Cancer stem cells: never Wnt away from the niche. Curr Opin Oncol. 2009;21:41-46. [PMID: 19125017 DOI: 10.1097/cco.0b013e32831d1faf]

Elevation of Plasminogen Activator Inhibitor-1 promotes differentiation of Cancer Stem-like Cell state by Hepatitis C Virus infection

Plasminogen activator inhibitor-1 (PAI-1) is a critical factor that regulates protein synthesis and degradation. The increased PAI-1 levels are detectable in the serum of patients with chronic hepatitis C virus (HCV) liver disease. The differentiation state and motility of HCV-induced cancer stem-like cells (CSC) play a major role in severe liver disease progression. However, the role of PAI-1 in the pathological process of chronic liver diseases remains unknown. In this study, we determined how PAI-1 affects the differentiation of CSC state in hepatocytes upon HCV infection. We found that HCV infection induced the expression of PAI-1 while decreasing miR-30c expression in Huh7.5.1 cells. Similar results were obtained from isolated hepatocytes from humanized liver mice after HCV infection. Moreover, decreased miR-30c expression in HCV-infected hepatocytes was associated with the increased levels of PAI-1 mRNA and protein. Notably, the increased PAI-1 levels resulted in the activation of Protein Kinase B/AKT, a major mediator of cell proliferation, in HCV-infected hepatocytes along with the increased expression of CSC markers such as Human Differentiated Protein (CD) 133, Epithelial cell adhesion molecule (EpCAM), Octamer 4 (Oct4), Nanog, Cyclin D1, and MYC. Moreover, blockade of PAI-1 activity by miR-30c mimic and anti-PAI-1 mAb abrogated the AKT activation with decreased expression of CSC markers. Our findings suggest that HCV infection induces the CSC state via PAI-1-mediated AKT activation in hepatocytes. It implicates that the manipulation of PAI-1 activity could provide potential therapeutics to prevent the development of HCV-associated chronic liver diseases.IMPORTANCEThe progression of chronic liver disease by HCV infection is considered a major risk factor for hepatocellular carcinoma (HCC), one of the major causes of death from cancer. Recent studies have demonstrated that increased CSC properties in HCV-infected hepatocytes are associated with the progression of HCC. Since proteins and miRNAs production by HCV-infected hepatocytes can play various roles in physiological processes, investigating these factors can potentially lead to new therapeutic targets. However, the mechanism of HCV associated progression of hepatocytes to CSC remains unclear. Here we identify the roles of PAI-1 and miR-30c in the progression of CSC during HCV infection in hepatocytes. Our data shows that increased secretion of PAI-1 following HCV infection promotes this CSC state and activation of AKT. We report that the inhibition of PAI-1 by miR-30c mimic reduces HCV associated CSC properties in hepatocytes. Taken together, targeting this interaction of secreted PAI-1 and miR-30c in HCV-infected hepatocytes may provide a potential therapeutic intervention against the progression to chronic liver diseases and HCC.

Cancer Stem Cells and Nucleolin as Drivers of Carcinogenesis

Cancer, one of the most mortal diseases worldwide, is characterized by the gain of specific features and cellular heterogeneity. Clonal evolution is an established theory to explain heterogeneity, but the discovery of cancer stem cells expanded the concept to include the hierarchical growth and plasticity of cancer cells. The activation of epithelial-to-mesenchymal transition and its molecular players are widely correlated with the presence of cancer stem cells in tumors. Moreover, the acquisition of certain oncological features may be partially attributed to alterations in the levels, location or function of nucleolin, a multifunctional protein involved in several cellular processes. This review aims at integrating the established hallmarks of cancer with the plasticity of cancer cells as an emerging hallmark; responsible for tumor heterogeneity; therapy resistance and relapse. The discussion will contextualize the involvement of nucleolin in the establishment of cancer hallmarks and its application as a marker protein for targeted anticancer therapies

The Roles of Matrix Metalloproteinases and Their Inhibitors in Human Diseases

Matrix metalloproteinases (MMPs) are a family of zinc-dependent extracellular matrix (ECM) remodeling endopeptidases that have the capacity to degrade almost every component of the ECM. The degradation of the ECM is of great importance, since it is related to embryonic development and angiogenesis. It is also involved in cell repair and the remodeling of tissues. When the expression of MMPs is altered, it can generate the abnormal degradation of the ECM. This is the initial cause of the development of chronic degenerative diseases and vascular complications generated by diabetes. In addition, this process has an association with neurodegeneration and cancer progression. Within the ECM, the tissue inhibitors of MMPs (TIMPs) inhibit the proteolytic activity of MMPs. TIMPs are important regulators of ECM turnover, tissue remodeling, and cellular behavior. Therefore, TIMPs (similar to MMPs) modulate angiogenesis, cell proliferation, and apoptosis. An interruption in the balance between MMPs and TIMPs has been implicated in the pathophysiology and progression of several diseases. This review focuses on the participation of both MMPs (e.g., MMP-2 and MMP-9) and TIMPs (e.g., TIMP-1 and TIMP-3) in physiological processes and on how their abnormal regulation is associated with human diseases. The inclusion of current strategies and mechanisms of MMP inhibition in the development of new therapies targeting MMPs was also considered.

Perspectives on the role of brain cellular players in cancer-associated brain metastasis: translational approach to understand molecular mechanism of tumor progression

Brain metastasis is one of the leading causes of death among cancer patients. Cancer cells migrate to various sites and harbor different niche in the body which help cancer cells in their survival. The brain is one of the safest place where cancer cells are protected from immune cells. Breast, lung, and melanoma cancer cells have high propensity to migrate towards the brain. To enter the brain, cancer cells have to cross the blood brain barrier. Survival and finding new niche in the brain are directed by several mechanisms in which different cellular players take part such as astrocytes, microglia, Schwann cells, satellite cells, oligodendrocytes, and ependymal cells. Usually, cancer cells highjack the machinery of brain cellular players to survive in the brain environment. It has been shown that co-culture of M2 macrophage with cancer cells leads to increased proliferation and survival of cancer cells. One of the challenges of understanding brain metastasis is appropriate model system to understand dynamic interaction of cancer cells and brain cellular players. To meet this challenge, microfluidic-based devices are employed which can mimic the dynamic conditions as well as can be used for culturing human cells for personalized therapy. In this review, we have systematically reviewed the current status of the role of cellular players in brain metastasis along with explaining how translational approach of microfluidics can be employed for finding new drug target as well as biomarker for brain metastasis. Finally, we have also commented on the mechanism of action of drugs against brain metastasis.

Metabolism-Based Therapeutic Strategies Targeting Cancer Stem Cells

Cancer heterogeneity constitutes the major source of disease progression and therapy failure. Tumors comprise functionally diverse subpopulations, with cancer stem cells (CSCs) as the source of this heterogeneity. Since these cells bear in vivo tumorigenicity and metastatic potential, survive chemotherapy and drive relapse, its elimination may be the only way to achieve long-term survival in patients. Thanks to the great advances in the field over the last few years, we know now that cellular metabolism and stemness are highly intertwined in normal development and cancer. Indeed, CSCs show distinct metabolic features as compared with their more differentiated progenies, though their dominant metabolic phenotype varies across tumor entities, patients and even subclones within a tumor. Following initial works focused on glucose metabolism, current studies have unveiled particularities of CSC metabolism in terms of redox state, lipid metabolism and use of alternative fuels, such as amino acids or ketone bodies. In this review, we describe the different metabolic phenotypes attributed to CSCs with special focus on metabolism-based therapeutic strategies tested in preclinical and clinical settings.

Mathematical modeling of bone marrow - peripheral blood dynamics in the disease state based on current emerging paradigms, part II

The cancer stem cell hypothesis has gained currency in recent times but concerns remain about its scientific foundations because of significant gaps that exist between research findings and comprehensive knowledge about cancer stem cells (CSCs). In this light, a mathematical model that considers hematopoietic dynamics in the diseased state of the bone marrow and peripheral blood is proposed and used to address findings about CSCs. The ensuing model, resulting from a modification and refinement of a recent model, develops out of the position that mathematical models of CSC development, that are few at this time, are needed to provide insightful underpinnings for biomedical findings about CSCs as the CSC idea gains traction. Accordingly, the mathematical challenges brought on by the model that mirror general challenges in dealing with nonlinear phenomena are discussed and placed in context. The proposed model describes the logical occurrence of discrete time delays, that by themselves present mathematical challenges, in the evolving cell populations under consideration. Under the challenging circumstances, the steady state properties of the model system of delay differential equations are obtained, analyzed, and the resulting mathematical predictions arising therefrom are interpreted and placed within the framework of findings regarding CSCs. Simulations of the model are carried out by considering various parameter scenarios that reflect different experimental situations involving disease evolution in human hosts. Model analyses and simulations suggest that the emergence of the cancer stem cell population alongside other malignant cells engenders higher dimensions of complexity in the evolution of malignancy in the bone marrow and peripheral blood at the expense of healthy hematopoietic development. The model predicts the evolution of an aberrant environment in which the malignant population particularly in the bone marrow shows tendencies of reaching an uncontrollable equilibrium state. Essentially, the model shows that a structural relationship exists between CSCs and non-stem malignant cells that confers on CSCs the role of temporally enhancing and stimulating the expansion of non-stem malignant cells while also benefitting from increases in their own population and these CSCs may be the main protagonists that drive the ultimate evolution of the uncontrollable equilibrium state of such malignant cells and these may have implications for treatment.

Inhibition of CREB binding protein-beta-catenin signaling down regulates CD133 expression and activates PP2A-PTEN signaling in tumor initiating liver cancer cells

Background

The WNT-beta-catenin pathway is known to regulate cellular homeostasis during development and tissue regeneration. Activation of WNT signaling increases the stability of cytoplasmic beta-catenin and enhances its nuclear translocation. Nuclear beta-catenin function is regulated by transcriptional co-factors such as CREB binding protein (CBP) and p300. Hyper-activated WNT-beta-catenin signaling is associated with many cancers. However, its role in inducing stemness to liver cancer cells, its autoregulation and how it regulates tumor suppressor pathways are not well understood. Here we have investigated the role of CBP-beta-catenin signaling on the expression of CD133, a known stem cell antigen and PP2A-PTEN pathway in tumor initiating liver cancer cells.

Methods

Human hepatoblastoma cell line HepG2 and clonally expanded CD133 expressing tumor initiating liver cells (TICs) from premalignant murine liver were used in this study. CBP-beta-catenin inhibitor ICG001 was used to target CBP-beta catenin signaling in liver cancer cells in vitro. Western blotting and real time PCR (qPCR) were used to quantify protein expression/phosphorylation and mRNA levels, respectively. CBP and CD133 gene silencing was performed by siRNA transfection. Fluorescence Activated Cell Sorting (FACS) was performed to quantify CD133 positive cells. Protein Phosphatase (PP2A) activity was measured after PP2AC immunoprecipitation.

Results

CBP inhibitor ICG001 and CBP silencing significantly reduced CD133 expression and anchorage independent growth in HepG2 and murine TICs. CD133 silencing in TICs decreased cell proliferation and expression levels of cell cycle regulatory genes, CyclinD1 and CyclinA2. ICG001 treatment and CBP silencing reduced the levels of phospho^{Ser380/Tyr382/383}PTEN, phospho^Ser473-AKT, Phospho-^Ser552beta-catenin in TICs. ICG001 mediated de-phosphorylation of PTEN in TICs was PP2A dependent and partly prevented by co-treatment with PP2A inhibitor okadaic acid.

Conclusions

CBP-beta-catenin signaling promotes stemness via CD133 induction and cell proliferation in TICs. We found a novel functional link between CBP-beta-catenin and PP2A-PTEN-AKT pathway in liver TICs. Therefore, CBP-beta-catenin-PP2A-PTEN-AKT signaling axis could be a novel therapeutic target to prevent liver tumor initiation and cancer recurrence.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0222-5) contains supplementary material, which is available to authorized users.

MiR-148a functions to suppress metastasis and serves as a prognostic indicator in triple-negative breast cancer

Triple-negative breast cancer (TNBC) presents a major challenge in the clinic due to its lack of reliable prognostic markers and targeted therapies. Accumulating evidence strongly supports the notion that microRNAs (miRNAs) are involved in tumorigenesis and could serve as biomarkers for diagnostic purposes. To identify miRNAs that functionally suppress metastasis of TNBC, we employed a concerted approach with selecting miRNAs that display differential expression profiles from bioinformatic analyses of breast cancer patient databases and validating top candidates with functional assays using breast cancer cell lines and mouse models. We have found that miR-148a exhibits properties as a tumor suppressor as its expression is inversely correlated with the ability of both human and mouse breast cancer cells to colonize the lung in mouse xenograft tumor models. Mechanistically, miR-148a appears to suppress the extravasation process of cancer cells, likely by targeting two genes WNT1 and NRP1 in a cell non-autonomous manner. Importantly, lower expression of miR-148a is detected in higher-grade tumor samples and correlated with increased likelihood to develop metastases and poor prognosis in subsets of breast cancer patients, particularly those with TNBC. Thus, miR-148a is functionally defined as a suppressor of breast cancer metastasis and may serve as a prognostic biomarker for this disease.

The Role of micro RNAs in Breast Cancer Metastasis: Preclinical Validation and Potential Therapeutic Targets

Despite the approval of several molecular therapies in the last years, breast cancer-associated death ranks as the second highest in women. This is due to metastatic disease, which represents a challenge for treatment. A better understanding of the molecular mechanisms of metastasis is, therefore, of paramount importance. In this review we summarize the role of micro RNAs (miRs) involved in metastasis of breast cancer. We present an overview on metastasis-promoting, -suppressing and context-dependent miRs with both activities. We have categorized the corresponding miRs according to their target classes, interaction with stromal cells or exosomes. The pathways affected by individual miRs are outlined in regard to in vitro properties, activity in metastasis-related in vivo models and clinical significance. Current approaches that may be suitable for therapeutic inhibition or restauration of miR activity are outlined. Finally, we discuss the delivery bottlenecks which present as a major challenge in nucleic acid (miR)-based therapies.

Road to stemness in hepatocellular carcinoma

Carcinogenic process has been proposed to relay on the capacity to induce local tissue damage and proliferative repair. Liver has a great regeneration capacity and currently, most studies point towards the dominant role of hepatocytes in regeneration at all levels of liver damage. The most frequent liver cancer is hepatocellular carcinoma (HCC). Historical findings originally led to the idea that the cell of origin of HCC might be a progenitor cell. However, current linage tracing studies put the progenitor hypothesis of HCC origin into question. In agreement with their dominant role in liver regeneration, mature hepatocytes are emerging as the cell of origin of HCC, although, the specific hepatocyte subpopulation of origin is yet to be determined. The relationship between the cancer cell of origin (CCO) and cancer-propagating cells, known as hepatic cancer stem cell (HCSC) is unknown. It has been challenging to identify the definitive phenotypic marker of HCSC, probably due to the existence of different cancer stem cells (CSC) subpopulations with different functions within HCC. There is a dynamic interconversion among different CSCs, and between CSC and non-CSCs. Because of that, CSC-state is currently defined as a description of a highly adaptable and dynamic intrinsic property of tumor cells, instead of a static subpopulation of a tumor. Altered conditions could trigger the gain of stemness, some of them include: EMT-MET, epigenetics, microenvironment and selective stimulus such as chemotherapy. This CSC heterogeneity and dynamism makes them out reach from therapeutic protocols directed to a single target. A further avenue of research in this line will be to uncover mechanisms that trigger this interconversion of cell populations within tumors and target it.

Target Therapies for Uterine Carcinosarcomas: Current Evidence and Future Perspectives

Carcinosarcomas (CS) in gynecology are very infrequent and represent only 2-5% of uterine cancers. Despite surgical cytoreduction and subsequent chemotherapy being the primary treatment for uterine CS, the overall five-year survival rate is 30 ± 9% and recurrence is extremely common (50-80%). Due to the poor prognosis of CS, new strategies have been developed in the last few decades, targeting known dysfunctional molecular pathways for immunotherapy. In this paper, we aimed to gather the available evidence on the latest therapies for the treatment of CS. We performed a systematic review using the terms "uterine carcinosarcoma", "uterine Malignant Mixed Müllerian Tumors", "target therapies", "angiogenesis therapy", "cancer stem cell therapy", "prognostic biomarker", and "novel antibody-drug". Based on our results, the differential expression and accessibility of epithelial cell adhesion molecule-1 on metastatic/chemotherapy-resistant CS cells in comparison to normal tissues and Human Epidermal Growth Factor Receptor 2 (HER2) open up new possibilities in the field of target therapy. Nevertheless, future investigations are needed to clarify the impact of these new therapies on survival rate and medium-/long-term outcomes.

Overcoming Therapeutic Resistance of Bone Sarcomas: Overview of the Molecular Mechanisms and Therapeutic Targets for Bone Sarcoma Stem Cells

Bone sarcomas are heterogeneous malignant tumors that exhibit clinical, histological, and molecular heterogeneity. Recent progress in their multimodal treatment has gradually improved patient prognosis; however, drug resistance and distant metastasis remain unresolved clinical problems. Recent investigations have suggested the existence of cancer stem-like cells (CSCs) in bone sarcomas, which represent a subpopulation of tumor cells with high tumor-forming ability. The hallmarks of CSCs include tumor- and metastasis-forming potential and drug resistance, which are responsible for poor prognoses of bone sarcoma patients. Therefore, elucidation of the molecular mechanisms of CSCs and identification of therapeutic targets could contribute to novel treatment strategies for bone sarcomas and improve patient prognosis. This paper provides an overview of the accumulating knowledge on bone sarcoma stem cells and preclinical analyses to overcome their lethal phenotypes, in addition to a discussion of their potential for novel therapeutics for bone sarcomas.

Cyclin D1 as a therapeutic target of renal cell carcinoma- a combined transcriptomics, tissue microarray and molecular docking study from the Kingdom of Saudi Arabia

BACKGROUND

Renal cell carcinoma (RCC) is a seventh ranked malignancy with poor prognosis. RCC is lethal at metastatic stage as it does not respond to conventional systemic treatments, and there is an urgent need to find out promising novel biomarkers for effective treatment. The goal of this study was to evaluate the biomarkers that can be potential therapeutic target and predict effective inhibitors to treat the metastatic stage of RCC.

METHODS

We conducted transcriptomic profiling to identify differentially expressed genes associated with RCC. Molecular pathway analysis was done to identify the canonical pathways and their role in RCC. Tissue microarrays (TMA) based immunohistochemical stains were used to validate the protein expression of cyclinD1 (CCND1) and were scored semi-quantitatively from 0 to 3+ on the basis of absence or presence of staining intensity in the tumor cell. Statistical analysis determined the association of CCND1 expression with RCC. Molecular docking analyses were performed to check the potential of two natural inhibitors, rutin and curcumin to bind CCND1.

RESULTS

We detected 1490 significantly expressed genes (1034, upregulated and 456, downregulated) in RCC using cutoff fold change 2 and p value < 0.05. Hes-related family bHLH transcription factor with YRPW motif 1 (HEY1), neuropilin 2 (NRP2), lymphoid enhancer-binding factor 1 (LEF1), and histone cluster 1 H3h (HIST1H3H) were most upregulated while aldolase B, fructose-bisphosphate (ALDOB), solute carrier family 12 (SLC12A1), calbindin 1 (CALB1) were the most down regulated genes in our dataset. Functional analysis revealed Wnt/β-catenin signaling as the significantly activated canonical pathway (z score = 2.53) involving cyclin D1 (CCND1). CCND1 was overexpressed in transcriptomic studies (FC = 2.26, p value = 0.0047) and TMA results also showed the positive expression of CCND1 in 53 % (73/139) of RCC cases. The ligands - rutin and curcumin bounded with CCND1 with good affinity.

CONCLUSION

CCND1 was one of the important upregulated gene identified in microarray and validated by TMA. Docking study showed that CCND1 may act as a potential therapeutic target and its inhibition could focus on the migratory, invasive, and metastatic potential of RCC. Further in vivo and in vitro molecular studies are needed to investigate the therapeutic target potential of CCND1 for RCC treatment.

Mathematical modeling of bone marrow--peripheral blood dynamics in the disease state based on current emerging paradigms, part I

Stemming from current emerging paradigms related to the cancer stem cell hypothesis, an existing mathematical model is expanded and used to study cell interaction dynamics in the bone marrow and peripheral blood. The proposed mathematical model is described by a system of nonlinear differential equations with delay, to quantify the dynamics in abnormal hematopoiesis. The steady states of the model are analytically and numerically obtained. Some conditions for the local asymptotic stability of such states are investigated. Model analyses suggest that malignancy may be irreversible once it evolves from a nonmalignant state into a malignant one and no intervention takes place. This leads to the proposition that a great deal of emphasis be placed on cancer prevention. Nevertheless, should malignancy arise, treatment programs for its containment or curtailment may have to include a maximum and extensive level of effort to protect normal cells from eventual destruction. Further model analyses and simulations predict that in the untreated disease state, there is an evolution towards a situation in which malignant cells dominate the entire bone marrow - peripheral blood system. Arguments are then advanced regarding requirements for quantitatively understanding cancer stem cell behavior. Among the suggested requirements are, mathematical frameworks for describing the dynamics of cancer initiation and progression, the response to treatment, the evolution of resistance, and malignancy prevention dynamics within the bone marrow - peripheral blood architecture.

