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Wnt-5a inhibits the canonical Wnt pathway by promoting GSK-3-independent beta-catenin degradation.

Topol L, Jiang X, Choi H, Garrett-Beal L, Carolan PJ, Yang Y - J. Cell Biol. (2003)

Bottom Line: Wnt-5a is considered a noncanonical Wnt as it does not signal by stabilizing beta-catenin in many biological systems.We have uncovered a new noncanonical pathway through which Wnt-5a antagonizes the canonical Wnt pathway by promoting the degradation of beta-catenin.This pathway is Siah2 and APC dependent, but GSK-3 and beta-TrCP independent.

View Article: PubMed Central - PubMed

Affiliation: Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA.

ABSTRACT
Wnts are secreted signaling molecules that can transduce their signals through several different pathways. Wnt-5a is considered a noncanonical Wnt as it does not signal by stabilizing beta-catenin in many biological systems. We have uncovered a new noncanonical pathway through which Wnt-5a antagonizes the canonical Wnt pathway by promoting the degradation of beta-catenin. This pathway is Siah2 and APC dependent, but GSK-3 and beta-TrCP independent. Furthermore, we provide evidence that Wnt-5a also acts in vivo to promote beta-catenin degradation in regulating mammalian limb development and possibly in suppressing tumor formation.

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Canonical Wnt signaling was increased in the Wnt-5a−/− limb buds. Gene expression in embryos was examined by whole mount in situ hybridization. (A) At 12.5 dpc, the expression of Sox9, which marks early chondrogenesis, was not detected in the distal-most limb bud of the Wnt-5a−/− limb (arrow). (B) Ectopic LacZ staining (arrow) was detected in the Wnt-5a−/−/TOPGAL distal limb at 12.5 dpc. (C) The β-catenin protein level was increased in the distal Wnt-5a−/− limb at 11.5 dpc. (D) Sfrp-2 expressing cells (red), but not control cells (blue), induced ectopic expression of ColII (arrows), a marker for chondrocyte differentiation in both wild-type and Wnt-5a−/− limbs.
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fig5: Canonical Wnt signaling was increased in the Wnt-5a−/− limb buds. Gene expression in embryos was examined by whole mount in situ hybridization. (A) At 12.5 dpc, the expression of Sox9, which marks early chondrogenesis, was not detected in the distal-most limb bud of the Wnt-5a−/− limb (arrow). (B) Ectopic LacZ staining (arrow) was detected in the Wnt-5a−/−/TOPGAL distal limb at 12.5 dpc. (C) The β-catenin protein level was increased in the distal Wnt-5a−/− limb at 11.5 dpc. (D) Sfrp-2 expressing cells (red), but not control cells (blue), induced ectopic expression of ColII (arrows), a marker for chondrocyte differentiation in both wild-type and Wnt-5a−/− limbs.

Mentions: To investigate whether Wnt-5a signaling also antagonizes the canonical Wnt pathway in vivo, we analyzed the limb development defects in the Wnt-5a−/− embryos. Wnt-5a is strongly expressed in the distal limb bud and its expression gradually fades proximally (Yamaguchi et al., 1999). In the Wnt-5a−/− limb, the distal digits are missing. It has been shown that this is not due to earlier regression of the apical ectodermal ridge (AER) or absence of the distal limb mesenchyme (Yamaguchi et al., 1999). Consistent with previous observations, we found that the expression of Sox9, the earliest marker for mesenchymal condensation and chondrocyte differentiation (Zhao et al., 1997), was not detected in the distal-most cells in the Wnt-5a−/− limb at 12.5 dpc (Fig. 5 A). These data demonstrate that chondrocyte differentiation, which is required for digit formation, was inhibited before mesenchymal condensation in the distal limb of the Wnt-5a−/− limb. This phenotype is different from that in the LRP6−/− limb, in which skeletal elements are missing along the anterior–posterior axis due to a disrupted AER (Pinson et al., 2000). As LRP6 is a Wnt coreceptor which acts specifically in the canonical Wnt pathway (Wehrli et al., 2000), it appears that Wnt-5a signals predominantly through a noncanonical Wnt pathway during mouse limb development. Because canonical Wnt signaling has been shown to inhibit chondrogenesis (Rudnicki and Brown, 1997), we directly assessed canonical Wnt pathway activity in the Wnt-5a−/− mutant limb using TOPGAL transgenic mice in which LacZ expression is under the control of LEF/TCF binding sites (DasGupta and Fuchs, 1999). Ectopic LacZ staining was detected in the distal limb of Wnt-5a−/−/TOPGAL mice at 12.5 dpc (Fig. 5 B), indicating that canonical Wnt activity has been elevated to a higher level in the distal part of the limb in the absence of Wnt-5a activity. Consistent with this, we found that β-catenin protein level was higher in Wnt-5a−/− limbs as compared with wild-type at 11.5 dpc (Fig. 5 C), suggesting that Wnt-5a signaling also promoted β-catenin degradation in the developing limb.


