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Institut National de la Santé et de la Recherche Médicale U. 467, Faculté de Médecine Necker, 75015 Paris, France
We have previously shown that
ouabain, which changes the electrochemical properties of cell membranes
by inhibiting Na+,K+-ATPase, induces the
expression of multidrug resistance (MDR-1) gene in several human cell
lines. Because the expressions of the MDR-1 and CFTR (which encodes the
cAMP-activated Cl
channel associated with cystic
fibrosis) genes are physiologically regulated in opposing directions,
we wanted to determine whether ouabain also decreases CFTR transcripts
and subsequently to analyze its mechanism of action. We found that the
submicromolar concentrations of ouabain that increase MDR-1 mRNAs
decrease the CFTR transcripts with analogous time-dependency in human
pulmonary Calu-3 cells. By altering or reproducing the ouabain-induced
changes in intracellular ionic activities (decreasing in external
Na+ or K+ or using Na+ ionophore),
we show that the ouabain-induced regulations of both CFTR and MDR-1
transcripts depend on the Na+/K+ pump
inhibition but that the decrease in CFTR mRNAs also proceeds from
cytoplasm reactions simultaneously activated by ouabain. These data,
which emphasize the complex mechanism of action of ouabain, suggest
that changes in intracellular ionic activities modulate CFTR/MDR-1 gene expressions.
cystic fibrosis transmembrane conductance regulator; Na+,K+-ATPase inhibition; gene expression; transduction mechanisms
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