IL-3 increases surface proteoglycan synthesis in haemopoietic 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 (FDCP-mix) but not in the bipotent (FDCP-1) progenitor cell line. The charge 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 flow cytometry using monoclonal antibodies to the core protein and GAG residues. In all cases the mean fluorescence intensities were higher for IL-3-treated than for untreated cells. Cell adhesion studies to dishes coated with the fibronectin 40 kD fragment, containing the heparin-binding domain, demonstrated that adhesiveness of IL-3-treated cells was higher than that of untreated cells. These results suggest that in multipotent haemopoietic cells IL-3 regulates the amount of membrane-associated proteoglycans, which in turn modify the adhesive interactions of cells with the heparin-binding domain of fibronectin.