Identification of Two Smad4 Proteins in Xenopus

Masuyama, Norihisa; Hanafusa, Hiroshi; Kusakabe, Morioh; Shibuya, H.; Nishida, Eisuke

doi:10.1074/jbc.274.17.12163

Cited by 91 publications

(72 citation statements)

References 53 publications

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“…However, the linker region between the two MH domains is divergent in the two genes. Smad4␣ is closely related to the mammalian Smad4, whereas Smad4␤/10 has a linker sequence that is only 34% identical to that of the human Smad4 (15,16). Characterization of the activities of the two Smad4 proteins by different groups has led to conflicting conclusions.…”

Section: Members Of the Tgf␤mentioning

confidence: 97%

“…On one hand, both Smad4s have been shown to form hetero-oligomer complex with Smad1 and Smad2 in response to BMP and activin signals, respectively, and overexpression of either gene enhances both Smad1-and Smad2-dependent mesoderm induction in ectodermal explants. Both Smad4s therefore act similarly to the conventional mammalian Smad4 as co-Smads (15,16). On the other hand, the divergent Smad4, Smad4␤/10, is found to induce neural markers directly without the presence of mesoderm in animal cap explants (14).…”

Section: Members Of the Tgf␤mentioning

confidence: 99%

“…2A), but Smad4␤ has been reported to have a different activity (15,16). To understand the potential differences between the two molecules, we overexpressed Smad4␤ and Smad10 in animal caps and compared their function side by side.…”

Section: Smad4␣ and Smad4␤ Have Different Activities From Smad10 Andmentioning

confidence: 99%

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Function of the Two Xenopus Smad4s in Early Frog Development

Chang

Brivanlou

Harland

2006

Journal of Biological Chemistry

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Signals from the transforming growth factor ␤ family members are transmitted in the cell through specific receptor-activated Smads and a common partner Smad4. Two Smad4 genes (␣ and ␤/10, or smad4 and smad4.2) have been isolated from Xenopus, and conflicting data are reported for Smad4␤/10 actions in mesodermal and neural induction. To further understand the functions of the Smad4s in early frog development, we analyzed their activities in detail. We report that Smad10 is a mutant form of Smad4␤ that harbors a missense mutation of a conserved arginine to histidine in the MH1 domain. The mutation results in enhanced association of Smad10 with the nuclear transcription corepressor Ski and leads to its neural inducing activity through inhibition of bone morphogenetic protein (BMP) signaling. In contrast to Smad10, both Smad4␣ and Smad4␤ enhanced BMP signals in ectodermal explants. Using antisense morpholino oligonucleotides (MOs) to knockdown endogenous Smad4 protein levels, we discovered that Smad4␤ was required for both activin-and BMP-mediated mesodermal induction in animal caps, whereas Smad4␣ affected only the BMP signals. Neither Smad4 was involved directly in neural induction. Expression of Smad4␤-MO in early frog embryos resulted in reduction of mesodermal markers and defects in axial structures, which were rescued by either Smad4␣ or Smad4␤. Smad4␣-MO induced only minor deficiency at late stages. As Smad4␤, but not Smad4␣, is expressed at high levels maternally and during early gastrulation, our data suggest that although Smad4␣ and Smad4␤ may have similar activities, they are differentially utilized during frog embryogenesis, with only Smad4␤ being essential for mesoderm induction.Members of the TGF␤ 2 superfamily of signaling molecules regulate diverse processes both during embryogenesis and in adult tissue homeostasis. In vertebrate embryos, TGF␤ family ligands play crucial roles in generation and patterning of mesodermal and endodermal tissues, in gastrulation, neural induction and patterning, and organogenesis (1-5). Two branches of the growth factor family function differently in various processes. TGF␤/activin/nodal-like molecules are involved in induction and patterning of early mesendoderm and left-right axis specification, whereas bone morphogenetic proteins (BMPs) control early dorsoventral patterning in all germ layers and subsequently modulate the formation of multiple organ systems. In adults, one predominant function of the TGF␤ signals is to regulate cell proliferation, and mutations in many signaling components of this pathway are associated with tumor formation (6, 7).TGF␤ signals are transmitted through two types of transmembrane serine/threonine kinase receptors. In the ligand-induced receptor complex, the type II receptor phosphorylates and activates the type I receptor, which in turn phosphorylates Smad proteins, the cytoplasmic signal transducers. Growth factors from the TGF␤/activin/nodal subfamily act through their specific type I receptors (ALK4, -5, and -7) to activate Smad2 and ...

