Wnt/beta-catenin signaling and small molecule inhibitors

Clonal cooperativity in heterogenous cancers

Tumor heterogeneity is a major obstacle to the development of effective therapies and is thus an important focus of cancer research. Genetic and epigenetic alterations, as well as altered tumor microenvironments, result in tumors made up of diverse subclones with different genetic and phenotypic characteristics. Intratumor heterogeneity enables competition, but also supports clonal cooperation via cell-cell contact or secretion of factors, resulting in enhanced tumor progression. Here, we summarize recent findings related to interclonal interactions within a tumor and the therapeutic implications of such interactions, with an emphasis on how different subclones collaborate with each other to promote proliferation, metastasis and therapy-resistance. Furthermore, we propose that disruption of clonal cooperation by targeting key factors (such as Wnt and Hedgehog, amongst others) can be an alternative approach to improving clinical outcomes.

Modulating the wnt signaling pathway with small molecules

Wnt signaling is a critical component during embryonic development and also plays an important role in regulating adult tissue homeostasis. Abnormal activation of Wnt signaling has been implicated in many cancers, while reduced activity of Wnt signaling leads to poor wound healing and structural formations. Thus, extensive efforts have been focused on developing small molecules that have potential to either inhibit or activate the pathway, hoping these molecules can offer leads for novel approaches in treating different human diseases. Many small-molecule inhibitors specifically target various elements, such as Frizzled, Disheveled, Porcupine, or Tankyrase, within the Wnt signaling pathways. These small molecules not only have the potential to be further developed as therapeutic reagents, but they may also be used as chemical probes to dissect the underlying mechanism of the Wnt signaling pathways. Therefore, their respective mechanisms and effective dosages are highly pertinent. Aiming to provide an overview of those molecules in a concise, easy-to-use manner, we summarize and organize the current research on them so that it may be helpful for utilization in different studies.

USP7 inhibitor P5091 inhibits Wnt signaling and colorectal tumor growth

Aberrant activation of Wnt/β-catenin signaling is closely associated with the development of various human cancers, especially colorectal cancers (CRC). The ubiquitin proteasome system (UPS) is essential in the regulation of Wnt signaling and inhibitors targeting the UPS could have great potential in CRC therapy. Ubiquitin-specific protease 7 (USP7), a deubiquitinating enzyme, plays a significant role in neoplastic diseases due to its well-known function of regulating the MDM2-p53 complex. Inspired by our recent study identifying the positive role of USP7 in the Wnt signaling, we report here that USP7 is overexpressed in colorectal carcinoma cell lines and tissues, which is closely related with the poor prognosis. USP7 knockdown inhibits the proliferation of CRC cells with different p53 status, and USP7 inhibition by its inhibitor P5091 attenuates the activity of Wnt signaling via enhanced ubiquitination and the subsequent degradation of β-catenin. In vitro, P5091 inhibited the proliferation and induced apoptosis of CRC cells. P5091 also suppressed in vivo tumor growth in the HCT116 xenograft mouse model, which is consistently associated with reduced expression of β-catenin and Wnt target genes. In conclusion, our preclinical study indicated that USP7 could be a potential drug target and its inhibitor P5091 deserves further development as anticancer agent for Wnt hyper-activated CRC therapy.

Activation of the Wnt Pathway by Mycobacterium tuberculosis: A Wnt-Wnt Situation

Mycobacterium tuberculosis (M. tuberculosis), an intracellular pathogenic Gram-positive bacterium, is the cause of tuberculosis (TB), a major worldwide human infectious disease. The innate immune system is the first host defense against M. tuberculosis. The recognition of this pathogen is mediated by several classes of pattern recognition receptors expressed on the host innate immune cells, including Toll-like receptors, Nod-like receptors, and C-type lectin receptors like Dectin-1, the Mannose receptor, and DC-SIGN. M. tuberculosis interaction with any of these receptors activates multiple signaling pathways among which the protein kinase C, the MAPK, and the NFκB pathways have been widely studied. These pathways have been implicated in macrophage invasion, M. tuberculosis survival, and impaired immune response, thus promoting a successful infection and disease. Interestingly, the Wnt signaling pathway, classically regarded as a pathway involved in the control of cell proliferation, migration, and differentiation in embryonic development, has recently been involved in immunoregulatory mechanisms in infectious and inflammatory diseases, such as TB, sepsis, psoriasis, rheumatoid arthritis, and atherosclerosis. In this review, we present the current knowledge supporting a role for the Wnt signaling pathway during macrophage infection by M. tuberculosis and the regulation of the immune response against M. tuberculosis. Understanding the cross talk between different signaling pathways activated by M. tuberculosis will impact on the search for new therapeutic targets to fuel the rational design of drugs aimed to restore the immunological response against M. tuberculosis.

Wnt/β-catenin signaling activates nephronectin expression in osteoblasts

Nephronectin (Npnt), an extracellular matrix protein, is considered to play critical roles as an adhesion molecule in the development and functions of various organs and tissues, such as the kidneys and bone. In the present study, we found that Wnt3a strongly enhanced Npnt mRNA expression in osteoblast-like MC3T3-E1 cells, while it also induced an increase in Npnt gene expression in both time- and dose-dependent manners via the Wnt/β-catenin signaling pathway. These results suggest novel mechanisms for Wnt3a-induced osteoblast proliferation and cell survival via Npnt gene expression.

ADNP Is a Therapeutically Inducible Repressor of WNT Signaling in Colorectal Cancer

Purpose: Constitutively active WNT signaling is a hallmark of colorectal cancers and a driver of malignant tumor progression. Therapeutic targeting of WNT signaling is difficult due to high pathway complexity and its role in tissue homeostasis. Here, we identify the transcription factor ADNP as a pharmacologically inducible repressor of WNT signaling in colon cancer.Experimental Design: We used transcriptomic, proteomic, and in situ analyses to identify ADNP expression in colorectal cancer and cell biology approaches to determine its function. We induced ADNP expression in colon cancer xenografts by low-dose ketamine in vivo Clinical associations were determined in a cohort of 221 human colorectal cancer cases.Results: ADNP was overexpressed in colon cancer cells with high WNT activity, where it acted as a WNT repressor. Silencing ADNP expression increased migration, invasion, and proliferation of colon cancer cells and accelerated tumor growth in xenografts in vivo Treatment with subnarcotic doses of ketamine induced ADNP expression, significantly inhibited tumor growth, and prolonged survival of tumor-bearing animals. In human patients with colon cancer, high ADNP expression was linked to good prognosis.Conclusions: Our findings indicate that ADNP is a tumor suppressor and promising prognostic marker, and that ketamine treatment with ADNP induction is a potential therapeutic approach that may add benefit to current treatment protocols for patients with colorectal cancer. Clin Cancer Res; 23(11); 2769-80. ©2016 AACR.

GalNAc-T14 promotes metastasis through Wnt dependent HOXB9 expression in lung adenocarcinoma

While metastasis, the main cause of lung cancer-related death, has been extensively studied, the underlying molecular mechanism remains unclear. A previous clinicogenomic study revealed that expression of N-acetylgalactosaminyltransferase (GalNAc-T14), is highly inversely correlated with recurrence-free survival in those with non-small cell lung cancer (NSCLC). However, the underlying molecular mechanism(s) has not been determined. Here, we showed that GalNAc-T14 expression was positively associated with the invasive phenotype. Microarray and biochemical analyses revealed that HOXB9, the expression of which was increased in a GalNAc-T14-dependent manner, played an important role in metastasis. GalNAc-T14 increased the sensitivity of the WNT response and increased the stability of the β-catenin protein, leading to induced expression of HOXB9 and acquisition of an invasive phenotype. Pharmacological inhibition of β-catenin in GalNAc-T14-expressing cancer cells suppressed HOXB9 expression and invasion. A meta-analysis of clinical genomics data revealed that expression of GalNAc-T14 or HOXB9 was strongly correlated with reduced recurrence-free survival and increased hazard risk, suggesting that targeting β-catenin within the GalNAc-T14/WNT/HOXB9 axis may be a novel therapeutic approach to inhibit metastasis in NSCLC.

Modelling TFE renal cell carcinoma in mice reveals a critical role of WNT signaling

TFE-fusion renal cell carcinomas (TFE-fusion RCCs) are caused by chromosomal translocations that lead to overexpression of the TFEB and TFE3 genes (Kauffman et al., 2014). The mechanisms leading to kidney tumor development remain uncharacterized and effective therapies are yet to be identified. Hence, the need to model these diseases in an experimental animal system (Kauffman et al., 2014). Here, we show that kidney-specific TFEB overexpression in transgenic mice, resulted in renal clear cells, multi-layered basement membranes, severe cystic pathology, and ultimately papillary carcinomas with hepatic metastases. These features closely recapitulate those observed in both TFEB- and TFE3-mediated human kidney tumors. Analysis of kidney samples revealed transcriptional induction and enhanced signaling of the WNT β-catenin pathway. WNT signaling inhibitors normalized the proliferation rate of primary kidney cells and significantly rescued the disease phenotype in vivo. These data shed new light on the mechanisms underlying TFE-fusion RCCs and suggest a possible therapeutic strategy based on the inhibition of the WNT pathway.

MiR-1207 overexpression promotes cancer stem cell-like traits in ovarian cancer by activating the Wnt/β-catenin signaling pathway

Wnt/β-catenin signaling pathway is strictly controlled by multiple negative regulators. However, how tumor cells override the negative regulatory effects to maintain constitutive activation of Wnt/β-catenin signaling, which is commonly observed in various cancers, remains puzzling. In current study, we reported that overexpression of miR-1207 in ovarian cancer activated Wnt/β-catenin signaling by directly targeting and suppressing secreted Frizzled-related protein 1 (SFRP1), AXIN2 and inhibitor of β-catenin and TCF-4 (ICAT), which are vital negative regulators of the Wnt/β-catenin pathway. We found that the expression of miR-1207 was ubiquitously upregulated in both ovarian cancer tissues and cells, which inversely correlated with patient overall survival. Furthermore, overexpression of miR-1207 enhanced, while silencing miR-1207 reduced, stem cell-like traits of ovarian cancer cells in vitro and in vivo, including tumor sphere formation capability and proportion of SP+ and CD133+ cells. Importantly, upregulating miR-1207 promoted, while silencing miR-1207 inhibited, the tumorigenicity of ovarian cancer cells. Hence, our results suggest that miR-1207 plays a vital role in promoting the cancer stem cell-like phenotype in ovarian cancer and might represent a potential target for anti-ovarian cancer therapy.

A Genome-Wide RNA Interference Screen Identifies a Role for Wnt/β-Catenin Signaling during Rift Valley Fever Virus Infection

Rift Valley fever virus (RVFV) is an arbovirus within the Bunyaviridae family capable of causing serious morbidity and mortality in humans and livestock. To identify host factors involved in bunyavirus replication, we employed genome-wide RNA interference (RNAi) screening and identified 381 genes whose knockdown reduced infection. The Wnt pathway was the most represented pathway when gene hits were functionally clustered. With further investigation, we found that RVFV infection activated Wnt signaling, was enhanced when Wnt signaling was preactivated, was reduced with knockdown of β-catenin, and was blocked using Wnt signaling inhibitors. Similar results were found using distantly related bunyaviruses La Crosse virus and California encephalitis virus, suggesting a conserved role for Wnt signaling in bunyaviral infection. We propose a model where bunyaviruses activate Wnt-responsive genes to regulate optimal cell cycle conditions needed to promote efficient viral replication. The findings in this study should aid in the design of efficacious host-directed antiviral therapeutics.

IMPORTANCE RVFV is a mosquito-borne bunyavirus that is endemic to Africa but has demonstrated a capacity for emergence in new territories (e.g., the Arabian Peninsula). As a zoonotic pathogen that primarily affects livestock, RVFV can also cause lethal hemorrhagic fever and encephalitis in humans. Currently, there are no treatments or fully licensed vaccines for this virus. Using high-throughput RNAi screening, we identified canonical Wnt signaling as an important host pathway regulating RVFV infection. The beneficial role of Wnt signaling was observed for RVFV, along with other disparate bunyaviruses, indicating a conserved bunyaviral replication mechanism involving Wnt signaling. These studies supplement our knowledge of the fundamental mechanisms of bunyavirus infection and provide new avenues for countermeasure development against pathogenic bunyaviruses.

miR-9 Acts as an OncomiR in Prostate Cancer through Multiple Pathways That Drive Tumour Progression and Metastasis

Identification of dysregulated microRNAs (miRNAs) in prostate cancer is critical not only for diagnosis, but also differentiation between the aggressive and indolent forms of the disease. miR-9 was identified as an oncomiR through both miRNA panel RT-qPCR as well as high-throughput sequencing analysis of the human P69 prostate cell line as compared to its highly tumorigenic and metastatic subline M12, and found to be consistently upregulated in other prostate cell lines including DU-145 and PC3. While miR-9 has been characterized as dysregulated either as an oncomiR or tumour suppressor in a variety of other cancers including breast, ovarian, and nasopharyngeal carcinomas, it has not been previously evaluated and proven as an oncomiR in prostate cancer. miR-9 was confirmed an oncomiR when found to be overexpressed in tumour tissue as compared to adjacent benign glandular epithelium through laser-capture microdissection of radical prostatectomy biopsies. Inhibition of miR-9 resulted in reduced migratory and invasive potential of the M12 cell line, and reduced tumour growth and metastases in male athymic nude mice. Analysis showed that miR-9 targets e-cadherin and suppressor of cytokine signalling 5 (SOCS5), but not NF-ĸB mRNA. Expression of these proteins was shown to be affected by modulation in expression of miR-9.

ROR2 is epigenetically inactivated in the early stages of colorectal neoplasia and is associated with proliferation and migration

BACKGROUND

Colorectal cancer (CRC) is closely linked to Wnt signalling, with 94 % of cases exhibiting a Wnt related mutation. ROR2 is a receptor tyrosine kinase that is thought to repress β-catenin dependent Wnt signalling. Our study aims to determine if ROR2 is epigenetically silenced in CRC and determine if in vitro silencing of ROR2 potentiates Wnt signalling, and alters the proliferative, migratory or invasive potential of cells.

METHODS

ROR2 expression was examined in CRC cell lines and patient adenomas using qRT-PCR, while COBRA and bisulphite sequencing was used to analyse ROR2 promoter methylation. 258 patient primary tumour samples from publicly available databases were also examined for ROR2 expression and methylation. In addition, the functional effects of ROR2 modulation were investigated in HCT116 cells following ROR2 siRNA knockdown and in RKO and SW620 cells following ectopic ROR2 expression.

RESULTS

Reduced ROR2 expression was found to correlate with ROR2 promoter hypermethylation in colorectal cancer cell lines, carcinomas and adenomas. ROR2 expression was downregulated in 76.7 % (23/30) of CRC cell lines with increasing ROR2 promoter hypermethylation correlating with progressively lower expression. Analysis of 239 primary tumour samples from a publicly available cohort also found a significant correlation between reduced ROR2 expression and increased promoter methylation. Methylation analysis of 88 adenomas and 47 normal mucosa samples found greater percentage of adenoma samples to be methylated. Additional analysis also revealed that adenoma samples with reduced ROR2 expression also possessed ROR2 promoter hypermethylation. ROR2 knockdown in the CRC cell line HCT116 significantly decreased expression of the β-catenin independent Wnt targets genes JNK and NFATC1, increased cellular proliferation and migration but decreased invasion. When ROR2 was ectopically expressed in RKO and SW620 cells, there was no significant change to either cellular proliferation or migration.

CONCLUSION

ROR2 is frequently epigenetically inactivated by promoter hypermethylation in the early stages of colorectal neoplasia and this may contribute to colorectal cancer progression by increasing cellular proliferation and migration.

The Wnt pathway: a key network in cell signalling dysregulated by viruses

Viruses are obligate parasites dependent on host cells for survival. Viral infection of a cell activates a panel of pattern recognition receptors that mediate antiviral host responses to inhibit viral replication and dissemination. Viruses have evolved mechanisms to evade and subvert this antiviral host response, including encoding proteins that hijack, mimic and/or manipulate cellular processes such as the cell cycle, DNA damage repair, cellular metabolism and the host immune response. Currently, there is an increasing interest whether viral modulation of these cellular processes, including the cell cycle, contributes to cancer development. One cellular pathway related to cell cycle signalling is the Wnt pathway. This review focuses on the modulation of this pathway by human viruses, known to cause (or associated with) cancer development. The main mechanisms where viruses interact with the Wnt pathway appear to be through (i) epigenetic modification of Wnt genes; (ii) cellular or viral miRNAs targeting Wnt genes; (iii) altering specific Wnt pathway members, often leading to (iv) nuclear translocation of β-catenin and activation of Wnt signalling. Given that diverse viruses affect this signalling pathway, modulating Wnt signalling could be a generalised critical process for the initiation or maintenance of viral pathogenesis, with resultant dysregulation contributing to virus-induced cancers. Further study of this virus-host interaction may identify options for targeted therapy against Wnt signalling molecules as a means to reduce virus-induced pathogenesis and the downstream consequences of infection. Copyright © 2016 John Wiley & Sons, Ltd.

Wnt/Beta-Catenin Signal Inhibitor HC-1 Sensitizes Oral Squamous Cell Carcinoma Cells to 5-Fluorouracil through Reduction of CD44-Positive Population

BACKGROUND

Oral squamous cell carcinoma is a prevalent and frequently lethal malignancy worldwide. Existence of treatment-resistant cancer stem cells is considered to be associated with tumor formation, recurrence and metastasis. Wnt/beta-catenin signal is one of the crucial signaling pathways for cancer stem cells. Wnt/beta-catenin signal inhibitor may reduce the population of cancer stem cells and improve therapeutic effects on the cancers.

METHODS

The effects of three derivatives of Wnt/beta-catenin signal inhibitors, HC-1, IC-2 and PN3-13, which we recently developed, on oral squamous cell carcinoma cell line HSC2, were examined by luciferase reporter assay, WST assay, cell sorting assay and apoptosis assay.

RESULTS

The reporter assay showed that these small molecule compounds reduced Wnt/beta-catenin transcriptional activity in HSC2 cells. Of these compounds, IC-2 and PN3-13 inhibited cell viability in a dose-dependent manner, whereas HC-1 did not at even higher concentrations. Notably, however, the cell-sorting assay revealed that HC-1 significantly reduces the CD44-positive population of oral squamous cell carcinoma cells, compared to other compounds without affecting cell viability. In addition, HC-1 increases the cytotoxicity of HSC2 cells to 5-fluorouracil. The combination treatment of HC-1 with 5-fluorouracil significantly increased the apoptotic cells whereas treatment by either compound did not.

CONCLUSION

These data suggest that HC-1 is an effective compound to target cancer stem cells, and the combination treatment of HC-1 and 5-fluorouracil can stimulate the tumor suppressive effect on oral squamous cell carcinoma cells.

Elevated glucose levels impair the WNT/β-catenin pathway via the activation of the hexosamine biosynthesis pathway in endometrial cancer

Endometrial cancer (EC) is one of the most common gynecological malignancies in the world. Associations between fasting glucose levels (greater than 5.6mmol/L) and the risk of cancer fatality have been reported. However, the underlying link between glucose metabolic disease and EC remains unclear. In the present study, we explored the influence of elevated glucose levels on the WNT/β-catenin pathway in EC. Previous studies have suggested that elevated concentrations of glucose can drive the hexosamine biosynthesis pathway (HBP) flux, thereby enhancing the O-GlcNAc modification of proteins. Here, we cultured EC cell lines, AN3CA and HEC-1-B, with various concentrations of glucose. Results showed that when treated with high levels of glucose, both lines showed increased expression of β-catenin and O-GlcNAcylation levels; however, these effects could be abolished by the HBP inhibitors, Azaserine and 6-Diazo-5-oxo-l-norleucine, and be restored by glucosamine. Moreover the AN3CA and HEC-1-B cells that were cultured with or without PUGNAc, an inhibitor of the O-GlcNAcase, showed that PUGNAc increased β-catenin levels. The results suggest that elevated glucose levels increase β-catenin expression via the activation of the HBP in EC cells. Subcellular fractionation experiments showed that AN3CA cells had a higher expression of intranuclear β-catenin in high glucose medium. Furthermore, TOP/FOP-Flash and RT-PCR results showed that glucose-induced increased expression of β-catenin triggered the transcription of target genes. In conclusion, elevated glucose levels, via HBP, increase the O-GlcNAcylation level, thereby inducing the over expression of β-catenin and subsequent transcription of the target genes in EC cells.

Knockdown of β-catenin by siRNA influences proliferation, apoptosis and invasion of the colon cancer cell line SW480

The aim of the present study was to explore the effect of knocking down the expression of β-catenin by small interference (si)RNA on the activity of the Wnt/β-catenin signaling pathway, and the proliferation, apoptosis and invasion abilities of the human colon cancer cell line SW480. For that purpose, double-stranded siRNA targeting β-catenin (β-catenin-siRNA) was synthesized and transfected into SW480 cells. Reverse transcription-polymerase chain reaction (RT-PCR) and western blotting were used to detect the messenger (m)RNA and protein levels of β-catenin in SW480 cells. To detect cell proliferation, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay was performed, while cell apoptosis and caspase-3 activity were detected by flow cytometry and caspase-3 activity assay, respectively. Matrigel invasion assay was performed to detect the influence of siRNA-mediated gene silencing on the invasion and metastasis of SW480 cells in vitro. The results of RT-PCR and western blot analysis demonstrated that, compared with the blank control, negative control and liposome groups, β-catenin-siRNA transfected SW480 cells had significantly decreased mRNA and protein levels of β-catenin. In addition, following β-catenin-siRNA transfection, the proliferation of SW480 cells was significantly lower than that of the blank control, negative control and liposome groups, while the apoptosis rate increased in β-catenin-siRNA transfected cells, compared with the aforementioned groups. Invasion assay showed that, following β-catenin-siRNA transfection, the number of SW480 cells infiltrating through the Matrigel membrane was significantly lower than that of the blank control, negative control and liposome groups. Following β-catenin-siRNA transfection, the caspase-3 activity in SW480 cells was lower than that in the blank control, negative control and liposome groups. These results indicate that siRNA-mediated silencing of β-catenin could inhibit the proliferation and invasion of SW480 cells and induce apoptosis, thus providing novel potential strategies for the clinical treatment of colon cancer, and may serve as a novel target for cancer therapy.

[Promoter methylation status of SFRP genes and induced apoptosis by demethylation in Jurkat cells]

目的

探讨人T淋巴细胞白血病（T-ALL）细胞株Jurkat细胞分泌性卷曲相关蛋白（SFRP）基因甲基化及去甲基化诱导细胞凋亡对Wnt/β-catenin信号通路的影响。

方法

以不同浓度（1.0、2.0、4.0 µmol/L）5-杂氮-2′-脱氧胞苷（5-Aza-CdR）对Jurkat细胞进行去甲基化处理，采用MTT法观察5-Aza-CdR对Jurkat细胞增殖的抑制作用，流式细胞术检测细胞凋亡率，甲基化特异性PCR(MSP)法检测药物处理前后SFRP基因的甲基化状态，实时荧光定量PCR检测SFRP基因以及RT-PCR检测survivin、c-myc和cyclin D1基因mRNA的表达改变，Western blot鉴定处理前后β-catenin的蛋白表达。

结果

1.0、2.0、4.0 µmol/L 5-Aza-CdR对Jurkat细胞的增殖有明显抑制作用，呈时间-剂量依赖性（P<0.05）；流式细胞术检测显示5-Aza-CdR作用Jurkat细胞48 h后，不同浓度5-Aza-CdR处理组与对照组比较细胞早期凋亡率明显升高（P<0.05）；SFRP1、SFRP2、SFRP4、SFRP5基因甲基化水平随5-Aza-CdR浓度升高而下降，呈剂量依赖性（P<0.05），同时mRNA表达水平较对照组明显上调（P<0.05）；Jurkat细胞总蛋白中β-catenin的蛋白表达随5-Aza-CdR浓度的升高而逐渐下降，呈剂量依赖性（P<0.05）；凋亡相关基因survivin、c-myc和cyclin D1的mRNA表达随5-Aza-CdR浓度的增高而降低，呈剂量依赖性（P<0.05）。

结论

逆转Jurkat细胞SFRP基因的甲基化，可以恢复SFRP基因转录表达，通过阻断β-catenin蛋白抑制Wnt/β-catenin信号通路的激活而诱导细胞凋亡。

MEKK2 mediates an alternative β-catenin pathway that promotes bone formation

Proper tuning of β-catenin activity in osteoblasts is required for bone homeostasis, because both increased and decreased β-catenin activity have pathologic consequences. In the classical pathway for β-catenin activation, stimulation with WNT ligands suppresses constitutive phosphorylation of β-catenin by glycogen synthase kinase 3β, preventing β-catenin ubiquitination and proteasomal degradation. Here, we have found that mitogen-activated protein kinase kinase kinase 2 (MAP3K2 or MEKK2) mediates an alternative pathway for β-catenin activation in osteoblasts that is distinct from the canonical WNT pathway. FGF2 activates MEKK2 to phosphorylate β-catenin at serine 675, promoting recruitment of the deubiquitinating enzyme, ubiquitin-specific peptidase 15 (USP15). USP15 in turn prevents the basal turnover of β-catenin by inhibiting its ubiquitin-dependent proteasomal degradation, thereby enhancing WNT signaling. Analysis of MEKK2-deficient mice and genetic interaction studies between Mekk2- and β-catenin-null alleles confirm that this pathway is an important physiologic regulator of bone mass in vivo. Thus, an FGF2/MEKK2 pathway mediates an alternative nonclassical pathway for β-catenin activation, and this pathway is a key regulator of bone formation by osteoblasts.

Profiling of potential driver mutations in sarcomas by targeted next generation sequencing

Comprehensive genetic profiling by massively parallel sequencing, commonly known as next generation sequencing (NGS), is becoming the foundation of personalized oncology. For sarcomas very few targeted treatments are currently in routine use. In clinical practice the preoperative diagnostic workup of soft tissue tumours largely relies on core needle biopsies. Although mostly sufficient for histopathological diagnosis, only very limited amounts of formalin fixated paraffin embedded tissue are often available for predictive mutation analysis. Targeted NGS may thus open up new possibilities for comprehensive characterization of scarce biopsies. We therefore set out to search for driver mutations by NGS in a cohort of 55 clinically and morphologically well characterized sarcomas using low input of DNA from formalin fixated paraffin embedded tissues. The aim was to investigate if there are any recurrent or targetable aberrations in cancer driver genes in addition to known chromosome translocations in different types of sarcomas. We employed a panel covering 207 mutation hotspots in 50 cancer-associated genes to analyse DNA from nine gastrointestinal stromal tumours, 14 synovial sarcomas, seven myxoid liposarcomas, 22 Ewing sarcomas and three Ewing-like small round cell tumours at a large sequencing depth to detect also mutations that are subclonal or occur at low allele frequencies. We found nine mutations in eight different potential driver genes, some of which are potentially actionable by currently existing targeted therapies. Even though no recurrent mutations in driver genes were found in the different sarcoma groups, we show that targeted NGS-based sequencing is clearly feasible in a diagnostic setting with very limited amounts of paraffin embedded tissue and may provide novel insights into mesenchymal cell signalling and potentially druggable targets. Interestingly, we also identify five non-synonymous sequence variants in 4 established cancer driver genes in DNA from normal tissue from sarcoma patients that may possibly predispose or contribute to neoplastic development.

FGFR Inhibitor Ameliorates Hypophosphatemia and Impaired Engrailed-1/Wnt Signaling in FGF2 High Molecular Weight Isoform Transgenic Mice

High molecular weight FGF2 transgenic (HMWTg) mouse phenocopies the Hyp mouse, homolog of human X-linked hypophosphatemic rickets with hypophosphatemis, and abnormal FGF23, FGFR, Klotho signaling in kidney. Since abnormal Wnt signaling was reported in Hyp mice we assessed whether Wnt signaling was impaired in HMWTg kidneys and the effect of blocking FGF receptor (FGFR) signaling. Bone mineral density and bone mineral content in female HMWTg mice were significantly reduced. HMWTg mice were gavaged with FGFR inhibitor NVP-BGJ398, or vehicle and were euthanized 24 h post treatment. Serum phosphate was significantly reduced and urine phosphate was significantly increased in HMWTg and was rescued by NVP-BGJ398. Analysis of kidneys revealed a significant reduction in Npt2a mRNA in HMWTg that was significantly increased by NVP-BGJ398. Increased FGFR1, KLOTHO, P-ERK1/2, and decreased NPT2a protein in HMWTg were rescued by NVP-BGJ398. Wnt inhibitor Engrailed-1 mRNA and protein was increased in HMWTg and was decreased by BGJ398. Akt mRNA and protein was decreased in HMWTg and was increased by NVP-BGJ398. The active form of glycogen synthase 3 beta (pGSK3-β) and phosphor-β-catenin were increased in HMWTg and were both decreased by NVP-BGJ398 while decreased active-β-catenin in HMWTg was increased by NVP-BGJ398. We conclude that FGFR blockade rescued hypophosphatemia by regulating FGF and WNT signaling in HMWTg kidneys. J. Cell. Biochem. 117: 1991-2000, 2016. © 2016 Wiley Periodicals, Inc.

Synthesis of rocaglamide derivatives and evaluation of their Wnt signal inhibitory activities

A new class of rocaglamide derivatives were synthesized by [3 + 2] cycloaddition and their Wnt signal inhibitory activities were evaluated.

A kinome siRNA screen identifies HGS as a potential target for liver cancers with oncogenic mutations in CTNNB1

BACKGROUND

Aberrant activation of the Wnt/β-catenin pathway is a major and frequent event in liver cancer, but inhibition of oncogenic β-catenin signaling has proven challenging. The identification of genes that are synthetically lethal in β-catenin-activated cancer cells would provide new targets for therapeutic drug design.

