Axin, a Negative Regulator of the Wnt Signaling Pathway, Directly Interacts with Adenomatous Polyposis Coli and Regulates the Stabilization of β-Catenin

The tumor suppressor Adenomatous polyposis coli (APC) plays a key role in regulating the canonical Wnt signaling pathway as an essential component of the β-catenin destruction complex. C-terminal truncations of APC are strongly implicated in both sporadic and familial forms of colorectal cancer. However, many questions remain as to how these mutations interfere with APC’s tumor suppressor activity. One set of motifs frequently lost in these cancer-associated truncations is the SAMP repeats that mediate interactions between APC and Axin. APC proteins in both vertebrates and Drosophila contain multiple SAMP repeats that lack high sequence conservation outside of the Axin-binding motif. In this study, we tested the functional redundancy between different SAMPs and how these domains are regulated, using Drosophila APC2 and its two SAMP repeats as our model. Consistent with sequence conservation–based predictions, we show that SAMP2 has stronger binding activity to Axin in vitro, but SAMP1 also plays an essential role in the Wnt destruction complex in vivo. In addition, we demonstrate that the phosphorylation of SAMP repeats is a potential mechanism to regulate their activity. Overall our findings support a model in which each SAMP repeat plays a mechanistically distinct role but they cooperate for maximal destruction complex function.

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MicroRNA-663 activates the canonical Wnt signaling through the adenomatous polyposis coli suppression

Immunology Letters ◽

10.1016/j.imlet.2015.05.011 ◽

2015 ◽

Vol 166 (1) ◽

pp. 45-54 ◽

Cited By ~ 17

Author(s):

Cheng-gui Miao ◽

Wei-jing Shi ◽

You-yi Xiong ◽

Hao Yu ◽

Xiao-lin Zhang ◽

...

Keyword(s):

Wnt Signaling ◽

Adenomatous Polyposis Coli ◽

Adenomatous Polyposis ◽

Polyposis Coli ◽

Canonical Wnt Signaling ◽

Canonical Wnt

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The microRNA miR-8 is a conserved negative regulator of Wnt signaling

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.0807763105 ◽

2008 ◽

Vol 105 (40) ◽

pp. 15417-15422 ◽

Cited By ~ 130

Author(s):

Jennifer A. Kennell ◽

Isabelle Gerin ◽

Ormond A. MacDougald ◽

Ken M. Cadigan

Keyword(s):

Wnt Signaling ◽

Signaling Pathway ◽

Target Genes ◽

Wnt Signaling Pathway ◽

Negative Regulator ◽

Animal Development ◽

Protein Levels ◽

Evolutionarily Conserved ◽

Multiple Levels

Wnt signaling plays many important roles in animal development. This evolutionarily conserved signaling pathway is highly regulated at all levels. To identify regulators of the Wnt/Wingless (Wg) pathway, we performed a genetic screen in Drosophila. We identified the microRNA miR-8 as an inhibitor of Wg signaling. Expression of miR-8 potently antagonizes Wg signaling in vivo, in part by directly targeting wntless, a gene required for Wg secretion. In addition, miR-8 inhibits the pathway downstream of the Wg signal by repressing TCF protein levels. Another positive regulator of the pathway, CG32767, is also targeted by miR-8. Our data suggest that miR-8 potently antagonizes the Wg pathway at multiple levels, from secretion of the ligand to transcription of target genes. In addition, mammalian homologues of miR-8 promote adipogenesis of marrow stromal cells by inhibiting Wnt signaling. These findings indicate that miR-8 family members play an evolutionarily conserved role in regulating the Wnt signaling pathway.

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Wnt/β-Catenin/Tcf Signaling Induces the Transcription of Axin2, a Negative Regulator of the Signaling Pathway

Molecular and Cellular Biology ◽

10.1128/mcb.22.4.1172-1183.2002 ◽

2002 ◽

Vol 22 (4) ◽

pp. 1172-1183 ◽

Cited By ~ 1080

Author(s):

Eek-hoon Jho ◽

Tong Zhang ◽

Claire Domon ◽

Choun-Ki Joo ◽

Jean-Noel Freund ◽

...

