The GAG chains of HSPG2 bind growth factors in the ECM, and serve as co-ligands or ligand enhancers when bound to receptors. For example, HS-bound FGF was released from cultured cells by treatments with MMP3, rat MMP13, and plasmin (Whitelock et al. 1996). The core protein of HSPG2 can be cleaved by cathepsin S (Liuzzo et al. 1999).