Folding, Misfolding, and Function of PMP22

项目摘要 腓骨肌萎缩症（CMT）是一种常见的遗传性周围神经病变。的 CMT病理学的标志是严重缺陷的PNS髓磷脂。目前没有治疗或治愈 这种疾病。大约75%的CMT病例是由野生型雪旺细胞过度表达引起的。 (WT)外周髓磷脂蛋白（PMP 22）由于三体（1A型CMT），低表达的PMP 22（对于 WT/无效病例），或改变PMP 22蛋白的遗传显性杂合（WT/突变体）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PMP 22中这些不同类型的缺陷导致的分子机制， 不同形式的CMT。在这里，我们提出解决关键的悬而未决的问题，关于分子 不同形式CMT的基础。 目标1.如何根据CMT 1A WT贩运和错误贩运WT PMP 22 过表达条件不同的折叠缺陷型DSS突变形式的PMP 22？我们将测试 错误折叠的WT PMP 22最终在胞质溶胶中的假设，而DSS突变体如L16 P PMP 22被捕获在ER或ER至高尔基体中间室（ERGIC）中。 目标2.确定BAG 6复合物（BAG 6/GET 4/UBL 4A）在细胞溶质运输中的作用 WT PMP 22我们的初步数据表明，WT PMP 22，而不是DSS突变形式的PMP 22， 与细胞溶质BAG 6复合物相互作用。这一目标将检验BAG 6复合物 作为错误折叠的WT PMP 22的保持酶，以促进其健康地穿梭于蛋白酶体，但是， CMT 1A中过量的PMP 22使蛋白酶体变性，导致侵袭体的形成， 最终被BAG 6诱导的自噬降解。 目标3。确定过量的WT PMP 22是否抑制特异性蛋白酶体复合物和/或诱导 髓鞘形成SC中eIF 2 α的磷酸化。根据我们的初步数据，这一目标将测试 假设WT PMP 22在SC中的过表达抑制26 S蛋白酶体并激活26 S蛋白酶体， 整合应激反应（ISR），导致eIF 2 α磷酸化抑制蛋白翻译。

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.