Roles of UBE3A-mediated p18 regulation in synaptogenesis and synaptic plasticity

UBE3A是泛素-蛋白酶体系统中的一种E3连接酶，在脑发育和功能中发挥着重要作用。 最佳的CNS UBE3A表达是至关重要的，因为它的缺乏会导致Angelman综合征(AS)，而它的过度表达则是非常重要的。 情绪表达会增加患自闭症的风险。然而，UBE3A在中枢神经系统中的确切功能在很大程度上仍不清楚。 在AS小鼠模型中，Ube3a缺乏会导致运动功能、学习和记忆以及社交能力的缺陷 互动。我们最近报道，Ube3a缺乏导致mTORC1激活增加，但 雷帕霉素作用靶点的两个核心复合体mTORC2活性降低 信号通路。然而，UBE3A缺乏是如何导致mTORC1过度激活的尚不清楚。 新的证据表明，氨基酸的存在对于mTORC1的充分激活是必不可少的。氨基 酸诱导的mTORC1激活依赖于mTORC1对晚期内切酶/溶酶体的募集 膜，涉及形成具有RagC或RagD的RAGA或RagB的杂二聚体的过程 通过绑定到Ragator。刺激器与溶酶体膜的锚定是通过其 组件，第18页。P18 N-末端的肉豆蔻酰化和棕榈酰化是其 溶酶体定位。我们的初步结果显示，由于ube3a的作用，p18水平升高。 在COS1细胞和AS小鼠脑中存在缺陷。我们进一步证明p18可以被Ube3a泛化。 COS1细胞。这些发现导致我们提出了一个中心假设，即在正常情况下，溶酶体 定位的p18水平受Ube3a介导的泛素化控制，该泛素化针对蛋白酶体的p18。 退化。这一假说的一个相关性是缺乏Ube3a介导的p18泛素化和AS中的降解 小鼠导致mTORC1/mTORC2信号不平衡，脊椎形态和突触可塑性异常。 我们将首先确定p18中的泛素化位点，并确定N末端的酰化是否影响Ube3a- 介导的p18泛素化。然后我们将确定ube3a介导的p18调控是否起重要作用。 在突触发生、突触可塑性和经验依赖性突触重塑中的作用 多学科方法。由于UBE3A缺乏和过度表达都与 神经发育障碍，了解UBE3A介导的p18和mTOR信号调节以及 它在突触发生和突触可塑性中的作用应该有助于阐明基本的神经生物学机制，如 以及几种神经和神经精神疾病。

UBE3A, an E3 ligase in the ubiquitin-proteasomal system, plays important roles in brain development and function. Optimal CNS UBE3A expression is crucial since its deficiency results in Angelman syndrome (AS), while its over- expression increases the risk for autism. Yet, the precise function of UBE3A in the CNS remains largely unknown. In AS mouse models, Ube3a deficiency leads to deficits in motor function, learning and memory, and social interactions. We have recently reported that Ube3a deficiency leads to increased activation of mTORC1 but decreased activation of mTORC2, the two core complexes in the mechanistic target of rapamycin (mTOR) signaling pathway. However, how UBE3A deficiency results in mTORC1 over-activation remains unknown. Emerging evidence indicates that the presence of amino acids is essential for full mTORC1 activation. Amino acid-induced mTORC1 activation depends on the recruitment of mTORC1 to late endosomal/lysosomal membranes, a process involving the formation of heterodimers of a RagA or RagB, with a RagC or RagD through binding to the Ragulator. The anchoring of Ragulator to lysosomal membrane is through one of its components, p18. Myristoylation and palmitoylation in the N-terminal domain of p18 are critical for its lysosomal localization. Our preliminary results revealed that p18 levels were increased as a result of Ube3a deficiency in COS1 cells and in AS mouse brain. We further showed that p18 could be ubiquitinated by Ube3a in COS1 cells. These findings led us to propose the central hypothesis that, under normal conditions, lysosomal localized p18 levels are controlled by Ube3a-mediated ubiquitination, which targets p18 for proteasomal degradation. A correlate of this hypothesis is that lack of Ube3a-mediated p18 ubiquitination and degradation in AS mice results in imbalanced mTORC1/mTORC2 signaling and abnormal spine morphology and synaptic plasticity. We will first identify the ubiquitination sites in p18 and determine whether N-terminal acylation affects Ube3a- mediated p18 ubiquitination. We will then determine whether Ube3a-mediated p18 regulation plays important roles in synaptogenesis, synaptic plasticity, and experience-dependent remodeling of synapses using a multidisciplinary approach. Since both UBE3A deficiency and overexpression are linked to neurodevelopmental disorders, understanding UBE3A-mediated regulation of p18 and of mTOR signaling and its role in synaptogenesis and synaptic plasticity should shed light on basic neurobiological mechanisms, as well as on several neurological and neuropsychiatric diseases.