c-Myc transforms human mammary epithelial cells through repression of the Wnt inhibitors DKK1 and SFRP1

Signaling pathway dysregulation in breast cancer

This article provides a comprehensive analysis of the signaling pathways implicated in breast cancer (BC), the most prevalent malignancy among women and a leading cause of cancer-related mortality globally. Special emphasis is placed on the structural dynamics of protein complexes that are integral to the regulation of these signaling cascades. Dysregulation of cellular signaling is a fundamental aspect of BC pathophysiology, with both upstream and downstream signaling cascade activation contributing to cellular process aberrations that not only drive tumor growth, but also contribute to resistance against current treatments. The review explores alterations within these pathways across different BC subtypes and highlights potential therapeutic strategies targeting these pathways. Additionally, the influence of specific mutations on therapeutic decision-making is examined, underscoring their relevance to particular BC subtypes. The article also discusses both approved therapeutic modalities and ongoing clinical trials targeting disrupted signaling pathways. However, further investigation is necessary to fully elucidate the underlying mechanisms and optimize personalized treatment approaches.

SFRP1 Expression is Inversely Associated With Metastasis Formation in Canine Mammary Tumours

BACKGROUND

Canine mammary tumours (CMTs) are the most frequent tumours in intact female dogs and show strong similarities with human breast cancer. In contrast to the human disease there are no standardised diagnostic or prognostic biomarkers available to guide treatment. We recently identified a prognostic 18-gene RNA signature that could stratify human breast cancer patients into groups with significantly different risk of distant metastasis formation. Here, we assessed whether expression patterns of these RNAs were also associated with canine tumour progression.

METHOD

A sequential forward feature selection process was performed on a previously published microarray dataset of 27 CMTs with and without lymph node (LN) metastases to identify RNAs with significantly differential expression to identify prognostic genes within the 18-gene signature. Using an independent set of 33 newly identified archival CMTs, we compared expression of the identified prognostic subset on RNA and protein basis using RT-qPCR and immunohistochemistry on FFPE-tissue sections.

RESULTS

While the 18-gene signature as a whole did not have any prognostic power, a subset of three RNAs: Col13a1, Spock2, and Sfrp1, together completely separated CMTs with and without LN metastasis in the microarray set. However, in the new independent set assessed by RT-qPCR, only the Wnt-antagonist Sfrp1 showed significantly increased mRNA abundance in CMTs without LN metastases on its own (p = 0.013) in logistic regression analysis. This correlated with stronger SFRP1 protein staining intensity of the myoepithelium and/or stroma (p < 0.001). SFRP1 staining, as well as β-catenin membrane staining, was significantly associated with negative LN status (p = 0.010 and 0.014 respectively). However, SFRP1 did not correlate with β-catenin membrane staining (p = 0.14).

CONCLUSION

The study identified SFRP1 as a potential biomarker for metastasis formation in CMTs, but lack of SFRP1 was not associated with reduced membrane-localisation of β-catenin in CMTs.

A New Wave of Targeting 'Undruggable' Wnt Signaling for Cancer Therapy: Challenges and Opportunities

Aberrant Wnt signaling activation is frequently observed in many cancers. The mutation acquisition of Wnt signaling leads to tumorigenesis, whereas the inhibition of Wnt signaling robustly suppresses tumor development in various in vivo models. Based on the excellent preclinical effect of targeting Wnt signaling, over the past 40 years, numerous Wnt-targeted therapies have been investigated for cancer treatment. However, Wnt signaling-targeting drugs are still not clinically available. A major obstacle to Wnt targeting is the concomitant side effects during treatment due to the pleiotropic role of Wnt signaling in development, tissue homeostasis, and stem cells. Additionally, the complexity of the Wnt signaling cascades across different cancer contexts hinders the development of optimized targeted therapies. Although the therapeutic targeting of Wnt signaling remains challenging, alternative strategies have been continuously developed alongside technological advances. In this review, we give an overview of current Wnt targeting strategies and discuss recent promising trials that have the potential to be clinically realized based on their mechanism of action. Furthermore, we highlight new waves of Wnt targeting that combine recently developed technologies such as PROTAC/molecular glue, antibody-drug conjugates (ADC), and anti-sense oligonucleotides (ASO), which may provide us with new opportunities to target 'undruggable' Wnt signaling.

Drug Discovery of DKK1 Inhibitors

Dickkopf-1 (DKK1) is a well-characterized Wnt inhibitor and component of the Wnt/β-catenin signaling pathway, whose dysregulation is associated with multiple abnormal pathologies including osteoporosis, Alzheimer's disease, diabetes, and various cancers. The Wnt signaling pathway has fundamental roles in cell fate determination, cell proliferation, and survival; thus, its mis-regulation can lead to disease. Although DKK1 is involved in other signaling pathways, including the β-catenin-independent Wnt pathway and the DKK1/CKAP4 pathway, the inhibition of DKK1 to propagate Wnt/β-catenin signals has been validated as an effective way to treat related diseases. In fact, strategies for developing DKK1 inhibitors have produced encouraging clinical results in different pathological models, and many publications provide detailed information about these inhibitors, which include small molecules, antibodies, and nucleic acids, and may function at the protein or mRNA level. However, no systematic review has yet provided an overview of the various aspects of their development and prospects. Therefore, we review the DKK1 inhibitors currently available or under study and provide an outlook on future studies involving DKK1 and drug discovery.