METHODS

We transfected the parental HuH6 hepatoblastoma cell line with a doxycycline-inducible shRNA against CTNNB1 (gene coding for β-catenin) to obtain an isogenic cell line pair with or without aberrant β-catenin signaling. Using this hepatoblastoma isogenic cell line pair, we performed a human kinome-wide siRNA screen to identify synthetic lethal interactions with oncogenic CTNNB1. The phenotypic readouts of the screen were cell proliferation, cell cycle arrest and apoptosis, which were assessed by image-based analysis. In addition, apoptosis was assessed by flow cytometric experiments and immunoblotting. The potential synthetic lethal relationship between candidates genes identified in the screen and oncogenic CTNNB1 was also investigated in a different cellular context, a colorectal HCT116 isogenic cell line pair.

RESULTS

We first determined the experimental conditions that led to the efficient expression of shRNA against CTNNB1 and maximal reduction of β-catenin signaling activity in response to doxycycline treatment. Following high throughput screening in which 687 genes coding for kinases and proteins related to kinases (such as pseudokinases and phosphatases) were targeted, we identified 52 genes required for HuH6 survival. The silencing of five of these genes selectively impaired the viability of HuH6 cells with high β-catenin signaling: HGS, STRADA, FES, BRAF and PKMYT1. Among these candidates, HGS depletion had the strongest inhibitory effect on cell growth and led to apoptosis specifically in HuH6 with high β-catenin activity, while HuH6 with low β-catenin activity were spared. In addition, HGS was identified as a potential synthetic lethal partner of oncogenic CTNNB1 in the HCT116 colorectal isogenic cell line pair.

CONCLUSIONS

These results demonstrate the existence of crosstalk between β-catenin signaling and HGS. Importantly, HGS depletion specifically affected cells with uncontrolled β-catenin signaling activity in two different types of cancer (Hepatoblastoma HuH6 and colorectal HCT116), and thus may represent a new potential target for novel therapeutic strategies in liver and colorectal cancer.

The Wnt signaling pathway in cancer

The Wnt signaling pathway is critically involved in both the development and homeostasis of tissues via regulation of their endogenous stem cells. Aberrant Wnt signaling has been described as a key player in the initiation of and/or maintenance and development of many cancers, via affecting the behavior of Cancer Stem Cells (CSCs). CSCs are considered by most to be responsible for establishment of the tumor and also for disease relapse, as they possess inherent drug-resistance properties. The development of new therapeutic compounds targeting the Wnt signaling pathway promises new hope to eliminate CSCs and achieve cancer eradication. However, a major challenge resides in developing a strategy efficient enough to target the dysregulated Wnt pathway in CSCs, while being safe enough to not damage the normal somatic stem cell population required for tissue homeostasis and repair. Here we review recent therapeutic approaches to target the Wnt pathway and their clinical applications.

Small-molecule inhibitors of Wnt signaling pathway: towards novel anticancer therapeutics

BACKGROUND

The Wnt signaling pathway involves secreted glycoproteins that bind to the Frizzled family receptors to activate intracellular signal transduction events that regulate cell proliferation, apoptosis, cell migration and many critical aspects of developmental biology.

DISCUSSION

Aberrant Wnt signaling underlies a wide range of pathologies in humans including tumor initiation, tumor growth, cell senescence, cell death, differentiation and metastasis. The inhibition of Wnt signaling offers a novel approach for anticancer therapeutics.

CONCLUSION

Focusing on recent developments, we reviewed the small-molecule inhibitors targeting various components of Wnt signaling pathways and the progress from the discovery of lead compounds to highly potent inhibitors with significant therapeutic potential.

Identification of the small molecule compound which induces hepatic differentiation of human mesenchymal stem cells

Human mesenchymal stem cells (MSCs) are expected to have utility as a cell source in regenerative medicine. Because we previously reported that suppression of the Wnt/β-catenin signal enhances hepatic differentiation of human MSCs, we synthesized twenty-three derivatives of small molecule compounds originally reported to suppress the Wnt/β-catenin signal in human colorectal cancer cells. We then screened these compounds for their ability to induce hepatic differentiation of human UE7T-13 MSCs. After screening using WST assay, TCF reporter assay, and albumin mRNA expression, IC-2, a derivative of ICG-001, was identified as a potent inducer of hepatic differentiation of human MSCs. IC-2 potently induced the expression of albumin, complement C3, tryptophan 2,3-dioxygenase (TDO2), EpCAM, C/EBPα, glycogen storage, and urea production. Furthermore, we examined the effects of IC-2 on human bone marrow mononuclear cell fractions sorted according to CD90 and CD271 expression. Consequently, CD90⁺ CD271⁺ cells were found to induce the highest production of urea and glycogen, important hepatocyte functions, in response to IC-2 treatment. CD90⁺ CD271⁺ cells also highly expressed albumin mRNA. As the CD90⁺ CD271⁺ population has been reported to contain a rich fraction of MSCs, IC-2 apparently represents a potent inducer of hepatic differentiation of human MSCs.

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We screened newly synthesized derivatives of small molecule compounds generated from known Wnt/β-catenin signal inhibitors.

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IC-2 was identified as an inducer of the differentiation of human mesenchymal stem cells into hepatocytes.

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IC-2 potently induces hepatic differentiation of human bone marrow mononuclear CD90⁺ CD271⁺ cells.

β catenin in health: A review

β catenin belongs to the armadillo family of proteins. It plays a crucial role in developmental and homeostatic processes. Wnts are a family of 19 secreted glycoproteins that transduce multiple signaling cascades, including the canonical Wnt/β catenin pathway, Wnt/Ca(2+) pathway and the Wnt/polarity pathway. This is a review on β catenin, Wnt proteins and their secretion, the signaling pathway, the associated factors and the crucial role of β catenin in odontogenesis.

Pharmacologic Wnt Inhibition Reduces Proliferation, Survival, and Clonogenicity of Glioblastoma Cells

Wingless (Wnt) signaling is an important pathway in gliomagenesis and in the growth of stem-like glioma cells. Using immunohistochemistry to assess the translocation of β-catenin protein, we identified intranuclear staining suggesting Wnt pathway activation in 8 of 43 surgical samples (19%) from adult patients with glioblastoma and in 9 of 30 surgical samples (30%) from pediatric patients with glioblastoma. Wnt activity, evidenced by nuclear β-catenin in our cohort and high expression of its target AXIN2 (axis inhibitor protein 2) in published glioma datasets, was associated with shorter patient survival, although this was not statistically significant. We determined the effects of the porcupine inhibitor LGK974 on 3 glioblastoma cell lines with elevated AXIN2 and found that it reduced Wnt pathway activity by 50% or more, as assessed by T-cell factor luciferase reporters. Wnt inhibition led to suppression of growth, proliferation in cultures, and modest induction of cell death. LGK974 reduced NANOG messenger RNA levels and the fraction of cells expressing the stem cell marker CD133 in neurosphere cultures, induced glial differentiation, and suppressed clonogenicity. These data indicate that LGK974 is a promising new agent that can inhibit the canonical Wnt pathway in vitro, slow tumor growth, and deplete stem-like clonogenic cells, thereby providing further support for targeting Wnt in patients with glioblastoma.

