SGK1 activates Na+-K+-ATPase in amphibian renal epithelial cells.
Serum- and glucocorticoid-induced kinase 1 (SGK1) is thought to be an important regulator of Na(+) reabsorption in the kidney. It has been proposed that SGK1 mediates the effects of aldosterone on transepithelial Na(+) transport. Previous studies have shown that SGK1 increases Na(+) transport and epithelial Na(+) channel (ENaC) activity in the apical membrane of renal epithelial cells. SGK1 has also been implicated in the modulation of Na(+)-K(+)-ATPase activity, the transporter responsible for basolateral Na(+) efflux, although this observation has not been confirmed in renal epithelial cells. We examined Na(+)-K(+)-ATPase function in an A6 renal epithelial cell line that expresses SGK1 under the control of a tetracycline-inducible promoter. The results showed that expression of a constitutively active mutant of SGK1 (SGK1(T)(S425D)) increased the transport activity of Na(+)-K(+)-ATPase 2.5-fold. The increase in activity was a direct consequence of activation of the pump itself. The onset of Na(+)-K(+)-ATPase activation was observed between 6 and 24 h after induction of SGK1 expression, a delay that is significantly longer than that required for activation of ENaC in the same cell line (1 h). SGK1 and aldosterone stimulated the Na(+) pump synergistically, indicating that the pathways mediated by these molecules operate independently. This observation was confirmed by demonstrating that aldosterone, but not SGK1(T)(S425D), induced an approximately 2.5-fold increase in total protein and plasma membrane Na(+)-K(+)-ATPase alpha(1)-subunit abundance. We conclude that aldosterone increases the abundance of Na(+)-K(+)-ATPase, whereas SGK1 may activate existing pumps in the membrane in response to chronic or slowly acting stimuli.
Alvarez de la Rosa
Diego
D
Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain. diego.alvarez@ull.es
Gimenez
Ignacio
I
Forbush
Biff
B
Canessa
Cecilia M
CM
D000450:Aldosterone / Q000378:metabolism; D000818:Animals; D037281:Calnexin / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D007686:Kidney Tubules, Distal / Q000166:cytology*; D010042:Ouabain / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012414:Rubidium Radioisotopes / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis; D000099184:Serum-Glucocorticoid Regulated Kinases
D000450:Aldosterone; D037281:Calnexin; D004791:Enzyme Inhibitors; D017874:Immediate-Early Proteins; D010042:Ouabain; D017346:Protein Serine-Threonine Kinases; D021122:Protein Subunits; D012414:Rubidium Radioisotopes; D000254:Sodium-Potassium-Exchanging ATPase; D000099184:Serum-Glucocorticoid Regulated Kinases