Reduction of intracellular pH inhibits constitutive expression of cyclooxygenase-2 in human colon cancer cells.
Cyclooxygenase-2 (COX-2) over-expression is critically involved in tumor formation. Intracellular pH (pHi) has been shown to be alkaline in cancer cells, and to be an important trigger for cell proliferation. This study therefore analyzed the relationship between pHi and COX-2 expression. HRT-18 and Caco-2 cells cultured in medium with bicarbonate maintained a pHi of approximately 7.6, which is higher than that of non-neoplastic cells. Cells grown in bicarbonate-free medium with a pH at 6.8 showed a reduction in pHi to approximately 7.0. Importantly, reduction of pHi resulted in a complete inhibition of COX-2 mRNA and protein expression. When cells were grown in bicarbonate-supplemented medium at pH 6.8, pHi maintained at approximately 7.6 and COX-2 expression was not inhibited. Additionally, analysis utilizing protein synthesis inhibitor cycloheximide demonstrated that pHi mediated inhibition of COX-2 mRNA expression requires de novo protein synthesis of regulatory protein(s). These data strongly suggest that an alkaline pHi is an important trigger for constitutive COX-2 expression. Defining pHi-mediated mechanisms that govern the constitutive COX-2 expression may help in developing new strategies to block COX-2 over-expression in cancer cells.
Pirkebner
Daniela
D
Tyrolean Cancer Research Institute, Innrain 66, Innsbruck, Austria.
Fuetsch
Michaela
M
Wittmann
Walter
W
Weiss
Helmut
H
Haller
Thomas
T
Schramek
Herbert
H
Margreiter
Raimund
R
Amberger
Albert
A
D018938:Caco-2 Cells; D003110:Colonic Neoplasms / Q000201:enzymology*; D003513:Cycloheximide / Q000494:pharmacology; D051546:Cyclooxygenase 2; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015151:Immunoblotting; D007424:Intracellular Fluid / Q000737:chemistry*; D007527:Isoenzymes / Q000096:biosynthesis* / Q000187:drug effects; D008565:Membrane Proteins; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis* / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D008565:Membrane Proteins; D003513:Cycloheximide; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases