FCH domain only-2 organizes clathrin-coated structures and interacts with Disabled-2 for low-density lipoprotein...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Clathrin-mediated endocytosis (CME) is vital for cellular uptake of receptors.
• Adaptor proteins like Disabled-2 (Dab2) and AP2 recruit cargo and accessory proteins for CME.
• Dab2 can mediate endocytosis independently of AP2, suggesting alternative accessory protein recruitment.

Purpose of the Study:

• To investigate if Dab2 recruits AP2-associated accessory proteins when AP2 is depleted.
• To identify and characterize Dab2-interacting proteins involved in endocytosis.
• To elucidate the role of FCH domain only-2 (FCHO2) in Dab2-mediated endocytosis.

Main Methods:

• Co-immunoprecipitation to identify Dab2-interacting proteins.
• Yeast three-hybrid assays to map interaction domains.
• siRNA-mediated depletion of FCHO2 and AP2 in HeLa cells.
• Confocal microscopy to observe receptor localization and clathrin structure dynamics.
• Quantification of receptor internalization rates.

Main Results:

• FCH domain only-2 (FCHO2) was identified as a major Dab2-interacting protein.
• The μ-homology domain (μHD) of FCHO2 binds to DPF motifs in Dab2, which also bind AP2.
• Disruption of the Dab2-FCHO2 interaction impaired Dab2-mediated LDLR endocytosis in AP2-depleted cells.
• FCHO2 depletion altered clathrin structure size and inhibited LDLR/transferrin receptor clustering.
• LDLR internalization was rescued in FCHO2-deficient cells with extended incubation time.

Conclusions:

• FCHO2 acts as a key accessory protein recruited by Dab2 during CME, particularly when AP2 levels are low.
• The interaction between Dab2 and FCHO2 is essential for efficient LDLR endocytosis under these conditions.
• FCHO2 plays a regulatory role in the size and dynamics of clathrin-coated structures during endocytosis.