Rose F, Kürth-Landwehr C, Sibelius U, Reuner K H, Aktories K, Seeger W, Grimminger F
Department of Internal Medicine and Institute of Clinical Chemistry and Pathobiochemistry, Justus-Liebig-University, Giessen. Freiburg, Germany.
Am J Respir Crit Care Med. 1999 Jan;159(1):206-12. doi: 10.1164/ajrccm.159.1.9801106.
Alveolar epithelial type II cells (AET2) respond with exocytosis of surfactant containing lamellar bodies to stimulation with mechanical stretch and secretagogues, a process that is fundamental for maintaining alveolar stability and lung gas exchange. In the present study in cultured rat AET2, we employed botulinum C2 toxin, a binary toxin which ADP ribosylates nonmuscle G-actin, as a specific tool to probe the role of the actin microfilament system in the surfactant secretory process. Incubation of AET2 with C2 toxin caused a dose-dependent decay of the cellular F-actin content to a minimum of 20% of baseline, concomitant with an increase in monomeric actin. In parallel, a significant augmentation of baseline surfactant secretion up to twofold elevated levels above control was noted, as assessed by the release of prelabeled phosphatidylcholine. Pretreatment with phalloidin, which stabilized F-actin and reduced the level of G-actin, prevented the C2 toxin-elicited enhancement of baseline surfactant secretion. Even low C2 toxin concentrations, resulting in a reduction of total cellular F-actin content of approximately 10%, sufficed to augment secretagogue (ATP) and, more impressively, mechanical stress elicited an increase in surfactant secretion; the response to the biophysical challenge more than doubled. When investigated in the absence of toxin, different secretagogues (ATP, phorbol ester, betamimetics) caused a rapid-onset, transient reduction of F-actin in the range between 15 and 25% as a consistent part of their secretory response pattern. These data suggest that the state of actin polymerization is intimately linked to the exocytosis process underlying surfactant secretion in AET2. Microfilament system-related compartmentalization effects and/or or the impact of the state of actin assembly on signaling events may be considered as underlying events.
肺泡II型上皮细胞（AET2）在受到机械拉伸和促分泌剂刺激时，会通过含有板层小体的表面活性剂胞吐作用做出反应，这一过程对于维持肺泡稳定性和肺气体交换至关重要。在本项针对培养的大鼠AET2的研究中，我们使用肉毒杆菌C2毒素（一种将非肌肉G-肌动蛋白进行ADP核糖基化的二元毒素）作为一种特异性工具，来探究肌动蛋白微丝系统在表面活性剂分泌过程中的作用。用C2毒素孵育AET2导致细胞F-肌动蛋白含量呈剂量依赖性下降至基线的20%，同时单体肌动蛋白增加。与此同时，通过预标记磷脂酰胆碱的释放评估发现，基线表面活性剂分泌显著增加，比对照水平高出两倍。用鬼笔环肽预处理可稳定F-肌动蛋白并降低G-肌动蛋白水平，从而阻止C2毒素引起的基线表面活性剂分泌增强。即使是低浓度的C2毒素，导致总细胞F-肌动蛋白含量降低约10%，也足以增强促分泌剂（ATP）的作用，更显著的是，机械应激会引起表面活性剂分泌增加；对生物物理刺激的反应增加了一倍多。在无毒素情况下进行研究时，不同的促分泌剂（ATP、佛波酯、β-激动剂）会导致F-肌动蛋白迅速出现短暂下降，下降幅度在15%至25%之间，这是其分泌反应模式的一个一致组成部分。这些数据表明，肌动蛋白聚合状态与AET2中表面活性剂分泌所依赖的胞吐过程密切相关。微丝系统相关的区室化效应和/或肌动蛋白组装状态对信号事件的影响可能被视为潜在机制。
