Limits...
Distinct molecular forms of beta-catenin are targeted to adhesive or transcriptional complexes.

Gottardi CJ, Gumbiner BM - J. Cell Biol. (2004)

Bottom Line: The Wnt-stimulated, TCF-selective form is monomeric and is regulated by the COOH terminus of beta-catenin, which selectively competes cadherin binding through an intramolecular fold-back mechanism.Phosphorylation of the cadherin reverses the TCF binding selectivity, suggesting another potential layer of regulation.In contrast, the main cadherin-binding form of beta-catenin is a beta-catenin-alpha-catenin dimer, indicating that there is a distinct molecular form of beta-catenin that can interact with both the cadherin and alpha-catenin.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA. c-gottardi@northwestern.edu.

ABSTRACT
Beta-catenin plays essential roles in both cell-cell adhesion and Wnt signal transduction, but what precisely controls beta-catenin targeting to cadherin adhesive complexes, or T-cell factor (TCF)-transcriptional complexes is less well understood. We show that during Wnt signaling, a form of beta-catenin is generated that binds TCF but not the cadherin cytoplasmic domain. The Wnt-stimulated, TCF-selective form is monomeric and is regulated by the COOH terminus of beta-catenin, which selectively competes cadherin binding through an intramolecular fold-back mechanism. Phosphorylation of the cadherin reverses the TCF binding selectivity, suggesting another potential layer of regulation. In contrast, the main cadherin-binding form of beta-catenin is a beta-catenin-alpha-catenin dimer, indicating that there is a distinct molecular form of beta-catenin that can interact with both the cadherin and alpha-catenin. We propose that participation of beta-catenin in adhesion or Wnt signaling is dictated by the regulation of distinct molecular forms of beta-catenin with different binding properties, rather than simple competition between cadherins and TCFs for a single constitutive form. This model explains how cells can control whether beta-catenin is used independently in cell adhesion and nuclear signaling, or competitively so that the two processes are coordinated and interrelated.

Show MeSH

Related in: MedlinePlus

Cadherin phosphorylation reverses β-catenin binding selectivity during Wnt signaling. (A) Phosphorylation of cad-GST increases β-catenin binding to cadherin compared with TCF. A cytosolic fraction from L cells transfected with Wnt3a were incubated with equimolar amounts of cad-GST, TCF-GST, and CK2-P-cad-GST-glutathione–coupled beads for 1 h at 4°C (see Fig. S1 for characterization of GST fusion proteins). The resulting anti–β-catenin and anti-GST immunoblots are shown. (B) Fraction of β-catenin that binds cadherin is a subset of fraction of β-catenin that binds TCF. Cytosolic fraction of Wnt cells was sequentially affinity precipitated with cad-GST (lanes 1–3) or TCF-GST (lanes 6–8) proteins. After cad-GST depletion (lanes 1–3), half of the cad-GST non-binding fraction (NB/2) was precipitated with TCF-GST (lane 4); the other half was precipitated with TCA to show amount remaining (lane 5, far right). After TCF-GST depletion (lanes 6–8), half of the TCF-GST non-binding fraction (NB/2, lane 9) was precipitated with cad-GST, whereas the other half was precipitated with TCA to show amount remaining (lane 10, far right). Lanes 5 and 10 reveal a fraction of β-catenin that binds neither TCF nor cadherin. This fraction is likely due to β-catenin already complexed with partners such as ICAT (Gottardi and Gumbiner, 2004). (C) Phosphorylated cadherin-GST and TCF-GST bind the same pool of β-catenin in Wnt-activated cells. Cytosolic fraction was precipitated with cad-GST (top blot), TCF-GST (bottom left) or P-cadherin-GST (bottom right) fusion proteins. After cad-GST depletion (lanes 2–4 and 7–9), there is a fraction of β-catenin that binds TCF-GST (lane 5) and P-cadherin-GST (lane 10). Note that after TCF-GST depletion (lanes 13–15), there is no β-catenin remaining to bind P-cadherin-GST (lane 16). After P-cadherin-GST depletion (lanes 18–20), there is no β-catenin remaining to bind TCF-GST (lane 21). Reciprocal depletions suggest that P-cadherin-GST and TCF-GST bind the same form of β-catenin.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172558&req=5

