Structural Basis of Smad2 Recognition by the Smad Anchor for Receptor Activation

Wu, Geng; Chen, Ye-Guang; Ozdamar, Barish; Gyuricza, Cassie A.; Chong, P. Andrew; Wrana, Jeffrey L.; Massagué, Joan; Shi, Yigong

doi:10.1126/science.287.5450.92

Cited by 269 publications

(281 citation statements)

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“…Both Smad2 and Smad3 bind to the cognate type I receptors mediated by SARA (6), and they appear to exhibit similar binding affinities (51). Hence, the phospho-Smad2/phosphoSmad3 ratio should closely resemble the Smad2/Smad3 ratio.…”

Section: Discussionmentioning

confidence: 99%

Activin A Signaling Induces Smad2, but Not Smad3, Requiring Protein Kinase A Activity in Granulosa Cells from the Avian Ovary

Schmierer

Schuster

Shkumatava

et al. 2003

Journal of Biological Chemistry

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Activin A signaling is an important regulator of ovarian granulosa cell function. The cytosolic signal transducer Smad2 is most highly expressed in chicken granulosa cells (cGC) of preovulatory follicles. Moreover, Smad2 shows predominant nuclear localization in freshly isolated cGC, indicating active Smad signaling in vivo. Primary cGC cultured in vitro require activin A to sustain high Smad2 levels, which otherwise drop dramatically in the absence of activin A. This activin A-dependent Smad2 expression is abrogated by protein kinase A (PKA) inhibitors, suggesting a role for PKA in activin signaling. In the absence of activin A, strong PKA activators such as follicle-stimulating hormone (FSH) and 8-bromo-cyclic AMP fail to elicit Smad2 induction. However, FSH and 8-bromo-cyclic AMP boost activin A-dependent Smad2 up-regulation, giving rise to Smad2 levels similar to expression in vivo levels. Interestingly, the effect is specific for Smad2, since expression of the structurally and functionally closely related Smad3 remains entirely unaffected. Hence, activin A induces Smad2, but not Smad3, to high levels requiring PKA activation. Since Smad2 and Smad3 target distinct yet overlapping sets of TGF-␤/activin-responsive genes, the selective Smad2 induction by FSH/activin A could allow FSH to efficiently modulate the transcriptional readout of activin A signaling in avian granulosa cells.

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Section: Discussionmentioning

confidence: 99%

Activin A Signaling Induces Smad2, but Not Smad3, Requiring Protein Kinase A Activity in Granulosa Cells from the Avian Ovary

Schmierer

Schuster

Shkumatava

et al. 2003

Journal of Biological Chemistry

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“…Smad proteins consist of two globular domains or MH1 and MH2 domains, respectively, connected by a flexible linker region. The MH1 domain is responsible for DNA-binding [22] whereas the MH2 domain establishes contacts with anchors for cytoplasmic retention [18], receptors for activation [12], nucleoporins for nucleocytoplasmic translocation [23], and partner Smads and other nuclear factors for the assembly of transcriptional complexes [19]. Activated Smad proteins are recognized by protein phosphatases and ubiquitin ligases that terminate the signaling process.…”

Section: Tgfb Signaling Pathwaysmentioning

confidence: 99%

The logic of TGFβ signaling

2006

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The identification of the TGFb cytokine signaling pathway, including membrane receptor serine/threonine kinases and Smad transcription factors as their substrates, has allowed the delineation of a process for conversion of these signals into programs of gene activation and repression that underlie critical cell fate and developmental decisions. The deconstruction of one of these responses -the cell cycle arrest response -into its elemental molecular parts has shed light into the mechanisms used by tumors to evade surveillance and cause metastasis.

