title: The NHE1 Na+/H+ exchanger recruits ezrin/radixin/moesin proteins to regulate Akt-dependent cell survival.
abstract: Apoptosis results in cell shrinkage and intracellular acidification, processes opposed by the ubiquitously expressed NHE1 Na(+)/H(+) exchanger. In addition to mediating Na(+)/H(+) transport, NHE1 interacts with ezrin/radixin/moesin (ERM), which tethers NHE1 to cortical actin cytoskeleton to regulate cell shape, adhesion, motility, and resistance to apoptosis. We hypothesize that apoptotic stress activates NHE1-dependent Na(+)/H(+) exchange, and NHE1-ERM interaction is required for cell survival signaling. Apoptotic stimuli induced NHE1-regulated Na(+)/H(+) transport, as demonstrated by ethyl-N-isopropyl-amiloride-inhibitable, intracellular alkalinization. Ectopic NHE1, but not NHE3, expression rescued NHE1-null cells from apoptosis induced by staurosporine or N-ethylmaleimide-stimulated KCl efflux. When cells were subjected to apoptotic stress, NHE1 and phosphorylated ERM physically associated within the cytoskeleton-enriched fraction, resulting in activation of the pro-survival kinase, Akt. NHE1-associated Akt activity and cell survival were inhibited in cells expressing ERM binding-deficient NHE1, dominant negative ezrin constructs, or ezrin mutants with defective binding to phosphoinositide 3-kinase, an upstream regulator of Akt. We conclude that NHE1 promotes cell survival by dual mechanisms: by defending cell volume and pH(i) through Na(+)/H(+) exchange and by functioning as a scaffold for recruitment of a signalplex that includes ERM, phosphoinositide 3-kinase, and Akt.
authors.affiliation: Department of Medicine, Rammelkamp Center for Research, MetroHealth Medical Center Campus, Case Western Reserve University, Cleveland, Ohio 44109-1998, USA.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Wu
authors.forename: Shenaz
authors.initials: S
authors.lastname: Khan
authors.forename: Sujata
authors.initials: S
authors.lastname: Lakhe-Reddy
authors.forename: George
authors.initials: G
authors.lastname: Jarad
authors.forename: Amitava
authors.initials: A
authors.lastname: Mukherjee
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Obejero-Paz
authors.forename: Martha
authors.initials: M
authors.lastname: Konieczkowski
authors.forename: John R
authors.initials: JR
authors.lastname: Sedor
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Schelling
mesh_terms: D017209:Apoptosis; D001798:Blood Proteins / Q000378:metabolism*; D002448:Cell Adhesion; D002460:Cell Line; D002470:Cell Survival; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005033:Ethylmaleimide / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D008565:Membrane Proteins / Q000378:metabolism*; D008840:Microfilament Proteins / Q000378:metabolism*; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D034622:RNA Interference; D015398:Signal Transduction; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism / Q000502:physiology*; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation; D000099149:Ezrin
chemical_list: D001798:Blood Proteins; D003598:Cytoskeletal Proteins; D005033:Ethylmaleimide; D008565:Membrane Proteins; D008840:Microfilament Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011189:Potassium Chloride; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017923:Sodium-Hydrogen Exchangers; D000099149:Ezrin; C069139:growth factor-activatable Na-H exchanger NHE-1; C071058:moesin; C071776:radixin; C494918:AKT1 protein, human