Human Molecular Genetics Advance Access published online on December 22, 2006
Human Molecular Genetics, doi:10.1093/hmg/ddl467
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© The Author 2006. Published by Oxford University Press. All rights reserved
Wild-type huntingtin participates in protein trafficking between the Golgi and the extracellular space
1 Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5120, USA 2 Stanford Human Genome Center, 975 California Ave., Palo Alto, CA 94304, USA
To whom correspondence should be addressed: Richard M. Myers Department of Genetics, M344 Stanford University School of Medicine Stanford, CA 94305-5120 USA Phone (650) 725-9687 Fax (650) 725-9689 myers{at}shgc.stanford.edu
Received October 9, 2006; Revised December 9, 2006; Accepted December 9, 2006
Huntington disease is an autosomal dominant neurodegenerative disease caused by an expanded CAG trinucleotide repeat in the first exon of the HD gene, which results in a toxic polyglutamine stretch within huntingtin, the protein it encodes. Understanding the normal function of this essential protein is vital to understanding the root of the disease, yet despite more than a decade of investigation, its role in the cell remains elusive. Identifying the subcellular localization of huntingtin and understanding its effects on global gene expression is critical to this endeavor. While most reports agree that huntingtin is predominantly a cytoplasmic protein, conflicting distribution patterns have been demonstrated at the subcellular level. Here, we examine wild-type huntingtin’s localization in cultured cells by expressing the full-length human protein tagged with enhanced green fluorescent protein (EGFP) within its unspliced genomic context. In fibrosarcoma and neuroblastoma cells, huntingtin shows discrete punctate, perinuclear localization overlapping largely with the trans-Golgi and cytoplasmic clathrin-coated vesicles, implicating huntingtin in vesicle trafficking. To determine whether huntingtin is involved trafficking a specific subset of proteins, we measured changes in global transcription levels in embryonic stem cells and neurons lacking huntingtin. Huntingtin null neurons exhibit a significant reduction in transcripts encoding proteins destined for the extracellular space, many of which are components of the extracellular matrix or involved in cellular adhesion, receptor binding, and hormone activity. Together these findings support a role for huntingtin in the intracellular trafficking of proteins required for the construction of the extracellular matrix.
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