gly71) in Cripto are crucial for enriching Nodal at the early endosome membrane.
• Cripto's CFC domain residues mediating ALK4 binding are required to prevent Nodal sequestration within the endosome.
• Cripto acts as a novel GPI-anchored protein controlling intraendosomal cargo sorting.

Conclusions:

• Cripto enhances Nodal activity by controlling its localization at the interface of endosomes and cytoplasmic effectors.
• This study reveals a new function for GPI-anchored proteins in regulating the intraendosomal sorting of signaling molecules.
• Cripto's mechanism provides insights into the spatial regulation of TGF-beta superfamily signaling.