Glycosaminoglycans bind granulocyte-macrophage colony-stimulating factor and modulate its mitogenic activity and signaling in human osteoblastic cells.
We recently demonstrated that granulocyte-macrophage colony-stimulating factor (GM-CSF) is an autocrine growth factor for human osteoblastic (hOB) cells. Since GM-CSF is a member of the heparin-binding factor family, we examined the interactions between GM-CSF and glycosaminoglycans (GAGs) present in the osteoblast microenvironment. Using a bioassay in which the mitogenic activity of recombinant human (rh) GM-CSF was measured after incubation in the presence of an hOB cell layer or extracellular matrix (ECM) produced by these cells, we showed that rhGM-CSF binds to GAG components present in the ECM and that the bound rhGM-CSF retains its ability to stimulate hOB cell proliferation. Heparan sulfate compounds on the hOB cell surface were also found to sequester GM-CSF. Moreover, treatment with sodium chlorate, an inhibitor of GAG sulfation, suppressed the mitogenic activity of rhGM-CSF on hOB cells. This inhibitory effect was rescued by a low dose of heparin. Heparin was also found to promote the effect of rhGM-CSF on hOB cell proliferation, allowing nonmitogenic high doses of rhGM-CSF to stimulate hOB cell growth. Western blot analysis showed that undersulfation of cellular GAGs by chlorate inhibited the increased tyrosine phosphorylation of proteins involved in GM-CSF signaling in cloned immortalized hOB cells. The data demonstrate that GM-CSF binds to proteoglycans on the hOB cell surface and in ECM produced by these cells and that the bound GM-CSF is biologically active. Furthermore, this study shows that cellular proteoglycans play an essential role in GM-CSF signaling and biological activity in hOBs.
Modrowski
D
D
INSERM Unité 349, Cell and Molecular Biology of Bone and Cartilage, Lariboisière Hospital, Paris, France.
Lomri
A
A
Marie
P J
PJ
D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D002704:Chlorates / Q000494:pharmacology; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism* / Q000494:pharmacology; D006497:Heparan Sulfate / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D008934:Mitogens / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology*; D013431:Sulfates / Q000378:metabolism
D002704:Chlorates; D016326:Extracellular Matrix Proteins; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006497:Heparan Sulfate; D008565:Membrane Proteins; D008934:Mitogens; D011994:Recombinant Proteins; D013431:Sulfates