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HIP1 functions in clathrin-mediated endocytosis through binding to clathrin and adaptor protein 2
M Metzler1, V Legendre-Guillemin, L Gan
1Centre for Molecular Medicine and Therapeutics, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia V5Z 4H4, Canada.
Insights
Huntingtin-interacting protein 1 (HIP1) is crucial for clathrin-mediated endocytosis in neurons. This study reveals HIP1
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Huntington disease is a neurodegenerative disorder caused by polyglutamine expansion in huntingtin.
- Mutant huntingtin exhibits reduced binding affinity to huntingtin-interacting protein 1 (HIP1).
Purpose of the Study:
- To investigate the role of HIP1 in neuronal cells.
- To determine HIP1's interaction with the endocytic machinery.
Main Methods:
- Immunofluorescence microscopy to assess HIP1 localization in neuronal cells.
- Biochemical purification of clathrin-coated vesicles (CCVs) from brain homogenates.
- Analysis of HIP1 binding domains and functional assays using HIP1 fragments.
Main Results:
- HIP1 colocalizes with clathrin-mediated endocytosis markers in neurons.
- HIP1 is significantly enriched on purified CCVs.
- HIP1 binds to clathrin adaptor protein 2 (AP2) and clathrin heavy chain via a specific fragment (amino acids 276-335).
- Expression of HIP1 fragments inhibits clathrin-mediated endocytosis.
Conclusions:
- HIP1 is a novel component of the neuronal endocytic machinery.
- HIP1's interaction with clathrin and AP2 is essential for its function in CCVs.
- HIP1 plays a critical role in regulating clathrin-mediated endocytosis.
Abstract:
Polyglutamine expansion in huntingtin is the underlying mutation leading to neurodegeneration in Huntington disease. This mutation influences the interaction of huntingtin with different proteins, including huntingtin-interacting protein 1 (HIP1), in which affinity to bind to mutant huntingtin is profoundly reduced. Here we demonstrate that HIP1 colocalizes with markers of clathrin-mediated endocytosis in neuronal cells and is highly enriched on clathrin-coated vesicles (CCVs) purified from brain homogenates. HIP1 binds to the clathrin adaptor protein 2 (AP2) and the terminal domain of the clathrin heavy chain, predominantly through a small fragment encompassing amino acids 276-335. This region, which contains consensus clathrin- and AP2-binding sites, functions in conjunction with the coiled-coil domain to target HIP1 to CCVs. Expression of various HIP1 fragments leads to a potent block of clathrin-mediated endocytosis. Our findings demonstrate that HIP1 is a novel component of the endocytic machinery.