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  • Title: Phosphatidylserine externalization during differentiation-triggered apoptosis of erythroleukemic cells.
    Author: Diaz C, Lee AT, McConkey DJ, Schroit AJ.
    Journal: Cell Death Differ; 1999 Mar; 6(3):218-26. PubMed ID: 10200572.
    Abstract:
    K562 erythroleukemia cells undergo apoptosis when induced to differentiate along the erythroid lineage with hemin. This event, characterized by DNA fragmentation, correlated with downregulation of the survival protein, BCL-xL, and decrease in mitochondrial transmembrane potential (deltapsi[m]) that ultimately resulted in cell death. Reorientation of phosphatidylserine (PS) from the cells inner-to-outer plasma membrane leaflet and inhibition of the aminophospholipid translocase was observed upon hemin-treatment. Constitutive expression of BCL-2 did not inhibit hemin-induced alterations in lipid asymmetry or decrease in deltapsi[m], and only moderately prevented DNA fragmentation. BCL-2, on the other hand, effectively inhibited actinomycin D-induced DNA fragmentation, the appearance of PS at the cells outer leaflet and the decrease in deltapsi[m]. The caspase inhibitor, z.VAD.fmk, blocked DNA fragmentation by both hemin and actinomycin D, but inhibited PS externalization only in the actinomycin D-treated cells. These results suggest that, unlike pharmacologically-induced apoptosis, PS externalization triggered by differentiation-induced apoptosis occurs by a mechanism that is associated with a decrease in deltapsi[m], but independent of BCL-2 and caspases.
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