title: SGK1 activity in Na+ absorbing airway epithelial cells monitored by assaying NDRG1-Thr346/356/366 phosphorylation.
abstract: Studies of HeLa cells and serum- and glucocorticoid-regulated kinase 1 (SGK1) knockout mice identified threonine residues in the n-myc downstream-regulated gene 1 protein (NDRG1-Thr(346/356/366)) that are phosphorylated by SGK1 but not by related kinases (Murray et al., Biochem J 385:1-12, 2005). We have, therefore, monitored the phosphorylation of NDRG1-Thr(346/356/366) in order to explore the changes in SGK1 activity associated with the induction and regulation of the glucocorticoid-dependent Na(+) conductance (G (Na)) in human airway epithelial cells. Transient expression of active (SGK1-S422D) and inactive (SGK1-K127A) SGK1 mutants confirmed that activating SGK1 stimulates NDRG1-Thr(346/356/366) phosphorylation. Although G (Na) is negligible in hormone-deprived cells, these cells displayed basal SGK1 activity that was sensitive to LY294002, an inhibitor of 3-phosphatidylinositol phosphate kinase (PI3K). Dexamethasone (0.2 muM) acutely activated SGK1 and the peak of this response (2-3 h) coincided with the induction of G (Na), and both responses were PI3K-dependent. While these data suggest that SGK1 might mediate the rise in G (Na), transient expression of the inactive SGK1-K127A mutant did not affect the hormonal induction of G (Na) but did suppress the activation of SGK1. Dexamethasone-treated cells grown on permeable supports formed confluent epithelial sheets that generated short circuit current due to electrogenic Na(+) absorption. Forskolin and insulin both stimulated this current and the response to insulin, but not forskolin, was LY294002-sensitive and associated with the activation of SGK1. While these data suggest that SGK1 is involved in the control of G (Na), its role may be minor, which could explain why sgk1 knockout has different effects upon different tissues.
authors.affiliation: Lung Membrane Transport Group, Division of Maternal and Child Health Sciences, College of Medicine, Dentistry and Nursing, University of Dundee, Dundee DD1 9SY, Scotland.
authors.forename: S K
authors.initials: SK
authors.lastname: Inglis
authors.forename: M
authors.initials: M
authors.lastname: Gallacher
authors.forename: S G
authors.initials: SG
authors.lastname: Brown
authors.forename: N
authors.initials: N
authors.lastname: McTavish
authors.forename: J
authors.initials: J
authors.lastname: Getty
authors.forename: E M
authors.initials: EM
authors.lastname: Husband
authors.forename: J T
authors.initials: JT
authors.lastname: Murray
authors.forename: S M
authors.initials: SM
authors.lastname: Wilson
mesh_terms: D000595:Amino Acid Sequence; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D004847:Epithelial Cells / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000166:cytology; D012964:Sodium / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases; D000099259:N-myc Downstream-Regulated Gene 1 Protein
chemical_list: D018797:Cell Cycle Proteins; D005576:Colforsin; D017362:Cyclic AMP Response Element-Binding Protein; D003907:Dexamethasone; D017874:Immediate-Early Proteins; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D012964:Sodium; D013912:Threonine; D000099184:Serum-Glucocorticoid Regulated Kinases; D000099259:N-myc Downstream-Regulated Gene 1 Protein
references.citation: Am J Physiol Lung Cell Mol Physiol. 2004 Aug;287(2):L411-9
references.pmid: 15090368
references.citation: Am J Physiol Renal Physiol. 2005 Mar;288(3):F505-12
references.pmid: 15536167
references.citation: Am J Physiol Renal Physiol. 2002 Jul;283(1):F105-13
references.pmid: 12060592
references.citation: J Clin Invest. 2002 Nov;110(9):1263-8
references.pmid: 12417564
references.citation: FEBS Lett. 2005 Feb 14;579(5):991-4
references.pmid: 15710380
references.citation: J Gen Physiol. 2004 Oct;124(4):395-407
references.pmid: 15452200
references.citation: Mol Endocrinol. 2000 Aug;14(8):1283-300
references.pmid: 10935551
references.citation: J Biol Chem. 2001 Mar 23;276(12):9406-12
references.pmid: 11096081
references.citation: J Biol Chem. 1999 Apr 30;274(18):12431-7
references.pmid: 10212217
references.citation: Am J Physiol Regul Integr Comp Physiol. 2006 Apr;290(4):R935-44
