Matrix Glycoproteins May Regulate the Local Concentrations of Different Hemopoietic Growth Factors
We compared the binding properties of granulocyte-macrophage colony-stimulating factor (GM-CSF), erythropoietin (epo) and interleukin-3 (IL-3) to test the hypothesis that binding to extracellular matrix (ECM) governs growth factor distribution in the marrow microenvironment. Since mitogens for cells of mesodermal and neuroectodermal origin bind to heparin , heparin-like molecules (e.g. heparan sulphate) are candidate growth factor-binding structures in the ECM associated with marrow-derived stromal cells. In contrast to the heparin-binding fibroblast growth factor (FGF), GM-CSF did not bind to heparin-sepharose beads. However, most recombinant (r), human (h), gibbon (g) and murine (m) IL-3 bound to the beads; intermediate levels of binding were shown by epo and native mIL-3. Like GM-CSF , epo and h/gIL-3 did not bind to intact marrow-derived stromal layers but more than 85% of mIL-3 (native and recombinant) bound under these conditions. Murine IL-3 and GM-CSF  bind to marrow-derived ECM but epo does not. The different binding properties of haemopoietic growth factors vis-a-vis matrix glycoproteins suggests that their distributions and concentrations may be determined by the local composition of the ECM.
KeywordsCellulose Filtration Albumin Agar Leukemia
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