Wnt-5a inhibits the canonical Wnt pathway by promoting GSK-3-independent beta-catenin degradation.

Topol L, Jiang X, Choi H, Garrett-Beal L, Carolan PJ, Yang Y - J. Cell Biol. (2003)

Canonical Wnt signaling was increased in the Wnt-5a−/− limb buds. Gene expression in embryos was examined by whole mount in situ hybridization. (A) At 12.5 dpc, the expression of Sox9, which marks early chondrogenesis, was not detected in the distal-most limb bud of the Wnt-5a−/− limb (arrow). (B) Ectopic LacZ staining (arrow) was detected in the Wnt-5a−/−/TOPGAL distal limb at 12.5 dpc. (C) The β-catenin protein level was increased in the distal Wnt-5a−/− limb at 11.5 dpc. (D) Sfrp-2 expressing cells (red), but not control cells (blue), induced ectopic expression of ColII (arrows), a marker for chondrocyte differentiation in both wild-type and Wnt-5a−/− limbs.
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fig5: Canonical Wnt signaling was increased in the Wnt-5a−/− limb buds. Gene expression in embryos was examined by whole mount in situ hybridization. (A) At 12.5 dpc, the expression of Sox9, which marks early chondrogenesis, was not detected in the distal-most limb bud of the Wnt-5a−/− limb (arrow). (B) Ectopic LacZ staining (arrow) was detected in the Wnt-5a−/−/TOPGAL distal limb at 12.5 dpc. (C) The β-catenin protein level was increased in the distal Wnt-5a−/− limb at 11.5 dpc. (D) Sfrp-2 expressing cells (red), but not control cells (blue), induced ectopic expression of ColII (arrows), a marker for chondrocyte differentiation in both wild-type and Wnt-5a−/− limbs.
Mentions: To investigate whether Wnt-5a signaling also antagonizes the canonical Wnt pathway in vivo, we analyzed the limb development defects in the Wnt-5a−/− embryos. Wnt-5a is strongly expressed in the distal limb bud and its expression gradually fades proximally (Yamaguchi et al., 1999). In the Wnt-5a−/− limb, the distal digits are missing. It has been shown that this is not due to earlier regression of the apical ectodermal ridge (AER) or absence of the distal limb mesenchyme (Yamaguchi et al., 1999). Consistent with previous observations, we found that the expression of Sox9, the earliest marker for mesenchymal condensation and chondrocyte differentiation (Zhao et al., 1997), was not detected in the distal-most cells in the Wnt-5a−/− limb at 12.5 dpc (Fig. 5 A). These data demonstrate that chondrocyte differentiation, which is required for digit formation, was inhibited before mesenchymal condensation in the distal limb of the Wnt-5a−/− limb. This phenotype is different from that in the LRP6−/− limb, in which skeletal elements are missing along the anterior–posterior axis due to a disrupted AER (Pinson et al., 2000). As LRP6 is a Wnt coreceptor which acts specifically in the canonical Wnt pathway (Wehrli et al., 2000), it appears that Wnt-5a signals predominantly through a noncanonical Wnt pathway during mouse limb development. Because canonical Wnt signaling has been shown to inhibit chondrogenesis (Rudnicki and Brown, 1997), we directly assessed canonical Wnt pathway activity in the Wnt-5a−/− mutant limb using TOPGAL transgenic mice in which LacZ expression is under the control of LEF/TCF binding sites (DasGupta and Fuchs, 1999). Ectopic LacZ staining was detected in the distal limb of Wnt-5a−/−/TOPGAL mice at 12.5 dpc (Fig. 5 B), indicating that canonical Wnt activity has been elevated to a higher level in the distal part of the limb in the absence of Wnt-5a activity. Consistent with this, we found that β-catenin protein level was higher in Wnt-5a−/− limbs as compared with wild-type at 11.5 dpc (Fig. 5 C), suggesting that Wnt-5a signaling also promoted β-catenin degradation in the developing limb.

Bottom Line: Wnt-5a is considered a noncanonical Wnt as it does not signal by stabilizing beta-catenin in many biological systems.We have uncovered a new noncanonical pathway through which Wnt-5a antagonizes the canonical Wnt pathway by promoting the degradation of beta-catenin.This pathway is Siah2 and APC dependent, but GSK-3 and beta-TrCP independent.

View Article: PubMed Central - PubMed

Affiliation: Genetic Disease Research Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892, USA.

ABSTRACT
Wnts are secreted signaling molecules that can transduce their signals through several different pathways. Wnt-5a is considered a noncanonical Wnt as it does not signal by stabilizing beta-catenin in many biological systems. We have uncovered a new noncanonical pathway through which Wnt-5a antagonizes the canonical Wnt pathway by promoting the degradation of beta-catenin. This pathway is Siah2 and APC dependent, but GSK-3 and beta-TrCP independent. Furthermore, we provide evidence that Wnt-5a also acts in vivo to promote beta-catenin degradation in regulating mammalian limb development and possibly in suppressing tumor formation.

Show MeSH
Related in: MedlinePlus