RESUMO
Defects in stem cell renewal or progenitor cell expansion underlie ageing-related diseases such as osteoporosis. Yet much remains unclear about the mechanisms regulating progenitor expansion. Here we show that the tyrosine kinase c-Abl plays an important role in osteoprogenitor expansion. c-Abl interacts with and phosphorylates BMPRIA and the phosphorylation differentially influences the interaction of BMPRIA with BMPRII and the Tab1-Tak1 complex, leading to uneven activation of Smad1/5/8 and Erk1/2, the canonical and non-canonical BMP pathways that direct the expression of p16(INK4a). c-Abl deficiency shunts BMP signalling from Smad1/5/8 to Erk1/2, leading to p16(INK4a) upregulation and osteoblast senescence. Mouse genetic studies revealed that p16(INK4a) controls mesenchymal stem cell maintenance and osteoblast expansion and mediates the effects of c-Abl deficiency on osteoblast expansion and bone formation. These findings identify c-Abl as a regulator of BMP signalling pathways and uncover a role for c-Abl in p16(INK4a) expression and osteoprogenitor expansion.
Assuntos
Proteínas Morfogenéticas Ósseas/metabolismo , Proliferação de Células , Senescência Celular , Inibidor p16 de Quinase Dependente de Ciclina/metabolismo , Células-Tronco Mesenquimais/enzimologia , Osteoblastos/enzimologia , Proteínas Proto-Oncogênicas c-abl/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Sequência de Aminoácidos , Animais , Receptores de Proteínas Morfogenéticas Ósseas Tipo I/genética , Receptores de Proteínas Morfogenéticas Ósseas Tipo I/metabolismo , Receptores de Proteínas Morfogenéticas Ósseas Tipo II/metabolismo , Células Cultivadas , Inibidor p16 de Quinase Dependente de Ciclina/deficiência , Inibidor p16 de Quinase Dependente de Ciclina/genética , Ativação Enzimática , Genótipo , Proteína 1 Inibidora de Diferenciação/metabolismo , MAP Quinase Quinase Quinases/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Dados de Sequência Molecular , Fenótipo , Fosforilação , Proteínas Proto-Oncogênicas c-abl/genética , Transdução de Sinais , Proteína Smad1/metabolismo , Proteína Smad5/metabolismo , Proteína Smad8/metabolismo , Fatores de Tempo , Transfecção , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
p53 is a well known tumor suppressor. We show that p53 also regulates osteoblast differentiation, bone formation, and osteoblast-dependent osteoclast differentiation. Indeed, p53(-/-) mice display a high bone mass phenotype, and p53(-/-) osteoblasts show accelerated differentiation, secondary to an increase in expression of the osteoblast differentiation factor osterix, as a result. Reporter assays indicate that p53 represses osterix transcription by the minimal promoter in a DNA-binding-independent manner. In addition, p53(-/-) osteoblasts have an enhanced ability to favor osteoclast differentiation, in association with an increase in expression of macrophage-colony stimulating factor, which is under the control of osterix. Furthermore, inactivating p53 is sufficient to rescue the osteoblast differentiation defects observed in mice lacking c-Abl, a p53-interacting protein. Thus, these results identify p53 as a novel regulator of osteoblast differentiation, osteoblast-dependent osteoclastogenesis, and bone remodeling.
