Human Molecular Genetics Advance Access originally published online on July 11, 2006
Human Molecular Genetics 2006 15(16):2523-2532; doi:10.1093/hmg/ddl173
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Ataxin-2 and its Drosophila homolog, ATX2, physically assemble with polyribosomes
Department of Genome Sciences, University of Washington School of Medicine, Seattle, WA 98195-7730, USA
* To whom correspondence should be addressed. Tel: +1 2066165997; Fax: +1 2066857301; Email: pallanck{at}u.washington.edu
Received September 8, 2005; Accepted July 6, 2006
Mutations resulting in the expansion of a polyglutamine tract in the protein ataxin-2 give rise to the neurodegenerative disorders spinocerebellar ataxia type 2 and Parkinson's disease. The normal cellular function of ataxin-2 and the mechanism by which polyglutamine expansion of ataxin-2 causes neurodegeneration are unknown. Here, we demonstrate that ataxin-2 and its Drosophila homolog, ATX2, assemble with polyribosomes and poly(A)-binding protein (PABP), a key regulator of mRNA translation. The assembly of ATX2 with polyribosomes is mediated independently by two distinct evolutionarily conserved regions of ATX2: an N-terminal Lsm/Lsm-associated domain (LsmAD), found in proteins that function in nuclear RNA processing and mRNA decay, and a PAM2 motif, found in proteins that interact physically with PABP. We further show that the PAM2 motif mediates a physical interaction of ATX2 with PABP in addition to promoting ATX2 assembly with polyribosomes. Our results suggest a model in which ATX2 binds mRNA directly through its Lsm/LsmAD domain and indirectly via binding PABP that is itself directly bound to mRNA. These findings, coupled with work on other ataxin-2 family members, suggest that ATX2 plays a direct role in translational regulation. Our results raise the possibility that polyglutamine expansions within ataxin-2 cause neurodegeneration by interfering with the translational regulation of particular mRNAs.
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