Doxorubicin induces apoptosis in a variety of cells. We investigated the expression and function of various tumor necrosis factor (TNF)alpha-homologues and their receptors. CEM cells did not differentially express any one of the TNFalpha-homologous receptors investigated nor TNF-related apoptosis-inducing ligand or TNF-related weakly apoptosis-inducing ligand (TWEAK) in the presence of doxorubicin. In addition to CD95 ligand, however, receptor activator of nuclear factor kappaB ligand (RANKL) was strongly up-regulated. Doxorubicin-induced apoptosis was greatly suppressed in the presence of either neutralizing antibody or RANK-Fc fusion protein. Moreover, neutralizing RANKL also prevented cytochrome c release from mitochondria. RANKL alone was unable to induce significant levels of apoptosis in CEM cells. However, doxorubicin-induced apoptosis was increased >2-fold when exogenous RANKL was added. Therefore, RANKL is necessary but not sufficient to account for early doxorubicin-induced apoptosis in CEM cells. This finding suggests improved chemotherapeutic efficiency of the anthracyclin against susceptible malignant cells in the presence with RANKL.
