title: Human BAMBI cooperates with Smad7 to inhibit transforming growth factor-beta signaling.
abstract: Transforming growth factor beta (TGF-beta) and related growth factors are essential regulators of embryogenesis and tissue homeostasis. The signaling pathways mediated by their receptors and Smad proteins are precisely modulated by various means. Xenopus BAMBI (bone morphogenic protein (BMP) and activin membrane-bound inhibitor) has been shown to function as a general negative regulator of TGF-beta/BMP/activin signaling. Here, we provide evidence that human BAMBI (hBAMBI), like its Xenopus homolog, inhibits TGF-beta- and BMP-mediated transcriptional responses as well as TGF-beta-induced R-Smad phosphorylation and cell growth arrest, whereas knockdown of endogenous BAMBI enhances the TGF-beta-induced reporter expression. Mechanistically, in addition to interfering with the complex formation between the type I and type II receptors, hBAMBI cooperates with Smad7 to inhibit TGF-beta signaling. hBAMBI forms a ternary complex with Smad7 and the TGF-beta type I receptor ALK5/TbetaRI and inhibits the interaction between ALK5/TbetaRI and Smad3, thus impairing Smad3 activation. These findings provide a novel insight to understand the molecular mechanism underlying the inhibitory effect of BAMBI on TGF-beta signaling.
authors.affiliation: Department of Biological Sciences and Biotechnology, State Key Laboratory of Biomembrane and Membrane Biotechnology, Tsinghua University, Beijing 100084, China.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Yan
authors.forename: Zhenghong
authors.initials: Z
authors.lastname: Lin
authors.forename: Feng
authors.initials: F
authors.lastname: Chen
authors.forename: Xingang
authors.initials: X
authors.lastname: Zhao
authors.forename: Hua
authors.initials: H
authors.lastname: Chen
authors.forename: Yuanheng
authors.initials: Y
authors.lastname: Ning
authors.forename: Ye-Guang
authors.initials: YG
authors.lastname: Chen
mesh_terms: D006801:Humans; D008565:Membrane Proteins / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D015398:Signal Transduction; D051900:Smad3 Protein / Q000037:antagonists & inhibitors; D051906:Smad7 Protein / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000037:antagonists & inhibitors*
chemical_list: C485671:BAMBI protein, human; D008565:Membrane Proteins; D018125:Receptors, Transforming Growth Factor beta; C497806:SMAD7 protein, human; D051900:Smad3 Protein; D051906:Smad7 Protein; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human