references.pmid: 16284089
references.citation: Curr Pharm Biotechnol. 2006 Jun;7(3):209-15
references.pmid: 16789905
references.citation: J Biol Chem. 2005 Feb 11;280(6):4518-23
references.pmid: 15576372
references.citation: Nat Rev Mol Cell Biol. 2006 Nov;7(11):867-73
references.pmid: 17057754
references.citation: EMBO J. 2001 Dec 17;20(24):7052-9
references.pmid: 11742982
references.citation: J Biol Chem. 2007 Sep 21;282(38):28264-73
references.pmid: 17652085
references.citation: Am J Physiol Cell Physiol. 2003 Feb;284(2):C404-14
references.pmid: 12388075
references.citation: Sci STKE. 2001 Nov 13;2001(108):re17
references.pmid: 11707620
references.citation: Mol Cell. 2008 Jun 20;30(6):701-11
references.pmid: 18570873
references.citation: Kidney Int. 2005 Nov;68(5):2164-72
references.pmid: 16221215
references.citation: Am J Physiol. 1999 Sep;277(3):C531-6
references.pmid: 10484339
references.citation: Biochem J. 1999 Apr 15;339 ( Pt 2):319-28
references.pmid: 10191262
references.citation: J Biol Chem. 1998 Nov 13;273(46):30770-6
references.pmid: 9804854
references.citation: Am J Physiol Lung Cell Mol Physiol. 2008 May;294(5):L942-54
references.pmid: 18310228
references.citation: J Biol Chem. 2004 Oct 29;279(44):45753-8
references.pmid: 15328345
references.citation: J Biol Chem. 2002 Apr 19;277(16):13539-47
references.pmid: 11805112
references.citation: Pflugers Arch. 2006 Oct;453(1):97-105
references.pmid: 16897044
references.citation: J Biol Chem. 2004 Sep 10;279(37):38134-42
references.pmid: 15234985
references.citation: J Biol Chem. 1999 Jun 11;274(24):16973-8
references.pmid: 10358046
references.citation: J Appl Physiol (1985). 2002 Oct;93(4):1542-8
references.pmid: 12235057
references.citation: Am J Physiol Lung Cell Mol Physiol. 2002 Apr;282(4):L631-41
references.pmid: 11880287
references.citation: Am J Physiol Renal Physiol. 2006 Oct;291(4):F714-21
references.pmid: 16720863
references.citation: Am J Physiol Renal Physiol. 2001 Feb;280(2):F303-13
references.pmid: 11208606
references.citation: Eur Respir J. 2004 Jan;23(1):146-58
references.pmid: 14738247
references.citation: Am J Physiol. 1998 Apr;274(4):E611-7
references.pmid: 9575821
references.citation: J Biol Chem. 2002 Jan 4;277(1):5-8
references.pmid: 11696533
references.citation: Am J Physiol Cell Physiol. 2003 Jun;284(6):C1645-53
references.pmid: 12606308
references.citation: Am J Physiol Renal Physiol. 2003 May;284(5):F938-47
references.pmid: 12540365
references.citation: Endocr Rev. 2002 Apr;23(2):258-75
references.pmid: 11943747
references.citation: EMBO J. 1999 Jun 1;18(11):3024-33
references.pmid: 10357815
references.citation: Am J Physiol. 1998 May;274(5):C1373-9
references.pmid: 9612225
references.citation: Am J Physiol Renal Physiol. 2001 Apr;280(4):F675-82
references.pmid: 11249859
references.citation: J Biol Chem. 2004 Feb 6;279(6):5042-6
references.pmid: 14645220
references.citation: Biochem J. 2004 Dec 15;384(Pt 3):477-88
references.pmid: 15461589
references.citation: Am J Physiol Lung Cell Mol Physiol. 2003 Aug;285(2):L443-50
references.pmid: 12704021
references.citation: Trends Biochem Sci. 1990 Mar;15(3):98-102
references.pmid: 2158158
references.citation: J Physiol. 2004 Jun 15;557(Pt 3):809-19
references.pmid: 15090610
references.citation: J Cyclic Nucleotide Res. 1981;7(4):201-24
references.pmid: 6278005
references.citation: Am J Physiol Renal Physiol. 2006 Dec;291(6):F1264-73
references.pmid: 17003223
references.citation: Proc Natl Acad Sci U S A. 1999 Mar 2;96(5):2514-9
references.pmid: 10051674
references.citation: Am J Physiol Cell Physiol. 2002 Mar;282(3):C494-500
references.pmid: 11832334
references.citation: Am J Physiol Cell Physiol. 2000 Jul;279(1):C236-47
references.pmid: 10898735
references.citation: Nat Med. 2004 May;10(5):487-93
references.pmid: 15077107
references.citation: J Biol Chem. 2006 Apr 14;281(15):9859-68
references.pmid: 16476738
references.citation: Am J Physiol Lung Cell Mol Physiol. 2002 Apr;282(4):L621-30
references.pmid: 11880286
references.citation: J Biol Chem. 1999 Jul 30;274(31):21544-54
references.pmid: 10419459
references.citation: Am J Physiol Lung Cell Mol Physiol. 2004 Oct;287(4):L843-51
references.pmid: 15208094