RESUMO
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.
Assuntos
Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Lactação/fisiologia , Glândulas Mamárias Animais/crescimento & desenvolvimento , Prolactina/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Fator de Transcrição STAT5/metabolismo , Transdução de Sinais/fisiologia , Animais , Western Blotting , Diferenciação Celular/fisiologia , Células Cultivadas , Primers do DNA/genética , Feminino , Imuno-Histoquímica , Glândulas Mamárias Animais/citologia , Camundongos , Camundongos Knockout , Gravidez , Proteínas Proto-Oncogênicas/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fator de Crescimento Transformador beta/metabolismoRESUMO
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.