Division of Digestive Diseases, Department of Medicine, Emory University, Atlanta, GA 30324, USA.
Mol Biol Cell. 2011 Oct;22(20):3812-25. doi: 10.1091/mbc.E11-04-0328. Epub 2011 Aug 24.
Na(+)/H(+) exchanger 3 (NHE3) is the major Na(+) transporter in the intestine. Serum- and glucocorticoid-induced kinase (SGK) 1 interacts with NHE regulatory factor 2 (NHERF2) and mediates activation of NHE3 by dexamethasone (Dex) in cultured epithelial cells. In this study, we compared short-term regulation of NHE3 by Dex in SGK1-null and NHERF2-null mice. In comparison to wild-type mice, loss of SGK1 or NHERF2 significantly attenuated regulation of NHE3 by Dex but did not completely obliterate the effect. We show that transfection of SGK2 or SGK3 in PS120 cells resulted in robust activation of NHE3 by Dex. However, unlike SGK1 or SGK2, SGK3 rapidly activated NHE3 within 15 min of Dex treatment in both PS120 and Caco-2bbe cells. Immunofluorescence analysis showed that SGK3 colocalized with NHE3 in recycling endosomes, whereas SGK1 and SGK2 were diffusely distributed. Mutation of Arg-90 of SGK3 disrupted the endosomal localization of SGK3 and delayed NHE3 activation. Activation of SGK3 and NHE3 by Dex was dependent on phosphoinositide 3-kinase (PI3K) and phosphoinositide-dependent kinase 1 (PDK1), and Dex induced translocation of PDK1 to endosomes. Our study identifies SGK3 as a novel endosomal kinase that acutely regulates NHE3 in a PI3K-dependent mechanism.
钠/氢交换器 3 (NHE3) 是肠道中主要的钠离子转运体。血清和糖皮质激素诱导激酶 (SGK) 1 与 NHE 调节因子 2 (NHERF2) 相互作用，并介导地塞米松 (Dex) 在培养的上皮细胞中对 NHE3 的激活。在这项研究中，我们比较了 SGK1 缺失和 NHERF2 缺失小鼠中 Dex 对 NHE3 的短期调节。与野生型小鼠相比，SGK1 或 NHERF2 的缺失显著减弱了 Dex 对 NHE3 的调节作用，但并未完全消除这种作用。我们表明，在 PS120 细胞中转染 SGK2 或 SGK3 可导致 Dex 对 NHE3 的强烈激活。然而，与 SGK1 或 SGK2 不同，SGK3 在 Dex 处理后 15 分钟内可迅速激活 PS120 和 Caco-2bbe 细胞中的 NHE3。免疫荧光分析显示，SGK3 与再循环内体中的 NHE3 共定位，而 SGK1 和 SGK2 则呈弥散分布。SGK3 的 Arg-90 突变破坏了 SGK3 的内体定位并延迟了 NHE3 的激活。Dex 激活 SGK3 和 NHE3 依赖于磷脂酰肌醇 3-激酶 (PI3K) 和磷脂酰肌醇依赖性激酶 1 (PDK1)，并且 Dex 诱导 PDK1 向内体易位。我们的研究确定 SGK3 为一种新型内体激酶，可通过 PI3K 依赖性机制急性调节 NHE3。
