Inhibition Of Canonical Wnt Signaling Research Articles

Chemical Genetics Reveals a Role of dCTP Pyrophosphatase 1 in Wnt Signaling

AbstractCell‐based screening is a powerful approach to identify novel chemical modulators and biological components of relevant biological processes. The canonical Wnt pathway is essential for normal embryonic development and tissue homeostasis, and its deregulation plays a crucial role in carcinogenesis. Therefore, the identification of new pathway members and regulators is of significant interest. By means of a cell‐based assay monitoring Wnt signaling we identified the pyrrolocoumarin Pyrcoumin as inhibitor of canonical Wnt signaling. Target identification and validation revealed that Pyrcoumin is a competitive inhibitor of dCTP pyrophosphatase 1 (dCTPP1). We demonstrate a yet unknown interaction of dCTPP1 with ubiquitin carboxyl‐terminal hydrolase (USP7) that is counteracted by dCTPP1 inhibitors. These findings indicate that dCTPP1 plays a role in regulation of Wnt/β‐catenin signaling most likely through a direct interaction with USP7.

Chemical Genetics Reveals a Role of dCTP Pyrophosphatase 1 in Wnt Signaling.

Cell-based screening is a powerful approach to identify novel chemical modulators and biological components of relevant biological processes. The canonical Wnt pathway is essential for normal embryonic development and tissue homeostasis, and its deregulation plays a crucial role in carcinogenesis. Therefore, the identification of new pathway members and regulators is of significant interest. By means of a cell-based assay monitoring Wnt signaling we identified the pyrrolocoumarin Pyrcoumin as inhibitor of canonical Wnt signaling. Target identification and validation revealed that Pyrcoumin is a competitive inhibitor of dCTP pyrophosphatase 1 (dCTPP1). We demonstrate a yet unknown interaction of dCTPP1 with ubiquitin carboxyl-terminal hydrolase (USP7) that is counteracted by dCTPP1 inhibitors. These findings indicate that dCTPP1 plays a role in regulation of Wnt/β-catenin signaling most likely through a direct interaction with USP7.

Abstract 1894: Canonical Wnt-associated extracellular matrix in adrenocortical carcinoma

Abstract Adrenocortical carcinoma (ACC) is a rare and often aggressive cancer that affects 1-2 people per million in the United States annually. Genomic alterations activating canonical Wnt signaling occur in approximately 40% of ACCs and are associated with poor prognosis. However, the biological consequences of constitutive canonical Wnt activation in ACC are poorly understood. To better characterize the transcriptional programs that are engaged in ACC, we performed independent component analysis on The Cancer Genome Atlas (TCGA) ACC transcriptome dataset to identify components of coordinately expressed genes. One of the components identified was significantly enriched for Wnt signaling (p = 0.001) and was strongly associated with somatic CTNNB1 (β-catenin) mutations (p = 2.276e-07). Interestingly, this Wnt-enriched component also showed enrichment for extracellular matrix (ECM)-receptor interaction (p = 0.00139), including (but not restricted to) expression of COL11A1 (Collagen alpha-1(XI)), LAMC3 (Laminin, gamma 3), and ITGA2 (Integrin, alpha 2), suggesting that Wnt signaling is regulating cell-ECM interactions and ECM composition in ACC. To follow up on this observation, we performed immunohistochemical staining on tissue microarrays (TMAs) containing 97 ACC samples. We observed a strong correlation of COL11A1 expression and nuclear β-catenin localization (p = 0.0088), suggesting COL11A1 expression may be regulated by canonical Wnt signaling. Furthermore, COL11A1 expression was associated with decreased overall survival (p = 0.0003) and decreased event-free survival (p = 0.0075). To determine whether ECM and ECM-receptor genes are regulated by canonical Wnt activity, the NCI-H295R human ACC cell line, harboring an activating CTNNB1 mutation, was used. Cells were treated with PKF115-584, an inhibitor of canonical Wnt signaling that disrupts β-catenin interaction with TCF/LEF transcription factors. PKF115-584 treatment significantly reduced expression of COL11A1, LAMC3, and ITGA2 in NCI-H295R cells at early timepoints (p≤0.05), consistent with our hypothesis that canonical Wnt signaling regulates expression of ECM components in ACC. At late timepoints following PKF115-584 treatment, NCI-H295R cell viability decreased, indicating that canonical Wnt activity may regulate cell survival in ACC. These results illustrate a novel role for canonical Wnt activity in ACC, and suggest that β-catenin-regulated transcription of ECM and ECM-receptor components may promote cancer cell survival and aggressive disease. Future studies are aimed at characterizing the contribution of extracellular proteins to ACC phenotypes. Citation Format: Morgan K. Penny, Antonio M. Lerario, Chris LaPensee, Thomas J. Giordano, Gary D. Hammer. Canonical Wnt-associated extracellular matrix in adrenocortical carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1894.