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Section: Members Of the Tgf␤mentioning

confidence: 97%

Section: Members Of the Tgf␤mentioning

confidence: 99%

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Function of the Two Xenopus Smad4s in Early Frog Development

Chang

Brivanlou

Harland

2006

Journal of Biological Chemistry

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“…Alternatively, growth inhibition could be mediated by an as yet unidentified mammalian Smad4 homologue that is able to compensate for Smad4 deficiency. Although such a Smad4 homologue has been identified in Xenopus and shown to possess distinct biological properties (43,44), its mammalian counterpart has not yet been identified. Several lines of evidence support the notion that some TGF␤-related responses do not require Smad4.…”

Section: Discussionmentioning

confidence: 99%

Targeted Disruption in Murine Cells Reveals Variable Requirement for Smad4 in Transforming Growth Factor β-related Signaling

Sirard¹,

Kim²,

Mirtsos³

et al. 2000

Journal of Biological Chemistry

149

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The tumor suppressor gene Smad4 has been proposed to be a common mediator of transforming growth factor ␤ (TGF␤)-related signaling pathways. We investigated the role of Smad4 in TGF␤-related pathways by targeted disruption of its locus in murine cell lines. TGF␤ responses, including growth arrest, induction of the endogenous PAI-1 gene, and other extracellular matrix components, were normal in Smad4-deficient fibroblasts. Assembly of a TGF␤-induced DNA-binding complex on one of two regulatory regions in the human plasminogen activator inhibitor (PAI)-1 promoter did not require Smad4 but was, instead, dependent on a TFE-3 binding site. In contrast, Smad4 was required for activation of the Xenopus Mix.2 promoter in response to TGF␤/activin. Smad4 was also involved in the regulation of the Msx homeobox protein family members in response to bone morphogenetic protein (BMP). Interestingly, the expression of the endogenous Msx-2 was reduced, whereas that of Msx-3 was activated in differentiating Smad4 ؊/؊ ES cells relative to wild-type cells. Moreover, reporter assays of the Msx-2 promoter revealed an absolute requirement for Smad4 in fibroblasts and ES cells for activation. Our results indicate that Smad4 is dispensable for critical TGF␤-induced responses but is required for others in murine fibroblasts. We have identified transcriptional targets for Smad4 in the BMP signaling pathway, which may contribute to the genetic defect observed in the Smad4-deficient embryos.

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“…A canonical nuclear export signal (NES) was identified in the N-terminal part of the linker region of Smad4 ( 142 DLSGLTLQ 149 ), and deletion or mutation of critical residues in this NES enhanced nuclear localization of Smad4 [17,18]. Interestingly, a variant of Smad4, XSmad4b that exists only in X. laevis and in no other vertebrates, lacks this NES and is constitutively nuclear [42]. Hence, this NES seems to be necessary to mediate nuclear export of Smad4.…”

Section: Smad Export From the Nucleusmentioning

confidence: 99%

Nucleocytoplasmic shuttling of Smad proteins

2008

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Nuclear accumulation of active Smad complexes is crucial for transduction of transforming growth factor β (TGF-β)-superfamily signals from transmembrane receptors into the nucleus. It is now clear that the nucleocytoplasmic distributions of Smads, in both the absence and the presence of a TGF-β-superfamily signal, are not static, but instead the Smads are continuously shuttling between the nucleus and the cytoplasm in both conditions. This article presents the evidence for continuous nucleocytoplasmic shuttling of Smads. It then reviews different mechanisms that have been proposed to mediate Smad nuclear import and export, and discusses how the Smad steady-state distributions in the absence and the presence of a TGF-β-superfamily signal are established. Finally, the biological relevance of continuous nucleocytoplasmic shuttling for signaling by TGF-β superfamily members is discussed.

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Identification of Two Smad4 Proteins in Xenopus

Cited by 91 publications

References 53 publications

Function of the Two Xenopus Smad4s in Early Frog Development

Function of the Two Xenopus Smad4s in Early Frog Development

Targeted Disruption in Murine Cells Reveals Variable Requirement for Smad4 in Transforming Growth Factor β-related Signaling

Nucleocytoplasmic shuttling of Smad proteins

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