Náray-Fejes-Tóth A, Canessa C, Cleaveland E S, Aldrich G, Fejes-Tóth G
Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire 03756-0001, USA.
J Biol Chem. 1999 Jun 11;274(24):16973-8. doi: 10.1074/jbc.274.24.16973.
The early phase of the stimulatory effect of aldosterone on sodium reabsorption in renal epithelia is thought to involve activation of apical sodium channels. However, the genes initiating this effect are unknown. We used a combination of polymerase chain reaction-based subtractive hybridization and differential display techniques to identify aldosterone-regulated immediate early genes in renal mineralocorticoid target cells. We report here that aldosterone rapidly increases mRNA levels of a putative Ser/Thr kinase, sgk (or serum- and glucocorticoid-regulated kinase), in its native target cells, i.e. in cortical collecting duct cells. The effect occurs within 30 min of the addition of aldosterone, is mediated through mineralocorticoid receptors, and does not require de novo protein synthesis. The full-length sequences of rabbit and mouse sgk cDNAs were determined. Both cDNAs show significant homology to rat and human sgk (88-94% at the nucleotide level, and 96-99% at the amino acid level). Coexpression of the mouse sgk in Xenopus oocytes with the three subunits of the epithelial Na+ channel results in a significantly enhanced Na+ current. These results suggest that sgk is an immediate early aldosterone-induced gene, and this protein kinase plays an important role in the early phase of aldosterone-stimulated Na+ transport.
醛固酮对肾上皮细胞钠重吸收的刺激作用早期阶段被认为涉及顶端钠通道的激活。然而，引发这种作用的基因尚不清楚。我们结合基于聚合酶链反应的消减杂交和差异显示技术，以鉴定肾盐皮质激素靶细胞中醛固酮调节的即早基因。我们在此报告，醛固酮在其天然靶细胞即皮质集合管细胞中迅速增加一种假定的丝氨酸/苏氨酸激酶sgk（或血清和糖皮质激素调节激酶）的mRNA水平。这种作用在添加醛固酮后30分钟内出现，通过盐皮质激素受体介导，且不需要从头合成蛋白质。测定了兔和小鼠sgk cDNA的全长序列。两种cDNA与大鼠和人类sgk均显示出显著同源性（核苷酸水平为88 - 94%，氨基酸水平为96 - 99%）。小鼠sgk与上皮钠通道的三个亚基在非洲爪蟾卵母细胞中共表达导致钠电流显著增强。这些结果表明sgk是醛固酮诱导的即早基因，且这种蛋白激酶在醛固酮刺激的钠转运早期阶段起重要作用。
