Wnt signaling through T-cell factor phosphorylation

Curcuphenol possesses an unusual histone deacetylase enhancing activity that counters immune escape in metastatic tumours

Curcuphenol, a common component of the culinary spices, naturally found in marine invertebrates and plants, has been identified as a novel candidate for reversing immune escape by restoring expression of the antigen presentation machinery (APM) in invasive cancers, thereby resurrecting the immune recognition of metastatic tumours. Two synthetic curcuphenol analogues, were prepared by informed design that demonstrated consistent induction of APM expression in metastatic prostate and lung carcinoma cells. Both analogues were subsequently found to possess a previously undescribed histone deacetylase (HDAC)-enhancing activity. Remarkably, the H3K27ac ChIPseq analysis of curcuphenol-treated cells reveals that the induced epigenomic marks closely resemble the changes in genome-wide pattern observed with interferon-γ, a cytokine instrumental for orchestrating innate and adaptive immunity. These observations link dietary components to modifying epigenetic programs that modulate gene expression guiding poised immunity.

Developmental genomics of limb malformations: Allelic series in association with gene dosage effects contribute to the clinical variability

Genetic heterogeneity, reduced penetrance, and variable expressivity, the latter including asymmetric body axis plane presentations, have all been described in families with congenital limb malformations (CLMs). Interfamilial and intrafamilial heterogeneity highlight the complexity of the underlying genetic pathogenesis of these developmental anomalies. Family-based genomics by exome sequencing (ES) and rare variant analyses combined with whole-genome array-based comparative genomic hybridization were implemented to investigate 18 families with limb birth defects. Eleven of 18 (61%) families revealed explanatory variants, including 7 single-nucleotide variant alleles and 3 copy number variants (CNVs), at previously reported "disease trait associated loci": BHLHA9, GLI3, HOXD cluster, HOXD13, NPR2, and WNT10B. Breakpoint junction analyses for all three CNV alleles revealed mutational signatures consistent with microhomology-mediated break-induced replication, a mechanism facilitated by Alu/Alu-mediated rearrangement. Homozygous duplication of BHLHA9 was observed in one Turkish kindred and represents a novel contributory genetic mechanism to Gollop-Wolfgang Complex (MIM: 228250), where triplication of the locus has been reported in one family from Japan (i.e., 4n = 2n + 2n versus 4n = 3n + 1n allelic configurations). Genes acting on limb patterning are sensitive to a gene dosage effect and are often associated with an allelic series. We extend an allele-specific gene dosage model to potentially assist, in an adjuvant way, interpretations of interconnections among an allelic series, clinical severity, and reduced penetrance of the BHLHA9-related CLM spectrum.

Roles of Wnt/β-catenin signaling pathway related microRNAs in esophageal cancer

MicroRNAs (miRNAs) are endogenous, noncoding, single-stranded small RNAs that regulate expression of tumor suppressor genes and oncogenes and are involved in almost all tumor-related processes. MiRNA dysregulation plays an important role in the occurrence and development of esophageal cancer through specific signal pathways, including the Wnt/β-catenin signaling pathway, and is closely related to the malignant characteristics of esophageal cancer. The interaction between miRNAs and the Wnt/β-catenin signaling pathway, which is specifically expressed in esophageal cancer tissues, shows potential as a new biomarker and therapeutic target. This article reviews the role of miRNAs related to the Wnt pathway in the carcinogenesis of esophageal carcinoma and its role in Wnt signal transduction. The content of this review can be used as the basis for formulating or improving the treatment strategy of esophageal cancer.

Silencing of KIF18B restricts proliferation and invasion and enhances the chemosensitivity of breast cancer via modulating Akt/GSK-3β/β-catenin pathway

Kinesin family member 18B (KIF18B) is a new tumor-associated protein that contributes to the carcinogenesis of multiple malignancies. However, the detailed relevance of KIF18B in breast cancer has not been fully elucidated. This work aimed was to evaluate a possible relationship between KIF18B and breast cancer progression. Our findings show KIF18B is increased in breast cancer and demonstrate that high KIF18B level predicts a reduced survival rate. Cellular functional studies revealed that knockdown of KIF18B markedly reduces the proliferation, invasion, and epithelial-mesenchymal transition of breast cancer cells and enhances their chemosensitivity toward doxorubicin. Further studies showed that KIF18B modulates the level of phospho-Akt, phospho-glycogen synthase kinase-3β, and β-catenin. Notably, suppression of Akt abolished KIF18B-overexpression-induced increases in activation of Wnt/β-catenin pathway. In addition, re-expression of β-catenin reversed KIF18B-silencing-induced cancer-promoting effect. In vivo animal experiments elucidated that knockdown of KIF18B significantly weakened the tumorigenicity of breast cancer cells. Taken together, data of this study illustrate that KIF18B exerts a potential cancer-promoting function in breast cancer via enhancement of Wnt/β-catenin pathway through modulation of the Akt/GSK-3β axis.

Rspo2 inhibits TCF3 phosphorylation to antagonize Wnt signaling during vertebrate anteroposterior axis specification

The Wnt pathway activates target genes by controlling the β-catenin-T-cell factor (TCF) transcriptional complex during embryonic development and cancer. This pathway can be potentiated by R-spondins, a family of proteins that bind RNF43/ZNRF3 E3 ubiquitin ligases and LGR4/5 receptors to prevent Frizzled degradation. Here we demonstrate that, during Xenopus anteroposterior axis specification, Rspo2 functions as a Wnt antagonist, both morphologically and at the level of gene targets and pathway mediators. Unexpectedly, the binding to RNF43/ZNRF3 and LGR4/5 was not required for the Wnt inhibitory activity. Moreover, Rspo2 did not influence Dishevelled phosphorylation in response to Wnt ligands, suggesting that Frizzled activity is not affected. Further analysis indicated that the Wnt antagonism is due to the inhibitory effect of Rspo2 on TCF3/TCF7L1 phosphorylation that normally leads to target gene activation. Consistent with this mechanism, Rspo2 anteriorizing activity has been rescued in TCF3-depleted embryos. These observations suggest that Rspo2 is a context-specific regulator of TCF3 phosphorylation and Wnt signaling.

Small-molecule probe reveals a kinase cascade that links stress signaling to TCF/LEF and Wnt responsiveness

Wnt signaling plays a central role in tissue maintenance and cancer. Wnt activates downstream genes through β-catenin, which interacts with TCF/LEF transcription factors. A major question is how this signaling is coordinated relative to tissue organization and renewal. We used a recently described class of small molecules that binds tubulin to reveal a molecular cascade linking stress signaling through ATM, HIPK2, and p53 to the regulation of TCF/LEF transcriptional activity. These data suggest a mechanism by which mitotic and genotoxic stress can indirectly modulate Wnt responsiveness to exert coherent control over cell shape and renewal. These findings have implications for understanding tissue morphogenesis and small-molecule anticancer therapeutics.

A novel isoform of Homeodomain-interacting protein kinase-2 promotes YAP/TEAD transcriptional activity in NSCLC cells

Homeodomain-interacting protein kinase-2 (HIPK2) can either promote or inhibit transcription depending on cellular context. In this study, we show that a new HIPK2 isoform increases TEAD reporter activity in NSCLC cells. We detected HIPK2 copy number gain in 5/6 (83.3%) NSCLC cell lines. In NSCLC patients with high HIPK2 mRNA expression in the Human Protein Atlas, the five-year survival rate is significantly lower than in patients with low expression (38% vs 47%; p = 0.047). We also found that 70/78 (89.7%) of NSCLC tissues have moderate to strong expression of the N-terminal HIPK2 protein. We detected and cloned a novel HIPK2 isoform 3 and found that its forced overexpression promotes TEAD reporter activity in NSCLC cells. Expressing HIPK2 isoform 3_K228A kinase-dead plasmid failed to increase TEAD reporter activity in NSCLC cells. Next, we showed that two siRNAs targeting HIPK2 decreased HIPK2 isoform 3 and YAP protein levels in NSCLC cells. Degradation of the YAP protein was accelerated after HIPK2 knockdown in NSCLC cells. Inhibition of HIPK2 isoform 3 decreased the mRNA expression of YAP downstream gene CTGF. The specific HIPK2 kinase inhibitor TBID decreased TEAD reporter activity, reduced cancer side populations, and inhibited tumorsphere formation of NSCLC cells. In summary, this study indicates that HIPK2 isoform 3, the main HIPK2 isoform expressed in NSCLC, promotes YAP/TEAD transcriptional activity in NSCLC cells. Our results suggest that HIPK2 isoform 3 may be a potential therapeutic target for NSCLC.

Developmentally regulated Tcf7l2 splice variants mediate transcriptional repressor functions during eye formation

Tcf7l2 mediates Wnt/β-Catenin signalling during development and is implicated in cancer and type-2 diabetes. The mechanisms by which Tcf7l2 and Wnt/β-Catenin signalling elicit such a diversity of biological outcomes are poorly understood. Here, we study the function of zebrafish tcf7l2alternative splice variants and show that only variants that include exon five or an analogous human tcf7l2 variant can effectively provide compensatory repressor function to restore eye formation in embryos lacking tcf7l1a/tcf7l1b function. Knockdown of exon five specific tcf7l2 variants in tcf7l1a mutants also compromises eye formation, and these variants can effectively repress Wnt pathway activity in reporter assays using Wnt target gene promoters. We show that the repressive activities of exon5-coded variants are likely explained by their interaction with Tle co-repressors. Furthermore, phosphorylated residues in Tcf7l2 coded exon5 facilitate repressor activity. Our studies suggest that developmentally regulated splicing of tcf7l2 can influence the transcriptional output of the Wnt pathway.

Dkk1 Controls Cell-Cell Interaction through Regulation of Non-nuclear β-Catenin Pools

Dickkopf-1 (Dkk1) is a secreted Wnt antagonist with a well-established role in head induction during development. Numerous studies have emerged implicating Dkk1 in various malignancies and neurodegenerative diseases through an unknown mechanism. Using zebrafish gastrulation as a model for collective cell migration, we unveil such a mechanism, identifying a role for Dkk1 in control of cell connectivity and polarity in vivo, independent of its known function. We find that Dkk1 localizes to adhesion complexes at the plasma membrane and regions of concentrated actomyosin, suggesting a direct involvement in regulation of local cell adhesion. Our results show that Dkk1 represses cell polarization and integrity of cell-cell adhesion, independently of its impact on β-catenin protein degradation. Concurrently, Dkk1 prevents nuclear localization of β-catenin by restricting its distribution to a discrete submembrane pool. We propose that redistribution of cytosolic β-catenin by Dkk1 concomitantly drives repression of cell adhesion and inhibits β-catenin-dependent transcriptional output.

Microarray Analysis of Human Blood During Electroconvulsive Therapy

INTRODUCTION

Electroconvulsive therapy (ECT) is currently regarded as a significant treatment option for intractable psychiatric disorders, such as catatonic schizophrenia or treatment-resistant depression; however, the underlying molecular mechanism for its therapeutic effect remains obscure.

METHODS

Employing microarray analysis (Human Genome U133 Plus 2.0 Array; Affymetrix, United States) of cDNA derived from the peripheral blood of patients with catatonic schizophrenia (n = 5), we detected a significant change in 145 genes (0.68%) before and after modified ECT (mECT). Moreover, we performed quantitative polymerase chain reaction validation of genes that had previously been suggested to be functionally related to schizophrenia.

RESULTS

Of 4 genes examined (AKT3, TCF7, PPP3R1, and GADD45B), only TCF7 was increased during the mECT procedure (P = 0.0025).

DISCUSSION

This study describes the first attempt to uncover the molecular mechanism of mECT using a microarray assay of mRNA derived from peripheral blood, and our results suggest that the TCF family may play a role in the functional mechanism of mECT.

TCF4 Is a Molecular Target of Resveratrol in the Prevention of Colorectal Cancer

The Wnt/β-catenin pathway plays an essential role in the tumorigenesis of colorectal cancer. T-cell factor-4 (TCF4) is a member of the TCF/LEF (lymphoid enhancer factor) family of transcription factors, and dysregulation of β-catenin is decisive for the initiation and progression of colorectal cancer. However, the role of TCF4 in the transcriptional regulation of its target gene remained poorly understood. Resveratrol is a dietary phytoalexin and present in many plants, including grape skin, nuts and fruits. Although resveratrol has been widely implicated in anti-tumorigenic and pro-apoptotic properties in several cancer models, the underlying cellular mechanisms are only partially understood. The current study was performed to elucidate the molecular mechanism of the anti-cancer activity of resveratrol in human colorectal cancer cells. The treatment of resveratrol and other phytochemicals decreased the expression of TCF4. Resveratrol decreases cellular accumulation of exogenously-introduced TCF4 protein, but did not change the TCF4 transcription. The inhibition of proteasomal degradation using MG132 (carbobenzoxy-Leu-Leu-leucinal) and lactacystin ameliorates resveratrol-stimulated down-regulation of TCF4. The half-life of TCF4 was decreased in the cells exposed to resveratrol. Resveratrol increased phosphorylation of TCF4 at serine/threonine residues through ERK (extracellular signal-regulated kinases) and p38-dependent pathways. The TCF4 knockdown decreased TCF/β-catenin-mediated transcriptional activity and sensitized resveratrol-induced apoptosis. The current study provides a new mechanistic link between resveratrol and TCF4 down-regulation and significant benefits for further preclinical and clinical practice.

Distinct DNA binding sites contribute to the TCF transcriptional switch in C. elegans and Drosophila

Regulation of gene expression by signaling pathways often occurs through a transcriptional switch, where the transcription factor responsible for signal-dependent gene activation represses the same targets in the absence of signaling. T-cell factors (TCFs) are transcription factors in the Wnt/ß-catenin pathway, which control numerous cell fate specification events in metazoans. The TCF transcriptional switch is mediated by many co-regulators that contribute to repression or activation of Wnt target genes. It is typically assumed that DNA recognition by TCFs is important for target gene location, but plays no role in the actual switch. TCF/Pangolin (the fly TCF) and some vertebrate TCF isoforms bind DNA through two distinct domains, a High Mobility Group (HMG) domain and a C-clamp, which recognize DNA motifs known as HMG and Helper sites, respectively. Here, we demonstrate that POP-1 (the C. elegans TCF) also activates target genes through HMG and Helper site interactions. Helper sites enhanced the ability of a synthetic enhancer to detect Wnt/ß-catenin signaling in several tissues and revealed an unsuspected role for POP-1 in regulating the C. elegans defecation cycle. Searching for HMG-Helper site clusters allowed the identification of a new POP-1 target gene active in the head muscles and gut. While Helper sites and the C-clamp are essential for activation of worm and fly Wnt targets, they are dispensable for TCF-dependent repression of targets in the absence of Wnt signaling. These data suggest that a fundamental change in TCF-DNA binding contributes to the transcriptional switch that occurs upon Wnt stimulation.

The DNA of cells must be correctly “read” so that the proper genes are expressed. Transcription factors are the primary “DNA readers”, and these proteins bind to specific DNA sequences. Using nematodes as a model system, we investigated the rules of DNA binding for a particular transcription factor, called POP-1, which mediates Wnt signaling, an important cell-cell communication pathway. In addition to its known DNA binding site, we found that POP-1 recognizes additional sequences, termed Helper sites, which are essential for activation of Wnt targets. We used this knowledge to discover that Wnt signaling is active in pacemaker cells in the nematode intestine, which control defecation, a rhythmic behavior with parallels to the vertebrate heartbeat. POP-1 has a dual role in regulating Wnt targets, repressing target genes in the absence of signaling and activating them upon signal stimulation. Surprisingly, we found that Helper sites are only required for activation and not repression, and that this is also the case in the fruit fly Drosophila. This work thus reveals an unexpected complexity in POP-1 DNA binding, which is likely to be relevant for its human counterparts, which play important roles in stem cell biology and cancer.

The SxxSS motif of T-cell factor-4 isoforms modulates Wnt/β-catenin signal activation in hepatocellular carcinoma cells

T-cell factor (TCF) proteins represent key transcription factors in Wnt signaling. We show that the SxxSS motif in TCF-4 regulates transcriptional activity in HCC cells. TCF-4K mutants increased transcriptional activity compared to TCF-4K (bearing the SxxSS); the binding pattern of co-factors in TCF-4K mutants was similar to that in TCF-4J (lacking the SxxSS). TCF activity in TCF-4K cells was suppressed by homeodomain-interacting protein kinase 2 (HIPK2), but not in TCF-4J cells. Together, our data indicates that the SxxSS motif in TCF-4K regulates transcriptional activity by modifying co-factors in the β-catenin/TCF-4 transcriptional complex and these events may be mediated through HIPK2.

Wnt signaling in vertebrate axis specification

The Wnt pathway is a major embryonic signaling pathway that controls cell proliferation, cell fate, and body-axis determination in vertebrate embryos. Soon after egg fertilization, Wnt pathway components play a role in microtubule-dependent dorsoventral axis specification. Later in embryogenesis, another conserved function of the pathway is to specify the anteroposterior axis. The dual role of Wnt signaling in Xenopus and zebrafish embryos is regulated at different developmental stages by distinct sets of Wnt target genes. This review highlights recent progress in the discrimination of different signaling branches and the identification of specific pathway targets during vertebrate axial development.

Phytochemicals attenuating aberrant activation of β-catenin in cancer cells

Phytochemicals are a rich source of chemoprevention agents but their effects on modulating the Wnt/β-catenin signaling pathway have remained largely uninvestigated. Aberrantly activated Wnt signaling can result in the abnormal stabilization of β-catenin, a key causative step in a broad spectrum of cancers. Here we report the modulation of lithium chloride-activated canonical Wnt/β-catenin signaling by phytochemicals that have antioxidant, anti-inflammatory or chemopreventive properties. The compounds were first screened with a cervical cancer-derived stable Wnt signaling reporter HeLa cell line. Positive hits were subsequently evaluated for β-catenin degradation, suppression of β-catenin nuclear localization and down-regulation of downstream oncogenic targets of Wnt/β-catenin pathway. Our study shows a novel degradation path of β-catenin protein in HeLa cells by Avenanthramide 2p (a polyphenol) and Triptolide (a diterpene triepoxide), respectively from oats and a Chinese medicinal plant. The findings present Avenanthramide 2p as a potential chemopreventive dietary compound that merits further study using in vivo models of cancers; they also provide a new perspective on the mechanism of action of Triptolide.

Activation of Wnt3a signaling stimulates intestinal epithelial repair by promoting c-Myc-regulated gene expression

In response to mucosal injury, epithelial cells modify the patterns of expressed genes to repair damaged tissue rapidly. Our previous studies have demonstrated that the transcription factor c-Myc is necessary for stimulation of epithelial cell renewal during mucosal healing, but the up-stream signaling initiating c-Myc gene expression after injury remains unknown. Wnts are cysteine-rich glycoproteins that act as short-range ligands to locally activate receptor-mediated signaling pathways and correlate with the increased expression of the c-Myc gene. The current study tested the hypothesis that Wnt3a signaling is implicated in intestinal epithelial repair after wounding by stimulating c-Myc expression. Elevated Wnt3a signaling in intestinal epithelial cells (IEC-6 line) by coculturing with stable Wnt3a-transfected fibroblasts or ectopic overexpression of the Wnt3a gene enhanced intestinal epithelial repair after wounding. This stimulatory effect on epithelial repair was prevented by silencing the Wnt coreceptor LRP6 or by c-Myc silencing. Activation of the Wnt3a signaling pathway increased β-catenin nuclear translocation by decreasing its phosphorylation and stimulated c-Myc expression during epithelial repair after wounding. In stable Wnt3a-transfected IEC-6 cells, increased levels of c-Myc were associated with an increase in expression of c-Myc-regulated genes cyclcin D1 and cyclin E, whereas c-Myc silencing inhibited expression of cyclin D1 and cyclin E and delayed epithelial repair. These results indicate that elevated Wnt3a signaling in intestinal epithelial cells after wounding stimulates epithelial repair by promoting c-Myc-regulated gene expression.

Maintaining embryonic stem cell pluripotency with Wnt signaling

Wnt signaling pathways control lineage specification in vertebrate embryos and regulate pluripotency in embryonic stem (ES) cells, but how the balance between progenitor self-renewal and differentiation is achieved during axis specification and tissue patterning remains highly controversial. The context- and stage-specific effects of the different Wnt pathways produce complex and sometimes opposite outcomes that help to generate embryonic cell diversity. Although the results of recent studies of the Wnt/β-catenin pathway in ES cells appear to be surprising and controversial, they converge on the same conserved mechanism that leads to the inactivation of TCF3-mediated repression.