RGD peptides induce apoptosis by direct caspase-3 activation

Abstract

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 differentiation¹,²,³, 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 pro-caspase-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)⁴, near the site of processing to produce the p12 and p17 subunits⁵. On the basis of the ability of RGD–DDX interactions to trigger integrin activation⁶, 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 pro-apoptotic properties of RGD peptides in models of angiogenesis, inflammation and cancer metastasis⁷,⁸,⁹.