Stability elements in the LRP6 cytoplasmic tail confer efficient signalling upon DIX-dependent polymerization

RHBDF1 regulates APC-mediated stimulation of the epithelial-to-mesenchymal transition and proliferation of colorectal cancer cells in part via the Wnt/β-catenin signalling pathway

The human rhomboid family-1 gene (RHBDF1) is an oncogene in breast and head and neck squamous cancers. Here, we show that RHBDF1 plays a significant role in colorectal cancer (CRC) formation and that the RHBDF1 expression level is higher in CRC than in corresponding normal tissues. Moreover, RHBDF1 promotes cell proliferation, invasion and migration in vitro. Furthermore, through overexpression and silencing of RHBDF1 and the mediator complex, our study demonstrates that RHBDF1 may positively regulate adenomatous polyposis coli (APC) in the Wnt/β-catenin signalling pathway to increase the expression levels of MMP-14 and Twist, which act as important epithelial-to-mesenchymal transition (EMT) stimulating factors. Additionally, RHBDF1 may regulate c-myc and CyclinD1 expression to influence cell proliferation. Finally, RHBDF1 overexpression and silencing influence CRC growth in BALB/c nude mice. In summary, our findings demonstrate that the regulatory effects of RHBDF1 on EMT and on cell proliferation are partially attributable to the Wnt/β-catenin signalling pathway.

Interaction between Wnt/β-catenin and RAS-ERK pathways and an anti-cancer strategy via degradations of β-catenin and RAS by targeting the Wnt/β-catenin pathway

Aberrant activation of the Wnt/β-catenin and RAS-extracellular signal-regulated kinase (ERK) pathways play important roles in the tumorigenesis of many different types of cancer, most notably colorectal cancer (CRC). Genes for these two pathways, such as adenomatous polyposis coli (APC) and KRAS are frequently mutated in human CRC, and involved in the initiation and progression of the tumorigenesis, respectively. Moreover, recent studies revealed interaction of APC and KRAS mutations in the various stages of colorectal tumorigenesis and even in metastasis accompanying activation of the cancer stem cells (CSCs). A key event in the synergistic cooperation between Wnt/β-catenin and RAS-ERK pathways is a stabilization of both β-catenin and RAS especially mutant KRAS by APC loss, and pathological significance of this was indicated by correlation of increased β-catenin and RAS levels in human CRC where APC mutations occur as high as 90% of CRC patients. Together with the notion of the protein activity reduction by lowering its level, inhibition of both β-catenin and RAS especially by degradation could be a new ideal strategy for development of anti-cancer drugs for CRC. In this review, we will discuss interaction between the Wnt/β-catenin and RAS-ERK pathways in the colorectal tumorigenesis by providing the mechanism of RAS stabilization by aberrant activation of Wnt/β-catenin. We will also discuss our small molecular anti-cancer approach controlling CRC by induction of specific degradations of both β-catenin and RAS via targeting Wnt/β-catenin pathway especially for the KYA1797K, a small molecule specifically binding at the regulator of G-protein signaling (RGS)-domain of Axin.

Membrane Targeting of Disheveled Can Bypass the Need for Arrow/LRP5

The highly conserved Wnt signaling pathway regulates cell proliferation and differentiation in vertebrates and invertebrates. Upon binding of a Wnt ligand to a receptor of the Fz family, Disheveled (Dsh/Dvl) transduces the signal during canonical and non-canonical Wnt signaling. The specific details of how this process occurs have proven difficult to study, especially as Dsh appears to function as a switch between different branches of Wnt signaling. Here we focus on the membrane-proximal events that occur once Dsh is recruited to the membrane. We show that membrane-tethering of the Dsh protein is sufficient to induce canonical Wnt signaling activation even in the absence of the Wnt co-receptor Arrow/LRP5/6. We map the protein domains required for pathway activation in membrane tethered constructs finding that both the DEP and PDZ domains are dispensable for canonical signaling only in membrane-tethered Dsh, but not in untethered/normal Dsh. These data lead to a signal activation model, where Arrow is required to localize Dsh to the membrane during canonical Wnt signaling placing Dsh downstream of Arrow.

Generating Cellular Diversity and Spatial Form: Wnt Signaling and the Evolution of Multicellular Animals

There were multiple prerequisites to the evolution of multicellular animal life, including the generation of multiple cell fates ("cellular diversity") and their patterned spatial arrangement ("spatial form"). Wnt proteins operate as primordial symmetry-breaking signals. By virtue of their short-range nature and their capacity to activate both lineage-specifying and cell-polarizing intracellular signaling cascades, Wnts can polarize cells at their site of contact, orienting the axis of cell division while simultaneously programming daughter cells to adopt diverging fates in a spatially stereotyped way. By coupling cell fate to position, symmetry-breaking Wnt signals were pivotal in constructing the metazoan body by generating cellular diversity and spatial form.

The phosphatase Pgam5 antagonizes Wnt/β-Catenin signaling in embryonic anterior-posterior axis patterning

The scaffold protein Dishevelled is a central intracellular component of Wnt signaling pathways. Various kinases have been described that regulate and modulate Wnt signaling through phosphorylation of Dishevelled. However, besides general protein phosphatases 1 and 2 (PP1 and PP2), no specific protein phosphatases have been identified. Here, we report on the identification and functional characterization of the protein phosphatase Pgam5 in vitro and in vivo in Xenopus Pgam5 is a novel antagonist of Wnt/β-Catenin signaling in human cells and Xenopus embryogenesis. In early development, Pgam5 is essential for head formation, and for establishing and maintaining the Wnt/β-Catenin signaling gradient that patterns the anterior-posterior body axis. Inhibition of Wnt/β-Catenin signaling and developmental function depend on Pgam5 phosphatase activity. We show that Pgam5 interacts with Dishevelled2 and that Dishevelled2 is a substrate of Pgam5. Pgam5 mediates a marked decrease in Dishevelled2 phosphorylation in the cytoplasm and in the nucleus, as well as decreased interaction between Dishevelled2, Tcf1 and β-Catenin, indicating that Pgam5 regulates Dishevelled function upstream and downstream of β-Catenin stabilization.

Constitutive scaffolding of multiple Wnt enhanceosome components by Legless/BCL9

Wnt/β-catenin signaling elicits context-dependent transcription switches that determine normal development and oncogenesis. These are mediated by the Wnt enhanceosome, a multiprotein complex binding to the Pygo chromatin reader and acting through TCF/LEF-responsive enhancers. Pygo renders this complex Wnt-responsive, by capturing β-catenin via the Legless/BCL9 adaptor. We used CRISPR/Cas9 genome engineering of Drosophila legless (lgs) and human BCL9 and B9L to show that the C-terminus downstream of their adaptor elements is crucial for Wnt responses. BioID proximity labeling revealed that BCL9 and B9L, like PYGO2, are constitutive components of the Wnt enhanceosome. Wnt-dependent docking of β-catenin to the enhanceosome apparently causes a rearrangement that apposes the BCL9/B9L C-terminus to TCF. This C-terminus binds to the Groucho/TLE co-repressor, and also to the Chip/LDB1-SSDP enhanceosome core complex via an evolutionary conserved element. An unexpected link between BCL9/B9L, PYGO2 and nuclear co-receptor complexes suggests that these β-catenin co-factors may coordinate Wnt and nuclear hormone responses.

Wnt signaling in cancer

Wnt signaling is one of the key cascades regulating development and stemness, and has also been tightly associated with cancer. The role of Wnt signaling in carcinogenesis has most prominently been described for colorectal cancer, but aberrant Wnt signaling is observed in many more cancer entities. Here, we review current insights into novel components of Wnt pathways and describe their impact on cancer development. Furthermore, we highlight expanding functions of Wnt signaling for both solid and liquid tumors. We also describe current findings how Wnt signaling affects maintenance of cancer stem cells, metastasis and immune control. Finally, we provide an overview of current strategies to antagonize Wnt signaling in cancer and challenges that are associated with such approaches.

A Comparative Perspective on Wnt/β-Catenin Signalling in Cell Fate Determination

The Wnt/β-catenin pathway is an ancient and highly conserved signalling pathway that plays fundamental roles in the regulation of embryonic development and adult homeostasis. This pathway has been implicated in numerous cellular processes, including cell proliferation, differentiation, migration, morphological changes and apoptosis. In this chapter, we aim to illustrate with specific examples the involvement of Wnt/β-catenin signalling in cell fate determination. We discuss the roles of the Wnt/β-catenin pathway in specifying cell fate throughout evolution, how its function in patterning during development is often reactivated during regeneration and how perturbation of this pathway has negative consequences for the control of cell fate.The origin of all life was a single cell that had the capacity to respond to cues from the environment. With evolution, multicellular organisms emerged, and as a result, subsets of cells arose to form tissues able to respond to specific instructive signals and perform specialised functions. This complexity and specialisation required two types of messages to direct cell fate: intra- and intercellular. A fundamental question in developmental biology is to understand the underlying mechanisms of cell fate choice. Amongst the numerous external cues involved in the generation of cellular diversity, a prominent pathway is the Wnt signalling pathway in all its forms.

Essential role of the Dishevelled DEP domain in a Wnt-dependent human-cell-based complementation assay

Dishevelled (DVL) assembles Wnt signalosomes through dynamic head-to-tail polymerisation by means of its DIX domain. It thus transduces Wnt signals to cytoplasmic effectors including β-catenin, to control cell fates during normal development, tissue homeostasis and also in cancer. To date, most functional studies of Dishevelled relied on its Wnt-independent signalling activity resulting from overexpression, which is sufficient to trigger polymerisation, bypassing the requirement for Wnt signals. Here, we generate a human cell line devoid of endogenous Dishevelled (DVL1- DVL3), which lacks Wnt signal transduction to β-catenin. However, Wnt responses can be restored by DVL2 stably re-expressed at near-endogenous levels. Using this assay to test mutant DVL2, we show that its DEP domain is essential, whereas its PDZ domain is dispensable, for signalling to β-catenin. Our results imply two mutually exclusive functions of the DEP domain in Wnt signal transduction - binding to Frizzled to recruit Dishevelled to the receptor complex, and dimerising to cross-link DIX domain polymers for signalosome assembly. Our assay avoids the caveats associated with overexpressing Dishevelled, and provides a powerful tool for rigorous functional tests of this pivotal human signalling protein.

Gtpbp2 is a positive regulator of Wnt signaling and maintains low levels of the Wnt negative regulator Axin

Background

Canonical Wnt signals, transduced by stabilized β-catenin, play similar roles across animals in maintaining stem cell pluripotency, regulating cell differentiation, and instructing normal embryonic development. Dysregulated Wnt/β-catenin signaling causes diseases and birth defects, and a variety of regulatory processes control this pathway to ensure its proper function and integration with other signaling systems. We previously identified GTP-binding protein 2 (Gtpbp2) as a novel regulator of BMP signaling, however further exploration revealed that Gtpbp2 can also affect Wnt signaling, which is a novel finding reported here.

Results

Knockdown of Gtpbp2 in Xenopus embryos causes severe axial defects and reduces expression of Spemann-Mangold organizer genes. Gtpbp2 knockdown blocks responses to ectopic Wnt8 ligand, such as organizer gene induction in ectodermal tissue explants and induction of secondary axes in whole embryos. However, organizer gene induction by ectopic Nodal2 is unaffected by Gtpbp2 knockdown. Epistasis tests, conducted by activating Wnt signal transduction at sequential points in the canonical pathway, demonstrate that Gtpbp2 is required downstream of Dishevelled and Gsk3β but upstream of β-catenin, which is similar to the previously reported effects of Axin1 overexpression in Xenopus embryos. Focusing on Axin in Xenopus embryos, we find that knockdown of Gtpbp2 elevates endogenous or exogenous Axin protein levels. Furthermore, Gtpbp2 fusion proteins co-localize with Dishevelled and co-immunoprecipitate with Axin and Gsk3b.

Conclusions

We conclude that Gtpbp2 is required for canonical Wnt/β-catenin signaling in Xenopus embryos. Our data suggest a model in which Gtpbp2 suppresses the accumulation of Axin protein, a rate-limiting component of the β-catenin destruction complex, such that Axin protein levels negatively correlate with Gtpbp2 levels. This model is supported by the similarity of our Gtpbp2-Wnt epistasis results and previously reported effects of Axin overexpression, the physical interactions of Gtpbp2 with Axin, and the correlation between elevated Axin protein levels and lost Wnt responsiveness upon Gtpbp2 knockdown. A wide variety of cancer-causing Wnt pathway mutations require low Axin levels, so development of Gtpbp2 inhibitors may provide a new therapeutic strategy to elevate Axin and suppress aberrant β-catenin signaling in cancer and other Wnt-related diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-016-0138-x) contains supplementary material, which is available to authorized users.

