PROTEOGLYCAN FORM OF COLONY-STIMULATING FACTOR-I (PROTEOGLYCAN-100) -STIMULATION OF ACTIVITY BY GLYCOSAMINOGLYCAN REMOVAL AND PROTEOLYTIC PROCESSING

A proteoglycan had been isolated from the conditioned media of a human osteosarcoma cell line and had tentatively been named proteoglycan-10 0 (PC-100) because of the size of its core glycoprotein, Amino acid se quencing of the purified proteoglycan and cDNA analysis were consisten t with the assumption that PC-100 is identical with the proteoglycan f orm of CSF-1 (Or macrophage colony-stimulating factor), PG-100 induced mouse macrophage differentiation, Proliferation of macrophages was st imulated in a dose-dependent manner, On a molar basis, however, about 100- to 300-fold higher doses of PG-100 than of recombinant human (rh) CSF-l were required for the half-maximal growth-stimulating effect, Up on enzymatic removal of the glycosaminoglycan chain, the purified core protein exhibited higher activity, but was still about 20-fold less a ctive than rhCSF-1, Incubation of the purified proteoglycan for 48 h a t 37 degrees C led to the formation of a glycosaminoglycan-free 50-kDa fragment either by autoproteolysis or by the action of a protease not yet identified, The purified fragment exhibited, almost the same biol ogic activity as rhCSF-1, The glycosaminoglycan chain of the growth fa ctor was not only shown to inhibit CSF-1 activity but also to increase the stability of the core protein when the CSF-l-producing osteosarco ma cells were maintained in a collagen lattice, These findings provide a link between a soluble, highly active cytokine and its extracellula r matrix storage form of comparatively low activity.