Surfactant Biology Laboratories, Pulmonary and Critical Care Division, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, USA.
Am J Respir Cell Mol Biol. 2011 Mar;44(3):404-14. doi: 10.1165/rcmb.2009-0382OC. Epub 2010 May 12.
Chronic interstitial lung disease in both adults and children is associated with mutations of the surfactant protein C (SP-C) proprotein. Among these, mutations within the distal COOH propeptide, known as the BRICHOS domain, are associated with a severe disease phenotype. We showed that prolonged expression of the BRICHOS mutants, SP-C(Δexon4) and SP-C(L188Q), destabilizes endoplasmic reticulum (ER) quality-control mechanisms (the unfolded protein response, or UPR), resulting in the induction of ER stress signaling, an inhibition of the ubiquitin/proteasome system, and the activation of apoptotic pathways. Based on recent observations that the UPR and ER stress can be linked to the induction of proinflammatory signaling, we hypothesized that the epithelial cell dysfunction mediated by SP-C BRICHOS mutants would activate proinflammatory signaling pathways. In a test of this hypothesis, A549 and human embryonic kidney epithelial (HEK293) cells, transiently transfected with either SP-C(Δexon4) or SP-C(L188Q) mutants, each promoted the upregulation of multiple UPR response genes, including homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1 (HERPUD1) and GRP78. Commensurate with these results, increases in IL-8 secretion occurred and were accompanied by the activation of c-Jun N-terminal kinase (JNK)/activating protein-1 signaling. The stimulation of IL-8 cytokine release was completely attenuated by treatment with the JNK-specific inhibitor, SP600125. In addition, SP-C(Δexon4), but not SP-C(L188Q), activated NFκB. The treatment of SP-C(Δexon4) transfected cells with 4-phenylbutyric acid, a small molecule chaperone known to improve protein folding, blocked the activation of NFκB, but not the release of IL-8. Taken together, the results support the role of JNK signaling in mediating SP-C BRICHOS-induced cytokine release, and provide a link between SP-C BRICHOS mutants and proinflammatory cytokine signaling.
成人和儿童的慢性间质性肺病与表面活性剂蛋白 C (SP-C) 前蛋白的突变有关。在这些突变中，位于远端 COOH 前肽内的突变，称为 BRICHOS 结构域，与严重的疾病表型有关。我们表明，BRICHOS 突变体 SP-C(Δexon4)和 SP-C(L188Q)的延长表达会破坏内质网 (ER) 质量控制机制（未折叠蛋白反应，或 UPR），导致 ER 应激信号的诱导、泛素/蛋白酶体系统的抑制和凋亡途径的激活。基于最近的观察结果，即 UPR 和 ER 应激可以与促炎信号的诱导相关联，我们假设 SP-C BRICHOS 突变体介导的上皮细胞功能障碍会激活促炎信号通路。在对该假设的检验中，用 SP-C(Δexon4)或 SP-C(L188Q)突变体瞬时转染的 A549 和人胚肾上皮 (HEK293) 细胞，每种细胞均促进多个 UPR 反应基因的上调，包括同型半胱氨酸诱导、内质网应激诱导、泛素样结构域成员 1 (HERPUD1) 和 GRP78。与这些结果一致，IL-8 分泌增加，并伴随着 c-Jun N-末端激酶 (JNK)/激活蛋白-1 信号的激活。用 JNK 特异性抑制剂 SP600125 处理完全抑制了 IL-8 细胞因子的释放。此外，SP-C(Δexon4)，而不是 SP-C(L188Q)，激活了 NFκB。用小分子伴侣 4-苯丁酸处理转染 SP-C(Δexon4)的细胞，可改善蛋白质折叠，阻断 NFκB 的激活，但不阻断 IL-8 的释放。总之，这些结果支持 JNK 信号在介导 SP-C BRICHOS 诱导的细胞因子释放中的作用，并提供了 SP-C BRICHOS 突变体与促炎细胞因子信号之间的联系。