Telomerase in Cancer: Function, Regulation, and Clinical Translation

Simple Summary

Cells undergoing malignant transformation must circumvent replicative senescence and eventual cell death associated with progressive telomere shortening that occurs through successive cell division. To do so, malignant cells reactivate telomerase to extend their telomeres and achieve cellular immortality, which is a “Hallmark of Cancer”. Here we review the telomere-dependent and -independent functions of telomerase in cancer, as well as its potential as a biomarker and therapeutic target to diagnose and treat cancer patients.

Abstract

During the process of malignant transformation, cells undergo a series of genetic, epigenetic, and phenotypic alterations, including the acquisition and propagation of genomic aberrations that impart survival and proliferative advantages. These changes are mediated in part by the induction of replicative immortality that is accompanied by active telomere elongation. Indeed, telomeres undergo dynamic changes to their lengths and higher-order structures throughout tumor formation and progression, processes overseen in most cancers by telomerase. Telomerase is a multimeric enzyme whose function is exquisitely regulated through diverse transcriptional, post-transcriptional, and post-translational mechanisms to facilitate telomere extension. In turn, telomerase function depends not only on its core components, but also on a suite of binding partners, transcription factors, and intra- and extracellular signaling effectors. Additionally, telomerase exhibits telomere-independent regulation of cancer cell growth by participating directly in cellular metabolism, signal transduction, and the regulation of gene expression in ways that are critical for tumorigenesis. In this review, we summarize the complex mechanisms underlying telomere maintenance, with a particular focus on both the telomeric and extratelomeric functions of telomerase. We also explore the clinical utility of telomeres and telomerase in the diagnosis, prognosis, and development of targeted therapies for primary, metastatic, and recurrent cancers.

RNA binding motif 47 (RBM47): emerging roles in vertebrate development, RNA editing and cancer

RNA-binding proteins (RBPs) are critical players in the post-transcriptional regulation of gene expression and are associated with each event in RNA metabolism. The term 'RNA-binding motif' (RBM) is assigned to novel RBPs with one or more RNA recognition motif (RRM) domains that are mainly involved in the nuclear processing of RNAs. RBM47 is a novel RBP conserved in vertebrates with three RRM domains whose contributions to various aspects of cellular functions are as yet emerging. Loss of RBM47 function affects head morphogenesis in zebrafish embryos and leads to perinatal lethality in mouse embryos, thereby assigning it to be an essential gene in early development of vertebrates. Its function as an essential cofactor for APOBEC1 in C to U RNA editing of several targets through substitution for A1CF in the A1CF-APOBEC1 editosome, established a new paradigm in the field. Recent advances in the understanding of its involvement in cancer progression assigned RBM47 to be a tumor suppressor that acts by inhibiting EMT and Wnt/[Formula: see text]-catenin signaling through post-transcriptional regulation. RBM47 is also required to maintain immune homeostasis, which adds another facet to its regulatory role in cellular functions. Here, we review the emerging roles of RBM47 in various biological contexts and discuss the current gaps in our knowledge alongside future perspectives for the field.

MYC Hyperactivates Wnt Signaling in APC/CTNNB1-Mutated Colorectal Cancer Cells through miR-92a-Dependent Repression of DKK3

Activation of Wnt signaling is among the earliest events in colon cancer development. It is achieved either via activating mutations in the CTNNB1 gene encoding β-catenin, the key transcription factor in the Wnt pathway, or most commonly by inactivating mutations affecting APC, a major β-catenin binding partner and negative regulator. However, our analysis of recent Pan Cancer Atlas data revealed that CTNNB1 mutations significantly co-occur with those affecting Wnt receptor complex components (e.g., Frizzled and LRP6), underscoring the importance of additional regulatory events even in the presence of common APC/CTNNB1 mutations. In our effort to identify non-mutational hyperactivating events, we determined that KRAS-transformed murine colonocytes overexpressing direct β-catenin target MYC show significant upregulation of the Wnt signaling pathway and reduced expression of Dickkopf 3 (DKK3), a reported ligand for Wnt co-receptors. We demonstrate that MYC suppresses DKK3 transcription through one of miR-17-92 cluster miRNAs, miR-92a. We further examined the role of DKK3 by overexpression and knockdown and discovered that DKK3 suppresses Wnt signaling in Apc-null murine colonic organoids and human colon cancer cells despite the presence of downstream activating mutations in the Wnt pathway. Conversely, MYC overexpression in the same cell lines resulted in hyperactive Wnt signaling, acquisition of epithelial-to-mesenchymal transition markers, and enhanced migration/invasion in vitro and metastasis in a syngeneic orthotopic mouse colon cancer model. IMPLICATIONS: Our results suggest that the MYC→miR-92a-|DKK3 axis hyperactivates Wnt signaling, forming a feed-forward oncogenic loop.

Single-cell transcriptomics reveals opposing roles of Shp2 in Myc-driven liver tumor cells and microenvironment

The mechanisms of Myc-driven liver tumorigenesis are inadequately understood. Herein we show that Myc-driven hepatocellular carcinoma (HCC) is dramatically aggravated in mice with hepatocyte-specific Ptpn11/Shp2 deletion. However, Myc-induced tumors develop selectively from the rare Shp2-positive hepatocytes in Shp2-deficent liver, and Myc-driven oncogenesis depends on an intact Ras-Erk signaling promoted by Shp2 to sustain Myc stability. Despite a stringent requirement of Shp2 cell autonomously, Shp2 deletion induces an immunosuppressive environment, resulting in defective clearance of tumor-initiating cells and aggressive tumor progression. The basal Wnt/β-catenin signaling is upregulated in Shp2-deficient liver, which is further augmented by Myc transfection. Ablating Ctnnb1 suppresses Myc-induced HCC in Shp2-deficient livers, revealing an essential role of β-catenin. Consistently, Myc overexpression and CTNNB1 mutations are frequently co-detected in HCC patients with poor prognosis. These data elucidate complex mechanisms of liver tumorigenesis driven by cell-intrinsic oncogenic signaling in cooperation with a tumor-promoting microenvironment generated by disrupting the specific oncogenic pathway.

Luminescence complementation technology for the identification of MYC:TRRAP inhibitors

Mechanism-based targeted therapies have exhibited remarkable success in treating otherwise untreatable or unresectable cancers. Novel targeted therapies that correct dysregulated transcriptional programs in cancer are an unmet medical need. The transcription factor MYC is the most frequently amplified gene in human cancer and is overexpressed because of mutations in an array of oncogenic signaling pathways. The fact that many cancer cells cannot survive without MYC – a phenomenon termed “MYC addiction” – provides a compelling case for the development of MYC-specific targeted therapies. We propose a new strategy to inhibit MYC function by disrupting its essential interaction with TRRAP using small molecules. To achieve our goal, we developed a platform using luminescence complementation for identifying small molecules as inhibitors of the MYC:TRRAP interaction. Here we present validation of this assay by measuring the disruption of TRRAP binding caused by substitutions to the invariant and essential MYC homology 2 region of MYC.

Generation of anisotropic strain dysregulates wild-type cell division at the interface between host and oncogenic tissue

Epithelial tissues are highly sensitive to anisotropies in mechanical force, with cells altering fundamental behaviors, such as cell adhesion, migration, and cell division.1-5 It is well known that, in the later stages of carcinoma (epithelial cancer), the presence of tumors alters the mechanical properties of a host tissue and that these changes contribute to disease progression.6-9 However, in the earliest stages of carcinoma, when a clonal cluster of oncogene-expressing cells first establishes in the epithelium, the extent to which mechanical changes alter cell behavior in the tissue as a whole remains unclear. This is despite knowledge that many common oncogenes, such as oncogenic Ras, alter cell stiffness and contractility.10-13 Here, we investigate how mechanical changes at the cellular level of an oncogenic cluster can translate into the generation of anisotropic strain across an epithelium, altering cell behavior in neighboring host tissue. We generated clusters of oncogene-expressing cells within otherwise normal in vivo epithelium, using Xenopus laevis embryos. We find that cells in kRasV12, but not cMYC, clusters have increased contractility, which introduces radial stress in the tissue and deforms surrounding host cells. The strain imposed by kRasV12 clusters leads to increased cell division and altered division orientation in neighboring host tissue, effects that can be rescued by reducing actomyosin contractility specifically in the kRasV12 cells. Our findings indicate that some oncogenes can alter the mechanical and proliferative properties of host tissue from the earliest stages of cancer development, changes that have the potential to contribute to tumorigenesis.

Stress-Mediated Reprogramming of Prostate Cancer One-Carbon Cycle Drives Disease Progression

One-carbon (1C) metabolism has a key role in metabolic programming with both mitochondrial (m1C) and cytoplasmic (c1C) components. Here we show that activating transcription factor 4 (ATF4) exclusively activates gene expression involved in m1C, but not the c1C cycle in prostate cancer cells. This includes activation of methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) expression, the central player in the m1C cycle. Consistent with the key role of m1C cycle in prostate cancer, MTHFD2 knockdown inhibited prostate cancer cell growth, prostatosphere formation, and growth of patient-derived xenograft organoids. In addition, therapeutic silencing of MTHFD2 by systemically administered nanoliposomal siRNA profoundly inhibited tumor growth in preclinical prostate cancer mouse models. Consistently, MTHFD2 expression is significantly increased in human prostate cancer, and a gene expression signature based on the m1C cycle has significant prognostic value. Furthermore, MTHFD2 expression is coordinately regulated by ATF4 and the oncoprotein c-MYC, which has been implicated in prostate cancer. These data suggest that the m1C cycle is essential for prostate cancer progression and may serve as a novel biomarker and therapeutic target. SIGNIFICANCE: These findings demonstrate that the mitochondrial, but not cytoplasmic, one-carbon cycle has a key role in prostate cancer cell growth and survival and may serve as a biomarker and/or therapeutic target.

CDK12 Promotes Breast Cancer Progression and Maintains Stemness by Activating c-myc/β -catenin Signaling

BACKGROUND

CDK12 is a promising therapeutic target in breast cancer with an effective ability of maintaining cancer cell stemness.

OBJECTIVE

We aim to investigate the mechanism of CDK12 in maintaining breast cancer stemness.

METHODS

CDK12 expression level was accessed by using RT-qPCR and IHC. CDK12-altered breast cancer cell lines MDA-MB-231-shCDK12 and SkBr-3-CDK12 were then established. CCK8, colony formation assays, and xenograft model were used to value the effect of CDK12 on tumorigenicity. Transwell assay, mammosphere formation, FACS, and lung metastasis model in vivo were determined. Western blot further characterized the mechanism of CDK12 in breast cancer stemness through the c-myc/β-catenin pathway.

