title: Mutant huntingtin inhibits clathrin-independent endocytosis and causes accumulation of cholesterol in vitro and in vivo.
abstract: We show that the mutant Huntington's disease (HD) protein (mhtt) specifically inhibits endocytosis in primary striatal neurons. Unexpectedly, mhtt does not inhibit clathrin-dependent endocytosis as was anticipated based on known interacting partners. Instead, inhibition occurs through a non-clathrin, caveolar-related pathway. Expression of mhtt inhibited internalization of BODIPY-lactosylceramide (LacCer), which is internalized by a caveolar-related mechanism. In contrast, endocytosis of Alexa Fluor 594-transferrin (Tfn) and epidermal growth factor, internalized through clathrin pathway, was unaffected by mhtt expression. Caveolin-1 (cav1), the major structural protein of caveolae binds cholesterol and is responsible for its trafficking inside cells. Mhtt interacts with cav-1 and caused a striking accumulation of intracellular cholesterol. Cholesterol accumulated in cultured neurons expressing mhtt in vitro and in brains of mhtt-expressing animals in vivo, and was observed after induction of mhtt expression in PC-12 cell lines. The accumulation occurred only when mhtt and cav1 were simultaneously expressed in cells. Knockdown of cav1 in mhtt-expressing neurons blocked cholesterol accumulation and restored LacCer endocytosis. Thus, mhtt and cav1 functionally interact to cause both cellular defects. These data provide the first direct link between mhtt and caveolar-related endocytosis and also suggest a possible mechanism for HD neurotoxicity where cholesterol homeostasis is perturbed.
authors.affiliation: Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, MN 55905, USA.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Trushina
authors.forename: Raman Deep
authors.initials: RD
authors.lastname: Singh
authors.forename: Roy B
authors.initials: RB
authors.lastname: Dyer
authors.forename: Sheng
authors.initials: S
authors.lastname: Cao
authors.forename: Vijay H
authors.initials: VH
authors.lastname: Shah
authors.forename: Robert G
authors.initials: RG
authors.lastname: Parton
authors.forename: Richard E
authors.initials: RE
authors.lastname: Pagano
authors.forename: Cynthia T
authors.initials: CT
authors.lastname: McMurray
mesh_terms: D000818:Animals; D051242:Caveolin 1 / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D002966:Clathrin / Q000378:metabolism*; D004705:Endocytosis; D006801:Humans; D000071058:Huntingtin Protein; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D011485:Protein Binding; D034741:RNA, Small Interfering / Q000235:genetics
chemical_list: D051242:Caveolin 1; D002966:Clathrin; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; D002784:Cholesterol