title: Integrin-mediated signaling regulates AP-1 transcription factors and proliferation in osteoblasts.
abstract: Since osteoblast proliferation is critical for bone development, the effect of bone extracellular matrix (ECM) proteins on osteoblast signaling and proliferation in serum-free medium was investigated. Proliferation was highest in primary rat calvarial osteoblasts cells grown on fibronectin but less on type I collagen; osteonectin and poly-L-lysine did not support early proliferation. Fibronectin and type I collagen binding requires integrins, whereas cell adhesion to osteonectin or poly-L-lysine does not involve integrins. Therefore, the role of integrins in osteoblast signaling, leading to the induction of AP-1 transcription factors (c-fos and c-jun) which are important in cell proliferation, was studied. c-fos and c-jun message levels were increased at 60 min in osteoblasts plated onto fibronectin or collagen, but not in cells on osteonectin or poly-L-lysine. Protein synthesis was not required for c-fos mRNA expression; however, kinase activity was necessary for c-fos induction. In cells plated onto fibronectin, c-fos mRNA levels were controlled by protein kinase C and phosphotyrosine kinase signaling pathways. In contrast, c-fos levels in collagen-adhering cells may involve protein kinase A. The signaling pathway involving the phosphorylation of focal adhesion kinase and mitogen-activated kinases was also shown to be transiently increased in osteoblasts on fibronectin and type I collagen, but not in cells on poly-L-lysine. These results demonstrate that osteoblast binding to the extracellular matrix through integrins induces c-fos and c-jun, and that both fibronectin and collagen affect these AP-1 transcription factors through protein kinase-sensitive pathways. Thus, osteoblast proliferation is modulated differentially by specific ECM components.
authors.affiliation: Department of Orthopaedics, MC-1110, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Cowles
authors.forename: L L
authors.initials: LL
authors.lastname: Brailey
authors.forename: G A
authors.initials: GA
authors.lastname: Gronowicz
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D018929:Cell Culture Techniques / Q000295:instrumentation; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D020099:Coated Materials, Biocompatible; D003094:Collagen / Q000378:metabolism; D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005109:Extracellular Matrix / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005353:Fibronectins / Q000378:metabolism; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005786:Gene Expression Regulation; D016762:Genes, fos; D016758:Genes, jun; D016023:Integrins / Q000276:immunology / Q000502:physiology*; D020935:MAP Kinase Signaling System; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015676:Osteonectin / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D010969:Plastics; D011107:Polylysine / Q000378:metabolism; D011485:Protein Binding; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D015398:Signal Transduction; D019699:Thrombospondins / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
chemical_list: D000906:Antibodies; D020099:Coated Materials, Biocompatible; D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; D016326:Extracellular Matrix Proteins; D005353:Fibronectins; D016023:Integrins; D019384:Nucleic Acid Synthesis Inhibitors; D009842:Oligopeptides; D015676:Osteonectin; D010969:Plastics; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D019699:Thrombospondins; D018808:Transcription Factor AP-1; C101396:glycyl-arginyl-alanyl-aspartyl-seryl-proline; C086456:glycyl- arginyl-glycyl-aspartyl-seryl-prolyl-lysine; D011107:Polylysine; D003094:Collagen; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496052:Ptk2 protein, rat; D011493:Protein Kinase C