IL-3 INCREASES SURFACE PROTEOGLYCAN SYNTHESIS IN HEMATOPOIETIC PROGENITORS AND THEIR ADHESIVENESS TO THE HEPARIN-BINDING DOMAIN OF FIBRONECTIN

Haemopoietic progenitor cells (HPC) synthesize and accumulate a single type of membrane-associated chondroitin sulphate proteoglycan (MA-PG) , which participates in HPC adhesiveness to fibronectin by interacting with its heparin-binding domain. Shortly after incubating cells with IL-3, we observed an increase in MA-PG synthesis in the multipotent (F DCP-mix) but not in the bipotent (FDCP-1) progenitor cell line. The ch arge density, hydrodynamic size, nature of the glycosaminoglycan (GAG) chains and stability of MA-PG from IL-3-treated and non-treated FDCP- mix cells were the same, suggesting that IL-3 affects the amount of MA -PG. The latter was evaluated by now cytometry using monoclonal antibo dies to the core protein and GAG residues. In all cases the mean fluor escence intensities were higher for IL-3-treated than for untreated ce lls. Cell adhesion studies to dishes coated with the fibronectin 40 kD fragment, containing the heparin-binding domain, demonstrated that ad hesiveness of IL-3-treated cells was higher than that of untreated cel ls. These results suggest that in multipotent haemopoietic cells IL-3 regulates the amount of membrane-associated proteoglycans, which in tu rn modify the adhesive interactions of cells with the heparin-binding domain of fibronectin.