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© The Rockefeller University Press,
0021-9525/2001//25 $5.00
The Journal of Cell Biology, Volume 153, Number 1,
, 2001 25-34
Original Article |
Tissue Transglutaminase Does Not Contribute to the Formation of Mutant Huntingtin Aggregates
gvwj{at}uab.edu
The cause of Huntington's disease (HD) is a pathological expansion of the polyglutamine domain within the NH2-terminal region of huntingtin. Neuronal intranuclear inclusions and cytoplasmic aggregates composed of the mutant huntingtin within certain neuronal populations are a characteristic hallmark of HD. Because in vitro expanded polyglutamine repeats are glutaminyl-donor substrates of tissue transglutaminase (tTG), it has been hypothesized that tTG may contribute to the formation of these aggregates in HD. Therefore, it is of fundamental importance to establish whether tTG plays a significant role in the formation of mutant huntingtin aggregates in the cell. Human neuroblastoma SH-SY5Y cells were stably transfected with truncated NH2-terminal huntingtin constructs containing 18 (wild type) or 82 (mutant) glutamines. In the cells expressing the mutant truncated huntingtin construct, numerous SDS-resistant aggregates were present in the cytoplasm and nucleus. Even though numerous aggregates were present in the mutant huntingtin-expressing cells, tTG did not coprecipitate with mutant truncated huntingtin. Further, tTG was totally excluded from the aggregates, and significantly increasing tTG expression had no effect on the number of aggregates or their intracellular localization (cytoplasm or nucleus). When a YFP-tagged mutant truncated huntingtin construct was transiently transfected into cells that express no detectable tTG due to stable transfection with a tTG antisense construct, there was extensive aggregate formation. These findings clearly demonstrate that tTG is not required for aggregate formation, and does not facilitate the process of aggregate formation. Therefore, in HD, as well as in other polyglutamine diseases, tTG is unlikely to play a role in the formation of aggregates.
Key Words: Huntington's disease • inclusions • polyglutamine • polar zipper • isopeptide bond
© 2001 The Rockefeller University Press
Drs. Chun and Lesort contributed equally to this work and should be considered co-first authors.Abbreviations used in this paper: HD, Huntington's disease; tTG, tissue transglutaminase.
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