Limits...
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.

Show MeSH

Related in: MedlinePlus

Wnt-5a decreased β-catenin activity and protein stability in the SW48 cells but not in SW480 cells. (A) Wnt-5a expression inhibits TOPFLASH activity in SW48 cells. (B) Wnt-5a expression reduced the protein level of β-catenin in SW48 cells. Both ΔSiah1 and ΔSiah2 blocked the activity of Wnt-5a in reducing β-catenin protein. (C) Wnt-5a also induces Siah2 expression in SW48 cells. (D) Wnt-5a expression in SW480 cells did not lead to the inhibition of β-catenin activity and protein degradation. Expression of APC inhibited β-catenin activity and promoted β-catenin degradation.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2172823&req=5

fig6: Wnt-5a decreased β-catenin activity and protein stability in the SW48 cells but not in SW480 cells. (A) Wnt-5a expression inhibits TOPFLASH activity in SW48 cells. (B) Wnt-5a expression reduced the protein level of β-catenin in SW48 cells. Both ΔSiah1 and ΔSiah2 blocked the activity of Wnt-5a in reducing β-catenin protein. (C) Wnt-5a also induces Siah2 expression in SW48 cells. (D) Wnt-5a expression in SW480 cells did not lead to the inhibition of β-catenin activity and protein degradation. Expression of APC inhibited β-catenin activity and promoted β-catenin degradation.

Mentions: Because mutations that cause β-catenin stabilization are associated with the development of colon cancers and Wnt-5a is expressed in the gut mesoderm (Lickert et al., 2001), we first tested whether Wnt-5a can inhibit the accumulation of β-catenin protein in the colon cancer cell line SW48, which contains intact APC and a Ser 33 to Tyr missense mutation in β-catenin that results in its stabilization. Wnt-5a expression led to reduced TOPFLASH reporter activity and decreased β-catenin protein levels (Fig. 6, A and B). Next, we found that Siah2 was activated by Wnt-5a in the SW48 cells (Fig. 6 C). Finally, we found that dominant negative forms of Siah1 and 2 were able to block the activity of Wnt-5a in degrading β-catenin (Fig. 6 B). In contrast, in the colon cancer cell line SW480, which contains wild-type β-catenin but no APC activity, expression of Wnt-5a did not lead to inhibition of TOPFLAH activity or β-catenin degradation (Fig. 6 D). These results are consistent with the conclusions drawn from our experiments in 293 cells: the activity of Wnt-5a in promoting β-catenin degradation requires Siah and APC. Together, our findings show that Wnt-5a, in contrast to many other Wnts, signals through a novel pathway that may involve the regulation of Siah2 expression to antagonize the canonical Wnt pathway in regulating embryonic development and, possibly, in suppressing the formation of a subset of tumors.


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)

Wnt-5a decreased β-catenin activity and protein stability in the SW48 cells but not in SW480 cells. (A) Wnt-5a expression inhibits TOPFLASH activity in SW48 cells. (B) Wnt-5a expression reduced the protein level of β-catenin in SW48 cells. Both ΔSiah1 and ΔSiah2 blocked the activity of Wnt-5a in reducing β-catenin protein. (C) Wnt-5a also induces Siah2 expression in SW48 cells. (D) Wnt-5a expression in SW480 cells did not lead to the inhibition of β-catenin activity and protein degradation. Expression of APC inhibited β-catenin activity and promoted β-catenin degradation.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172823&req=5

fig6: Wnt-5a decreased β-catenin activity and protein stability in the SW48 cells but not in SW480 cells. (A) Wnt-5a expression inhibits TOPFLASH activity in SW48 cells. (B) Wnt-5a expression reduced the protein level of β-catenin in SW48 cells. Both ΔSiah1 and ΔSiah2 blocked the activity of Wnt-5a in reducing β-catenin protein. (C) Wnt-5a also induces Siah2 expression in SW48 cells. (D) Wnt-5a expression in SW480 cells did not lead to the inhibition of β-catenin activity and protein degradation. Expression of APC inhibited β-catenin activity and promoted β-catenin degradation.
Mentions: Because mutations that cause β-catenin stabilization are associated with the development of colon cancers and Wnt-5a is expressed in the gut mesoderm (Lickert et al., 2001), we first tested whether Wnt-5a can inhibit the accumulation of β-catenin protein in the colon cancer cell line SW48, which contains intact APC and a Ser 33 to Tyr missense mutation in β-catenin that results in its stabilization. Wnt-5a expression led to reduced TOPFLASH reporter activity and decreased β-catenin protein levels (Fig. 6, A and B). Next, we found that Siah2 was activated by Wnt-5a in the SW48 cells (Fig. 6 C). Finally, we found that dominant negative forms of Siah1 and 2 were able to block the activity of Wnt-5a in degrading β-catenin (Fig. 6 B). In contrast, in the colon cancer cell line SW480, which contains wild-type β-catenin but no APC activity, expression of Wnt-5a did not lead to inhibition of TOPFLAH activity or β-catenin degradation (Fig. 6 D). These results are consistent with the conclusions drawn from our experiments in 293 cells: the activity of Wnt-5a in promoting β-catenin degradation requires Siah and APC. Together, our findings show that Wnt-5a, in contrast to many other Wnts, signals through a novel pathway that may involve the regulation of Siah2 expression to antagonize the canonical Wnt pathway in regulating embryonic development and, possibly, in suppressing the formation of a subset of tumors.

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