Thrombospondin: One of a family of glycoproteins (carbohydrates complexed with proteins) that are made in cells, secreted by cells, and incorporated into cells including blood platelets (thrombocytes) from which they take their name. Five distinct forms have been identified; they are termed thrombospondin-1, thrombospondin-2, thrombospondin-3, thrombospondin-4, and thrombospondin-5.
The thrombospondins are known to interact with blood coagulation and anticoagulant factors. They are involved in cell adhesion, platelet aggregation (clumping), cell proliferation (growth), angiogenesis (blood vessel formation), tumor metastasis, and tissue repair.
Thrombospondin-1 and thrombospondin-2 have been shown to be potent inhibitors of angiogenesis and suppressors of tumor growth in laboratory mice. (Proc Natl Acad Sci USA 1999;96:14888-14893.)