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“…SARA is an anchoring protein that specifically binds to Smad2 and 3, transporting them to the receptor complex and increasing the efficiency of phosphorylation by the receptors (15). Crystallographic studies of Smad2 and Smad3 MH2 bound to the 60-residue SBD of SARA have provided evidence for an extensive hydrophobic interaction surface on the MH2 (26,27). The bound SBD wraps around the MH2, forming an extended structure comprised of a prolinerich rigid coil region, an ␣-helix, and a ␤-strand.…”

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confidence: 99%

Disorder in a Target for the Smad2 Mad Homology 2 Domain and Its Implications for Binding and Specificity

Chong

Ozdamar

Wrana

et al. 2004

Journal of Biological Chemistry

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The Smad2 Mad homology 2 (MH2) domain binds to a diverse group of proteins which do not share a common sequence motif. We have used NMR to investigate the structure of one of these interacting proteins, the Smad binding domain (SBD) of Smad anchor for receptor activation (SARA). Our results indicate that the unbound SBD is highly disordered and forms no stable secondary or tertiary structures. Additionally we have used fluorescence binding studies to study the interaction between the MH2 domain and SBD and find that no region of the SBD dominates the interaction between the MH2 and the SBD. Our results are consistent with a series of hydrophobic patches on the MH2 that are able to recognize disordered regions of proteins. These findings elucidate a mechanism by which a single domain (MH2) can specifically recognize a diverse set of proteins which are unrelated by sequence, lead to a clearer picture of how MH2 domains function in the transforming growth factor-␤-signaling pathway and suggest possible mechanisms for controlling interactions with MH2 domains.The TGF-␤ 1 superfamily of cytokines plays an essential role in a variety of cellular responses including differentiation, cell fate specification, and growth inhibition (1-4). Dysregulation of TGF-␤ signaling has been associated with many diseases, such as human cancers, fibrosis, hereditary hemorrhagic telangiectasia (2, 5), and Marfan syndrome (6). TGF-␤ signal transduction is mediated intracellularly by the Smad proteins, including the R-Smads (receptor-regulated Smads), the I-Smads (inhibitor Smads), and the Co-Smad (common Smad). Ligand binding to the TGF-␤ receptor complex or a homologous complex leads to receptor phosphorylation of the R-Smads (7, 8). Subsequently, the phosphorylated R-Smads can interact with the Co-Smad, Smad4, and accumulate in the nucleus (9, 10). In the nucleus the Smad proteins bind to transcription factors and promoter regions and play a role in the transcription of various genes (11, 12).The R-Smads and Smad4 consist of a conserved N-terminal Mad homology 1 (MH1) domain and a conserved C-terminal MH2 domain joined by a poorly conserved linker region. The MH1 domain is known to function in binding DNA (13). The MH2 domain appears to exhibit many different roles and binds to many different proteins. Although many modular protein domains involved in signal transduction, such as SH3, SH2, WW, PTB, and PDZ domains, interact with a recognizable sequence motif (14), MH2 domains appear to be able to bind to a wide variety of ligands that do not share a single common motif. For example the MH2 domain of Smad2 binds a plethora of non-homologous proteins including SARA (15), the TGF-␤ receptors, FoxH1 (16), Mixer (17), TGIF (18,19), CBP (20), AML1 (21,22), Ski (23,24), and SIP1 (25). These interacting partners represent a diverse group of protein types, encompassing receptors, membrane anchoring proteins, and transcription factors. Furthermore, they have no region of sequence or structural similarity in common. A key question is how the M...

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Structural Basis of Smad2 Recognition by the Smad Anchor for Receptor Activation

Cited by 269 publications

References 20 publications

Activin A Signaling Induces Smad2, but Not Smad3, Requiring Protein Kinase A Activity in Granulosa Cells from the Avian Ovary

Activin A Signaling Induces Smad2, but Not Smad3, Requiring Protein Kinase A Activity in Granulosa Cells from the Avian Ovary

The logic of TGFβ signaling

Disorder in a Target for the Smad2 Mad Homology 2 Domain and Its Implications for Binding and Specificity

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