Huntingtin-associated protein 1 (HAP1) interacts with the p150(Glued) subunit of dynactin

Huntington's disease (HD) is an inherited neurodegenerative disease caused by expansion of a polyglutamine repeat in the HD protein huntingtin. Huntingtin's localization within the cell includes an association with cytoskeletal elements and vesicles. We previously identified a protein (HAP1) which binds to huntingtin in a glutamine repeat length-dependent manner. We now report that HAP1 interacts with cytoskeletal proteins, namely the p150(Glued) subunit of dynactin and the pericentriolar protein PCM-1. Structural predictions indicate that both HAP1 and the interacting proteins have a high probability of forming coiled coils. We examined the interaction of HAP1 with p150(Glued). Binding of HAP1 to p150(Glued) (amino acids 879-1150) was confirmed in vitro by binding of p150(Glued) to a HAP1-GST fusion protein immobilized on glutathione-Sepharose beads. Also, HAP1 co-immunoprecipitated with p150(Glued) from brain extracts, indicating that the interaction occurs in vivo. Like HAP1, p150(Glued) is highly expressed in neurons in brain and both proteins are enriched in a nerve terminal vesicle-rich fraction. Double label immunofluorescence experiments in NGF-treated PC12 cells using confocal microscopy revealed that HAP1 and p150(Glued) partially co-localize. These results suggest that HAP1 might function as an adaptor protein using coiled coils to mediate interactions among cytoskeletal, vesicular and motor proteins. Thus, HAP1 and huntingtin may play a role in vesicle trafficking within the cell and disruption of this function could contribute to the neuronal dysfunction and death seen in HD.