Subcellular localization of the Huntington's disease gene product in cell lines by immunofluorescence and biochemical subcellular fractionation

Huntington's disease is a progressive neurodegenerative disorder, which is caused by expansion of a polymorphic (CAG)n repeat in the coding region of the Huntington's disease gene. The function of huntingtin has not been elucidated so far. Accordingly, detailed subcellular localization studies remain useful. In an immunohistochemical study, we have reported huntingtin to be present in the cytoplasm of cells in the majority of the tissues studied. In addition, we detected a signal in the nucleus of cells in some tissues, including neuronal cells. We have further extended these studies in various mammalian cell lines, using a panel of (affinity-purified) polyclonal huntingtin antibodies in immunofluorescence, confocal laser scanning microscopy and biochemical subcellular fractionation studies. In mouse embryonic fibroblasts, human skin fibroblasts and in mouse neuroblastoma cells huntingtin was present in the cytoplasm. All five antibodies, directed against different parts of huntingtin, also showed a signal in the nucleus. This signal could be competed by the original antigen. The localization of huntingtin in both cytoplasm and nucleus, was confirmed by biochemical subcellular fractionation studies. However, in most other studies, a nuclear location for huntingtin has not been found. Our results suggest, however, that besides its function(s) in the cytoplasm, a nuclear function of huntingtin at some stages of differentiation or in some phases of the cell cycle may not be excluded.