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The Netrin-related domain of Sfrp1 interacts with Wnt ligands and antagonizes their activity in the anterior neural plate.

Lopez-Rios J, Esteve P, Ruiz JM, Bovolenta P - Neural Dev (2008)

Bottom Line: This activity requires intact tertiary structure and is shared by the distantly related Netrin-1NTR.In contrast, the Sfrp1CRD cannot mirror the function of the entire molecule in vivo but interacts with Fz receptors and antagonizes Wnt8-mediated beta-catenin transcriptional activity.On the basis of these results, we propose that SFRP modulation of Wnt signalling may involve multiple and differential interactions among Wnt, Fz and SFRPs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de NeurobiologĂ­a Molecular Celular y del Desarrollo, Instituto Cajal, CSIC, Dr. Arce 37, Madrid, 28002, Spain. Javier.Lopez-Rios@unibas.ch

ABSTRACT

Background: Secreted frizzled related proteins (SFRPs) are multifunctional modulators of Wnt and BMP (Bone Morphogenetic Protein) signalling necessary for the development of most organs and the homeostasis of different adult tissues. SFRPs fold in two independent domains: the cysteine rich domain (SfrpCRD) related to the extracellular portion of Frizzled (Fz, Wnt receptors) and the Netrin module (SfrpNTR) defined by homologies with molecules such as Netrin-1, inhibitors of metalloproteinases and complement proteins. Due to its structural relationship with Fz, it is believed that SfrpCRD interferes with Wnt signalling by binding and sequestering the ligand. In contrast, the functional relevance of the SfrpNTR has been barely addressed.

Results: Here, we combine biochemical studies, mutational analysis and functional assays in cell culture and medaka-fish embryos to show that the Sfrp1NTR mimics the function of the entire molecule, binds to Wnt8 and antagonizes Wnt canonical signalling. This activity requires intact tertiary structure and is shared by the distantly related Netrin-1NTR. In contrast, the Sfrp1CRD cannot mirror the function of the entire molecule in vivo but interacts with Fz receptors and antagonizes Wnt8-mediated beta-catenin transcriptional activity.

Conclusion: On the basis of these results, we propose that SFRP modulation of Wnt signalling may involve multiple and differential interactions among Wnt, Fz and SFRPs.

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Related in: MedlinePlus

SFRP mode of action may rely on multiple interactions with Wnt ligands and/or Frizzled receptors. Schematic representation of possible mechanisms by which SFRPs could modulate Wnt/Frizzled signalling. (a) SFRPs can antagonize Wnt activity by directly binding to the ligand through its Netrin-related domain. (b) SFRPs could interact directly with Frizzled receptors through their corresponding CRD motifs and prevent signal transduction. (c) Frizzled, Wnt and SFRP molecules could form heterotrimeric complexes, where SFRP could present the Wnt ligand to the Frizzled receptor thanks to the differential interactions of the CRD and NTR domains. (d) In the absence of Wnt ligands, SFRPs can directly bind a Frizzled receptor and transduce a signal. See the text for further details.
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Figure 9: SFRP mode of action may rely on multiple interactions with Wnt ligands and/or Frizzled receptors. Schematic representation of possible mechanisms by which SFRPs could modulate Wnt/Frizzled signalling. (a) SFRPs can antagonize Wnt activity by directly binding to the ligand through its Netrin-related domain. (b) SFRPs could interact directly with Frizzled receptors through their corresponding CRD motifs and prevent signal transduction. (c) Frizzled, Wnt and SFRP molecules could form heterotrimeric complexes, where SFRP could present the Wnt ligand to the Frizzled receptor thanks to the differential interactions of the CRD and NTR domains. (d) In the absence of Wnt ligands, SFRPs can directly bind a Frizzled receptor and transduce a signal. See the text for further details.

Mentions: We have provided functional and biochemical evidence that the NTR, but not the CRD, domain of Sfrp1 mimics the function of the entire molecule. These results challenge several reports implying that the CRD domain of SFRPs, due to its homology with the proposed Wnt binding region on Fz receptors, interferes with Wnt signalling by binding and sequestering the ligand [8,9]. These apparent contradictions can, however, be reconciled with two assumptions. First, SFRPs of different subgroups have different biochemical interactions with Wnt ligands. In support of this assumption, plasmon resonance binding studies using Sfrp1, 2, 3, 4 and Wnt3a and Wnt5 have shown that Wnt5 binds preferentially to Sfrp1 and 2, while Wnt3a binds at least two sites in Sfrp1, 2, 4 and one in Sfrp3 [16]. Second, SFRP molecules interact with both Wnt and Fz in multiple ways and these interactions can modulate signal transduction in either a positive or negative manner. In this view, there are several possible mechanisms by which SFRPs can modulate Wnt signalling (Figure 9). SFRP could sequester Wnt ligands through the NTR domain, thus acting as antagonists (Figure 9a; this study) or act in a dominant-negative manner through the formation of inactive complexes with Fz receptors, preventing signal activation (Figure 9b; as proposed previously [8], and this study). Alternatively, SFRPs could favour Wnt-Fz interaction by simultaneously binding to both molecules and, thus, synergizing with signal activation (Figure 9c), as reported previously [4]. Finally, in the absence of Wnt ligands, SfrpCRD-FzCRD heterodimer formation could trigger signal transduction (Figure 9d), as proposed previously [24]. Notably, the activation of the Fz receptors by a proposed ligand-antagonist is not unique to SFRP1, as Dickkopf2, which belongs to a different family of Wnt antagonists, can activate Wnt canonical signalling cooperating with at least three different Fzs [38].


