Ji Hong-Long, Song Weifeng, Gao Zhiqian, Su Xue-Feng, Nie Hong-Guang, Jiang Yi, Peng Ji-Bin, He Yu-Xian, Liao Ying, Zhou Yong-Jian, Tousson Albert, Matalon Sadis
Department of Anesthesiology, University of Alabama at Birmingham School of Medicine, Birmingham, Alabama 35233-6810, USA.
Am J Physiol Lung Cell Mol Physiol. 2009 Mar;296(3):L372-83. doi: 10.1152/ajplung.90437.2008. Epub 2008 Dec 26.
Among the multiple organ disorders caused by the severe acute respiratory syndrome coronavirus (SARS-CoV), acute lung failure following atypical pneumonia is the most serious and often fatal event. We hypothesized that two of the hydrophilic structural coronoviral proteins (S and E) would regulate alveolar fluid clearance by decreasing the cell surface expression and activity of amiloride-sensitive epithelial sodium (Na(+)) channels (ENaC), the rate-limiting protein in transepithelial Na(+) vectorial transport across distal lung epithelial cells. Coexpression of either S or E protein with human alpha-, beta-, and gamma-ENaC in Xenopus oocytes led to significant decreases of both amiloride-sensitive Na(+) currents and gamma-ENaC protein levels at their plasma membranes. S and E proteins decreased the rate of ENaC exocytosis and either had no effect (S) or decreased (E) rates of endocytosis. No direct interactions among SARS-CoV E protein with either alpha- or gamma-ENaC were indentified. Instead, the downregulation of ENaC activity by SARS proteins was partially or completely restored by administration of inhibitors of PKCalpha/beta1 and PKCzeta. Consistent with the whole cell data, expression of S and E proteins decreased ENaC single-channel activity in oocytes, and these effects were partially abrogated by PKCalpha/beta1 inhibitors. Finally, transfection of human airway epithelial (H441) cells with SARS E protein decreased whole cell amiloride-sensitive currents. These findings indicate that lung edema in SARS infection may be due at least in part to activation of PKC by SARS proteins, leading to decreasing levels and activity of ENaC at the apical surfaces of lung epithelial cells.
在严重急性呼吸综合征冠状病毒（SARS-CoV）引发的多器官功能障碍中，非典型肺炎后的急性肺衰竭是最严重且往往致命的事件。我们推测，两种亲水性结构冠状病毒蛋白（S蛋白和E蛋白）会通过降低氨氯地平敏感性上皮钠（Na⁺）通道（ENaC）的细胞表面表达和活性来调节肺泡液体清除，ENaC是跨肺远端上皮细胞的跨上皮Na⁺向量转运中的限速蛋白。在非洲爪蟾卵母细胞中，S蛋白或E蛋白与人α-、β-和γ-ENaC共表达导致氨氯地平敏感性Na⁺电流和质膜上γ-ENaC蛋白水平显著降低。S蛋白和E蛋白降低了ENaC胞吐速率，且对胞吞速率要么无影响（S蛋白）要么有降低作用（E蛋白）。未发现SARS-CoV E蛋白与α-或γ-ENaC之间存在直接相互作用。相反，通过给予PKCalpha/beta1和PKCzeta抑制剂，SARS蛋白对ENaC活性的下调作用部分或完全恢复。与全细胞数据一致，S蛋白和E蛋白的表达降低了卵母细胞中ENaC单通道活性，且PKCalpha/beta1抑制剂部分消除了这些作用。最后，用SARS E蛋白转染人气道上皮（H441）细胞降低了全细胞氨氯地平敏感性电流。这些发现表明，SARS感染中的肺水肿可能至少部分归因于SARS蛋白激活PKC，导致肺上皮细胞顶端表面ENaC水平和活性降低。
