HUNTINGTIN-ASSOCIATED PROTEIN-1 (HAP1) INTERACTS WITH THE P150(GLUED)SUBUNIT OF DYNACTIN

Huntington's disease (HD) is an inherited neurodegenerative disease ca used by expansion of a polyglutamine repeat in the HD protein huntingt in. Huntingtin's localization within the cel includes an association w ith cytoskeletal elements and vesicles. We previously identified a pro tein (HAP1) which binds to huntingtin in a glutamine repeat length-dep endent manner. We now report that HAP1 interacts with cytoskeletal pro teins, namely the p150(Glued) subunit of dynactin and the pericentriol ar protein PCM-1. Structural predictions indicate that both HAP1 and t he interacting proteins have a high probability of forming coiled coil s. We examined the interaction of HAP1 with p150(Glued). Binding of HA P1 to p150(Glued) (amino acids 879-1150) was confirmed in vitro by bin ding of p150(Glued) to a HAP1-GST fusion protein immobilized on glutat hione-Sepharose beads. Also, HAP1 co-immunoprecipitated with p150(Glue d) from brain extracts, indicating that the interaction occurs in vivo . Like HAP1, p150(Glued) is highly expressed in neurons in brain and b oth proteins are enriched in a nerve terminal vesicle-rich fraction. D ouble label immunofluorescence experiments in NGF-treated PC12 cells u sing confocal microscopy revealed that HAP1 and p150(Glued) partially co-localize. These results suggest that HAP1 might function as an adap tor protein using coiled coils to mediate interactions among cytoskele tal, vesicular and motor proteins. Thus, HAP1 and huntingtin may play a role in vesicle trafficking within the cell and disruption of this f unction could contribute to the neuronal dysfunction and death seen in HD.