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Isolation of a 40-kDa Huntingtin-associated protein
1Division of Neurobiology, Department of Psychiatry, Department of Neuroscience, and The Program in Cellular and Molecular Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2196, USA. mfpeters@jhmi.edu
Insights
Researchers identified HAP40, a novel protein associated with huntingtin. This discovery offers potential insights into Huntington's disease mechanisms and the protein's role in neurotoxicity.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Huntington's disease (HD) stems from expanded CAG repeats in the huntingtin gene, leading to polyglutamine expansion.
- The normal function of huntingtin protein and the neurotoxic mechanisms of mutant huntingtin remain unclear.
- Identifying huntingtin-associated proteins (HAPs) may elucidate HD pathogenesis.
Purpose of the Study:
- To identify novel proteins interacting with huntingtin.
- To investigate the role of huntingtin-associated proteins in Huntington's disease.
Main Methods:
- Copurification and coimmunoprecipitation assays to identify and validate huntingtin-associated proteins.
- Analysis of HAP40 gene (F8A) location and expression.
- Cellular localization studies of HAP40 in the presence and absence of huntingtin.
Main Results:
- A novel 40-kDa protein, termed HAP40, was identified as copurifying with huntingtin.
- HAP40 is encoded by the F8A gene, located within intron 22 of the factor VIII gene.
- HAP40 interacts with full-length huntingtin but not an N-terminal fragment, and its localization shifts from cytoplasmic to nuclear depending on huntingtin presence.
Conclusions:
- HAP40 is a novel huntingtin-associated protein potentially involved in normal huntingtin function.
- HAP40 may play a role in the aberrant nuclear localization of mutant huntingtin in Huntington's disease.
Abstract:
Huntington's disease is caused by an expanded CAG trinucleotide repeat coding for a polyglutamine stretch within the huntingtin protein. Currently, the function of normal huntingtin and the mechanism by which expanded huntingtin causes selective neurotoxicity remain unknown. Clues may come from the identification of huntingtin-associated proteins (HAPs). Here, we show that huntingtin copurifies with a single novel 40-kDa protein termed HAP40. HAP40 is encoded by the open reading frame factor VIII-associated gene A (F8A) located within intron 22 of the factor VIII gene. In transfected cell extracts, HAP40 coimmunoprecipitates with full-length huntingtin but not with an N-terminal huntingtin fragment. Recombinant HAP40 is cytoplasmic in the presence of huntingtin but is actively targeted to the nucleus in the absence of huntingtin. These data indicate that HAP40 is likely to contribute to the function of normal huntingtin and is a candidate for involvement in the aberrant nuclear localization of mutant huntingtin found in degenerating neurons in Huntington's disease.