Surfactant Protein A2 Mutations Associated with Pulmonary Fibrosis Lead to Protein Instability and Endoplasmic Reticulum Stress
Surfactant Protein A2 Mutations Associated with Pulmonary Fibrosis Lead to Protein Instability and Endoplasmic Reticulum Stress
复制标题
DOI：
10.1074/jbc.m110.121467
复制
发表时间：
2010-07-16
影响因子：
4.8
通讯作者：
Garcia, Christine Kim
中科院分区：
文献类型：
--
作者：
Maitra, Meenakshi;Wang, Yongyu;Garcia, Christine Kim
编码表面活性剂蛋白A2 （SP-A2, SFTPA2）基因的罕见杂合突变与成人发病的肺纤维化和肺腺癌有关。我们之前的研究表明，两种重组SP-A2突变蛋白（G231V和F198S）保留在A549细胞的内质网（ER）内，而不分泌到培养基中。突变蛋白的致病机制尚不清楚。在这里，我们分析了A549细胞和原代II型肺泡上皮细胞中表面活性剂蛋白A2 （SP-A2）的所有常见和罕见变异。我们发现，与所有其他SP-A2变体相比，突变蛋白不分泌到具有野生型SP-A异构体的培养基中，形成较少的细胞内二聚体和三聚体低聚物，部分不溶于转染A549细胞的0.5% Nonidet P-40裂解物，并且在凝乳胰蛋白酶蛋白水解消化中表现出更大的蛋白质不稳定性。G231V和F198S突变体SP-A2蛋白都通过er关联降解途径被破坏。突变蛋白的表达增加了BiP报告结构的转录、BiP蛋白的表达和内质网应激诱导的XBP-1剪接产物的产生。来自G231V杂合突变个体的人类支气管肺泡洗涤样本与正常家庭成员的SP-A总量相似，这表明疾病的机制并不涉及分泌SP-A的明显缺乏，而是涉及II型肺泡上皮细胞内质网应激的增加。
Rare heterozygous mutations in the gene encoding surfactant protein A2 (SP-A2, SFTPA2) are associated with adult-onset pulmonary fibrosis and adenocarcinoma of the lung. We have previously shown that two recombinant SP-A2 mutant proteins (G231V and F198S) remain within the endoplasmic reticulum (ER) of A549 cells and are not secreted into the culture medium. The pathogenic mechanism of the mutant proteins is unknown. Here we analyze all common and rare variants of the surfactant protein A2, SP-A2, in both A549 cells and in primary type II alveolar epithelial cells. We show that, in contrast with all other SP-A2 variants, the mutant proteins are not secreted into the medium with wild-type SP-A isoforms, form fewer intracellular dimer and trimer oligomers, are partially insoluble in 0.5% Nonidet P-40 lysates of transfected A549 cells, and demonstrate greater protein instability in chymotrypsin proteolytic digestions. Both the G231V and F198S mutant SP-A2 proteins are destroyed via the ER-association degradation pathway. Expression of the mutant proteins increases the transcription of a BiP-reporter construct, expression of BiP protein, and production of an ER stress-induced XBP-1 spliced product. Human bronchoalveolar wash samples from individuals who are heterozygous for the G231V mutation have similar levels of total SP-A as normal family members, which suggests that the mechanism of disease does not involve an overt lack of secreted SP-A but instead involves an increase in ER stress of resident type II alveolar epithelial cells.