RESULTS

Our results showed a higher level of CDK12 exhibited in breast cancer samples. Tumor formation, cancer cell mobility, spheroid forming, and the epithelial-mesenchymal transition will be enhanced in the CDK12high group. In addition, CDK12 was associated with lung metastasis and maintained breast cancer cell stemness. CDK12high cancer cells presented higher tumorigenicity and a population of CD44+ subset compared with CDK12low cells. Our study demonstrated c-myc positively expressed with CDK12. The c-myc/β-catenin signaling was activated by CDK12, which is a potential mechanism to initiate breast cancer stem cell renewal and may serve as a potential biomarker of breast cancer prognosis.

CONCLUSION

CDK12 overexpression promotes breast cancer tumorigenesis and maintains the stemness of breast cancer by activating c-myc/β-catenin signaling. Inhibiting CDK12 expression may become a potential therapy for breast cancer.

Temporal control of Wnt signaling is required for habenular neuron diversity and brain asymmetry

Precise temporal coordination of signaling processes is pivotal for cellular differentiation during embryonic development. A vast number of secreted molecules are produced and released by cells and tissues, and travel in the extracellular space. Whether they induce a signaling pathway and instruct cell fate, however, depends on a complex network of regulatory mechanisms, which are often not well understood. The conserved bilateral left-right asymmetrically formed habenulae of the zebrafish are an excellent model for investigating how signaling control facilitates the generation of defined neuronal populations. Wnt signaling is required for habenular neuron type specification, asymmetry and axonal connectivity. The temporal regulation of this pathway and the players involved have, however, have remained unclear. We find that tightly regulated temporal restriction of Wnt signaling activity in habenular precursor cells is crucial for the diversity and asymmetry of habenular neuron populations. We suggest a feedback mechanism whereby the tumor suppressor Wnt inhibitory factor Wif1 controls the Wnt dynamics in the environment of habenular precursor cells. This mechanism might be common to other cell types, including tumor cells.

TAZ functions as a tumor suppressor in multiple myeloma by downregulating MYC

Multiple myeloma (MM) is an incurable blood cancer that is often characterized by amplification and overexpression of the MYC oncogene. Despite efforts, direct targeting of MYC is not yet possible; therefore, alternative strategies to inhibit MYC activity are necessary. TAZ is a transcriptional coactivator downstream of the Hippo-signaling pathway that functions as an oncogene in many solid tumors. However, its role in hematological malignancies is largely unexplored. Here, we show that, in contrast to solid tumors, expression of TAZ is lower in hematological malignancies, and that high expression of TAZ correlates with better patient outcomes. We further show that TAZ is hypermethylated in MM patient samples and in a panel of MM cell lines. Genetic overexpression of TAZ or pharmacological upregulation of TAZ by treatment with the demethylating agent decitabine induces apoptosis. Importantly, TAZ-induced apoptosis is independent of canonical Hippo components LATS1 or the TEA-domain family of transcription factors. Instead, RNA-sequencing analysis revealed that overexpression of TAZ represses a MYC transcriptional program and we show that increased TAZ expression correlates with decreased MYC expression in both cell-line models and patient samples. Furthermore, promoter derepression of TAZ expression sensitizes MM cell lines through a reciprocal reduction in MYC expression using additional therapeutics such as bortezomib, trichostatin A, and panobinostat. Our findings uncover an unexpected role for TAZ in MM tumorigenesis and provide a compelling rationale for exploring the therapeutic potential of upregulating TAZ expression to restore sensitivity to specific therapeutics in MM.

Long non-coding RNA PVT1 interacts with MYC and its downstream molecules to synergistically promote tumorigenesis

Numerous studies have shown that non-coding RNAs play crucial roles in the development and progression of various tumor cells. Plasmacytoma variant translocation 1 (PVT1) mainly encodes a long non-coding RNA (lncRNA) and is located on chromosome 8q24.21, which constitutes a fragile site for genetic aberrations. PVT1 is well-known for its interaction with its neighbor MYC, which is a qualified oncogene that plays a vital role in tumorigenesis. In the past several decades, increasing attention has been paid to the interaction mechanism between PVT1 and MYC, which will benefit the clinical treatment and prognosis of patients. In this review, we summarize the coamplification of PVT1 and MYC in cancer, the positive feedback mechanism, and the latest promoter competition mechanism of PVT1 and MYC, as well as how PVT1 participates in the downstream signaling pathway of c-Myc by regulating key molecules. We also briefly describe the treatment prospects and research directions of PVT1 and MYC.

