TRUNCATED N-TERMINAL FRAGMENTS OF HUNTINGTIN WITH EXPANDED GLUTAMINE REPEATS FORM NUCLEAR AND CYTOPLASMIC AGGREGATES IN CELL-CULTURE

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by an expanding CAG repeat coding for polyglutamine in the hunt ingtin protein. Recent data have suggested the possibility that an N-t erminal fragment of huntingtin may aggregate in neurons of patients wi th HD, both in the cytoplasm, forming dystrophic neurites, and in the nucleus, forming intranuclear neuronal inclusion bodies. An animal mod el of HD using the short N-terminal fragment of huntingtin has also be en found to have intranuclear inclusions and this same fragment can ag gregate in vitro. We have now developed a cell culture model demonstra ting that N-terminal fragments of huntingtin with expanded glutamine r epeats aggregate both in the cytoplasm and in the nucleus. Neuroblasto ma cells transiently transfected with full-length huntingtin construct s with either a normal or expanded repeat had diffuse cytoplasmic loca lization of the protein. In contrast, cells transfected with truncated N-terminal fragments showed aggregation only if the glutamine repeat was expanded. The aggregates were often ubiquitinated. The shorter tru ncated product appeared to form more aggregates in the nucleus. Cells transfected with the expanded repeat construct but not the normal repe at construct showed enhanced toxicity to the apoptosis-inducing agent staurosporine. These data indicate that N-terminal truncated fragments of huntingtin with expanded glutamine repeats can aggregate in cells in culture and that this aggregation can be toxic to cells. This model will be useful for future experiments to test mechanisms of aggregati on and toxicity and potentially for testing experimental therapeutic i nterventions.