Division of Neurobiology, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Hum Mol Genet. 2020 May 28;29(8):1340-1352. doi: 10.1093/hmg/ddaa061.
Nemo-like kinase (NLK), an evolutionarily conserved serine/threonine kinase, is highly expressed in the brain, but its function in the adult brain remains not well understood. In this study, we identify NLK as an interactor of huntingtin protein (HTT). We report that NLK levels are significantly decreased in HD human brain and HD models. Importantly, overexpression of NLK in the striatum attenuates brain atrophy, preserves striatal DARPP32 levels and reduces mutant HTT (mHTT) aggregation in HD mice. In contrast, genetic reduction of NLK exacerbates brain atrophy and loss of DARPP32 in HD mice. Moreover, we demonstrate that NLK lowers mHTT levels in a kinase activity-dependent manner, while having no significant effect on normal HTT protein levels in mouse striatal cells, human cells and HD mouse models. The NLK-mediated lowering of mHTT is associated with enhanced phosphorylation of mHTT. Phosphorylation defective mutation of serine at amino acid 120 (S120) abolishes the mHTT-lowering effect of NLK, suggesting that S120 phosphorylation is an important step in the NLK-mediated lowering of mHTT. A further mechanistic study suggests that NLK promotes mHTT ubiquitination and degradation via the proteasome pathway. Taken together, our results indicate a protective role of NLK in HD and reveal a new molecular target to reduce mHTT levels.
Nemo 样激酶（NLK）是一种进化上保守的丝氨酸/苏氨酸激酶，在大脑中高度表达，但在成年大脑中的功能尚不清楚。在这项研究中，我们鉴定 NLK 是亨廷顿蛋白（HTT）的相互作用蛋白。我们报告 NLK 水平在 HD 人脑和 HD 模型中显著降低。重要的是，NLK 在纹状体中的过表达可减轻脑萎缩，保持纹状体 DARPP32 水平并减少 HD 小鼠中突变 HTT（mHTT）聚集。相比之下，NLK 的遗传减少会加重 HD 小鼠中的脑萎缩和 DARPP32 丧失。此外，我们证明 NLK 以激酶活性依赖性方式降低 mHTT 水平，而对小鼠纹状体细胞、人细胞和 HD 小鼠模型中的正常 HTT 蛋白水平没有明显影响。NLK 介导的 mHTT 降低与 mHTT 的磷酸化增强有关。在氨基酸 120 处丝氨酸的磷酸化缺陷突变（S120）消除了 NLK 对 mHTT 降低的作用，表明 S120 磷酸化是 NLK 介导的 mHTT 降低的重要步骤。进一步的机制研究表明，NLK 通过蛋白酶体途径促进 mHTT 的泛素化和降解。总之，我们的结果表明 NLK 在 HD 中具有保护作用，并揭示了降低 mHTT 水平的新分子靶标。
