High-frequency canonical Wnt activation in multiple sarcoma subtypes drives proliferation through a TCF/β-catenin target gene, CDC25A

Disruption of TCF/β-Catenin Binding Impairs Wnt Signaling and Induces Apoptosis in Soft Tissue Sarcoma Cells

Soft tissue sarcomas (STS) are malignant tumors of mesenchymal origin and represent around 1% of adult cancers, being a very heterogeneous group of tumors with more than 50 different subtypes. The Wnt signaling pathway is involved in the development and in the regulation, self-renewal, and differentiation of mesenchymal stem cells, and plays a role in sarcomagenesis. In this study, we have tested pharmacologic inhibition of Wnt signaling mediated by disruption of TCF/β-catenin binding and AXIN stabilization, being the first strategy more efficient in reducing cell viability and downstream effects. We have shown that disruption of TCF/β-catenin binding with PKF118-310 produces in vitro antitumor activity in a panel of prevalent representative STS cell lines and primary cultures. At the molecular level, PKF118-310 treatment reduced β-catenin nuclear localization, reporter activity, and target genes, resulting in an increase in apoptosis. Importantly, combination of PKF118-310 with doxorubicin resulted in enhanced reduction of cell viability, suggesting that Wnt inhibition could be a new combination regime in these patients. Our findings support the usefulness of Wnt inhibitors as new therapeutic strategies for the prevalent STS. Mol Cancer Ther; 16(6); 1166–76. ©2017 AACR.

Oncopig Soft-Tissue Sarcomas Recapitulate Key Transcriptional Features of Human Sarcomas

Human soft-tissue sarcomas (STS) are rare mesenchymal tumors with a 5-year survival rate of 50%, highlighting the need for further STS research. Research has been hampered by limited human sarcoma cell line availability and the large number of STS subtypes, making development of STS cell lines and animal models representative of the diverse human STS subtypes critical. Pigs represent ideal human disease models due to their similar size, anatomy, metabolism, and genetics compared to humans. The Oncopig encodes inducible KRAS^G12D and TP53^R167H transgenes, allowing for STS modeling in a spatial and temporal manner. This study utilized Oncopig STS cell line (fibroblast) and tumor (leiomyosarcoma) RNA-seq data to compare Oncopig and human STS expression profiles. Altered expression of 3,360 and 7,652 genes was identified in Oncopig STS cell lines and leiomyosarcomas, respectively. Transcriptional hallmarks of human STS were observed in Oncopig STS, including altered TP53 signaling, Wnt signaling activation, and evidence of epigenetic reprogramming. Furthermore, master regulators of Oncopig STS expression were identified, including FOSL1, which was previously identified as a potential human STS therapeutic target. These results demonstrate the Oncopig STS model’s ability to mimic human STS transcriptional profiles, providing a valuable resource for sarcoma research and cell line development.

Clinical Observations and Molecular Variables of Primary Vascular Leiomyosarcoma

IMPORTANCE

Vascular leiomyosarcomas are a rare subtype of leiomyosarcomas that most commonly affect the inferior vena cava and account for 5% of all leiomyosarcomas. These tumors are aggressive malignant tumors for which adjuvant modalities have not shown increased efficacy compared with surgery.

OBJECTIVES

To evaluate the outcomes of patients with vascular leiomyosarcoma and the association between vascular leiomyosarcomas and immunohistochemical molecular markers, to determine their potential prognostic and therapeutic utility.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective medical record review of a cohort of 77 patients who presented to the University of Texas MD Anderson Cancer Center in Houston during the period from January 1993 to April 2012. Data were analyzed during the period from November 2012 to May 2015. All of the patients received a confirmed diagnosis of vascular leiomyosarcoma. Immunohistochemical studies for biomarkers were performed on a tissue microarray that included 26 primary specimens of vascular leiomyosarcoma.

MAIN OUTCOMES AND MEASURES

Demographic and clinical factors were evaluated to assess clinical course, patterns of recurrence, and survival outcomes for patients with primary vascular leiomyosarcoma. A univariate Cox proportional hazards model was used to correlate disease-specific survival and time to recurrence with potential prognostic indicators.

RESULTS

Sixty-three patients with localized disease who underwent surgical resection formed the study population, and their data were used for subsequent outcomes analysis. The median age at diagnosis was 58 years (range, 22-78 years). The majority of patients were female (41 patients [65%]) and white (51 patients [81%]). The 5-year disease-specific survival rate after tumor resection was 65%. The median time to local recurrence was 43 months, the median time to distant recurrence was 25 months, and the median time to concurrent local and distant recurrences was 15 months (P = .04). Strong expressions of cytoplasmic β-catenin (hazard ratio, 5.33 [95% CI, 0.97-29.30]; P = .06) and insulinlike growth factor 1 receptor (hazard ratio, 2.74 [95% CI, 1.14-6.56]; P = .02) were associated with inferior disease-specific survival.

CONCLUSIONS AND RELEVANCE

Vascular leiomyosarcomas are aggressive malignant tumors, with high recurrence rates. Expressions of β-catenin and insulinlike growth factor 1 receptor were associated with poor disease-specific survival. Prospective studies should evaluate the clinical and therapeutic utility of these molecular markers.

Nuclear phosphorylated Y142 β-catenin accumulates in astrocytomas and glioblastomas and regulates cell invasion

Glioblastoma multiforme (GBM) is a fast growing brain tumor characterized by extensive infiltration into the surrounding tissue and one of the most aggressive cancers. GBM is the most common glioma (originating from glial-derived cells) that either evolves from a low grade astrocytoma or appears de novo. Wnt/β-catenin and Hepatocyte Growth Factor (HGF)/c-Met signaling are hyperactive in human gliomas, where they regulate cell proliferation, migration and stem cell behavior. We previously demonstrated that β-catenin is phosphorylated at Y142 by recombinant c-Met kinase and downstream of HGF signaling in neurons. Here we studied phosphoY142 (PY142) β-catenin and dephospho S/T β-catenin (a classical Wnt transducer) in glioma biopsies, GBM cell lines and biopsy-derived glioma cell cultures. We found that PY142 β-catenin mainly localizes in the nucleus and signals through transcriptional activation in GBM cells. Tissue microarray analysis confirmed strong nuclear PY142 β-catenin immunostaining in astrocytoma and GBM biopsies. By contrast, active β-catenin showed nuclear localization only in GBM samples. Western blot analysis of tumor biopsies further indicated that PY142 and active β-catenin accumulate independently, correlating with the expression of Snail/Slug (an epithelial-mesenchymal transition marker) and Cyclin-D1 (a regulator of cell cycle progression), respectively, in high grade astrocytomas and GBMs. Moreover, GBM cells stimulated with HGF showed increasing levels of PY142 β-catenin and Snail/Slug. Importantly, the expression of mutant Y142F β-catenin decreased cell detachment and invasion induced by HGF in GBM cell lines and biopsy-derived cell cultures. Our results identify PY142 β-catenin as a nuclear β-catenin signaling form that downregulates adhesion and promotes GBM cell invasion.

β-Catenin-Independent Roles of Wnt/LRP6 Signaling

Wnt/LRP6 signaling is best known for the β-catenin-dependent regulation of target genes. However, pathway branches have recently emerged, including Wnt/STOP signaling, which act independently of β-catenin and transcription. We review here the molecular mechanisms underlying β-catenin-independent Wnt/LRP6 signaling cascades and their implications for cell biology, development, and physiology.

Activation of Wnt/β-Catenin in Ewing Sarcoma Cells Antagonizes EWS/ETS Function and Promotes Phenotypic Transition to More Metastatic Cell States

Ewing sarcomas are characterized by the presence of EWS/ETS fusion genes in the absence of other recurrent genetic alterations and mechanisms of tumor heterogeneity that contribute to disease progression remain unclear. Mutations in the Wnt/β-catenin pathway are rare in Ewing sarcoma but the Wnt pathway modulator LGR5 is often highly expressed, suggesting a potential role for the axis in tumor pathogenesis. We evaluated β-catenin and LGR5 expression in Ewing sarcoma cell lines and tumors and noted marked intra- and inter-tumor heterogeneity. Tumors with evidence of active Wnt/β-catenin signaling were associated with increased incidence of tumor relapse and worse overall survival. Paradoxically, RNA sequencing revealed a marked antagonism of EWS/ETS transcriptional activity in Wnt/β-catenin-activated tumor cells. Consistent with this, Wnt/β-catenin-activated cells displayed a phenotype that was reminiscent of Ewing sarcoma cells with partial EWS/ETS loss of function. Specifically, activation of Wnt/β-catenin induced alterations to the actin cytoskeleton, acquisition of a migratory phenotype, and upregulation of EWS/ETS-repressed genes. Notably, activation of Wnt/β-catenin signaling led to marked induction of tenascin C (TNC), an established promoter of cancer metastasis, and an EWS/ETS-repressed target gene. Loss of TNC function in Ewing sarcoma cells profoundly inhibited their migratory and metastatic potential. Our studies reveal that heterogeneous activation of Wnt/β-catenin signaling in subpopulations of tumor cells contributes to phenotypic heterogeneity and disease progression in Ewing sarcoma. Significantly, this is mediated, at least in part, by inhibition of EWS/ETS fusion protein function that results in derepression of metastasis-associated gene programs. Cancer Res; 76(17); 5040-53. ©2016 AACR.

Direct Targeting of β-Catenin by a Small Molecule Stimulates Proteasomal Degradation and Suppresses Oncogenic Wnt/β-Catenin Signaling

The Wnt/β-catenin signaling pathway plays a major role in tissue homeostasis, and its dysregulation can lead to various human diseases. Aberrant activation of β-catenin is oncogenic and is a critical driver in the development and progression of human cancers. Despite the significant potential of targeting the oncogenic β-catenin pathway for cancer therapy, the development of specific inhibitors remains insufficient. Using a T cell factor (TCF)-dependent luciferase-reporter system, we screened for small-molecule compounds that act against Wnt/β-catenin signaling and identified MSAB (methyl 3-{[(4-methylphenyl)sulfonyl]amino}benzoate) as a selective inhibitor of Wnt/β-catenin signaling. MSAB shows potent anti-tumor effects selectively on Wnt-dependent cancer cells in vitro and in mouse cancer models. MSAB binds to β-catenin, promoting its degradation, and specifically downregulates Wnt/β-catenin target genes. Our findings might represent an effective therapeutic strategy for cancers addicted to the Wnt/β-catenin signaling pathway.

Aberrant activation of Wnt/β-catenin signaling drives proliferation of bone sarcoma cells

Bone sarcomas such as osteosarcoma and chondrosarcoma are frequently refractory to conventional chemotherapy and radiotherapy that exhibit poor prognosis. The Wnt signaling are evolutionarily conserved and implicated in cell proliferation and sarcomagenesis. However, the potential role of the Wnt signaling in bone sarcomas is still unclear. Here we demonstrate aberrant activation of Wnt/β-catenin signaling in bone sarcoma cells, involving an autocrine Wnt signaling loop with upregulation of specific Wnt ligands and receptors. Activation of Wnt/β-catenin signaling with Wnt3a or GSK-3β inhibitor drives the proliferation of bone sarcoma cells, whereas downregulation of activated Wnt signaling with dnTCF4 or siLEF1 suppresses bone sarcoma proliferation and induces cell cycle arrest. Taken together, our findings establish the evidence that aberrant activation of Wnt/β-catenin pathway involving an autocrine Wnt singaling drives the proliferation of bone sarcoma cells, and identify the autocrine activation of the Wnt/β-catenin signaling as a potential novel therapeutic target for bone sarcomas.

Deciphering signaling networks in osteosarcoma pathobiology

Osteosarcoma is the most frequent type of primary bone tumors among children and adolescents. During the past years, little progress has been made regarding prognosis of osteosarcoma patients, especially for those with metastatic disease. Genomic instability and gene alterations are common, but current data do not reveal a consistent and repeatable pattern of osteosarcoma development, thus paralleling the tumor's high heterogeneity. Critical signal transduction pathways have been implicated in osteosarcoma pathobiology and are being evaluated as therapeutic targets, including receptor activator for nuclear factor-κB (RANK), Wnt, Notch, phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin, and mechanotransduction pathways. Herein, we recapitulate and discuss recent advances in the context of molecular mechanisms and signaling networks that contribute to osteosarcoma progression and metastasis, towards patient-tailored and novel-targeted treatments.

Oxidized ATM promotes abnormal proliferation of breast CAFs through maintaining intracellular redox homeostasis and activating the PI3K-AKT, MEK-ERK, and Wnt-β-catenin signaling pathways

Abnormal proliferation is one characteristic of cancer-associated fibroblasts (CAFs), which play a key role in tumorigenesis and tumor progression. Oxidative stress (OS) is the root cause of CAFs abnormal proliferation. ATM (ataxia-telangiectasia mutated protein kinase), an important redox sensor, is involved in DNA damage response and cellular homeostasis. Whether and how oxidized ATM regulating CAFs proliferation remains unclear. In this study, we show that there is a high level of oxidized ATM in breast CAFs in the absence of double-strand breaks (DSBs) and that oxidized ATM plays a critical role in CAFs proliferation. The effect of oxidized ATM on CAFs proliferation is mediated by its regulation of cellular redox balance and the activity of the ERK, PI3K-AKT, and Wnt signaling pathways. Treating cells with antioxidant N-acetyl-cysteine (NAC) partially rescues the proliferation defect of the breast CAFs caused by ATM deficiency. Administrating cells with individual or a combination of specific inhibitors of the ERK, PI3K-AKT, and Wnt signaling pathways mimics the effect of ATM deficiency on breast CAF proliferation. This is mainly ascribed to the β-catenin suppression and down-regulation of c-Myc, thus further leading to the decreased cyclinD1, cyclinE, and E2F1 expression and the enhanced p21(Cip1) level. Our results reveal an important role of oxidized ATM in the regulation of the abnormal proliferation of breast CAFs. Oxidized ATM could serve as a potential target for treating breast cancer.

The fusion protein SS18-SSX1 employs core Wnt pathway transcription factors to induce a partial Wnt signature in synovial sarcoma

Expression of the SS18/SYT-SSX fusion protein is believed to underlie the pathogenesis of synovial sarcoma (SS). Recent evidence suggests that deregulation of the Wnt pathway may play an important role in SS but the mechanisms whereby SS18-SSX might affect Wnt signaling remain to be elucidated. Here, we show that SS18/SSX tightly regulates the elevated expression of the key Wnt target AXIN2 in primary SS. SS18-SSX is shown to interact with TCF/LEF, TLE and HDAC but not β-catenin in vivo and to induce Wnt target gene expression by forming a complex containing promoter-bound TCF/LEF and HDAC but lacking β-catenin. Our observations provide a tumor-specific mechanistic basis for Wnt target gene induction in SS that can occur in the absence of Wnt ligand stimulation.

The molecular landscape of extraskeletal osteosarcoma: A clinicopathological and molecular biomarker study

Extraskeletal osteosarcoma (ESOSA) is a rare soft tissue neoplasm representing <5% of osteosarcomas and <1% of all soft-tissue sarcomas. Herein, we investigate the clinicopathological and molecular features of ESOSA and explore potential parameters that may affect outcome. Thirty-two cases were retrieved and histomorphology was reviewed. Clinical history and follow-up were obtained through electronic record review. DNA from formalin-fixed paraffin-embedded (FFPE) tissue was extracted and processed from 27 cases. Genome-wide DNA copy number (CN) alterations and allelic imbalances were analyzed by single nucleotide polymorphism array using Affymetrix OncoScan FFPE Assay. Massive high-throughput deep parallel sequencing was performed using a customized panel targeting 410 cancer genes. Log rank, Fisher's exact test and Cox proportional hazards were used for statistical analysis. In this series of 32 patients (male n = 12, female n = 20), the average age was 66 years (19-93) and median follow up was 24 months (range 6-120 months). Frequent genomic alterations included CN losses in tumour suppressor genes including CDKN2A (70%), TP53 (56%) and RB1 (49%). Mutations affecting methylation/demethylation, chromatin remodeling and WNT/SHH pathways were identified in 40%, 27%, and 27%, respectively. PIK3CA and TERT promoter variant mutations were identified in 11% of the cases. Cases harbouring simultaneous TP53 and RB1 biallelic CN losses were associated with worse overall survival and local recurrence (p = 0.04, p = 0.02, respectively). CDKN2A losses and positive margins were also associated with worse overall survival (p = 0.002; p = 0.03, respectively). Our findings suggest that age above 60, positive margin status, simultaneous biallelic TP53 and RB1 losses and CDKN2A loss are associated with a worse outcome in ESOSA. Comparison between conventional paediatric osteosarcoma and ESOSA shows that, while both share genetic similarities, there are notable dissimilarities and mechanistic differences in the molecular pathways involved in ESOSA.

Targeting the WNT Signaling Pathway in Cancer Therapeutics

The WNT signaling cascade is integral in numerous biological processes including embryonic development, cell cycle regulation, inflammation, and cancer. Hyperactivation of WNT signaling secondary to alterations to varying nodes of the pathway have been identified in multiple tumor types. These alterations converge into increased tumorigenicity, sustained proliferation, and enhanced metastatic potential. This review seeks to evaluate the evidence supporting the WNT pathway in cancer, the therapeutic strategies in modulating this pathway, and potential challenges in drug development.

Targeted Chemotherapy in Bone and Soft-Tissue Sarcoma

Historically surgical intervention has been the mainstay of therapy for bone and soft-tissue sarcomas, augmented with adjuvant radiation for local control. Although cytotoxic chemotherapy revolutionized the treatment of many sarcomas, classic treatment regimens are fraught with side effects while outcomes have plateaued. However, since the approval of imatinib in 2002, research into targeted chemotherapy has increased exponentially. With targeted therapies comes the potential for decreased side effects and more potent, personalized treatment options. This article reviews the evolution of medical knowledge regarding sarcoma, the basic science of sarcomatogenesis, and the major targets and pathways now being studied.

FOXO1 inhibits osteosarcoma oncogenesis via Wnt/β-catenin pathway suppression

Recent advances have highlighted profound roles of FOXO transcription factors, especially FOXO1, in bone development and remodeling. The regulation of bone development by FOXOs seems to be stage-specific or context dependent. FOXOs promote maintenance and differentiation of early progenitors of the osteoblast lineage and repress proliferation of committed osteoblast precursors; FOXO1 is vital for osteocyte survival. Considering the versatile roles played by FOXOs in bone development and tumorigenesis, it is plausible that FOXO1, the main FOXO in bone with a non-redundant role, might have influence on osteosarcoma (OS) oncogenesis. Indeed, recent results have implicated that FOXO1 has a tumor-suppressing role in OS. In the present study, we found that FOXO1 expression was generally low or absent in OS, with a minority of cases having moderate expression. Whole-genome sequencing (WGS) revealed that the FOXO1 locus was frequently involved in copy number variation and loss of heterozygosity in OS, indicating that chromosomal aberrations might be partially responsible for the heterogeneity in FOXO1 expression. FOXO1 activation in OS cell lines inhibited cancer cell survival, which can be attributed to modulation of target genes, including BIM and repressed Wnt/β-catenin signaling. FOXO1 inhibition promoted cell proliferation, enhanced colony formation and attenuated osteogenic differentiation of OS cell lines. To conclude, our results proved FOXO1 as a tumor suppressor in OS at least partially by suppression of the Wnt/β-catenin pathway.

Self-renewing diploid Axin2(+) cells fuel homeostatic renewal of the liver

The source of new hepatocytes in the uninjured liver has remained an open question. By lineage tracing using the Wnt-responsive gene Axin2, we identify a population of proliferating and self-renewing cells adjacent to the central vein in the liver lobule. These pericentral cells express the early liver progenitor marker Tbx3, are diploid, and thus differ from mature hepatocytes, which are mostly polyploid. The descendants of pericentral cells differentiate into Tbx3-negative, polyploid hepatocytes and can replace all hepatocytes along the liver lobule during homeostatic renewal. Adjacent central vein endothelial cells provide Wnt signals that maintain the pericentral cells, thereby constituting the niche. Thus, we identify a cell population in the liver that subserves homeostatic hepatocyte renewal, characterize its anatomical niche, and identify molecular signals that regulate its activity.

Deregulation of the Hippo pathway in soft-tissue sarcoma promotes FOXM1 expression and tumorigenesis

Genetic aberrations responsible for soft-tissue sarcoma formation in adults are largely unknown, with targeted therapies sorely needed for this complex and heterogeneous family of diseases. Here we report that that the Hippo pathway is deregulated in many soft-tissue sarcomas, resulting in elevated expression of the effector molecule Yes-Associated Protein (YAP). Based on data gathered from human sarcoma patients, a novel autochthonous mouse model, and mechanistic analyses, we determined that YAP-dependent expression of the transcription factor forkhead box M1 (FOXM1) is necessary for cell proliferation/tumorigenesis in a subset of soft-tissue sarcomas. Notably, FOXM1 directly interacts with the YAP transcriptional complex via TEAD1, resulting in coregulation of numerous critical pro-proliferation targets that enhance sarcoma progression. Finally, pharmacologic inhibition of FOXM1 decreases tumor size in vivo, making FOXM1 an attractive therapeutic target for the treatment of some sarcoma subtypes.

The Wnt/β-catenin pathway in human fibrotic-like diseases and its eligibility as a therapeutic target

The canonical Wnt signaling pathway is involved in a variety of biological processes like cell proliferation, cell polarity, and cell fate determination. This pathway has been extensively investigated as its deregulation is linked to different diseases, including various types of cancer, skeletal defects, birth defect disorders (including neural tube defects), metabolic diseases, neurodegenerative disorders and several fibrotic diseases like desmoid tumors. In the "on state", beta-catenin, the key effector of Wnt signaling, enters the nucleus where it binds to the members of the TCF-LEF family of transcription factors and exerts its effect on gene transcription. Disease development can be caused by direct or indirect alterations of the Wnt/β-catenin signaling.

In the first case germline or somatic mutations of the Wnt components are associated to several diseases such as the familial adenomatous polyposis (FAP) - caused by germline mutations of the tumor suppressor adenomatous polyposis coli gene (APC) - and the desmoid-like fibromatosis, a sporadic tumor associated with somatic mutations of the β-catenin gene (CTNNB1).

In the second case, epigenetic modifications and microenvironmental factors have been demonstrated to play a key role in Wnt pathway activation. The natural autocrine Wnt signaling acts through agonists and antagonists competing for the Wnt receptors. Anomalies in this regulation, whichever is their etiology, are an important part in the pathogenesis of Wnt pathway linked diseases. An example is promoter hypermethylation of Wnt antagonists, such as SFRPs, that causes gene silencing preventing their function and consequently leading to the activation of the Wnt pathway. Microenvironmental factors, such as the extracellular matrix, growth factors and inflammatory mediators, represent another type of indirect mechanism that influence Wnt pathway activation. A favorable microenvironment can lead to aberrant fibroblasts activation and accumulation of ECM proteins with subsequent tissue fibrosis that can evolve in fibrotic disease or tumor.

Since the development and progression of several diseases is the outcome of the Wnt pathway cross-talk with other signaling pathways and inflammatory factors, it is important to consider not only direct inhibitors of the Wnt signaling pathway but also inhibitors of microenvironmental factors as promising therapeutic approaches for several tumors of fibrotic origin.

The Wnt/β-catenin pathway in human fibrotic-like diseases and its eligibility as a therapeutic target

The canonical Wnt signaling pathway is involved in a variety of biological processes like cell proliferation, cell polarity, and cell fate determination. This pathway has been extensively investigated as its deregulation is linked to different diseases, including various types of cancer, skeletal defects, birth defect disorders (including neural tube defects), metabolic diseases, neurodegenerative disorders and several fibrotic diseases like desmoid tumors. In the "on state", beta-catenin, the key effector of Wnt signaling, enters the nucleus where it binds to the members of the TCF-LEF family of transcription factors and exerts its effect on gene transcription. Disease development can be caused by direct or indirect alterations of the Wnt/β-catenin signaling. In the first case germline or somatic mutations of the Wnt components are associated to several diseases such as the familial adenomatous polyposis (FAP) - caused by germline mutations of the tumor suppressor adenomatous polyposis coli gene (APC) - and the desmoid-like fibromatosis, a sporadic tumor associated with somatic mutations of the β-catenin gene (CTNNB1). In the second case, epigenetic modifications and microenvironmental factors have been demonstrated to play a key role in Wnt pathway activation. The natural autocrine Wnt signaling acts through agonists and antagonists competing for the Wnt receptors. Anomalies in this regulation, whichever is their etiology, are an important part in the pathogenesis of Wnt pathway linked diseases. An example is promoter hypermethylation of Wnt antagonists, such as SFRPs, that causes gene silencing preventing their function and consequently leading to the activation of the Wnt pathway. Microenvironmental factors, such as the extracellular matrix, growth factors and inflammatory mediators, represent another type of indirect mechanism that influence Wnt pathway activation. A favorable microenvironment can lead to aberrant fibroblasts activation and accumulation of ECM proteins with subsequent tissue fibrosis that can evolve in fibrotic disease or tumor. Since the development and progression of several diseases is the outcome of the Wnt pathway cross-talk with other signaling pathways and inflammatory factors, it is important to consider not only direct inhibitors of the Wnt signaling pathway but also inhibitors of microenvironmental factors as promising therapeutic approaches for several tumors of fibrotic origin.

3D tissue-engineered model of Ewing's sarcoma

Despite longstanding reliance upon monolayer culture for studying cancer cells, and numerous advantages from both a practical and experimental standpoint, a growing body of evidence suggests that more complex three-dimensional (3D) models are necessary to properly mimic many of the critical hallmarks associated with the oncogenesis, maintenance and spread of Ewing's sarcoma (ES), the second most common pediatric bone tumor. And as clinicians increasingly turn to biologically-targeted therapies that exert their effects not only on the tumor cells themselves, but also on the surrounding extracellular matrix, it is especially important that preclinical models evolve in parallel to reliably measure antineoplastic effects and possible mechanisms of de novo and acquired drug resistance. Herein, we highlight a number of innovative methods used to fabricate biomimetic ES tumors, encompassing both the surrounding cellular milieu and the extracellular matrix (ECM), and suggest potential applications to advance our understanding of ES biology, preclinical drug testing, and personalized medicine.

Translational biology of osteosarcoma

For the past 30 years, improvements in the survival of patients with osteosarcoma have been mostly incremental. Despite evidence of genomic instability and a high frequency of chromothripsis and kataegis, osteosarcomas carry few recurrent targetable mutations, and trials of targeted agents have been generally disappointing. Bone has a highly specialized immune environment and many immune signalling pathways are important in bone homeostasis. The success of the innate immune stimulant mifamurtide in the adjuvant treatment of non-metastatic osteosarcoma suggests that newer immune-based treatments, such as immune checkpoint inhibitors, may substantially improve disease outcome.

Cell cycle and cell fate in the developing nervous system: the role of CDC25B phosphatase

Deciphering the core machinery of the cell cycle and cell division has been primarily the focus of cell biologists, while developmental biologists have identified the signaling pathways and transcriptional programs controlling cell fate choices. As a result, until recently, the interplay between these two fundamental aspects of biology have remained largely unexplored. Increasing data show that the cell cycle and regulators of the core cell cycle machinery are important players in cell fate decisions during neurogenesis. Here, we summarize recent data describing how cell cycle dynamics affect the switch between proliferation and differentiation, with an emphasis on the roles played by the cell cycle regulators, the CDC25 phosphatases.

Enrichment of the β-catenin-TCF complex at the S and G2 phases ensures cell survival and cell cycle progression

Wnt-β-catenin (β-catenin is also known as CTNNB1 in human) signaling through the β-catenin-TCF complex plays crucial roles in tissue homeostasis. Wnt-stimulated β-catenin-TCF complex accumulation in the nucleus regulates cell survival, proliferation and differentiation through the transcription of target genes. Compared with their levels in G1, activation of the receptor LRP6 and cytosolic β-catenin are both upregulated in G2 cells. However, accumulation of the Wnt pathway negative regulator AXIN2 also occurs in this phase. Therefore, it is unclear whether Wnt signaling is active in G2 phase cells. Here, we established a bimolecular fluorescence complementation (BiFC) biosensor system for the direct visualization of the β-catenin-TCF interaction in living cells. Using the BiFC biosensor and co-immunoprecipitation experiments, we demonstrate that levels of the nucleus-localized β-catenin-TCF complex increase during the S and G2 phases, and declines in the next G1 phase. Accordingly, a subset of Wnt target genes is transcribed by the β-catenin-TCF complex during both the S and G2 phases. By contrast, transient inhibition of this complex disturbs both cell survival and G2/M progression. Our results suggest that in S and G2 phase cells, Wnt-β-catenin signaling is highly active and functions to ensure cell survival and cell cycle progression.

Autocrine Activation of the Wnt/β-Catenin Pathway by CUX1 and GLIS1 in Breast Cancers

Autocrine activation of the Wnt/β-catenin pathway occurs in several cancers, notably in breast tumors, and is associated with higher expression of various Wnt ligands. Using various inhibitors of the FZD/LRP receptor complex, we demonstrate that some adenosquamous carcinomas that develop in MMTV-CUX1 transgenic mice represent a model for autocrine activation of the Wnt/β-catenin pathway. By comparing expression profiles of laser-capture microdissected mammary tumors, we identify Glis1 as a transcription factor that is highly expressed in the subset of tumors with elevated Wnt gene expression. Analysis of human cancer datasets confirms that elevated WNT gene expression is associated with high levels of CUX1 and GLIS1 and correlates with genes of the epithelial-to-mesenchymal transition (EMT) signature: VIM, SNAI1 and TWIST1 are elevated whereas CDH1 and OCLN are decreased. Co-expression experiments demonstrate that CUX1 and GLIS1 cooperate to stimulate TCF/β-catenin transcriptional activity and to enhance cell migration and invasion. Altogether, these results provide additional evidence for the role of GLIS1 in reprogramming gene expression and suggest a hierarchical model for transcriptional regulation of the Wnt/β-catenin pathway and the epithelial-to-mesenchymal transition.

Integrated analysis of the Wnt responsive proteome in human cells reveals diverse and cell-type specific networks

Wnt signalling is a fundamentally important signalling pathway that regulates many aspects of metazoan development and is frequently dysregulated in cancer. Although many of the core components of the Wnt signalling pathway, such as β-catenin, have been extensively studied, the broad systems level responses of the mammalian cell to Wnt signalling are less well understood. In addition, the cell- or tissue-specific protein networks that modulate Wnt signalling in the diverse tissues or developmental stages in which it functions remain to be defined. To address these questions, we undertook a broad survey of the Wnt response in different human cell lines using both interaction and expression proteomics approaches. Our data reveal both similar and divergent responses of pathways and processes in the three cell-lines analyzed as well as a marked attenuation of the response to exogenous Wnt treatment in cells harbouring a stabilizing (activating) mutation of β-catenin. We also identify cell-type specific components of the Wnt signalling network and find that by integrating expression and interaction proteomics data a more complete description of the Wnt interaction network can be achieved. Finally, our results attest to the power of LC-MS/MS to reveal novel cellular responses in even relatively well studied biological pathways such as Wnt signalling.

Human Sarcoma growth is sensitive to small-molecule mediated AXIN stabilization

Sarcomas are mesenchymal tumors showing high molecular heterogeneity, reflected at the histological level by the existence of more than fifty different subtypes. Genetic and epigenetic evidences link aberrant activation of the Wnt signaling to growth and progression of human sarcomas. This phenomenon, mainly accomplished by autocrine loop activity, is sustained by gene amplification, over-expression of Wnt ligands and co-receptors or epigenetic silencing of endogenous Wnt antagonists. We previously showed that pharmacological inhibition of Wnt signaling mediated by Axin stabilization produced in vitro and in vivo antitumor activity in glioblastoma tumors. Here, we report that targeting different sarcoma cell lines with the Wnt inhibitor/Axin stabilizer SEN461 produces a less transformed phenotype, as supported by modulation of anchorage-independent growth in vitro. At the molecular level, SEN461 treatment enhanced the stability of the scaffold protein Axin1, a key negative regulator of the Wnt signaling with tumor suppressor function, resulting in downstream effects coherent with inhibition of canonical Wnt signaling. Genetic phenocopy of small molecule Axin stabilization, through Axin1 over-expression, coherently resulted in strong impairment of soft-agar growth. Importantly, sarcoma growth inhibition through pharmacological Axin stabilization was also observed in a xenograft model in vivo in female CD-1 nude mice. Our findings suggest the usefulness of Wnt inhibitors with Axin stabilization activity as a potentialyl clinical relevant strategy for certain types of sarcomas.

Senescence bypass in mesenchymal stem cells: a potential pathogenesis and implications of pro-senescence therapy in sarcomas

Cellular senescence is a mechanism that limits the lifespan of somatic cells as the results of replicative proliferation and response to stresses, and that prevents undesired oncogenic changes constituting a barrier against immortalization and tumorigenesis. Mesenchymal stem cells (MSCs) reside in a variety of tissues, and participates in tissue maintenance with their multipotent differentiation ability. MSCs are also considered to be as cells of origin for certain type of sarcomas. We reviewed the mechanisms of cellular senescence in MSCs and hypothesized senescence bypass as the potential pathogenesis for sarcoma development, and proposed the possibility of senescence induction therapy for an alternative treatment strategy against sarcomas, especially cells with the resistance to conventional chemo and radiotherapy including sarcoma stem cells.

RECQ DNA helicases and osteosarcoma

The RECQ family of DNA helicases is a conserved group of enzymes that are important for maintaining genomic integrity. In humans, there are five RECQ helicase genes, and mutations in three of them-BLM, WRN, and RECQL4-are associated with the genetic disorders Bloom syndrome, Werner syndrome, and Rothmund-Thomson syndrome (RTS), respectively. Importantly all three diseases are cancer predisposition syndromes. Patients with RTS are highly and uniquely susceptible to developing osteosarcoma; thus, RTS provides a good model to study the pathogenesis of osteosarcoma. The "tumor suppressor" role of RECQL4 and the other RECQ helicases is an area of active investigation. This chapter reviews what is currently known about the cellular functions of RECQL4 and how these may relate to tumorigenesis, as well as ongoing efforts to understand RECQL4's functions in vivo using animal models. Understanding the RECQ pathways may provide insight into avenues for novel cancer therapies in the future.

β-Catenin transcriptional activity is minimal in canine osteosarcoma and its targeted inhibition results in minimal changes to cell line behaviour

Canine osteosarcoma (OS) is an aggressive malignancy associated with poor outcomes. Therapeutic improvements are likely to develop from an improved understanding of signalling pathways contributing to OS development and progression. The Wnt signalling pathway is of interest for its role in osteoblast differentiation, its dysregulation in numerous cancer types, and the relative frequency of cytoplasmic accumulation of β-catenin in canine OS. This study aimed to determine the biological impact of inhibiting canonical Wnt signalling in canine OS, by utilizing either β-catenin siRNA or a dominant-negative T-cell factor (TCF) construct. There were no consistent, significant changes in cell line behaviour with either method compared to parental cell lines. Interestingly, β-catenin transcriptional activity was three-fold higher in normal canine primary osteoblasts compared to canine OS cell lines. These results suggest canonical Wnt signalling is minimally active in canine OS and its targeted inhibition is not a relevant therapeutic strategy.

Identification of putative target genes for amplification within 11q13.2 and 3q27.1 in esophageal squamous cell carcinoma

BACKGROUND

Genomic aberration is a common feature of human cancers and also is one of the basic mechanisms that lead to overexpression of oncogenes and underexpression of tumor suppressor genes. Our study aims to identify frequent genomic changes and candidate copy number driving genes in esophageal squamous cell carcinoma (ESCC).

METHODS

We used array comparative genomic hybridization to identify recurrent genomic alterations and screened the candidate targets of selected amplification regions by quantitative and semi-quantitative RT-PCR.

RESULTS

Thirty-four gains and 16 losses occurred in more than 50 % of ESCCs. High-level amplifications at 7p11.2, 8p12, 8q24.21, 11q13.2-q13.3, 12p11.21, 12q12 and homozygous deletions at 2q22.1, 8p23.1-p21.2, 9p21.3 and 14q11.2 were also identified. 11q13.2 was a frequent amplification region, in which five genes including CHKA, GAL, KIAA1394, LRP5 and PTPRCAP were overexpressed in tumor tissues than paracancerous normal tissues. The expression of ALG3 at 3q27.1 was higher in ESCCs, especially in patients with lymph node metastasis.

CONCLUSIONS

Target gene identification of amplifications or homozygous deletions will help to reveal the mechanism of tumor formation and explore new therapy method.

SS18-SSX fusion protein-induced Wnt/β-catenin signaling is a therapeutic target in synovial sarcoma

Synovial sarcoma is a high-grade soft tissue malignancy characterized by a specific reciprocal translocation t(X;18), which leads to the fusion of the SS18 (SYT) gene to one of three SSX genes (SSX1, SSX2 or SSX4). The resulting chimeric SS18-SSX protein is suggested to act as an oncogenic transcriptional regulator. Despite multimodal therapeutic approaches, metastatic disease is often lethal and the development of novel targeted therapeutic strategies is required. Several expression-profiling studies identified distinct gene expression signatures, implying a consistent role of Wnt/β-catenin signaling in synovial sarcoma tumorigenesis. Here we investigate the functional and therapeutic relevance of Wnt/β-catenin pathway activation in vitro and in vivo. Immunohistochemical analyses of nuclear β-catenin and Wnt downstream targets revealed activation of canonical Wnt signaling in a significant subset of 30 primary synovial sarcoma specimens. Functional aspects of Wnt signaling including dependence of Tcf/β-catenin complex activity on the SS18-SSX fusion proteins were analyzed. Efficient SS18-SSX-dependent activation of the Tcf/β-catenin transcriptional complex was confirmed by TOPflash reporter luciferase assays and immunoblotting. In five human synovial sarcoma cell lines, inhibition of the Tcf/β-catenin protein-protein interaction significantly blocked the canonical Wnt/β-catenin signaling cascade, accompanied by the effective downregulation of Wnt targets (AXIN2, CDC25A, c-MYC, DKK1, CyclinD1 and Survivin) and the specific suppression of cell viability associated with the induction of apoptosis. In SYO-1 synovial sarcoma xenografts, administration of small molecule Tcf/β-catenin complex inhibitors significantly reduced tumor growth, associated with diminished AXIN2 protein levels. In summary, SS18-SSX-induced Wnt/β-catenin signaling appears to be of crucial biological importance in synovial sarcoma tumorigenesis and progression, representing a potential molecular target for the development of novel therapeutic strategies.

β-Catenin-independent activation of TCF1/LEF1 in human hematopoietic tumor cells through interaction with ATF2 transcription factors

The role of Wnt signaling in embryonic development and stem cell maintenance is well established and aberrations leading to the constitutive up-regulation of this pathway are frequent in several types of human cancers. Upon ligand-mediated activation, Wnt receptors promote the stabilization of β-catenin, which translocates to the nucleus and binds to the T-cell factor/lymphoid enhancer factor (TCF/LEF) family of transcription factors to regulate the expression of Wnt target genes. When not bound to β-catenin, the TCF/LEF proteins are believed to act as transcriptional repressors. Using a specific lentiviral reporter, we identified hematopoietic tumor cells displaying constitutive TCF/LEF transcriptional activation in the absence of β-catenin stabilization. Suppression of TCF/LEF activity in these cells mediated by an inducible dominant-negative TCF4 (DN-TCF4) inhibited both cell growth and the expression of Wnt target genes. Further, expression of TCF1 and LEF1, but not TCF4, stimulated TCF/LEF reporter activity in certain human cell lines independently of β-catenin. By a complementary approach in vivo, TCF1 mutants, which lacked the ability to bind to β-catenin, induced Xenopus embryo axis duplication, a hallmark of Wnt activation, and the expression of the Wnt target gene Xnr3. Through generation of different TCF1-TCF4 fusion proteins, we identified three distinct TCF1 domains that participate in the β-catenin-independent activity of this transcription factor. TCF1 and LEF1 physically interacted and functionally synergized with members of the activating transcription factor 2 (ATF2) family of transcription factors. Moreover, knockdown of ATF2 expression in lymphoma cells phenocopied the inhibitory effects of DN-TCF4 on the expression of target genes associated with the Wnt pathway and on cell growth. Together, our findings indicate that, through interaction with ATF2 factors, TCF1/LEF1 promote the growth of hematopoietic malignancies in the absence of β-catenin stabilization, thus establishing a new mechanism for TCF1/LEF1 transcriptional activity distinct from that associated with canonical Wnt signaling.

The Wnt signaling pathway plays a crucial role during embryonic development and in the maintenance of stem cell populations in various organs and tissues. Aberrant activation of this pathway through different mechanisms participates in the onset and progression of several types of human cancers. In the presence of Wnt ligands, stabilized β-catenin acts as a transcriptional activator to induce the expression of target genes through binding to the TCF/LEF family of transcription factors. Using in vitro and in vivo models, we show that TCF/LEF proteins can be activated independently of β-catenin through cooperation with members of the ATF2 subfamily of transcription factors. This novel alternative mechanism of TCF/LEF activation is constitutively up-regulated in certain hematopoietic tumor cells, where it regulates the expression of TCF/LEF target genes and promotes cell growth.

Targeting the Wnt pathway in synovial sarcoma models

Synovial sarcoma is an aggressive soft-tissue malignancy of children and young adults, with no effective systemic therapies. Its specific oncogene, SYT-SSX (SS18-SSX), drives sarcoma initiation and development. The exact mechanism of SYT-SSX oncogenic function remains unknown. In an SYT-SSX2 transgenic model, we show that a constitutive Wnt/β-catenin signal is aberrantly activated by SYT-SSX2, and inhibition of Wnt signaling through the genetic loss of β-catenin blocks synovial sarcoma tumor formation. In a combination of cell-based and synovial sarcoma tumor xenograft models, we show that inhibition of the Wnt cascade through coreceptor blockade and the use of small-molecule CK1α activators arrests synovial sarcoma tumor growth. We find that upregulation of the Wnt/β-catenin cascade by SYT-SSX2 correlates with its nuclear reprogramming function. These studies reveal the central role of Wnt/β-catenin signaling in SYT-SSX2-induced sarcoma genesis, and open new venues for the development of effective synovial sarcoma curative agents.

SIGNIFICANCE

Synovial sarcoma is an aggressive soft-tissue cancer that afflicts children and young adults, and for which there is no effective treatment. The current studies provide critical insight into our understanding of the pathogenesis of SYT–SSX-dependent synovial sarcoma and pave the way for the development of effective therapeutic agents for the treatment of the disease in humans.

Insulin receptor tyrosine kinase substrate activates EGFR/ERK signalling pathway and promotes cell proliferation of hepatocellular carcinoma

Insulin receptor tyrosine kinase substrate (IRTKS) is closely associated with actin remodelling and membrane protrusion, but its role in the pathogenesis of malignant tumours, including hepatocellular carcinoma (HCC), is still unknown. In this study, we showed that IRTKS was frequently upregulated in HCC samples, and its expression level was significantly associated with tumour size. Enforced expression of IRTKS in human HCC cell lines significantly promoted their proliferation and colony formation in vitro, and their capacity to develop tumour xenografts in vivo, whereas knockdown of IRTKS resulted in the opposite effects. Furthermore, the bromodeoxyuridine (BrdU) incorporation analyses and propidium iodide staining indicated that IRTKS can promote the entry into S phase of cell cycle progression. Significantly, IRTKS can interact with epidermal growth factor receptor (EGFR), results in the phosphorylation of extracellular signal-regulated kinase (ERK). By contrast, inhibition of ERK activation can attenuate the effects of IRTKS overexpression on cellular proliferation. Taken together, these data demonstrate that IRTKS promotes the proliferation of HCC cells by enhancing EGFR-ERK signalling pathway.

Cancer biology: a new RING to Wnt signaling

The β-catenin-dependent Wnt signaling pathway has key roles in embryonic development and adult tissues and is defective in various cancers. Recent studies highlight the function of two transmembrane RING finger ubiquitin ligases in modulating Wnt signaling and reveal roles for mutations in the RING finger proteins in cancer.

LGR5 is Expressed by Ewing Sarcoma and Potentiates Wnt/β-Catenin Signaling

Ewing sarcoma (ES) is an aggressive bone and soft tissue tumor of putative stem cell origin that predominantly occurs in children and young adults. Although most patients with localized ES can be cured with intensive therapy, the clinical course is variable and up to one third of patients relapse following initial remission. Unfortunately, little is yet known about the biologic features that distinguish low-risk from high-risk disease or the mechanisms of ES disease progression. Recent reports have suggested that putative cancer stem cells exist in ES and may contribute to an aggressive phenotype. The cell surface receptor leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5) is a somatic stem cell marker that functions as an oncogene in several human cancers, most notably colorectal carcinoma. LGR5 is a receptor for the R-spondin (RSPO) family of ligands and RSPO-mediated activation of LGR5 potentiates Wnt/β-catenin signaling, contributing to stem cell proliferation and self-renewal. Given its presumed stem cell origin, we investigated whether LGR5 contributes to ES pathogenesis. We found that LGR5 is expressed by ES and that its expression is relatively increased in cells and tumors that display a more aggressive phenotype. In particular, LGR5 expression was increased in putative cancer stem cells. We also found that neural crest-derived stem cells express LGR5, raising the possibility that expression of LGR5 may be a feature of ES cells of origin. LGR5-high ES cells showed nuclear localization of β-catenin and robust activation of TCF reporter activity when exposed to Wnt ligand and this was potentiated by RSPO. However, modulation of LGR5 or exposure to RSPO had no impact on proliferation confirming that Wnt/β-catenin signaling in ES cells does not recapitulate signaling in epithelial cells. Together these studies show that the RSPO-LGR5-Wnt-β-catenin axis is present and active in ES and may contribute to tumor pathogenesis.

Gene expression patterns of hemizygous and heterozygous KIT mutations suggest distinct oncogenic pathways: a study in NIH3T3 cell lines and GIST samples

Objective

Most gain of function mutations of tyrosine kinase receptors in human tumours are hemizygous. Gastrointestinal stromal tumours (GIST) with homozygous mutations have a worse prognosis. We aimed to identify genes differentially regulated by hemizygous and heterozygous KIT mutations.

Materials and Methods

Expression of 94 genes and 384 miRNA was analysed with low density arrays in five NIH3T3 cell lines expressing the full-length human KIT cDNA wild-type (WT), hemizygous KIT mutation with del557-558 (D6) or del564-581 (D54) and heterozygous WT/D6 or WT/D54. Expression of 5 of these genes and 384 miRNA was then analysed in GISTs samples.

Results

Unsupervised and supervised hierarchical clustering of the mRNA and miRNA profiles showed that heterozygous mutants clustered with KIT WT expressing cells while hemizygous mutants were distinct. Among hemizygous cells, D6 and D54 expressing cells clustered separately. Most deregulated genes have been reported as potentially implicated in cancer and severals, as ANXA8 and FBN1, are highlighted by both, mRNA and miRNA analyses. MiRNA and mRNA analyses in GISTs samples confirmed that their expressions varied according to the mutation of the alleles. Interestingly, RGS16, a membrane protein of the regulator of G protein family, correlate with the subcellular localization of KIT mutants and might be responsible for regulation of the PI3K/AKT signalling pathway.

Conclusion

Patterns of mRNA and miRNA expression in cells and tumours depend on heterozygous/hemizygous status of KIT mutations, and deletion/presence of TYR568 & TYR570 residues. Thus each mutation of KIT may drive specific oncogenic pathways.

Genome-wide analyses on high-grade osteosarcoma: making sense of a genomically most unstable tumor

High-grade osteosarcoma is an extremely genomically unstable tumor. This, together with other challenges, such as the heterogeneity within and between tumor samples, and the rarity of the disease, renders it difficult to study this tumor on a genome-wide level. Now that most laboratories change from genome-wide microarray experiments to Next-Generation Sequencing it is important to discuss the lessons we have learned from microarray studies. In this review, we discuss the challenges of high-grade osteosarcoma data analysis. We give an overview of microarray studies that have been conducted so far on both osteosarcoma tissue samples and cell lines. We discuss recent findings from integration of different data types, which is particularly relevant in a tumor with such a complex genomic profile. Finally, we elaborate on the translation of results obtained with bioinformatics into functional studies, which has lead to valuable findings, especially when keeping in mind that no new therapies with a significant impact on survival have been developed in the past decades.

Pharmacological inhibition of the Wnt acyltransferase PORCN prevents growth of WNT-driven mammary cancer

Porcupine (PORCN) is a membrane bound O-acyltransferase that is required for Wnt palmitoylation, secretion, and biologic activity. All evaluable human Wnts require PORCN for their activity, suggesting that inhibition of PORCN could be an effective treatment for cancers dependent on excess Wnt activity. In this study, we evaluated the PORCN inhibitor Wnt-C59 (C59), to determine its activity and toxicity in cultured cells and mice. C59 inhibits PORCN activity in vitro at nanomolar concentrations, as assessed by inhibition of Wnt palmitoylation, Wnt interaction with the carrier protein Wntless/WLS, Wnt secretion, and Wnt activation of β-catenin reporter activity. In mice, C59 displayed good bioavailability, as once daily oral administration was sufficient to maintain blood concentrations well above the IC(50). C59 blocked progression of mammary tumors in MMTV-WNT1 transgenic mice while downregulating Wnt/β-catenin target genes. Surprisingly, mice exhibit no apparent toxicity, such that at a therapeutically effective dose there were no pathologic changes in the gut or other tissues. These results offer preclinical proof-of-concept that inhibiting mammalian Wnts can be achieved by targeting PORCN with small-molecule inhibitors such as C59, and that this is a safe and feasible strategy in vivo.

