A human HAP1 homologue. Cloning, expression, and interaction with huntingtin

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Huntington's disease (HD) results from expanded glutamine repeats in the huntingtin protein.
• Expanded repeats cause abnormal protein interactions, leading to a gain-of-function mechanism in HD.

Purpose of the Study:

• To identify and characterize the human homologue of rat huntingtin-associated protein 1 (HAP1).
• To investigate the role of human HAP1 (hHAP) in Huntington's disease pathology.

Main Methods:

• Cloning of the human HAP1 homologue (hHAP).
• Sequence analysis and comparison with rat HAP1.
• Analysis of hHAP gene and protein expression in human brain tissues, including HD brains.
• In vitro binding assays, immunoprecipitation, and coexpression studies to confirm hHAP-huntingtin interaction.

Main Results:

• hHAP shares significant sequence identity with rat HAP1, particularly in the huntingtin-binding region.
• hHAP is specifically expressed in human brain tissues as a 75-kDa protein with a 4.1-kilobase transcript.
• hHAP expression is reduced in HD brains, paralleling huntingtin expression.
• hHAP binds to huntingtin, and this binding is enhanced by longer glutamine repeats.
• Unlike rat HAP1, only a single major hHAP isoform is detected in primate brains.

Conclusions:

• The identification of hHAP provides a crucial tool for studying its role in HD.
• Differences in hHAP sequence and expression compared to rat HAP1 may indicate a specific function in human HD pathogenesis.
• The enhanced binding of hHAP to huntingtin with expanded repeats supports its involvement in HD.