IDENTIFICATION AND LOCALIZATION OF HUNTINGTIN IN BRAIN AND HUMAN LYMPHOBLASTOID CELL-LINES WITH ANTI-FUSION PROTEIN ANTIBODIES

The Huntington disease (HD) phenotype is associated with expansion of a trinucleotide repeat in the IT15 gene, which is predicted to encode a 348-kDa protein named huntingtin. We used polyclonal and monoclonal anti-fusion protein antibodies to identify native huntingtin in rat, m onkey, and human. Western blots revealed a protein with the expected m olecular weight which is present in the soluble fraction of rat and mo nkey brain tissues and lymphoblastoid cell lines from control cases. I n lymphoblastoid cell lines from juvenile-onset heterozygote HD cases, both normal and mutant huntingtin are expressed, and increasing repea t expansion leads to lower levels of the mutant protein. Immunocgtoche mistry indicates that huntingtin is located in neurons throughout the brain, with the highest levels evident in larger neurons. In the human striatum, huntingtin is enriched in a patch-like distribution, potent ially corresponding to the first areas affected in HD. Subcellular loc alization of huntingtin is consistent with a cytosolic protein primari ly found in somatodendritic regions. Huntingtin appears to particularl y associate with microtubules, although some is also associated with s ynaptic vesicles. On the basis of the localization of huntingtin in as sociation with microtubules, we speculate that the mutation impairs th e cytoskeletal anchoring or transport of mitochondria, vesicles, or ot her organelles or molecules.