Folding, Misfolding, and Function of PMP22

项目摘要 Charcot-Marie-Tooth病(CMT)是一种常见的衰弱遗传性周围神经病。这个 CMT的病理特征是PNS髓鞘严重缺陷。目前还没有治疗或治愈的方法 这种病。大约75%的CMT是由野生型雪旺细胞过度表达引起的 (WT)三体(1A型CMT)所致的外周血髓鞘蛋白(PMP22)，PMP22表达不足(对于 WT/空例)，或改变PMP22蛋白的遗传显性杂合(WT/突变)突变 序列(E型CMT或更严重的DeJerine-Sottas综合征-DSS)。重要的问题仍然存在 关于PMP22中这些不同类型缺陷导致的分子机制 不同形式的CMT。在这里，我们建议解决有关分子的关键悬而未决的问题 不同形式的CMT的基础。 目标1.在CMT1AWT框架下，WT PMP22的贩运和误贩运 PMP22的过度表达条件不同于折叠缺陷的DSS突变形式？我们将测试 假设错误折叠的WT PMP22最终出现在细胞质中，而DSS突变体如L16P PMP22被困在内质网或内质网到高尔基体的中间隔室(ERGIC)。 目的2.确定BAG6复合体(BAG6/GET4/UBL4A)在胞浆转运中的作用 WT PMP22。我们的初步数据表明，WT PMP22，而不是DSS突变体形式的PMP22 与胞质中的BAG6复合体相互作用。这一目标将检验BAG6复合体的假设 作为错误折叠的WT PMP22的保持酶，以促进其健康地穿梭到蛋白酶体，但 CMT1A中过量的PMP22会压倒蛋白酶体，导致侵袭体的形成，而侵袭体是 最终被BAG6诱导的自噬降解。 目的3.确定过量的WT PMP22是否抑制特定的蛋白酶体复合体和/或诱导 髓鞘干细胞中eif2α的磷酸化。在我们初步数据的推动下，这一目标将考验 假设WT PMP22在干细胞中过表达抑制26S蛋白酶体并激活 整合应激反应，导致eIF2α的磷酸化，以抑制蛋白质翻译。

Project Summary Charcot-Marie-Tooth Disease (CMT) is a common debilitating hereditary peripheral neuropathy. The hallmark of CMT pathology is severely defective PNS myelin. There is currently no treatment or cure for this disease. Roughly 75% of all cases of CMT are caused by Schwann cell overexpression of wild type (WT) peripheral myelin protein (PMP22) due to trisomy (type 1A CMT), underexpression of PMP22 (for the WT/null case), or genetically dominant heterozygous (WT/mutant) mutations that alter the PMP22 protein sequence (type E CMT or the more severe Dejerine-Sottas Syndrome--DSS). Important questions remain regarding the molecular mechanisms by which these different classes of defects in PMP22 result in different forms of CMT. Here we propose to address key outstanding questions regarding the molecular bases for the different forms of CMT. Aim 1. How does the trafficking and mis-trafficking of WT PMP22 under CMT1A WT overexpression conditions differ from a folding-defective DSS mutant form of PMP22? We will test the hypothesis that misfolded WT PMP22 ends up in the cytosol, whereas DSS mutants such as L16P PMP22 are trapped in the ER or ER-to-Golgi intermediate compartment (ERGIC). Aim 2. Determine the role of the BAG6 complex (BAG6/GET4/UBL4A) in the cytosolic trafficking of WT PMP22. Our preliminary data suggests that WT PMP22, but not DSS mutant forms of PMP22 interacts with the cytosolic BAG6 complex. This aim will test the hypothesis that the BAG6 complex serves as a holdase for misfolded WT PMP22 to facilitate its healthy shuttling to the proteasome, but that excess PMP22 in CMT1A overwhelms the proteasome, resulting in formation of aggresomes, which are eventually degraded by BAG6-induced autophagy. Aim 3. Determine if excess WT PMP22 inhibits specific proteasome complexes and/or induces phosphorylation of eIF2α in myelinating SCs. Prompted by our preliminary data, this Aim will test the hypothesis that overexpression of WT PMP22 in SCs inhibits the 26S proteasome and activates an integrated stress response (ISR), resulting in phosphorylation of eIF2α to suppress protein translation.