β-Catenin in Pluripotency

Heparinized Gelatin-Based Hydrogels for Differentiation of Induced Pluripotent Stem Cells

Chemically defined hydrogels are increasingly utilized to define the effects of extracellular matrix (ECM) components on cellular fate determination of human embryonic and induced pluripotent stem cell (hESC and hiPSCs). In particular, hydrogels cross-linked by orthogonal click chemistry, including thiol-norbornene photopolymerization and inverse electron demand Diels–Alder (iEDDA) reactions, are explored for 3D culture of hESC/hiPSCs owing to the specificity, efficiency, cytocompatibility, and modularity of the cross-linking reactions. In this work, we exploited the modularity of thiol-norbornene photopolymerization to create a biomimetic hydrogel platform for 3D culture and differentiation of hiPSCs. A cell-adhesive, protease-labile, and cross-linkable gelatin derivative, gelatin-norbornene (GelNB), was used as the backbone polymer for constructing hiPSC-laden biomimetic hydrogels. GelNB was further heparinized via the iEDDA click reaction using tetrazine-modified heparin (HepTz), creating GelNB-Hep. GelNB or GelNB-Hep was modularly cross-linked with either inert macromer poly(ethylene glycol)-tetra-thiol (PEG4SH) or another bioactive macromer-thiolated hyaluronic acid (THA). The formulations of these hydrogels were modularly tuned to afford biomimetic matrices with similar elastic moduli but varying bioactive components, enabling the understanding of each bioactive component on supporting hiPSC growth and ectodermal, mesodermal, and endodermal fate commitment under identical soluble differentiation cues.

E-cadherin maintains the undifferentiated state of mouse spermatogonial progenitor cells via β-catenin

Background

Cadherins play a pivotal role in facilitating intercellular interactions between spermatogonial progenitor cells (SPCs) and their surrounding microenvironment. Specifically, E-cadherin serves as a cellular marker of SPCs in many species. Depletion of E-cadherin in mouse SPCs showed no obvious effect on SPCs homing and spermatogenesis.

Results

Here, we investigated the regulatory role of E-cadherin in regulating SPCs fate. Specific deletion of E-cadherin in germ cells was shown to promote SPCs differentiation, evidencing by reduced PLZF⁺ population and increased c-Kit⁺ population in mouse testes. E-cadherin loss down-regulated the expression level of β-catenin, leading to the reduced β-catenin in nuclear localization for transcriptional activity. Remarkably, increasing expression level of Cadherin-22 (CDH22) appeared specifically after E-cadherin deletion, indicating CDH22 played a synergistic effect with E-cadherin in SPCs. By searching for the binding partners of β-catenin, Lymphoid enhancer-binding factor 1 (LEF1), T-cell factor (TCF3), histone deacetylase 4 (HDAC4) and signal transducer and activator 3 (STAT3) were identified as suppressors of SPCs differentiation by regulating acetylation of differentiation genes with PLZF.

Conclusions

Two surface markers of SPCs, E-cadherin and Cadherin-22, synergically maintain the undifferentiation of SPCs via the pivotal intermediate molecule β-catenin. LEF1, TCF3, STAT3 and HDAC4 were identified as co-regulatory factors of β-catenin in regulation of SPC fate. These observations revealed a novel regulatory pattern of cadherins on SPCs fate.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00880-w.

Pluripotency Stemness and Cancer: More Questions than Answers

Embryonic stem cells and induced pluripotent stem cells provided us with fascinating new knowledge in recent years. Mechanistic insight into intricate regulatory circuitry governing pluripotency stemness and disclosing parallels between pluripotency stemness and cancer instigated numerous studies focusing on roles of pluripotency transcription factors, including Oct4, Sox2, Klf4, Nanog, Sall4 and Tfcp2L1, in cancer. Although generally well substantiated as tumour-promoting factors, oncogenic roles of pluripotency transcription factors and their clinical impacts are revealing themselves as increasingly complex. In certain tumours, both Oct4 and Sox2 behave as genuine oncogenes, and reporter genes driven by composite regulatory elements jointly recognized by both the factors can identify stem-like cells in a proportion of tumours. On the other hand, cancer stem cells seem to be biologically very heterogeneous both among different tumour types and among and even within individual tumours. Pluripotency transcription factors are certainly implicated in cancer stemness, but do not seem to encompass its entire spectrum. Certain cancer stem cells maintain their stemness by biological mechanisms completely different from pluripotency stemness, sometimes even by engaging signalling pathways that promote differentiation of pluripotent stem cells. Moreover, while these signalling pathways may well be antithetical to stemness in pluripotent stem cells, they may cooperate with pluripotency factors in cancer stem cells - a paradigmatic example is provided by the MAPK-AP-1 pathway. Unexpectedly, forced expression of pluripotency transcription factors in cancer cells frequently results in loss of their tumour-initiating ability, their phenotypic reversion and partial epigenetic normalization. Besides the very different signalling contexts operating in pluripotent and cancer stem cells, respectively, the pronounced dose dependency of reprogramming pluripotency factors may also contribute to the frequent loss of tumorigenicity observed in induced pluripotent cancer cells. Finally, contradictory cell-autonomous and non-cell-autonomous effects of various signalling molecules operate during pluripotency (cancer) reprogramming. The effects of pluripotency transcription factors in cancer are thus best explained within the concept of cancer stem cell heterogeneity.

Metabolic Contributions of Wnt Signaling: More Than Controlling Flight

The canonical Wnt signaling pathway is ubiquitous throughout the body and influences a diverse array of physiological processes. Following the initial discovery of the Wnt signaling pathway during wing development in Drosophila melanogaster, it is now widely appreciated that active Wnt signaling in mammals is necessary for the development and growth of various tissues involved in whole-body metabolism, such as brain, liver, pancreas, muscle, and adipose. Moreover, elegant gain- and loss-of-function studies have dissected the tissue-specific roles of various downstream effector molecules in the regulation of energy homeostasis. This review attempts to highlight and summarize the contributions of the Wnt signaling pathway and its downstream effectors on whole-body metabolism and their influence on the development of metabolic diseases, such as diabetes and obesity. A better understanding of the Wnt signaling pathway in these tissues may aid in guiding the development of future therapeutics to treat metabolic diseases.

Stem cells' centrosomes: How can organelles identified 130 years ago contribute to the future of regenerative medicine?

At the core of regenerative medicine lies the expectation of repair or replacement of damaged tissues or whole organs. Donor scarcity and transplant rejection are major obstacles, and exactly the obstacles that stem cell-based therapy promises to overcome. These therapies demand a comprehensive understanding of the asymmetric division of stem cells, i.e. their ability to produce cells with identical potency or differentiated cells. It is believed that with better understanding, researchers will be able to direct stem cell differentiation. Here, we describe extraordinary advances in manipulating stem cell fate that show that we need to focus on the centrosome and the centrosome-derived primary cilium. This belief comes from the fact that this organelle is the vehicle that coordinates the asymmetric division of stem cells. This is supported by studies that report the significant role of the centrosome/cilium in orchestrating signaling pathways that dictate stem cell fate. We anticipate that there is sufficient evidence to place this organelle at the center of efforts that will shape the future of regenerative medicine.

Primary Ciliary Signaling in the Skin-Contribution to Wound Healing and Scarring

Primary cilia (PC) are solitary, post-mitotic, microtubule-based, and membrane-covered protrusions that are found on almost every mammalian cell. PC are specialized cellular sensory organelles that transmit environmental information to the cell. Signaling through PC is involved in the regulation of a variety of cellular processes, including proliferation, differentiation, and migration. Conversely, defective, or abnormal PC signaling can contribute to the development of various pathological conditions. Our knowledge of the role of PC in organ development and function is largely based on ciliopathies, a family of genetic disorders with mutations affecting the structure and function of PC. In this review, we focus on the role of PC in their major signaling pathways active in skin cells, and their contribution to wound healing and scarring. To provide comprehensive insights into the current understanding of PC functions, we have collected data available in the literature, including evidence across cell types, tissues, and animal species. We conclude that PC are underappreciated subcellular organelles that significantly contribute to both physiological and pathological processes of the skin development and wound healing. Thus, PC assembly and disassembly and PC signaling may serve as attractive targets for antifibrotic and antiscarring therapies.

Transient Receptor Potential Ion Channels Mediate Adherens Junctions Dysfunction in a Toluene Diisocyanate-Induced Murine Asthma Model

Disruption of epithelial cell-cell junctions is essential for the initiation and perpetuation of airway inflammation in asthma. We've previously reported compromised epithelial barrier integrity in a toluene diisocyanate (TDI)-induced occupational asthma model. This study is aimed to explore the role of transient receptor potential vanilloid 4 (TRPV4) and transient receptor potential ankyrin 1 (TRPA1) in the dysfunction of adherens junctions in TDI-induced asthma. Mice were sensitized and challenged with TDI for a chemical-induced asthma model. Selective blockers of TRPV4 glycogen synthase kinase (GSK)2193874, 5 and 10 mg/kg) and TRPA1 (HC030031, 10 and 20 mg/kg) were intraperitoneally given to the mice. Immunohistochemistry revealed different expression pattern of TRPV4 and TRPA1 in lung. TDI exposure increased TRPV4 expression in the airway, which can be suppressed by GSK2193874, while treatment with neither TDI alone nor TDI together with HC030031 led to changes of TRPA1 expression in the lung. Blocking either TRPV4 or TRPA1 blunted TDI-induced airway hyperreactivity, airway neutrophilia and eosinophilia, as well as Th2 responses in a dose-dependent manner. At the same time, membrane levels of E-cadherin and β-catenin were significantly decreased after TDI inhalation, which were inhibited by GSK2193874 or HC030031. Moreover, GSK2193874 and HC030031 also suppressed serine phosphorylation of glycogen synthase kinase 3β, tyrosine phosphorylation of β-catenin, as well as activation and nuclear transport of β-catenin in mice sensitized and challenged with TDI. Our study suggested that both TRPV4 and TRPA1 contribute critically to E-cadherin and β-catenin dysfunction in TDI-induced asthma, proposing novel therapeutic targets for asthma.

WNT Signaling in Tumors: The Way to Evade Drugs and Immunity

WNT/β-catenin signaling is involved in many physiological processes. Its implication in embryonic development, cell migration, and polarization has been shown. Nevertheless, alterations in this signaling have also been related with pathological events such as sustaining and proliferating the cancer stem cell (CSC) subset present in the tumor bulk. Related with this, WNT signaling has been associated with the maintenance, expansion, and epithelial-mesenchymal transition of stem cells, and furthermore with two distinctive features of this tumor population: therapeutic resistance (MDR, multidrug resistance) and immune escape. These mechanisms are developed and maintained by WNT activation through the transcriptional control of the genes involved in such processes. This review focuses on the description of the best known WNT pathways and the molecules involved in them. Special attention is given to the WNT cascade proteins deregulated in tumors, which have a decisive role in tumor survival. Some of these proteins function as extrusion pumps that, in the course of chemotherapy, expel the drugs from the cells; others help the tumoral cells hide from the immune effector mechanisms. Among the WNT targets involved in drug resistance, the drug extrusion pump MDR-1 (P-GP, ABCB1) and the cell adhesion molecules from the CD44 family are highlighted. The chemokine CCL4 and the immune checkpoint proteins CD47 and PD-L1 are included in the list of WNT target molecules with a role in immunity escape. This pathway should be a main target in cancer therapy as WNT signaling activation is essential for tumor progression and survival, even in the presence of the anti-tumoral immune response and/or antineoplastic drugs. The appropriate design and combination of anti-tumoral strategies, based on the modulation of WNT mediators and/or protein targets, could negatively affect the growth of tumoral cells, improving the efficacy of these types of therapies.

Cellular signalling by primary cilia in development, organ function and disease

Primary cilia project in a single copy from the surface of most vertebrate cell types; they detect and transmit extracellular cues to regulate diverse cellular processes during development and to maintain tissue homeostasis. The sensory capacity of primary cilia relies on the coordinated trafficking and temporal localization of specific receptors and associated signal transduction modules in the cilium. The canonical Hedgehog (HH) pathway, for example, is a bona fide ciliary signalling system that regulates cell fate and self-renewal in development and tissue homeostasis. Specific receptors and associated signal transduction proteins can also localize to primary cilia in a cell type-dependent manner; available evidence suggests that the ciliary constellation of these proteins can temporally change to allow the cell to adapt to specific developmental and homeostatic cues. Consistent with important roles for primary cilia in signalling, mutations that lead to their dysfunction underlie a pleiotropic group of diseases and syndromic disorders termed ciliopathies, which affect many different tissues and organs of the body. In this Review, we highlight central mechanisms by which primary cilia coordinate HH, G protein-coupled receptor, WNT, receptor tyrosine kinase and transforming growth factor-β (TGFβ)/bone morphogenetic protein (BMP) signalling and illustrate how defects in the balanced output of ciliary signalling events are coupled to developmental disorders and disease progression.

Inhibition of transcription factor T-cell factor 3 (TCF3) using the oligodeoxynucleotide strategy increases embryonic stem cell stemness: possible application in regenerative medicine

The transcription factor T-cell factor 3 (TCF3), one component of the Wnt pathway, is known as a cell-intrinsic inhibitor of many pluripotency genes in embryonic stem cells (ESCs) that influences the balance between pluripotency and differentiation. In this study, the effects of inhibition of TCF3 transcription factor on the stemness of mouse ESCs (mESCs) were investigated using the decoy oligodeoxynucleotides (ODNs) strategy. The TCF3 decoy and its scramble ODNs were designed and synthesized. The interaction specificity of the TCF3 decoy with the TCF3 transcription factor was evaluated by the electrophoretic mobility shift assay. Subcellular localization was carried out using fluorescence and confocal microscopy. Self-renewal and pluripotency of mESCs were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), cell cycle and apoptosis, alkaline phosphatase (ALP), embryoid body (EB) formation, and real-time assays. All experiments were performed in triplicate. The results showed that knockdown of TCF3 by decoy ODNs transfection in mESCs led to an increase in the cell proliferation, ALP enzyme activity, and master regulatory stemness genes and a decrease in the number and diameter of EBs. These results supported TCF3 as a potential target to maintain the pluripotency and self-renewal capacity of mESCs. Knockdown of the TCF3 transcription factor using decoy ODNs can be a promising method to maintain the stemness of stem cells in regenerative medicine and cell therapy researches.

Wnt/β-Catenin/TCF Pathway Is a Phase-Dependent Promoter of Colony Formation and Mesendodermal Differentiation During Human Somatic Cell Reprogramming

Somatic cell reprogramming is a biphasic phenomenon that goes through a mesenchymal-to-epithelial transition, called initiation phase, followed by a maturation phase wherein reprogramming cells acquire pluripotency. Here, we show that these phases display a differential response to Wnt signaling activation. Wnt signaling increases colony formation by promoting cellular epithelialization during the initiation phase in a TCF7-dependent manner. However, during maturation phase, it is also responsible for inducing mesendodermal differentiation, which is negatively regulated by TCF7L1. Thus, Wnt signaling inhibition or TCF7L1 overexpression downregulates mesendodermal gene expression without perturbing pluripotency. Together, our results demonstrate that a phase-specific modulation of Wnt signaling leads to an improved reprogramming efficiency in terms of colony output and pluripotency acquisition. This work provides new insights into the cell context-dependent roles of Wnt signaling during human somatic cell reprogramming.

GSK-3 as a novel prognostic indicator in leukemia

While leukemias represent a diverse set of diseases with malignant cells derived from myeloid or lymphoid origin, a common feature is the dysregulation of signal transduction pathways that influence leukemogeneisis, promote drug resistance, and favor leukemia stem cells. Mutations in PI3K, PTEN, RAS, or other upstream regulators can activate the AKT kinase which has central roles in supporting cell proliferation and survival. A major target of AKT is Glycogen Synthase Kinase 3 (GSK3). GSK3 has two isoforms (alpha and beta) that were studied as regulators of metabolism but emerged as central players in cancer in the early 1990s. GSK3 is unique in that the isoforms are constitutively active. Active GSK3 promotes destruction of oncogenic proteins such as beta Catenin, c-MYC, and MCL-1 and thus has tumor suppressor properties. In AML, inactivation of GSK3 is associated with poor overall survival. Interestingly in some leukemias GSK3 targets a tumor suppressor and thus the kinases can act as tumor promoters in those instances. An example is GSK3 targeting p27Kip1 in AML with MLL translocation. This review will cover the role of GSK3 in various leukemias both as tumor suppressor and tumor promoter. We will also briefly cover current state of GSK3 inhibitors for leukemia therapy.

Capturing Human Naïve Pluripotency in the Embryo and in the Dish

Although human embryonic stem cells (hESCs) were first derived almost 20 years ago, it was only recently acknowledged that they share closer molecular and functional identity to postimplantation lineage-primed murine epiblast stem cells than to naïve preimplantation inner cell mass-derived mouse ESCs (mESCs). A myriad of transcriptional, epigenetic, biochemical, and metabolic attributes have now been described that distinguish naïve and primed pluripotent states in both rodents and humans. Conventional hESCs and human induced pluripotent stem cells (hiPSCs) appear to lack many of the defining hallmarks of naïve mESCs. These include important features of the naïve ground state murine epiblast, such as an open epigenetic architecture, reduced lineage-primed gene expression, and chimera and germline competence following injection into a recipient blastocyst-stage embryo. Several transgenic and chemical methods were recently reported that appear to revert conventional human PSCs to mESC-like ground states. However, it remains unclear if subtle deviations in global transcription, cell signaling dependencies, and extent of epigenetic/metabolic shifts in these various human naïve-reverted pluripotent states represent true functional differences or alternatively the existence of distinct human pluripotent states along a spectrum. In this study, we review the current understanding and developmental features of various human pluripotency-associated phenotypes and discuss potential biological mechanisms that may support stable maintenance of an authentic epiblast-like ground state of human pluripotency.

Membrane translocation of t-SNARE protein syntaxin-4 abrogates ground-state pluripotency in mouse embryonic stem cells

Embryonic stem (ES) and induced pluripotent stem (iPS) cells are attractive tools for regenerative medicine therapies. However, aberrant cell populations that display flattened morphology and lose ground-state pluripotency often appear spontaneously, unless glycogen synthase kinase 3β (GSK3β) and mitogen-activated protein kinase kinase (MEK1/2) are inactivated. Here, we show that membrane translocation of the t-SNARE protein syntaxin-4 possibly is involved in this phenomenon. We found that mouse ES cells cultured without GSK3β/MEK1/2 inhibitors (2i) spontaneously extrude syntaxin-4 at the cell surface and that artificial expression of cell surface syntaxin-4 induces appreciable morphological changes and mesodermal differentiation through dephosphorylation of Akt. Transcriptome analyses revealed several candidate elements responsible for this, specifically, an E-to P-cadherin switch and a marked downregulation of Zscan4 proteins, which are DNA-binding proteins essential for ES cell pluripotency. Embryonic carcinoma cell lines F9 and P19CL6, which maintain undifferentiated states independently of Zscan4 proteins, exhibited similar cellular behaviors upon stimulation with cell surface syntaxin-4. The functional ablation of E-cadherin and overexpression of P-cadherin reproduced syntaxin-4-induced cell morphology, demonstrating that the E- to P-cadherin switch executes morphological signals from cell surface syntaxin-4. Thus, spontaneous membrane translocation of syntaxin-4 emerged as a critical element for maintenance of the stem-cell niche.

The receptor for advanced glycation end products is required for β-catenin stabilization in a chemical-induced asthma model

BACKGROUND AND PURPOSE

Cytoplasmic retention of β-catenin will lead to its nuclear translocation and subsequent interaction with the transcription factor TCF/LEF that regulates target gene expression. We have previously demonstrated aberrant expression of β-catenin in a model of asthma induced by toluene diisocyanate (TDI). The aim of this study was to examine whether the receptor for advanced glycation end products (RAGE) can regulate β-catenin expression in TDI-induced asthma.

EXPERIMENTAL APPROACH

Male BALB/c mice were sensitized and challenged with TDI to generate a chemically-induced asthma model. Inhibitors of RAGE, FPS-ZM1 and the RAGE antagonist peptide (RAP), were injected i.p. after each challenge. Airway resistance was measured in vivo and bronchoalveolar lavage fluid was analysed. Lungs were examined by histology and immunohistochemistry. Western blotting and quantitative PCR were also used.

KEY RESULTS

Expression of RAGE and of its ligands HMGB1, S100A12, S100B, HSP70 was increased in TDI-exposed lungs. These increases were inhibited by FPS-ZM1 or RAP. Either antagonist blunted airway reactivity, airway inflammation and goblet cell metaplasia, and decreased release of Th2 cytokines. TDI exposure decreased level of membrane β-catenin, phosphorylated Akt (Ser(473) ), inactivated GSK3β (Ser(9) ), dephosphorylated β-catenin at Ser(33) /(37) /Thr(41) , which controls its cytoplasmic degradation, increased phosphorylated β-catenin at Ser(552) , raised cytoplasmic and nuclear levels of β-catenin and up-regulated its targeted gene expression (MMP2, MMP7, MMP9, VEGF, cyclin D1, fibronectin), all of which were reversed by RAGE inhibition.

CONCLUSION AND IMPLICATIONS

RAGE was required for stabilization of β-catenin in TDI-induced asthma, identifying protective effects of RAGE blockade in this model.

Genetic factors conferring metastasis in osteosarcoma

Osteosarcoma (OS) is a deadly bone malignancy affecting mostly children and adolescents. OS has outstandingly complex genetic alterations likely due to p53-independent genomic instability. Based on analysis of recent published research we claim existence of various genetic mechanisms of osteosarcomagenesis conferring great variability to different OS properties including metastatic potential. We also propose a model explaining how diverse genetic mechanisms occur and providing a framework for future research. P53-independent preexisting genomic instability, which precedes and frequently causes TP53 genetic alterations, is central in our model. In addition, our analyses reveal a possible cooperation between aberrantly activated HIF-1α and AP-1 genetic pathways in OS metastasis. We also review the involvement of noncoding RNA genes in OS metastasis.

Concise Review: Primary Cilia: Control Centers for Stem Cell Lineage Specification and Potential Targets for Cell-Based Therapies

Directing stem cell lineage commitment prevails as the holy grail of translational stem cell research, particularly to those interested in the application of mesenchymal stem cells and adipose-derived stem cells in tissue engineering. However, elucidating the mechanisms underlying their phenotypic specification persists as an active area of research. In recent studies, the primary cilium structure has been intimately associated with defining cell phenotype, maintaining stemness, as well as functioning in a chemo, electro, and mechanosensory capacity in progenitor and committed cell types. Many hypothesize that the primary cilium may indeed be another important player in defining and controlling cell phenotype, concomitant with lineage-dictated cytoskeletal dynamics. Many of the studies on the primary cilium have emerged from disparate areas of biological research, and crosstalk amongst these areas of research is just beginning. To date, there has not been a thorough review of how primary cilia fit into the current paradigm of stem cell differentiation and this review aims to summarize the current cilia work in this context. The goal of this review is to highlight the cilium's function and integrate this knowledge into the working knowledge of stem cell biologists and tissue engineers developing regenerative medicine technologies. Stem Cells 2016;34:1445-1454.