Registered report: Wnt activity defines colon cancer stem cells and is regulated by the microenvironment

The Reproducibility Project: Cancer Biology seeks to address growing concerns about reproducibility in scientific research by replicating selected results from a substantial number of high-profile papers in the field of cancer biology. The papers, which were published between 2010 and 2012, were selected on the basis of citations and Altmetric scores (Errington et al., 2014). This Registered report describes the proposed replication plan of key experiments from ‘Wnt activity defines colon cancer stem cells and is regulated by the microenvironment’ by Vermeulen and colleagues, published in Nature Cell Biology in 2010 (Vermeulen et al., 2010). The key experiments that will be replicated are those reported in Figures 2F, 6D, and 7E. In these experiments, Vermeulen and colleagues utilize a reporter for Wnt activity and show that colon cancer cells with high levels of Wnt activity also express cancer stem cell markers (Figure 2F; Vermeulen et al., 2010). Additionally, treatment either with conditioned medium derived from myofibroblasts or with hepatocyte growth factor restored clonogenic potential in low Wnt activity colon cancer cells in vitro (Figure 6D; Vermeulen et al., 2010) and in vivo (Figure 7E; Vermeulen et al., 2010). The Reproducibility Project: Cancer Biology is a collaboration between the Center for Open Science and Science Exchange and the results of the replications will be published in eLife.

DOI:http://dx.doi.org/10.7554/eLife.07301.001

RNA-directed epigenetic silencing of Periostin inhibits cell motility

The over-expression of Periostin, a member of the fasciclin family of proteins, has been reported in a number of cancers and, in particular, in metastatic tumours. These include breast, ovarian, lung, colon, head and neck, pancreatic, prostate, neuroblastoma and thyroid cancers. It is thought that Periostin plays a major role in the development of metastases owing to its apparent involvement in restructuring of the extracellular matrix to create a microenvironment favouring invasion and metastases, angiogenesis, independent proliferation, avoidance of apoptosis and the ability for cells to re-enter the cell cycle. As such we reasoned that targeted suppression of Periostin at the promoter and epigenetic level could result in the stable inhibition of cell motility. We find here that promoter-directed small antisense non-coding RNAs can induce transcriptional gene silencing of Periostin that results ultimately in a loss of cellular motility. The observations presented here suggest that cell motility and possibly metastasis can be controlled by transcriptional and epigenetic regulation of Periostin, offering a potentially new and novel manner to control the spread of cancerous cells.

Cancer stem cells: the promise and the potential

Despite the advancement of treatment modalities, many cancer patients experience tumor recurrence and metastasis at regional or distant sites. Evolving understanding of tumor biology has led to the hypothesis that tumors may possess a stem cell-like subpopulation known as cancer stem cells (CSCs) that may be involved in driving tumor propagation and pathogenesis. Like normal stem cells (NSCs), CSCs can be identified by markers such as CD133, CD44, and ALDH. CSCs have the ability to self-renew and differentiate into different tumor components through stemness pathways, such as Wnt, TGF-β, STAT, and Hippo-YAP/TAZ, among others. In NSCs, stemness pathways are strictly regulated and control many important biologic processes, including embryogenesis and intestinal crypt cellular regulation. In contrast, stemness pathways in CSCs are significantly dysregulated. Combining current drugs with the targeting of these stemness pathways may significantly improve patient prognosis. The aim of this supplement is to update clinicians on the accumulated evidence characterizing the role of CSCs in tumor initiation, heterogeneity, therapy resistance, and recurrence and metastasis, and the potential for effectively treating patients.

Molecular biology of liver cancer stem cells

Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers worldwide. The concept of cancer stem cells (CSCs) is based primarily on the clinical and experimental observations that indicate the existence of a subpopulation of cells with the capacity to self-renew and differentiate as well as show increased resistance to radiation and chemotherapy. They are considered as the factors responsible for the cases of tumor relapse. Hepatic progenitor cells (HPCs) could form the basis of some hepatocellular carcinomas (HCC) and cholangiocarcinomas. Liver CSCs have been reported in multiple subtypes of HCC and are considered as the master regulators of HCC initiation, tumor metastasis, and progression. HPCs activators such as epithelial cell adhesion molecule (EpCAM), Wnt/β-catenin, transforming growth factor-beta (TGF-β), Notch and Hedgehog signaling systems expedite tumorigenesis or conversely, serve as a powerful cancer-prevention tool. Recent work has also identified Sal-like protein 4 (SALL4) and some epigenetic regulations as important molecules, while several therapeutic drugs that directly control HPCs have been tested both in vivo and in vitro. However, liver CSCs clearly have a complex pathogenesis, with the potential for considerable crosstalk and redundancy in signaling pathways. Hence, the targeting of single molecules or pathways may have limited benefit for treatment. In addition to the direct control of liver CSCs, many other factors are needed for CSC maintenance including angiogenesis, vasculogenesis, invasion and migration, hypoxia, immune evasion, multiple drug resistance, and radioresistance. Here, we provide a brief review of molecular signaling in liver CSCs and present insights into new therapeutic strategies for their targeting.

Molecular biology of liver cancer stem cells

Hepatocellular carcinoma (HCC) is one of the most common and lethal cancers worldwide. The concept of cancer stem cells (CSCs) is based primarily on the clinical and experimental observations that indicate the existence of a subpopulation of cells with the capacity to self-renew and differentiate as well as show increased resistance to radiation and chemotherapy. They are considered as the factors responsible for the cases of tumor relapse. Hepatic progenitor cells (HPCs) could form the basis of some hepatocellular carcinomas (HCC) and cholangiocarcinomas. Liver CSCs have been reported in multiple subtypes of HCC and are considered as the master regulators of HCC initiation, tumor metastasis, and progression. HPCs activators such as epithelial cell adhesion molecule (EpCAM), Wnt/β-catenin, transforming growth factor-beta (TGF-β), Notch and Hedgehog signaling systems expedite tumorigenesis or conversely, serve as a powerful cancer-prevention tool. Recent work has also identified Sal-like protein 4 (SALL4) and some epigenetic regulations as important molecules, while several therapeutic drugs that directly control HPCs have been tested both in vivo and in vitro. However, liver CSCs clearly have a complex pathogenesis, with the potential for considerable crosstalk and redundancy in signaling pathways. Hence, the targeting of single molecules or pathways may have limited benefit for treatment. In addition to the direct control of liver CSCs, many other factors are needed for CSC maintenance including angiogenesis, vasculogenesis, invasion and migration, hypoxia, immune evasion, multiple drug resistance, and radioresistance. Here, we provide a brief review of molecular signaling in liver CSCs and present insights into new therapeutic strategies for their targeting.

