title: c-Raf promotes angiogenesis during normal growth plate maturation.
abstract: Extracellular phosphate plays a key role in growth plate maturation by inducing Erk1/2 (Mapk3/1) phosphorylation, leading to hypertrophic chondrocyte apoptosis. The Raf kinases induce Mek1/2 (Map2k1/2) and Erk1/2 phosphorylation; however, a role for Raf kinases in endochondral bone formation has not been identified. Ablation of both A-Raf (Araf) and B-Raf (Braf) in chondrocytes does not alter growth plate maturation. Because c-Raf (Raf1) phosphorylation is increased by extracellular phosphate and c-Raf is the predominant isoform expressed in hypertrophic chondrocytes, chondrocyte-specific c-Raf knockout mice (c-Raf(f/f);ColII-Cre(+)) were generated to define a role for c-Raf in growth plate maturation. In vivo studies demonstrated that loss of c-Raf in chondrocytes leads to expansion of the hypertrophic layer of the growth plate, with decreased phospho-Erk1/2 immunoreactivity and impaired hypertrophic chondrocyte apoptosis. However, cultured hypertrophic chondrocytes from these mice did not exhibit impairment of phosphate-induced Erk1/2 phosphorylation. Studies performed to reconcile the discrepancy between the in vitro and in vivo hypertrophic chondrocyte phenotypes revealed normal chondrocyte differentiation in c-Raf(f/f);ColII-Cre(+) mice and lack of compensatory increase in the expression of A-Raf and B-Raf. However, VEGF (Vegfa) immunoreactivity in the hypertrophic chondrocytes of c-Raf(f/f);ColII-Cre(+) mice was significantly reduced, associated with increased ubiquitylation of VEGF protein. Thus, c-Raf plays an important role in growth plate maturation by regulating vascular invasion, which is crucial for replacement of terminally differentiated hypertrophic chondrocytes by bone.
authors.affiliation: Division of Endocrinology, Diabetes, and Hypertension, Brigham and Women's Hospital, Boston, MA 02115, USA Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Eva S
authors.initials: ES
authors.lastname: Liu
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA Department of Pediatrics and Adolescent Medicine, Medical University Vienna, 1090, Vienna, Austria.
authors.forename: Adalbert
authors.initials: A
authors.lastname: Raimann
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA.
authors.forename: Byongsoo Timothy
authors.initials: BT
authors.lastname: Chae
authors.affiliation: Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Janaina S
authors.initials: JS
authors.lastname: Martins
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: Endocrine Unit, Massachusetts General Hospital, Boston, MA 02114, USA Harvard Medical School, Boston, MA 02115, USA demay@helix.mgh.harvard.edu.
authors.forename: Marie B
authors.initials: MB
authors.lastname: Demay
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D005260:Female; D006132:Growth Plate / Q000166:cytology* / Q000378:metabolism*; D008297:Male; D051379:Mice; D010012:Osteogenesis / Q000235:genetics / Q000502:physiology; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*
chemical_list: D019908:Proto-Oncogene Proteins c-raf
keywords: Angiogenesis; Chondrocyte apoptosis; Growth plate; Mouse; VEGF; c-Raf