OLIGOMERIZATION OF EXPANDED-POLYGLUTAMINE DOMAIN FLUORESCENT FUSION PROTEINS IN CULTURED-MAMMALIAN-CELLS

Six inherited neurologic diseases, including Huntington's disease, res ult from the expansion of a CAG domain of the disease genes to produce a domain of more than 40 glutamines in the expressed protein. The mec hanism by which expansion of this polyglutamine domain causes disease is unknown. Recent studies demonstrated oligomerization of polyglutami ne-domain proteins in mammalian neurons. To study oligomerization of p olyglutamine proteins and to identify heterologous protein interaction s, varying length polyglutamine-green fluorescent protein fusion prote ins were expressed in cultured COS-7 cells. The 19- and 35-glutamine f usion proteins (non-pathologic length) distributed diffusely throughou t the cytoplasm. In contrast, 56- and 80-glutamine fusion proteins (pa thologic length) formed fibrillar arrays resembling those previously o bserved in neurons in Huntington's disease and in a transgenic mouse m odel. These aggregates were intranuclear and intracytoplasmic. Intracy toplasmic aggregates were surrounded by collapsed intermediate filamen ts, The intermediate filament protein vimentin co-immunoisolated with expanded polyglutamine fusion proteins. This cellular model will exped ite investigations into oligomerization of polyglutamine proteins and their interactions with other proteins. (C) 1997 Academic Press.