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Updated: Dec 24, 2025
Efficient and Scalable Production of Full-length Human Huntingtin Variants in Mammalian Cells using a Transient Expression System
Published on: December 10, 2021
Cdk5 phosphorylation of huntingtin reduces its cleavage by caspases: implications for mutant huntingtin toxicity
Shouqing Luo1, Coralie Vacher, Janet E Davies
1Department of Medical Genetics, Cambridge Institute for Medical Research, Addenbrooke's Hospital, Cambridge, CB2 2XY, England, UK.
Insights
Cyclin-dependent kinase 5 (CDK5) phosphorylation of huntingtin (HTT) reduces its cleavage, aggregation, and toxicity in Huntington's disease (HD). In HD, reduced CDK5 activity impairs this protective mechanism, worsening neurodegeneration.
Area of Science:
- Neuroscience
- Molecular Biology
- Genetics
Background:
- Huntington's disease (HD) is a fatal neurodegenerative disorder.
- It is caused by an expanded polyglutamine (polyQ) tract in the huntingtin (HTT) protein.
- Cleavage of mutant HTT releases toxic N-terminal fragments, contributing to cellular toxicity.
Purpose of the Study:
- To investigate the interaction between huntingtin (HTT) and cyclin-dependent kinase 5 (CDK5).
- To determine the role of CDK5 phosphorylation in regulating mutant HTT cleavage and toxicity.
- To explore the impact of polyQ expansion on CDK5 activity in Huntington's disease.
Main Methods:
- Co-immunoprecipitation and immunofluorescence to study HTT-CDK5 interaction and colocalization.
- In vitro kinase assays to assess CDK5 phosphorylation of HTT.
- Cellular models expressing mutant HTT fragments to evaluate cleavage, aggregation, and toxicity.
- Analysis of CDK5 activity in brain tissue from Huntington's disease transgenic mice.
Main Results:
- HTT interacts with and colocalizes to cellular membrane fractions with CDK5.
- CDK5 phosphorylates HTT at Serine 434, reducing caspase-mediated cleavage at residue 513.
- CDK5 phosphorylation attenuated mutant HTT (htt588) aggregation and toxicity in cellular models.
- CDK5 activity was reduced in the brains of HD transgenic mice, linked to impaired CDK5-p35 interaction due to polyQ-expanded HTT fragments.
Conclusions:
- CDK5-mediated phosphorylation of HTT provides a protective mechanism against cleavage, aggregation, and toxicity.
- Reduced CDK5 activity in Huntington's disease compromises this protective pathway.
- Targeting the CDK5 pathway may offer a therapeutic strategy for Huntington's disease.
Abstract:
Huntington's disease (HD) is a neurodegenerative disorder caused by an expanded polyglutamine (polyQ) tract in the huntingtin (htt) protein. Mutant htt toxicity is exposed after htt cleavage by caspases and other proteases release NH(2)-terminal fragments containing the polyQ expansion. Here, we show htt interacts and colocalizes with cdk5 in cellular membrane fractions. Cdk5 phosphorylates htt at Ser434, and this phosphorylation reduces caspase-mediated htt cleavage at residue 513. Reduced mutant htt cleavage resulting from cdk5 phosphorylation attenuated aggregate formation and toxicity in cells expressing the NH(2)-terminal 588 amino acids (htt588) of mutant htt. Cdk5 activity is reduced in the brains of HD transgenic mice compared with controls. This result can be accounted for by the polyQ-expanded htt fragments reducing the interaction between cdk5 and its activator p35. These data predict that the ability of cdk5 phosphorylation to protect against htt cleavage, aggregation, and toxicity is compromised in cells expressing toxic fragments of htt.
