The EARP Complex and Its Interactor EIPR-1 Are Required for Cargo Sorting to Dense-Core Vesicles

Area of Science:

• Cell Biology
• Neuroscience
• Molecular Biology

Background:

• Dense-core vesicles are essential secretory organelles in neurons and neuroendocrine cells.
• The biogenesis and cargo-sorting mechanisms of dense-core vesicles remain incompletely understood.
• Previous work identified RAB-2 as a key regulator of dense-core vesicle cargo selection.

Purpose of the Study:

• To identify novel proteins involved in dense-core vesicle biogenesis and cargo sorting.
• To elucidate the functional relationships between RAB-2, EIPR-1, and the EARP complex in dense-core vesicle trafficking.
• To characterize the role of EIPR-1 and EARP in the formation and function of dense-core vesicles.

Main Methods:

• Forward genetic screen in Caenorhabditis elegans to identify mutants with defective dense-core vesicle function.
• Behavioral assays and cargo trafficking analysis in mutant strains.
• Genetic epistasis experiments to determine pathway interactions.
• Proteomic analysis in rat insulinoma cells to investigate protein-protein interactions.

Main Results:

• Identified the WD40 domain protein EIPR-1 and the endosome-associated recycling protein (EARP) complex as critical for dense-core vesicle cargo sorting.
• Mutants lacking EIPR-1 or EARP exhibit cargo-sorting defects similar to RAB-2 pathway mutants.
• Genetic data indicate that RAB-2, EIPR-1, and EARP function within a common pathway.
• EIPR-1 physically interacts with the EARP complex, suggesting a novel interaction.

Conclusions:

• EIPR-1 and the EARP complex are essential conserved factors for dense-core vesicle cargo sorting.
• Dense-core vesicle cargo sorting relies on EARP-dependent trafficking through an endosomal sorting compartment.
• These findings reveal a new pathway involving EIPR-1 and EARP that regulates the formation and function of specialized secretory vesicles.