title: Acute activation of NHE3 by dexamethasone correlates with activation of SGK1 and requires a functional glucocorticoid receptor.
abstract: Glucocorticoids stimulate the intestinal absorption of Na(+) and water partly by regulation of the Na(+)/H(+) exchanger 3 (NHE3). Previous studies have shown both genomic and nongenomic regulation of NHE3 by glucocorticoids. Serum and glucocorticoid-inducible kinase 1 (SGK1) has been shown to be part of this cascade, where phosphorylation of NHE3 by SGK1 initiates the translocation of NHE3 to the cell surface. In the present work, we examined a series of changes in SGK1 and NHE3 induced by glucocorticoids using human colonic Caco-2 and opossum kidney cells. We found that dexamethasone rapidly stimulated SGK1 mRNAs, but a significant change in protein abundance was not detected. Instead, there was an increase in SGK1 kinase activity as early as at 2 h. An increase in NHE3 protein abundance was not detected until 12 h of dexamethasone exposure, although the transport activity was significantly stimulated at 4 h. These data demonstrate that the changes of SGK1 precede those of NHE3. Chronic regulation (24 h) of NHE3 was blocked completely by prevention of protein synthesis with cycloheximide or actinomycin D and by the glucocorticoid receptor blocker RU486. The acute effect of dexamethasone was similarly abrogated by RU486, but was insensitive to cycloheximide and actinomycin D. Similarly, the stimulation of SGK1 activity by dexamethasone was blocked by RU486 but not by actinomycin D. Together, these data show that the acute effect of glucocorticoids on NHE3 is mediated by a glucocorticoid receptor dependent mechanism that activates SGK1 in a nongenomic manner.
authors.affiliation: Department of Physiology, Emory University School of Medicine, 615 Michael Street, Atlanta, GA 30322, USA.
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Wang
authors.forename: Huanchun
authors.initials: H
authors.lastname: Zhang
authors.forename: Florian
authors.initials: F
authors.lastname: Lang
authors.forename: C Chris
authors.initials: CC
authors.lastname: Yun
mesh_terms: D018938:Caco-2 Cells; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D017874:Immediate-Early Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015735:Mifepristone / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors / Q000502:physiology*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000009:adverse effects* / Q000037:antagonists & inhibitors / Q000502:physiology*; D013997:Time Factors; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D003513:Cycloheximide; D003609:Dactinomycin; D003907:Dexamethasone; D005938:Glucocorticoids; D006727:Hormone Antagonists; D017874:Immediate-Early Proteins; D015735:Mifepristone; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors; D011965:Receptors, Glucocorticoid; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000099184:Serum-Glucocorticoid Regulated Kinases; C000613385:SLC9A3 protein, human