Reactive astrocytes promote the metastatic growth of breast cancer stem-like cells by activating Notch signalling in brain

Brain metastasis of breast cancer profoundly affects the cognitive and sensory functions as well as morbidity of patients, and the 1 year survival rate among these patients remains less than 20%. However, the pathological mechanism of brain metastasis is as yet poorly understood. In this report, we found that metastatic breast tumour cells in the brain highly expressed IL-1β which then ‘activated’ surrounding astrocytes. This activation significantly augmented the expression of JAG1 in the astrocytes, and the direct interaction of the reactivated astrocytes and cancer stem-like cells (CSCs) significantly stimulated Notch signalling in CSCs. We also found that the activated Notch signalling in CSCs up-regulated HES5 followed by promoting self-renewal of CSCs. Furthermore, we have shown that the blood-brain barrier permeable Notch inhibitor, Compound E, can significantly suppress the brain metastasis in vivo. These results represent a novel paradigm for the understanding of how metastatic breast CSCs re-establish their niche for their self-renewal in a totally different microenvironment, which opens a new avenue to identify a novel and specific target for the brain metastatic disease.

Wnt/β-catenin signaling and disease

The WNT signal transduction cascade controls myriad biological phenomena throughout development and adult life of all animals. In parallel, aberrant Wnt signaling underlies a wide range of pathologies in humans. In this Review, we provide an update of the core Wnt/β-catenin signaling pathway, discuss how its various components contribute to disease, and pose outstanding questions to be addressed in the future.

Drugging Wnt signalling in cancer

Aberrant regulation of the Wnt signalling pathway has emerged as a prevalent theme in cancer biology. This chapter summarizes the research that provides a proof of concept for inhibiting Wnt signalling in cancer, the potential means by which this could be achieved, and some recent advances towards this goal. A brief discussion of molecular diagnostics and possible safety concerns is also provided.

Wnt signaling in cancer

Aberrant regulation of the Wnt signaling pathway is a prevalent theme in cancer biology. From the earliest observation that Wnt overexpression could lead to malignant transformation of mouse mammary tissue to the most recent genetic discoveries gleaned from tumor genome sequencing, the Wnt pathway continues to evolve as a central mechanism in cancer biology. This article summarizes the evidence supporting a role for Wnt signaling in human cancer. This includes a review of the genetic mutations affecting Wnt pathway components, as well as some of epigenetic mechanisms that alter expression of genes relevant to Wnt. I also highlight some research on the cooperativity of Wnt with other signaling pathways in cancer. Finally, some emphasis is placed on laboratory research that provides a proof of concept for the therapeutic inhibition of Wnt signaling in cancer.

Sequential activation and inactivation of Dishevelled in the Wnt/beta-catenin pathway by casein kinases

Dishevelled (Dvl) is a key component in the Wnt/β-catenin signaling pathway. Dvl can multimerize to form dynamic protein aggregates, which are required for the activation of downstream signaling. Upon pathway activation by Wnts, Dvl becomes phosphorylated to yield phosphorylated and shifted (PS) Dvl. Both activation of Dvl in Wnt/β-catenin signaling and Wnt-induced PS-Dvl formation are dependent on casein kinase 1 (CK1) δ/ε activity. However, the overexpression of CK1 was shown to dissolve Dvl aggregates, and endogenous PS-Dvl forms irrespective of whether or not the activating Wnt triggers the Wnt/β-catenin pathway. Using a combination of gain-of-function, loss-of-function, and domain mapping approaches, we attempted to solve this discrepancy regarding the role of CK1ε in Dvl biology. We analyzed mutual interaction of CK1δ/ε and two other Dvl kinases, CK2 and PAR1, in the Wnt/β-catenin pathway. We show that CK2 acts as a constitutive kinase whose activity is required for the further action of CK1ε. Furthermore, we demonstrate that the two consequences of CK1ε phosphorylation are separated both spatially and functionally; first, CK1ε-mediated induction of TCF/LEF-driven transcription (associated with dynamic recruitment of Axin1) is mediated via a PDZ-proline-rich region of Dvl. Second, CK1ε-mediated formation of PS-Dvl is mediated by the Dvl3 C terminus. Furthermore, we demonstrate with several methods that PS-Dvl has decreased ability to polymerize with other Dvls and could, thus, act as the inactive signaling intermediate. We propose a multistep and multikinase model for Dvl activation in the Wnt/β-catenin pathway that uncovers a built-in de-activation mechanism that is triggered by activating phosphorylation of Dvl by CK1δ/ε.

Expression of Reg family proteins in embryonic stem cells and its modulation by Wnt/beta-catenin signaling

Regenerating islet (Reg) proteins are involved in the proliferation and differentiation of diverse cell types. However, whether embryonic stem cells (ESCs) express Reg genes and their corresponding proteins remains unknown. In this study, we probed the expression of Reg family members by mouse ESCs (mESCs). Mouse Reg1 and Reg3gamma were detected in undifferentiated stem cells. Furthermore, we tested if gastrin--an inducer of Reg1 expression in committed cells--up-regulates the Reg1 gene in mESCs. Gastrin did not affect the expression of Reg1 either in self-renewing mESCs or under conditions permitting their differentiation. Moreover, overexpression of Reg genes found in various forms of cancer has been linked to dysregulated activation of the canonical Wnt/beta-catenin cascade. Given the important roles of Wnt signaling in stem cells, we investigated if activation of Wnt alters the expression of Reg genes in mESCs. Wnt activation led to an increase in Reg1 gene expression with a concomitant increase in the amount of secreted Reg1 protein. Finally, the expression pattern of genes indicative of differentiation was examined in mESCs that were either exposed to soluble Reg1 or overexpressed the Reg1 gene. This is the first account of expression of Reg family members by ESCs. Our results show that the canonical Wnt cascade affects Reg expression and warrants further studies into the potential roles of Reg proteins in stem cell physiology.

Gene expression profiling reveals new aspects of PIK3CA mutation in ERalpha-positive breast cancer: major implication of the Wnt signaling pathway

Background

The PI3K/AKT pathway plays a pivotal role in breast cancer development and maintenance. PIK3CA, encoding the PI3K catalytic subunit, is the oncogene exhibiting a high frequency of gain-of-function mutations leading to PI3K/AKT pathway activation in breast cancer. PIK3CA mutations have been observed in 30% to 40% of ERα-positive breast tumors. However the physiopathological role of PIK3CA mutations in breast tumorigenesis remains largely unclear.

Methodology/Principal Findings

To identify relevant downstream target genes and signaling activated by aberrant PI3K/AKT pathway in breast tumors, we first analyzed gene expression with a pangenomic oligonucleotide microarray in a series of 43 ERα-positive tumors with and without PIK3CA mutations. Genes of interest were then investigated in 249 ERα-positive breast tumors by real-time quantitative RT-PCR. A robust collection of 19 genes was found to be differently expressed in PIK3CA-mutated tumors. PIK3CA mutations were associated with over-expression of several genes involved in the Wnt signaling pathway (WNT5A, TCF7L2, MSX2, TNFRSF11B), regulation of gene transcription (SEC14L2, MSX2, TFAP2B, NRIP3) and metal ion binding (CYP4Z1, CYP4Z2P, SLC40A1, LTF, LIMCH1).

Conclusion/Significance

This new gene set should help to understand the behavior of PIK3CA-mutated cancers and detailed knowledge of Wnt signaling activation could lead to novel therapeutic strategies.

A Distinct Slow-Cycling Cancer Stem-like Subpopulation of Pancreatic Adenocarcinoma Cells is maintained in Vivo

Pancreatic adenocarcinoma has the worst prognosis of any major malignancy, with <5% of patients surviving five years. This can be contributed to the often late diagnosis, lack of sufficient treatment and metastatic spread. Heterogeneity within tumors is increasingly becoming a focus in cancer research, as novel therapies are required to target the most aggressive subpopulations of cells that are frequently termed cancer stem cells (CSCs). In the current study, we describe the identification of a slow-cycling cancer stem-like population of cells in vivo in BxPC-3 and Panc03.27 xenografts. A distinct slow-cycling label-retaining population of cells (DiI+/SCC) was found both at the edge of tumors, and in small circumscribed areas within the tumors. DiI+/SCC in these areas display an epithelial-to-mesenchymal transition (EMT) fingerprint, including an upregulation of the mesenchymal markers vimentin and N-cadherin and a loss of the epithelial marker E-cadherin. DiI+/SCC also displayed a critical re-localization of beta-catenin from the membrane to the nucleus. Additionally, the DiI+/SCC population was found to express the developmental signaling molecule sonic hedgehog. This study represents a novel step in defining the biological activities of a tumorigenic subpopulation within the heterogeneous tumor microenvironment in vivo. Understanding the interactions and functions of a CSC population within the context of the tumor microenvironment is critical to design targeted therapeutics.

Urothelial carcinoma: stem cells on the edge

Tumors are heterogeneous collections of cells with highly variable abilities to survive, grow, and metastasize. This variability likely stems from epigenetic and genetic influences, either stochastic or hardwired by cell type-specific lineage programs. That differentiation underlies tumor cell heterogeneity was elegantly demonstrated in hematopoietic tumors, in which rare primitive cells (cancer stem cells (CSCs)) resembling normal hematopoietic stem cells are ultimately responsible for tumor growth and viability. Because of the compelling clinical implications CSCs pose--across the entire spectrum of cancers--investigators applied the CSC model to cancers arising in tissues with crudely understood differentiation programs. Instead of relying on differentiation, these studies used empirically selected markers and statistical arguments to identify CSCs. The empirical approach has stimulated important questions about "stemness" in cancer cells as well as the validity and stoichiometry of CSC assays. The recent identification of urothelial differentiation programs in urothelial carcinomas (UroCas) supports the idea that solid epithelial cancers (carcinomas) develop and differentiate analogously to normal epithelia and provides new insights about the spatial localization and molecular makeup of carcinoma CSCs. Importantly, CSCs from invasive UroCas (UroCSCs) appear well situated to exchange important signals with adjacent stroma, to escape immune surveillance, and to survive cytotoxic therapy. These signals have potential roles in treatment resistance and many participate in druggable cellular pathways. In this review, we discuss the implications of these findings in understanding CSCs and in better understanding how UroCas form, progress, and should be treated.

