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Description

Huntingtin-associated protein 1 (UniProt: P54256, also known as HAP1) is encoded by the Hap1 gene (Gene ID: 29430) in rat. HAP1 is a huntingtin-associated protein that is enriched in the brain. It specifically associates with HTT/huntingtin and this binding is enhanced by an expanded polyglutamine repeats within HTT that affects HAP1 interaction properties. Both HTT and HAP1 are reported to be involved in intracellular trafficking and HAP1 is proposed to link HTT to motor proteins and/or transport cargos. HAP1 localizes to large nonmembrane-bound cytoplasmic bodies (stigmoid bodies) in various types of neurons. The formation of stigmoid bodies is regulated by the ratio of isoform A to isoform B of HAP1. HAP1 plays a role in vesicular transport within neurons that involves microtubule-associated transporters and is shown to be attenuated by association with mutant HTT. In rodents, two HAP1 isoforms (HAP1A and HAP1B) have been described that differ in their carboxy terminal. However, humans contain only the HAP1A isoform. In murine models, targeted disruption of the HAP1 gene results in significantly depressed feeding behavior and premature postnatal death. Pups with Hap1 -/- show decreased feeding, malnutrition, dehydration, and premature death. (Ref.: Tang, TS et al., (2003). Neuron 39 (2), 227-239, Chan, EY., et al. (2002). Hum. Mol. Gen. 11(8), 945-959).