Mechanism and Function of Arc Palmitoylation

 描述（由申请人提供）：突触功效的活性依赖性变化，例如在长时程增强（LTP）和长时程抑制（LTD）期间发生的那些变化，被认为是学习和记忆的基础。LTP和LTD中的一个关键事件是诱导一组立即早期基因产物，包括活性调节的细胞骨架相关蛋白（arc，也称为arg 3.1）。Arc的最佳特征功能是增强树突棘中AMPA受体的内吞内化，这是与LTD相关的过程。Arc也参与了内体表面淀粉样前体蛋白（APP）的蛋白水解加工。为了介导这些活动，Arc必须与细胞膜结合，但其与膜结合的机制尚不清楚。在解决这个问题时，我们发现Arc在神经元中经历棕榈酰化，使其能够直接插入脂质双层。与其他形式的蛋白质脂化不同，棕榈酰化是可逆的，因此可能受到条件调控。目标1 我们计划定义Arc棕榈酰化的机制和生化后果。我们将确定Arc棕榈酰化的水平是否对LTP和LTD诱导范式有反应，我们将确定23种已知的人类棕榈酰酰基转移酶形式中的哪一种负责修饰Arc。使用生物化学和成像方法的组合，我们将确定棕榈酰化如何影响Arc的亚细胞分布，其在活细胞膜上自组装的能力，以及其对酪氨酸磷酸化的敏感性，这是我们研究中发现的另一种Arc修饰。在目标2中，我们将进行电生理学研究，旨在了解弧棕榈酰化如何影响突触可塑性。我们先前的工作暗示Arc参与了突触强度的减弱和兴奋性突触的消除。初步数据表明，这些影响可能是由弧棕榈酰化介导的。Arc表达的变化与许多认知障碍有关，包括精神发育迟滞、阿尔茨海默病和物质滥用。因此，阐明Arc调控的新机制具有潜在的临床意义。

 DESCRIPTION (provided by applicant): Activity dependent changes in synaptic efficacy, such as those which occur during long-term potentiation (LTP) and long-term depression (LTD), are believed to underlie learning and memory. A key event in both LTP and LTD is the induction of a set of immediate-early gene products, including the activity-regulated cytoskeletal- associated protein (arc, also known as arg 3.1). The best characterized function of Arc is enhancement of the endocytic internalization of AMPA receptors in dendritic spines, a process associated with LTD. Arc has also been implicated in the proteolytic processing of amyloid precursor protein (APP) on the surface of endosomes. To mediate these activities, Arc must associate with cellular membranes, but the mechanism of its binding to membranes is not understood. In addressing this question, we found that Arc undergoes palmitoylation in neurons, allowing it to insert directly into the lipid bilayer. Unlike other forms of protein lipidation, palmitoylation is reversible and, hence, may be subject to conditional regulation. In Aim 1 of this project we propose to define the mechanism and biochemical consequences of Arc palmitoylation. We will determine if the level of Arc palmitoylation is responsive to LTP- and LTD-inducing paradigms, and we will identify which of the 23 known human forms of palmitoyl acyltransferase is (are) responsible for modifying Arc. Using a combination of biochemical and imaging approaches, we will determine how palmitoylation influences the subcellular distribution of Arc, its ability to self-assemble on the membranes of living cells, and its susceptibility to undergo tyrosine phosphorylation, another Arc modification identified in our studies. In Aim 2 we will carry out electrophysiological investigations aimed at understanding how Arc palmitoylation affects synaptic plasticity. Our previous work implicated Arc in the weakening of synaptic strength and the elimination of excitatory synapses. Preliminary data indicate that these effects may be mediated by Arc palmitoylation. Changes in Arc expression have been linked to numerous cognitive disorders, including mental retardation, Alzheimer's disease, and substance abuse. Therefore, elucidation of novel mechanisms of Arc regulation has potential clinical significance.