Role of ERAD in Epithelial Cell Homeostasis

表面活性蛋白C（SP-C）仅由肺II型上皮细胞合成， 将蛋白原加工成疏水性成熟肽，以分泌到肺泡腔中。SP-C基因突变最近与家族性和散发性间质性肺病有关。我们的初步研究结果表明，在转基因小鼠的II型上皮细胞中表达疾病相关的SP-C突变导致上皮细胞死亡，并严重扰乱肺形态发生，强烈表明SP-C基因突变可导致肺部疾病。本申请的中心假设是SP-C基因中的突变导致前蛋白的错误折叠和ERAD途径的饱和，导致蛋白质的细胞毒性形式的积累。提出了四个具体目标，以测试 以下假设：（1）不能通过ERAD快速降解突变型proSP-C，导致 前蛋白的细胞毒性形式的积累;（2）新的ERAD蛋白参与突变proSP-C的检测和/或降解;（3）质量控制受体特异性地检测突变proSP-C并分选前蛋白以通过泛素-蛋白酶体途径降解;和（4）体内ERAD的增加将加速突变proSP-C的降解，从而预防/减少突变proSP-C诱导的肺畸形发生。这项工作的长期目标是鉴定选择性增强ERAD的蛋白质，作为与蛋白质错误折叠相关的疾病的潜在治疗靶点。

Surfactant protein C (SP-C) is exclusively synthesized by pulmonary type II epithelial cells which process the proprotein to the hydrophobic mature peptide for secretion into the alveolar airspace. Mutations in the SP-C gene were recently linked to familial and sporadic interstitial lung disease. The results of our preliminary studies indicate that expression of a disease-associated SP-C mutation in type II epithelial cells of transgenic mice leads to epithelial cell death and profoundly perturbed lung morphogenesis strongly suggesting that mutations in the SP-C gene can cause lung disease. The central hypothesis of this application is that mutations in the SP-C gene result in misfolding of the proprotein and saturation of the ERAD pathway leading to accumulation of a cytotoxic form of the protein. Four specific aims are proposed to test the following hypotheses: (1) The inability to rapidly degrade mutant proSP-C via ERAD results in accumulation of a cytotoxic form of the proprotein; (2) Novel ERAD proteins are involved in the detection and/or degradation of mutant proSP-C; (3) A quality control receptor specifically detects mutant proSP-C and sorts the proprotein for degradation via the ubiquitin-proteasome pathway; and (4) Augmentation of ERAD in vivo will accelerate degradation of mutant proSP-C, thereby preventing/reducing mutant proSP-C induced lung dysmorphogenesis. The long term goal of this work is to identify proteins that selectively enhance ERAD for use as potential therapeutic targets in diseases associated with protein misfolding.