Liddle's syndrome mutations increase Na+ transport through dual effects on epithelial Na+ channel surface expression and proteolytic cleavage
Liddle's syndrome mutations increase Na+ transport through dual effects on epithelial Na+ channel surface expression and proteolytic cleavage
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DOI：
10.1073/pnas.0511184103
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发表时间：
2006-02-21
影响因子：
11.1
通讯作者：
Snyder, PM
中科院分区：
文献类型：
--
作者：
Knight, KK;Olson, DR;Snyder, PM
Liddle综合征是一种遗传性高血压，由上皮Na+通道（ENaC）中C-末端PY基序缺失或破坏突变引起。先前的工作表明，这些突变通过破坏ENaC与Nedd 4 -2的结合来增加ENaC在细胞表面的表达，Nedd 4 - 2是一种E3泛素蛋白连接酶，靶向ENaC进行降解。然而，目前还不确定是否仅此机制负责; ENaC通道的活性增加也可能导致Liddle综合征中的过度Na+转运。ENaC活性部分受其切割状态控制;蛋白水解切割产生具有高开放状态概率的通道，而未切割的通道是无活性的。在这里，我们发现Liddle综合征突变对ENaC表面表达有两种不同的影响，这两种影响都有助于增加Na+转运。首先，这些突变增加了ENaC在细胞表面的表达;其次，它们增加了ENaC在细胞表面被切割（活性）的部分。这种不成比例的增加切割再现的显性负Nedd 4 -2或ENaC泛素化位点的突变，干扰破坏ENaC内吞作用和溶酶体降解的表达。相反，Nedd 4 -2的过表达具有相反的效果，降低了细胞表面切割的ENaC的分数。因此，这些数据不仅表明Nedd 4 -2部分通过控制细胞表面切割和未切割ENaC的相对表达来调节上皮Na+转运，而且还提供了Liddle综合征突变改变ENaC活性的机制。
Liddle's syndrome, an inherited form of hypertension, is caused by mutations that delete or disrupt a C-terminal PY motif in the epithelial Na+ channel (ENaC). Previous work indicates that these mutations increase expression of ENaC at the cell surface by disrupting its binding to Nedd4-2, an E3 ubiquitin-protein ligase that targets ENaC for degradation. However, it remains uncertain whether this mechanism alone is responsible; increased activity of ENaC channels could also contribute to excessive Na+ transport in Liddle's syndrome. ENaC activity is controlled in part by its cleavage state; proteolytic cleavage produces channels with a high open-state probability, whereas uncleaved channels are inactive. Here, we found that Liddle's syndrome mutations have two distinct effects of ENaC surface expression, both of which contribute to increased Na+ transport. First, these mutations increased ENaC expression at the cell surface; second, they increased the fraction of ENaC at the cell surface that was cleaved (active). This disproportionate increase in cleavage was reproduced by expression of a dominant-negative Nedd4-2 or mutation of ENaC ubiquitination sites, interventions that disrupt ENaC endocytosis and lysosomal degradation. Conversely, overexpression of Nedd4-2 had the opposite effect, decreasing the fraction of cleaved ENaC at the cell surface. Thus, the data riot only suggest that Nedd4-2 regulates epithelial Na+ transport in part by controlling the relative expression of cleaved and uncleaved ENaC at the cell surface but also provide a mechanism by which Liddle's syndrome mutations alter ENaC activity.