PP2A in Neurodevelopmental Disorders

项目总结/摘要 神经发育障碍，包括智力残疾、自闭症、青少年顽固性癫痫发作，以及 精神分裂症对社会经济影响很大，但病因学却知之甚少。近期大规模 测序工作确定了新生突变是神经发育障碍的主要原因。最多的 新突变出现在父系生殖细胞中，赋予突变精原细胞生长优势， 被称为“自私的精原选择” 蛋白磷酸酶2（PP 2A），主要的Ser/Thr磷酸酶之一，是已知的生长调节剂， 分化和疑似肿瘤抑制因子。一种催化（C）、支架（A）和 可变调节亚基（B、B“、B”），PP 2A可以在哺乳动物细胞中以>50个亚基组合存在， 可能具有不同的定位、底物和调节机制。新生突变的激增， 自2015年以来发现的PP 2A定义了两类新的常染色体显性精神发育迟滞。最 常见类型是由12个PP 2A调节亚基基因之一的复发性错义突变引起的， PPP 2 R5 D，其产物B ′-β在人类睾丸和大脑中占主导地位。相同的de novo PPP 2 R5 D 突变导致人类过度生长，这是一种通常与智力残疾和自闭症有关的综合症。 这一探索性的建议旨在确定复发性从头突变的分子机制， PPP 2 R5 D（B 'E2）导致神经发育障碍。因为有些神经发育障碍 可逆的，我们的研究结果可能会导致新的药理学干预。根据我们发表的研究 在发现精神发育迟滞中PP 2A突变之前，我们假设， PPP 2 R5 D通过一种新的功能改变机制引起神经发育障碍。我们特别 表明引入酸性底物结合表面碱性氨基酸改变PP 2A底物 特异性损害一些和有利于其他去磷酸化事件。这反过来又可以增强 生长/增殖信号传导途径超过介导细胞周期退出、分化和增殖的信号传导途径。 形态发生为了解决这一假设，本提案的两个目标将描述共有序列 对于野生型和突变型PP 2A酶的去磷酸化，通过定量分析鉴定其细胞底物， 磷酸化组学，并揭示神经元发育的细胞模型中的表型。基本见解 从这一建议，预计将铺平道路，为新的患者来源的细胞模型，动物模型，诊断 测试，以及最终用于神经发育障碍的PP 2A靶向治疗。

Project Summary / Abstract Neurodevelopmental disorders including intellectual disability, autism, juvenile intractable seizures, and schizophrenia have high socioeconomic impact, yet poorly understood etiologies. Recent large scale sequencing efforts identified de novo mutations as a major cause of neurodevelopmental disorders. Most de novo mutations arise in the paternal germline to confer a growth advantage to mutant spermatogonia in what has been termed “selfish spermatogonial selection”. Protein phosphatase 2 (PP2A), one of the major Ser/Thr phosphatases is a known regulator of growth and differentiation and a suspected tumor suppressor. A trimeric enzyme of catalytic (C), scaffolding (A), and variable regulatory subunits (B,B',B''), PP2A can exist in >50 subunit combinations in mammalian cells, presumably with distinct localization, substrates, and regulatory mechanisms. A surge of de novo mutations in PP2A uncovered since 2015 defined two new classes of autosomal-dominant mental retardation. The most common class is caused by recurrent missense mutations in one of the 12 PP2A regulatory subunit genes, PPP2R5D, the product of which, B' predominates in human testes and brain. The same de novo PPP2R5D mutations cause human overgrowth, a syndrome commonly associated with intellectual disability and autism. This exploratory proposal seeks to identify molecular mechanisms by which recurrent de novo mutations in PPP2R5D (B') cause neurodevelopmental disorders. Because some neurodevelopmental disorders are reversible, our results may lead to new pharmacological interventions. Predicated by our published work predating the discovery of PP2A mutations in mental retardation, we hypothesize that de novo mutations in PPP2R5D cause neurodevelopmental disorders by a novel change-of-function mechanism. Specifically, we suggest that basic amino acids introduced into an acidic substrate-binding surface alter PP2A substrate specifity to impair some and favor other dephosphorylation events. This in turn may enhance growth/proliferative signaling pathways over those that mediate cell cycle exit, differentiation, and morphogenesis. To address this hypothesis, the two aims of this proposal will delineate consensus sequences for dephosphorylation by wild-type and mutant PP2A enzymes, identify their cellular substrates by quantitative phosphoproeomics, and uncover phenotypes in cell models of neuronal development. Fundamental insights from this proposal are expected to pave the way for new patient-derived cell models, animal models, diagnostic tests, as well as ultimately for PP2A-targeted therapies of neurodevelopmental disorders.