Keyword(s):

Wnt Signaling ◽

Signaling Pathway ◽

Wnt Pathway ◽

Genomic Sequence ◽

Wnt Signaling Pathway ◽

Genomic Region ◽

Negative Regulator ◽

Mobility Shift ◽

Specific Expression

ABSTRACT Axin2/Conductin/Axil and its ortholog Axin are negative regulators of the Wnt signaling pathway, which promote the phosphorylation and degradation of β-catenin. While Axin is expressed ubiquitously, Axin2 mRNA was seen in a restricted pattern during mouse embryogenesis and organogenesis. Because many sites of Axin2 expression overlapped with those of several Wnt genes, we tested whether Axin2 was induced by Wnt signaling. Endogenous Axin2 mRNA and protein expression could be rapidly induced by activation of the Wnt pathway, and Axin2 reporter constructs, containing a 5.6-kb DNA fragment including the promoter and first intron, were also induced. This genomic region contains eight Tcf/LEF consensus binding sites, five of which are located within longer, highly conserved noncoding sequences. The mutation or deletion of these Tcf/LEF sites greatly diminished induction by β-catenin, and mutation of the Tcf/LEF site T2 abolished protein binding in an electrophoretic mobility shift assay. These results strongly suggest that Axin2 is a direct target of the Wnt pathway, mediated through Tcf/LEF factors. The 5.6-kb genomic sequence was sufficient to direct the tissue-specific expression of d2EGFP in transgenic embryos, consistent with a role for the Tcf/LEF sites and surrounding conserved sequences in the in vivo expression pattern of Axin2. Our results suggest that Axin2 participates in a negative feedback loop, which could serve to limit the duration or intensity of a Wnt-initiated signal.

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Regulation of Wnt signaling by the tumor suppressor adenomatous polyposis coli does not require the ability to enter the nucleus or a particular cytoplasmic localization

Molecular Biology of the Cell ◽

10.1091/mbc.e11-11-0965 ◽

2012 ◽

Vol 23 (11) ◽

pp. 2041-2056 ◽

Cited By ~ 22

Author(s):

David M. Roberts ◽

Mira I. Pronobis ◽

John S. Poulton ◽

Eric G. Kane ◽

Mark Peifer

Keyword(s):

Colon Cancer ◽

Tumor Suppressor ◽

Wnt Signaling ◽

Cancer Cells ◽

Adenomatous Polyposis Coli ◽

Subcellular Location ◽

Adenomatous Polyposis ◽

Colon Cancer Cells ◽

Polyposis Coli ◽

Drosophila Embryos

Wnt signaling plays key roles in development and disease. The tumor suppressor adenomatous polyposis coli (APC) is an essential negative regulator of Wnt signaling. Its best-characterized role is as part of the destruction complex, targeting the Wnt effector β-catenin (βcat) for phosphorylation and ultimate destruction, but several studies suggested APC also may act in the nucleus at promoters of Wnt-responsive genes or to shuttle βcat out for destruction. Even in its role in the destruction complex, APC's mechanism of action remains mysterious. We have suggested APC positions the destruction complex at the appropriate subcellular location, facilitating βcat destruction. In this study, we directly tested APC's proposed roles in the nucleus or in precisely localizing the destruction complex by generating a series of APC2 variants to which we added tags relocalizing otherwise wild-type APC to different cytoplasmic locations. We tested these for function in human colon cancer cells and Drosophila embryos. Strikingly, all rescue Wnt regulation and down-regulate Wnt target genes in colon cancer cells, and most restore Wnt regulation in Drosophila embryos null for both fly APCs. These data suggest that APC2 does not have to shuttle into the nucleus or localize to a particular subcellular location to regulate Wnt signaling.

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PLA2G7/PAF-AH as protective factor and potential negative regulator of the Wnt signaling pathway in BRCA1 mutant ovarian cancer

10.1055/s-0040-1718211 ◽

2020 ◽

Author(s):

Y Liao ◽

S Badmann ◽

T Kaltofen ◽

D Mayr ◽

E Schmoeckel ◽

...

Keyword(s):

Ovarian Cancer ◽

Wnt Signaling ◽

Signaling Pathway ◽

Protective Factor ◽

Wnt Signaling Pathway ◽

Negative Regulator

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Structural and Functional Characterization of the Wnt Inhibitor APC Membrane Recruitment 1 (Amer1)

Journal of Biological Chemistry ◽

10.1074/jbc.m111.224881 ◽

2011 ◽

Vol 286 (22) ◽

pp. 19204-19214 ◽

Cited By ~ 27

Author(s):

Kristina Tanneberger ◽

Astrid S. Pfister ◽

Vitezslav Kriz ◽

Vitezslav Bryja ◽

Alexandra Schambony ◽

...

