Acid increases MAPK-mediated proliferation in Barrett's esophageal adenocarcinoma cells via intracellular acidification through a Cl-/HCO3- exchanger.
Abundant epidemiological evidence links acid reflux to adenocarcinoma in Barrett's esophagus, but few studies have examined the cellular mechanisms by which acid promotes this neoplastic progression. We hypothesized that extracellular acid exposure causes intracellular acidification that triggers MAPK signaling and proliferation in Barrett's epithelial cells. We tested that hypothesis in a Barrett's-derived esophageal adenocarcinoma cell line (SEG-1). SEG-1 cells were exposed to varying concentrations of acid, and intracellular pH (pH(i)) was measured by 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein microfluorimetry. After acid exposure, ERK and p38 MAPK activation were measured by Western blot analysis and an immune complex kinase assay. Proliferation was measured by Coulter counter cell counts and a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide incorporation assay. Exposure of SEG-1 cells to solutions with a pH between 3 and 6.5 caused a rapid, reversible decrease in pH(i) to a level approximately equal to extracellular pH. Acid exposure caused a rapid activation of both ERK and p38 MAPKs and also resulted in pH-dependent increases in cell number, with a maximum increase of 41% observed at pH 6.0. The MAPK activation and proliferation in SEG-1 cells induced by acid exposure could be blocked by pretreatment with disodium 4,4'-diisothiocyanatostilbine-2,2'-disulfonate (DIDS), which prevents intracellular acidification by inhibiting the Cl(-)/HCO(3)(-) exchanger. In conclusion, in SEG-1 cells, extracellular acid exposure causes intracellular acidification, which activates MAPK and causes proliferation. The magnitude of these effects is pH dependent, and the effects can be inhibited by preventing intracellular acidification with DIDS.
Sarosi
George A
GA
Dept. of Surgery, Medical University of Texas Southwestern Medical Center, Dallas, TX 75216, USA.
Jaiswal
Kshama
K
Herndon
Emily
E
Lopez-Guzman
Christie
C
Spechler
Stuart J
SJ
Souza
Rhonda F
RF
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000143:Acids / Q000494:pharmacology*; D000230:Adenocarcinoma; D001471:Barrett Esophagus; D002455:Cell Division / Q000187:drug effects; D027963:Chloride-Bicarbonate Antiporters / Q000037:antagonists & inhibitors / Q000502:physiology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000143:Acids; D027963:Chloride-Bicarbonate Antiporters; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid