BBSRC-SFI application: Mechanisms & consequences of HDACs in the NCoR complex, in controlling the activity of MutSb in trinucleotide repeat expansions

Lead Research Organisation: University of Leicester
Department Name: Molecular and Cell Biology


Our DNA is protected from unwanted changes by a genetic 'spellchecker' called mismatch repair. Mismatch repair normally prevents DNA mutations and cancer. Thus, mismatch repair function is a protector of the genome and a natural component for healthy ageing. This protection comes at an unexpected price however: increased risk for inherited neurological diseases such as Huntington's disease. A few mismatch repair proteins somehow become corrupted and enhance mutations that cause these neurological diseases. This research will address how mismatch repair contributes to this risk, and it will develop new ways to detect and avoid the problem. This research will help meet the unmet needs of patients and their families who are affected by these neurological diseases.

The research is a strategic partnering of expertise from the U.K. and Ireland. The U.K. partner is world-renowned for his track record on cellular components that act as important control points to regulate the healthy ageing process. The Irish partner is an expert in mismatch repair and Huntington's disease. Together, the two teams will combine their efforts to improve our understanding of regulation of mismatch repair and to provide new insights into how to avoid the mutations that cause Huntington's disease.

Technical Summary

DNA trinucleotide repeats are three-base runs that are naturally present in many genes. Like other microsatellites, the length of trinucleotide repeats (TNRs) is normally maintained during healthy ageing by the DNA mismatch repair (MMR) system, a powerful and conserved anti-mutation activity. MMR acts as a genetic spellchecker to remove DNA polymerase errors and restore them to the original sequence. The presence of MMR stabilizes the genome, including normal-length TNRs, by 100-1,000 fold. The situation is dramatically different for long TNRs (more than 30 repeats). Long TNRs are very unstable and frequently expand (gain length) in families affected with the ageing-related neurological disorder, Huntington's disease (HD). Expansion of the CAG repeat within the HD gene causes the disease. Surprisingly, the MMR protein complex MutSbeta actively promotes expansions and exacerbates disease. In other words, TNR expansions are accelerated by the presence of MutSbeta, not its absence. Thus regulation of MutSbeta is key for understanding TNR expansions. The co-applicant's lab discovered that histone deacetylases (HDAC) 3 and 5 are key controllers of MutSbeta; indeed, HDAC3/HDAC5 are just as important to fuel expansions as MutSbeta, and the two HDACs work in the same genetic network as MutSbeta. The fact that HDAC3 and HDAC5 regulate TNR expansions via MutSbeta is a paradigm shift that connects HDACs to DNA mutagenesis at biologically critical genes. This research proposal seeks to understand the biochemical mechanism and biological consequences of SMRT/NCoR/HDAC3/HDAC5 control of MutSbeta with regard to TNR expansions. The U.K.-Ireland partnership combines the HDAC expertise of the applicant with the mismatch repair expertise of the co-applicant. The study will explore the novel connection between the SMRT complex, MutSbeta and triplet repeat expansions using an integrated system of biochemistry, protein chemistry, genetics and possibly structural biology.

Planned Impact

1. Disseminate research outcomes
Scientific community: This research project will have direct impact on the HDAC community, the DNA repair community and in the neurological disease arena. Publications will be deposited with the open-access Leicester Research Archive ( and with NUI Galway's ARAN ( Both PI's and both postdoctoral research associates will attend international conferences to present results and disseminate the new findings.
Lay community: Free information will be contributed to LE1 (University of Leicester) and to Ollscéala, (NUI Galway) (

2. Engagement with the press
Engagement with the press will be coordinated through the press offices of the University of Leicester and NUI Galway. Previous press releases from the Schwabe group include the discovery of the role of inositol phosphate signaling in class-1 HDAC activity ("Breakthrough discovery into the regulation of a key cancer drug target" EurekAlert 1st July 2013. Press releases from the Lahue group include the discovery of HDAC function in triplet repeat expansions ("New Discovery in Fight Against Huntington's Disease" 21st Feb 2012) and subsequent interview on national Irish radio station.

3. Engagement with schools
The UK researchers will participate in outreach activities organised by the Centre for Excellence in Teaching & Learning in Genetics (GENIE) to explain biomedical science to schoolchildren and other visitors. This will include participation in the annual 'Dynamic DNA' event held at the University of Leicester. At NUI Galway, the Irish researchers will engage with the science and outreach programme Cell Explorers (!about2/cqs8). With funding from SFI, Cell Explorers visits primary schools and a hands-on workshop at the annual Galway Science and Technology Festival. Both PI's will regularly engage with prospective students and parents at annual University Open Days.

