A single common portal for clathrin-mediated endocytosis of distinct cargo governed by cargo-selective adaptors

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Clathrin-coated vesicles mediate endocytosis, requiring adaptor proteins for transmembrane cargo sorting.
• RNA interference (RNAi) studies show AP-2 adaptor complex depletion only partially affects clathrin-dependent cargo internalization.
• This suggests alternative sorting proteins and potentially distinct clathrin coats for different cargo.

Purpose of the Study:

• To investigate the roles of Dab2 and ARH proteins in the sorting and internalization of low-density lipoprotein (LDL) receptors.
• To determine if distinct clathrin coats are responsible for segregating different endocytic cargo.
• To elucidate the redundancy and specificity of endocytic adaptor proteins.

Main Methods:

• Utilized RNA interference (RNAi) to deplete Dab2 and ARH proteins in cells.
• Observed the effects of protein depletion on LDL receptor and transferrin internalization.
• Analyzed the co-localization of AP-2, Dab2, ARH, transferrin, and LDL receptors within clathrin structures.

Main Results:

• Diminishing both Dab2 and ARH via RNAi resulted in significant accumulation of LDL receptors at the cell surface.
• Uptake of transferrin, dependent on AP-2, proceeded normally even without Dab2 and ARH, indicating functional delegation.
• AP-2, Dab2, ARH, transferrin, and LDL receptors were found together in most surface clathrin structures, challenging the specialized clathrin coat hypothesis.

Conclusions:

• Dab2 and ARH act redundantly to recognize the FXNPXY internalization signal of the LDL receptor.
• Endocytic sorting operations are delegated at the cell surface, with distinct proteins handling different cargo.
• Low Dab2 expression in hepatocytes likely explains hypercholesterolemia observed upon ARH loss.