Thrombospondin (TSP1) mediates in vitro proliferation of human MG-63 osteoblastic cells induced by alpha-thrombin.
Thrombospondin (TSP) is a 450-kDa glycoprotein synthesized and secreted by human MG-63 osteoblastic cells. In this study, we have first studied the effect of alpha-thrombin on TSP expression by human MG-63 cells. In situ hybridization indicated that TSP mRNA level in thrombin-treated MG-63 cells was increased when compared to unstimulated cells. As judged by immunofluorescence, thrombin-treatment of MG-63 cells resulted in increased cell surface expression of TSP when compared to quiescent cells. Because thrombin stimulates proliferation of osteoblastic cells, the involvement of TSP in proliferation of thrombin-stimulated osteoblastic cells was then investigated using a serum-free mitogenesis assay. Both alpha-thrombin (0.01 to 0.15 U/ml) and TSP (5 to 600 ng/ml) caused a dose-dependent increase in [3H]thymidine incorporation by MG-63 cells. Proliferation of osteoblastic cells induced by alpha-thrombin or TSP was specifically and totally inhibited by anti-TSP monoclonal antibodies (3-10 micrograms/ml) or by indomethacin (1 microM), an inhibitor of prostaglandin synthesis. Anti-TSP antibodies which inhibited cell proliferation also inhibit TSP expression to the surface of these cells. Our experiments support the existence of a mechanism whereby TSP bound to the cell surface of thrombin-treated MG-63 cells stimulates secretion of prostaglandins which, in turn, allow cell proliferation to proceed.
Abbadia
Z
Z
INSERM Unit Research 234, Hôpital Edouard Herriot, Lyon, France.
Clezardin
P
P
Serre
C M
CM
Amiral
J
J
Delmas
P D
PD
D002455:Cell Division / Q000187:drug effects; D005455:Fluorescent Antibody Technique; D006801:Humans; D017403:In Situ Hybridization; D008562:Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology*; D019699:Thrombospondins; D014407:Tumor Cells, Cultured
D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D019699:Thrombospondins; D013917:Thrombin