Thrombospondins as matricellular modulators of cell function

Thrombospondins (TSPs) are a small family of secreted, modular glycoproteins whose functions, at a mechanistic level, are not well understood, despite increasing scrutiny in recent years. TSP1 and TSP2 form one subgroup and are trimers with a chain molecular mass of about 145 kDa. The pentameric TSPs 3-5 are significantly smaller, with a subunit molecular mass of about 100 kDa (1), and their physiological roles are probably distinct. This Perspective will concern itself with TSP1 and TSP2.