TNF-α-Induced Apoptosis of Macrophages Following Inhibition of NF-κB: A Central Role for Disruption of Mitochondria

Previously, we established that suppressing the constitutive activation of NF-kappaB in in vitro matured human macrophages resulted in apoptosis initiated by a decrease of the Bcl-2 family member, A1, and the loss of mitochondrial transmembrane potential (Deltapsi(m)). This study was performed to characterize the mechanism of TNF-alpha-induced apoptosis in macrophages following the inhibition of NF-kappaB. The addition of TNF-alpha markedly enhanced the loss of Deltapsi(m) and the induction of apoptotic cell death. Although caspase 8 was activated and contributed to DNA fragmentation, it was not necessary for the TNF-alpha-induced loss of Deltapsi(m). The inhibition of NF-kappaB alone resulted in the release of cytochrome c from the mitochondria, while both cytochrome c and second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI were released following the addition of TNF-alpha. Furthermore, c-Jun N-terminal kinase activation, which was sustained following treatment with TNF-alpha when NF-kappaB was inhibited, contributed to DNA fragmentation. These observations demonstrate that cytochrome c and second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI may be differentially released from the mitochondria, and that the sustained activation of c-Jun N-terminal kinase modulated the DNA fragmentation independent of the loss of Deltapsi(m).