Human mesenchymal stem cell-engineered hepatic cell sheets accelerate liver regeneration in mice

Mesenchymal stem cells (MSCs) are an attractive cell source for cell therapy. Based on our hypothesis that suppression of Wnt/β-catenin signal enhances hepatic differentiation of human MSCs, we developed human mesenchymal stem cell-engineered hepatic cell sheets by a small molecule compound. Screening of 10 small molecule compounds was performed by WST assay, TCF reporter assay, and albumin mRNA expression. Consequently, hexachlorophene suppressed TCF reporter activity in time- and concentration-dependent manner. Hexachlorophene rapidly induced hepatic differentiation of human MSCs judging from expression of liver-specific genes and proteins, PAS staining, and urea production. The effect of orthotopic transplantation of human mesenchymal stem cell-engineered hepatic cell sheets against acute liver injury was examined in one-layered to three-layered cell sheets system. Transplantation of human mesenchymal stem cell-engineered hepatic cell sheets enhanced liver regeneration and suppressed liver injury. The survival rates of the mice were significantly improved. High expression of complement C3 and its downstream signals including C5a, NF-κB, and IL-6/STAT-3 pathway was observed in hepatic cell sheets-grafted tissues. Expression of phosphorylated EGFR and thioredoxin is enhanced, resulting in reduction of oxidative stress. These findings suggest that orthotopic transplantation of hepatic cell sheets manufactured from MSCs accelerates liver regeneration through complement C3, EGFR and thioredoxin.

Polyphenol Compound as a Transcription Factor Inhibitor

A target-based approach has been used to develop novel drugs in many therapeutic fields. In the final stage of intracellular signaling, transcription factor–DNA interactions are central to most biological processes and therefore represent a large and important class of targets for human therapeutics. Thus, we focused on the idea that the disruption of protein dimers and cognate DNA complexes could impair the transcriptional activation and cell transformation regulated by these proteins. Historically, natural products have been regarded as providing the primary leading compounds capable of modulating protein–protein or protein-DNA interactions. Although their mechanism of action is not fully defined, polyphenols including flavonoids were found to act mostly as site-directed small molecule inhibitors on signaling. There are many reports in the literature of screening initiatives suggesting improved drugs that can modulate the transcription factor interactions responsible for disease. In this review, we focus on polyphenol compound inhibitors against dimeric forms of transcription factor components of intracellular signaling pathways (for instance, c-jun/c-fos (Activator Protein-1; AP-1), c-myc/max, Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and β-catenin/T cell factor (Tcf)).

Potential Therapeutic Targets in Uterine Sarcomas

Uterine sarcomas are rare tumors accounting for 3,4% of all uterine cancers. Even after radical hysterectomy, most patients relapse or present with distant metastases. The very limited clinical benefit of adjuvant cytotoxic treatments is reflected by high mortality rates, emphasizing the need for new treatment strategies. This review summarizes rising potential targets in four distinct subtypes of uterine sarcomas: leiomyosarcoma, low-grade and high-grade endometrial stromal sarcoma, and undifferentiated uterine sarcoma. Based on clinical reports, promising approaches for uterine leiomyosarcoma patients include inhibition of VEGF and mTOR signaling, preferably in combination with other targeted or cytotoxic compounds. Currently, the only targeted therapy approved in leiomyosarcoma patients is pazopanib, a multitargeted inhibitor blocking VEGFR, PDGFR, FGFR, and c-KIT. Additionally, preclinical evidence suggests effect of the inhibition of histone deacetylases, tyrosine kinase receptors, and the mitotic checkpoint protein aurora kinase A. In low-grade endometrial stromal sarcomas, antihormonal therapies including aromatase inhibitors and progestins have proven activity. Other potential targets are PDGFR, VEGFR, and histone deacetylases. In high-grade ESS that carry the YWHAE/FAM22A/B fusion gene, the generated 14-3-3 oncoprotein is a putative target, next to c-KIT and the Wnt pathway. The observation of heterogeneity within uterine sarcoma subtypes warrants a personalized treatment approach.

Macrophages derived from THP-1 promote the osteogenic differentiation of mesenchymal stem cells through the IL-23/IL-23R/β-catenin pathway

Abnormal bone formation is a clinically significant dilemma for many conditions in response to injury, inflammation or genetic disease. However, the effects of inflammation on the osteogenic differentiation of mesenchymal stem cells (MSCs) remain unclear. IL-23 secretion from macrophages might contribute to the development of bone formation. Here, we investigated the stimulatory effects of THP-1 macrophage conditioned medium (MΦ CM) on the osteogenic differentiation of human MSCs and the associated signaling pathways. The osteogenic differentiation of MSCs was induced after exposure to osteogenic differentiation medium (OM). MΦ CM significantly increased alkaline phosphate (ALP) activity and calcium mineralization in MSCs. Osteogenic marker genes, including RUNX2, ALP and osteocalcin (OCN), were also up-regulated in MSCs after exposure to MΦ CM. Moreover, western blotting revealed that MΦ CM treatment induced STAT3 and β-catenin activation in MSCs. Furthermore, blockade of IL-23 in MΦ CM not only impaired the osteogenic-promotion effects of macrophage but also decreased the expression of osteogenic maker genes. However, IL-23R silencing suppressed MΦ CM-induced calcium mineralization and osteogenic maker gene expression in MSCs. These data suggest that macrophages derived from THP-1 promote the osteoblastic differentiation of MSCs through the IL-23/IL-23R/β-catenin pathway and macrophages might contribute to the development of bone formation in inflammation.

Suppression of Hepatocellular Carcinoma by Inhibition of Overexpressed Ornithine Aminotransferase

Hepatocellular carcinoma is the second leading cause of cancer death worldwide. DNA microarray analysis identified the ornithine aminotransferase (OAT) gene as a prominent gene overexpressed in hepatocellular carcinoma (HCC) from Psammomys obesus. In vitro studies demonstrated inactivation of OAT by gabaculine (1), a neurotoxic natural product, which suppressed in vitro proliferation of two HCC cell lines. Alpha-fetoprotein (AFP) secretion, a biomarker for HCC, was suppressed by gabaculine in both cell lines, but not significantly. Because of the active site similarity between GABA aminotransferase (GABA-AT) and OAT, a library of 24 GABA-AT inhibitors was screened to identify a more selective inhibitor of OAT. (1S,3S)-3-Amino-4-(hexafluoropropan-2-ylidene)cyclopentane-1-carboxylic acid (2) was found to be an inactivator of OAT that only weakly inhibits GABA-AT, l-aspartate aminotransferase, and l-alanine aminotransferase. In vitro administration of 2 significantly suppressed AFP secretion in both Hep3B and HepG2 HCC cells; in vivo, 2 significantly suppressed AFP serum levels and tumor growth in HCC-harboring mice, even at 0.1 mg/kg. Overexpression of the OAT gene in HCC and the ability to block the growth of HCC by OAT inhibitors support the role of OAT as a potential therapeutic target to inhibit HCC growth. This is the first demonstration of suppression of HCC by an OAT inactivator.

Tankyrase Inhibition Blocks Wnt/β-Catenin Pathway and Reverts Resistance to PI3K and AKT Inhibitors in the Treatment of Colorectal Cancer

PURPOSE

Oncogenic mutations in the KRAS/PI3K/AKT pathway are one of the most frequent alterations in cancer. Although PI3K or AKT inhibitors show promising results in clinical trials, drug resistance frequently emerges. We previously revealed Wnt/β-catenin signaling hyperactivation as responsible for such resistance in colorectal cancer. Here we investigate Wnt-mediated resistance in patients treated with PI3K or AKT inhibitors in clinical trials and evaluate the efficacy of a new Wnt/tankyrase inhibitor, NVP-TNKS656, to overcome such resistance.

EXPERIMENTAL DESIGN

Colorectal cancer patient-derived sphere cultures and mouse tumor xenografts were treated with NVP-TNKS656, in combination with PI3K or AKT inhibitors.We analyzed progression-free survival of patients treated with different PI3K/AKT/mTOR inhibitors in correlation with Wnt/β-catenin pathway activation, oncogenic mutations, clinicopathological traits, and gene expression patterns in 40 colorectal cancer baseline tumors.

