Sgk1 mediates osmotic induction of NPR-A gene in rat inner medullary collecting duct cells.
We have shown previously that increased extracellular osmolality stimulates expression and promoter activity of the type A natriuretic peptide receptor (NPR-A) gene in rat inner medullary collecting duct (IMCD) cells through a mechanism that involves activation of p38 mitogen-activated protein kinase (MAPK). The serum and glucocorticoid inducible kinase (Sgk) is thought to participate in the regulation of sodium handling in distal tubular segments. We sought to determine whether this kinase might be involved in the osmotic stimulation of NPR-A gene promoter activity. Exposure of cultured IMCD cells to an additional 75 mmol/L NaCl in culture media (final osmolality 475 mosm/kg) resulted in an approximately 4-fold increase in Sgk1 protein levels after 7 hours. The Sgk1 induction was almost completely inhibited by the p38 MAPK inhibitor SB203580, indicating that NaCl activates Sgk1 through the p38 MAPK pathway. Transient transfection of a mouse Sgk1 expression vector along with a -1590 NPR-A luciferase reporter resulted in an approximately 3-fold increment in reporter activity, which was significantly reduced by cotransfection with a kinase-dead Sgk1 mutant. The NaCl-dependent induction was partially blocked (approximately 40% inhibition) by cotransfection of the kinase-dead Sgk1 mutant. Neither Sgk1 nor the kinase-dead mutant had any effect on endothelial nitric oxide synthase (eNOS) promoter activity, and the Sgk1 mutant and 8-bromo-cyclic guanosine monophosphate were, to some degree, additive in reducing osmotically stimulated NPR-A promoter activity. Collectively, these data imply that Sgk1 operates over an eNOS-independent, p38 MAPK-dependent pathway in mediating osmotic induction of the NPR-A gene promoter.
Diabetes Center, 1119 HSW, University of California at San Francisco, San Francisco, CA 94143-0540, USA. schen@diabetes.ucsf.edu
Songcang
S
Chen
James A
JA
McCormick
Kavitha
K
Prabaker
Jian
J
Wang
David
D
Pearce
David G
DG
Gardner
D000818:Animals; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D017930:Genes, Reporter; D006162:Guanylate Cyclase / Q000096:biosynthesis* / Q000235:genetics; D007093:Imidazoles / Q000494:pharmacology; D017874:Immediate-Early Proteins; D007685:Kidney Tubules, Collecting / Q000166:cytology* / Q000378:metabolism; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009318:Natriuresis / Q000502:physiology; D009687:Nuclear Proteins; D009994:Osmolar Concentration; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000502:physiology*; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D017461:Receptors, Atrial Natriuretic Factor / Q000096:biosynthesis* / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D014162:Transfection; D048051:p38 Mitogen-Activated Protein Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases
D006152:Cyclic GMP; D006162:Guanylate Cyclase; D007093:Imidazoles; D017874:Immediate-Early Proteins; D008156:Luciferases; D020928:Mitogen-Activated Protein Kinases; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D011725:Pyridines; D012333:RNA, Messenger; D017461:Receptors, Atrial Natriuretic Factor; D011993:Recombinant Fusion Proteins; D012462:Saline Solution, Hypertonic; D048051:p38 Mitogen-Activated Protein Kinases; D000099184:Serum-Glucocorticoid Regulated Kinases; C016276:8-bromocyclic GMP; C091715:atrial natriuretic factor receptor A; C093642:SB 203580