The influence of reactive oxygen species on cell cycle progression in mammalian cells

Cell cycle regulation is performed by cyclins and cyclin dependent kinases (CDKs). Recently, it has become clear that reactive oxygen species (ROS) influence the presence and activity of these enzymes and thereby control cell cycle progression. In this review, we first describe the discovery of enzymes specialized in ROS production: the NADPH oxidase (NOX) complexes. This discovery led to the recognition of ROS as essential players in many cellular processes, including cell cycle progression. ROS influence cell cycle progression in a context-dependent manner via phosphorylation and ubiquitination of CDKs and cell cycle regulatory molecules. We show that ROS often regulate ubiquitination via intermediate phosphorylation and that phosphorylation is thus the major regulatory mechanism influenced by ROS. In addition, ROS have recently been shown to be able to activate growth factor receptors. We will illustrate the diverse roles of ROS as mediators in cell cycle regulation by incorporating phosphorylation, ubiquitination and receptor activation in a model of cell cycle regulation involving EGF-receptor activation. We conclude that ROS can no longer be ignored when studying cell cycle progression.

Prevailing importance of the hedgehog signaling pathway and the potential for treatment advancement in sarcoma

The hedgehog signaling pathway is important in embryogenesis and post natal development. Constitutive activation of the pathway due to mutation of pathway components occurs in ~25% of medulloblastomas and also in basal cell carcinomas. In many other malignancies the therapeutic role for hedgehog inhibition though intriguing, based on preclinical data, is far from assured. Hedgehog inhibition is not an established part of the treatment paradigm of sarcoma but the scientific rationale for a possible benefit is compelling. In chondrosarcoma there is evidence of hedgehog pathway activation and an ontologic comparison between growth plate chondrocyte differentiation and different chondrosarcoma subtypes. Immunostaining epiphyseal growth plate for Indian hedgehog is particularly positive in the zone of pre-hypertrophic chondrocytes which correlates ontologically with conventional chondrosarcoma. In Ewing sarcoma/PNET tumors the Gli1 transcription factor is a direct target of the EWS-FLI1 oncoprotein present in 85% of cases. In many cases of rhabdomyosarcomas there is increased expression of Gli1 (Ragazzini et al., 2004). Additionally, a third of embryonal rhabdomyosarcomas have loss of Chr.9q22 that encompasses the patched locus (Bridge et al., 2000). The potential to treat osteosarcoma by inhibition of Gli2 and the role of the pathway in ovarian fibromas and other connective tissue tumors is also discussed (Nagao et al., 2011; Hirotsu et al., 2010). Emergence of acquired secondary resistance to targeted therapeutics is an important issue that is also relevant to hedgehog inhibition. In this context secondary resistance of medulloblastomas to treatment with a smoothened antagonist in two tumor mouse models is examined.

Precise regulation of porcupine activity is required for physiological Wnt signaling

Gradients of diverse Wnt proteins regulate development, renewal, and differentiation. Porcupine (PORCN) is a membrane-bound O-acyltransferase that is required for post-translational modification of all Wnts to enable their transport, secretion, and activity. Mutations in PORCN are associated with focal dermal hypoplasia (FDH), whereas gene deletion causes embryonic lethality in mice. To study the protein in more detail, zinc finger nucleases were used to edit the PORCN genomic locus, establishing two HT1080 fibrosarcoma clones null for PORCN activity that facilitate the study of PORCN structure and function. We establish that PORCN is a key non-redundant node for the regulation of global Wnt signaling because PORCN null cells are completely incapable of autocrine Wnt signaling. The strength of Wnt signaling is exquisitely sensitive to PORCN expression, with a dynamic range of at least 3 orders of magnitude, suggesting that PORCN activity is a key modulator of all Wnt ligand activity. Consistent with this, we find that multiple FDH-associated mutants have only subtle alterations in enzyme activity yet are associated with a severe FDH phenotype. These studies support an essential regulatory role of PORCN in shaping Wnt signaling gradients.

Comparison of gene expression profiling in sarcomas and mesenchymal stem cells identifies tumorigenic pathways in chemically induced rat sarcoma model

Mesenchymal stem cells (MSCs) are believed to be the cell of origin for most sarcomas including osteosarcoma and malignant fibrous histiocytoma (MFH/UPS). To identify the signaling pathways involved in sarcoma pathogenesis, we compared gene expression profiles in rat osteosarcoma and MFH cells with those in syngeneic rat MSCs. Analysis of genes that characterize MSCs such as CD44, CD105, CD73, and CD90 showed higher expression in MSCs compared to sarcomas. Pathways involved in focal and cell adhesion, cytokine-cytokine receptors, extracellular matrix receptors, chemokines, and Wnt signaling were down-regulated in both sarcomas. Meanwhile, DNA replication, cell cycle, mismatch repair, Hedgehog signaling, and metabolic pathways were upregulated in both sarcomas. Downregulation of p21^Cip1 and higher expression of CDK4-cyclinD1 and CDK2-cyclinE could accelerate cell cycle in sarcomas. The current study indicated that these rat sarcomas could be a good model for their human counterparts and will provide the further insights into the molecular pathways and mechanisms involved in sarcoma pathogenesis.

Clinical significance of sFRP1 protein expression in pancreatic ductal adenocarcinoma

AIM: To detect the expression of secreted frizzled-related protein 1 (sFRP1) protein in different pancreatic tissues (normal pancreatic duct, NP; pancreatic ductal adenocarcinoma, PDAC; pancreatic intraepithelial neoplasia, PanIN; and intraductal papillary mucinous neoplasm, IPMN) and evaluate its significance in the carcinogenesis of PDAC.

METHODS: Immunohistochemical detection of sFRP1 protein was performed in 21 foci of NP, 73 foci of PanIN-1, 29 foci of PanIN-2, 16 foci of PanIN-3, 20 cases of IPMN-adenoma (IPMA), 13 cases of IPMN-borderline (IPMB), 19 cases of IPMN-carcinoma (IPMC), and 50 cases of PDAC. The correlation between sFRP1 expression and clinicopathologic characteristics of PDAC was analyzed.

RESULTS: Immunohistochemical score (IHCS) of sFRP1 expression escalated with the severity of tissue atypia along the progressive multistage: NP→PanIN-1→PanIN-2, PanIN-3, PDAC or NP→IPMA, IPMB→IPMC, PDAC. sFRP1 expression was significantly associated with tumor differentiation and neural infiltration.

CONCLUSION: sFRP-1 expression enhancement is an early event in the carcinogenesis of PDAC, representing an important molecular characteristic of neural infiltration.

Perspectives on cancer stem cells in osteosarcoma

Osteosarcoma is an aggressive pediatric tumor of growing bones that, despite surgery and chemotherapy, is prone to relapse. These mesenchymal tumors are derived from progenitor cells in the osteoblast lineage that have accumulated mutations to escape cell cycle checkpoints leading to excessive proliferation and defects in their ability to differentiate appropriately into mature bone-forming osteoblasts. Like other malignant tumors, osteosarcoma is often heterogeneous, consisting of phenotypically distinct cells with features of different stages of differentiation. The cancer stem cell hypothesis posits that tumors are maintained by stem cells and it is the incomplete eradication of a refractory population of tumor-initiating stem cells that accounts for drug resistance and tumor relapse. In this review we present our current knowledge about the biology of osteosarcoma stem cells from mouse and human tumors, highlighting new insights and unresolved issues in the identification of this elusive population. We focus on factors and pathways that are implicated in maintaining such cells, and differences from paradigms of epithelial cancers. Targeting of the cancer stem cells in osteosarcoma is a promising avenue to explore to develop new therapies for this devastating childhood cancer.