Heterogeneity of Myc expression in breast cancer exposes pharmacological vulnerabilities revealed through executable mechanistic modeling

Cells with higher levels of Myc proliferate more rapidly and supercompetitively eliminate neighboring cells. Nonetheless, tumor cells in aggressive breast cancers typically exhibit significant and stable heterogeneity in their Myc levels, which correlates with refractoriness to therapy and poor prognosis. This suggests that Myc heterogeneity confers some selective advantage on breast tumor growth and progression. To investigate this, we created a traceable MMTV-Wnt1-driven in vivo chimeric mammary tumor model comprising an admixture of low-Myc- and reversibly switchable high-Myc-expressing clones. We show that such tumors exhibit interclonal mutualism wherein cells with high-Myc expression facilitate tumor growth by promoting protumorigenic stroma yet concomitantly suppress Wnt expression, which renders them dependent for survival on paracrine Wnt provided by low-Myc-expressing clones. To identify any therapeutic vulnerabilities arising from such interdependency, we modeled Myc/Ras/p53/Wnt signaling cross talk as an executable network for low-Myc, for high-Myc clones, and for the 2 together. This executable mechanistic model replicated the observed interdependence of high-Myc and low-Myc clones and predicted a pharmacological vulnerability to coinhibition of COX2 and MEK. This was confirmed experimentally. Our study illustrates the power of executable models in elucidating mechanisms driving tumor heterogeneity and offers an innovative strategy for identifying combination therapies tailored to the oligoclonal landscape of heterogenous tumors.

Induction of LEF1 by MYC activates the WNT pathway and maintains cell proliferation

Background

While regulated WNT activity is required for normal development and stem cell maintenance, mutations that lead to constitutive activation of the WNT pathway cause cellular transformation and drive colorectal cancer. Activation of the WNT pathway ultimately leads to the nuclear translocation of β-catenin which, in complex with TCF/LEF factors, promotes the transcription of genes necessary for growth. The proto-oncogene MYC is one of the most critical genes activated downstream the WNT pathway in colon cancer. Here, we investigate the converse regulation of the WNT pathway by MYC.

Methods

We performed RNA-seq analyses to identify genes regulated in cells expressing MYC. We validated the regulation of genes in the WNT pathway including LEF1 by MYC using RT-qPCR, Western blotting, and ChIP-seq. We investigated the importance of LEF1 for the viability of MYC-expressing cells in in fibroblasts, epithelial cells, and colon cells. Bioinformatic analyses were utilized to define the expression of MYC-regulated genes in human colon cancer and metabolomics analyses were used to identify pathways regulated by LEF1 in MYC expressing cells.

Results

MYC regulates the levels of numerous WNT-related genes, including the β-catenin co-transcription factor LEF1. MYC activates the transcription of LEF1 and is required for LEF1 expression in colon cancer cells and in primary colonic cells transformed by APC loss of function, a common mutation in colon cancer patients. LEF1 caused the retention of β-catenin in the nucleus, leading to the activation of the WNT pathway in MYC-expressing cells. Consequently, MYC-expressing cells were sensitive to LEF1 inhibition. Moreover, we describe two examples of genes induced in MYC-expressing cells that require LEF1 activity: the peroxisome proliferator activated receptor delta (PPARδ) and the Acyl CoA dehydrogenase 9 (ACAD9).

Conclusions

We demonstrated that MYC is a transcriptional regulator of LEF1 in colonic cells. Our work proposes a novel pathway by which MYC regulates proliferation through activating LEF1 expression which in turn activates the WNT pathway.

Graphical Abstract

DKK1 promotes hepatocellular carcinoma inflammation, migration and invasion: Implication of TGF-β1

Dickkopf-1 (DKK1), an inhibitor of the most frequently impaired signaling pathway in hepatocellular carcinoma (HCC), the Wnt/beta-catenin pathway, seems to fulfill contradictory functions in the process of tumorigenesis, acting either as an oncogenic promoter of metastasis or as a tumor suppressor. Elevated serum levels of DKK1 have been reported in HCC; however, little is known about its functional significance. In the current study, we treated HepG2/C3A and PLC/PRF/5 with the recombinant protein DKK1. Cytotoxicity was first determined by the WST-8 assay. AFP expression was measured at both the mRNA and protein levels. Expression of the oncogenes MYC, CCND1, hTERT, and MDM2 and the tumor suppressor genes TP53, P21 and RB was assessed. Western blot analysis of non-phosphorylated ẞ-catenin and Sanger sequencing were performed to explain the functional differences between the two cell lines. Subsequently, inflammation, migration and invasion were evaluated by qPCR, ELISA, the Boyden chamber assay, zymography, and MMP-2 and MMP-9 western blot analysis. Knockdown of DKK1 and TGF-β1 were also performed. Our results suggest that DKK1 exerts an oncogenic effect on HepG2/C3A cell line by upregulating the expression of oncogenes and downregulating that of tumor suppressor genes, whereas the opposite effect was demonstrated in PLC/PRF/5 cells. This differential impact of DKK1 can be explained by the mutations that affect the canonical Wnt pathway that were detected in exon 3 of the CTNNB1 gene in the HepG2 cell line. We further confirmed that DKK1 promotes inflammation, tumor invasion and migration in both cell types. The canonical pathway was not responsible for the DKK1 proinvasive effect, as indicated by the active ẞ-catenin levels in the two cell lines upon DKK1 treatment. Interestingly, knockdown of TGF-β1 negatively affected the DKK1 proinvasive effect. Taken together, DKK1 appears to facilitate tumor invasion and migration through TGF- β1 by remodeling the tumor microenvironment and inducing inflammation. This finding endorses the relevance of TGF-β1 as a therapeutic target.

MYC-driven regulation of long non-coding RNA profiles in breast cancer cells

AIM

MYC deregulation contributes to breast cancer development and progression. Deregulated expression levels of long non-coding RNAs (lncRNA) have been demonstrated to be critical players in development and/or maintenance of breast cancer. In this study we aimed to evaluate lncRNA expressions depending on MYC overexpression and knockdown in breast cancer cells.

MATERIALS AND METHODS

Cells were infected with lentiviral vectors by either knockdown or overexpression of c-MYC. LncRNA cDNA was transcribed from total RNA samples and lncRNAs were evaluated by qRT-PCR.

RESULTS

Our results indicated that some of the lncRNAs having tumor suppressor (GAS5, MEG3, lincRNA-p21) and oncogenic roles (HOTAIR) are regulated by c-MYC.

CONCLUSION

We observed that c-MYC regulates lncRNAs that have important roles on proliferation, cell cycle and etc. Further studies will give us a light to identify molecular mechanisms related to MYC-lncRNA regulatory pathways in breast cancer.

The role of Wnt signaling pathway in tumor metabolic reprogramming

The occurrence and development of tumors is a complex process involving long-term multi-factor participation. In this process, tumor cells from a set of abnormal metabolic patterns that are different from normal cells. This abnormal metabolic change is called metabolic reprogramming of tumors. Wnt signaling pathway is one of the critical signaling pathways regulating cell proliferation and differentiation. In recent years, it has been found that Wnt signaling participates in the occurrence and development of malignant tumors by affecting metabolic reprogramming. This paper reviews the role of Wnt signaling in tumor metabolic reprogramming to provide crucial theoretical guidance for targeted therapy and drug response of tumors.

The ERH gene regulates migration and invasion in 5637 and T24 bladder cancer cells

Background

This study aimed to determine whether the enhancer of the rudimentary homolog (ERH) gene regulates cell migration and invasion in human bladder urothelial carcinoma (BUC) T24 cells and the underlying mechanism.

Methods

First, we knocked down ERH in BUC T24 and 5637 cells by shRNA and then used wound healing cell scratch migration assays, transwell cell migration assays, transwell cell invasion chamber experiments and nude mouse tail vein transfer assays to determine the migration and invasion ability after ERH was knocked down. Moreover, we used gene expression profiling chip analysis and further functional experiments to explore the possible mechanism through which ERH knockdown downregulated metastasis ability in T24 cells.

Results

Wound healing cell scratch migration assays, transwell cell migration assays, transwell cell invasion chamber experiments and nude mouse tail vein transfer assays all showed that the metastasis ability was significantly inhibited in human BUC T24 and 5637 cells with ERH knockdown. A gene expression profiling chip analysis in T24 cells showed that the MYC gene may be an important downstream target of the ERH gene, and the functional experiments showed that MYC is a functional target of ERH in BUC T24 cells.

Conclusion

ERH knockdown could inhibit the metastasis of BUC T24 cells in vitro and in vivo. This study further explored the mechanism of the ERH gene in the metastasis of the T24 human bladder cancer cell line and found that ERH may regulate MYC gene expression. The results of this research provide a basis for the clinical application of ERH as a potential target for BUC treatment.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5423-9) contains supplementary material, which is available to authorized users.

Suppression of stromal-derived Dickkopf-3 (DKK3) inhibits tumor progression and prolongs survival in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis, and it is unclear whether its stromal infiltrate contributes to its aggressiveness. Here, we demonstrate that Dickkopf-3 (DKK3) is produced by pancreatic stellate cells and is present in most human PDAC. DKK3 stimulates PDAC growth, metastasis, and resistance to chemotherapy with both paracrine and autocrine mechanisms through NF-κB activation. Genetic ablation of DKK3 in an autochthonous model of PDAC inhibited tumor growth, induced a peritumoral infiltration of CD8+ T cells, and more than doubled survival. Treatment with a DKK3-blocking monoclonal antibody inhibited PDAC progression and chemoresistance and prolonged survival. The combination of DKK3 inhibition with immune checkpoint inhibition was more effective in reducing tumor growth than either treatment alone and resulted in a durable improvement in survival, suggesting that DKK3 neutralization may be effective as a single targeted agent or in combination with chemotherapy or immunotherapy for PDAC.

Targeting histone methyltransferase G9a inhibits growth and Wnt signaling pathway by epigenetically regulating HP1α and APC2 gene expression in non-small cell lung cancer

BACKGROUND

Dysregulated histone methyltransferase G9a may represent a potential cancer therapeutic target. The roles of G9a in tumorigenesis and therapeutics are not well understood in non-small cell lung cancer (NSCLC). Here we investigated the impact of G9a on tumor growth and signaling pathways in NSCLC.

METHODS

Immunohistochemistry analyzed G9a expression in NSCLC tissues. Both siRNA and selective inhibitor were used to target G9a. The impact of targeting G9a on key genes, signaling pathways and growth were investigated in NSCLC cells by RNA sequencing analysis, rescue experiments, and xenograft models.

RESULTS

Overexpression of G9a (≥ 5% of cancer cells showing positive staining) was found in 43.2% of 213 NSCLC tissues. Multiple tumor-associated genes including HP1α, APC2 are differentially expressed; and signaling pathways involved in cellular growth, adhesion, angiogenesis, hypoxia, apoptosis, and canonical Wnt signaling pathways are significantly altered in A549, H1299, and H1975 cells upon G9a knockdown. Additionally, targeting G9a by siRNA-mediated knockdown or by a selective G9a inhibitor UNC0638 significantly inhibited tumor growth, and dramatically suppressed Wnt signaling pathway in vitro and in vivo. Furthermore, we showed that treatment with UNC0638 restores the expression of APC2 expression in these cells through promoter demethylation. Restoring HP1α and silencing APC2 respectively attenuated the inhibitory effects on cell proliferation and Wnt signaling pathway in cancer cells in which G9a was silenced or suppressed.

CONCLUSIONS

These findings demonstrate that overexpressed G9a represents a promising therapeutic target, and targeting G9a potentially suppresses growth and Wnt signaling pathway partially through down-regulating HP1α and epigenetically restoring these tumor suppressors such as APC2 that are silenced in NSCLC.

c-Myc deregulation induces mRNA capping enzyme dependency

c-Myc is a potent driver of many human cancers. Since strategies for directly targeting c-Myc protein have had limited success, upstream regulators and downstream effectors of c-Myc are being investigated as alternatives for therapeutic intervention. c-Myc regulates transcription and formation of the mRNA cap, which is important for transcript maturation and translation. However, the direct mechanism by which c-Myc upregulates mRNA capping is unclear. mRNA cap formation initiates with the linkage of inverted guanosine via a triphosphate bridge to the first transcribed nucleotide, catalysed by mRNA capping enzyme (CE/RNGTT). Here we report that c-Myc increases the recruitment of catalytically active CE to RNA polymerase II and to its target genes. c-Myc-induced target gene expression, cell proliferation and cell transformation is highly dependent on CE, but only when c-Myc is deregulated. Cells retaining normal control of c-Myc expression are insensitive to repression of CE. c-Myc expression is also dependent on CE. Therefore, inhibiting CE provides an attractive route for selective therapeutic targeting of cancer cells which have acquired deregulated c-Myc.

MYC leads the way

Members of the MYC family of proto-oncogenes are the most commonly deregulated genes in all human cancers. MYC proteins drive an increase in cellular proliferation and facilitate multiple aspects of tumor initiation and progression, thereby controlling all hallmarks of cancer. MYC's ability to drive metabolic reprogramming of tumor cells leading to biomass accumulation and cellular proliferation is the most studied function of these oncogenes. MYC also regulates tumor progression and is often implicated in resistance to chemotherapy and in metastasis. While most oncogenic functions of MYC are attributed to its role as a transcription factor, more recently, new roles of MYC as a pro-survival factor in the cytoplasm suggest a previously unappreciated diversity in MYC's roles in cancer progression. This review will focus on the role of MYC in invasion and will discuss the canonical functions of MYC in Epithelial to Mesenchymal Transition and the cytoplasmic functions of MYC-nick in collective migration.

Myc cooperates with β-catenin to drive gene expression in nephron progenitor cells

For organs to achieve their proper size, the processes of stem cell renewal and differentiation must be tightly regulated. We previously showed that in the developing kidney, Wnt9b regulates distinct β-catenin-dependent transcriptional programs in the renewing and differentiating populations of the nephron progenitor cells. How β-catenin stimulated these two distinct programs was unclear. Here, we show that β-catenin cooperates with the transcription factor Myc to activate the progenitor renewal program. Although in multiple contexts Myc is a target of β-catenin, our characterization of a cell type-specific enhancer for the Wnt9b/β-catenin target gene Fam19a5 shows that Myc and β-catenin cooperate to activate gene expression controlled by this element. This appears to be a more general phenomenon as we find that Myc is required for the expression of every Wnt9b/β-catenin progenitor renewal target assessed as well as for proper nephron endowment in vivo This study suggests that, within the developing kidney, tissue-specific β-catenin activity is regulated by cooperation with cell type-specific transcription factors. This finding not only provides insight into the regulation of β-catenin target genes in the developing kidney, but will also advance our understanding of progenitor cell renewal in other cell types/organ systems in which Myc and β-catenin are co-expressed.

Chronic Cigarette Smoke-Induced Epigenomic Changes Precede Sensitization of Bronchial Epithelial Cells to Single-Step Transformation by KRAS Mutations

We define how chronic cigarette smoke-induced time-dependent epigenetic alterations can sensitize human bronchial epithelial cells for transformation by a single oncogene. The smoke-induced chromatin changes include initial repressive polycomb marking of genes, later manifesting abnormal DNA methylation by 10 months. At this time, cells exhibit epithelial-to-mesenchymal changes, anchorage-independent growth, and upregulated RAS/MAPK signaling with silencing of hypermethylated genes, which normally inhibit these pathways and are associated with smoking-related non-small cell lung cancer. These cells, in the absence of any driver gene mutations, now transform by introducing a single KRAS mutation and form adenosquamous lung carcinomas in mice. Thus, epigenetic abnormalities may prime for changing oncogene senescence to addiction for a single key oncogene involved in lung cancer initiation.