Abstract 1832: Ligand-dependent Wnt signaling directs metabolic adaptations to promote pancreatic tumorigenesis

Abstract Wnt/β-catenin signaling plays important roles in pancreatic adenocarcinoma (PDA) tumor initiation and progression via broad-ranging effects on proliferation, differentiation, survival, and stemness. Although Wnt has been shown to promote glycolysis in colon cancer, its role in regulating metabolism in PDA has not been explored in any detail. For this study, the AsPC-1 cell line was selected as an exemplar of ligand-dependent autocrine Wnt signaling in PDA. AsPC-1 harbors an inactivating mutation in RNF43 that confers Wnt growth-dependency and response to LGK974, a PORCN inhibitor that blocks Wnt ligand secretion and signaling. Global transcriptomic, proteomic, and metabolomic analysis revealed several metabolites and putative mediators of metabolism that are directly or indirectly linked to autocrine Wnt signaling in AsPC-1. In contrast to colon cancer, pharmacologic inhibition of Wnt by LGK974 in AsPC-1 led to the accumulation of pyruvate and lactate, as well as reduced tricarboxylic acid cycle metabolites and decreased mitochondrial membrane potential as measured by tetramethylrhodamine assay. These metabolic changes were accompanied by cell cycle arrest and downregulation of transcriptional programs involved in cell cycle progression, DNA replication, and nucleotide metabolism. Pyruvate analogs dichloroacetate and oxamate, that respectively target pyruvate dehydrogenase kinase and lactate dehydrogenase, restored mitochondrial membrane potential in the context of LGK974. Importantly, LGK974 results were phenocopied by siRNA-mediated knockdown of WNT7B. Thus, inhibition of mitochondrial oxidative phosphorylation by LGK974 in RNF43-mutant PDA appears mechanistically linked to its inhibition of canonical Wnt signaling, an adaptation and potential metabolic vulnerability that could be leveraged to therapeutic advantage via combinatorial strategies. Altogether, these results suggest tissue context and differing mechanisms of Wnt pathway activation or signal strength may profoundly influence its role in regulating cancer metabolism. Citation Format: Kristina Y. Aguilera, Rana Riahi, Edris A. Saadat, Anna R. Lay, Thuc Le, Anthony Cabebe, Timothy R. Donahue, Caius Radu, David W. Dawson. Ligand-dependent Wnt signaling directs metabolic adaptations to promote pancreatic tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1832.

Inhibition of CBP/\u03b2-catenin and porcupine attenuates Wnt signaling and induces apoptosis in head and neck carcinoma cells