The evolving roles of canonical WNT signaling in stem cells and tumorigenesis: implications in targeted cancer therapies

The canonical WNT/β-catenin signaling pathway governs a myriad of biological processes underlying the development and maintenance of adult tissue homeostasis, including regulation of stem cell self-renewal, cell proliferation, differentiation, and apoptosis. WNTs are secreted lipid-modified glycoproteins that act as short-range ligands to activate receptor-mediated signaling pathways. The hallmark of the canonical pathway is the activation of β-catenin-mediated transcriptional activity. Canonical WNTs control the β-catenin dynamics as the cytoplasmic level of β-catenin is tightly regulated via phosphorylation by the 'destruction complex', consisting of glycogen synthase kinase 3β (GSK3β), casein kinase 1α (CK1α), the scaffold protein AXIN, and the tumor suppressor adenomatous polyposis coli (APC). Aberrant regulation of this signaling cascade is associated with varieties of human diseases, especially cancers. Over the past decade, significant progress has been made in understanding the mechanisms of canonical WNT signaling. In this review, we focus on the current understanding of WNT signaling at the extracellular, cytoplasmic membrane, and intracellular/nuclear levels, including the emerging knowledge of cross-talk with other pathways. Recent progresses in developing novel WNT pathway-targeted therapies will also be reviewed. Thus, this review is intended to serve as a refresher of the current understanding about the physiologic and pathogenic roles of WNT/β-catenin signaling pathway, and to outline potential therapeutic opportunities by targeting the canonical WNT pathway.

Disinhibition of the HECT E3 ubiquitin ligase WWP2 by polymerized Dishevelled

Dishevelled is a pivot in Wnt signal transduction, controlling both β-catenin-dependent transcription to specify proliferative cell fates, and cell polarity and other non-nuclear events in post-mitotic cells. In response to Wnt signals, or when present at high levels, Dishevelled forms signalosomes by dynamic polymerization. Its levels are controlled by ubiquitylation, mediated by various ubiquitin ligases, including NEDD4 family members that bind to a conserved PPxY motif in Dishevelled (mammalian Dvl1-3). Here, we show that Dvl2 binds to the ubiquitin ligase WWP2 and unlocks its ligase activity from autoinhibition. This disinhibition of WWP2 depends on several features of Dvl2 including its PPxY motif and to a lesser extent its DEP domain, but crucially on the ability of Dvl2 to polymerize, indicating that WWP2 is activated in Wnt signalosomes. We show that Notch intracellular domains are substrates for Dvl-activated WWP2 and their transcriptional activity is consequently reduced, providing a molecular mechanism for cross-talk between Wnt and Notch signalling. These regulatory interactions are conserved in Drosophila whose WWP2 orthologue, Suppressor-of-deltex, downregulates Notch signalling upon activation by Dishevelled in developing wing tissue. Attentuation of Notch signalling by Dishevelled signalosomes could be important during the transition of cells from the proliferative to the post-mitotic state.

Regulation of endogenous transmembrane receptors through optogenetic Cry2 clustering

Transmembrane receptors are the predominant conduit through which cells sense and transduce extracellular information into intracellular biochemical signals. Current methods to control and study receptor function, however, suffer from poor resolution in space and time and often employ receptor overexpression, which can introduce experimental artifacts. We report a genetically-encoded approach, termed Clustering Indirectly using Cryptochrome 2 (CLICR), for spatiotemporal control over endogenous transmembrane receptor activation, enabled through the optical regulation of target receptor clustering and downstream signaling using non-covalent interactions with engineered Arabidopsis Cryptochrome 2 (Cry2). CLICR offers a modular platform to enable photocontrol of the clustering of diverse transmembrane receptors including FGFR, PDGFR, and integrins in multiple cell types including neural stem cells. Furthermore, light-inducible manipulation of endogenous receptor tyrosine kinase (RTK) activity can modulate cell polarity and establish phototaxis in fibroblasts. The resulting spatiotemporal control over cellular signaling represents a powerful new optogenetic framework for investigating and controlling cell function and fate.

Maternal Wnt/STOP signaling promotes cell division during early Xenopus embryogenesis

During Xenopus development, Wnt signaling is thought to function first after midblastula transition to regulate axial patterning via β-catenin-mediated transcription. Here, we report that Wnt/glycogen synthase kinase 3 (GSK3) signaling functions posttranscriptionally already in mature oocytes via Wnt/stabilization of proteins (STOP) signaling. Wnt signaling is induced in oocytes after their entry into meiotic metaphase II and declines again upon exit into interphase. Wnt signaling inhibits Gsk3 and thereby protects proteins from polyubiquitination and degradation in mature oocytes. In a protein array screen, we identify a cluster of mitotic effector proteins that are polyubiquitinated in a Gsk3-dependent manner in Xenopus. Consequently inhibition of maternal Wnt/STOP signaling, but not β-catenin signaling, leads to early cleavage arrest after fertilization. The results support a novel role for Wnt signaling in cell cycle progression independent of β-catenin.

Spatio-temporal model of endogenous ROS and raft-dependent WNT/beta-catenin signaling driving cell fate commitment in human neural progenitor cells

Canonical WNT/β-catenin signaling is a central pathway in embryonic development, but it is also connected to a number of cancers and developmental disorders. Here we apply a combined in-vitro and in-silico approach to investigate the spatio-temporal regulation of WNT/β-catenin signaling during the early neural differentiation process of human neural progenitors cells (hNPCs), which form a new prospect for replacement therapies in the context of neurodegenerative diseases. Experimental measurements indicate a second signal mechanism, in addition to canonical WNT signaling, being involved in the regulation of nuclear β-catenin levels during the cell fate commitment phase of neural differentiation. We find that the biphasic activation of β-catenin signaling observed experimentally can only be explained through a model that combines Reactive Oxygen Species (ROS) and raft dependent WNT/β-catenin signaling. Accordingly after initiation of differentiation endogenous ROS activates DVL in a redox-dependent manner leading to a transient activation of down-stream β-catenin signaling, followed by continuous auto/paracrine WNT signaling, which crucially depends on lipid rafts. Our simulation studies further illustrate the elaborate spatio-temporal regulation of DVL, which, depending on its concentration and localization, may either act as direct inducer of the transient ROS/β-catenin signal or as amplifier during continuous auto-/parcrine WNT/β-catenin signaling. In addition we provide the first stochastic computational model of WNT/β-catenin signaling that combines membrane-related and intracellular processes, including lipid rafts/receptor dynamics as well as WNT- and ROS-dependent β-catenin activation. The model’s predictive ability is demonstrated under a wide range of varying conditions for in-vitro and in-silico reference data sets. Our in-silico approach is realized in a multi-level rule-based language, that facilitates the extension and modification of the model. Thus, our results provide both new insights and means to further our understanding of canonical WNT/β-catenin signaling and the role of ROS as intracellular signaling mediator.

Human neural progenitor cells offer the promising perspective of using in-vitro grown neural cell populations for replacement therapies in the context of neurodegenerative diseases, such as Parkinson’s or Huntington’s disease. However, to control hNPC differentiation within the scope of stem cell engineering, a thorough understanding of cell fate determination and its endogenous regulation is required. Here we investigate the spatio-temporal regulation of WNT/β-catenin signaling in the process of cell fate commitment in hNPCs, which has been reported to play a crucial role for the differentiation process of hNPCs. Based on a combined in-vitro and in-silico approach we demonstrate an elaborate interplay between endogenous ROS and lipid raft dependent WNT/beta-catenin signaling controlling the nuclear beta-catenin levels throughout the initial phase of neural differentiation. The stochastic multi-level computational model we derive from our experimental measurements adds to the family of existing WNT models, addressing major biochemical and spatial aspects of WNT/beta-catenin signaling that have not been considered in existing models so far. Cross validation studies manifest its predictive capability for other cells and cell lines rendering the model a suitable basis for further studies also in the context of embryonic development, developmental disorders and cancers.

Silencing dishevelled-1 sensitizes paclitaxel-resistant human ovarian cancer cells via AKT/GSK-3β/β-catenin signalling

OBJECTIVES

Expression of dishevelled-1 (DVL1) has recently been linked to cancer progression, however, its role in resistance to cancer therapy is unclear. In this study, we aimed to explore the function of DVL1 in paclitaxel-resistant human ovarian cancer cells.

MATERIALS AND METHODS

The MTT assay was used to assess effects of DVL1 silencing on sensitivity of cells that were otherwise resistant to paclitaxel (Taxol). Western blotting and immunofluorescence staining were used to examine effects of DVL1 on AKT/GSK-3β/β-catenin signalling.

RESULTS

Dishevelled-1 was found to be over-expressed in a paclitaxel-resistant cell line derived from human ovarian cancer cell line A2780 (A2780/Taxol line) as well as parental A2780 cells. Down-regulation of DVL1 (using the inhibitor 3289-8625 or siRNA (siDVL1) against DVL1) sensitized A2780/Taxol cells to paclitaxel. Over-expression of DVL1 in A2780 cells increased protein levels of P-gp, BCRP and Bcl-2, which are known targets of β-catenin. Silencing DVL1 in A2780/Taxol cells also reduced levels of these proteins, and led to accumulation of β-catenin. In addition, DVL1 aberrantly activated AKT/GSK-3β/β-catenin signalling. Inactivation of AKT signalling attenuated DVL1-mediated inhibition of GSK-3β and accumulation of β-catenin, in both A2780 and A2780/Taxol cells.

CONCLUSIONS

Taken together, these results suggest that silencing DVL1 sensitized A2780/Taxol cells to paclitaxel, by down-regulating AKT/GSK-3β/β-catenin signalling, providing a novel strategy for chemosensitization of ovarian cancer to paclitaxel-induced cytotoxicity.

Ras-activated Dsor1 promotes Wnt signaling in Drosophila development

Wnt/Wingless (Wg) and Ras/MAPK signaling both play fundamental roles in growth, cell-fate determination, and when dysregulated, can lead to tumorigenesis. Several conflicting modes of interaction between Ras/MAPK and Wnt signaling have been identified in specific cellular contexts, causing synergistic or antagonistic effects on target genes. We find novel evidence that the dual specificity kinase MEK, Downstream of Raf1 (Dsor1), is required for Wnt signaling. Knockdown of Dsor1 results in loss of Wg target gene expression, as well as reductions in stabilized Armadillo (Arm; Drosophila β-catenin). We have identified a close physical interaction between Dsor1 and Arm, and find that catalytically inactive Dsor1 causes a reduction inactive Arm. These results suggest that Dsor1 normally counteracts the Axin-mediated destruction of Arm. We find that Ras-Dsor1 activity is independent of upstream activation by EGFR, rather it appears to be activated by the insulin-like growth factor receptor to promote Wg signaling. Together our results suggest novel crosstalk between Insulin and Wg signaling via Dsor1.

Signalosome assembly by domains undergoing dynamic head-to-tail polymerization

A key mechanism for guarding against inappropriate activation of signaling molecules is their weak affinity for effectors, which prevents them from undergoing accidental signal-transducing interactions due to fluctuations in their cellular concentration. The molecular devices that overcome these weak affinities are the signalosomes: dynamic clusters of transducing molecules assembled typically at signal-activated receptors. Signalosomes contain high local concentrations of protein-binding sites, and thus have a high avidity for their low-affinity ligands that generate signal responses. This review focuses on three domains - DIX (dishevelled and axin), PB1 (Phox and Bem1), and SAM (sterile alpha motif) - that undergo dynamic head-to-tail polymerization to assemble signalosomes and similar particles that require transient high local concentrations of protein-binding sites.

In vivo analysis of formation and endocytosis of the Wnt/β-catenin signaling complex in zebrafish embryos

After activation by Wnt/β-Catenin ligands, a multi-protein complex assembles at the clustering membrane-bound receptors and intracellular signal transducers into the so-called Lrp6-signalosome. However, the mechanism of signalosome formation and dissolution is yet not clear. Our imaging studies of live zebrafish embryos show that the signalosome is a highly dynamic structure. It is continuously assembled by Dvl2-mediated recruitment of the transducer complex to the activated receptors and partially disassembled by endocytosis. We find that, after internalization, the ligand-receptor complex and the transducer complex take separate routes. The Wnt–Fz–Lrp6 complex follows a Rab-positive endocytic path. However, when still bound to the transducer complex, Dvl2 forms intracellular aggregates. We show that this endocytic process is not only essential for ligand-receptor internalization but also for signaling. The μ2-subunit of the endocytic Clathrin adaptor Ap2 interacts with Dvl2 to maintain its stability during endocytosis. Blockage of Ap2μ2 function leads to Dvl2 degradation, inhibiton of signalosome formation at the plasma membrane and, consequently, reduction of signaling. We conclude that Ap2μ2-mediated endocytosis is important to maintain Wnt/β-catenin signaling in vertebrates.

14-3-3 and β-catenin are secreted on extracellular vesicles to activate the oncogenic Wnt pathway

Aberrant activation of the canonical Wnt signal transduction pathway is involved in a large number of human diseases. β-catenin, the key effector protein of the canonical Wnt pathway, functions in the nucleus with T-cell factor/lymphoid enhancer factor (TCF/LEF) to activate expression of Wnt target genes. Here we show that members of the 14-3-3 protein family bind disheveled-2 (Dvl-2) and glycogen synthase-3β (GSK-3β) to attenuate the interaction between GSK-3β and β-catenin. Importantly, 14-3-3 and β-catenin form "bleb-like" structures and are secreted via extracellular vesicles to induce Wnt signaling activity in target cells. Our data suggest a novel way of transducing the oncogenic Wnt signal in which β-catenin is regulated by 14-3-3ζ through the formation of "oncosomes" that contain both the 14-3-3 and β-catenin proteins.

Endocytosis and signaling during development

The development of multicellular organisms relies on an intricate choreography of intercellular communication events that pattern the embryo and coordinate the formation of tissues and organs. It is therefore not surprising that developmental biology, especially using genetic model organisms, has contributed significantly to the discovery and functional dissection of the associated signal-transduction cascades. At the same time, biophysical, biochemical, and cell biological approaches have provided us with insights into the underlying cell biological machinery. Here we focus on how endocytic trafficking of signaling components (e.g., ligands or receptors) controls the generation, propagation, modulation, reception, and interpretation of developmental signals. A comprehensive enumeration of the links between endocytosis and signal transduction would exceed the limits of this review. We will instead use examples from different developmental pathways to conceptually illustrate the various functions provided by endocytic processes during key steps of intercellular signaling.

New insights into the regulation of Axin function in canonical Wnt signaling pathway

The Wnt signaling pathway plays crucial roles during embryonic development, whose aberration is implicated in a variety of human cancers. Axin, a key component of canonical Wnt pathway, plays dual roles in modulating Wnt signaling: on one hand, Axin scaffolds the “β-catenin destruction complex” to promote β-catenin degradation and therefore inhibits the Wnt signal transduction; on the other hand, Axin interacts with LRP5/6 and facilitates the recruitment of GSK3 to the plasma membrane to promote LRP5/6 phosphorylation and Wnt signaling. The differential assemblies of Axin with these two distinct complexes have to be tightly controlled for appropriate transduction of the “on” or “off” Wnt signal. So far, there are multiple mechanisms revealed in the regulation of Axin activity, such as post-transcriptional modulation, homo/hetero-polymerization and auto-inhibition. These mechanisms may work cooperatively to modulate the function of Axin, thereby playing an important role in controlling the canonical Wnt signaling. In this review, we will focus on the recent progresses regarding the regulation of Axin function in canonical Wnt signaling.

LRP6 exerts non-canonical effects on Wnt signaling during neural tube closure

Low-density lipoprotein receptor related protein 6 (Lrp6) mutational effects on neurulation were examined using gain (Crooked tail, Lrp6(Cd)) and loss (Lrp6(-)) of function mouse lines. Two features often associated with canonical Wnt signaling, dorsal-ventral patterning and proliferation, were no different from wild-type (WT) in the Lrp6(Cd/Cd) neural tube. Lrp6(-/-) embryos showed reduced proliferation and subtle patterning changes in the neural folds. Cell polarity defects in both Lrp6(Cd/Cd) and Lrp6(-/-) cranial folds were indicated by cell shape, centrosome displacement and failure of F-actin and GTP-RhoA accumulation at the apical surface. Mouse embryonic fibroblasts (MEFs) derived from Lrp6(Cd/Cd) or Lrp6(-/-) embryos exhibited elevated and decreased RhoA basal activity levels, respectively. While ligand-independent activation of canonical Wnt signaling, bypassing Lrp-Frizzled receptors, did not activate RhoA, non-canonical Wnt5a stimulation of RhoA activity was impaired in Lrp6(-/-) MEFs. RhoA inhibition exacerbated NTDs in cultured Lrp6 knockout embryos compared with WT littermates. In contrast, a ROCK inhibitor rescued Lrp6(Cd/Cd) embryos from NTDs. Lrp6 co-immunoprecipitated with Disheveled-associated activator of morphogenesis 1 (DAAM1), a formin promoting GEF activity in Wnt signaling. Biochemical and cell biological data revealed intracellular accumulation of Lrp6(Cd) protein where interaction with DAAM1 could account for observed elevated RhoA activity. Conversely, null mutation that eliminates Lrp6 interaction with DAAM1 led to lower basal RhoA activity in Lrp6(-/-) embryos. These results indicate that Lrp6 mediates not only canonical Wnt signaling, but can also modulate non-canonical pathways involving RhoA-dependent mechanisms to impact neurulation, possibly through intracellular complexes with DAAM1.

Carboxypeptidase E: a negative regulator of the canonical Wnt signaling pathway

Aberrant activation of the canonical Wnt signal transduction pathway is involved in many diseases including cancer and is especially implicated in the development and progression of colorectal cancer. The key effector protein of the canonical Wnt pathway is β-catenin, which functions with T-cell factor/lymphoid enhancer factor to activate expression of Wnt target genes. In this study, we used a new functional screen based on cell survival in the presence of cDNAs encoding proteins that activate the Wnt pathway thus identifying novel Wnt signaling components. Here we identify carboxypeptidase E (|CPE) and its splice variant, ΔN-CPE, as novel regulators of the Wnt pathway. We show that whereas ΔN-CPE activates the Wnt signal, the full-length CPE (F-CPE) protein is an inhibitor of Wnt/β-catenin signaling. F-CPE forms a complex with the Wnt3a ligand and the Frizzled receptor. Moreover, F-CPE disrupts disheveled-induced signalosomes that are important for transducing the Wnt signal and reduces β-catenin protein levels and activity. Taken together, our data indicate that F-CPE and ΔN-CPE regulate the canonical Wnt signaling pathway negatively and positively, respectively, and demonstrate that this screening approach can be a rapid means for isolation of novel Wnt signaling components.

