RESUMO
Tob inhibits bone morphogenetic protein (BMP) signaling by interacting with receptor-regulated Smads in osteoblasts. Here we provide evidence that Tob also interacts with the inhibitory Smads 6 and 7. A yeast two-hybrid screen identified Smad6 as a protein interacting with Tob. Tob co-localizes with Smad6 at the plasma membrane and enhances the interaction between Smad6 and activated BMP type I receptors. Furthermore, we have isolated Xenopus Tob2, and show that it cooperates with Smad6 in inducing secondary axes when expressed in early Xenopus embryos. Finally, Tob and Tob2 cooperate with Smad6 to inhibit endogenous BMP signaling in Xenopus embryonic explants and in cultured mammalian cells. Our results provide both in vitro and in vivo evidence that Tob inhibits endogenous BMP signaling by facilitating inhibitory Smad functions.
Assuntos
Proteínas Morfogenéticas Ósseas/metabolismo , Proteínas de Transporte/fisiologia , Proteínas de Ciclo Celular/fisiologia , Transdução de Sinais , Sequência de Aminoácidos , Animais , Northern Blotting , Proteínas de Ciclo Celular/metabolismo , Membrana Celular/metabolismo , Clonagem Molecular , Citoplasma/metabolismo , Proteínas de Ligação a DNA/metabolismo , Epitopos , Genes Reporter , Immunoblotting , Hibridização In Situ , Peptídeos e Proteínas de Sinalização Intracelular , Camundongos , Microscopia de Fluorescência , Dados de Sequência Molecular , Osteoblastos/metabolismo , Testes de Precipitina , Ligação Proteica , RNA Mensageiro/metabolismo , Homologia de Sequência de Aminoácidos , Proteína Smad6 , Proteína Smad7 , Fatores de Tempo , Transativadores/metabolismo , Transfecção , Fator de Crescimento Transformador beta/metabolismo , Técnicas do Sistema de Duplo-Híbrido , Xenopus , Proteínas de XenopusRESUMO
tob is a member of antiproliferative family genes. Mice lacking tob are prone to spontaneous formation of tumors. The occurrence rate of diethylnitrosamine-induced liver tumors is higher in tob(-/-) mice than in wild-type mice. tob(-/-)p53(-/-) mice show accelerated tumor formation in comparison with single null mice. Expression of cyclin D1 mRNA is increased in the absence of Tob and is reduced by Tob. Tob acts as a transcriptional corepressor and suppresses the cyclin D1 promoter activity through an interaction with histone deacetylase. Levels of tob mRNA are often decreased in human cancers, implicating tob in cancer development.
