The antiangiogenic factor 16K human prolactin induces caspase-dependent apoptosis by a mechanism that requires activation of nuclear factor-kappaB

We have previously shown that the 16-kDa N-terminal fragment of human prolactin (16K hPRL) has antiangiogenic properties, including the ability to induce apoptosis in vascular endothelial cells. Here, we examined whether the nuclear factor-kappaB (NF-kappaB) signaling pathway was involved in mediating the apoptotic action of 16K hPRL in bovine adrenal cortex capillary endothelial cells. In a dose-dependent manner, treatment with 16K hPRL induced inhibitor kappaB-alpha degradation permitting translocation of NF-kappaB to the nucleus and reporter gene activation. Inhibition of NF-kappaB activation by overexpression of a nondegradable inhibitor kappaB-alpha mutant or treatment with NF-kappaB inhibitors blocked 16K hPRL-induced apoptosis. Treatment with 16K hPRL activated the initiator caspases-8 and -9 and the effector caspase-3, all of which were essential for stimulation of DNA fragmentation. This activation of the caspase cascade by 16K hPRL was also NF-kappaB dependent. These findings support the conclusion that NF-kappaB signaling plays a central role in 16K hPRL-induced apoptosis in vascular endothelial cells.