sgk: an essential convergence point for peptide and steroid hormone regulation of ENaC-mediated Na+ transport.
To study the role of sgk (serum, glucocorticoid-induced kinase) in hormonal regulation of Na+ transport mediated by the epithelial Na+ channel (ENaC), clonal cell lines stably expressing human sgk, an S422A sgk mutant, or a D222A sgk mutant were created in the background of the A6 model renal epithelial cell line. Expression of normal sgk results in a 3.5-fold enhancement of basal transport and potentiation of the natriferic response to antidiuretic hormone (ADH). Transfection of a S422A mutant form of sgk, which cannot be phosphorylated by phosphatidylinositol-dependent kinase (PDK)-2, results in a cell line that is indistinguishable from the parent line in basal and hormone-stimulated Na+ transport. The D222A sgk mutant, which lacks kinase activity, functions as a dominant-negative mutant inhibiting basal as well as peptide- and steroid hormone-stimulated Na+ transport. Thus sgk activity is necessary for ENaC-mediated Na+ transport. Phosphorylation and activation by PDK-2 are necessary for sgk stimulation of ENaC. Expression of normal sgk over endogenous levels results in a potentiated natriferic response to ADH, suggesting that the enzyme is a rate-limiting step for the hormone response. In contrast, sgk does not appear to be the rate-limiting step for the cellular response to aldosterone or insulin.
Faletti
Carla J
CJ
Biology Department, Indiana University-Purdue University at Indianapolis, 723 W. Michigan Street, Indianapolis, IN 46202, USA.
Perrotti
Nicola
N
Taylor
Simeon I
SI
Blazer-Yost
Bonnie L
BL
D000450:Aldosterone / Q000378:metabolism; D000584:Amiloride / Q000378:metabolism; D000818:Animals; D002458:Cell Fractionation; D002460:Cell Line; D004232:Diuretics / Q000378:metabolism; D053503:Epithelial Sodium Channels; D006490:Hemostatics / Q000378:metabolism; D006801:Humans; D017874:Immediate-Early Proteins; D007328:Insulin / Q000378:metabolism; D017136:Ion Transport; D009687:Nuclear Proteins; D018408:Patch-Clamp Techniques; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014667:Vasopressins / Q000378:metabolism; D014982:Xenopus laevis; D000099184:Serum-Glucocorticoid Regulated Kinases
D000450:Aldosterone; D000584:Amiloride; D004232:Diuretics; D053503:Epithelial Sodium Channels; D006490:Hemostatics; D017874:Immediate-Early Proteins; D007328:Insulin; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D012964:Sodium; D015222:Sodium Channels; D014667:Vasopressins; D000099184:Serum-Glucocorticoid Regulated Kinases