Nucleo-cytoplasmic shuttling of APC can maximize β‐catenin/TCF concentration

Multiple roles of Adenomatous Polyposis Coli gene in Wnt Signalling - a Computational Model

The Adenomatous Polyposis Coli (APC) gene is a multifunctional gene that plays a major role in regulating the Wnt signalling pathway. The Wnt pathway, when activated by Wnt signalling molecules, initiates cell division. Mutation of APC disrupts the regulation and causes continuous activation of the Wnt pathway even in the absence of Wnt signals, thus causing uncontrolled cell proliferation. APC regulates the Wnt pathway by controlling the formation of the nuclear complex β-catenin/TCF that initiates the transcription of the Wnt target genes. There are at least five mechanisms by which APC can regulate the formation of the β-catenin/TCF complex: This paper presents a computational model for the Wnt pathway that explicitly includes the above five roles of APC in regulating β-catenin/TCF formation. We use this computational model to perform in-silico experiments to study the effect of different functional losses of APC on the level of β-catenin/TCF complex. The simulations also demonstrate the different outcomes that could be expected when the system is governed by different hypotheses.

The role of the Hes1 crosstalk hub in Notch-Wnt interactions of the intestinal crypt

The Notch pathway plays a vital role in determining whether cells in the intestinal epithelium adopt a secretory or an absorptive phenotype. Cell fate specification is coordinated via Notch's interaction with the canonical Wnt pathway. Here, we propose a new mathematical model of the Notch and Wnt pathways, in which the Hes1 promoter acts as a hub for pathway crosstalk. Computational simulations of the model can assist in understanding how healthy intestinal tissue is maintained, and predict the likely consequences of biochemical knockouts upon cell fate selection processes. Chemical reaction network theory (CRNT) is a powerful, generalised framework which assesses the capacity of our model for monostability or multistability, by analysing properties of the underlying network structure without recourse to specific parameter values or functional forms for reaction rates. CRNT highlights the role of β-catenin in stabilising the Notch pathway and damping oscillations, demonstrating that Wnt-mediated actions on the Hes1 promoter can induce dynamic transitions in the Notch system, from multistability to monostability. Time-dependent model simulations of cell pairs reveal the stabilising influence of Wnt upon the Notch pathway, in which β-catenin- and Dsh-mediated action on the Hes1 promoter are key in shaping the subcellular dynamics. Where Notch-mediated transcription of Hes1 dominates, there is Notch oscillation and maintenance of fate flexibility; Wnt-mediated transcription of Hes1 favours bistability akin to cell fate selection. Cells could therefore regulate the proportion of Wnt- and Notch-mediated control of the Hes1 promoter to coordinate the timing of cell fate selection as they migrate through the intestinal epithelium and are subject to reduced Wnt stimuli. Furthermore, mutant cells characterised by hyperstimulation of the Wnt pathway may, through coupling with Notch, invert cell fate in neighbouring healthy cells, enabling an aberrant cell to maintain its neighbours in mitotically active states.

Ginkgo biloba exocarp extracts inhibits angiogenesis and its effects on Wnt/β-catenin-VEGF signaling pathway in Lewis lung cancer

ETHNOPHARMACOLOGICAL RELEVANCE

A fruit of Ginkgo biloba L. also known as Ginkgo biloba, can be used for the treatment of cancer in Chinese traditional medicine. The scientific name of succulent skin, which is the episperm of Ginkgo nuts, is exocarp. Experiment shows that Ginkgo biloba exocarp extracts (GBEE) has the effects of immune promotion, cancer inhibition and etc.

AIM OF STUDY

Study on the activity of GBEE against Lewis lung cancer (LLC) angiogenesis and its partial molecular mechanism.

MATERIALS AND METHODS

The effect of GBEE on proliferation of LLC cells was detected by MTT method in vitro. The metastasis model of LLC was set up. The C57BL/6J mice were randomly separated into normal control, model control, positive control and GBEE (50, 100, 200mg/kg) treatment groups, n=10. The mice in normal group and model group were both intragastric gavage (i.g.) normal saline (NS) in a volume of 0.1mL/10g (b.w.), positive group were intraperitoneal (i.p.) injection cyclophosphamide (CPA) at a dose of 20mg/kg (b.w.) , the GBEE treatment groups were respectively i.g. GBEE 50, 100, and 200mg/kg (b.w.), once a day for 20d. After treatment, we calculated the tumor inhibition rate and anti-metastasis rate. The microvessel density (MVD) was measured by immunohistochemistry method in transplanted tumor. The expression levels of vascular en-dothelial growth factor (VEGF) and VEGFR2 mRNA or Wnt3a, β-catenin, VEGF, VEGFR2 and p-Akt/Akt protein expression were respectively tested by Quantitative Reverse transcription Polymerase chain reaction (qRT-PCR) or western blot in vitro and vivo.

RESULTS

GBEE suppressed the growth of LLC cells in a dose-dependent way at the dose of 5, 10, 20, 40, 80 and 160µg/mL in vitro. It can suppressed Wnt3a and β-catenin protein expression and the content of mRNA of VEGF and VEGFR2 in LLC cells significantly. In vivo, we discovered GBEE can retard the growth of LLC transplanted tumor in a dose-dependent way at the dose of 50, 100, 200mg/kg, suppressing tumor lung metastasis. The expression of CD34 was reduced, which means MVD was inhibited and so do β-catenin, VEGF, VEGFR2 and p-AKT/AKT protein expression and VEGF and VEGFR2 mRNA expression levels in LLC transplanted tumor of C57BL/6 mice.

CONCLUSIONS

GBEE played the effects of anti-tumor and anti-metastatic depending upon the inhibition of tumor angiogenesis, which may be closely relevant to its effect in blockage of Wnt /β-catenin-VEGF signaling pathway in LLC.

TCF7L2 mediates the cellular and behavioral response to chronic lithium treatment in animal models

The mechanism of lithium's therapeutic action remains obscure, hindering the discovery of safer treatments for bipolar disorder. Lithium can act as an inhibitor of the kinase GSK3α/β, which in turn negatively regulates β-catenin, a co-activator of LEF1/TCF transcription factors. However, unclear is whether therapeutic levels of lithium activate β-catenin in the brain, and whether this activation could have a therapeutic significance. To address this issue we chronically treated mice with lithium. Although the level of non-phospho-β-catenin increased in all of the brain areas examined, β-catenin translocated into cellular nuclei only in the thalamus. Similar results were obtained when thalamic and cortical neurons were treated with a therapeutically relevant concentration of lithium in vitro. We tested if TCF7L2, a member of LEF1/TCF family that is highly expressed in the thalamus, facilitated the activation of β-catenin. Silencing of Tcf7l2 in thalamic neurons prevented β-catenin from entering the nucleus, even when the cells were treated with lithium. Conversely, when Tcf7l2 was ectopically expressed in cortical neurons, β-catenin shifted to the nucleus, and lithium augmented this process. Lastly, we silenced tcf7l2 in zebrafish and exposed them to lithium for 3 days, to evaluate whether TCF7L2 is involved in the behavioral response. Lithium decreased the dark-induced activity of control zebrafish, whereas the activity of zebrafish with tcf7l2 knockdown was unaltered. We conclude that therapeutic levels of lithium activate β-catenin selectively in thalamic neurons. This effect is determined by the presence of TCF7L2, and potentially contributes to the therapeutic response.

Mathematical and Statistical Techniques for Systems Medicine: The Wnt Signaling Pathway as a Case Study

The last decade has seen an explosion in models that describe phenomena in systems medicine. Such models are especially useful for studying signaling pathways, such as the Wnt pathway. In this chapter we use the Wnt pathway to showcase current mathematical and statistical techniques that enable modelers to gain insight into (models of) gene regulation and generate testable predictions. We introduce a range of modeling frameworks, but focus on ordinary differential equation (ODE) models since they remain the most widely used approach in systems biology and medicine and continue to offer great potential. We present methods for the analysis of a single model, comprising applications of standard dynamical systems approaches such as nondimensionalization, steady state, asymptotic and sensitivity analysis, and more recent statistical and algebraic approaches to compare models with data. We present parameter estimation and model comparison techniques, focusing on Bayesian analysis and coplanarity via algebraic geometry. Our intention is that this (non-exhaustive) review may serve as a useful starting point for the analysis of models in systems medicine.

Computational modeling of the interplay between cadherin-mediated cell adhesion and Wnt signaling pathway

Wnt signaling and cadherin-mediated adhesion have been implicated in both processes of embryonic development and the progression of carcinomas. Recent experimental studies revealed that Wnt signaling and cadherin-mediated cell adhesion have close crosstalk with each other. A comprehensive model that investigates the dynamic balance of β-catenins in Wnt signaling and cell adhesion will improve our understanding to embryonic development and carcinomas. We constructed a network model to evaluate the dynamic interplay between adhesion and Wnt signaling. The network is decomposed into three interdependent modules: the cell adhesion, the degradation circle and the transcriptional regulation. In the cell adhesion module, we consider the effect of cadherin’s lateral clustering. We found adhesion negatively contributes to Wnt signaling through competition for cytoplasmic β-catenins. In the network of degradation circle, we incorporated features from various existing models. Our simulations reproduced the most recent experimental phenomena with semi-quantitative accuracy. Finally, in the transcriptional regulation module, we developed a function selection strategy to analyze the outcomes of genetic feedback loops in modulating the gene expression of Wnt targets. The specific cellular phenomena such as cadherin switch and Axin oscillation were archived and their biological insights were discussed. Our model provides the theoretical basis of how spatial organization regulates the dynamics of cellular signaling pathways. We suggest that cell adhesion affects Wnt signaling in both negative and positive ways. Cadherins can inhibit Wnt signaling not only in a way as a stoichiometric binding partner of β-catenins that sequesters them from signaling, but also in a way through their clustering to impacts the rate at which β-catenins are involved in the destruction loop. Additionally, cadherin clustering increases the phosphorylation rate of β-catenins and promotes its signaling in nucleus.

Analysis of Wnt signaling β-catenin spatial dynamics in HEK293T cells

Background

Wnt/β-catenin signaling is involved in different stages of mammalian development and implicated in various cancers (e.g. colorectal cancer). Recent experimental and computational studies have revealed characteristics of the pathway, however a cell-specific spatial perspective is lacking. In this study, a novel 3D confocal quantitation protocol is developed to acquire spatial (two cellular compartments: nucleus and cytosol-membrane) and temporal quantitative data on target protein (e.g. β-catenin) concentrations in Human Epithelial Kidney cells (HEK293T) during perturbation (with either cycloheximide or Wnt3A). Computational models of the Wnt pathway are constructed and interrogated based on this data.

Results

A single compartment Wnt pathway model is compared with a simple β-catenin two compartment model to investigate Wnt3A signaling in HEK293T cells. When protein synthesis is inhibited, β-catenin decreases at the same rate in both cellular compartments, suggesting diffusional transport is fast compared to β-catenin degradation in the cytosol. With Wnt3A stimulation, the total amount of β-catenin rises throughout the cell, however the increase is initially (~first hour) faster in the nuclear compartment. While both models were able to reproduce the whole cell changes in β-catenin, only the compartment model reproduced the Wnt3A induced changes in β-catenin distribution and it was also the best fit for the data obtained when active transport was included alongside passive diffusion transport.

Conclusions

This integrated 3D quantitation imaging protocol and computational modeling approach allowed cell-specific compartment models of the signaling pathways to be constructed and analyzed. The Wnt models constructed in this study are the first for HEK293T and have suggested potential roles of inter-compartment transport to the dynamics of signaling.

Analysing the impact of nucleo-cytoplasmic shuttling of β-catenin and its antagonists APC, Axin and GSK3 on Wnt/β-catenin signalling

The canonical Wnt signalling pathway plays a critical role in development and disease. The key player of the pathway is β-catenin. Its activity is mainly regulated by the destruction complex consisting of APC, Axin and GSK3. In the nucleus, the complex formation of β-catenin and TCF initiates target gene expression. Our study provides a comprehensive analysis of the role of nucleo-cytoplasmic shuttling of APC, Axin, and GSK3 and the inactivation of β-catenin by the destruction complex in Wnt/β-catenin signalling. We address the following questions: Can nucleo-cytoplasmic shuttling of APC, Axin and GSK3 increase the [β-catenin/TCF] concentration? And, how is the [β-catenin/TCF] concentration influenced by phosphorylation and subsequent degradation of nuclear β-catenin? Based on experimental findings, we develop a compartmental model and conduct several simulation experiments. Our analysis reveals the following key findings: 1) nucleo-cytoplasmic shuttling of β-catenin and its antagonists can yield a spatial separation between the said proteins, which results in a breakdown of β-catenin degradation, followed by an accumulation of β-catenin and hence leads to an increase of the [β-catenin/TCF] concentration. Our results strongly suggest that Wnt signalling can benefit from nucleo-cytoplasmic shuttling of APC, Axin and GSK3, although they are in general β-catenin antagonising proteins. 2) The total robustness of the [β-catenin/TCF] output is closely linked to its absolute concentration levels. We demonstrate that the compartmental separation of β-catenin and the destruction complex does not only lead to a maximization, but additionally to an increased robustness of [β-catenin/TCF] signalling against perturbations in the cellular environment. 3) A nuclear accumulation of the destruction complex renders the pathway robust against fluctuations in Wnt signalling and against changes in the compartmental distribution of β-catenin. 4) Elucidating the impact of destruction complex inhibition, we show that the [β-catenin/TCF] concentration is more effectively enhanced by inhibition of the kinase GSK3 rather than the binding of β-catenin to the destruction complex.

Toward a quantitative understanding of the Wnt/β-catenin pathway through simulation and experiment

Wnt signaling regulates cell survival, proliferation, and differentiation throughout development and is aberrantly regulated in cancer. The pathway is activated when Wnt ligands bind to specific receptors on the cell surface, resulting in the stabilization and nuclear accumulation of the transcriptional co-activator β-catenin. Mathematical and computational models have been used to study the spatial and temporal regulation of the Wnt/β-catenin pathway and to investigate the functional impact of mutations in key components. Such models range in complexity, from time-dependent, ordinary differential equations that describe the biochemical interactions between key pathway components within a single cell, to complex, multiscale models that incorporate the role of the Wnt/β-catenin pathway target genes in tissue homeostasis and carcinogenesis. This review aims to summarize recent progress in mathematical modeling of the Wnt pathway and to highlight new biological results that could form the basis for future theoretical investigations designed to increase the utility of theoretical models of Wnt signaling in the biomedical arena.

Elucidating the sources of β-catenin dynamics in human neural progenitor cells

Human neural progenitor cells (hNPCs) form a new prospect for replacement therapies in the context of neurodegenerative diseases. The Wnt/β-catenin signaling pathway is known to be involved in the differentiation process of hNPCs. RVM cells form a common cell model of hNPCs for in vitro investigation. Previous observations in RVM cells raise the question of whether observed kinetics of the Wnt/β-catenin pathway in later differentiation phases are subject to self-induced signaling. However, a concern when investigating RVM cells is that experimental results are possibly biased by the asynchrony of cells w.r.t. the cell cycle. In this paper, we present, based on experimental data, a computational modeling study on the Wnt/β-catenin signaling pathway in RVM cell populations asynchronously distributed w.r.t. to their cell cycle phases. Therefore, we derive a stochastic model of the pathway in single cells from the reference model in literature and extend it by means of cell populations and cell cycle asynchrony. Based on this, we show that the impact of the cell cycle asynchrony on wet-lab results that average over cell populations is negligible. We then further extend our model and the thus-obtained simulation results provide additional evidence that self-induced Wnt signaling occurs in RVM cells. We further report on significant stochastic effects that directly result from model parameters provided in literature and contradict experimental observations.

Nuclear translocation of β-catenin is essential for glioma cell survival

Identification of molecular pathways that are essential for cancer cell survival is vital for understanding the underlying biology, as well as to design effective cancer therapeutics. β-catenin, a multifunctional oncogenic protein, participates in cell development. Its multifaceted functions primarily lie to the subcellular distribution. The present study demonstrated that β-catenin accumulated in the nucleus to a greater extent in high-grade gliomas compared with low-grade gliomas. In addition, nuclear localization correlated with a worse prognosis for patients, as determined by immunohistochemical analysis of 74 glioma samples. Nuclear expression of β-catenin was down-regulated in LN229 and U87 glioma cells by a small molecule inhibitor of β-catenin/TCF4 signaling, demonstrating strongly inhibited β-catenin/TCF4 transcriptional activity and STAT3 luciferase activity, as well as decreased mRNA and protein levels of nuclear β-catenin, TCF4, EGFR, AKT1, AKT2 and STAT3. Furthermore, repressed nuclear translocation of β-catenin resulted in inhibition of proliferation and invasiveness, and also induced apoptosis of glioma cells. Similar results were also observed in vivo; intratumoral injection of such small molecule inhibitor downregulated expression of nuclear β-catenin, TCF4, and components of the EGFR pathway, and also delayed tumor growth in nude mice harboring subcutaneous U87 xenografts. Results from the present study provided evidence that nuclear accumulation of β-catenin participated in malignant progression of gliomas and implicated poor prognosis, highlighting it as a potential therapeutic target for gliomas.