Sphingosine generation, cytochrome c release, and activation of caspase-7 in doxorubicin-induced apoptosis of MCF7 breast adenocarcinoma cells

Treatment of human breast carcinoma MCF7 cells with doxorubicin, one of the most active antineoplastic agents used in clinical oncology, induces apopt osis and leads to increases in sphingosine levels. The transient generation of this sphingolipid mediator preceded cytochrome c release from the mitoc hondria and activation of the executioner caspase-7 in MCF7 cells which do not express caspase-3. Bcl-x(L) overexpression did not affect sphingosine g eneration whereas it reduced apoptosis triggered by doxorubicin and complet ely blocked apoptosis triggered by sphingosine, Exogenous sphingosine-induc ed apoptosis was also accompanied by cytochrome c release and activation of caspase-7 in a Bcl-x(L)-sensitive manner. Furthermore, neither doxorubicin nor sphingosine treatment affected expression of Fas ligand or induced act ivation of the apical caspase-8, indicating a Fas/Fas ligand-independent me chanism. Our results suggest that a further metabolite of ceramide, sphingo sine, may also be involved in mitochondria-mediated apoptotic signaling ind uced by doxorubicin in human breast cancer cells.