Keyword(s):

Plasma Membrane ◽

Wnt Signaling ◽

Adenomatous Polyposis Coli ◽

Target Genes ◽

Functional Characterization ◽

Negative Control ◽

Membrane Localization ◽

Adenomatous Polyposis ◽

Polyposis Coli ◽

Wnt Inhibitor

Amer1/WTX binds to the tumor suppressor adenomatous polyposis coli and acts as an inhibitor of Wnt signaling by inducing β-catenin degradation. We show here that Amer1 directly interacts with the armadillo repeats of β-catenin via a domain consisting of repeated arginine-glutamic acid-alanine (REA) motifs, and that Amer1 assembles the β-catenin destruction complex at the plasma membrane by recruiting β-catenin, adenomatous polyposis coli, and Axin/Conductin. Deletion or specific mutations of the membrane binding domain of Amer1 abolish its membrane localization and abrogate negative control of Wnt signaling, which can be restored by artificial targeting of Amer1 to the plasma membrane. In line, a natural splice variant of Amer1 lacking the plasma membrane localization domain is deficient for Wnt inhibition. Knockdown of Amer1 leads to the activation of Wnt target genes, preferentially in dense compared with sparse cell cultures, suggesting that Amer1 function is regulated by cell contacts. Amer1 stabilizes Axin and counteracts Wnt-induced degradation of Axin, which requires membrane localization of Amer1. The data suggest that Amer1 exerts its negative regulatory role in Wnt signaling by acting as a scaffold protein for the β-catenin destruction complex and promoting stabilization of Axin at the plasma membrane.

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Association between Serum Dickkopf-1 (DKK-1) Glycoprotein and Calcific Deposits on Cardiac Valves and Carotid Intimal-Medial Thickness in Hemodialysis Patients

Cardiorenal Medicine ◽

10.1159/000507183 ◽

2020 ◽

Vol 10 (5) ◽

pp. 313-322

Author(s):

Dalia Younis ◽

Ahmed Bahie ◽

Rasha Elzehery ◽

Ghada El-Kannishy ◽

Ahmed M. Wahab

Keyword(s):

Wnt Signaling ◽

Signaling Pathway ◽

Wnt Signaling Pathway ◽

Significant Negative Correlation ◽

Negative Regulator ◽

Intimal Medial Thickness ◽

Carotid Intimal Medial Thickness ◽

Cardiac Valve Calcification ◽

Calcific Deposits ◽

Score Range

Background: Cardiac valve calcification (CVC) is common in hemodialysis (HD) patients, and associated with cardiovascular and all-cause mortality. Once believed to be a passive process, it is now understood that the Wnt signaling pathway has a major role. The aim of the current study was to assess the relationship between circulating DKK-1, a negative regulator of the Wnt signaling pathway, and CVC, as well as carotid intimal-medial thickness (CIMT) in HD patients. Methods: We enrolled 74 consecutive adults on maintenance HD. Echocardiographic calcification of the mitral valve (MV) and aortic valve (AV) were detected according to Wilkins score (range 0–4), and the study of Tenenbaum et al. [Int J Cardiol. 2004 Mar;94(1):7–13] (range 0–4), respectively. CVC severity was calculated by a supposed score (range 0–8) that represents the sum of calcification grade of MV and AV. CVC severity was classified into absent (CVC score = 0), mild (CVC score = 1–2), moderate (CVC score = 3–4), and severe (CVC score ≥5). Demographic and biochemical data were collected in addition to serum DKK-1 levels and CIMT. Results: CVC was present in 67 patients (91.0%). There was a highly significant negative correlation between serum DKK-1 level and CVC score (r = –0.492; p ≤ 0.001), as well as CIMT (r = –0.611; p ≤ 0.001). Age and CIMT were independent determinants of CVC. Conclusions: CVC is almost present in all HD patients. DKK-1 seems to have a direct relation with CVC and CIMT in HD patients. Age is the strongest independent determinant of CVC.

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