AbstractPeptides containing the Arg-Gly-Asp (RGD) motif inhibit cell adhesion and exhibit a variety of other biologic effects including anticoagulant and antimetastatic activities. The aim of the present study was to examine the anchorage-independent effects of an RGD-containing peptide, Arg-Gly-Asp-Ser (RGDS), on human umbilical vein endothelial cells (HUVECs). Assays were performed on HUVECs seeded onto collagen IV; under these experimental conditions RGDS did not exert antiadhesive effects but significantly reduced FGF-2-dependent chemotaxis after 4 hours of treatment and reduced proliferation after 24 hours of treatment. Experiments carried out with caspase-specific inhibitors indicated that the observed antichemotactic effects required caspase 8 and caspase 9 activation. RGDS activated both caspase 8 and caspase 9 after 4 hours of treatment and caspase 3 after 24 hours of treatment, and markedly enhanced HUVEC apoptosis by transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)/Hoechst staining and fluorescence-activated cell sorting (FACS) analysis. Finally, confocal microscopy showed that RGDS localizes in the cytoplasm of live HUVECs within 4 hours and in vitro experiments showed that RGDS directly interacts with recombinant caspases 8 and 9 in a specific way. In summary, these results indicate that RGDS directly binds and activates caspases 8 and 9, inhibits chemotaxis, and induces apoptosis of HUVECs with a mechanism independent from its antiadhesive effect.