PurposeActivation of the Wnt pathway contributes to the development of head and neck squamous cell carcinomas (HNSCC) and its inhibition has recently emerged as a promising therapeutic strategy. Here, we aimed at identifying suitable molecular targets for down-regulation of canonical Wnt signaling in HNSCC cells.MethodsCandidate target genes (PORCN, WNT3A, FZD2, FZD5, LRP5, DVL1, CIP2A, SET, KDM1A, KDM4C, KDM6A, CBP, CARM1, KMT2A, TCF7, LEF1, PYGO1, XIAP) were silenced using siRNA and selected targets were subsequently blocked using small molecule inhibitors. The effect of this treatment on the expression of β-catenin-dependent genes was assessed by qRT-PCR. The effect of the inhibitors on cell viability was evaluated using a resazurin assay in HNSCC-derived cell lines. A luciferase reporter assay was used for confirmation of the inhibition of Wnt-dependent gene expression. Cell migration was evaluated using a scratch wound healing assay. Cytometric analysis of propidium iodide stained cells was used for cell cycle distribution evaluation, whereas cytometric analysis of caspase 3/7 activity was used for apoptosis induction evaluation.ResultsWe found that inhibition of Porcupine and CBP/β-catenin interaction by IWP-2 and PRI-724, respectively, most strongly affected β-catenin-dependent gene expression in HNSCC cells. These inhibitors also induced apoptosis and affected HNSCC cell migration.ConclusionsTargeting Porcupine or the CBP/β-catenin interaction seems to be an effective strategy for the inhibition of canonical Wnt signaling in HNSCC cells. Further studies are required to confirm the possible therapeutic effect of IWP-2 and PRI-724 in HNSCC.

New roles for Wnt and BMP signaling in neural anteroposterior patterning.

During amphibian development, neural patterning occurs via a two-step process. Spemann's organizer secretes BMP antagonists that induce anterior neural tissue. A subsequent caudalizing step re-specifies anterior fated cells to posterior fates such as hindbrain and spinal cord. The neural patterning paradigm suggests that a canonical Wnt-signaling gradient acts along the anteroposterior axis to pattern the nervous system. Wnt activity is highest in the posterior, inducing spinal cord, at intermediate levels in the trunk, inducing hindbrain, and is lowest in anterior fated forebrain, while BMP-antagonist levels are constant along the axis. Our results in Xenopus laevis challenge this paradigm. We find that inhibition of canonical Wnt signaling or its downstream transcription factors eliminates hindbrain, but not spinal cord fates, an observation not compatible with a simple high-to-low Wnt gradient specifying all fates along the neural anteroposterior axis. Additionally, we find that BMP activity promotes posterior spinal cord cell fate formation in an FGF-dependent manner, while inhibiting hindbrain fates. These results suggest a need to re-evaluate the paradigms of neural anteroposterior pattern formation during vertebrate development.

Inducible Dickkopf 1-mediated inhibition of canonical Wnt signaling ameliorates cartilage destruction during experimental osteoarthritis

Inducible Dickkopf 1-mediated inhibition of canonical Wnt signaling ameliorates cartilage destruction during experimental osteoarthritis

Muscle‐Specific Over‐Expression of the NAD+‐Dependent Nuclear Sirtuin SIRT6, Suppresses Cancer‐Associated Cachexia

IntroductionInvoluntary loss of muscle mass, termed as cachexia, is associated with many terminal diseases. Almost 30% of cancer patients succumb to death due to cachexia rather than to the primary disease itself. Earlier we had observed that mice deficient for SIRT6, a chromatin‐associated lysine deacylase had reduced muscle mass and degenerative changes in their muscles, such as induction of fibrosis and infiltration of inflammatory cells. We have reported that SIRT6 down‐regulated myostatin (Mstn) expression, a major negative regulator of muscle growth and differentiation, by attenuating NF‐κB binding to Mstn promoter. The present study was undertaken to explore the possibility whether muscle‐specific overexpression of SIRT6 could have dual benefit in suppressing cancer‐associated cachexia as well as retarding tumor growth.MethodsImmunoblotting, RT‐qPCR, histology, plasma cytokine profiling and ELISA assays were carried out to assess effect of SIRT6 overexpression in tumor‐induced muscle samples.ResultsWe generated Rosa26‐Fl‐STOP‐SIRT6‐Flag mice and crossed them with Myl1tm1(cre)Sjb mice to obtain skeletal muscle‐specific overexpression of SIRT6. Two‐month old control (SIRT6‐endogenous) and SIRT6 muscle‐specific overexpresser male mice were injected, subcutaneously, with B16F10 mouse melanoma cells. After 14 days, when tumor dimensions reached 2 cm in control mice, gastrocnemius muscles were harvested for further analysis. Skeletal muscle‐specific overexpression of SIRT6 was confirmed by immuno‐blotting. Skeletal muscle‐specific overexpression of SIRT6 reduced tumor volume significantly (40% reduction, n=7, p<0.01) and increased muscle mass by five‐fold in the melanoma‐challenged male mice, compared to tumor‐bearing controls (n=10). Mstn protein expression was reduced significantly (p<0.001) with SIRT6 overexpression in muscles. H&E staining of the gastrocnemius muscle revealed that SIRT6 overexpression aided in maintaining the cross‐sectional diameter of muscle fibers in tumor‐bearing mice. We also observed that plasma insulin levels, which were downregulated in control tumor‐bearing mice, were upregulated significantly (p<0.005) by skeletal muscle‐specific overexpression of SIRT6. Our results indicate that muscle‐specific overexpression of SIRT6 influences multiple targets to suppress tumor growth as well as associated muscle loss. It normalizes insulin secretion by down‐regulating WNT4, a canonical Wnt signaling inhibitor, as well as CXCL10, an interferon‐inducible circulating inflammatory chemokine, both reported to be negative regulators of beta‐cell function.ConclusionsInsulin supplementation is shown to slow down tumor growth, and cancer‐induced muscle wasting. Our results indicate that moderate overexpression of SIRT6 protects mice from developing cancer‐cachexia in two ways: by impeding tumor growth and attenuating tumor‐induced muscle degeneration. Therefore, SIRT6 could be a novel target for drug design.Support or Funding InformationRO1 HL‐136712This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

