Induction of osteoblast differentiation indexes by PTHrP in MG-63 cells involves multiple signaling pathways.
Parathyroid hormone (PTH)-related peptide (PTHrP) can modulate the proliferation and differentiation of a number of cell types including osteoblasts. PTHrP can activate a G protein-coupled PTH/PTHrP receptor, which can interface with several second-messenger systems. In the current study, we have examined the signaling pathways involved in stimulated type I collagen and alkaline phosphatase expression in the human osteoblast-derived osteosarcoma cells, MG-63. By use of Northern blotting and histochemical analysis, maximum induction of these two markers of osteoblast differentiation occurred after 8 h of treatment with 100 nM PTHrP-(1-34). Chemical inhibitors of adenylate cyclase (H-89) or of protein kinase C (chelerythrine chloride) each diminished PTHrP-mediated type I collagen and alkaline phosphatase stimulation in a dose-dependent manner. These effects of PTHrP could also be blocked by inhibiting the Ras-mitogen-activated protein kinase (MAPK) pathway with a Ras farnesylation inhibitor, B1086, or with a MAPK inhibitor, PD-98059. Transient transfection of MG-63 cells with a mutant form of Galpha, which can sequester betagamma-subunits, showed significant downregulation of PTHrP-stimulated type I collagen expression, as did inhibition of phosphatidylinositol 3-kinase (PI 3-kinase) by wortmannin. Consequently, the betagamma-PI 3-kinase pathway may be involved in PTHrP stimulation of Ras. Collectively, these results demonstrate that, acting via its G protein-coupled receptor, PTHrP can induce indexes of osteoblast differentiation by utilizing multiple, perhaps parallel, signaling pathways.
Carpio
L
L
Department of Medicine, McGill University Health Center, Montreal, Quebec H3A 1A1, Canada.
Gladu
J
J
Goltzman
D
D
Rabbani
S A
SA
D000470:Alkaloids; D053119:Benzophenanthridines; D015152:Blotting, Northern; D002454:Cell Differentiation / Q000187:drug effects*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000502:physiology; D006801:Humans; D007546:Isoquinolines / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009154:Mutation; D010006:Osteoblasts / Q000187:drug effects*; D012516:Osteosarcoma; D044162:Parathyroid Hormone-Related Protein; D010617:Phenanthridines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011506:Proteins / Q000494:pharmacology*; D015398:Signal Transduction; D013449:Sulfonamides; D014162:Transfection; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism
D000470:Alkaloids; D053119:Benzophenanthridines; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D019205:GTP-Binding Protein alpha Subunits, Gs; D020962:Heterotrimeric GTP-Binding Proteins; D007546:Isoquinolines; D020928:Mitogen-Activated Protein Kinases; D044162:Parathyroid Hormone-Related Protein; D010617:Phenanthridines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D011506:Proteins; D013449:Sulfonamides; D018631:ras Proteins; C470121:PTHLH protein, human; C016299:chelerythrine; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide