Wnt/β-catenin signaling regulates telomerase in stem cells and cancer cells

Wnt/catenin signaling in adult stem cell physiology and disease

Wnt signaling plays an important role in development and disease. In this review we focus on the role of the canonical Wnt signaling pathway in somatic stem cell biology and its critical role in tissue homeostasis. We present current knowledge how Wnt/β-catenin signaling affects tissue stem cell behavior in various organ systems, including the gut, mammary gland, the hematopoietic and nervous system. We discuss evidence that canonical Wnt signaling can both maintain potency and an undifferentiated state as well as cause differentiation in somatic stem cells, depending on the cellular and environmental context. Based on studies by our lab and others, we will attempt to explain the dichotomous behavior of this signaling pathway in determining cell fate decisions and put special emphasis on the interaction of β-catenin with two highly homologous co-activator proteins, CBP and p300, to shed light on the their differential role in the outcome of Wnt/β-catenin signaling. Furthermore, we review current knowledge regarding the aberrant regulation of Wnt/β-catenin signaling in cancer biology, particularly its pivotal role in the context of cancer stem cells. Finally, we discuss data demonstrating that small molecule modulators of the β-catenin/co-activator interaction can be used to shift the balance between undifferentiated proliferation and differentiation, which potentially presents a promising therapeutic approach to stem cell based disease mechanisms.

Protein kinases and associated pathways in pluripotent state and lineage differentiation

Protein kinases (PKs) mediate the reversible conversion of substrate proteins to phosphorylated forms, a key process in controlling intracellular signaling transduction cascades. Pluripotency is, among others, characterized by specifically expressed PKs forming a highly interconnected regulatory network that culminates in a finely-balanced molecular switch. Current high-throughput phosphoproteomic approaches have shed light on the specific regulatory PKs and their function in controlling pluripotent states. Pluripotent cell-derived endothelial and hematopoietic developments represent an example of the importance of pluripotency in cancer therapeutics and organ regeneration. This review attempts to provide the hitherto known kinome profile and the individual characterization of PK-related pathways that regulate pluripotency. Elucidating the underlying intrinsic and extrinsic signals may improve our understanding of the different pluripotent states, the maintenance or induction of pluripotency, and the ability to tailor lineage differentiation, with a particular focus on endothelial cell differentiation for anti-cancer treatment, cell-based tissue engineering, and regenerative medicine strategies.

Occurrence of trichoepithelioma in a cat: Histopathologic and immunohistochemical study

Trichoepitheliomas are benign follicular appendage tumors with differentiation to all three segments of the hair follicle. A 2 years old female domestic short hair cat presented with a mass on the tail. The mass was surgically excised and for histopathologic and immunohistochemical studies, was sent to Department of Pathology. Histologically, the tumor was encapsulated and consisted of many islands of follicular epithelium and also cysts structures which varied in size and shape. The cells of epithelium islands were round to oval and had variable amounts of slightly, eosinophilic cytoplasm and euchromatic nuclei. The cystic structures were lined by a complex layer of squamous epithelium. Often, cells under went an abrupt transition between basal layers and keratinization without the development of a granular cell layer. No tendency of malignancy was seen in this case. According to mentioned characteristics, trichoepithelioma was diagnosed. By immunohistochemical study it was confirmed that this tumor had epithelial origin because squamous tumor cells reacted with the pan-cytokeratin antibody. The expression of β-catenin was predominately cytoplasmic and also together with numerous positive nuclei but membranous expression was inconsistenet. Distribution of neoplastic cells with β-catenin expression was more than 75% and labeling intensity was strong in both cytoplasm and nuclei. According to author's knowledge, this is the first report of trichoepithelioma in cat in Iran and also investigation of β-catenin expression in feline trichoepithelioma in veterinary literature.

Telomerase reverse transcriptase potentially promotes the progression of oral squamous cell carcinoma through induction of epithelial-mesenchymal transition

In recent years, researchers have found the critical role of telomerase in cellular transformation, proliferation, stemness and cell survival. High levels of telomerase reverse transcriptase (TERT) expression and telomerase activation have been reported in most cancer cells. Moreover, overexpression of human TERT (hTERT) is reported to be correlated with advanced invasive stage of the tumor progression and poor prognosis. Epithelial-mesenchymal transition (EMT), characterized by the loss of the cell-cell contact of epithelial cells and the acquisition of migratory and motile properties, is known to be a central mechanism responsible for invasiveness and metastasis of various cancers. Thus, we investigated whether hTERT plays a potential role in the development of EMT. As we expected, our clinical results showed that hTERT is overexpressed in oral epithelial dysplasia (OED) and OSCC tissues and correlates with clinical aggressiveness of oral squamous cell carcinoma (OSCC) patients. We then overexpressed hTERT in primary human oral epithelial cells (HOECS) and found that hTERT has the potential to prolong the lifespan, a process confering the characteristics of EMT by activating the Wnt/β-catenin pathway. Our findings provided an explanation for the aggressive nature of human tumors overexpressing hTERT and the possibly mechanism that links hTERT to EMT property, which represents a possible therapeutic target in highly metastatic cancers.

Oncogenesis and induced pluripotency - commonalities of signalling pathways

Rapid progress in the field of adult cells reprogramming back into a stem cell-like fate revealed shared mechanisms of action with tumoural reprogramming. A hallmark of stem cells - self-renewal and differentiation potential - seems to be tightly interlaced with large proliferation capacity and cellular plasticity of cancer cells. In this review, we briefly summarise the core transcription factors critical to maintenance of ES cell signature and overexpressed in many types of cancer, as well as signalling pathways involved in both induced pluripotency and oncogenesis, with particular regard to the role of tumour suppressor p53.

Long-term safety issues of iPSC-based cell therapy in a spinal cord injury model: oncogenic transformation with epithelial-mesenchymal transition

Previously, we described the safety and therapeutic potential of neurospheres (NSs) derived from a human induced pluripotent stem cell (iPSC) clone, 201B7, in a spinal cord injury (SCI) mouse model. However, several safety issues concerning iPSC-based cell therapy remain unresolved. Here, we investigated another iPSC clone, 253G1, that we established by transducing OCT4, SOX2, and KLF4 into adult human dermal fibroblasts collected from the same donor who provided the 201B7 clone. The grafted 253G1-NSs survived, differentiated into three neural lineages, and promoted functional recovery accompanied by stimulated synapse formation 47 days after transplantation. However, long-term observation (for up to 103 days) revealed deteriorated motor function accompanied by tumor formation. The tumors consisted of Nestin⁺ undifferentiated neural cells and exhibited activation of the OCT4 transgene. Transcriptome analysis revealed that a heightened mesenchymal transition may have contributed to the progression of tumors derived from grafted cells.

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Grafted iPSC (253G1)-derived neurospheres formed tumors after long-term observation

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Activation of the OCT4 transgene is potentially related to tumor formation

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Tumor progression may have been caused by mesenchymal transition of grafted cells

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Integration-free iPSCs should be chosen to avoid transgene-induced tumorigenesis

Hallmarks of the ageing lung

Ageing is the main risk factor for major non-communicable chronic lung diseases, including chronic obstructive pulmonary disease, most forms of lung cancer and idiopathic pulmonary fibrosis. While the prevalence of these diseases continually increases with age, their respective incidence peaks at different times during the lifespan, suggesting specific effects of ageing on the onset and/or pathogenesis of chronic obstructive pulmonary disease, lung cancer and idiopathic pulmonary fibrosis. Recently, the nine hallmarks of ageing have been defined as cell-autonomous and non-autonomous pathways involved in ageing. Here, we review the available evidence for the involvement of each of these hallmarks in the pathogenesis of chronic obstructive pulmonary disease, lung cancer, or idiopathic pulmonary fibrosis. Importantly, we propose an additional hallmark, “dysregulation of the extracellular matrix”, which we argue acts as a crucial modifier of cell-autonomous changes and functions, and as a key feature of the above-mentioned lung diseases.

miR-19b regulates hTERT mRNA expression through targeting PITX1 mRNA in melanoma cells

Human telomerase reverse transcriptase (hTERT) plays a crucial role in cancer development. We previously identified paired-like homeodomain1 (PITX1) as an hTERT suppressor gene. However, the underlying mechanisms that are involved in the regulation of PITX1 remain unknown. Here, we report that the microRNA-19b (miR-19b) regulates hTERT expression and cell proliferation through inhibition of PITX1. Compared with normal melanocyte cells, miR-19b expression was higher in most melanoma cells and was accompanied by downregulation of PITX1. Moreover, overexpression of miR-19b inhibited PITX1 mRNA translation through a miR-19b binding site within the 3'UTR of the PITX1 mRNA. Our combined findings indicate the participation of miR-19b as a novel upstream effector of hTERT transcription via direct targeting of PITX1.

Werner Syndrome-specific induced pluripotent stem cells: recovery of telomere function by reprogramming

Werner syndrome (WS) is a rare human autosomal recessive premature aging disorder characterized by early onset of aging-associated diseases, chromosomal instability, and cancer predisposition. The function of the DNA helicase encoded by WRN, the gene responsible for WS, has been studied extensively. WRN helicase is involved in the maintenance of chromosome integrity through DNA replication, repair, and recombination by interacting with a variety of proteins associated with DNA repair and telomere maintenance. The accelerated aging associated with WS is reportedly caused by telomere dysfunction, and the underlying mechanism of the disease is yet to be elucidated. Although it was reported that the life expectancy for patients with WS has improved over the last two decades, definitive therapy for these patients has not seen much development. Severe symptoms of the disease, such as leg ulcers, cause a significant decline in the quality of life in patients with WS. Therefore, the establishment of new therapeutic strategies for the disease is of utmost importance. Induced pluripotent stem cells (iPSCs) can be established by the introduction of several pluripotency genes, including Oct3/4, Sox2, Klf4, and c-myc into differentiated cells. iPSCs have the potential to differentiate into a variety of cell types that constitute the human body, and possess infinite proliferative capacity. Recent studies have reported the generation of iPSCs from the cells of patients with WS, and they have concluded that reprogramming represses premature senescence phenotypes in these cells. In this review, we summarize the findings of WS patient-specific iPSCs (WS iPSCs) and focus on the roles of telomere and telomerase in the maintenance of these cells. Finally, we discuss the potential use of WS iPSCs for clinical applications.

Role of Krüppel-like factors in cancer stem cells

Cancer stem cells (CSCs), or cancer cells with stem cell properties, are a rare population of tumor bulk and are recognized to be responsible for cancer recurrence, drug resistance, and metastasis. However, the molecular mechanisms of how to regulate the differentiation and self-renewing of CSCs are poorly understood. Krüppel-like factors (KLFs) are essential DNA-binding transcriptional regulators with diverse functions in various cellular processes, including differentiation, proliferation, inflammation, migration, and pluripotency. Recent progress has highlighted the significance of KLFs in tumor progression and CSCs. The regulatory functions of KLFs in the development of cancer and CSCs have become a burgeoning area of intense research. In this review, we summarize the current understanding and progress of the transcriptional regulation of KLFs in CSCs and discuss the functional implications of targeting CSCs by KLFs for cancer therapeutics.

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.

Gene regulatory networks mediating canonical Wnt signal-directed control of pluripotency and differentiation in embryo stem cells

Canonical Wnt signaling supports the pluripotency of embryonic stem cells (ESCs) but also promotes differentiation of early mammalian cell lineages. To explain these paradoxical observations, we explored the gene regulatory networks at play. Canonical Wnt signaling is intertwined with the pluripotency network comprising Nanog, Oct4, and Sox2 in mouse ESCs. In defined media supporting the derivation and propagation of ESCs, Tcf3 and β-catenin interact with Oct4; Tcf3 binds to Sox motif within Oct-Sox composite motifs that are also bound by Oct4-Sox2 complexes. Furthermore, canonical Wnt signaling upregulates the activity of the Pou5f1 distal enhancer via the Sox motif in ESCs. When viewed in the context of published studies on Tcf3 and β-catenin mutants, our findings suggest Tcf3 counters pluripotency by competition with Sox2 at these sites, and Tcf3 inhibition is blocked by β-catenin entry into this complex. Wnt pathway stimulation also triggers β-catenin association at regulatory elements with classic Lef/Tcf motifs associated with differentiation programs. The failure to activate these targets in the presence of a mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) inhibitor essential for ESC culture suggests MEK/ERK signaling and canonical Wnt signaling combine to promote ESC differentiation.

Clinico-Pathological Correlation of β-Catenin and Telomere Dysfunction in Head and Neck Squamous Cell Carcinoma Patients

BACKGROUND

Tumorigenesis is a complex process of accumulated alteration in function of multiple genes and pathways. Wnt signalling pathway is involved in various differentiation events during embryonic development and is conserved in various species.

OBJECTIVE

A multicentre collaborative initiative is undertaken to study the occurrence, prognosis and molecular mechanism of HNSCC (Head and Neck Squamous Cell Carcinoma) which is highly prevalent in eastern parts of India. From a large cohort of HNSCC tissue repository, 67 cases were selected for multi-parametric investigation.

RESULTS

67 cases showed stable β-catenin expression. We have seen correlation, if any, of the transcription factor - β-catenin, telomere maintenance and shelterin complex proteins - TRF2, Rap1 and hTert with respect to tumor differentiation and telomere dysfunction. Immunohistochemistry of β-catenin protein showed stable and high expression in tumor when compared to stroma. MDSCC (Moderately Differentiated Squamous cell carcinoma) cases expressed nuclear expression of β-catenin in invasive fronts and showed increased genomic instability. Higher frequency of Anaphase bridges was observed ranging from <3% in normal cut margin to 13% in WDSCC (Well differentiated squamous cell carcinoma) and 18% in MDSCC (Moderately differentiated Squamous cell carcinoma). There was significant decrease in telomere length in MDSCC (<4) when compared to the normal cut margin samples (<7). Quantitative Real Time-PCR confirmed a significant correlationship between stable β-catenin expression and poor clinical and pathological outcome.

CONCLUSION

The Stabilisation and accumulation of β-catenin was significant and correlated well with de-differentiation process as well as prognosis and therapy outcome of the patients in the cohort. Expression status of molecular markers such as β-catenin, hTert, TRF2 and RAP1 correlate significantly with the process of tumorigenesis and prognosis and may play a role in therapeutic management of Head and neck patients.

A decline in Wnt3a signaling is necessary for mesenchymal stem cells to proceed to replicative senescence

Umbilical cord blood-derived mesenchymal stem cells are a promising source of cells for regeneration therapy due to their multipotency, high proliferative capacity, relatively noninvasive collection, and ready availability. However, extended cell culture inevitably triggers cellular senescence-the irreversible arrest of cell division-thereby limiting the proliferative lifespan of adult stem cells. Wnt/β-catenin signaling plays a functional role as a key regulator of self-renewal and differentiation in mesenchymal stem cells (MSCs), and thus Wnt/β-catenin signaling and cellular senescence might be closely connected. Here, we show that the expression levels of canonical Wnt families decrease as MSCs age during subculture. Activation of the Wnt pathway by treatment with Wnt3a-conditioned medium or glycogen synthase kinase 3β inhibitors, such as SB-216763 and 6-bromoindirubin-3'-oxime, delays the progression of cellular senescence as shown by the decrease in the senescence effectors p53 and pRb, lowered senescence-associated β-galactosidase activity, and increased telomerase activity. In contrast, suppression of the Wnt pathway by treatment with dickkopf-1 (an antagonist of the Wnt coreceptor) and β-catenin siRNA transfection promotes senescence in MSCs. Interestingly, the magnitude of the response to enhanced Wnt3a/β-catenin signaling appears to depend on the senescent state during extended culture, particularly after multiple passages. These results suggest that Wnt3a signaling might be a predominant factor that could be used to overcome senescence in long-term cultured MSCs by directly intervening in the proliferative capacity and MSC senescence. The functional role of Wnt3a/β-catenin signaling in hedging cellular senescence may allow the development of new approaches for stem cell-based therapies.

Common telomerase reverse transcriptase promoter mutations in hepatocellular carcinomas from different geographical locations

AIM: To determine the mutation status of human telomerase reverse transcriptase gene (TERT) promoter region in hepatocellular carcinoma (HCC) from different geographical regions.

METHODS: We analyzed the genomic DNA sequences of 59 HCC samples comprising 15 cell lines and 44 primary tumors, collected from patients living in Asia, Europe and Africa. We amplified a 474 bp DNA fragment of the promoter region of TERT gene including the 1295228 and 1295250 sequence of chromosome 5 by using PCR. Amplicons were then sequenced by Sanger technique and the sequence data were analyzed with by using DNADynamo software in comparison with wild type TERT gene sequence as a reference.

RESULTS: The TERT mutations were found highly frequent in HCC. Eight of the fifteen tested cell lines displayed C228T mutation, and one had C250T mutation with a mutation frequency up to 60%. All of the mutations were heterozygous and mutually exclusive. Ten out of forty-four tumors displayed C228T mutation, and additional five tumors had C250T mutation providing evidence for mutation frequency of 34% in primary tumors. Considering the geographic origins of HCC tumors tested, TERT promoter mutation frequencies were higher in African (53%), when compared to non-African (24%) tumors (P = 0.056). There was also a weak inverse correlation between TERT promoter mutations and murine double minute 2 single nucleotide polymorphism 309 TG polymorphism (P = 0.058). Mutation frequency was nearly two times higher in established HCC cell lines (60%) compared to the primary tumors (34%).

CONCLUSION: TERT promoter is one of most frequent mutational targets in liver cancer, and hepatocellular carcinogenesis is highly associated with the loss of telomere-dependent cellular senescence control.

miR-203 Functions as a Tumor Suppressor by Inhibiting Epithelial to Mesenchymal Transition in Ovarian Cancer

OBJECTIVE

Ovarian cancer is a gynecological malignancy that has a high mortality rate in women due to metastatic progression and recurrence. miRNAs are small, endogenous, noncoding RNAs that function as tumor suppressors or oncogenes in various human cancers by selectively suppressing the expression of target genes. The objective of this study is to investigate the role of miR-203 in ovarian cancer.

METHODS

miR-203 was expressed in ovarian cancer SKOV3 and OVCAR3 cells using lentiviral vector and cell proliferation, migration, invasion were examined using MTT, transwell and Matrigel assays, respectively. Tumor growth was examined using Xenograft mouse model.

RESULTS

miR-203 expression was downregulated, whereas expression of its target gene Snai2 was upregulated in human ovarian serous carcinoma tissue as compared to normal ovaries. In addition, high miR-203 expression was associated with long-term survival rate of ovarian cancer patients. miR-203 overexpression inhibited cell proliferation, migration, and invasion of SKOV3 and OVCAR3 ovarian cancer cells. Furthermore, miR-203 overexpression inhibited the epithelial to mesenchymal transition (EMT) in ovarian cancer cells. Silencing Snai2 with lentiviral short hairpin (sh) RNA mimics miR-203-mediated inhibition of EMT and tumor cell invasion. Xenografts of miR-203-overexpressing ovarian cancer cells in immunodeficient mice exhibited a significantly reduced tumor growth.

CONCLUSION

miR-203 functions as a tumor suppressor by down regulating Snai2 in ovarian cancer.

Photochemical internalisation, a minimally invasive strategy for light-controlled endosomal escape of cancer stem cell-targeting therapeutics

Despite progress in radio-, chemo- and photodynamic-therapy (PDT) of cancer, treatment resistance still remains a major problem for patients with aggressive tumours.

SETDB1 accelerates tumourigenesis by regulating the WNT signalling pathway

We investigated the oncogenic role of SETDB1, focusing on non-small cell lung cancer (NSCLC), which has high expression of this protein. A total of 387 lung cancer cases were examined by immunohistochemistry; 72% of NSCLC samples were positive for SETDB1 staining, compared to 46% samples of normal bronchial epithelium (106 cases) (p <0.0001). The percentage of positive cells and the intensity of staining increased significantly with increased grade of disease. Forced expression of SETDB1 in NSCLC cell lines enhanced their clonogenic growth in vitro and markedly increased tumour size in a murine xenograft model, while silencing (shRNA) SETDB1 in NSCLC cells slowed their proliferation. SETDB1 positively stimulated activity of the WNT-β-catenin pathway and diminished P53 expression, resulting in enhanced NSCLC growth in vitro and in vivo. Our finding suggests that therapeutic targeting of SETDB1 may benefit patients whose tumours express high levels of SETDB1.

Pre-clinical efficacy of combined therapy with novel β-catenin antagonist BC2059 and histone deacetylase inhibitor against AML cells

The canonical WNT-β-catenin pathway is essential for self-renewal, growth and survival of AML stem/blast progenitor cells (BPCs). Deregulated WNT signaling inhibits degradation of β-catenin, causing increased nuclear translocation and co-factor activity of β-catenin with the transcriptional regulator TCF4/LEF1 in AML BPCs. Here, we determined the pre-clinical anti-AML activity of the anthraquinone oxime-analog BC2059 (BC), known to attenuate β-catenin levels. BC treatment disrupted the binding of β-catenin with the scaffold protein TBL1 (transducin β-like 1) and proteasomal degradation and decline in the nuclear levels of β-catenin. This was associated with reduced transcriptional activity of TCF4 and expression of its target genes, cyclin D1, c-MYC and survivin. BC treatment dose-dependently induced apoptosis of cultured and primary AML BPCs. Treatment with BC also significantly improved the median survival of immune-depleted mice engrafted with either cultured or primary AML BPCs exhibiting nuclear expression of β-catenin. Co-treatment with the pan-histone deacetylase inhibitor panobinostat and BC synergistically induced apoptosis of cultured and primary AML BPCs, including those expressing FLT3-ITD, as well as further significantly improved the survival of immune-depleted mice engrafted with primary AML BPCs. These findings underscore the promising pre-clinical activity and warrant further testing of BC against human AML, especially those expressing FLT3-ITD.

Trans-ancestry mutational landscape of hepatocellular carcinoma genomes

Diverse epidemiological factors are associated with hepatocellular carcinoma (HCC) prevalence in different populations. However, the global landscape of the genetic changes in HCC genomes underpinning different epidemiological and ancestral backgrounds still remains uncharted. Here a collection of data from 503 liver cancer genomes from different populations uncovered 30 candidate driver genes and 11 core pathway modules. Furthermore, a collaboration of two large-scale cancer genome projects comparatively analyzed the trans-ancestry substitution signatures in 608 liver cancer cases and identified unique mutational signatures that predominantly contribute to Asian cases. This work elucidates previously unexplored ancestry-associated mutational processes in HCC development. A combination of hotspot TERT promoter mutation, TERT focal amplification and viral genome integration occurs in more than 68% of cases, implicating TERT as a central and ancestry-independent node of hepatocarcinogenesis. Newly identified alterations in genes encoding metabolic enzymes, chromatin remodelers and a high proportion of mTOR pathway activations offer potential therapeutic and diagnostic opportunities.

Stem cell signaling. An integral program for tissue renewal and regeneration: Wnt signaling and stem cell control

Stem cells fuel tissue development, renewal, and regeneration, and these activities are controlled by the local stem cell microenvironment, the "niche." Wnt signals emanating from the niche can act as self-renewal factors for stem cells in multiple mammalian tissues. Wnt proteins are lipid-modified, which constrains them to act as short-range cellular signals. The locality of Wnt signaling dictates that stem cells exiting the Wnt signaling domain differentiate, spatially delimiting the niche in certain tissues. In some instances, stem cells may act as or generate their own niche, enabling the self-organization of patterned tissues. In this Review, we discuss the various ways by which Wnt operates in stem cell control and, in doing so, identify an integral program for tissue renewal and regeneration.

Signals that regulate the oncogenic fate of neural stem cells and progenitors

Brain tumors have frequently been associated with a neural stem cell (NSC) origin and contain stem-like tumor cells, so-called brain tumor stem cells (BTSCs) that share many features with normal NSCs. A stem cell state of BTSCs confers resistance to radiotherapy and treatment with alkylating agents. It is also a hallmark of aggressive brain tumors and is maintained by transcriptional networks that are also active in embryonic stem cells. Advances in reprogramming of somatic cells into induced pluripotent stem (iPS) cells have further identified genes that drive stemness. In this review, we will highlight the possible drivers of stemness in medulloblastoma and glioma, the most frequent types of primary malignant brain cancer in children and adults, respectively. Signals that drive expansion of developmentally defined neural precursor cells are also active in corresponding brain tumors. Transcriptomal subgroups of human medulloblastoma and glioma match features of NSCs but also more restricted progenitors. Lessons from genetically-engineered mouse (GEM) models show that temporally and regionally defined NSCs can give rise to distinct subgroups of medulloblastoma and glioma. We will further discuss how acquisition of stem cell features may drive brain tumorigenesis from a non-NSC origin. Genetic alterations, signaling pathways, and therapy-induced changes in the tumor microenvironment can drive reprogramming networks and induce stemness in brain tumors. Finally, we propose a model where dysregulation of microRNAs (miRNAs) that normally provide barriers against reprogramming plays an integral role in promoting stemness in brain tumors.

Telomerase reverse transcriptase in the regulation of gene expression

Telomerase plays a pivotal role in the pathology of aging and cancer by maintaining genome integrity, controlling cell proliferation, and regulating tissue homeostasis. Telomerase is essentially composed of an RNA component, Telomerase RNA or TERC, which serves as a template for telomeric DNA synthesis, and a catalytic subunit, telomerase reverse transcriptase (TERT). The canonical function of TERT is the synthesis of telomeric DNA repeats, and the maintenance of telomere length. However, accumulating evidence indicates that TERT may also have some fundamental functions that are independent of its enzymatic activity. Among these telomere-independent activities of hTERT, the role of hTERT in gene transcription has been investigated in detail. Transcriptional regulation is a fundamental process in biological systems. Several studies have shown a direct involvement of hTERT in gene transcription. This mini-review will focus on the role of hTERT in gene transcription regulation, and discuss its possible mechanisms. [BMB Reports 2014; 47(1): 8-14]

A peripheral ameloblastic fibro-odontoma in a 3-year-old girl: case report, immunohistochemical analysis, and literature review

Ameloblastic fibro-odontoma (AFO) predominantly occurs in the jaw bones of children and young adults. Extraosseous AFO is extremely rare. We describe a peripheral ameloblastic fibro-odontoma in the maxillary gingiva of a 3-year-old girl. The clinical appearance resembled fiery red reactive gingival lesions. The histopathological examination of the excised lesion showed small islands and cords of odontogenic epithelium with cellular myxoid stroma in the subepithelial tissue. The mass contained calcified material and an enamel-like deposit. Many small blood vessels appeared in the connective tissue surrounding the odontogenic epithelium. The immunohistochemical assays showed strong reactivity for amelogenin, β-catenin, CD44, and CD31 in the tissue sections. There was no recurrence after the 1-year follow-up. Because this lesion clinically resembles other nonneoplastic lesions and is very rare in gingiva, establishing a correct diagnosis is achieved only based on specific histological characteristics. Conservative excision of the tumor is the treatment of choice.

SLIT/ROBO2 signaling promotes mammary stem cell senescence by inhibiting Wnt signaling

WNT signaling stimulates the self-renewal of many types of adult stem cells, including mammary stem cells (MaSCs), but mechanisms that limit this activity are poorly understood. Here, we demonstrate that SLIT2 restricts stem cell renewal by signaling through ROBO2 in a subset of basal cells to negatively regulate WNT signaling. The absence of SLIT/ROBO2 signaling leads to increased levels of nuclear β-catenin. Robo2 loss does not increase the number of stem cells; instead, stem cell renewal is enhanced in the absence of SLIT/ROBO2 signaling. This is due to repressed expression of p16(INK4a), which, in turn, delays MaSC senescence. Together, our studies support a model in which SLITs restrict the expansion of MaSCs by countering the activity of WNTs and limiting self-renewal.

Doxycycline inducible Krüppel-like factor 4 lentiviral vector mediates mesenchymal to epithelial transition in ovarian cancer cells

Ovarian cancer presents therapeutic challenges due to its typically late detection, aggressive metastasis, and therapeutic resistance. The transcription factor Krüppel-like factor 4 (KLF4) has been implicated in human cancers as a tumor suppressor or oncogene, although its role depends greatly on the cellular context. The role of KLF4 in ovarian cancer has not been elucidated in mechanistic detail. In this study, we investigated the role of KLF4 in ovarian cancer cells by transducing the ovarian cancer cell lines SKOV3 and OVCAR3 with a doxycycline-inducible KLF4 lentiviral vector. Overexpression of KLF4 reduced cell proliferation, migration, and invasion. The epithelial cell marker gene E-cadherin was significantly upregulated, whereas the mesenchymal cell marker genes vimentin, twist1and snail2 (slug) were downregulated in both KLF4-expressing SKOV3 and OVCAR3 cells. KLF4 inhibited the transforming growth factor β (TGFβ)-induced epithelial to mesenchymal transition (EMT) in ovarian cancer cells. Taken together, our data demonstrate that KLF4 functions as a tumor suppressor gene in ovarian cancer cells by inhibiting TGFβ-induced EMT.

Can we safely target the WNT pathway?

WNT-β-catenin signalling is involved in a multitude of developmental processes and the maintenance of adult tissue homeostasis by regulating cell proliferation, differentiation, migration, genetic stability and apoptosis, as well as by maintaining adult stem cells in a pluripotent state. Not surprisingly, aberrant regulation of this pathway is therefore associated with a variety of diseases, including cancer, fibrosis and neurodegeneration. Despite this knowledge, therapeutic agents specifically targeting the WNT pathway have only recently entered clinical trials and none has yet been approved. This Review examines the problems and potential solutions to this vexing situation and attempts to bring them into perspective.

Telomerase variant A279T induces telomere dysfunction and inhibits non-canonical telomerase activity in esophageal carcinomas

BACKGROUND

Although implicated in the pathogenesis of several chronic inflammatory disorders and hematologic malignancies, telomerase mutations have not been thoroughly characterized in human cancers. The present study was performed to examine the frequency and potential clinical relevance of telomerase mutations in esophageal carcinomas.

METHODS

Sequencing techniques were used to evaluate mutational status of telomerase reverse transcriptase (TERT) and telomerase RNA component (TERC) in neoplastic and adjacent normal mucosa from 143 esophageal cancer (EsC) patients. MTS, flow cytometry, time lapse microscopy, and murine xenograft techniques were used to assess proliferation, apoptosis, chemotaxis, and tumorigenicity of EsC cells expressing either wtTERT or TERT variants. Immunoprecipitation, immunoblot, immunofluorescence, promoter-reporter and qRT-PCR techniques were used to evaluate interactions of TERT and several TERT variants with BRG-1 and β-catenin, and to assess expression of cytoskeletal proteins, and cell signaling. Fluorescence in-situ hybridization and spectral karyotyping techniques were used to examine telomere length and chromosomal stability.

RESULTS

Sequencing analysis revealed one deletion involving TERC (TERC del 341-360), and two non-synonymous TERT variants [A279T (2 homozygous, 9 heterozygous); A1062T (4 heterozygous)]. The minor allele frequency of the A279T variant was five-fold higher in EsC patients compared to healthy blood donors (p<0.01). Relative to wtTERT, A279T decreased telomere length, destabilized TERT-BRG-1-β-catenin complex, markedly depleted β-catenin, and down-regulated canonical Wnt signaling in cancer cells; these phenomena coincided with decreased proliferation, depletion of additional cytoskeletal proteins, impaired chemotaxis, increased chemosensitivity, and significantly decreased tumorigenicity of EsC cells. A279T expression significantly increased chromosomal aberrations in mouse embryonic fibroblasts (MEFs) following Zeocin™ exposure, as well as Li Fraumeni fibroblasts in the absence of pharmacologically-induced DNA damage.

CONCLUSIONS

A279T induces telomere dysfunction and inhibits non-canonical telomerase activity in esophageal cancer cells. These findings warrant further analysis of A279T expression in esophageal cancers and premalignant esophageal lesions.

β-Catenin-regulated ALDH1A1 is a target in ovarian cancer spheroids

Cancer cells form three dimensional (3D) multicellular aggregates (or spheroids) under non-adherent culture conditions. In ovarian cancer (OC), spheroids serve as a vehicle for cancer cell dissemination in the peritoneal cavity, protecting cells from environmental stress-induced anoikis. To identify new targetable molecules in OC spheroids, we investigated gene expression profiles and networks upregulated in three dimensional (3D) versus traditional monolayer culture conditions. We identified ALDH1A1, a cancer stem cell marker as being overexpressed in OC spheroids and directly connected to key elements of the β-catenin pathway. B-catenin function and ALDH1A1 expression were increased in OC spheroids vs. monolayers and in successive spheroid generations, suggesting that 3D aggregates are enriched in cells with stem cell characteristics. B-catenin knockdown decreased ALDH1A1 expression levels and β-catenin coimmunoprecipitated with the ALDH1A1 promoter, suggesting that ALDH1A1 is a direct β-catenin target. Both siRNA mediated β-catenin knockdown and A37, a novel ALDH1A1 small molecule enzymatic inhibitor described here for the first time, disrupted OC spheroid formation and cell viability (p<0.001). B-catenin knockdown blocked tumor growth and peritoneal metastasis in an OC xenograft model. These data strongly support the role of β-catenin regulated ALDH1A1 in the maintenance of OC spheroids and propose new ALDH1A1 inhibitors targeting this cell population.

Transcriptional outcome of telomere signalling

Telomeres protect chromosome ends from degradation and inappropriate DNA damage response activation through their association with specific factors. Interestingly, these telomeric factors are able to localize outside telomeric regions, where they can regulate the transcription of genes involved in metabolism, immunity and differentiation. These findings delineate a signalling pathway by which telomeric changes control the ability of their associated factors to regulate transcription. This mechanism is expected to enable a greater diversity of cellular responses that are adapted to specific cell types and telomeric changes, and may therefore represent a pivotal aspect of development, ageing and telomere-mediated diseases.

Telomerase as a "stemness" enzyme

Pluripotent or multipotent stem cells are involved in development and tissue homeostasis; they have the ability to self-renew and differentiate into various types of functional cells. To maintain these properties, stem cells must undergo sustained or unlimited proliferation that requires the stabilization of telomeres, which are essential for chromosome end protection. Telomerase, an RNA-dependent DNA polymerase, synthesizes telomeric DNA. Through the lengthening of telomeres the lifespans of cells are extended, or indefinite proliferation is conferred; this is intimately associated with stem cell phenotype. This review highlights our current understanding of telomerase as a "stemness" enzyme and discusses the underlying implications.

The H3K4 methyltransferase Setd1a is first required at the epiblast stage, whereas Setd1b becomes essential after gastrulation

Histone 3 lysine 4 (H3K4) methylation is a universal epigenetic mark. In mammals, there are six H3K4 methyltransferases related to yeast Set1 and fly Trithorax, including two orthologs of Set1: Setd1a and Setd1b. Here we show that mouse Setd1a is required for gastrulation, whereas Setd1b-deficient embryos survive to E11.5 but are grossly retarded. Setd1a knockout embryos implant but do not proceed past the epiblast. Furthermore, Setd1a is not required until the inner cell mass has formed, at which stage it has replaced Mll2 as the major H3K4 methyltransferase. Setd1a is required for embryonic, epiblast and neural stem cell survival and neural stem cell reprogramming, whereas Setd1b is dispensable. Deletion of Setd1a in embryonic stem cells resulted in rapid losses of bulk H3K4 methylation, pluripotency gene expression and proliferation, with G1 pileup. Setd1b overexpression could not rescue the proliferation defects caused by loss of Setd1a in embryonic stem cells. The precise developmental requirement for Setd1a suggests that gastrulation is regulated by a switch between the major H3K4 methyltransferases.

Telomeres and telomerase in T cells of tumor immunity

Telomeres are specific nucleoprotein structures at the end of a eukaryotic chromosomes characterized by repeats of the sequence TTAGGG and regulated by the enzyme telomerase which prevents their degradation, loss, rearrangement and end-to-end fusion. During activation, T lymphocytes actively divide, albeit through only a finite number of cell divisions due to shortening of telomeres. However, studies have demonstrated that human telomerase reverse transcriptase (hTERT), thought to be the major component regulating telomerase activity, can enhance the proliferation of T cells when overexpressed. There are many treatments for cancers, most of which are targeting the telomere and telomerase of tumor cells. However, the hTERT-transduced T cells improve their potential for proliferation, making them an appropriate cell resource for tumor adoptive immunotherapy, a procedure whereby T cells are isolated from patients, expanded ex vivo and eventually delivered back into the patients, provides a new approach for tumor therapy through improved overall survival rates in cancer patients. In this review, we will focus on the telomerase activity in T cells, the regulation of telomerase activity, and hTERT-transduced T cells used in adoptive immunotherapy for cancer.

Wnt signaling regulates pulp volume and dentin thickness

Odontoblasts, cementoblasts, ameloblasts, and osteoblasts all form mineralized tissues in the craniofacial complex, and all these cell types exhibit active Wnt signaling during postnatal life. We set out to understand the functions of this Wnt signaling, by evaluating the phenotypes of mice in which the essential Wnt chaperone protein, Wntless was eliminated. The deletion of Wls was restricted to cells expressing Osteocalcin (OCN), which in addition to osteoblasts includes odontoblasts, cementoblasts, and ameloblasts. Dentin, cementum, enamel, and bone all formed in OCN-Cre;Wls(fl/fl) mice but their homeostasis was dramatically affected. The most notable feature was a significant increase in dentin volume and density. We attribute this gain in dentin volume to a Wnt-mediated misregulation of Runx2. Normally, Wnt signaling stimulates Runx2, which in turn inhibits dentin sialoprotein (DSP); this inhibition must be relieved for odontoblasts to differentiate. In OCN-Cre;Wls(fl/fl) mice, Wnt pathway activation is reduced and Runx2 levels decline. The Runx2-mediated repression of DSP is relieved and odontoblast differentiation is accordingly enhanced. This study demonstrates the importance of Wnt signaling in the homeostasis of mineralized tissues of the craniofacial complex.

WITHDRAWN: Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.semcdb.2014.03.022. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

Lamin A-related progeroid syndromes are genetically determined, extremely rare and severe. In the past ten years, our knowledge and perspectives for these diseases has widely progressed, through the progressive dissection of their pathophysiological mechanisms leading to precocious and accelerated aging, from the genes mutations discovery until therapeutic trials in affected children. A-type lamins are major actors in several structural and functional activities at the nuclear periphery, as they are major components of the nuclear lamina. However, while this is usually poorly considered, they also play a key role within the rest of the nucleoplasm, whose defects are related to cell senescence. Although nuclear shape and nuclear envelope deformities are obvious and visible events, nuclear matrix disorganization and abnormal composition certainly represent the most important causes of cell defects with dramatic pathological consequences. Therefore, lamin-associated diseases should be better referred as laminopathies instead of envelopathies, this later being too restrictive, considering neither the key structural and functional roles of soluble lamins in the entire nucleoplasm, nor the nuclear matrix contribution to the pathophysiology of lamin-associated disorders and in particular in defective lamin A processing-associated aging diseases. Based on both our understanding of pathophysiological mechanisms and the biological and clinical consequences of progeria and related diseases, therapeutic trials have been conducted in patients and were terminated less than 10 years after the gene discovery, a quite fast issue for a genetic disease. Pharmacological drugs have been repurposed and used to decrease the toxicity of the accumulated, unprocessed and truncated prelaminA in progeria. To date, none of them may be considered as a cure for progeria and these clinical strategies were essentially designed toward reducing a subset of the most dramatic and morbid features associated to progeria. New therapeutic strategies under study, in particular targeting the protein expression pathway at the mRNA level, have shown a remarkable efficacy both in vitro in cells and in vivo in mice models. Strategies intending to clear the toxic accumulated proteins from the nucleus are also under evaluation. However, although exceedingly rare, improving our knowledge of genetic progeroid syndromes and searching for innovative and efficient therapies in these syndromes is of paramount importance as, even before they can be used to save lives, they may significantly (i) expand the affected childrens' lifespan and preserve their quality of life; (ii) improve our understanding of aging-related disorders and other more common diseases; and (iii) expand our fundamental knowledge of physiological aging and its links with major physiological processes such as those involved in oncogenesis.

Noncanonical functions of telomerase: implications in telomerase-targeted cancer therapies

Telomerase plays a pivotal role in bypassing cellular senescence and maintaining telomere homeostasis, essential properties required for the sustenance and progression of cancer. However, recent investigations have uncovered extratelomeric properties of telomerase that are independent of its role in telomere extension. This review summarizes recent insights to the noncanonical functions of telomerase reverse transcriptase (TERT) catalytic subunit, in particular in cancer progression, and highlights two major signaling mechanisms involved in the cross-talk with TERT-the NF-κB and Wnt/β-catenin pathways. We propose a feed-forward regulatory loop mechanism underlying TERT activation in cancers in which TERT acts as a transcriptional modulator of oncogenic signaling pathways that sustain its own levels and control the induction of target genes critical for tumor cell survival and proliferation. Finally, we provide a new perspective on telomerase-targeted cancer therapies and suggest possible interventions targeting the nontelomeric roles of TERT. This therapeutic strategy can be used in the future targeting of other telomerase components that exhibit novel nontelomeric functions in cancer and other ailments.

Comparison of Markers and Functional Attributes of Human Adipose-Derived Stem Cells and Dedifferentiated Adipocyte Cells from Subcutaneous Fat of an Obese Diabetic Donor

Objective: Adipose tissue is a robust source of adipose-derived stem cells (ADSCs) that may be able to provide secreted factors that promote the ability of wounded tissue to heal. However, adipocytes also have the potential to dedifferentiate in culture to cells with stem cell-like properties that may improve their behavior and functionality for certain applications. Approach: ADSCs are adult mesenchymal stem cells that are cultured from the stromal vascular fraction of adipose tissue. However, adipocytes are capable of dedifferentiating into cells with stem cell properties. In this case study, we compare ADSC and dedifferentiated fat (DFAT) cells from the same patient and fat depot for mesenchymal cell markers, embryonic stem cell markers, ability to differentiate to adipocytes and osteoblasts, senescence and telomerase levels, and ability of conditioned media (CM) to stimulate migration of human dermal fibroblasts (HDFs). Innovation and Conclusions: ADSCs and DFAT cells displayed identical levels of CD90, CD44, CD105, and were CD34- and CD45-negative. They also expressed similar levels of Oct4, BMI1, KLF4, and SALL4. DFAT cells, however, showed higher efficiency in adipogenic and osteogenic capacity. Telomerase levels of DFAT cells were double those of ADSCs, and senescence declined in DFAT cells. CM from both cell types altered the migration of fibroblasts. Despite reports of ADSCs from a number of human depots, there have been no comparisons of the ability of dedifferentiated DFAT cells from the same donor and depot to differentiate or modulate migration of HDFs. Since ADSCs were from an obese diabetic donor, reprogramming of DFAT cells may help improve a patient's cells for regenerative medicine applications.

Telomere regulation in pluripotent stem cells

Pluripotent stem cells (PSCs) have the potential to produce any types of cells from all three basic germ layers and the capacity to self-renew and proliferate indefinitely in vitro. The two main types of PSCs, embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), share common features such as colony morphology, high expression of Oct4 and Nanog, and strong alkaline phosphatase activity. In recent years, increasing evidences suggest that telomere length represents another important internal factor in maintaining stem cell pluripotency. Telomere length homeostasis and its structural integrity help to protect chromosome ends from recombination, end fusion, and DNA damage responses, ensuring the divisional ability of mammalian cells. PSCs generally exhibit high telomerase activity to maintain their extremely long and stable telomeres, and emerging data indicate the alternative lengthening of telomeres (ALT) pathway may play an important role in telomere functions too. Such characteristics are likely key to their abilities to differentiate into diverse cell types in vivo. In this review, we will focus on the function and regulation of telomeres in ESCs and iPSCs, thereby shedding light on the importance of telomere length to pluripotency and the mechanisms that regulate telomeres in PSCs.

Modulation of Wnt Activity and Cell Physiology by Butyrate in LT97 Microadenoma Cells

Dietary fiber intake is linked to a reduced risk of colon cancer. This effect may in part be due to butyrate, the fermentation product of fiber in the colon. Butyrate is a short-chain fatty acid that acts as a histone deacetylase inhibitor (HDACi). Butyrate induces apoptosis and represses clonal growth of colorectal cancer (CRC) cells, in a manner dependent upon the hyperactivation of Wnt /beta-catenin signaling. While fiber has been linked to CRC prevention, in vitro studies on the action of butyrate have used CRC cell lines, instead of cells representative of earlier stages of colonic neoplasia, which are the likely target of butyrate-mediated preventive activity. The LT97 cell line is derived from a microadenoma, the earliest stage of colonic neoplasia from which cells can be isolated. We characterized LT97 cells with respect to effects of butyrate on Wnt signaling and apoptosis, and we determined whether modulation of CREB binding protein (CBP)/p300 activity influences the ability of butyrate to induce Wnt activity and apoptosis. We report that in LT97 cells, butyrate induces apoptosis, strongly upregulates Wnt signaling, and the upregulation of Wnt signaling is dependent upon CBP/p300 activity. In addition, findings from overexpression experiments suggest differences between CBP and p300 in their ability to influence Wnt signaling in LT97 cells; p300, but not CBP, stimulates basal Wnt activity. We also evaluated differences in gene expression between early stage LT97 cells and late stage metastatic SW620 CRC cells that exhibit markedly different cellular phenotypes. The comparative gene expression analyses revealed differences that may impact neoplastic progression and the sensitivity to the effects of butyrate. The findings have implications for the prevention of CRC by fiber/butyrate.

Using zebrafish models to explore genetic and epigenetic impacts on evolutionary developmental origins of aging

Can we reset, reprogram, rejuvenate, or reverse the organismal aging process? Certain genetic manipulations could at least reset and reprogram epigenetic dynamics beyond phenotypic plasticity and elasticity in cells, which can be manipulated further into organisms. However, in a whole complex aging organism, how can we rejuvenate intrinsic resources and infrastructures in an intact and noninvasive manner? The incidence of diseases increases exponentially with age, accompanied by progressive deteriorations of physiological functions in organisms. Aging-associated diseases are sporadic but essentially inevitable complications arising from senescence. Senescence is often considered the antithesis of early development, but yet there may be factors and mechanisms in common between these 2 phenomena to rejuvenate over the dynamic process of aging. The association between early development and late-onset disease with advancing age is thought to come from a consequence of developmental plasticity, the phenomenon by which one genotype can give rise to a range of physiologically and/or morphologically adaptive states based on diverse epigenotypes in response to intrinsic or extrinsic environmental cues and genetic perturbations. We hypothesized that the future aging process can be predictive based on adaptivity during the early developmental period. Modulating the thresholds and windows of plasticity and its robustness by molecular genetic and chemical epigenetic approaches, we have successfully conducted experiments to isolate zebrafish mutants expressing apparently altered senescence phenotypes during their embryonic and/or larval stages ("embryonic/larval senescence"). Subsequently, at least some of these mutant animals were found to show a shortened life span, whereas others would be expected to live longer into adulthood. We anticipate that previously uncharacterized developmental genes may mediate the aging process and play a pivotal role in senescence. On the other hand, unexpected senescence-related genes might also be involved in the early developmental process and its regulation. The ease of manipulation using the zebrafish system allows us to conduct an exhaustive exploration of novel genes, genotypes, and epigenotypes that can be linked to the senescence phenotype, which facilitates searching for the evolutionary and developmental origins of aging in vertebrates.

High frequency of telomerase reverse-transcriptase promoter somatic mutations in hepatocellular carcinoma and preneoplastic lesions

Somatic mutations activating telomerase reverse-trancriptase promoter were recently identified in several tumour types. Here we identify frequent similar mutations in human hepatocellular carcinomas (59%), cirrhotic preneoplastic macronodules (25%) and hepatocellular adenomas with malignant transformation in hepatocellular carcinomas (44%). In hepatocellular tumours, telomerase reverse-transcripase- and CTNNB1-activating mutations are significantly associated. Moreover, preliminary data suggest that telomerase reverse-trancriptase promoter mutations can increase the expression of telomerase transcript. In conclusion, telomerase reverse-trancriptase promoter mutation is the earliest recurrent genetic event identified in cirrhotic preneoplastic lesions so far and is also the most frequent genetic alteration in hepatocellular carcinomas, arising from both the cirrhotic or non-cirrhotic liver.

Telomerase reverse-trancriptase promoter mutations have been recently found in human melanomas. Here, Nault et al. identify telomerase reverse-trancriptase promoter mutations as the most frequent somatic genetic alterations in hepatocellular carcinomas and as the first mutation identified in cirrhotic preneoplastic lesions.

Beta-catenin is vital for the integrity of mouse embryonic stem cells

β-Catenin mediated Wnt-signaling is assumed to play a major function in embryonic stem cells in maintaining their stem cell character and the exit from this unique trait. The complexity of β-catenin action and conflicting results on the role of β-catenin in maintaining the pluripotent state have made it difficult to understand its precise cellular and molecular functions. To attempt this issue we have generated new genetically modified mouse embryonic stem cell lines allowing for the deletion of β-catenin in a controlled manner by taking advantage of the Cre-ER-T2 system and analyzed the effects in a narrow time window shortly after ablation. By using this approach, rather then taking long term cultured β-catenin null cell lines we demonstrate that β-catenin is dispensable for the maintenance of pluripotency associated genes. In addition we observed that the removal of β-catenin leads to a strong increase of cell death, the appearance of multiple clustered functional centrosomes most likely due to a mis-regulation of the polo-like-kinase 2 and furthermore, alterations in chromosome segregation. Our study demonstrates the importance of β-catenin in maintaining correct cellular functions and helps to understand its role in embryonic stem cells.

Identification of proteins related to epigenetic regulation in the malignant transformation of aberrant karyotypic human embryonic stem cells by quantitative proteomics

Previous reports have demonstrated that human embryonic stem cells (hESCs) tend to develop genomic alterations and progress to a malignant state during long-term in vitro culture. This raises concerns of the clinical safety in using cultured hESCs. However, transformed hESCs might serve as an excellent model to determine the process of embryonic stem cell transition. In this study, ITRAQ-based tandem mass spectrometry was used to quantify normal and aberrant karyotypic hESCs proteins from simple to more complex karyotypic abnormalities. We identified and quantified 2583 proteins, and found that the expression levels of 316 proteins that represented at least 23 functional molecular groups were significantly different in both normal and abnormal hESCs. Dysregulated protein expression in epigenetic regulation was further verified in six pairs of hESC lines in early and late passage. In summary, this study is the first large-scale quantitative proteomic analysis of the malignant transformation of aberrant karyotypic hESCs. The data generated should serve as a useful reference of stem cell-derived tumor progression. Increased expression of both HDAC2 and CTNNB1 are detected as early as the pre-neoplastic stage, and might serve as prognostic markers in the malignant transformation of hESCs.

Wnt signaling regulates homeostasis of the periodontal ligament

BACKGROUND AND OBJECTIVE

In health, the periodontal ligament maintains a constant width throughout an organism's lifetime. The molecular signals responsible for maintaining homeostatic control over the periodontal ligament are unknown. The purpose of this study was to investigate the role of Wnt signaling in this process by removing an essential chaperone protein, Wntless (Wls), from odontoblasts and cementoblasts, and observing the effects of Wnt depletion on cells of the periodontal complex.

MATERIAL AND METHODS

The Wnt responsive status of the periodontal complex was assessed using two strains of Wnt reporter mice: Axin2(LacZ/+) and Lgr5(LacZ/+) . The function of this endogenous Wnt signal was evaluated by conditionally eliminating the Wntless (Wls) gene using an osteocalcin Cre driver. The resulting OCN-Cre;Wls (fl/fl) mice were examined using micro-computed tomography and histology, immunohistochemical analyses for osteopontin, Runx2 and fibromodulin, in-situ hybridization for osterix and alkaline phosphatase activity.

RESULTS

The adult periodontal ligament is Wnt responsive. Elimination of Wnt signaling in the periodontal complex of OCN-Cre;Wls(fl/fl) mice resulted in a wider periodontal ligament space. This pathologically increased periodontal width is caused by a reduction in the expression of osteogenic genes and proteins, which results in thinner alveolar bone. A concomitant increase in fibrous tissue occupying the periodontal space was observed, along with a disruption in the orientation of the periodontal ligament.

CONCLUSION

The periodontal ligament is a Wnt-dependent tissue. Cells in the periodontal complex are Wnt responsive, and eliminating an essential component of the Wnt signaling network leads to a pathological widening of the periodontal ligament space. Osteogenic stimuli are reduced, and a disorganized fibrillary matrix results from the depletion of Wnt signaling. Collectively, these data underscore the importance of Wnt signaling in homeostasis of the periodontal ligament.