SFRP1 exerts effects on gastric cancer cells through GSK3β/Rac1‑mediated restraint of TGFβ/Smad3 signaling.

Secreted frizzled-related protein 1 (sFRP1) is an inhibitor of canonical Wnt signaling; however, previous studies have determined a tumor-promoting function of sFRP1 in a number of different cancer types. A previous study demonstrated that sFRP1 overexpression was associated with an aggressive phenotype and the activation of transforming growth factor β (TGFβ) signaling. sFRP1 overexpression and sFRP1 knockdown cell models were established. Immunoblotting was conducted to examine the protein levels of the associated molecules. Immunofluorescence staining followed by confocal microscopy was performed to visualize the cytoskeleton alterations and subcellular localization of key proteins. sFRP1 overexpression restored glycogen synthase kinase 3β (GSK3β) activity, which activated Rac family small GTPase 1 (Rac1). GSK3β and Rac1 mediated the effect of sFRP1 on the positive regulation of cell growth and migration/invasion. Inhibition of GSK3β or Rac1 abolished the regulation of sFRP1 on TGFβ/SMAD family member 3 (Smad3) signaling and the aggressive phenotype; however, GSK3β or Rac1 overexpression increased cell migration/invasion and restrained Smad3 activity by preventing its nuclear translocation and limiting its transcriptional activity. The present study demonstrated a tumor-promoting function of sFRP1-overexpression by selectively activating TGFβ signaling in gastric cancer cells. GSK3β and Rac1 serve an important function in mediating the sFRP1-induced malignant alterations and signaling changes.

Endocytic trafficking factor VPS45 is essential for spatial regulation of lens fiber differentiation in zebrafish.

ABSTRACTIn vertebrate lens, lens epithelial cells cover the anterior half of the lens fiber core. Lens epithelial cells proliferate, move posteriorly and start to differentiate into lens fiber cells at the lens equator. Although FGF signaling promotes this equatorial commencement of lens fiber differentiation, the underlying mechanism is not fully understood. Here, we show that lens epithelial cells abnormally enter lens fiber differentiation without passing through the equator in zebrafish vps45 mutants. VPS45 belongs to the Sec1/Munc18-like protein family and promotes endosome trafficking, which differentially modulates signal transduction. Ectopic lens fiber differentiation in vps45 mutants does not depend on FGF, but is mediated through activation of TGFβ signaling and inhibition of canonical Wnt signaling. Thus, VPS45 normally suppresses lens fiber differentiation in the anterior region of lens epithelium by modulating TGFβ and canonical Wnt signaling pathways. These data indicate a novel role of endosome trafficking to ensure equator-dependent commencement of lens fiber differentiation.

Antagonistic role of Klotho-derived peptides dynamics in the pancreatic cancer treatment through obstructing WNT-1 and Frizzled binding

Klotho is an anti-aging protein that is engaged in the suppression of canonical WNT signaling. In this study, we investigated the expression pattern of human WNTs and Klotho in the pancreatic cancer. In the cancerous cells, WNT-1 exhibited much higher expression as compared to other WNTs, while no WNT expression was detected in the normal tissue. In contrast, Klotho expression was significantly low in the cancerous tissue. Based on these observations, we intended to explore Klotho binding to WNT-1 and cystein-rich domains (CRDs) of Frizzled (FZD) homologs through molecular docking and dynamics simulation assays. Interestingly, similar region of WNT-1 was detected in binding with Klotho and CRDs of FZD-1/2. FZD-CRDs were grasped by the association of peripheral hydrophobic residues of WNT-1 U-shaped cavity. Subsequently, WNT-1-bound Klotho-peptides were isolated and reevaluated for their binding abilities against WNT-1 and FZD-CRDs., The conformational readjustements of these complexes were deeply analyzed by calculating the size of WNT-1 U-shaped cavity. In comparison to apo-WNT-1, cavity opening was markedly enhanced (8.2 Å to 15.64 Å, 32.89 Å and 35.11 Å) in WNT-1-a, WNT-1-c and WNT-1-e complexes, respectively. Thus Klotho-derived peptides may facilitate distinct conformational changes in the WNT-1-FZD associated region. As a result, aberrant loss of FZD binding may lead to augment WNT signaling. Overall, current study opens up new avenues in the pancreatic cancer therapeutics through antagonizing WNT-1 by Klotho.

Klotho expression is a prerequisite for proper muscle stem cell function and regeneration of skeletal muscle

BackgroundKlotho is a well-known anti-aging hormone, which serves as a suppressor of aging through a variety of mechanisms. Aging of skeletal muscle is concomitant with a decrease in muscle stem cell function resulting in impaired regeneration.MethodsHere we investigate the functional role of the anti-aging hormone Klotho for muscle stem cell function after cardiotoxin-induced injury of skeletal muscle using a klotho hypomorphic mouse line, which is characterized by a premature aging phenotype. Furthermore, we perform floating single myofiber cultures with their adjacent muscle stem cells to investigate the interplay between canonical Wnt signaling and Klotho function.ResultsWe demonstrate that muscle stem cell numbers are significantly decreased in klotho hypomorphic mice. Furthermore, we show that muscle stem cell function is also severely impaired upon loss of klotho expression, in culture and during regeneration in vivo. Moreover, we demonstrate that addition of recombinant Klotho protein inhibits aberrant excessive Wnt signaling in aged muscle stem cells thereby restoring their functionality.ConclusionsThe anti-aging hormone Klotho counteracts aberrant canonical Wnt signaling in muscle stem cells and might be one of the naturally occurring inhibitors of canonical Wnt signaling in skeletal muscle.

Abstract 4508: Glypican-3 (GPC3) signaling pathway involved in breast cancer progression

Abstract GPC3 is a proteoglycan downregulated in breast tumors. Employing LM3 murine mammary adenocarcinoma cell line (ER-, PR-), we have previously shown that GPC3 acts as a metastasis suppressor and induces a reversion of the epithelial to mesenchymal transition (EMT). GPC3 overexpressing LM3 cells presented an inhibition of canonical Wnt and Akt pathways. On the other hand, non-canonical Wnt (JNK) and p38 signaling were activated. However, the hierarchical sequence through which GPC3 modulates those pathways has not been determined yet.The aim of this work was to study the molecular mechanism involved in the GPC3 effect on breast tumor progression, focusing on canonical Wnt pathway. We investigated the receptor complex with which GPC3 is interacting and the relationships among the pathways modulated by this glypican. We determined by IP that GPC3 could physically interact with the Wnt receptor Fz. Our results suggested that GPC3 binds to Fz and blocks the binding of the canonical Wnt factors. We also confirmed by the determination of cytoplasmic β-Catenin levels through WB and their transcriptional activity employing gene reporter assay, that GPC3 is inhibiting this pathway. We showed by qPCR array that GPC3 also modulates canonical Wnt signaling in a genomic way. Of 84 examined genes, only Wnt5b (non-canonical factor) was upregulated in LM3-GPC3 cells, 66 genes were downregulated (several Fzds, LRP5/6, DVL1 and DVL2, Frat1, Ccnd1, Ccnd2, Ccnd3, Csnk1d, jun and myc, among others), and the expression of 17 genes was not modified (including several Wnt factors). Finally, LM3-GPC3 cells were treated with SB203589, SP600125 (p38 and JNK pharmacological inhibitors respectively), LiCl (canonical Wnt activator) or transduced with a constitutively active variant of Akt1 (CA Akt). The effect of the treatments on the other pathways activity was evaluated by WB. We showed that the Akt inhibition found in LM3-GPC3 cells is required for the activation of the non-canonical Wnt pathway, as well as for the inhibition of the canonical one, but it had no effects on p38 signaling. p38 activation was necessary for non-canonical Wnt upregulation and for Akt and canonical Wnt inhibition. Canonical Wnt inhibition was essential for Akt downregulation as well as for p38 and non-canonical Wnt signaling activation. We demonstrated that in addition to the significant role of JNK in the non-canonical Wnt pathway, it also regulates canonical signalling. Non-canonical Wnt activity also participates in p38 activation but has no effect on Akt activity.In sum, we have described the receptor complex with which GPC3 interacts, as well as the canonical Wnt signaling inhibition induced by GPC3 - both genomic and non-genomic - and finally several interactions among Wnt, Akt and p38 pathways. We believe that our results provide additional information regarding the molecular mechanism of GPC3 involved in metastasis suppression. Citation Format: Dolores Fernandez, Magali Cercato, Macarena Guereño, Maria G. Peters. Glypican-3 (GPC3) signaling pathway involved in breast cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4508.

Spatiotemporal dynamics of canonical Wnt signaling during embryonic eye development and posterior capsular opacification (PCO)

The appropriate spatial and temporal regulation of canonical Wnt signaling is vital for eye development. However, the literature often conflicts on the distribution of canonical Wnt signaling in the eye. Here, using a sensitive mouse transgenic reporter line, we report a detailed re-evaluation of the spatiotemporal dynamics of canonical Wnt signaling in the developing eye. Canonical Wnt activity was dynamic in the optic vesicle and later in the retina, while it was absent from the ectodermal precursors of the lens and corneal epithelium. However, later in corneal development, canonical Wnt reporter activity was detected in corneal stroma and endothelium precursors as they form from the neural crest, although this was lost around birth. Interestingly, while no canonical Wnt signaling was detected in the corneal limbus or basal cells at any developmental stage, it was robust in adult corneal wing and squamous epithelial cells. While canonical Wnt reporter activity was also absent from the postnatal lens, upon lens injury intended to model cataract surgery, it upregulated within 12 h in remnant lens epithelial cells, and co-localized with alpha smooth muscle actin in fibrotic lens epithelial cells from 48 h post-surgery onward. This pattern correlated with downregulation of the inhibitor of canonical Wnt signaling, Dkk3. These data demonstrate that canonical Wnt signaling is dynamic within the developing eye and upregulates in lens epithelial cells in response to lens injury. As canonical Wnt signaling can collaborate with TGFβ to drive fibrosis in other systems, these data offer the first evidence in a lens-injury model that canonical Wnt may synergize with TGFβ signaling to drive fibrotic posterior capsular opacification (PCO).

Fluoxetine Inhibits Canonical Wnt Signaling to Impair Embryoid Body Morphogenesis: Potential Teratogenic Mechanisms of a Commonly Used Antidepressant.

Fluoxetine is one of the most commonly prescribed antidepressants in the selective serotonin reuptake inhibitor (SSRI) class. Epidemiologic studies have suggested a link between maternal fluoxetine use during pregnancy and an increased incidence of birth defects. However, the mechanisms by which fluoxetine adversely impacts embryonic developments are unknown. Here, we used the mouse P19C5 embryoid body (EB) as a 3D morphogenesis model to investigate the developmental toxicity of fluoxetine. Morphological and molecular changes in P19C5 EBs replicate the processes of axial elongation and patterning seen in early embryos, and these changes are specifically and sensitively altered by exposure to developmental toxicants. Treatment with fluoxetine, or its major metabolite, norfluoxetine, adversely affected EB morphogenesis at concentrations of 6 µM and above. Treatment with other serotonin reuptake inhibitors or serotonin itself did not impair EB morphogenesis, suggesting that the adverse effects of fluoxetine are independent of serotonin signaling. Gene expression analyses showed that various key developmental regulators were affected by fluoxetine, particularly those involved in mesodermal differentiation. Reporter assays demonstrated that fluoxetine inhibited canonical Wnt signaling, and that the pharmacologic activation of canonical Wnt signaling partially alleviated the morphogenetic effects of fluoxetine. Fluoxetine also exhibited cytostatic effects independently of inhibition of the serotonin transporter or canonical Wnt signaling. These results suggest that the SSRI-independent actions of fluoxetine, namely inhibition of canonical Wnt signaling and reduction of cellular proliferation, are largely responsible for the observed adverse morphogenetic impacts. This study provides mechanistic insight for further investigations on the teratogenicity of fluoxetine.

DKK1 and Kremen Expression Predicts the Osteoblastic Response to Bone Metastasis

Bone metastasis is a complication of advanced breast and prostate cancer. Tumor-secreted Dickkopf homolog 1 (DKK1), an inhibitor of canonical Wnt signaling and osteoblast differentiation, was proposed to regulate the osteoblastic response to metastatic cancer in bone. The objectives of this study were to compare DKK1 expression with the in vivo osteoblastic response in a panel of breast and prostate cancer cell lines, and to discover mechanisms that regulate cancer DKK1 expression. DKK1 expression was highest in MDA-MB-231 and PC3 cells that produce osteolytic lesions, and hence a suppressed osteoblastic response, in animal models of bone metastasis. LnCaP, C4-2B, LuCaP23.1, T47D, ZR-75-1, MCF-7, ARCaP and ARCaPM cancer cells that generate osteoblastic, mixed or no bone lesions had the lowest DKK1 expression. The cell lines with negligible expression, LnCaP, C4-2B and T47D, exhibited methylation of the DKK1 promoter. Canonical Wnt signaling activity was then determined and found in all cell lines tested, even in the MDA-MB-231 and PC3 cell lines despite sizeable amounts of DKK1 protein expression expected to block canonical Wnt signaling. A mechanism of DKK1 resistance in the osteolytic cell lines was investigated and determined to be at least partially due to down-regulation of the DKK1 receptors Kremen1 and Kremen2 in the MDA-MB-231 and PC3 cell lines. Combined DKK1 and Kremen expression in cancer cells may serve as predictive markers of the osteoblastic response of breast and prostate cancer bone metastasis.

Mtf2-PRC2 control of canonical Wnt signaling is required for definitive erythropoiesis

Polycomb repressive complex 2 (PRC2) accessory proteins play substoichiometric, tissue-specific roles to recruit PRC2 to specific genomic loci or increase enzymatic activity, while PRC2 core proteins are required for complex stability and global levels of trimethylation of histone 3 at lysine 27 (H3K27me3). Here, we demonstrate a role for the classical PRC2 accessory protein Mtf2/Pcl2 in the hematopoietic system that is more akin to that of a core PRC2 protein. Mtf2−/− erythroid progenitors demonstrate markedly decreased core PRC2 protein levels and a global loss of H3K27me3 at promoter-proximal regions. The resulting de-repression of transcriptional and signaling networks blocks definitive erythroid development, culminating in Mtf2−/− embryos dying by e15.5 due to severe anemia. Gene regulatory network (GRN) analysis demonstrated Mtf2 directly regulates Wnt signaling in erythroblasts, leading to activated canonical Wnt signaling in Mtf2-deficient erythroblasts, while chemical inhibition of canonical Wnt signaling rescued Mtf2-deficient erythroblast differentiation in vitro. Using a combination of in vitro, in vivo and systems analyses, we demonstrate that Mtf2 is a critical epigenetic regulator of Wnt signaling during erythropoiesis and recast the role of polycomb accessory proteins in a tissue-specific context.

