The antiangiogenic factor 16K PRL induces programmed cell death in endothelial cells by caspase activation

We asked whether the antiangiogenic action of 16K human PRL (hPRL), in addi tion to blocking mitogen-induced vascular endothelial cell proliferation, i nvolved activation of programmed cell death, Treatment with recombinant 16K hPRL increased DNA fragmentation in cultured bovine brain capillary endoth elial (BBE) and human umbilical vein endothelial (HUVE) cells in a time- an d dose-dependent fashion, independent of the serum concentration. The activ ation of apoptosis by 16K hPRL was specific for endothelial cells, and the activity of the peptide could be inhibited by heat denaturation, trypsin di gestion, and immunoneutralization, but not by treatment with the endotoxin blocker, polymyxin-B, 16K hPRL-induced apoptosis was correlated with the ra pid activation of caspases 1 and 3 and was blocked by pharmacological inhib ition of caspase activity, Caspase activation was followed by inactivation of two caspase substrates, poly(ADP-ribose) polymerase (PARP) and the inhib itor of caspase-activated deoxyribonuclease (DNase) (ICAD), Furthermore, 16 K hPRL increased the conversion of Bcl-X to its proapoptotic form, suggesti ng that the Bcl-2 protein family may also be involved in 16K hPRL-induced a poptosis. These findings support the hypothesis that the antiangiogenic act ion of 16K hPRL includes the activation of programmed cell death of vascula r endothelial cells.