fig8: Cadherin phosphorylation reverses β-catenin binding selectivity during Wnt signaling. (A) Phosphorylation of cad-GST increases β-catenin binding to cadherin compared with TCF. A cytosolic fraction from L cells transfected with Wnt3a were incubated with equimolar amounts of cad-GST, TCF-GST, and CK2-P-cad-GST-glutathione–coupled beads for 1 h at 4°C (see Fig. S1 for characterization of GST fusion proteins). The resulting anti–β-catenin and anti-GST immunoblots are shown. (B) Fraction of β-catenin that binds cadherin is a subset of fraction of β-catenin that binds TCF. Cytosolic fraction of Wnt cells was sequentially affinity precipitated with cad-GST (lanes 1–3) or TCF-GST (lanes 6–8) proteins. After cad-GST depletion (lanes 1–3), half of the cad-GST non-binding fraction (NB/2) was precipitated with TCF-GST (lane 4); the other half was precipitated with TCA to show amount remaining (lane 5, far right). After TCF-GST depletion (lanes 6–8), half of the TCF-GST non-binding fraction (NB/2, lane 9) was precipitated with cad-GST, whereas the other half was precipitated with TCA to show amount remaining (lane 10, far right). Lanes 5 and 10 reveal a fraction of β-catenin that binds neither TCF nor cadherin. This fraction is likely due to β-catenin already complexed with partners such as ICAT (Gottardi and Gumbiner, 2004). (C) Phosphorylated cadherin-GST and TCF-GST bind the same pool of β-catenin in Wnt-activated cells. Cytosolic fraction was precipitated with cad-GST (top blot), TCF-GST (bottom left) or P-cadherin-GST (bottom right) fusion proteins. After cad-GST depletion (lanes 2–4 and 7–9), there is a fraction of β-catenin that binds TCF-GST (lane 5) and P-cadherin-GST (lane 10). Note that after TCF-GST depletion (lanes 13–15), there is no β-catenin remaining to bind P-cadherin-GST (lane 16). After P-cadherin-GST depletion (lanes 18–20), there is no β-catenin remaining to bind TCF-GST (lane 21). Reciprocal depletions suggest that P-cadherin-GST and TCF-GST bind the same form of β-catenin.

Mentions: We also asked whether modification of the cadherin could affect β-catenin binding selectivity. A previous study showed that the serine-rich, β-catenin binding region of the cadherin is phosphorylated in vivo (Stappert and Kemler, 1994), and this phosphorylation can enhance β-catenin binding to the cadherin (Lickert et al., 2000; Huber and Weis, 2001). We therefore wished to explore whether β-catenin binding selectivity for TCF in Wnt stimulated cells would be altered by cadherin phosphorylation in our binding assay. Phosphorylation of the cadherin greatly enhances binding to β-catenin compared with unphosphorylated cadherin (Fig. 8 A and Fig. S1, available at http://www.jcb.org/cgi/content/full/jcb.200402153/DC1). Indeed, phospho-cadherin is able to binding the same fraction of β-catenin that binds TCF (Fig. 8, B and C), suggesting that cadherin phosphorylation allows the monomeric, closed form of β-catenin to bind the cadherin. Thus, although Wnt signaling generates a form of β-catenin that exhibits preferential binding to TCF over the cadherin, this mechanism can be overridden by extensive phosphorylation of the cadherin.


Distinct molecular forms of beta-catenin are targeted to adhesive or transcriptional complexes.

Gottardi CJ, Gumbiner BM - J. Cell Biol. (2004)

Cadherin phosphorylation reverses β-catenin binding selectivity during Wnt signaling. (A) Phosphorylation of cad-GST increases β-catenin binding to cadherin compared with TCF. A cytosolic fraction from L cells transfected with Wnt3a were incubated with equimolar amounts of cad-GST, TCF-GST, and CK2-P-cad-GST-glutathione–coupled beads for 1 h at 4°C (see Fig. S1 for characterization of GST fusion proteins). The resulting anti–β-catenin and anti-GST immunoblots are shown. (B) Fraction of β-catenin that binds cadherin is a subset of fraction of β-catenin that binds TCF. Cytosolic fraction of Wnt cells was sequentially affinity precipitated with cad-GST (lanes 1–3) or TCF-GST (lanes 6–8) proteins. After cad-GST depletion (lanes 1–3), half of the cad-GST non-binding fraction (NB/2) was precipitated with TCF-GST (lane 4); the other half was precipitated with TCA to show amount remaining (lane 5, far right). After TCF-GST depletion (lanes 6–8), half of the TCF-GST non-binding fraction (NB/2, lane 9) was precipitated with cad-GST, whereas the other half was precipitated with TCA to show amount remaining (lane 10, far right). Lanes 5 and 10 reveal a fraction of β-catenin that binds neither TCF nor cadherin. This fraction is likely due to β-catenin already complexed with partners such as ICAT (Gottardi and Gumbiner, 2004). (C) Phosphorylated cadherin-GST and TCF-GST bind the same pool of β-catenin in Wnt-activated cells. Cytosolic fraction was precipitated with cad-GST (top blot), TCF-GST (bottom left) or P-cadherin-GST (bottom right) fusion proteins. After cad-GST depletion (lanes 2–4 and 7–9), there is a fraction of β-catenin that binds TCF-GST (lane 5) and P-cadherin-GST (lane 10). Note that after TCF-GST depletion (lanes 13–15), there is no β-catenin remaining to bind P-cadherin-GST (lane 16). After P-cadherin-GST depletion (lanes 18–20), there is no β-catenin remaining to bind TCF-GST (lane 21). Reciprocal depletions suggest that P-cadherin-GST and TCF-GST bind the same form of β-catenin.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172558&req=5