Optogenetic protein clustering and signaling activation in mammalian cells

We report an optogenetic method based on Arabidopsis thaliana cryptochrome 2 for rapid and reversible protein oligomerization in response to blue light. We demonstrated its utility by photoactivating the β-catenin pathway, achieving a transcriptional response higher than that obtained with the natural ligand Wnt3a. We also demonstrated the modularity of this approach by photoactivating RhoA with high spatiotemporal resolution, thereby suggesting a previously unknown mode of activation for this Rho GTPase.

Wnt/beta-catenin signaling and small molecule inhibitors

Wnt/β-catenin signaling is a branch of a functional network that dates back to the first metazoans and it is involved in a broad range of biological systems including stem cells, embryonic development and adult organs. Deregulation of components involved in Wnt/β-catenin signaling has been implicated in a wide spectrum of diseases including a number of cancers and degenerative diseases. The key mediator of Wnt signaling, β-catenin, serves several cellular functions. It functions in a dynamic mode at multiple cellular locations, including the plasma membrane, where β-catenin contributes to the stabilization of intercellular adhesive complexes, the cytoplasm where β-catenin levels are regulated and the nucleus where β-catenin is involved in transcriptional regulation and chromatin interactions. Central effectors of β-catenin levels are a family of cysteine-rich secreted glycoproteins, known as Wnt morphogens. Through the LRP5/6-Frizzled receptor complex, Wnts regulate the location and activity of the destruction complex and consequently intracellular β- catenin levels. However, β-catenin levels and their effects on transcriptional programs are also influenced by multiple other factors including hypoxia, inflammation, hepatocyte growth factor-mediated signaling, and the cell adhesion molecule E-cadherin. The broad implications of Wnt/β-catenin signaling in development, in the adult body and in disease render the pathway a prime target for pharmacological research and development. The intricate regulation of β-catenin at its various locations provides alternative points for therapeutic interventions.

Frizzled and LRP5/6 receptors for Wnt/β-catenin signaling

Frizzled and LRP5/6 are Wnt receptors that upon activation lead to stabilization of cytoplasmic β-catenin. In this study, we review the current knowledge of these two families of receptors, including their structures and interactions with Wnt proteins, and signaling mechanisms from receptor activation to the engagement of intracellular partners Dishevelled and Axin, and finally to the inhibition of β-catenin phosphorylation and ensuing β-catenin stabilization.

Inhibition of GSK3 by Wnt signalling--two contrasting models

The key read-out of Wnt signalling is a change in the transcriptional profile of the cell, which is driven by β-catenin. β-catenin levels are normally kept low by a phosphorylation event that is mediated by glycogen synthase kinase 3 (GSK3, α- and β-isoforms), which targets β-catenin for ubiquitylation and proteasomal degradation. Wnt blocks this phosphorylation event, thereby allowing β-catenin to accumulate and to co-activate transcription in the nucleus. Exactly how Wnt inhibits GSK3 activity towards β-catenin is unclear and has been the focus of intensive research. Recent studies on the role of conserved PPPSPxS motifs in the cytoplasmic tail of low-density lipoprotein receptor-related protein (LRP, isoforms 5 and 6) culminated in a biochemical model: Wnt induces the phosphorylation of LRP6 PPPSPxS motifs, which consequently access the catalytic pocket of GSK3 as pseudo-substrates, thus directly blocking its activity against β-catenin. A distinct cell-biological model was proposed more recently: Wnt proteins induce the uptake of GSK3 into multivesicular bodies (MVBs), an event that sequesters the enzyme away from newly synthesised β-catenin substrate in the cytoplasm, thus blocking its phosphorylation. This new model is based on intriguing observations but also challenges a body of existing evidence, so will require further experimental consolidation. We shall consider whether the two models apply to different modes of Wnt signaling: acute versus chronic.

Endocytic control of growth factor signalling: multivesicular bodies as signalling organelles

Signal transduction and endocytosis are intertwined processes. The internalization of ligand-activated receptors by endocytosis has classically been thought to attenuate signals by targeting receptors for degradation in lysosomes, but it can also maintain signals in early signalling endosomes. In both cases, localization to multivesicular endosomesen route to lysosomes is thought to terminate signalling. However, during WNT signal transduction, sequestration of the enzyme glycogen synthase kinase 3 (GSK3) inside multivesicular endosomes results in the stabilization of many cytosolic proteins. Thus, the role of endocytosis during signal transduction may be more diverse than anticipated, and multivesicular endosomes may constitute a crucial signalling organelle.

Functional dissection of phosphorylation of Disheveled in Drosophila

Disheveled/Dsh proteins (Dvl in mammals) are core components of both Wnt/Wg-signaling pathways: canonical β-catenin signaling and Frizzled (Fz)-planar cell polarity (PCP) signaling. Although Dsh is a key cytoplasmic component of both Wnt/Fz-pathways, regulation of its signaling specificity is not well understood. Dsh is phosphorylated, but the functional significance of its phosphorylation remains unclear. We have systematically investigated the phosphorylation of Dsh by combining mass-spectrometry analyses, biochemical studies, and in vivo genetic methods in Drosophila. Our approaches identified multiple phospho-residues of Dsh in vivo. Our data define three novel and unexpected conclusions: (1) strikingly and in contrast to common assumptions, all conserved serines/threonines are non-essential for Dsh function in either pathway; (2) phosphorylation of conserved Tyrosine473 in the DEP domain is critical for PCP-signaling - Dsh(Y473F) behaves like a PCP-specific allele; and (3) defects associated with the PCP specific dsh(1) allele, Dsh(K417M), located within a putative Protein Kinase C consensus site, are likely due to a post-translational modification requirement of Lys417, rather than phosphorylation nearby. In summary, our combined data indicate that while many Ser/Thr and Tyr residues are indeed phosphorylated in vivo, strikingly most of these phosphorylation events are not critical for Dsh function with the exception of DshY473.

Rad6B acts downstream of Wnt signaling to stabilize β-catenin: Implications for a novel Wnt/β-catenin target

BACKGROUND

Aberrant Wnt/β-catenin signaling is associated with breast cancer even though genetic mutations in Wnt signaling components are rare. We have previously demonstrated that Rad6B, an ubiquitin conjugating enzyme, stabilizes β-catenin via polyubiqutin modifications that render β-catenin insensitive to proteasomal degradation. Rad6B is a transcriptional target of β-catenin, creating a positive feedback loop between Rad6B expression and β-catenin activation.

METHODS

To isolate subpopulations expressing high or low Rad6B levels, we transfected MDA-MB-231 or WS-15 human breast cancer cells with ZsGreen fluorescent reporter vector in which the expression of ZsGreen was placed under the control of Rad6B promoter. ZsGreenhigh and ZsGreenlow subpopulations, reflective of high and low Rad6B promoter activity, respectively, were isolated by FACS. To determine the relevance of Wnt signaling in Rad6B-mediated β-catenin stabilization/activation, the ZsGreenhigh cells were transfected with signaling-defective Wnt coreceptor LRP6Δ173. Rad6B expression and promoter activity were determined by RT-PCR, Western blot and Rad6B promoter-mediated luciferase assays. β-catenin levels and transcriptional activity were determined by Western blot and TOP/FOP Flash reporter assays. Tumor formation and morphologies of ZsGreenlow, ZsGreenhigh, and ZsGreenhigh/LRP6Δ173 cells compared to unsorted vector controls were evaluated in nude mice. Expression of Wnt signaling related genes was profiled using the Wnt signaling pathway RT2 Profiler PCR arrays.

RESULTS

ZsGreenhigh subpopulations showed high Rad6B expression and Rad6B promoter activity as compared to ZsGreenlow cells. ZsGreenhigh (high Rad6B expressors) also showed elevated β-catenin levels and TOP/Flash activity. Inhibiting Wnt signaling in the high Rad6B expressors decreased ZsGreen fluorescence, Rad6B gene expression, β-catenin levels and TOP/Flash activity. Tumors derived from high Rad6B expressors were predominantly composed of cells with epithelial mesenchymal transition (EMT) phenotype as compared to control tumors that were composed of both cuboidal and EMT-type cells. Tumors derived from low Rad6B expressors lacked EMT phenotype. Inhibition of LRP6 function in the high Rad6B expressors abrogated the EMT phenotype. Gene expression profiling showed upregulation of several Wnt signaling pathway regulators in high Rad6B expressors that were downregulated by interference of Wnt signaling with mutant LRP6 or by Rad6B silencing.

CONCLUSIONS

These data reveal a functional link between the canonical Wnt pathway and Rad6B in β-catenin activation and breast cancer progression.

Transmembrane protein 198 promotes LRP6 phosphorylation and Wnt signaling activation

Wnt/β-catenin signaling is fundamental in embryogenesis and tissue homeostasis in metazoans. Upon Wnt stimulation, cognate coreceptors LRP5 and LRP6 ([LRP5/6] low-density lipoprotein receptor-related proteins 5 and 6) are activated via phosphorylation at key residues. Although several kinases have been implicated, the LRP5/6 activation mechanism remains unclear. Here, we report that transmembrane protein 198 (TMEM198), a previously uncharacterized seven-transmembrane protein, is able to specifically activate LRP6 in transducing Wnt signaling. TMEM198 associates with LRP6 and recruits casein kinase family proteins, via the cytoplasmic domain, to phosphorylate key residues important for LRP6 activation. In mammalian cells, TMEM198 is required for Wnt signaling and casein kinase 1-induced LRP6 phosphorylation. During Xenopus embryogenesis, maternal and zygotic tmem198 mRNAs are widely distributed in the ectoderm and mesoderm. TMEM198 is required for Wnt-mediated neural crest formation, antero-posterior patterning, and particularly engrailed-2 expression in Xenopus embryos. Thus, our results identified TMEM198 as a membrane scaffold protein that promotes LRP6 phosphorylation and Wnt signaling activation.

Cortical localization of APC2 plays a role in actin organization but not in Wnt signaling in Drosophila

The tumor suppressor Adenomatous polyposis coli (APC) has roles in both Wnt signaling and in actin and microtubule organization. Within the cell, APC proteins have been reported to localize in the cytoplasm, at the cell cortex and in the nucleus. How these localizations relate to the functions of the protein is an aspect of APC biology that is poorly understood. Using Drosophila S2 cells, we have dissected the structural and functional requirements for the cortical localization of Drosophila APC2. Here, we show that both the Armadillo repeats and a novel C-terminal domain are necessary for the cortical localization of APC2 in S2 cells and in the embryo, and that neither domain alone is sufficient for this localization. Furthermore, we show that the Armadillo repeats mediate self-association of APC2 molecules. To test the function of the cortical localization of APC2, we asked whether an APC2 protein deleted for the C-terminal localization domain could rescue APC mutant defects in Wnt signaling and actin organization in the Drosophila embryo. We show that although cortical localization is required for the APC2 function in organizing actin, cortical localization is dispensable for its role in regulating Wnt signaling.

Dishevelled interacts with the DIX domain polymerization interface of Axin to interfere with its function in down-regulating β-catenin

Wnt/β-catenin signaling controls numerous steps in normal animal development and can also cause cancer if inappropriately activated. In the absence of Wnt, β-catenin is targeted continuously for proteasomal degradation by the Axin destruction complex, whose activity is blocked upon Wnt stimulation by Dishevelled, which recruits Axin to the plasma membrane and assembles it into a signalosome. This key event during Wnt signal transduction depends on dynamic head-to-tail polymerization by the DIX domain of Dishevelled. Here, we use rescue assays in Drosophila tissues and functional assays in human cells to show that polymerization-blocking mutations in the DIX domain of Axin disable its effector function in down-regulating Armadillo/β-catenin and its response to Dishevelled during Wnt signaling. Intriguingly, NMR spectroscopy revealed that the purified DIX domains of the two proteins interact with each other directly through their polymerization interfaces, whereby the same residues mediate both homo- and heterotypic interactions. This result implies that Dishevelled has the potential to act as a "natural" dominant-negative, binding to the polymerization interface of Axin's DIX domain to interfere with its self-assembly, thereby blocking its effector function.

Probing the physical nature and composition of signalsomes

Background

Recent advances in our understanding of cell signaling have revealed assemblies of signaling components often viewed in fluorescence microscopy as very large, irregular "punctae". These punctae are often dynamic in nature, appearing to act as mobile scaffolds that function in integrating protein-protein interactions from large arrays of signaling components. The visualization of these punctae, termed "signalsomes" when applied to protein assemblies involved in cell signaling provokes the question, what is the physical nature of these structures made visible in live cells through the expression of fluorescently-tagged fusion molecules?

