Related Experiment Videos
Huntingtin interacting protein 1 induces apoptosis via a novel caspase-dependent death effector domain
A S Hackam1, A S Yassa, R Singaraja
1Centre for Molecular Medicine and Therapeutics and Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada.
Insights
Huntingtin interacting protein 1 (HIP-1) is identified as a proapoptotic protein that mediates cell death. This discovery suggests HIP-1 may play a role in the molecular mechanisms underlying Huntington disease.
Area of Science:
- Neurobiology
- Molecular Biology
- Cell Biology
Background:
- Huntington disease (HD) is a neurodegenerative disorder caused by expanded glutamine tracts in huntingtin.
- Huntingtin interacting protein 1 (HIP-1) interacts with mutant huntingtin, but its function remained unknown.
Purpose of the Study:
- To elucidate the function of HIP-1.
- To investigate HIP-1's role in apoptosis and its potential involvement in Huntington disease pathogenesis.
Main Methods:
- Overexpression of HIP-1 and its domains in cells.
- Bioinformatics analysis to identify functional domains.
- Cell death assays and inhibition studies using apoptosis regulators.
Main Results:
- HIP-1 overexpression induces rapid caspase 3-dependent cell death.
- A novel death effector domain (DED) in HIP-1 is responsible for its toxicity.
- HIP-1 toxicity is mediated via the intrinsic apoptosis pathway and inhibited by Bcl-x(L).
- A specific phenylalanine residue (F398) in the HIP-1 DED is critical for its proapoptotic activity.
Conclusions:
- HIP-1 is a novel proapoptotic protein.
- HIP-1's proapoptotic activity is mediated by its DED and involves the intrinsic apoptosis pathway.
- HIP-1 may act as a molecular accomplice in the pathogenesis of Huntington disease.
Abstract:
Huntington disease is a devastating neurodegenerative disease caused by the expansion of a polymorphic glutamine tract in huntingtin. The huntingtin interacting protein (HIP-1) was identified by its altered interaction with mutant huntingtin. However, the function of HIP-1 was not known. In this study, we identify HIP-1 as a proapoptotic protein. Overexpression of HIP-1 resulted in rapid caspase 3-dependent cell death. Bioinformatics analyses identified a novel domain in HIP-1 with homology to death effector domains (DEDs) present in proteins involved in apoptosis. Expression of the HIP-1 DED alone resulted in cell death indistinguishable from HIP-1, indicating that the DED is responsible for HIP-1 toxicity. Furthermore, substitution of a conserved hydrophobic phenylalanine residue within the HIP-1 DED at position 398 eliminated HIP-1 toxicity entirely. HIP-1 activity was found to be independent of the DED-containing caspase 8 but was significantly inhibited by the antiapoptotic protein Bcl-x(L), implicating the intrinsic pathway of apoptosis in HIP-1-induced cell death. Co-expression of a normal huntingtin fragment capable of binding HIP-1 significantly reduced cell death. Our data identify HIP-1 as a novel proapoptotic mediator and suggest that HIP-1 may be a molecular accomplice in the pathogenesis of Huntington disease.