Soundararajan Rama, Melters Daniël, Shih I-Chia, Wang Jian, Pearce David
Division of Nephrology, Department of Medicine, University of California, San Francisco, CA 94143, USA.
Proc Natl Acad Sci U S A. 2009 May 12;106(19):7804-9. doi: 10.1073/pnas.0809892106. Epub 2009 Apr 20.
Hormonal control of transepithelial sodium (Na(+)) transport utilizes phosphatidylinositide 3'-kinase (PI3K) and Raf-MAPK/ERK kinase (MEK)-ERK-dependent signaling pathways, which impact numerous cell functions. How signals transmitted by these pathways are sorted and appropriately transmitted to alter Na(+) transport without altering other physiologic processes is not well understood. Here, we report the identification of a signaling complex that selectively modulates the cell surface expression of the epithelial sodium channel (ENaC), an ion channel that is essential for fluid and electrolyte balance in mammals. Raf-1 and the ubiquitin ligase, Nedd4-2, are constitutively-expressed inhibitory components of this ENaC regulatory complex, which interact with, and decrease the expression of, cell surface ENaC. The activities of Nedd4-2 and Raf-1 are inhibited cooperatively by the PI3K-dependent kinase serum- and glucocorticoid-induced kinase 1 (SGK1), and the Raf-1-interacting protein glucocorticoid-induced leucine zipper (GILZ1), which are aldosterone-stimulated components of the complex. Together, SGK1 and GILZ1 synergistically stimulate ENaC cell surface expression. Interestingly, GILZ1 and SGK1 do not have synergistic, and in fact have opposite, effects on an unrelated activity, FKHRL1-driven gene transcription. Together, these data suggest that GILZ1 and SGK1 provide a physical and functional link between the PI3K- and Raf-1-dependent signaling modules and represent a unique mechanism for specifically controlling Na(+) transport without inappropriately activating other cell functions.
上皮细胞钠(Na⁺)转运的激素调控利用磷脂酰肌醇3'-激酶(PI3K)和Raf-丝裂原活化蛋白激酶/细胞外信号调节激酶(MEK)-细胞外信号调节激酶(ERK)依赖性信号通路,这些通路影响众多细胞功能。这些通路传递的信号如何被分类并适当传递以改变Na⁺转运而不改变其他生理过程,目前尚不清楚。在此,我们报告鉴定出一种信号复合物,其可选择性调节上皮钠通道(ENaC)的细胞表面表达,ENaC是一种对哺乳动物体内液体和电解质平衡至关重要的离子通道。Raf-1和泛素连接酶Nedd4-2是该ENaC调节复合物的组成性表达抑制成分,它们与细胞表面ENaC相互作用并降低其表达。Nedd4-2和Raf-1的活性被PI3K依赖性激酶血清和糖皮质激素诱导激酶1(SGK1)以及与Raf-1相互作用的蛋白糖皮质激素诱导亮氨酸拉链(GILZ1)协同抑制,GILZ1是该复合物中受醛固酮刺激的成分。SGK1和GILZ1共同协同刺激ENaC细胞表面表达。有趣的是,GILZ1和SGK1对一种不相关的活性,即FKHRL1驱动的基因转录没有协同作用,实际上具有相反的作用。总之,这些数据表明GILZ1和SGK1在PI3K和Raf-1依赖性信号模块之间提供了物理和功能联系,并代表了一种特异性控制Na⁺转运而不不适当地激活其他细胞功能的独特机制。