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Polyglutamine expansion of huntingtin impairs its nuclear export

Abstract

Proteins with polyglutamine (polyQ) expansions accumulate in the nucleus and affect gene expression1,2. The mechanism by which mutant huntingtin (htt) accumulates intranuclearly is not known; wild-type htt, a 350-kDa protein of unknown function, is normally found in the cytoplasm3,4,5. N-terminal fragments of mutant htt, which contain a polyQ expansion (>37 glutamines), have no conserved nuclear localization sequences or nuclear export sequences but can accumulate in the nucleus and cause neurological problems in transgenic mice6,7. Here we report that N-terminal htt shuttles between the cytoplasm and nucleus in a Ran GTPase–independent manner. Small N-terminal htt fragments interact with the nuclear pore protein translocated promoter region (Tpr), which is involved in nuclear export. PolyQ expansion and aggregation decrease this interaction and increase the nuclear accumulation of htt. Reducing the expression of Tpr by RNA interference or deletion of ten amino acids of N-terminal htt, which are essential for the interaction of htt with Tpr, increased the nuclear accumulation of htt. These results suggest that Tpr has a role in the nuclear export of N-terminal htt and that polyQ expansion reduces this nuclear export to cause the nuclear accumulation of htt.

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Figure 1: Nuclear accumulation of htt is determined by protein size and polyQ misfolding.
Figure 2: Nuclear transport of mutant htt is not dependent on Ran GTPase.
Figure 3: N-terminal htt interacts with the nuclear pore protein Tpr.
Figure 4: PolyQ expansion and misfolding reduces the association of htt with Tpr.
Figure 5: Expression of Tpr affects the nuclear distribution of htt.
Figure 6: N-terminal region of htt binds Tpr and affects protein nuclear localization.

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Acknowledgements

We thank H. Zhou for technical help, E. Griffis and M. Powers for tsBN2 cells and advice, S. Warren for HeLa cells, L. Thompson for plasmids of 1-17-NLS-GFP and NLS-GFP and L. Gerace for a rabbit antibody to Tpr. This work was supported by grants from National Institute of Health (to X.J.L. and C.A.R.), Hereditary Disease Foundation (to X.J.L.), The Wellcome Trust (to G.P.B.) and Huntington's Disease Society of America (to G.P.B. and C.A.R.).

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Correspondence to Xiao-Jiang Li.

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Supplementary information

Supplementary Fig. 1

Confocal images of HEK293 cells expressing GFP-120Q. (PDF 194 kb)

Supplementary Fig. 2

Decreasing proteasome activity increases the nuclear accumulation of soluble mutant htt. (PDF 195 kb)

Supplementary Fig. 3

Decreased proteasome activity is associated with increased nuclear accumulation of N-terminal htt in cultured primary neurons. (PDF 221 kb)

Supplementary Fig. 4

Subcellular distribution of NLS-htt-80Q in tsBN2 cells that were treated with the protein synthesis inhibitor cyclohexamide. (PDF 117 kb)

Supplementary Fig. 5

Controls for the specific interaction of N-terminal htt with Tpr. (PDF 157 kb)

Supplementary Fig. 6

Tpr expression does not alter the nuclear distribution of other polyQ proteins. (PDF 134 kb)

Supplementary Methods (PDF 72 kb)

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Cornett, J., Cao, F., Wang, CE. et al. Polyglutamine expansion of huntingtin impairs its nuclear export. Nat Genet 37, 198–204 (2005). https://doi.org/10.1038/ng1503

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