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Abstract：
Aldosterone-induced serum- and glucocorticoid-inducible kinase isoform 1 (SGK1) contributes to the regulation of the epithelial sodium channel (ENaC), the activity of which is critical for long term blood pressure control. Aldosterone-induced SGK1 is thought to enhance ENaC surface expression by phosphorylating Nedd4-2 and thereby preventing ENaC retrieval and degradation. In outside-out membrane patches of Xenopus laevis oocytes heterologously expressing ENaC, amiloride-sensitive ENaC currents were enhanced by phosphatase inhibitors and were dependent on cytosolic Mg(2+). This indicates that a kinase is involved in channel regulation. Indeed, recombinant constitutively active SGK1, included in the pipette solution, caused a sustained 2- to 3-fold increase of ENaC currents. Deletion of the C terminus of alphaENaC largely reduced the stimulatory effect of SGK1, whereas stimulation by SGK1 did not require the presence of the C termini of the beta- or gamma-subunits. Replacing the serine residue Ser(621) of the SGK1 consensus motif in the C terminus of the alpha-subunit by an alanine specifically abolished the stimulatory effect of SGK. Our findings indicate that SGK1 can stimulate ENaC activity independently of an inhibition of Nedd4-2-mediated channel retrieval. This defines a novel regulatory pathway likely to be relevant for aldosterone-induced stimulation of ENaC in vivo.
摘要：
醛固酮诱导的血清和糖皮质激素诱导的激酶亚型1（SGK1）有助于上皮钠通道（ENaC）的调节，其活动对长期血压控制至关重要。醛固酮诱导的SGK1被认为通过磷酸化Nedd4-2增强ENaC表面表达，从而阻止ENaC恢复和降解。在异源表达ENaC的非洲爪猿卵母细胞的外膜斑块中，阿米洛利敏感的ENaC电流被磷酸酶抑制剂增强，并且依赖于细胞溶质Mg（2）。这表明激酶参与通道调节。的确,重组组成型活性SGK1，包含在移液管溶液中，导致ENaC电流持续增加2至3倍。αENaC的C末端的缺失在很大程度上降低了SGK1的刺激作用,而SGK1的刺激不需要存在β-或γ-亚基的C末端。用丙氨酸取代α-亚基C末端的SGK1共有基序的丝氨酸残基Ser(621)特异性地消除了SGK的刺激作用。我们的发现表明，SGK1可以刺激ENaC活性，而与抑制Nedd4-2介导的通道恢复无关。这定义了可能与醛固酮诱导的体内ENaC刺激相关的新调节途径。
