title: Raf Kinases Are Essential for Phosphate Induction of ERK1/2 Phosphorylation in Hypertrophic Chondrocytes and Normal Endochondral Bone Development.
abstract: Hypophosphatemia causes rickets by impairing hypertrophic chondrocyte apoptosis. Phosphate induction of MEK1/2-ERK1/2 phosphorylation in hypertrophic chondrocytes is required for phosphate-mediated apoptosis and growth plate maturation. MEK1/2 can be activated by numerous molecules including Raf isoforms. A- and B-Raf ablation in chondrocytes does not alter skeletal development, whereas ablation of C-Raf decreases hypertrophic chondrocyte apoptosis and impairs vascularization of the growth plate. However, ablation of C-Raf does not impair phosphate-induced ERK1/2 phosphorylationin vitro, but leads to rickets by decreasing VEGF protein stability. To determine whether Raf isoforms are required for phosphate-induced hypertrophic chondrocyte apoptosis, mice lacking all three Raf isoforms in chondrocytes were generated. Raf deletion caused neonatal death and a significant expansion of the hypertrophic chondrocyte layer of the growth plate, accompanied by decreased cleaved caspase-9. This was associated with decreased phospho-ERK1/2 immunoreactivity in the hypertrophic chondrocyte layer and impaired vascular invasion. These data further demonstrated that Raf kinases are required for phosphate-induced ERK1/2 phosphorylation in cultured hypertrophic chondrocytes and perform essential, but partially redundant roles in growth plate maturation.
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114; Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Garyfallia
authors.initials: G
authors.lastname: Papaioannou
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114.
authors.forename: Elizabeth T
authors.initials: ET
authors.lastname: Petit
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114; Harvard Medical School, Boston, Massachusetts 02115; Division of Endocrinology, Diabetes, and Hypertension, Brigham and Women's Hospital, Boston, Massachusetts 02115.
authors.forename: Eva S
authors.initials: ES
authors.lastname: Liu
authors.affiliation: Department of Microbiology, Immunobiology and Genetics, Center of Molecular Biology, Max F. Perutz Laboratories, University of Vienna, Doktor-Bohr-Gasse 9, Vienna 1030, Austria.
authors.forename: Manuela
authors.initials: M
authors.lastname: Baccarini
authors.affiliation: Department of Molecular and Cell Biology, University of Leicester, University Road, Leicester LE1 7RH, United Kingdom.
authors.forename: Catrin
authors.initials: C
authors.lastname: Pritchard
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, Massachusetts 02114; Harvard Medical School, Boston, Massachusetts 02115. Electronic address: demay@helix.mgh.harvard.edu.
authors.forename: Marie B
authors.initials: MB
authors.lastname: Demay
mesh_terms: D000818:Animals; D017209:Apoptosis; D001846:Bone Development; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D020219:Chondrogenesis; D006132:Growth Plate / Q000254:growth & development* / Q000378:metabolism; D008810:Mice, Inbred C57BL; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D048491:Proto-Oncogene Proteins A-raf / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D048490:raf Kinases / Q000378:metabolism
chemical_list: D010710:Phosphates; D020033:Protein Isoforms; C482120:Braf protein, mouse; D048491:Proto-Oncogene Proteins A-raf; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D048490:raf Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3
keywords: Raf kinase; apoptosis; caspase; chondrocyte; growth plate; phosphate; rickets