title: Regulation of NHE3 by lysophosphatidic acid is mediated by phosphorylation of NHE3 by RSK2.
abstract: Na(+)/H(+) exchange by Na(+)/H(+) exchanger 3 (NHE3) is a major route of sodium absorption in the intestine and kidney. We have shown previously that lysophosphatidic acid (LPA), a small phospholipid produced ubiquitously by all types of cells, stimulates NHE3 via LPA5 receptor. Stimulation of NHE3 activity by LPA involves LPA5 transactivating EGF receptor (EGFR) in the apical membrane. EGFR activates proline-rich tyrosine kinase 2 (Pyk2) and ERK, both of which are necessary for NHE3 regulation. However, Pyk2 and ERK are regulated by EGFR via independent pathways and appear to converge on an unidentified intermediate that ultimately targets NHE3. The p90 ribosomal S6 kinase (RSK) family of Ser/Thr protein kinases is a known effector of EGFR and ERK. Hence, we hypothesized that RSK may be the convergent effector of Pyk2 and ERK although it is not known whether Pyk2 regulates RSK. In this study, we show that Pyk2 is necessary for the maintenance of phosphoinositide-dependent kinase 1 (PDK1) autophosphorylation, and knockdown of Pyk2 or PDK1 mitigated LPA-induced phosphorylation of RSK and stimulation of NHE3 activity. Additionally, we show that RSK2, but not RSK1, is responsible for NHE3 regulation. RSK2 interacts with NHE3 at the apical membrane domain, where it phosphorylates NHE3. Alteration of S663 of NHE3 ablated LPA-induced phosphorylation of NHE3 and stimulation of the transport activity. Our study identifies RSK2 as a new kinase that regulates NHE3 activity by direct phosphorylation.
authors: Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia;
authors: Yi Ran
authors: YR
authors: No
authors: Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia;
authors: Peijian
authors: P
authors: He
authors: Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia;
authors: Byong Kwon
authors: BK
authors: Yoo
authors: Division of Digestive Diseases, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia; Winship Cancer Institute, Emory University, Atlanta, Georgia ccyun@emory.edu.
authors: C Chris
authors: CC
authors: Yun
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000201:enzymology*; D066246:ErbB Receptors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051418:Focal Adhesion Kinase 2 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008246:Lysophospholipids / Q000494:pharmacology*; D008810:Mice, Inbred C57BL; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation; D034622:RNA Interference; D020239:Receptor Cross-Talk; D049368:Receptors, Lysophosphatidic Acid / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: C512992:LPAR5 protein, human; D008246:Lysophospholipids; D049368:Receptors, Lysophosphatidic Acid; C000613385:SLC9A3 protein, human; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; C512478:EGFR protein, human; D066246:ErbB Receptors; D051418:Focal Adhesion Kinase 2; C103547:PTK2B protein, human; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D048049:Extracellular Signal-Regulated MAP Kinases; C032881:lysophosphatidic acid
keywords: Na+/H+ exchanger 3; lysophosphatidic acid; phosphorylation; ribosomal S6 kinase