RGD peptides induce apoptosis by direct caspase-3 activation

Synthetic Peptides containing the arginine-glycine-aspartate (RGD) motif have been used extensively as inhibitors of integrin-ligand interactions in studies of cell adhesion, migration, growth and differentiation, because the RGD motif is an integrin-recognition motif found in many ligands. Here we report that RGD-containing Peptides are able to directly induce Apoptosis without any requirement for integrin-mediated cell clustering or signals. We show that RGD-containing Peptides enter cells and directly induce autoprocessing and enzymatic activity of procaspase-3, a pro-apoptotic protein. Using the breast carcinoma cell line MCF-7, which has a functional deletion of the Caspase-3 gene, we confirm that Caspase-3 is required for RGD-mediated cell death. In addition to an RGD motif, pro-caspase-3 also contains a potential RGD-binding motif, aspartate-aspartate-methionine (DDM), near the site of processing to produce the p12 and p17 subunits. On the basis of the ability of RGD-DDX interactions to trigger Integrin activation, we suggest that RGD Peptides induce Apoptosis by triggering conformational changes that promote pro-caspase-3 autoprocessing and activation. These findings provide an alternative molecular explanation for the potent proapoptotic properties of RGD Peptides in models of angiogenesis, inflammation and Cancer metastasis.