title: Huntingtin-associated protein-1 (HAP1) regulates endocytosis and interacts with multiple trafficking-related proteins.
abstract: Huntingtin-associated protein 1 (HAP1) was initially identified as a binding partner of huntingtin, mutations in which underlie Huntington's disease. Subcellular localization and protein interaction data indicate that HAP1 may be important in vesicle trafficking, cell signalling and receptor internalization. In this study, a proteomics approach was used for the identification of novel HAP1-interacting partners to attempt to shed light on the physiological function of HAP1. Using affinity chromatography with HAP1-GST protein fragments bound to Sepharose columns, this study identified a number of trafficking-related proteins that bind to HAP1. Interestingly, many of the proteins that were identified by mass spectrometry have trafficking-related functions and include the clathrin light chain B and Sec23A, an ER to Golgi trafficking vesicle coat component. Using co-immunoprecipitation and GST-binding assays the association between HAP1 and clathrin light chain B has been validated in vitro. This study also finds that HAP1 co-localizes with clathrin light chain B. In line with a physiological function of the HAP1-clathrin interaction this study detected a dramatic reduction in vesicle retrieval and endocytosis in adrenal chromaffin cells. Furthermore, through examination of transferrin endocytosis in HAP1-/-cortical neurons, this study has determined that HAP1 regulates neuronal endocytosis. In this study, the interaction between HAP1 and Sec23A was also validated through endogenous co-immunoprecipitation in rat brain homogenate. Through the identification of novel HAP1 binding partners, many of which have putative trafficking roles, this study provides us with new insights into the mechanisms underlying the important physiological function of HAP1 as an intracellular trafficking protein through its protein-protein interactions.
authors.affiliation: Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, SA, Australia.
authors.forename: Kimberly D
authors.initials: KD
authors.lastname: Mackenzie
authors.affiliation: Sansom Institute, University of South Australia, Adelaide, SA, Australia.
authors.forename: Yoon
authors.initials: Y
authors.lastname: Lim
authors.affiliation: Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, SA, Australia.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Duffield
authors.affiliation: Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, SA, Australia.
authors.forename: Timothy
authors.initials: T
authors.lastname: Chataway
authors.affiliation: Sansom Institute, University of South Australia, Adelaide, SA, Australia.
authors.forename: Xin-Fu
authors.initials: XF
authors.lastname: Zhou
authors.affiliation: Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, SA, Australia; South Australian Health and medical Research Institute, Adelaide, SA, Australia. Electronic address: damien.keating@flinders.edu.au.
authors.forename: Damien J
authors.initials: DJ
authors.lastname: Keating
mesh_terms: D000818:Animals; D004705:Endocytosis / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D027361:Organic Anion Transporters / Q000235:genetics; D060066:Protein Interaction Maps / Q000235:genetics; D021381:Protein Transport / Q000235:genetics; D040901:Proteomics; D051381:Rats; D033921:Vesicular Transport Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D009419:Nerve Tissue Proteins; D027361:Organic Anion Transporters; D033921:Vesicular Transport Proteins; C096896:HAP1 protein, human; C512739:SEC23A protein, human; C487009:SLCO6A1 protein, human
keywords: Clathrin; Endocytosis; Exocytosis; Huntingtin-associated protein-1; Receptors; Vesicles