Mutations in the human naked cuticle homolog NKD1 found in colorectal cancer alter Wnt/Dvl/beta-catenin signaling

Colorectal cancer: Genetic alterations, novel biomarkers, current therapeutic strategies and clinical trials

Colorectal cancer (CRC) is the third most commonly detected cancer with a serious global health issue. The rates for incidence and mortality for CRC are alarming, especially since the prognosis is abysmal when the CRC is diagnosed at an advanced or metastatic stage. Both type of (modifiable/ non-modifiable) types of risk factors are established for CRC. Despite the advances in recent technology and sophisticated research, the survival rate is still meager due to delays in diagnosis. Therefore, there is urgently required to identify critical biomarkers aiming at early diagnosis and improving effective therapeutic strategies. Additionally, a complete understanding of the dysregulated pathways like PI3K/Akt, Notch, and Wnt associated with CRC progression and metastasis is very beneficial in designing a therapeutic regimen. This review article focused on the dysregulated signaling pathways, genetics and epigenetics alterations, and crucial biomarkers of CRC. This review also provided the list of clinical trials targeting signaling cascades and therapies involving small molecules. This review discusses up-to-date information on novel diagnostic and therapeutic strategies alongside specific clinical trials.

Distinct mouse models of Stargardt disease display differences in pharmacological targeting of ceramides and inflammatory responses

Mutations in many visual cycle enzymes in photoreceptors and retinal pigment epithelium (RPE) cells can lead to the chronic accumulation of toxic retinoid byproducts, which poison photoreceptors and the underlying RPE if left unchecked. Without a functional ATP-binding cassette, sub-family A, member 4 (ABCA4), there is an elevation of all-trans-retinal and prolonged buildup of all-trans-retinal adducts, resulting in a retinal degenerative disease known as Stargardt-1 disease. Even in this monogenic disorder, there is significant heterogeneity in the time to onset of symptoms among patients. Using a combination of molecular techniques, we studied Abca4 knockout (simulating human noncoding disease variants) and Abca4 knock-in mice (simulating human misfolded, catalytically inactive protein variants), which serve as models for Stargardt-1 disease. We compared the two strains to ascertain whether they exhibit differential responses to agents that affect cytokine signaling and/or ceramide metabolism, as alterations in either of these pathways can exacerbate retinal degenerative phenotypes. We found different degrees of responsiveness to maraviroc, a known immunomodulatory CCR5 antagonist, and to the ceramide-lowering agent AdipoRon, an agonist of the ADIPOR1 and ADIPOR2 receptors. The two strains also display different degrees of transcriptional deviation from matched WT controls. Our phenotypic comparison of the two distinct Abca4 mutant-mouse models sheds light on potential therapeutic avenues previously unexplored in the treatment of Stargardt disease and provides a surrogate assay for assessing the effectiveness for genome editing.

Identification of Novel Biomarkers for Response to Preoperative Chemoradiation in Locally Advanced Rectal Cancer with Genetic Algorithm-Based Gene Selection

BACKGROUND

The conventional treatment for patients with locally advanced colorectal tumors is preoperative chemo-radiotherapy (PCRT) preceding surgery. This treatment strategy has some long-term side effects, and some patients do not respond to it. Therefore, an evaluation of biomarkers that may help predict patients' response to PCRT is essential.

METHODS

We took advantage of genetic algorithm to search the space of possible combinations of features to choose subsets of genes that would yield convenient performance in differentiating PCRT responders from non-responders using a logistic regression model as our classifier.

RESULTS

We developed two gene signatures; first, to achieve the maximum prediction accuracy, the algorithm yielded 39 genes, and then, aiming to reduce the feature numbers as much as possible (while maintaining acceptable performance), a 5-gene signature was chosen. The performance of the two gene signatures was (accuracy = 0.97 and 0.81, sensitivity = 0.96 and 0.83, and specificity = 86 and 0.77) using a logistic regression classifier. Through analyzing bias and variance decomposition of the model error, we further investigated the involved genes by discovering and validating another 28-gene signature which possibly points towards two different sub-systems involved in the response of the patients to treatment.

CONCLUSIONS

Using genetic algorithm as our gene selection method, we have identified two groups of genes that can differentiate PCRT responders from non-responders in patients of the studied dataset with considerable performance.

IMPACT

After passing standard requirements, our gene signatures may be applicable as a robust and effective PCRT response prediction tool for colorectal cancer patients in clinical settings and may also help future studies aiming to further investigate involved pathways gain a clearer picture for the course of their research.

Clinical Significance of NKD Inhibitor of WNT Signaling Pathway 1 (NKD1) in Glioblastoma

Introduction. As the most malignant type of gliomas, glioblastoma is characterized with disappointing prognosis. Here, we aimed to investigate expression and function of NKD inhibitor of Wnt signaling pathway 1 (NKD1), an antagonist of Wnt-beta-catenin signaling pathways, in glioblastoma. Methods. The mRNA level of NKD1 was firstly retrieved from TCGA glioma dataset to evaluate its correlation with clinical characteristics and its value in prognosis prediction. Then, its protein expression level in glioblastoma was tested by immunohistochemistry staining in a retrospectively cohort collected from our medical center (n = 66). Univariate and multivariate survival analyses were conducted to assess its effect on glioma prognosis. Two glioblastoma cell lines, U87 and U251, were used to further investigate the tumor-related role of NKD1 through overexpression strategy in combination with cell proliferation assays. Immune cell enrichment in glioblastoma and its correlation with NKD1 level was finally assessed using bioinformatics analyses. Results. NKD1 shows a lower expression level in glioblastoma compared to that in the normal brain or other glioma subtypes, which is independently correlated to a worse prognosis in both the TCGA cohort and our retrospective cohort. Overexpressing NKD1 in glioblastoma cell lines can significantly attenuate cell proliferation. In addition, expression of NKD1 in glioblastoma is negatively correlated to the T cell infiltration, indicating it may have crosstalk with the tumor immune microenvironment. Conclusions. NKD1 inhibits glioblastoma progression and its downregulated expression indicates a poor prognosis.

The functional roles of the circRNA/Wnt axis in cancer

CircRNAs, covalently closed noncoding RNAs, are widely expressed in a wide range of species ranging from viruses to plants to mammals. CircRNAs were enriched in the Wnt pathway. Aberrant Wnt pathway activation is involved in the development of various types of cancers. Accumulating evidence indicates that the circRNA/Wnt axis modulates the expression of cancer-associated genes and then regulates cancer progression. Wnt pathway-related circRNA expression is obviously associated with many clinical characteristics. CircRNAs could regulate cell biological functions by interacting with the Wnt pathway. Moreover, Wnt pathway-related circRNAs are promising potential biomarkers for cancer diagnosis, prognosis evaluation, and treatment. In our review, we summarized the recent research progress on the role and clinical application of Wnt pathway-related circRNAs in tumorigenesis and progression.

Identification of colon tumor marker NKD1 via integrated bioinformatics analysis and experimental validation

Background

Colorectal cancer is an important death‐related disease in the worldwide. However, specific colon cancer tumor markers currently used for diagnosis and treatment are few. The purpose of this study is to screen the potential colon cancer markers by bioinformatics and verify the results with experiments.

Methods

Gene expression data were downloaded from two different databases: TCGA database and GEO datasets, which were then analyzed by two different methods (difference analysis and WGCNA method). Venn and PPI analysis obtained the potential core genes, which were then performed the GO enrichment and KEGG pathway analysis. Expressions levels of NKD1 in colon carcinoma tissues were further confirmed by immunohistochemical staining and western blot assays. Moreover, the function was measured by MTT, clone formation, and tumor transplantation experiments. Importantly, co‐immunoprecipitation, immunofluorescence, and protein stability assays were further performed to explore the underlying mechanism of NKD1 promoting cell proliferation.

Results

Nine potential core genes highly expressed in colon cancer samples were screened out by bioinformatics analysis. NKD1, one of the hub genes, highly expressed in the colon carcinoma tissues could enhance the proliferation of colon cancer cells. Mechanism research demonstrated that NKD1 was essential for the combination between Wnt signalosome (DVL) and β‐catenin, and that NKD1 knockout remarkably decreased the β‐catenin expression. Immunofluorescence assays further implied that NKD1 knockout significantly inhibited β‐catenin nuclear accumulation. Importantly, the stability of β‐catenin proteins was maintained by NKD1 in the colon cancer cells.

Conclusion

We believe that NKD1 well expressed in the colorectal carcinoma tissues can enhance the proliferation of colon cancer cells. Furthermore, the functions that NKD1 may have in colon cancer cells should be different from that NKD1 has played in the zebrafish. Thus, NKD1 could be a specific colorectal cancer marker.

Wnt Signaling Cascades and Their Role in Coronary Artery Health and Disease

The Wnt signaling is classified as two distinct pathways of canonical Wnt/β-catenin signaling, and the non-canonical pathways of planar cell polarity and Wnt/Ca²⁺ pathways. However, the scientific discoveries in recent years have shown that canonical and non-canonical Wnts pathways are intertwined and have complex interaction with other major signaling pathways such as hedgehog, Hippo and TOR signaling. Wnt signaling plays important roles in cell proliferation, differentiation and migration during embryonic development. The impairment of these pathways during embryonic development often leads to major congenital defects. In adult organisms Wnt expression is more restricted to proliferating tissues, where it plays a key role in tissue regeneration. In addition, the disruption of homeostatic processes of multicellular organisms may give rise to reactivation and/or altered activation of Wnt signaling, leading to development of malignant tumors and chronic diseases such as type-2 diabetes and adult cardiovascular diseases.

Coronary artery disease (CAD) is the leading cause of death in the world. The disease is the consequences of two distinct disease processes: Atherosclerosis, a primarily inflammatory disease and plaque erosion, a disease process associated with endothelial cell defect and smooth muscle proliferation with only modest contribution of inflammatory cells. The atherosclerosis is itself a multifactorial disease that is initiated by lipid deposition and endothelial dysfunction, triggering vascular inflammation via recruitment and aggregation of monocytes and their transformation to foam cell by the uptake of modified low-density lipoprotein (LDL), culminating in an atheromatous plaque core formation. Further accumulation of lipids, infiltration and proliferation of vascular smooth muscle cells (VSMCs) and extracellular matrix deposition result in intimal hyperplasia. Myocardial infarction is the ultimate consequence of these processes and is caused by plaque rupture and hypercoagulation. In vivo studies have established the role of the Wnt pathway in all phases of atherosclerosis development, though much remains unknown or controversial. Less is known about the mechanisms that induce plaque erosion. The limited evidence in mouse models of Wnt coreceptor LRP6 mutation and heterozygous TCF7L2 knock out mice implicate altered Wnt signaling also in the pathogenesis of plaque erosion. In this article we focus and review the role of the Wnt pathway in CAD pathophysiology from clinical and experimental standpoints.

Expression and prognostic significance of NKD2 in ovarian cancer

PURPOSE

Naked2 (NKD2) is a negative regulator of Wnt signaling pathway and associates with transforming growth factor secretion. The role of NKD2 in ovarian cancer is unknown.

PATIENTS AND METHODS

Gene expression profiles were measured and compared in nine patients by RNA sequencing. NKD2 expressions in ovarian cancer were measured by reverse transcription polymerase chain reaction and western blot. Tissue slides of 79 patients were stained and scored for NKD2 expression. In vitro experiments were conducted to explore the role of NKD2 in ovarian cancer. The prognostic role of NKD2 was evaluated by survival analysis.

RESULTS

NKD2 was upregulated in patients with better survival by mRNA and protein expression. Patients were classified as NKD2-high group (n = 30) and NKD2-low group (n = 49) according to immunohistochemical score. High NKD2 was correlated with lower recurrence rate (P = 0.002) and higher percentage of platinum-sensitive recurrence (P = 0.006). Median progression-free survival was significantly longer for NKD2-high patients than NKD2-low patients (49.1 vs.14.1 months, P < 0.001). Accordingly, there was a significantly difference in terms of overall survival time between two groups (hazard ratio: 3.04; 95% confidence interval: 1.58-5.85, P < 0.001). Multivariate regression suggested that NKD2 was independently prognostic factors in terms of progression-free survival (hazard ratio: 2.91; 95% confidence interval: 1.61-5.27, P < 0.001) and overall survival (hazard ratio: 3.6; 95% confidence interval: 1.80-7.21, P < 0.001). In vitro studies further demonstrated that NKD2 suppressed ovarian cancer cell proliferation, colony formation and cell migration.

CONCLUSION

NKD2 is a novel prognostic marker and could suppress tumor progression in ovarian cancer.

Genome-wide CRISPR screen identifies LGALS2 as an oxidative stress-responsive gene with an inhibitory function on colon tumor growth

Colorectal cancer is the third leading cause of cancer-related deaths in the United States and the third most common cancer in men and women. Around 20% colon cancer cases are closely linked with colitis. Both environmental and genetic factors are thought to contribute to colon inflammation and tumor development. However, the genetic factors regulating colitis and colon tumorigenesis remain elusive. Since reactive oxygen species (ROS) is vitally involved in tissue inflammation and tumorigenesis, here we employed a genome-wide CRISPR knockout screening approach to systemically identify the genetic factors involved in the regulation of oxidative stress. Next generation sequencing (NGS) showed that over 600 gRNAs including the ones targeting LGALS2 were highly enriched in cells survived after sublethal H₂O₂ challenge. LGALS2 encodes the glycan-binding protein Galectin 2 (Gal2), which is predominantly expressed in the gastrointestinal tract and downregulated in human colon tumors. To examine the role of Gal2 in colitis, we employed the dextran sodium sulfate (DSS)-induced acute colitis model in mice with (WT) or without Lgals2 (Gal2-KO) and showed that Gal2 deficiency ameliorated DSS-induced colitis. We further demonstrated that Gal2-KO mice developed significantly larger tumors than WT mice using Azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced colorectal cancer model. We found that STAT3 phosphorylation was significantly increased in Gal2-deficient tumors as compared to those in WT mice. Gal2 overexpression decreased the proliferation of human colon tumor epithelial cells and blunted H₂O₂-induced STAT3 phosphorylation. Overall, our results demonstrate that Gal2 plays a suppressive role in colon tumor growth and highlights the therapeutic potential of Gal2 in colon cancer.

Feedback control of Wnt signaling based on ultrastable histidine cluster co-aggregation between Naked/NKD and Axin

Feedback control is a universal feature of cell signaling pathways. Naked/NKD is a widely conserved feedback regulator of Wnt signaling which controls animal development and tissue homeostasis. Naked/NKD destabilizes Dishevelled, which assembles Wnt signalosomes to inhibit the β-catenin destruction complex via recruitment of Axin. Here, we discover that the molecular mechanism underlying Naked/NKD function relies on its assembly into ultra-stable decameric core aggregates via its conserved C-terminal histidine cluster (HisC). HisC aggregation is facilitated by Dishevelled and depends on accumulation of Naked/NKD during prolonged Wnt stimulation. Naked/NKD HisC cores co-aggregate with a conserved histidine cluster within Axin, to destabilize it along with Dishevelled, possibly via the autophagy receptor p62, which binds to HisC aggregates. Consistent with this, attenuated Wnt responses are observed in CRISPR-engineered flies and human epithelial cells whose Naked/NKD HisC has been deleted. Thus, HisC aggregation by Naked/NKD provides context-dependent feedback control of prolonged Wnt responses.

A Nine-Gene Signature for Predicting the Response to Preoperative Chemoradiotherapy in Patients with Locally Advanced Rectal Cancer

Preoperative chemoradiotherapy (PCRT) and subsequent surgery is the standard multimodal treatment for locally advanced rectal cancer (LARC), albeit PCRT response varies among the individuals. This creates a dire necessity to identify a predictive model to forecast treatment response outcomes and identify patients who would benefit from PCRT. In this study, we performed a gene expression study using formalin-fixed paraffin-embedded (FFPE) tumor biopsy samples from 156 LARC patients (training cohort n = 60; validation cohort n = 96); we identified the nine-gene signature (FGFR3, GNA11, H3F3A, IL12A, IL1R1, IL2RB, NKD1, SGK2, and SPRY2) that distinctively differentiated responders from non-responders in the training cohort (accuracy = 86.9%, specificity = 84.8%, sensitivity = 81.5%) as well as in an independent validation cohort (accuracy = 81.0%, specificity = 79.4%, sensitivity = 82.3%). The signature was independent of all pathological and clinical features and was robust in predicting PCRT response. It is readily applicable to the clinical setting using FFPE samples and Food and Drug Administration (FDA) approved hardware and reagents. Predicting the response to PCRT may aid in tailored therapies for respective responders to PCRT and improve the oncologic outcomes for LARC patients.

Role of β-Catenin Activation Levels and Fluctuations in Controlling Cell Fate

Cells have developed numerous adaptation mechanisms to external cues by controlling signaling-pathway activity, both qualitatively and quantitatively. The Wnt/β-catenin pathway is a highly conserved signaling pathway involved in many biological processes, including cell proliferation, differentiation, somatic cell reprogramming, development, and cancer. The activity of the Wnt/β-catenin pathway and the temporal dynamics of its effector β-catenin are tightly controlled by complex regulations. The latter encompass feedback loops within the pathway (e.g., a negative feedback loop involving Axin2, a β-catenin transcriptional target) and crosstalk interactions with other signaling pathways. Here, we provide a review shedding light on the coupling between Wnt/β-catenin activation levels and fluctuations across processes and cellular systems; in particular, we focus on development, in vitro pluripotency maintenance, and cancer. Possible mechanisms originating Wnt/β-catenin dynamic behaviors and consequently driving different cellular responses are also reviewed, and new avenues for future research are suggested.

Therapeutic potential of targeting the Wnt/β-catenin signaling pathway in colorectal cancer

Aberrant Wnt/β-catenin signaling has often been reported in different cancers, particularly colorectal cancer (CRC), and this signaling cascade is central to carcinogenesis. Approximately 80% of CRC cases harbor mutations in the adenomatous polyposis coli gene, and half of the remaining cases feature mutations in the β-catenin gene that affect the Wnt/β-catenin signaling pathway. Unsurprisingly, the Wnt/β-catenin signaling pathway has potential value as a therapeutic target in the treatment of CRC. Several inhibitors of the Wnt/β-catenin signaling pathway have been developed for CRC treatment, but so far no molecular therapeutic targeting this pathway has been incorporated into oncological practice. In this review, we discuss the role of Wnt/β-catenin signaling in CRC and its potential as a target of innovative therapeutic approaches for CRC.

