Early ionic events associated with phorbol ester induced differentiation and inhibition of cell growth in hematopoietic tumor cell lines.
The effects of 12-O-tetradecanoylphorbol-13 acetate (TPA) on DNA synthesis, phenotypic expression, cytoplasmic Ca2+ (Ca2+i), intracellular pH (pHi) and membrane potential were studied in the monoblastic U-937 and the erythroleukemic K-562 cells. In both cell lines DNA synthesis was inhibited and in the U-937 cells this was accompanied by the appearance of macrophage differentiation markers. The erythroid characteristics of K-562 cells, on the other hand, were markedly suppressed. Intracellular pH (pHi) was increased by TPA treatment; however, while the alkalinization of K-562 cells was dependent on the presence of extracellular Na+, the response of U-937 cells was unaffected by the removal of this cation. In each cell type the protein kinase C (PKC) inhibitor H-7 largely attenuated the TPA induced increase of pHi. Moreover, the alpha-stereoisomer of TPA, which does not activate PKC, had no effects. TPA caused a dose-dependent decrease in Ca2+i which was more pronounced in U-937 cells. Measurements of membrane potential revealed a marked TPA depolarization of the K-562 cells, but no such effects were observed in the U-937 cell line. The depolarizing response of K-562 cells could be abolished by substituting extracellular Na+ with choline+, indicating the presence of a TPA sensitive Na+ permeability. The results show that the phorbol ester TPA, which inhibits proliferation and causes phenotypic modulation, also induced a number of early, apparently PKC dependent and cell type specific, changes of intracellular ion activities. The possible role of intracellular ion fluxes in the regulation of cell growth and differentiation is discussed.
Larsson
R
R
Department of Medical Cell Biology, University of Uppsala, Sweden.
Nygren
P
P
Forsbeck
K
K
Gylfe
E
E
Nilsson
K
K
D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects*; D004247:DNA / Q000096:biosynthesis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D004915:Leukemia, Erythroblastic, Acute / Q000378:metabolism / Q000473:pathology; D016403:Lymphoma, Large B-Cell, Diffuse / Q000378:metabolism / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
D004247:DNA; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium