title: Trophic factor withdrawal: p38 mitogen-activated protein kinase activates NHE1, which induces intracellular alkalinization.
abstract: Trophic factor withdrawal induces cell death by mechanisms that are incompletely understood. Previously we reported that withdrawal of interleukin-7 (IL-7) or IL-3 produced a rapid intracellular alkalinization, disrupting mitochondrial metabolism and activating the death protein Bax. We now observe that this novel alkalinization pathway is mediated by the pH regulator NHE1, as shown by the requirement for sodium, blocking by pharmacological inhibitors or use of an NHE1-deficient cell line, and the altered phosphorylation of NHE1. Alkalinization also required the stress-activated p38 mitogen-activated protein kinase (MAPK). Inhibition of p38 MAPK activity with pharmacological inhibitors or expression of a dominant negative kinase prevented alkalinization. Activated p38 MAPK directly phosphorylated the C terminus of NHE1 within a 40-amino-acid region. Analysis by mass spectroscopy identified four phosphorylation sites on NHE1, Thr 717, Ser 722, Ser 725, and Ser 728. Thus, loss of trophic cytokine signaling induced the p38 MAPK pathway, which phosphorylated NHE1 at specific sites, inducing intracellular alkalinization.
authors.affiliation: Laboratory of Molecular Immunoregulation, Center for Cancer Research, National Cancer Institute-Frederick Cancer Research and Development Center, Frederick, Maryland 21702, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Khaled
authors.forename: A N
authors.initials: AN
authors.lastname: Moor
authors.forename: A
authors.initials: A
authors.lastname: Li
authors.forename: K
authors.initials: K
authors.lastname: Kim
authors.forename: D K
authors.initials: DK
authors.lastname: Ferris
authors.forename: K
authors.initials: K
authors.lastname: Muegge
authors.forename: R J
authors.initials: RJ
authors.lastname: Fisher
authors.forename: L
authors.initials: L
authors.lastname: Fliegel
authors.forename: S K
authors.initials: SK
authors.lastname: Durum
mesh_terms: D051698:Activating Transcription Factor 2; D000468:Alkalies; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007377:Interleukin-3 / Q000378:metabolism / Q000494:pharmacology; D015851:Interleukin-7 / Q000378:metabolism / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D020935:MAP Kinase Signaling System; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: D051698:Activating Transcription Factor 2; D000468:Alkalies; D017362:Cyclic AMP Response Element-Binding Protein; D007377:Interleukin-3; D015851:Interleukin-7; D017923:Sodium-Hydrogen Exchangers; D014157:Transcription Factors; C069139:growth factor-activatable Na-H exchanger NHE-1; D019893:Ribosomal Protein S6 Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase