Rapid upregulation of serum and glucocorticoid-regulated kinase (sgk) gene expression by corticosteroids in vivo

Brennan, Francine E.; Fuller, Peter J.

doi:10.1016/s0303-7207(00)00274-4

Cited by 95 publications

(68 citation statements)

References 34 publications

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“…Immunohistochemical studies have shown that in the renal collecting duct SGK1 is not expressed in intercalated cells but in principal cells consistent with a specific co-expression of SGK1 and ENaC (19). SGK1 mRNA and protein levels are also increased by aldosterone in distal colon (17,18,20). These findings suggest that SGK1 is a mediator of aldosterone action in classic mineralocorticoid target tissues.…”

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confidence: 84%

A Novel Pathway of Epithelial Sodium Channel Activation Involves a Serum- and Glucocorticoid-inducible Kinase Consensus Motif in the C Terminus of the Channel's α-Subunit

Diakov

Korbmacher

2004

Journal of Biological Chemistry

156

145

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Aldosterone-induced serum-and glucocorticoid-inducible kinase isoform 1 (SGK1) contributes to the regulation of the epithelial sodium channel (ENaC), the activity of which is critical for long term blood pressure control. Aldosterone-induced SGK1 is thought to enhance ENaC surface expression by phosphorylating Nedd4-2 and thereby preventing ENaC retrieval and degradation. In outside-out membrane patches of Xenopus laevis oocytes heterologously expressing ENaC, amiloride-sensitive ENaC currents were enhanced by phosphatase inhibitors and were dependent on cytosolic Mg 2؉ . This indicates that a kinase is involved in channel regulation. Indeed, recombinant constitutively active SGK1, included in the pipette solution, caused a sustained 2-to 3-fold increase of ENaC currents. Deletion of the C terminus of ␣ENaC largely reduced the stimulatory effect of SGK1, whereas stimulation by SGK1 did not require the presence of the C termini of the ␤-or ␥-subunits. Replacing the serine residue Ser 621 of the SGK1 consensus motif in the C terminus of the ␣-subunit by an alanine specifically abolished the stimulatory effect of SGK. Our findings indicate that SGK1 can stimulate ENaC activity independently of an inhibition of Nedd4-2-mediated channel retrieval. This defines a novel regulatory pathway likely to be relevant for aldosterone-induced stimulation of ENaC in vivo.The appropriate regulation of the epithelial sodium channel (ENaC) 1 in the kidney is critically important for the maintenance of body sodium balance and hence for long term regulation of arterial blood pressure (1). Indeed, two human genetic diseases provide direct evidence that molecular dysfunction of ENaC has severe effects on arterial blood pressure. Loss-offunction mutations of ENaC cause urinary sodium loss, hyperkalemia, and low blood pressure in patients with pseudohypoaldosteronism type 1 (2). In contrast, gain-of-function mutations of ENaC are found in patients with so-called Liddle's syndrome (pseudohyperaldosteronism) and result in increased renal sodium re-absorption, hypokalemia, and severe arterial hypertension (3).ENaC is composed of three subunits called ␣, ␤, and ␥ (4). The C termini of the ENaC subunits each contain a proline-rich PPXY (PY) motif, which is believed to be important for interaction with the ubiquitin-protein ligases Nedd4 and Nedd4-2, promoting the ubiquitination, endocytosis, and proteasomal degradation of the channel (5-8). The functional importance of the PY motif was recognized in Liddle's syndrome where mutations and/or deletions of the PY motif in ␤ or ␥ ENaC reduce the endocytic retrieval of ENaC from the membrane (9, 10). This results in an increase in the number of ENaC channels in the membrane, which in turn is thought to cause hyperabsorption of Na ϩ and hypertension in patients with Liddle's syndrome (11,12).The most important hormone to regulate ENaC activity is the mineralocorticoid aldosterone. The effects of aldosterone include transcriptional, translational, and post-translational modifications of ENaC and inv...

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mentioning

confidence: 84%

A Novel Pathway of Epithelial Sodium Channel Activation Involves a Serum- and Glucocorticoid-inducible Kinase Consensus Motif in the C Terminus of the Channel's α-Subunit

Diakov

Korbmacher

2004

Journal of Biological Chemistry

156

145

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“…28 Expression of sgk1 is rapidly upregulated in vivo in kidney and colon by aldosterone. 32,33 The role of sgk1 in the renal response has been reviewed by McCormick et al 28 In addition to interactions with Nedd4 -2, there is recent evidence that sgk1 may phosphorylate the C terminus of the ENaC ␣-subunit and alter the activity of the channel. 34 It has also been suggested that sgk1 may regulate ENaC subunit gene expression.…”

Section: Epithelial Aldosterone-induced Proteinsmentioning

confidence: 99%

Mechanisms of Mineralocorticoid Action

Fuller¹,

Young²

2005

Hypertension

280

169

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Abstract-Sodium transport in epithelial tissues is regulated by the physiological mineralocorticoid aldosterone. The response to aldosterone is mediated by the mineralocorticoid receptor (MR), for which the crystal structure of the ligand-binding domain has recently been established. The classical mode of action for this receptor involves the regulation of gene transcription. Several genes have now been shown to be regulated by aldosterone in epithelial tissues. Of these, the best characterized is serum-and glucocorticoid-regulated kinase, which increases sodium influx through the epithelial sodium channel. Turnover of these channels in the cell membrane is mediated by Nedd4 -2, a ubiquitin protein ligase; serum-and glucocorticoid-regulated kinase interacts with and phosphorylates Nedd4 -2, thereby rendering it unable to bind the sodium channels. Key Words: aldosterone Ⅲ sodium channels Ⅲ fibrosis T he isolation of aldosterone just over 50 years ago established it as the primary physiological mineralocorticoid. 1 Sodium transport, and hence salt balance, is regulated by a number of mechanisms; however, aldosterone has a critical role. Aldosterone exerts its effects on the distal nephron (and colon) as the last point of sodium reabsorption; it is thus the final arbiter. 2,3 The importance of aldosterone in the maintenance of sodium homeostasis is seen in a series of monogenetic causes of hypertension, 2 in Conn's syndrome, and in disorders in which mineralocorticoid action is compromised with consequent, life-threatening salt losses. 3 Although other pathophysiological consequences of aldosterone excess were identified by Selye 4 over 60 years ago, their significance has only recently been appreciated. Evidence from the Randomized ALdactone Evaluation Study (RALES) and EPlerenone neuroHormonal Efficacy and SUrvival Study (EPHESUS) trials of beneficial effects of mineralocorticoid antagonist therapy on morbidity and mortality in cardiac failure has focused attention beyond the kidney to effects of mineralocorticoids more broadly in the cardiovascular system. 5 Although an understanding of the molecular basis of aldosterone action has tended to lag behind advances in the biology of other steroid hormones, the last decade has seen significant advances toward an understanding of the mechanisms of mineralocorticoid action. The primary mediator of the response to aldosterone is the mineralocorticoid receptor (MR), the ligand-binding domain (LBD) of which has been recently crystallized. 6 -8 Although the MR primarily acts as a transcription factor, recent evidence suggests that it may also mediate nongenomic (or nonnuclear) activation of second messenger pathways. In addition, there is a growing body of evidence that some actions of aldosterone may involve a receptor other than the MR. The cellular and molecular mediators, including proteins induced by aldosterone, have been characterized in sodium transporting epithelia; however, the critical molecular events in the vasculature remain to be determined. In this brief r...

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“…However, the transcriptional activation of SGK1 by aldosterone shows a different time course than by glucocorticoids. SGK1 mRNA is rapidly activated by aldosterone, peaking at 1 h and declining thereafter (49). Glucocorticoids also activate SGK1 mRNA as early as 30 min, but its expression is maintained at least for 24 h (50).…”

Section: Fig 4 Protein Expression Of Nherf2 and Nherf1mentioning

confidence: 99%

Glucocorticoid Activation of Na+/H+Exchanger Isoform 3 Revisited

Yun

Chen

Läng

2002

Journal of Biological Chemistry

168

211

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The stimulative effect of glucocorticoids on intestinal salt and water absorption has been known for more than two decades. However, molecular mechanisms underlying this activation remain elusive. Previous studies showed that methylprednisolone specifically increased Na ؉ /H ؉ exchanger isoform (NHE) 3 mRNA in ileum and kidney without affecting NHE1 mRNA levels. These results suggest that glucocorticoids activate NHE3 activity by induction of NHE3 transcripts. We recently found in PS120 and opossum kidney cells that chronic incubation with dexamethasone activated NHE3 independent of gene induction, indicating that the transcriptional activation may not be the only determining factor in the NHE3 activation. Furthermore, dexamethasone activated NHE3 activity only in the presence of a NHE3 regulatory protein, NHERF2, which was previously shown to confer cAMP-dependent inhibition of NHE3. This activation of NHE3 could not be duplicated by NHERF1. We identified serum-and glucocorticoid-induced protein kinase, SGK1, as the protein interacting with PDZ domains of NHERF2 to regulate NHE3 activity. The expression of SGK1 enhanced NHE3 transport in PS120 fibroblasts. In addition, the "kinase-dead" SGK1 blocked activation of NHE3 by dexamethasone in opossum kidney cells. These data demonstrated that glucocorticoid activation of NHE3 requires the activation of SGK1 and the presence of NHERF2 acting as a scaffold protein.

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Rapid upregulation of serum and glucocorticoid-regulated kinase (sgk) gene expression by corticosteroids in vivo

Cited by 95 publications

References 34 publications

A Novel Pathway of Epithelial Sodium Channel Activation Involves a Serum- and Glucocorticoid-inducible Kinase Consensus Motif in the C Terminus of the Channel's α-Subunit

A Novel Pathway of Epithelial Sodium Channel Activation Involves a Serum- and Glucocorticoid-inducible Kinase Consensus Motif in the C Terminus of the Channel's α-Subunit

Mechanisms of Mineralocorticoid Action

Glucocorticoid Activation of Na+/H+Exchanger Isoform 3 Revisited

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