Abstract
Huntington disease is a dominantly inherited neurodegenerative condition caused by polyglutamine expansion in the N terminus of the huntingtin protein (Htt). The first 17 amino acids (N17) of Htt play a key role in regulating its toxicity and aggregation. Both nuclear export and cytoplasm retention functions have been ascribed to N17. We have determined that N17 acts as a nuclear export sequence (NES) within Htt exon and when fused to yellow fluorescent protein. We have defined amino acids within N17 that constitute the nuclear export sequence (NES). Mutation of any of the conserved residues increases nuclear accumulation of Htt exon 1. Nuclear export of Htt is sensitive to leptomycin B and is reduced by knockdown of exportin 1. In HEK293 cells, NES mutations decrease overall Htt aggregation but increase the fraction of cells with nuclear inclusions. In primary cultured neurons, NES mutations increase nuclear accumulation and increase overall aggregation. This work defines a bona fide nuclear export sequence within N17 and links it to effects on protein aggregation. This may help explain the important role of N17 in controlling Htt toxicity.
Highlights
Trafficking of huntingtin (Htt) fragments influences its toxicity
There remains considerable debate about the molecular mechanisms that govern the subcellular localization of huntingtin protein (Htt) fragments
We have found that N17 contains a bona fide nuclear export sequence (NES), consisting of four hydrophobic amino acids, leucine 4, 7, 14, and phenylalanine 11
Summary
Trafficking of huntingtin (Htt) fragments influences its toxicity. Results: A leucine-rich NES lies within the first 17 amino acids (N17) of Htt that controls subcellular localization and aggregation. The first 17 amino acids (N17) of Htt play a key role in regulating its toxicity and aggregation Both nuclear export and cytoplasm retention functions have been ascribed to N17. This work defines a bona fide nuclear export sequence within N17 and links it to effects on protein aggregation This may help explain the important role of N17 in controlling Htt toxicity. It has been reported that hyperphosphorylation of Ser-13 and Ser-16 promotes relocation of Htt from the cytoplasm to the nucleus [11, 12, 15] This region is very important in regulating Htt aggregation, subcellular localization, and toxicity. We have defined an NES motif in the N17 region and have studied its effects on subcellular localization and aggregation of Htt exon 1 in non-neural cells and primary cultured neurons
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