Ectodermal Wnt controls nasal pit morphogenesis through modulation of the BMP/FGF/JNK signaling axis

BACKGROUND

Mutations of WNT3, WNT5A, WNT9B, and WNT11 genes are associated with orofacial birth defects, including nonsyndromic cleft lip with cleft palate in humans. However, the source of Wnt ligands and their signaling effects on the orofacial morphogenetic process remain elusive.

RESULTS

Using Foxg1-Cre to impair Wnt secretion through the inactivation of Gpr177/mWls, we investigate the relevant regulation of Wnt production and signaling in nasal-facial development. Ectodermal ablation of Gpr177 leads to severe facial deformities resulting from dramatically reduced cell proliferation and increased cell death due to a combined loss of WNT, FGF and BMP signaling in the developing facial prominence. In the invaginating nasal pit, the Gpr177 disruption also causes a detrimental effect on migration of the olfactory epithelial cells into the mesenchymal region. The blockage of Wnt secretion apparently impairs the olfactory epithelial cells through modulation of JNK signaling.

CONCLUSIONS

Our study thus suggests the head ectoderm, including the facial ectoderm and the neuroectoderm, as the source of canonical as well as noncanonical Wnt ligands during early development of the nasal-facial prominence. Both β-catenin-dependent and -independent signaling pathways are required for proper development of these morphogenetic processes.

IGF-binding protein 2 is a candidate target of therapeutic potential in cancer

Insulin-like growth factor (IGF)-binding protein 2(IGFBP2), a key member of IGF family, has been reported as a notable oncogene in most human epithelium cancers. Increasing evidences suggested that IGFBP2 might be a candidate target of therapuetic potential by regulating key cancer metastasis and invasion-associated signaling networks, but there is still confusion about the mechanism on how IGFBP2 takes part in these processes. In this review, we summarized the current points of view that IGFBP2 functions in signaling pathways during tumorigenesis and tumor progression and discussed its potential clinical applications as a therapeutic target.

Involvement of the Wnt signaling pathway in feeder‑free culture of human induced pluripotent stem cells

Activin A maintains the pluripotency of human induced pluripotent stem (hiPS) cells. A combination of activin A and CHIR99021 (CHIR), a specific inhibitor of glycogen synthase‑3β, is suitable for feeder‑free culture of hiPS cells. In the present study, the specific role of the Wnt signaling pathway in cells cultured under different conditions was investigated. Following transfection with the reporter plasmids, TOPflash and FOPflash, hiPS cells were cultured in medium, containing activin A, CHIR, leukemia inhibitory factor (LIF) or SB431542, a specific inhibitor of activin A. A luciferase reporter assay was performed 48 h later. Western blot analysis was performed to determine the expression levels of β‑catenin and tubulin‑α. The activity of Wnt in hiPS cells was suppressed by culture in the presence of activin A. The activation of the Wnt pathway was most marked when the cells were cultured with a combination of activin A and CHIR. Addition of SB431542 into the culture revealed no significant change in the Wnt pathway. Western blot analysis revealed that β‑catenin accumulated most often in cells cultured with activin A and CHIR. β‑catenin also accumulated in cells cultured with activin A alone. Culture with activin A and CHIR most effectively stimulated the Wnt signaling pathway, as measured by luciferase assays using TOPflash and FOP flash as reporter plasmids. β‑catenin accumulated in the hiPS cells cultured with activin A, via a mechanism, which remains to be elucidated. The Wnt signaling pathway may be important for hiPS cell growth in feeder‑free culture.