title: The Na+/H+ exchanger, NHE1, differentially regulates mitogen-activated protein kinase subfamilies after osmotic shrinkage in Ehrlich Lettre Ascites cells.
abstract: Osmotic stress modulates mitogen activated protein kinase (MAPK) activities, leading to altered gene transcription and cell death/survival balance, however, the mechanisms involved are incompletely elucidated. Here, we show, using a combination of biochemical and molecular biology approaches, that three MAPKs exhibit unique interrelationships with the Na(+)/H(+) exchanger, NHE1, after osmotic cell shrinkage: Extracellular Signal Regulated Kinase (ERK1/2) is inhibited in an NHE1-dependent, pH(i)-independent manner, c-Jun N-terminal kinase (JNK1/2) is stimulated, in part through NHE1-mediated intracellular alkalinization, and p38 MAPK is activated in an NHE1-independent manner, and contributes to NHE1 activation and ERK inhibition. Shrinkage-induced ERK1/2 inhibition was attenuated in Ehrlich Lettre Ascites cells by NHE1 inhibitors (EIPA, cariporide) or removal of extracellular Na(+), and mimicked by human (h) NHE1 expression in cells lacking endogenous NHE1 activity. The effect of NHE1 on ERK1/2 was pH(i)-independent and upstream of MEK1/2. Shrinkage-activation of JNK1/2 was attenuated by EIPA, augmented by hNHE1 expression, and abolished in the presence of HCO(3)(-). Basal JNK activity was augmented at alkaline pH(i). Shrinkage-activation of p38 MAPK was NHE1-independent, and p38 MAPK inhibition (SB203580) attenuated NHE1 activation and ERK1/2 inhibition. Long-term shrinkage elicited caspase-3 activation and a loss of cell viability, which was augmented by ERK1/2 or JNK1/2 inhibition, and attenuated by p38 MAPK inhibition.
authors.affiliation: Dept. of Molecular Biology, University of Copenhagen, Copenhagen, Denmark. sfpedersen@aki.ku.dk
authors.forename: Stine Falsig
authors.initials: SF
authors.lastname: Pedersen
authors.forename: Barbara Vasek
authors.initials: BV
authors.lastname: Darborg
authors.forename: Maria
authors.initials: M
authors.lastname: Rasmussen
authors.forename: Jesper
authors.initials: J
authors.lastname: Nylandsted
authors.forename: Else Kay
authors.initials: EK
authors.lastname: Hoffmann
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology*; D027682:Cation Transport Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D009997:Osmotic Pressure / Q000187:drug effects; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D027682:Cation Transport Proteins; D004791:Enzyme Inhibitors; C490998:SLC9A1 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases