Thrombospondin 1, abbreviated as THBS1, is a protein that in humans is encoded by the THBS1 gene. Thrombospondin 1 is a subunit of a disulfide-linked homotrimeric protein. This protein is an adhesive glycoprotein that mediates cell-to-cell and cell-to-matrix interactions. This protein can bind to fibrinogen, fibronectin, laminin, collagens types V and VII and integrins alpha-V/beta-1. This protein has been shown to play roles in platelet aggregation, angiogenesis, and tumorigenesis. Function The thrombospondin-1 protein is a member of the thrombospondin family. It is a multi-domain matrix glycoprotein that has been shown to be a natural inhibitor of neovascularization and tumorigenesis in healthy tissue. Both positive and negative modulation of endothelial cell adhesion, motility, and growth have been attributed to TSP1. This should not be surprising considering that TSP1 interacts with at least 12 cell adhesion receptors, including CD36, αv integrins, β1 integrins, syndecan, and integrin-associated protein (IAP or CD47). It also interacts with numerous proteases involved in angiogenesis, including plasminogen, urokinase, matrix metalloproteinase, thrombin, cathepsin, and elastase. Thrombospondin-1 binds to the reelin receptors, ApoER2 and VLDLR, thereby affecting neuronal migration in the rostral migratory stream. The various functions of the TSRs have been attributed to several recognition motifs. Characterization of these motifs has led to the use of recombinant proteins that contain these motifs; these recombinant proteins are deemed useful in cancer therapy. The TSP-1 3TSR (a recombinant version of the THBS1 antiangiogenic domain containing all three thrombosopondin-1 type 1 repeats) can activate transforming growth factor beta 1 (TGFβ1) and inhibit endothelial cell migration, angiogenesis, and tumor growth. Structure Thrombospondin's activity has been mapped to several domains, in particular the amino-terminal heparin-binding domain, the procollagen domain, the properdin-like type I repeats, and the globular carboxy-terminal domain. The protein also contains type II repeats with epidermal growth factor-like homology and type III repeats that contain an RGD sequence. N-terminus The N-terminal heparin-binding domain of TSP1, when isolated as a 25kDa fragment, has been shown to be a potent inducer of cell migration at high concentrations. However, when the heparin-binding domain of TSP1 is cleaved, the remaining anti-angiogenic domains have been shown to have decreased anti-angiogenic activity at low concentrations where increased endothelial cell (EC) migration occurs. This may be explained in part by the ability of the heparin-binding domain to mediate attachment of TSP1 to cells, allowing the other domains to exert their effects. The separate roles that the heparin-binding region of