The Netrin-related domain of Sfrp1 interacts with Wnt ligands and antagonizes their activity in the anterior neural plate.

Lopez-Rios J, Esteve P, Ruiz JM, Bovolenta P - Neural Dev (2008)

SFRP mode of action may rely on multiple interactions with Wnt ligands and/or Frizzled receptors. Schematic representation of possible mechanisms by which SFRPs could modulate Wnt/Frizzled signalling. (a) SFRPs can antagonize Wnt activity by directly binding to the ligand through its Netrin-related domain. (b) SFRPs could interact directly with Frizzled receptors through their corresponding CRD motifs and prevent signal transduction. (c) Frizzled, Wnt and SFRP molecules could form heterotrimeric complexes, where SFRP could present the Wnt ligand to the Frizzled receptor thanks to the differential interactions of the CRD and NTR domains. (d) In the absence of Wnt ligands, SFRPs can directly bind a Frizzled receptor and transduce a signal. See the text for further details.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2542364&req=5

Figure 9: SFRP mode of action may rely on multiple interactions with Wnt ligands and/or Frizzled receptors. Schematic representation of possible mechanisms by which SFRPs could modulate Wnt/Frizzled signalling. (a) SFRPs can antagonize Wnt activity by directly binding to the ligand through its Netrin-related domain. (b) SFRPs could interact directly with Frizzled receptors through their corresponding CRD motifs and prevent signal transduction. (c) Frizzled, Wnt and SFRP molecules could form heterotrimeric complexes, where SFRP could present the Wnt ligand to the Frizzled receptor thanks to the differential interactions of the CRD and NTR domains. (d) In the absence of Wnt ligands, SFRPs can directly bind a Frizzled receptor and transduce a signal. See the text for further details.
Mentions: We have provided functional and biochemical evidence that the NTR, but not the CRD, domain of Sfrp1 mimics the function of the entire molecule. These results challenge several reports implying that the CRD domain of SFRPs, due to its homology with the proposed Wnt binding region on Fz receptors, interferes with Wnt signalling by binding and sequestering the ligand [8,9]. These apparent contradictions can, however, be reconciled with two assumptions. First, SFRPs of different subgroups have different biochemical interactions with Wnt ligands. In support of this assumption, plasmon resonance binding studies using Sfrp1, 2, 3, 4 and Wnt3a and Wnt5 have shown that Wnt5 binds preferentially to Sfrp1 and 2, while Wnt3a binds at least two sites in Sfrp1, 2, 4 and one in Sfrp3 [16]. Second, SFRP molecules interact with both Wnt and Fz in multiple ways and these interactions can modulate signal transduction in either a positive or negative manner. In this view, there are several possible mechanisms by which SFRPs can modulate Wnt signalling (Figure 9). SFRP could sequester Wnt ligands through the NTR domain, thus acting as antagonists (Figure 9a; this study) or act in a dominant-negative manner through the formation of inactive complexes with Fz receptors, preventing signal activation (Figure 9b; as proposed previously [8], and this study). Alternatively, SFRPs could favour Wnt-Fz interaction by simultaneously binding to both molecules and, thus, synergizing with signal activation (Figure 9c), as reported previously [4]. Finally, in the absence of Wnt ligands, SfrpCRD-FzCRD heterodimer formation could trigger signal transduction (Figure 9d), as proposed previously [24]. Notably, the activation of the Fz receptors by a proposed ligand-antagonist is not unique to SFRP1, as Dickkopf2, which belongs to a different family of Wnt antagonists, can activate Wnt canonical signalling cooperating with at least three different Fzs [38].

Bottom Line: This activity requires intact tertiary structure and is shared by the distantly related Netrin-1NTR.In contrast, the Sfrp1CRD cannot mirror the function of the entire molecule in vivo but interacts with Fz receptors and antagonizes Wnt8-mediated beta-catenin transcriptional activity.On the basis of these results, we propose that SFRP modulation of Wnt signalling may involve multiple and differential interactions among Wnt, Fz and SFRPs.

View Article: PubMed Central - HTML - PubMed

Affiliation: Departamento de NeurobiologĂ­a Molecular Celular y del Desarrollo, Instituto Cajal, CSIC, Dr. Arce 37, Madrid, 28002, Spain. Javier.Lopez-Rios@unibas.ch

ABSTRACT

Background: Secreted frizzled related proteins (SFRPs) are multifunctional modulators of Wnt and BMP (Bone Morphogenetic Protein) signalling necessary for the development of most organs and the homeostasis of different adult tissues. SFRPs fold in two independent domains: the cysteine rich domain (SfrpCRD) related to the extracellular portion of Frizzled (Fz, Wnt receptors) and the Netrin module (SfrpNTR) defined by homologies with molecules such as Netrin-1, inhibitors of metalloproteinases and complement proteins. Due to its structural relationship with Fz, it is believed that SfrpCRD interferes with Wnt signalling by binding and sequestering the ligand. In contrast, the functional relevance of the SfrpNTR has been barely addressed.

Results: Here, we combine biochemical studies, mutational analysis and functional assays in cell culture and medaka-fish embryos to show that the Sfrp1NTR mimics the function of the entire molecule, binds to Wnt8 and antagonizes Wnt canonical signalling. This activity requires intact tertiary structure and is shared by the distantly related Netrin-1NTR. In contrast, the Sfrp1CRD cannot mirror the function of the entire molecule in vivo but interacts with Fz receptors and antagonizes Wnt8-mediated beta-catenin transcriptional activity.

Conclusion: On the basis of these results, we propose that SFRP modulation of Wnt signalling may involve multiple and differential interactions among Wnt, Fz and SFRPs.

Show MeSH
Related in: MedlinePlus