Results

Steric-exclusion chromatography on wide-bore matrices, fluorescence correlation spectroscopy, and advanced proteomics permits the analysis of several important physical properties of signalsomes. Wnt canonical signaling is essential to normal cell development and dysregulation can lead to cancers in humans. Punctae/signalsomes have been reported based upon the study of fluorescently-tagged mammalian Dishevelleds. Dishevelleds are phosphoprotein scaffolds that demonstrate dynamic character and mobility in cells stimulated with Wnt3a. Recent studies have successfully isolated Dvl3-based signalsomes from mouse totipotent embryonic teratocarcinoma F9 cells in culture and sized by application of steric exclusion chromatography (SEC), displaying large discrete M_r (0.5 and 2 MDa). Activation of the Wnt canonical β-catenin/LEF-Tcf-sensitive transcriptional response leads to an upfield shift of >5 MDa of the Dvl3-based signalsome. Fluorescence correlation spectroscopy (fcs) is a single molecule analysis performed in live cells that experimentally measures the diffusion coefficient and permits calculation of MW of the signalsome (0.2 and 30 MDa species in vivo), which also reveal an upfield shift in MW in response to Wnt3a. Proteomics provides for molecular dissection of the composition of the signalsome isolated from untreated and Wnt3a-treated cells.

Conclusion

Dvl3-based punctae/signalsomes made visible by fluorescent microscopy now can be interrogated by advanced physical means, defining such properties as signalsome M_r/MW, molecular composition, and intracellular locale.

Wnt signaling requires sequestration of glycogen synthase kinase 3 inside multivesicular endosomes

Canonical Wnt signaling requires inhibition of Glycogen Synthase Kinase 3 (GSK3) activity, but the molecular mechanism by which this is achieved remains unclear. Here, we report that Wnt signaling triggers the sequestration of GSK3 from the cytosol into multivesicular bodies (MVBs), so that this enzyme becomes separated from its many cytosolic substrates. Endocytosed Wnt colocalized with GSK3 in acidic vesicles positive for endosomal markers. After Wnt addition, endogenous GSK3 activity decreased in the cytosol, and GSK3 became protected from protease treatment inside membrane-bounded organelles. Cryoimmunoelectron microscopy showed that these corresponded to MVBs. Two proteins essential for MVB formation, HRS/Vps27 and Vps4, were required for Wnt signaling. The sequestration of GSK3 extended the half-life of many other proteins in addition to β-Catenin, including an artificial Wnt-regulated reporter protein containing GSK3 phosphorylation sites. We conclude that multivesicular endosomes are essential components of the Wnt signal-transduction pathway.

Canonical and noncanonical Wnts use a common mechanism to activate completely unrelated coreceptors

Wnt ligands signal through β-catenin and are critically involved in cell fate determination and stem/progenitor self-renewal. Wnts also signal through β-catenin-independent or noncanonical pathways that regulate crucial events during embryonic development. The mechanism of noncanonical receptor activation and how Wnts trigger canonical as opposed to noncanonical signaling have yet to be elucidated. We demonstrate here that prototype canonical Wnt3a and noncanonical Wnt5a ligands specifically trigger completely unrelated endogenous coreceptors-LRP5/6 and Ror1/2, respectively-through a common mechanism that involves their Wnt-dependent coupling to the Frizzled (Fzd) coreceptor and recruitment of shared components, including dishevelled (Dvl), axin, and glycogen synthase kinase 3 (GSK3). We identify Ror2 Ser 864 as a critical residue phosphorylated by GSK3 and required for noncanonical receptor activation by Wnt5a, analogous to the priming phosphorylation of low-density receptor-related protein 6 (LRP6) in response to Wnt3a. Furthermore, this mechanism is independent of Ror2 receptor Tyr kinase functions. Consistent with this model of Wnt receptor activation, we provide evidence that canonical and noncanonical Wnts exert reciprocal pathway inhibition at the cell surface by competition for Fzd binding. Thus, different Wnts, through their specific coupling and phosphorylation of unrelated coreceptors, activate completely distinct signaling pathways.

The various roles of ubiquitin in Wnt pathway regulation

Wnt signaling mediates key developmental and homeostatic processes including stem cell maintenance, growth and cell fate specification, cell polarity and migration. Inappropriate activation of Wnt signaling is linked to a range of human disorders, most notably cancer and neurodegenerative diseases. In the Wnt/β-catenin cascade, signaling events converge on the regulation of ubiquitin-mediated degradation of the crucial transcriptional regulator β-catenin. The emerging mechanisms by which ubiquitin modification of proteins controls cellular pathways comprise both proteolytic and nonproteolytic functions. In nonproteolytic functions, ubiquitin acts as a signaling device in the control of protein activity, subcellular localization and complex formation. Here, we review and discuss recent developments that implicate ubiquitin-mediated mechanisms at multiple steps of Wnt pathway activation.

Dvl2 promotes intestinal length and neoplasia in the ApcMin mouse model for colorectal cancer

APC mutations cause activation of Wnt/beta-catenin signaling, which invariably leads to colorectal cancer. Similarly, overexpressed Dvl proteins are potent activators of beta-catenin signaling. Screening a large tissue microarray of different staged colorectal tumors by immunohistochemistry, we found that Dvl2 has a strong tendency to be overexpressed in colorectal adenomas and carcinomas, in parallel to nuclear beta-catenin and Axin2 (a universal transcriptional target of Wnt/beta-catenin signaling). Furthermore, deletion of Dvl2 reduced the intestinal tumor numbers in a dose-dependent way in the Apc(Min) model for colorectal cancer. Interestingly, the small intestines of Dvl2 mutants are shortened, reflecting in part a reduction of their crypt diameter and cell size. Consistent with this, mammalian target of rapamycin (mTOR) signaling is highly active in normal intestinal crypts in which Wnt/beta-catenin signaling is active, and activated mTOR signaling (as revealed by staining for phosphorylated 4E-BP1) serves as a diagnostic marker of Apc(Min) mutant adenomas. Inhibition of mTOR signaling in Apc(Min) mutant mice by RAD001 (everolimus) reduces their intestinal tumor load, similarly to Dvl2 deletion. mTOR signaling is also consistently active in human hyperplastic polyps and has a significant tendency for being active in adenomas and carcinomas. Our results implicate Dvl2 and mTOR in the progression of colorectal neoplasia and highlight their potential as therapeutic targets in colorectal cancer.