Peptides Derived from Two Separate Domains of the Matrix Protein Thrombospondin-1 Have Anti-Angiogenlc Activity
Thrombospondin-1 (TSP1) is a large modular matrix protein containing three identical disulfide-linked 180-kD chains that inhibits neovascularization in vivo (Good et al., 1990). To determine which of the structural motifs present in the 180-kD TSP1 polypeptide mediate the anti-angiogenic activity, a series of protease-generated fragments were tested using several in vitro and in vivo assays that reflect angiogenic activity. The majority of the anti-angiogenic activity of TSP1 resides in the central 70-kD stalk region which alone could block neovascularization induced by bFGF in the rat cornea in vivo and inhibit both migration in a modified Boyden chamber and [~H]thymidine incorporation stimulated by bFGF in cultured capillary endothelial cells. Although TSP1 has been shown to bind active TGF/31, this cytokine could not account for the inhibitory effects of the stalk region of TSP1 on cultured endothelial cells.