DGDA, a local sequence of the kringle 2 domain, is a functional motif of the tissue-type plasminogen activator's antiangiogenic kringle domain

Antiangiogenic activity can be elicited by the kringle domains 1 and 2 of tissue-type plasminogen activator (TK1-2), or the kringle 2 domain alone. In a previous report, we showed that the anti-migratory effect of TK1-2 is mediated in part by its interference with integrin α2β1. Since integrin α2β1 interacts with collagen type I through the DGEA (Asp-Gly-Glu-Ala) amino acid sequence, and a similar sequence, DGDA (Asp-Gly-Asp-Ala), exists in the kringle 2 domain, we investigated whether the DGDA sequence has a role in antiangiogenic activity of TK1-2. In an adhesion assay, the DGDA peptide inhibited adhesion of human umbilical vein endothelial cells (HUVECs) to immobilized TK1-2. Pretreatment of the DGDA peptide also blocked anti-migratory activity of TK1-2. When the DGDA peptide alone was tested for antiangiogenic activity, it effectively inhibited VEGF-induced migration of HUVECs and tube formation on Matrigel. In addition, the DGDA peptide decreased differentiation of endothelial progenitor cells on collagen type I matrix. These data suggest that the DGDA sequence presents a functional epitope of TK1-2 and that it can be used as a potential novel antiangiogenic peptide.