title: Lysyl oxidase propeptide inhibits FGF-2-induced signaling and proliferation of osteoblasts.
abstract: Pro-lysyl oxidase is secreted as a 50-kDa proenzyme and is then cleaved to a 30-kDa mature enzyme (lysyl oxidase (LOX)) and an 18-kDa propeptide (lysyl oxidase propeptide (LOX-PP)). The presence of LOX-PP in the cell layers of phenotypically normal osteoblast cultures led us to investigate the effects of LOX-PP on osteoblast differentiation. Data indicate that LOX-PP inhibits terminal mineralization in primary calvaria osteoblast cultures when added at early stages of differentiation, with no effects seen when present at later stages. LOX-PP was found to inhibit serum- and FGF-2-stimulated DNA synthesis and FGF-2-stimulated cell growth. Enzyme-linked immunosorbent assay and Western blot analyses show that LOX-PP inhibits FGF-2-induced ERK1/2 phosphorylation, signaling events that mediate the FGF-2-induced proliferative response. LOX-PP inhibits FGF-2-stimulated phosphorylation of FRS2alpha and FGF-2-stimulated DNA synthesis, even after inhibition of sulfation of heparan sulfate proteoglycans. These data point to a LOX-PP target at or near the level of fibroblast growth factor receptor binding or activation. Ligand binding assays on osteoblast cell layers with (125)I-FGF-2 demonstrate a concentration-dependent inhibition of FGF-2 binding to osteoblasts by LOX-PP. In vitro binding assays with recombinant fibroblast growth factor receptor protein revealed that LOX-PP inhibits FGF-2 binding in an uncompetitive manner. We propose a working model for the respective roles of LOX enzyme and LOX-PP in osteoblast phenotype development in which LOX-PP may act to inhibit the proliferative response possibly to allow cells to exit from the cell cycle and progress to the next stages of differentiation.
authors.affiliation: Department of Periodontology and Oral Biology, Boston University Goldman School of Dental Medicine, Boston, MA 02118, USA.
authors.forename: Siddharth R
authors.initials: SR
authors.lastname: Vora
authors.forename: Amitha H
authors.initials: AH
authors.lastname: Palamakumbura
authors.forename: Maria
authors.initials: M
authors.lastname: Mitsi
authors.forename: Ying
authors.initials: Y
authors.lastname: Guo
authors.forename: Nicole
authors.initials: N
authors.lastname: Pischon
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Nugent
authors.forename: Philip C
authors.initials: PC
authors.lastname: Trackman
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002113:Calcification, Physiologic / Q000187:drug effects / Q000502:physiology; D002417:Cattle; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D049109:Cell Proliferation; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D016222:Fibroblast Growth Factor 2 / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D008249:Protein-Lysine 6-Oxidase / Q000235:genetics / Q000378:metabolism*; D011869:Radioligand Assay; D051381:Rats; D017468:Receptors, Fibroblast Growth Factor / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D012886:Skull / Q000166:cytology
chemical_list: D011498:Protein Precursors; D017468:Receptors, Fibroblast Growth Factor; D016222:Fibroblast Growth Factor 2; D004247:DNA; D008249:Protein-Lysine 6-Oxidase