Centre for Chromosome Biology, National University of Ireland Galway, H9W2TY Galway, Ireland.
Leicester Institute of Chemical and Molecular Biology, Department of Molecular and Cell Biology, University of Leicester, LE1 7RH Leicester, United Kingdom.
Proc Natl Acad Sci U S A. 2020 Sep 22;117(38):23597-23605. doi: 10.1073/pnas.2013223117. Epub 2020 Sep 8.
Trinucleotide repeat (TNR) expansions cause nearly 20 severe human neurological diseases which are currently untreatable. For some of these diseases, ongoing somatic expansions accelerate disease progression and may influence age of onset. This new knowledge emphasizes the importance of understanding the protein factors that drive expansions. Recent genetic evidence indicates that the mismatch repair factor MutSβ (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 MutSβ 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 MutSβ 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 MutSβ is partially dependent on HDAC3 activity. Together, these results indicate that MutSβ 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.
三核苷酸重复（TNR）扩展导致近 20 种严重的人类神经疾病，目前尚无治疗方法。对于其中一些疾病，正在进行的体细胞扩展会加速疾病进展，并可能影响发病年龄。这一新知识强调了了解导致扩展的蛋白质因素的重要性。最近的遗传证据表明，错配修复因子 MutSβ（Msh2-Msh3 复合物）和组蛋白去乙酰化酶 HDAC3 在同一途径中发挥作用，以驱动三核苷酸重复扩展。在这里，我们检验了 HDAC3 去乙酰化 MutSβ 并激活其驱动扩展的假设。使用 HDAC3 选择性抑制剂 RGFP966 来研究其在人类组织培养细胞中的生物学和生物化学后果。HDAC3 抑制有效地抑制了重复扩展，而不会阻碍经典的错配修复活性。Msh3 中的五个关键赖氨酸残基是 HDAC3 去乙酰化的直接靶标。在表达 Msh3 的细胞中，这些赖氨酸残基突变为精氨酸，RGFP966 对扩展的抑制作用在很大程度上被绕过，这与直接去乙酰化假设一致。RGFP966 处理不会改变 MutSβ 亚基的丰度或复合物形成，但会部分控制其亚细胞定位。Msh3 中的去乙酰化位点与核定位信号重叠，我们表明 MutSβ 的定位部分依赖于 HDAC3 活性。总之，这些结果表明 MutSβ 是 HDAC3 去乙酰化的关键靶标，并为三核苷酸重复扩展的创新调节机制提供了见解。结果表明，扩展活性可能是可治疗的，并支持 HDAC3 选择性抑制作为某些三核苷酸重复扩展疾病的有吸引力的治疗方法。