Cancer genesis across the age spectrum: associations with tissue development, maintenance, and senescence

Cancer genesis across the age spectrum is a complex, multifactorial process, and parallels changes in site-specific tissue development, maintenance, and senescence. Cancer is not a single disease, and different tumor and stem cells may demonstrate various manifestations of abnormal function. Mutations in DNA, some random and some explained by exogenous insults, accompanied by changes in the tissue microenvironment, generally precede the onset of aberrant replication and apoptosis. Moreover, increasing evidence suggests that genetic programs normally active only during development of human beings may be reactivated during tumorigenesis. The complicated underlying biology of human growth, development, and carcinogenesis is reflected in the highly disparate patterns in site-specific cancer incidence rates across age groups. In childhood, the peak years of an organ system's increase in size correlate with peak years of cancer incidence. Conversely, in most adult-onset cancers, it is exposure to exogenous toxins, the failure of maintenance and repair, and finally, dysfunction(s) in the normal cellular aging process that likely play a role in the development of these malignancies. Additional basic science investigations and epidemiologic studies will assist in our understanding of the mechanisms that underlie the notable difference in site-specific cancer incidence according to age.

Stromal fibroblasts in digestive cancer

The normal gastrointestinal stroma consists of extra-cellular matrix and a community of stromal cells including fibroblasts, myofibroblasts, smooth muscle cells, pericytes, endothelium and inflammatory cells. α-smooth muscle actin (α-SMA) positive stromal fibroblasts, often referred to as myofibroblasts or activated fibroblasts, are critical in the development of digestive cancer and help to create an environment that is permissive of tumor growth, angiogenesis and invasion. This review focusses on the contribution of activated fibroblasts in carcinogenesis and where possible directly applies this to, and draws on examples from, gastrointestinal cancer. In particular, the review expands on the definition, types and origins of activated fibroblasts. It examines the molecular biology of stromal fibroblasts and their contribution to the peritumoral microenvironment and concludes by exploring some of the potential clinical applications of this exciting branch of cancer research. Understanding the origin and biology of activated fibroblasts will help in the development of an integrated epithelial-stromal sequence to cancer that will ultimately inform cancer pathogenesis, natural history and future therapeutics.

Ror2 receptor requires tyrosine kinase activity to mediate Wnt5A signaling

The Wnts include a large family of secreted proteins that serve as important signals during embryonic development and adult homeostasis. In the most well understood Wnt signaling pathway, Wnt binding to Frizzled and low density lipoprotein receptor-related protein induces β-catenin protein stabilization and entry into the nucleus, resulting in changes in target gene transcription. Emerging evidence suggests that Wnt5a can inhibit Wnt/β-catenin signaling through interaction with the receptor Ror2. The Ror2 protein belongs to the receptor tyrosine kinase superfamily and contains several recognizable structural motifs. However, limited information is available regarding which specific domains are required for the inhibitory signaling activity of Wnt5a. Through mutation and deletion analysis, we have analyzed which specific domains and residues, including those necessary for tyrosine kinase activity, mediate the Wnt5a signal. To determine whether Ror2 can inhibit canonical Wnt signaling in vivo, we examined the effect of Ror2 loss on the expression of the Wnt reporter Axin2^LacZ, finding increased reporter activity in Ror2 null mice, demonstrating that Ror2 can also inhibit Wnt/β-catenin signaling in the context of intact tissues.

Omental milky spots--highly efficient "natural filter" for screening gastric cancer stem cells

Over the last decades, cancer stem cells (CSCs) have been identified in different solid tumors and three strategies have been employed to identify them as follows: (1) expression of cell surface markers, (2) ability to exclude fluorescent dye Hoescht 33342 in a cell population termed "side population" (SP), and (3) formation of tumorspheres in suspension culture. But these methods focus on a minor subset of tumor cells, initial CSCs are still hidden among them and genuine CSCs have not yet been isolated and purified. Here we propose a new strategy to identify and isolate gastric cancer stem cells--using omental milky spots to screen gastric cancer stem cells in peritoneal metastasis mouse models of gastric cancer. This strategy directly target cancer stem cells--which can cause a new tumor by itself. Omental milky spots and their macrophages become a highly efficient "natural filter" for screening gastric cancer stem cells.

Tobacco smoke induces polycomb-mediated repression of Dickkopf-1 in lung cancer cells

Limited information is available about epigenetic mechanisms by which cigarette smoke enhances the initiation and progression of lung cancer. To examine this issue, A549 and Calu-6 lung cancer cells were cultured in normal media with or without tobacco smoke condensate (TSC) under clinically relevant exposure conditions. Ten-day TSC exposure dramatically increased the tumorigenicity of lung cancer cells in nude mice. Microarray and quantitative reverse transcription-PCR (RT-PCR) experiments revealed that this phenomenon coincided with diminished expression of Dickkopf-1 (Dkk-1). Western blot, chromatin immunoprecipitation, methylation-specific PCR, and pyrosequencing experiments showed that repression of Dkk-1 coincided with decreased H4K16Ac, increased H3K27me3, and recruitment of SirT1, EZH2, SUZ12, and Bmi1 without DNA hypermethylation within the Dkk-1 promoter despite prolonged TSC exposures. Removal of TSC from culture media resulted in loss of promoter-associated polycomb repressor complexes and reexpression of Dkk-1. siRNA-mediated knockdown of EZH2 and SirT1 partially abrogated TSC-mediated inhibition of Dkk-1 expression. Western blot and quantitative RT-PCR array experiments showed that TSC exposure as well as knockdown of Dkk-1 activated Wnt signaling and significantly up-regulated Wnt5a in lung cancer cells. Knockdown of Dkk-1 recapitulated the dramatic protumorigenic effects of TSC exposure in Calu-6 cells. Despite the transient nature of Dkk-1 repression following TSC exposure in vitro, Dkk-1 remained silenced in tumor xenografts derived from TSC-treated Calu-6 cells. Collectively, these data provide evidence that cigarette smoke directly engages polycomb machinery to activate a signaling network implicated in maintenance of cancer stem cells.