Extracellular proteins that modulate cell-matrix interactions : SPARC, tenascin, and thrombospondin

We describe in this review a group of secreted glycoproteins that presently includes SPARC, tenascin (TN), and thrombospondin (TSP) but that is likely to include other macromolecules with related functions. These proteins do not function primarily and generally as cell adhesion factors, in the sense that they foster both attachment and spreading in most cells. Instead, for many cells, these proteins exert an "anti-adhesive" function that leads to cell rounding and partial detachment from a substratum. SPARC, TN, and TSP possess certain common attributes.