Efflux inhibition by IWR-1-endo confers sensitivity to doxorubicin effects in osteosarcoma cells

Osteosarcoma is the most common bone tumor that affects children and young adults. Despite advances in the use of combination chemotherapy regimens, response to neoadjuvant chemotherapy in osteosarcoma remains a key determinant of patient outcome. Recently, highly potent small molecule inhibitors of canonical Wnt signaling through the poly(ADP-ribose) polymerase (PARP)-family enzymes, tankyrases 1 & 2 (Tnks1/2), have been considered as possible chemotherapy sensitizing agents. The goal of this study was to determine the ability of the highly specific Tnks1/2 inhibitor IWR-1-endo to sensitize chemotherapy-resistant osteosarcoma to doxorubicin. We found that IWR-1-endo significantly inhibited cellular efflux, as measured by cellular retention of Calcein AM and doxorubicin. In a model of doxorubicin resistant osteosarcoma, pre-treatment with IWR-1-endo strongly sensitized to doxorubicin. This sensitization reduced the doxorubicin IC50 in doxorubicin-resistant cells, but not in chemotherapy naïve cells and caused doxorubicin-treated cells to accumulate at the G2/M checkpoint. Further, we found that sensitization with IWR-1-endo produced increased γH2AX foci formation, indicating increased DNA damage by doxorubicin. Taken together, our findings show that IWR-1-endo increases cellular responses to doxorubicin, by blocking efflux transport in a drug-resistant model of osteosarcoma.

In silico discovery of quinoxaline derivatives as novel LRP5/6-sclerostin interaction inhibitors

The Wnt/β-catenin signaling pathway is a key regulator of bone homeostasis. Sclerostin act as an extracellular inhibitor of canonical Wnt signaling through high-affinity binding to the Wnt co-receptor LRP5/6. Disruption of the interaction between LRP5/6 and sclerostin has been recognized as a therapeutic target for osteoporosis. We identified a quinoxaline moiety as a new small-molecule inhibitor of the LRP5/6-sclerostin interaction through pharmacophore-based virtual screening, docking simulations, and in vitro assays. Structure-activity relationship studies and binding mode hypotheses were used to optimize the scaffold and yield the compound BMD4503-2, which recovered the downregulated activity of the Wnt/β-catenin signaling pathway by competitive binding to the LRP5/6-sclerostin complex. Overall, this study showed that the optimized structure-based drug design was a promising approach for the development of small-molecule inhibitors of the LRP5/6-sclerostin interaction. A novel scaffold offered considerable insights into the structural basis for binding to LRP5/6 and disruption of the sclerostin-mediated inhibition of Wnt signaling.

Functions of the APC tumor suppressor protein dependent and independent of canonical WNT signaling: implications for therapeutic targeting.

The acquisition of biallelic mutations in the APC gene is a rate-limiting step in the development of most colorectal cancers and occurs in the earliest lesions. APC encodes a 312-kDa protein that localizes to multiple subcellular compartments and performs diverse functions. APC participates in a cytoplasmic complex that promotes the destruction of the transcriptional licensing factor β-catenin; APC mutations that abolish this function trigger constitutive activation of the canonical WNT signaling pathway, a characteristic found in almost all colorectal cancers. By negatively regulating canonical WNT signaling, APC counteracts proliferation, promotes differentiation, facilitates apoptosis, and suppresses invasion and tumor progression. APC further antagonizes canonical WNT signaling by interacting with and counteracting β-catenin in the nucleus. APC also suppresses tumor initiation and progression in the colorectal epithelium through functions that are independent of canonical WNT signaling. APC regulates the mitotic spindle to facilitate proper chromosome segregation, localizes to the cell periphery and cell protrusions to establish cell polarity and appropriate directional migration, and inhibits DNA replication by interacting directly with DNA. Mutations in APC are often frameshifts, insertions, or deletions that introduce premature stop codons and lead to the production of truncated APC proteins that lack its normal functions and possess tumorigenic properties. Therapeutic approaches in development for the treatment of APC-deficient tumors are focused on the inhibition of canonical WNT signaling, especially through targets downstream of APC in the pathway, or on the restoration of wild-type APC expression.