fig8: Cadherin phosphorylation reverses β-catenin binding selectivity during Wnt signaling. (A) Phosphorylation of cad-GST increases β-catenin binding to cadherin compared with TCF. A cytosolic fraction from L cells transfected with Wnt3a were incubated with equimolar amounts of cad-GST, TCF-GST, and CK2-P-cad-GST-glutathione–coupled beads for 1 h at 4°C (see Fig. S1 for characterization of GST fusion proteins). The resulting anti–β-catenin and anti-GST immunoblots are shown. (B) Fraction of β-catenin that binds cadherin is a subset of fraction of β-catenin that binds TCF. Cytosolic fraction of Wnt cells was sequentially affinity precipitated with cad-GST (lanes 1–3) or TCF-GST (lanes 6–8) proteins. After cad-GST depletion (lanes 1–3), half of the cad-GST non-binding fraction (NB/2) was precipitated with TCF-GST (lane 4); the other half was precipitated with TCA to show amount remaining (lane 5, far right). After TCF-GST depletion (lanes 6–8), half of the TCF-GST non-binding fraction (NB/2, lane 9) was precipitated with cad-GST, whereas the other half was precipitated with TCA to show amount remaining (lane 10, far right). Lanes 5 and 10 reveal a fraction of β-catenin that binds neither TCF nor cadherin. This fraction is likely due to β-catenin already complexed with partners such as ICAT (Gottardi and Gumbiner, 2004). (C) Phosphorylated cadherin-GST and TCF-GST bind the same pool of β-catenin in Wnt-activated cells. Cytosolic fraction was precipitated with cad-GST (top blot), TCF-GST (bottom left) or P-cadherin-GST (bottom right) fusion proteins. After cad-GST depletion (lanes 2–4 and 7–9), there is a fraction of β-catenin that binds TCF-GST (lane 5) and P-cadherin-GST (lane 10). Note that after TCF-GST depletion (lanes 13–15), there is no β-catenin remaining to bind P-cadherin-GST (lane 16). After P-cadherin-GST depletion (lanes 18–20), there is no β-catenin remaining to bind TCF-GST (lane 21). Reciprocal depletions suggest that P-cadherin-GST and TCF-GST bind the same form of β-catenin.
Mentions: We also asked whether modification of the cadherin could affect β-catenin binding selectivity. A previous study showed that the serine-rich, β-catenin binding region of the cadherin is phosphorylated in vivo (Stappert and Kemler, 1994), and this phosphorylation can enhance β-catenin binding to the cadherin (Lickert et al., 2000; Huber and Weis, 2001). We therefore wished to explore whether β-catenin binding selectivity for TCF in Wnt stimulated cells would be altered by cadherin phosphorylation in our binding assay. Phosphorylation of the cadherin greatly enhances binding to β-catenin compared with unphosphorylated cadherin (Fig. 8 A and Fig. S1, available at http://www.jcb.org/cgi/content/full/jcb.200402153/DC1). Indeed, phospho-cadherin is able to binding the same fraction of β-catenin that binds TCF (Fig. 8, B and C), suggesting that cadherin phosphorylation allows the monomeric, closed form of β-catenin to bind the cadherin. Thus, although Wnt signaling generates a form of β-catenin that exhibits preferential binding to TCF over the cadherin, this mechanism can be overridden by extensive phosphorylation of the cadherin.

Bottom Line: The Wnt-stimulated, TCF-selective form is monomeric and is regulated by the COOH terminus of beta-catenin, which selectively competes cadherin binding through an intramolecular fold-back mechanism.Phosphorylation of the cadherin reverses the TCF binding selectivity, suggesting another potential layer of regulation.In contrast, the main cadherin-binding form of beta-catenin is a beta-catenin-alpha-catenin dimer, indicating that there is a distinct molecular form of beta-catenin that can interact with both the cadherin and alpha-catenin.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Virginia School of Medicine, Charlottesville, VA 22908, USA. c-gottardi@northwestern.edu.

ABSTRACT
Beta-catenin plays essential roles in both cell-cell adhesion and Wnt signal transduction, but what precisely controls beta-catenin targeting to cadherin adhesive complexes, or T-cell factor (TCF)-transcriptional complexes is less well understood. We show that during Wnt signaling, a form of beta-catenin is generated that binds TCF but not the cadherin cytoplasmic domain. The Wnt-stimulated, TCF-selective form is monomeric and is regulated by the COOH terminus of beta-catenin, which selectively competes cadherin binding through an intramolecular fold-back mechanism. Phosphorylation of the cadherin reverses the TCF binding selectivity, suggesting another potential layer of regulation. In contrast, the main cadherin-binding form of beta-catenin is a beta-catenin-alpha-catenin dimer, indicating that there is a distinct molecular form of beta-catenin that can interact with both the cadherin and alpha-catenin. We propose that participation of beta-catenin in adhesion or Wnt signaling is dictated by the regulation of distinct molecular forms of beta-catenin with different binding properties, rather than simple competition between cadherins and TCFs for a single constitutive form. This model explains how cells can control whether beta-catenin is used independently in cell adhesion and nuclear signaling, or competitively so that the two processes are coordinated and interrelated.

Show MeSH
Related in: MedlinePlus