4. Exploitation and application
HDACs are emerging as important drug targets for the treatment of cancer and neurological diseases like Huntington's. Prof Lahue's group is involved currently involved in pre-clinical testing of an HDAC3-specific inhibitor for Huntington's disease. The unpublished results show suppression of somatic CAG repeat expansions in the HD gene upon treatment with the HDAC3 inhibitor. The proposed research will directly test the hypothesis that HDAC3, acting in the SMRT/NCoR/HDAC5 complex, regulates the DNA repair protein MutSbeta to control triplet repeat expansions. If so, it will provide the opportunity to identify acetylated forms of MutSbeta as new biomarkers for genomic instability. The multinational company BioMarin Pharmaceutical is license-holder for the HDAC3 inhibitor and provides the compound gratis to Prof Lahue. We will seek to maintain and expand the fruitful relationship with BioMarin with an eye towards obtaining additional funding for the pre-clinical aspects of this work. Prof. Lahue is in frequent contact with NUI Galway's Ignite Technology Transfer Office, which assists in all intellectual property opportunities. Any commercial opportunities that arise from the proposed research will be explored with Ignite.

The University of Leicester has a vigorous and experienced Enterprise & Business Development team and an embedded unit 'The Biobator', dedicated to exploitation of activities arising from work in biomedical research. Prof Schwabe and his postdoctoral research associate will meet with their enterprise office regularly to explore potential routes to commercial opportunities associated with the generation of their structural and functional data. This will allow having mechanisms in place to optimise the commercialisation/intellectual property of the work and in this way allow timely publication of the results for the wider academic community.


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Williams GM (2020) HDAC3 deacetylates the DNA mismatch repair factor MutSß to stimulate triplet repeat expansions. in Proceedings of the National Academy of Sciences of the United States of America

Description Trinucleotide repeat (TNR) expansions cause nearly 20 severe human neurological diseases which are currently untreatable. Expansions can occur both between generations (inherited expansions) and within tissues of an individual (somatic expansions). For some of these diseases, ongoing somatic expansions accelerate disease progression and may influence age of onset. This emphasizes the importance of understanding the protein factors that drive expansions. Recent genetic evidence indicates that the mismatch repair factor MutSß (Msh2-Msh3 complex) and the histone deacetylase HDAC3 function in the same pathway to drive triplet repeat expansions. Here we tested the hypothesis that HDAC3 deacetylates MutSß and thereby activates it to drive expansions. The HDAC3-selective inhibitor RGFP966 was used to examine its biological and biochemical consequences in human tissue culture cells. HDAC3 inhibition efficiently suppresses repeat expansion without impeding canonical mismatch repair activity. Five key lysine residues in Msh3 are direct targets of HDAC3 deacetylation. In cells expressing Msh3 in which these lysine residues are mutated to arginine, the inhibitory effect of RGFP966 on expansions is largely bypassed, consistent with the direct deacetylation hypothesis. RGFP966 treatment does not alter MutSß subunit abundance or complex formation but does partially control its subcellular localization. Deacetylation sites in Msh3 overlap a nuclear localization signal, and we show that localization of MutSß is partially dependent on HDAC3 activity. Together, these results indicate that MutSß is a key target of HDAC3 deacetylation and provide insights into an innovative regulatory mechanism for triplet repeat expansions. The results suggest expansion activity may be druggable and support HDAC3-selective inhibition as an attractive therapy in some triplet repeat expansion diseases.
Exploitation Route Triplet repeat expansions cause nearly 20 inherited neurological diseases. The molecular mechanism of expansions is of interest at two levels. First is the basic science of how triplet repeats expand, and the second is the therapeutic opportunity to treat expansion diseases. This study presents evidence that addresses both areas of interest. We show that the histone deacetylase HDAC3 acts directly on the DNA mismatch repair protein MutSß to stimulate CAG•CTG repeat expansions. This basic science insight into the mechanism also provides an explanation for how HDAC3 inhibition in Huntington's disease mice leads to suppression of triplet repeat expansions and could therefore be considered as a therapy for Huntington's disease and potentially other CAG•CTG repeat expansion diseases.

Our results therefore suggest that under some circumstances there may be benefit in using HDAC inhibitors to prevent triplet repeat expansions.
Sectors Healthcare