Regular Article
Wild-Type and Mutant Huntingtins Function in Vesicle Trafficking in the Secretory and Endocytic Pathways

https://doi.org/10.1006/exnr.1998.6832Get rights and content

Abstract

Huntingtin is a cytoplasmic protein that is found in neurons and somatic cells. In patients with Huntington's disease (HD), the NH2-terminal region of huntingtin has an expanded polyglutamine tract. An abnormal protein interaction by mutant huntingtin has been proposed as a mechanism for HD pathogenesis. Huntingtin associates with vesicle membranes and interacts with proteins involved in vesicle trafficking. It is unclear where along vesicle transport pathways wild-type and mutant huntingtins are found and whether polyglutamine expansion affects this localization. To distinguish wild-type and mutant huntingtin, fibroblasts from normals and HD patients with two mutant alleles (homozygotes) were examined. Immunofluorescence confocal microscopy showed that mutant huntingtin localized with clathrin in membranes of thetransGolgi network and in clathrin-coated and noncoated endosomal vesicles in the cytoplasm and along plasma membranes. Separation of organelles in Nycodenz gradients showed that in normal and HD homozygote patient cells, huntingtin was present in membrane fractions enriched in clathrin. Similar results were obtained in fibroblasts from heterozyote juvenile HD patients who had a highly expanded polyglutamine tract in the HD allele. Western blot analysis of membrane fractions from rat brain showed that wild-type huntingtin was present in fractions that contained purified clathrin-coated membranes or a mixture of clathrin-coated and noncoated membranes. Electron microscopy of huntingtin immunoreactivity in rat brain revealed labeling along dendritic plasma membranes in association with clathrin-coated pits and clusters of noncoated endosomal vesicles 40–60 nm in diameter. These data suggest that wild-type and mutant huntingtin can influence vesicle transport in the secretory and endocytic pathways through associations with clathrin-coated vesicles.

References (40)

  • J.P. Vonsattel et al.

    Neuropathological classification of Huntington's disease

    J. Neuropathol. Exp. Neurol.

    (1985)
  • M. DiFiglia et al.

    Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain

    Science

    (1997)
  • N. Aronin et al.

    Clues to huntingtin's normal and abnormal function

    J. NIH Res.

    (1995)
  • C.A. Gutekunst et al.

    Identification and localization of huntingtin in brain and human lymphoblastoid cell lines with anti-fusion protein antibodies

    Proc. Natl. Acad. Sci. USA

    (1995)
  • M.A. Kalchman et al.

    HIP1, a human homologue ofS. cerevisiae

    Nature Genet.

    (1997)
  • E.E. Wanker et al.

    HIP-1: A huntingtin interacting protein isolated by the yeast two-hybrid system

    Human Mol. Genet.

    (1997)
  • X.J. Li et al.

    A huntingtin-associated protein enriched in brain with implications for HD pathology

    Nature

    (1995)
  • X.J. Li et al.

    Huntingtin-associated protein (HAP1): Discrete neuronal localizations in the brain resemble those of neuronal nitric oxide synthase

    Proc. Natl. Acad. Sci. USA

    (1996)
  • P.G. Bhide et al.

    Expression of normal and mutant huntingtin in the developing brain

    J. Neurosci.

    (1996)
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