title: Reduction of protein phosphatase 2A Cα enhances bone formation and osteoblast differentiation through the expression of bone-specific transcription factor Osterix.
abstract: The serine/threonine protein phosphatase 2A (PP2A) participates in regulating many important physiological processes such as control of cell cycle, growth, and division. On the other hand, Osterix is a zinc-finger-containing transcription factor that is essential for the differentiation of osteoblasts and regulation of many bone-related genes. Here we examined the effect of okadaic acid (OA), a specific inhibitor of PP2A, on bone formation in vivo and the molecular mechanism regulated by PP2A Cα in osteoblast differentiation. Administration of 1nM OA to the calvarial region in mice increased bone mineral density, as shown by μCT, while histomorphological analysis showed an increase in mineral apposition and bone thickness in the same region. In addition, treatment with 1nM OA stimulated osteoblast differentiation and the expression of Osterix, bone sialoprotein (Bsp), and osteocalcin (OCN) in mouse osteoblastic MC3T3-E1 cells. Moreover, the expression and phosphatase activity of PP2A Cα was decreased in the initial step of osteoblast differentiation, which was in parallel with an increase in Osterix expression. To further clarify the role of PP2A Cα in osteoblast differentiation, we constructed PP2A knock-down cells by infecting MC3T3-E1 cells with a lentivirus expressing shRNA specific for the PP2A Cα. Accordingly, the silencing of PP2A Cα in MC3T3-E1 cells dramatically increased osteoblast differentiation and mineralization, which were accompanied with expressions of Osterix, Bsp, and OCN. Our data indicate that PP2A Cα plays an important role in the regulation of bone formation and osteoblast differentiation through the bone-related genes.
authors.affiliation: Department of Histology and Oral Histology, Institute of Health Biosciences, The University of Tokushima Graduate School, Kuramoto, Tokushima 770-8504, Japan. okamura@dent.tokushima-u.ac.jp
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Okamura
authors.forename: Kaya
authors.initials: K
authors.lastname: Yoshida
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Ochiai
authors.forename: Tatsuji
authors.initials: T
authors.lastname: Haneji
mesh_terms: D016475:3T3 Cells; D000818:Animals; D015519:Bone Density / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D058574:Integrin-Binding Sialoprotein / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D019319:Okadaic Acid / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D015675:Osteocalcin / Q000235:genetics / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects / Q000502:physiology*; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012886:Skull / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D058574:Integrin-Binding Sialoprotein; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; D015675:Osteocalcin; D019319:Okadaic Acid; D054648:Protein Phosphatase 2