RESUMO
In endothelial cells, two type I receptors of the transforming growth factor ß (TGF-ß) family, ALK1 and ALK5, coordinate to regulate embryonic angiogenesis in response to BMP9/10 and TGF-ß. Whereas TGF-ß binds to and activates ALK5, leading to Smad2/3 phosphorylation and inhibition of endothelial cell proliferation and migration, BMP9/10 and TGF-ß also bind to ALK1, resulting in the activation of Smad1/5. SnoN is a negative regulator of ALK5 signaling through the binding and repression of Smad2/3. Here we uncover a positive role of SnoN in enhancing Smad1/5 activation in endothelial cells to promote angiogenesis. Upon ligand binding, SnoN directly bound to ALK1 on the plasma membrane and facilitated the interaction between ALK1 and Smad1/5, enhancing Smad1/5 phosphorylation. Disruption of this SnoN-Smad interaction impaired Smad1/5 activation and up-regulated Smad2/3 activity. This resulted in defective angiogenesis and arteriovenous malformations, leading to embryonic lethality at E12.5. Thus, SnoN is essential for TGF-ß/BMP9-dependent biological processes by its ability to both positively and negatively modulate the activities of Smad-dependent pathways.
Assuntos
Receptores de Ativinas Tipo I/metabolismo , Embrião de Mamíferos/irrigação sanguínea , Fibroblastos/metabolismo , Neovascularização Fisiológica , Proteínas Proto-Oncogênicas/fisiologia , Proteína Smad1/metabolismo , Proteína Smad5/metabolismo , Receptores de Ativinas Tipo I/genética , Receptores de Activinas Tipo II , Animais , Apoptose , Western Blotting , Movimento Celular , Proliferação de Células , Embrião de Mamíferos/citologia , Embrião de Mamíferos/metabolismo , Endotélio Vascular/citologia , Endotélio Vascular/metabolismo , Feminino , Fibroblastos/citologia , Imunofluorescência , Humanos , Técnicas Imunoenzimáticas , Imunoprecipitação , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fosforilação , Artéria Pulmonar/citologia , Artéria Pulmonar/metabolismo , RNA Mensageiro/genética , Reação em Cadeia da Polimerase em Tempo Real , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de Sinais , Proteína Smad1/genética , Proteína Smad5/genéticaRESUMO
Mammary epithelial cells undergo structural and functional differentiation at late pregnancy and parturition to produce and secrete milk. Both TGF-ß and prolactin pathways are crucial regulators of this process. However, how the activities of these two antagonistic pathways are orchestrated to initiate lactation has not been well defined. Here, we show that SnoN, a negative regulator of TGF-ß signaling, coordinates TGF-ß and prolactin signaling to control alveologenesis and lactogenesis. SnoN expression is induced at late pregnancy by the coordinated actions of TGF-ß and prolactin. The elevated SnoN promotes Stat5 signaling by enhancing its stability, thereby sharply increasing the activity of prolactin signaling at the onset of lactation. SnoN-/- mice display severe defects in alveologenesis and lactogenesis, and mammary epithelial cells from these mice fail to undergo proper morphogenesis. These defects can be rescued by an active Stat5. Thus, our study has identified a new player in the regulation of milk production and revealed a novel function of SnoN in mammary alveologenesis and lactogenesis in vivo through promotion of Stat5 signaling.