The Nkd EF-hand domain modulates divergent wnt signaling outputs in zebrafish

Wnt proteins regulate diverse biological responses by initiating two general outcomes: β-catenin-dependent transcription and β-catenin-independent activation of signaling cascades, the latter including modulation of calcium and regulation of cytoskeletal dynamics (Planar Cell Polarity, PCP). It has been difficult to elucidate the mechanisms by which Wnt signals are directed to effect one or the other outcome due to shared signaling proteins between the β-catenin-dependent and -independent pathways, such as the Dishevelled binding protein Naked. While all Naked paralogs contain a putative calcium-binding domain, the EF-Hand, Drosophila Naked does not bind calcium. Here we find a lineage-specific evolutionary change within the Drosophila Naked EF-hand that is not shared with other insects or vertebrates. We demonstrate the necessary role of the EF-hand for Nkd localization changes in calcium fluxing cells and using in vivo assays, we identify a role for the zebrafish Naked EF-hand in PCP but not in β-catenin antagonism. In contrast, Drosophila-like Nkd does not function in PCP, but is a robust antagonist of Wnt/β-catenin signaling. This work reveals that the zebrafish Nkd1 EF-hand is essential to balance Wnt signaling inputs and modulate the appropriate outputs, while the Drosophila-like EF-Hand primarily functions in β-catenin signaling.

Downregulation of NKD1 in human osteosarcoma and its clinical significance

Naked cuticle homolog 1 (NKD1), a negative modulator of the canonical Wnt/β‑catenin pathway, is expressed in multiple normal tissues. However, there is little information regarding NKD1 expression in osteosarcoma. The aim of the present study was to explore the expression and clinicopathological significance of NKD1 in human osteosarcoma. In the present study, NKD1 protein and mRNA expression levels were detected by western blotting and reverse transcription‑quantitative polymerase chain reaction, respectively. The results revealed that NKD1 expression levels were significantly lower in osteosarcoma tissues compared with normal bone tissue, and were significantly lower in patients with lung metastasis compared with patients without lung metastasis. In addition, with increasing Enneking stage, the NKD1 expression levels decreased. These data indicated that reduction of NKD1 may be associated with carcinogenesis, lung metastasis and Enneking stage in osteosarcoma. This interpretation is consistent with the results obtained from experiments on MG63 osteosarcoma cells in vitro. In order to explore the function of NKD1 in osteosarcoma, the expression of NKD1 in the human osteosarcoma MG‑63 cell line was upregulated by transfection with an adenovirus containing an NKD1 vector. The results revealed that upregulation of NKD1 expression reduced the proliferation and migration of osteosarcoma cells by inhibiting expression of β‑catenin, cyclin D1 and MMP‑9 protein. These data suggested that the downregulation of NKD1 may be involved in the proliferation and migration of osteosarcoma cells through the activation of the canonical Wnt signaling pathway, and it may be a potential prognostic marker and therapeutic target for patients with osteosarcoma.

Circulating Tumor DNA as Biomarkers for Cancer Detection

Detection of circulating tumor DNAs (ctDNAs) in cancer patients is an important component of cancer precision medicine ctDNAs. Compared to the traditional physical and biochemical methods, blood-based ctDNA detection offers a non-invasive and easily accessible way for cancer diagnosis, prognostic determination, and guidance for treatment. While studies on this topic are currently underway, clinical translation of ctDNA detection in various types of cancers has been attracting much attention, due to the great potential of ctDNA as blood-based biomarkers for early diagnosis and treatment of cancers. ctDNAs are detected and tracked primarily based on tumor-related genetic and epigenetic alterations. In this article, we reviewed the available studies on ctDNA detection and described the representative methods. We also discussed the current understanding of ctDNAs in cancer patients and their availability as potential biomarkers for clinical purposes. Considering the progress made and challenges involved in accurate detection of specific cell-free nucleic acids, ctDNAs hold promise to serve as biomarkers for cancer patients, and further validation is needed prior to their broad clinical use.

Dishevelled stability is positively regulated by PKCζ-mediated phosphorylation induced by Wnt agonists

Dishevelled (Dvl) proteins are central mediators of both canonical and non-canonical Wnt signaling. It is well known that, upon Wnt stimulation, Dvl becomes phosphorylated. However, how Wnt-induced phosphorylation of Dvl is regulated and its consequences are poorly understood. Here we found that Dvl proteins are overexpressed in colon cancer cells. In addition, we found that Wnt3a treatment rapidly induces hyperphosphorylation and stabilization of Dvl2 and Dvl3. The latter can be blocked by inhibition of Protein Kinase C (PKC)α, PKCδ, and PKCζ isoforms. We also found that Wnt3a-induced phosphorylation of Dvl3 by PKCζ is required to avoid Dvl3 degradation via proteasome. This demonstrated, to our knowledge for the first time, that hyperphosphorylation of Dvl by PKCζ results in Dvl stabilization. This is clear contrast with the consequences reported to date of CK1δ/ε-mediated Dvl phosphorylation upon Wnt treatment. Mapping the interaction domain between PKCζ and Dvl3 indicated that, although the Dvl-DIX domain is required to stabilize PKCζ-phosphorylated Dvl, it is not the region phosphorylated by this kinase. Our data show that the Dvl-DEP domain, required for specific interaction with PKCζ, is the site phosphorylated by this kinase, and also probably the Dvl-C terminus. Our findings suggest a model of positive regulation of PKCζ-mediated Dvl signaling activity, to produce a strong and sustained response to Wnt3a treatment by stabilizing Dvl protein levels.

Upregulation of miR-501-5p activates the wnt/β-catenin signaling pathway and enhances stem cell-like phenotype in gastric cancer

Background

miRNAs are critical post-transcriptional regulators of gene expression and key mediators of tumourigenesis. miR-501-5p is newly identified to be involved in the tumor progression, but its biological role and mechanism remain largely unknown. This study is aimed to study the role of miR-501-5p in the progression of gastric cancer.

Methods

Real-time PCR analysis was used to determine miR-501-5p expression in gastric cancer cell lines, clinical tissues and 112 clinicopathologically characterized gastric cancer specimens. The role of miR-501-5p in maintaining gastric cancer stem cell like phenotype was examined by tumor-sphere formation assay and expression of stem cell markers. Luciferase reporter assay, cellular fractionation and western blot analysis were used to determined that miR-501-5p activated the wnt/β-catenin signaling by directly targeting DKK1, NKD1 and GSK3β.

Results

Herein, our results revealed that miR-501-5p was markedly upregulated in gastric cancer cell lines and clinical tissues. High miR-501-5p levels predicted poor overall survival in gastric cancer patients. Gain-of-function and loss-of-function studies showed that ectopic expression of miR-501-5p enhanced the cancer stem cell-like phenotype in gastric cancer cells. Notably,wnt/β-catenin signaling was hyperactivated in gastric cancer cells that overexpress miR-501-5p, and mediated miR-501-5p-induced cancer stem cell-like phenotype. Furthermore, miR-501-5p directly targeted and suppressed multiple repressors of the wnt/β-catenin signaling cascade, including DKK1, NKD1 and GSK3β. These results demonstrate that miR-501-5p maintains constitutively activated wnt/β-catenin signaling by directly targeting DKK1, NKD1 and GSK3β, which promotes gastric cancer stem cell like phenotype.

Conclusions

Taken together, our findings reveal a new regulatory mechanism of miR-501-5p and suggest that miR-501-5p might be a potential target in gastric cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0432-x) contains supplementary material, which is available to authorized users.

NKD1 correlates with a poor prognosis and inhibits cell proliferation by inducing p53 expression in hepatocellular carcinoma

Naked cuticle 1 (NKD1), a negative regulator of the Wnt signaling pathway, is abnormally expressed in many types of malignant tumors. Yet the role and mechanism of NKD1 in hepatocellular carcinoma (HCC) cell proliferation and its relationship with HCC patients' prognosis have been poorly characterized. In the present study, real-time polymerase chain reaction (PCR) was used to examine the mRNA expression patterns of NKD1 in the tissues of 60 patients with HCC and corresponding adjacent non-tumor tissues and found that NKD1 mRNA expression in HCC tissues was relatively lower than that in non-tumor tissues and negatively correlated with tumor size. Kaplan-Meier survival curves uncovered that patients with lower NKD1 expression had a poorer post-operative prognosis than those with higher expression. In addition, over-expression of NKD1 inhibited the HCC cell proliferation ability, whereas knockdown of NKD1 had the opposite effect. In vivo assays showed that mice injected with SMMC-7721 + control cells had bigger tumor nodules than those injected with SMMC-7721 + NKD1. Mechanism studies demonstrated that NKD1 repressed HCC cell proliferation by inducing p53 expression. Taken together, our study revealed that NKD1 mRNA expression was downregulated in HCC tissues and correlated with a poor prognosis. NKD1 inhibited HCC cell proliferation by inducing p53 expression.

Zfp703 Is a Wnt/β-Catenin Feedback Suppressor Targeting the β-Catenin/Tcf1 Complex

The Wnt/β-catenin signaling pathway controls embryonic development and adult stem cell maintenance through the regulation of transcription. Failure to downregulate Wnt signaling can result in embryonic malformations and cancer, highlighting the important role of negative regulators of the pathway. The Wnt pathway activates several negative feedback targets, including axin2 and Dkk1, that function at different levels of the signaling cascade; however, none have been identified that directly target active β-catenin/Tcf1 transcriptional complexes. We show that Zfp703 is a Wnt target gene that inhibits Wnt/β-catenin activity in Wnt reporter assays and in Wnt-dependent mesoderm differentiation in embryonic stem cells. Zfp703 binds directly to Tcf1 to inhibit β-catenin/Tcf1 complex formation and does so independently of the Groucho/Tle transcriptional corepressor. We propose that Zfp703 is a novel feedback suppressor of Wnt/β-catenin signaling that functions by inhibiting the association of β-catenin with Tcf1 on Wnt response elements in target gene enhancers.

HOXA5 Counteracts Stem Cell Traits by Inhibiting Wnt Signaling in Colorectal Cancer

Hierarchical organization of tissues relies on stem cells, which either self-renew or produce committed progenitors predestined for lineage differentiation. Here we identify HOXA5 as an important repressor of intestinal stem cell fate in vivo and identify a reciprocal feedback between HOXA5 and Wnt signaling. HOXA5 is suppressed by the Wnt pathway to maintain stemness and becomes active only outside the intestinal crypt where it inhibits Wnt signaling to enforce differentiation. In colon cancer, HOXA5 is downregulated, and its re-expression induces loss of the cancer stem cell phenotype, preventing tumor progression and metastasis. Tumor regression by HOXA5 induction can be triggered by retinoids, which represent tangible means to treat colon cancer by eliminating cancer stem cells.

Paired-like Homeodomain Transcription factor 2 expression by breast cancer bone marrow disseminated tumor cells is associated with early recurrent disease development

The presence of disseminated tumor cells (DTCs) in the bone marrow (BM) of breast cancer patients is prognostic for early relapse. In the present study, we analyzed the gene expression profiles from BM cells of breast cancer patients to identify molecular signatures associated with DTCs and their relevance to metastatic outcome. We analyzed BM from 30 patients with stage II/III breast cancer by gene expression profiling and correlated expression with metastatic disease development. A candidate gene, PITX2, was analyzed for expression and phenotype in breast cancer cell lines. PITX2 was knocked down in the MDAMB231 cell lines for gene expression analysis and cell invasiveness. Expression of various signaling pathway molecules was confirmed by RT-PCR. We found that the expression of Paired-like Homeobox Transcription factor-2 (PITX2) is absent in the BM of normal healthy volunteers and, when detected in the BM of breast cancer patients, is significantly correlated with early metastatic disease development (p = 0.0062). Suppression of PITX2 expression significantly reduced invasiveness in MDAMB231 cells. Three genes-NKD1, LEF1, and DKK4-were significantly downregulated in response to PITX2 suppression. Expression of PITX2 in BM of early-stage breast cancer patients is associated with risk for early disease recurrence. Furthermore, PITX2 likely plays a role in the metastatic process through its effect on the expression of genes associated with the Wnt/beta-Catenin signaling pathway.

Epigenetic silencing of NKD2, a major component of Wnt signaling, promotes breast cancer growth

Naked cuticle homolog 2 (NKD2) has been reported to antagonize Wnt signaling in zebrafish, mouse and mammals. The aim of this study is to investigate the epigenetic changes and mechanisms of NKD2 in human breast cancer development. Six breast cancer cell lines (MCF-7, ZR75-1, MDA-MB-468, MDA-MB-231, T47D and BT474) and 68 cases of primary human breast cancer were studied using methylation specific PCR, immunohistochemistry, western blot, flow cytometry techniques and a xenograft mouse model. The expression of NKD1 and NKD2 was regulated by promoter region methylation in breast cancer cells. No NKD1 methylation was found in primary human breast cancer. NKD2 was methylated in 51.4% (35/68) of human primary breast cancer samples. NKD2 methylation was significantly associated with reduction of NKD2 expression, and tumor stage (p < 0.05). NKD2 suppressed breast cancer cell proliferation both in vitro and in vivo. NKD2 induced G1/S arrest and inhibited Wnt signaling in breast cancer cells. In conclusion, NKD2 is frequently methylated in human breast cancer, and the expression of NKD2 is regulated by promoter region methylation. NKD2 suppresses breast cancer proliferation by inhibiting Wnt signaling.

Wnt ligand-dependent activation of the negative feedback regulator Nkd1

Nkd1, a negative feedback regulator of the Wnt pathway, localizes with Dvl2 to the putative Wnt signalosome, where it becomes activated by Wnt. Activated Nkd1 moves away from the membrane to become more cytosolic, where it interacts with β-catenin to prevent nuclear accumulation.

Misregulation of Wnt signaling is at the root of many diseases, most notably colorectal cancer, and although we understand the activation of the pathway, we have a very poor understanding of the circumstances under which Wnt signaling turns itself off. There are numerous negative feedback regulators of Wnt signaling, but two stand out as constitutive and obligate Wnt-induced regulators: Axin2 and Nkd1. Whereas Axin2 behaves similarly to Axin in the destruction complex, Nkd1 is more enigmatic. Here we use zebrafish blastula cells that are responsive Wnt signaling to demonstrate that Nkd1 activity is specifically dependent on Wnt ligand activation of the receptor. Furthermore, our results support the hypothesis that Nkd1 is recruited to the Wnt signalosome with Dvl2, where it becomes activated to move into the cytoplasm to interact with β-catenin, inhibiting its nuclear accumulation. Comparison of these results with Nkd function in Drosophila generates a unified and conserved model for the role of this negative feedback regulator in the modulation of Wnt signaling.

NKD1 marks intestinal and liver tumors linked to aberrant Wnt signaling

The activity of the Wnt pathway undergoes complex regulation to ensure proper functioning of this principal signaling mechanism during development of adult tissues. The regulation may occur at several levels and includes both positive and negative feedback loops. In the present study we employed one of such negative feedback regulators, naked cuticle homolog 1 (Nkd1), to follow the Wnt pathway activity in the intestine and liver and in neoplasia originated in these organs. Using lineage tracing in transgenic mice we localized Nkd1 mRNA to the bottom parts of the small intestinal crypts and hepatocytes surrounding the central vein of the hepatic lobule. Furthermore, in two mouse models of intestinal tumorigenesis, Nkd1 expression levels were elevated in tumors when compared to healthy tissue. We utilized a collection of human intestinal polyps and carcinomas to confirm that NKD1 represents a robust marker of neoplastic growth. In addition, expression analysis of NKD1 in liver cancer showed that high expression levels of the gene distinguish a subclass of hepatocellular carcinomas related to aberrant Wnt signaling. Finally, our results were confirmed by bioinformatic analysis of large publicly available datasets that included gene expression profiling and high-throughput sequencing data of human colon and liver cancer specimens.

Intracellular galectins in cancer cells: potential new targets for therapy (Review)

Dysregulation of galectin expression is frequently observed in cancer tissues. Such an abnormal expression pattern often correlates with aggressiveness and relapse in many types of cancer. Because galectins have the ability to modulate functions that are important for cell survival, migration and metastasis, they also represent attractive targets for cancer therapy. This has been well-exploited for extracellular galectins, which bind glycoconjugates expressed on the surface of cancer cells. Although the existence of intracellular functions of galectins has been known for many years, an increasing number of studies indicate that these proteins can also alter tumor progression through their interaction with intracellular ligands. In fact, in some instances, the interactions of galectins with their intracellular ligands seem to occur independently of their carbohydrate recognition domain. Such findings call for a change in the basic assumptions, or paradigms, concerning the activity of galectins in cancer and may force us to revisit our strategies to develop galectin antagonists for the treatment of cancer.

NEDD4L is downregulated in colorectal cancer and inhibits canonical WNT signaling

The NEDD4 family of E3 ubiquitin ligases includes nine members. Each is a modular protein, containing an N-terminal C2 domain for cell localization, two-to-four central WW domains for substrate recognition, and a C-terminal, catalytic HECT domain, which is responsible for catalyzing the ubiquitylation reaction. Members of this family are known to affect pathways central to the pathogenesis of colorectal cancer, including the WNT, TGFβ, EGFR, and p53 pathways. Recently, NEDD4 mRNA was reported to be overexpressed in colorectal cancer, but tumor stage was not considered in the analysis. Expression of the other family members has not been studied in colorectal cancer. Herein, we determined the expression patterns of all nine NEDD4 family members in 256 patients who presented with disease ranging from premalignant adenoma to stage IV colorectal cancer. NEDD4 mRNA was significantly increased in all stages of colorectal cancer. In contrast, NEDD4L mRNA, the closest homolog to NEDD4, was the most highly downregulated family member, and was significantly downregulated in all tumor stages. We also found NEDD4L protein was significantly decreased by western blotting in colorectal cancer samples compared to adjacent normal mucosa. In addition, NEDD4L, but not catalytically inactive NEDD4L, inhibited canonical WNT signaling at or below the level of β-catenin in vitro. These findings suggest that NEDD4L may play a tumor suppressive role in colorectal cancer, possibly through inhibition of canonical WNT signaling.

From zebrafish heart jogging genes to mouse and human orthologs: using Gene Ontology to investigate mammalian heart development

For the majority of organs in developing vertebrate embryos, left-right asymmetry is controlled by a ciliated region; the left-right organizer node in the mouse and human, and the Kuppfer's vesicle in the zebrafish. In the zebrafish, laterality cues from the Kuppfer's vesicle determine asymmetry in the developing heart, the direction of 'heart jogging' and the direction of 'heart looping'.  'Heart jogging' is the term given to the process by which the symmetrical zebrafish heart tube is displaced relative to the dorsal midline, with a leftward 'jog'. Heart jogging is not considered to occur in mammals, although a leftward shift of the developing mouse caudal heart does occur prior to looping, which may be analogous to zebrafish heart jogging. Previous studies have characterized 30 genes involved in zebrafish heart jogging, the majority of which have well defined orthologs in mouse and human and many of these orthologs have been associated with early mammalian heart development.    We undertook manual curation of a specific set of genes associated with heart development and we describe the use of Gene Ontology term enrichment analyses to examine the cellular processes associated with heart jogging.  We found that the human, mouse and zebrafish 'heart jogging orthologs' are involved in similar organ developmental processes across the three species, such as heart, kidney and nervous system development, as well as more specific cellular processes such as cilium development and function. The results of these analyses are consistent with a role for cilia in the determination of left-right asymmetry of many internal organs, in addition to their known role in zebrafish heart jogging.    This study highlights the importance of model organisms in the study of human heart development, and emphasises both the conservation and divergence of developmental processes across vertebrates, as well as the limitations of this approach.

From zebrafish heart jogging genes to mouse and human orthologs: using Gene Ontology to investigate mammalian heart development

For the majority of organs in developing vertebrate embryos, left-right asymmetry is controlled by a ciliated region; the left-right organizer node in the mouse and human, and the Kuppfer’s vesicle in the zebrafish. In the zebrafish, laterality cues from the Kuppfer’s vesicle determine asymmetry in the developing heart, the direction of ‘heart jogging’ and the direction of ‘heart looping’.  ‘Heart jogging’ is the term given to the process by which the symmetrical zebrafish heart tube is displaced relative to the dorsal midline, with a leftward ‘jog’. Heart jogging is not considered to occur in mammals, although a leftward shift of the developing mouse caudal heart does occur prior to looping, which may be analogous to zebrafish heart jogging. Previous studies have characterized 30 genes involved in zebrafish heart jogging, the majority of which have well defined orthologs in mouse and human and many of these orthologs have been associated with early mammalian heart development. 

 

We undertook manual curation of a specific set of genes associated with heart development and we describe the use of Gene Ontology term enrichment analyses to examine the cellular processes associated with heart jogging.  We found that the human, mouse and zebrafish ‘heart jogging orthologs’ are involved in similar organ developmental processes across the three species, such as heart, kidney and nervous system development, as well as more specific cellular processes such as cilium development and function. The results of these analyses are consistent with a role for cilia in the determination of left-right asymmetry of many internal organs, in addition to their known role in zebrafish heart jogging. 

 

This study highlights the importance of model organisms in the study of human heart development, and emphasises both the conservation and divergence of developmental processes across vertebrates, as well as the limitations of this approach.

Prophylactic effect of a peptide vaccine targeting TM4SF5 against colon cancer in a mouse model

Expression of transmembrane 4 superfamily member 5 protein (TM4SF5) was implicated in hepatocellular carcinoma (HCC) and colon cancer. Previously, we have shown that immunization with TM4SF5 peptide-CpG-DNA-liposome complex induces production of TM4SF5-specific antibodies and protects mice from HCC progression in an allograft model. Here, we confirmed expression of TM4SF5 in the mouse colon cancer cell line CT-26 and found that anti-TM4SF5 antibody inhibits growth of CT-26 cells. We then immunized mice with TM4SF5 peptide-CpG-DNA-liposome complex and transplanted CT-26 cells to investigate the vaccination effects. Robust production of TM4SF5-specific antibodies was induced by challenge with CT-26 cells and the tumor growth was significantly suppressed in the immunized mice. The peptide vaccine targeting TM4SF5 consequently showed a prophylactic effect against colon cancer development in a mouse model. These results suggest that the peptide vaccine can be potentially applied in humans to treat colon cancer.

Protein kinase C delta negatively modulates canonical Wnt pathway and cell proliferation in colon tumor cell lines

The tumor suppressor Adenomatous Polyposis coli (APC) gene is mutated or lost in most colon cancers. Alterations in Protein kinase C (PKC) isozyme expression and aberrant regulation also comprise early events in intestinal carcinomas. Here we show that PKCδ expression levels are decreased in colon tumor cell lines with respect to non-malignant cells. Reciprocal co-immunoprecipitation and immunofluorescence studies revealed that PKCδ interacts specifically with both full-length (from non-malignant cells) and truncated APC protein (from cancerous cells) at the cytoplasm and at the cell nucleus. Selective inhibition of PKCδ in cancer SW480 cells, which do not possess a functional β-catenin destruction complex, did not affect β-catenin-mediated transcriptional activity. However, in human colon carcinoma RKO cells, which have a normal β-catenin destruction complex, negatively affected β-catenin-mediated transcriptional activity, cell proliferation, and the expression of Wnt target genes C-MYC and CYCLIN D1. These negative effects were confirmed by siRNA-mediated knockdown of PKCδ and by the expression of a dominant negative form of PKCδ in RKO cells. Remarkably, the PKCδ stably depleted cells exhibited augmented tumorigenic activity in grafted mice. We show that PKCδ functions in a mechanism that involves regulation of β-catenin degradation, because PKCδ inhibition induces β-catenin stabilization at the cytoplasm and its nuclear presence at the C-MYC enhancer even without Wnt3a stimulation. In addition, expression of a dominant form of PKCδ diminished APC phosphorylation in intact cells, suggesting that PKCδ may modulate canonical Wnt activation negatively through APC phosphorylation.

A small molecule that promotes cardiac differentiation of human pluripotent stem cells under defined, cytokine- and xeno-free conditions

Human pluripotent stem cells (hPSCs), including embryonic stem cells and induced pluripotent stem cells, are potentially useful in regenerative therapies for heart disease. For medical applications, clinical-grade cardiac cells must be produced from hPSCs in a defined, cost-effective manner. Cell-based screening led to the discovery of KY02111, a small molecule that promotes differentiation of hPSCs to cardiomyocytes. Although the direct target of KY02111 remains unknown, results of the present study suggest that KY02111 promotes differentiation by inhibiting WNT signaling in hPSCs but in a manner that is distinct from that of previously studied WNT inhibitors. Combined use of KY02111 and WNT signaling modulators produced robust cardiac differentiation of hPSCs in a xeno-free, defined medium, devoid of serum and any kind of recombinant cytokines and hormones, such as BMP4, Activin A, or insulin. The methodology has potential as a means for the practical production of human cardiomyocytes for regeneration therapies.

Physiological inhibitors of Wnt signaling

Wnt signaling is crucial for cell proliferation and differentiation. It represents a complex network with mechanisms of self-regulation through positive and negative feedback. Recent increasing interest in this signaling pathway has led to the discovery of many new proteins that down-regulate Wnt activity. Here, we provide a short description of the most important and best-studied inhibitors, group them according to the target molecule within the Wnt cascade, and discuss their clinical potential. Although most of the inhibitors discussed here may also interact with proteins from other signaling pathways, we focus only on their ability to modulate Wnt signaling.

Naked1 antagonizes Wnt signaling by preventing nuclear accumulation of β-catenin

Cyto-nuclear shuttling of β-catenin is at the epicenter of the canonical Wnt pathway and mutations in genes that result in excessive nuclear accumulation of β-catenin are the driving force behind the initiation of many cancers. Recently, Naked Cuticle homolog 1 (Nkd1) has been identified as a Wnt-induced intracellular negative regulator of canonical Wnt signaling. The current model suggests that Nkd1 acts between Disheveled (Dvl) and β-catenin. Here, we employ the zebrafish embryo to characterize the cellular and biochemical role of Nkd1 in vivo. We demonstrate that Nkd1 binds to β-catenin and prevents its nuclear accumulation. We also show that this interaction is conserved in mammalian cultured cells. Further, we demonstrate that Nkd1 function is dependent on its interaction with the cell membrane. Given the conserved nature of Nkd1, our results shed light on the negative feedback regulation of Wnt signaling through the Nkd1-mediated negative control of nuclear accumulation of β-catenin.

Frequent truncating mutation of TFAM induces mitochondrial DNA depletion and apoptotic resistance in microsatellite-unstable colorectal cancer

The mitochondrial transcription factor A (TFAM) is required for mitochondrial DNA (mtDNA) replication and transcription. Disruption of TFAM results in heart failure and premature aging in mice. But very little is known about the role of TFAM in cancer development. Here, we report the identification of frequent frameshift mutations in the coding mononucleotide repeat of TFAM in sporadic colorectal cancer (CRC) cell lines and in primary tumors with microsatellite instability (MSI), but not in microsatellite stable (MSS) CRC cell lines and tumors. The presence of the TFAM truncating mutation, in CRC cells with MSI, reduced the TFAM protein level in vivo and in vitro and correlated with mtDNA depletion. Furthermore, forced overexpression of wild-type TFAM in RKO cells carrying a TFAM truncating mutation suppressed cell proliferation and inhibited RKO cell-induced xenograft tumor growth. Moreover, these cells showed more susceptibility to cisplatin-induced apoptosis due to an increase of cytochrome b (Cyt b) expression and its release from mitochondria. An interaction assay between TFAM and the heavy-strand promoter (HSP) of mitochondria revealed that mutant TFAM exhibited reduced binding to HSP, leading to reduction in Cyt b transcription. Collectively, these data provide evidence that a high incidence of TFAM truncating mutations leads to mitochondrial copy number reduction and mitochondrial instability, distinguishing most CRC with MSI from MSS CRC. These mutations may play an important role in tumorigenesis and cisplatin-induced apoptotic resistance of most microsatellite-unstable CRCs.

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.

Galectin-4 functions as a tumor suppressor of human colorectal cancer

Development of colorectal cancer (CRC) involves a series of genetic alterations with altered expression of proteins and cell signaling pathways. Here, we identified that galectin-4 (gal-4), a marker of differentiation, was down-regulated in CRC. The goal of this work was to determine the function of gal-4 in CRC. Toward this goal, the human colon biopsies and tissue microarrays containing a gradient of pathology were analyzed for gal-4 expression by immunohistochemistry. Cell proliferation, migration, motility, forced expression, knockdown, cell cycle and apoptosis assays were used to characterize gal-4 function. Immunohistochemistry identified that gal-4 expression was significantly down-regulated in adenomas and was essentially absent in invasive carcinomas. Forced expression of gal-4 in gal-4 -ve cells induced cell cycle arrest and retarded cell migration and motility. Further, gal-4 sensitized the cells to camptothecin-induced apoptosis. Gal-4 knockdown resulted in increased cell proliferation, migration and motility. Gal-4 was found to be associated with Wnt signaling proteins. Finally, gal-4 expression led to down-regulation of Wnt signaling target genes. This study demonstrates that loss of gal-4 is a common and specific event in CRC. This study also shows that gal-4 exhibits tumor suppressive effects in CRC cells in vitro. Through its ability to interact with and down-regulate the functions of Wnt signaling pathway, gal-4 reveals a new dimension in the control of the Wnt signaling pathway. Thus, gal-4 may prove to be an important molecule in understanding the biology of CRC.

Zebrafish Nkd1 promotes Dvl degradation and is required for left-right patterning

The establishment of the left-right (LR) axis in zebrafish embryos relies on signals from the dorsal forerunner cells (DFC) and the Kupffer's vesicle (KV). While the Wnt signaling network influences many aspects of embryonic development, its precise role in LR patterning is still unclear. One branch of the Wnt network leads to stabilization of β-catenin and activation of downstream target genes. Other Wnt ligands appear to act independently of β-catenin to modulate calcium release and influence cell polarity. Central to regulation of β-catenin and coordination of convergent extension (CE) movements is Dishevelled (Dvl). Naked Cuticle (Nkd) binds Dvl and modulates β-catenin-dependent and independent Wnt signaling. Here, we analyze the expression patterns of three zebrafish Nkd homologs and find enriched expression of nkd1 in DFCs and KV. Dvl is degraded upon Nkd1 overexpression in zebrafish. Knockdown of Nkd1 specifically in the DFC results in β-catenin nuclear localization and transcriptional activation as well as alterations to DFC migration, KV formation, ciliogenesis and LR patterning. Furthermore, we identify asymmetric expression of the Nodal antagonist charon around the KV and show that Nkd1 knockdown impacts asymmetric charon expression. Our findings show that Nkd1 acts as a β-catenin antagonist in the DFCs necessary for LR patterning.