RESULTS

Combination with NVP-TNKS656 promoted apoptosis in PI3K or AKT inhibitor-resistant cells with high nuclear β-catenin content. High FOXO3A activity conferred sensitivity to NVP-TNKS656 treatment. Thirteen of 40 patients presented high nuclear β-catenin content and progressed earlier upon PI3K/AKT/mTOR inhibition. Nuclear β-catenin levels predicted drug response, whereas clinicopathologic traits, gene expression profiles, or frequent mutations (KRAS, TP53, or PIK3CA) did not.

CONCLUSIONS

High nuclear β-catenin content independently predicts resistance to PI3K and AKT inhibitors. Combined treatment with a Wnt/tankyrase inhibitor reduces nuclear β-catenin, reverts such resistance, and represses tumor growth. FOXO3A content and activity predicts response to Wnt/β-catenin inhibition and together with β-catenin may be predictive biomarkers of drug response providing a rationale to stratify colorectal cancer patients to be treated with PI3K/AKT/mTOR and Wnt/β-catenin inhibitors.

Genomic and transcriptome profiling identified both human and HBV genetic variations and their interactions in Chinese hepatocellular carcinoma

Interaction between HBV and host genome integrations in hepatocellular carcinoma (HCC) development is a complex process and the mechanism is still unclear. Here we described in details the quality controls and data mining of aCGH and transcriptome sequencing data on 50 HCC samples from the Chinese patients, published by Dong et al. (2015) (GEO#: GSE65486). In additional to the HBV-MLL4 integration discovered, we also investigated the genetic aberrations of HBV and host genes as well as their genetic interactions. We reported human genome copy number changes and frequent transcriptome variations (e.g. TP53, CTNNB1 mutation, especially MLL family mutations) in this cohort of the patients. For HBV genotype C, we identified a novel linkage disequilibrium region covering HBV replication regulatory elements, including basal core promoter, DR1, epsilon and poly-A regions, which is associated with HBV core antigen over-expression and almost exclusive to HBV-MLL4 integration.

Precise Classification of Cervical Carcinomas Combined with Somatic Mutation Profiling Contributes to Predicting Disease Outcome

Introduction

Squamous cell carcinoma (SCC), adenocarcinoma (AC), and adenosquamous carcinoma (ASC) are the most common histological subtypes of cervical cancer. Differences in the somatic mutation profiles of these subtypes have been suggested. We investigated the prevalence of somatic hot-spot mutations in three well-defined cohorts of SCC, AC, and ASC and determined the additional value of mutation profiling in predicting disease outcome relative to well-established prognostic parameters.

Materials and Methods

Clinicopathological data were collected for 301 cervical tumors classified as SCC (n=166), AC (n=55), or ASC (n=80). Mass spectrometry was used to analyze 171 somatic hot-spot mutations in 13 relevant genes.

Results

In 103 (34%) tumors, 123 mutations were detected (36% in SCC, 38% in AC, and 28% in ASC), mostly in PIK3CA (20%) and KRAS (7%). PIK3CA mutations occurred more frequently in SCC than AC (25% vs. 11%, P=0.025), whereas KRAS mutations occurred more frequently in AC than SCC (24% vs. 3%, P<0.001) and ASC (24% vs. 3%, P<0.001). A positive mutation status correlated with worse disease-free survival (HR 1.57, P=0.043). In multivariate analysis, tumor diameter, parametrial infiltration, and lymph node metastasis, but not the presence of a somatic mutation, were independent predictors of survival.

Conclusion

Potentially targetable somatic mutations occurred in 34% of cervical tumors with different distributions among histological subtypes. Precise classification of cervical carcinomas in combination with mutation profiling is valuable for predicting disease outcome and may guide the development and selection of tumor-specific treatment approaches.

Tankyrases: structure, function and therapeutic implications in cancer

Several cellular signaling pathways are regulated by ADP-ribosylation, a posttranslational modification catalyzed by members of the ARTD superfamily. Tankyrases are distinguishable from the rest of this family by their unique domain organization, notably the sterile alpha motif responsible for oligomerization and ankyrin repeats mediating protein-protein interactions. Tankyrases are involved in various cellular functions, such as telomere homeostasis, Wnt/β-catenin signaling, glucose metabolism, and cell cycle progression. In these processes, Tankyrases regulate the interactions and stability of target proteins by poly (ADP-ribosyl)ation. Modified proteins are subsequently recognized by the E3 ubiquitin ligase RNF146, poly-ubiquitinated and predominantly guided to 26S proteasomal degradation. Several small molecule inhibitors have been described for Tankyrases; they compete with the co-substrate NAD+ for binding to the ARTD catalytic domain. The recent, highly potent and selective inhibitors possess several properties of lead compounds and can be used for proof-of-concept studies in cancer and other Tankyrase linked diseases.

Oxygen regulates proliferation of neural stem cells through Wnt/β-catenin signalling

Reduced oxygen levels (1-5% O2, named herein 'physioxia') are beneficial for stem cell cultures leading to enhanced proliferation, better survival and higher differentiation potential, but the underlying molecular mechanisms remain elusive. A potential link between physioxia and the canonical Wnt pathway was found recently, but the differential involvement of this signalling pathway for the various stem cell properties such as proliferation, stem cell maintenance, and differentiation capacity remains enigmatic. We here demonstrate increased Wnt target gene transcription and stabilised active β-catenin upon physioxic cell culture in primary tissue-specific foetal mouse neural stem cells. Knock-out of the main oxygen sensing molecule, hypoxia-inducible factor-1α (Hif-1α), had no impact on Wnt activation assuming that physioxia induces the Wnt pathway independently of Hif-1α. To determine the physiological relevance of physioxia-induced Wnt/β-catenin signalling, we examined proliferation, cell cycle kinetics, survival and stem cell maintenance upon Wnt activation and inhibition. Whereas survival and stem cell maintenance seem to be independent of the Wnt pathway, our studies provide first evidence that Wnt/β-catenin signalling positively stimulates proliferation of physioxic cells by affecting cell cycle regulation. Together, our results provide mechanistic insight into oxygen-mediated regulation of the self-renewal activity of neural stem cells.

Identification of targets for rational pharmacological therapy in childhood craniopharyngioma

Introduction

Pediatric adamantinomatous craniopharyngioma (ACP) is a histologically benign but clinically aggressive brain tumor that arises from the sellar/suprasellar region. Despite a high survival rate with current surgical and radiation therapy (75–95 % at 10 years), ACP is associated with debilitating visual, endocrine, neurocognitive and psychological morbidity, resulting in excheptionally poor quality of life for survivors. Identification of an effective pharmacological therapy could drastically decrease morbidity and improve long term outcomes for children with ACP.

Results

Using mRNA microarray gene expression analysis of 15 ACP patient samples, we have found several pharmaceutical targets that are significantly and consistently overexpressed in our panel of ACP relative to other pediatric brain tumors, pituitary tumors, normal pituitary and normal brain tissue. Among the most highly expressed are several targets of the kinase inhibitor dasatinib – LCK, EPHA2 and SRC; EGFR pathway targets – AREG, EGFR and ERBB3; and other potentially actionable cancer targets – SHH, MMP9 and MMP12. We confirm by western blot that a subset of these targets is highly expressed in ACP primary tumor samples.

Conclusions

We report here the first published transcriptome for ACP and the identification of targets for rational therapy. Experimental drugs targeting each of these gene products are currently being tested clinically and pre-clinically for the treatment of other tumor types. This study provides a rationale for further pre-clinical and clinical studies of novel pharmacological treatments for ACP. Development of mouse and cell culture models for ACP will further enable the translation of these targets from the lab to the clinic, potentially ushering in a new era in the treatment of ACP.

Organ In Vitro Culture: What Have We Learned about Early Kidney Development?

When Clifford Grobstein set out to study the inductive interaction between tissues in the developing embryo, he developed a method that remained important for the study of renal development until now. From the late 1950s on, in vitro cultivation of the metanephric kidney became a standard method. It provided an artificial environment that served as an open platform to study organogenesis. This review provides an introduction to the technique of organ culture, describes how the Grobstein assay and its variants have been used to study aspects of mesenchymal induction, and describes the search for natural and chemical inducers of the metanephric mesenchyme. The review also focuses on renal development, starting with ectopic budding of the ureteric bud, ureteric bud branching, and the generation of the nephron and presents the search for stem cells and renal progenitor cells that contribute to specific structures and tissues during renal development. It also presents the current use of Grobstein assay and its modifications in regenerative medicine and tissue engineering today. Together, this review highlights the importance of ex vivo kidney studies as a way to acquire new knowledge, which in the future can and will be implemented for developmental biology and regenerative medicine applications.

Identification of HBV-MLL4 Integration and Its Molecular Basis in Chinese Hepatocellular Carcinoma

To gain molecular insights of HBV integration that may contribute to HCC tumorigenesis, we performed whole transcriptome sequencing and whole genome copy number profiling of hepatocellular carcinoma (HCC) samples from 50 Chinese patients. We identified a total of 33 HBV-human integration sites in 16 of 44 HBV-positive HCC tissues, which were enriched in HBV genotype C-infected patients. In addition, significantly recurrent HBV-MLL4 integration (18%; 8/44) was found in this cohort of patients. Using long-range PCR and Sanger sequencing, we comprehensively characterized gDNA and cDNA sequences that encode for the HBV-MLL4 transcripts, and we revealed that HBV integration into MLL4 exons led to much higher mRNA expression of MLL4 than the integration into MLL4 introns due to an alternative splicing mechanism. Moreover, the HBV-MLL4 integration occurred almost exclusively in CTNNB1 and TP53 wild-type patients. The integration was also associated with a distinct gene expression profile. In conclusion, this is the first report on the molecular basis of the MLL4 integration driving MLL4 over-expression. HBV-MLL4 integration occurred frequently in Chinese HCC patients, representing a unique molecular segment for HCC with HBV infection.

Targeting the canonical Wnt/β-catenin pathway in hematological malignancies

The canonical Wnt/β-catenin pathway plays an important role in different developmental processes through the regulation of stem cell functions. In the activation of the canonical Wnt/β-catenin pathway, β-catenin protein is imported into the nucleus and activates transcription of target genes including cyclin D1 and c-myc. Aberrant activation of the Wnt/β-catenin pathway contributes to carcinogenesis and malignant behaviors, and Wnt signaling is essential for the maintenance of cancer stem cells. The canonical Wnt/β-catenin pathway has been investigated extensively as a target in cancer treatment and several specific inhibitors of this signaling pathway have been identified through high-throughput screening. In this review, the significance of the canonical Wnt/β-catenin pathway in hematological carcinogenesis and screening methods for specific inhibitors are discussed.

Pyrimidinone nicotinamide mimetics as selective tankyrase and wnt pathway inhibitors suitable for in vivo pharmacology

The canonical Wnt pathway plays an important role in embryonic development, adult tissue homeostasis, and cancer. Germline mutations of several Wnt pathway components, such as Axin, APC, and ß-catenin, can lead to oncogenesis. Inhibition of the poly(ADP-ribose) polymerase (PARP) catalytic domain of the tankyrases (TNKS1 and TNKS2) is known to inhibit the Wnt pathway via increased stabilization of Axin. In order to explore the consequences of tankyrase and Wnt pathway inhibition in preclinical models of cancer and its impact on normal tissue, we sought a small molecule inhibitor of TNKS1/2 with suitable physicochemical properties and pharmacokinetics for hypothesis testing in vivo. Starting from a 2-phenyl quinazolinone hit (compound 1), we discovered the pyrrolopyrimidinone compound 25 (AZ6102), which is a potent TNKS1/2 inhibitor that has 100-fold selectivity against other PARP family enzymes and shows 5 nM Wnt pathway inhibition in DLD-1 cells. Moreover, compound 25 can be formulated well in a clinically relevant intravenous solution at 20 mg/mL, has demonstrated good pharmacokinetics in preclinical species, and shows low Caco2 efflux to avoid possible tumor resistance mechanisms.

β-catenin links von Hippel-Lindau to aurora kinase A and loss of primary cilia in renal cell carcinoma

von Hippel-Lindau (VHL) gene mutations are associated with clear cell renal cell carcinoma (ccRCC). A hallmark of ccRCC is loss of the primary cilium. Loss of this key organelle in ccRCC is caused by loss of VHL and associated with increased Aurora kinase A (AURKA) and histone deacetylase 6 (HDAC6) activities, which drive disassembly of the primary cilium. However, the underlying mechanism by which VHL loss increases AURKA levels has not been clearly elucidated, although it has been suggested that hypoxia-inducible factor-1α (HIF-1α) mediates increased AURKA expression in VHL-null cells. By contrast, we found that elevated AURKA expression is not increased by HIF-1α, suggesting an alternate mechanism for AURKA dysregulation in VHL-null cells. We report here that AURKA expression is driven by β-catenin transcription in VHL-null cells. In a panel of RCC cell lines, we observed nuclear accumulation of β-catenin and increased AURKA signaling to HDAC6. Moreover, HIF-1α inhibited AURKA expression by inhibiting β-catenin transcription. VHL knockdown activated β-catenin and elevated AURKA expression, decreased primary cilia formation, and caused significant shortening of cilia length in cells that did form cilia. The β-catenin responsive transcription inhibitor iCRT14 reduced AURKA levels and rescued ciliary defects, inducing a significant increase in primary cilia formation in VHL-deficient cells. These data define a role for β-catenin in regulating AURKA and formation of primary cilia in the setting of VHL deficiency, opening new avenues for treatment with β-catenin inhibitors to rescue ciliogenesis in ccRCC.

The CREB-binding protein inhibitor ICG-001 suppresses pancreatic cancer growth

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal cancer due in part to a lack of highly robust cytotoxic or molecular-based therapies. Recent studies investigating ligand-mediated Wnt/β-catenin signaling have highlighted its importance in pancreatic cancer initiation and progression, as well as its potential as a therapeutic target in PDAC. The small-molecule ICG-001 binds cAMP-responsive element binding (CREB)-binding protein (CBP) to disrupt its interaction with β-catenin and inhibit CBP function as a coactivator of Wnt/β-catenin-mediated transcription. Given its ability to inhibit Wnt/β-catenin-mediated transcription in vitro and in vivo, as well as its efficacy in preclinical models of colorectal cancer and other Wnt-driven diseases, we examined ICG-001 and its potential role as a therapeutic in PDAC. ICG-001 alone significantly inhibited anchorage-dependent and -independent growth of multiple PDAC lines, and augmented in vitro growth inhibition when used in combination with gemcitabine. ICG-001 had only variable modest effects on PDAC apoptosis and instead mediated PDAC growth inhibition primarily through robust induction of G₁ cell-cycle arrest. These effects, however, seemed decoupled from its inhibition of Wnt/β-catenin-mediated transcription. DNA microarrays performed on PDAC cells in the context of ICG-001 treatment revealed ICG-001 altered the expression of several genes with well-established roles in DNA replication and cell-cycle progression, including direct actions on SKP2 and CDKN1A. ICG-001 also significantly prolonged survival in an in vivo orthotopic xenograft model of PDAC, indicating ICG-001 or derived compounds that disrupt CBP activity are potentially useful small-molecule therapeutics for pancreatic cancer.