Acts as a carrier protein that release fibroblast-binding factors (FGFs) from the extracellular matrix (EM) storage and thus enhance the mitogenic activity of FGFs. Enhances FGF2 signaling during tissue repair, angiogenesis and in tumor growth (By similarity). Found in a complex with FGFBP1, FGF1 and FGF2. Interacts with FGF1, FGF2, FGF7, FGF10, FGF22 and HSPG2 (By similarity). Extracellular and plasma membrane-associated. Expressed in gut, eye, thymus, skin, lung, tongue, Purkinje cells and cerebral chorioid plexus (at protein level). Down-regulated by retinoids. Belongs to the fibroblast growth factor-binding protein family.