Intracellular Ca2+ potentiates Na+/H+ exchange and cell differentiation induced by phorbol ester in U937 cells.
The human cell line U937 differentiates to monocyte macrophage-like cells in response to tumour-promoting phorbol esters. This effect is attributed to activation of protein kinase C. We show here that U937 cell differentiation induced by 12-O-tetradecanoylphorbol 13-acetate (TPA) is associated with cytoplasmic alkalinization. Ethyl-isopropyl-amiloride (EIPA), a potent inhibitor of Na+/H+ exchange, blocked both cytoplasmic alkalinization and cell differentiation. Cell acidification by addition of 2-4 mM sodium propionate also blocked TPA-induced U937 cell differentiation. These results suggest that a sustained cell alkalinization mediated by activation of Na+/H+ exchange is essential for TPA-induced differentiation in U937 cells. The increase of cytoplasmic free calcium concentration ([Ca2+]i) by addition of the calcium ionophore ionomycin enhanced TPA-induced alkalinization by increasing the apparent affinity of the Na+/H+ antiporter for intracellular H+. Treatment with ionomycin also potentiated differentiation of U937 cells induced by TPA. This synergism suggests that [Ca2+]i either potentiates the activation of protein kinase C or triggers additional transducing mechanisms. The key events of this interaction occur during the first 30 min of treatment, even though cell differentiation manifests much later.
Alvarez
J
J
Departamento de Bioquímica y Biologia Molecular y Fisiologia, Universidad de Valladolid, Madrid, Spain.
García-Sancho
J
J
Mollinedo
F
F
Sanchez
A
A
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects*; D002460:Cell Line; D004987:Ethers / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin; D007700:Kinetics; D008264:Macrophages; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D002352:Carrier Proteins; D004987:Ethers; D017923:Sodium-Hydrogen Exchangers; D015759:Ionomycin; D000584:Amiloride; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; C039614:ethylisopropylamiloride