title: A-Raf and C-Raf differentially regulate mechanobiological response of osteoblasts to guide mechanical stress-induced differentiation.
abstract: Regulation of osteoblast activity by mechanical stress is important for bone remodeling. However, the precise mechanotransduction mechanism that triggers the anabolic reaction of osteoblasts is largely unknown. In this study, we performed RNA interference (RNAi) screening to identify the signaling molecules upstream of ERK, which was responsible for osteogenesis. Of twenty-two mitogen-activated protein kinase (MAPK) kinase kinases (MAP3Ks), we identified A-Raf and C-Raf as upstream MAP3Ks of the mechanical stretch-activated ERK pathway. Subsequently we screened the mechanosensitive cation channel, and identified P2X7 as an upstream molecule of the ERK pathway. Intriguingly, P2X7 functioned as an upstream activator of A-Raf but not of C-Raf. Furthermore, A-Raf contributed to mechanical stretch-induced osteoblast differentiation. In contrast, C-Raf but not A-Raf protected osteoblasts from mechanical stretch-induced apoptosis. These results suggested that A-Raf and C-Raf were involved in mechanobiological osteogenesis in a distinct way: A-Raf was responsible for osteogenesis while C-Raf for anti-apoptotic protection and promotion.
authors.affiliation: Department of Oral Implantology, State Key Laboratory of Oral Diseases, West China College of Stomatology, Sichuan University, Chengdu, Sichuan, China; Department of Advanced Prosthetic Dentistry, Graduate School of Dentistry, Tohoku University, Sendai, Miyagi, Japan.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Department of Advanced Prosthetic Dentistry, Graduate School of Dentistry, Tohoku University, Sendai, Miyagi, Japan; Tohoku Medical Megabank Organization, Tohoku University, Sendai, Miyagi, Japan. Electronic address: jaymzhetfield@dent.tohoku.ac.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Matsui
authors.affiliation: Department of Molecular and Cellular Biology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi, Japan; Department of Oral Cancer Therapeutics, Graduate School of Dentistry, Tohoku University, Sendai, Miyagi, Japan.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Horiuchi
authors.affiliation: Department of Oral Implantology, State Key Laboratory of Oral Diseases, West China College of Stomatology, Sichuan University, Chengdu, Sichuan, China.
authors.forename: Xing
authors.initials: X
authors.lastname: Liang
authors.affiliation: Department of Advanced Prosthetic Dentistry, Graduate School of Dentistry, Tohoku University, Sendai, Miyagi, Japan.
authors.forename: Keiichi
authors.initials: K
authors.lastname: Sasaki
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology* / Q000502:physiology; D048491:Proto-Oncogene Proteins A-raf / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D058486:Receptors, Purinergic P2X7 / Q000235:genetics / Q000378:metabolism; D013314:Stress, Mechanical
chemical_list: D058486:Receptors, Purinergic P2X7; D048491:Proto-Oncogene Proteins A-raf; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases; D020930:MAP Kinase Kinase Kinases
keywords: A-Raf; Bone mechanobiology; C-Raf; ERK; Osteoblast differentiation