Combined activity of temozolomide and the mTOR inhibitor temsirolimus in metastatic melanoma involves DKK1

The BRAFV600E inhibitor vemurafenib achieves remarkable clinical responses in patients with BRAF-mutant melanoma, but its effects are limited by the onset of drug resistance. In the case of resistance, chemotherapy can still be applied as second line therapy. However, it yields low response rates and strategies are urgently needed to potentiate its effects. In a previous study, we showed that the inhibition of the PI3K-AKT-mTOR pathway significantly increases sensitivity of melanoma cells to chemotherapeutic drugs (J. Invest. Dermatol. 2009, 129, 1500). In this study, the combination of the mTOR inhibitor temsirolimus with the chemotherapeutic agent temozolomide significantly increases growth inhibition and apoptosis in melanoma cells compared to temsirolimus or temozolomide alone. The combination of temozolomide with temsirolimus is not only effective in established but also in newly isolated and vemurafenib-resistant metastatic melanoma cell lines. These effects are associated with the downregulation of the anti-apoptotic protein Mcl-1 and the upregulation of the Wnt antagonist Dickkopf homologue 1 (DKK1). Knock-down of DKK1 suppresses apoptosis induction by the combination of temsirolimus and temozolomide. These data suggest that the inhibition of the mTOR pathway increases sensitivity of melanoma cells towards temozolomide. Chemosensitisation is associated with enhanced expression of the Wnt antagonist DKK1.

Long non-coding RNAs as novel biomarkers for breast cancer invasion and metastasis

Breast cancer (BC) is now the most common malignancy worldwide, with high prevalence and lethality among women. Invasion and metastasis are the major reasons for breast cancer-associated mortality. However, the underlying mechanism of invasion and metastasis has not been entirely elucidated. Long non-coding RNAs (lncRNAs) are a large class of non-coding transcripts that are >200 bases in length and cannot encode proteins. Evidence has indicated that lncRNAs regulate gene expression at the levels of epigenetic modification, transcription and post-transcription. In addition, they are involved in diverse tumor biological processes, including cell proliferation, apoptosis, invasion, metastasis and angiogenesis. The present review focuses on the recent progress of lncRNAs in breast cancer invasion and metastasis, aiming to provide novel strategies for the clinical prevention, diagnosis and treatment of breast cancer.

MYC Mediates mRNA Cap Methylation of Canonical Wnt/β-Catenin Signaling Transcripts By Recruiting CDK7 and RNA Methyltransferase

MYC is a pleiotropic transcription factor that activates and represses a wide range of target genes and is frequently deregulated in human tumors. While much is known about the role of MYC in transcriptional activation and repression, MYC can also regulate mRNA cap methylation through a mechanism that has remained poorly understood. Here, it is reported that MYC enhances mRNA cap methylation of transcripts globally, specifically increasing mRNA cap methylation of genes involved in Wnt/β-catenin signaling. Elevated mRNA cap methylation of Wnt signaling transcripts in response to MYC leads to augmented translational capacity, elevated protein levels, and enhanced Wnt signaling activity. Mechanistic evidence indicates that MYC promotes recruitment of RNA methyltransferase (RNMT) to Wnt signaling gene promoters by enhancing phosphorylation of serine 5 on the RNA polymerase II carboxy-terminal domain, mediated in part through an interaction between the TIP60 acetyltransferase complex and TFIIH.

IMPLICATIONS

MYC enhances mRNA cap methylation above and beyond transcriptional induction. Mol Cancer Res; 15(2); 213-24. ©2016 AACR.

NBAT1 suppresses breast cancer metastasis by regulating DKK1 via PRC2

Long noncoding RNA NBAT1 (neuroblastoma associated transcript 1) regulates cell proliferation and invasion by interacting with PRC2 (polycomb repressive complex 2) member EZH2 (enhancer of zeste 2). Decreased expression of NBAT1 is associated with poor clinical outcome in neuroblastomas. However, the roles of NBAT1 in other cancers remain unknown. Here, we report that NBAT1 is down-regulated in various types of cancer. Particularly, reduced NBAT1 in breast cancer is associated with tumor metastasis and poor patient prognosis. In vitro, ectopic NBAT1 inhibits migration and invasion of breast cancer cells. Mechanistic study shows that NBAT1 is associated with PRC2 member EZH2 and regulates global gene expression profile. Among them, DKK1 (dickkopf WNT signaling pathway inhibitor 1) is found to be regulated by NBAT1 in a PRC2 dependent manner, and is responsible for NBAT1's effects in inhibiting migration and invasion of breast cancer cells. Taken together, our study demonstrates that long noncoding RNA NBAT1 is a potential breast cancer prognostic marker, as well as a potential therapeutic target to inhibit breast cancer metastasis.

Combined detection of serum Dickkopf-1 and its autoantibodies to diagnose esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) can be treated effectively if diagnosed at an early stage. We evaluated whether measurement of Dickkopf-1 (DKK-1) in combination of DKK-1 autoantibodies in serum may benefit early diagnosis of ESCC. Serum DKK-1 and DKK-1 autoantibodies were measured by enzyme-linked immunosorbent assay in a training cohort (185 ESCC samples vs. 97 normal controls) and validated in a validation cohort (104 ESCC samples vs. 53 normal controls). Receiver operating characteristic (ROC) was applied to calculate diagnostic accuracy. Testing of DKK-1 and DKK-1 autoantibodies together could differentiate ESCC from normal controls (area under the ROC curve [AUC] 0.769, 95% confidence interval (CI), 0.715-0.823, 50.3% sensitivity, and 90.7% specificity in the training cohort; AUC 0.752, 95% CI, 0.675-0.829, 50.0% sensitivity, and 84.9% specificity in the validation cohort). Importantly, the diagnostic performance of the combination of DKK-1 and DKK-1 autoantibodies persisted in early ESCC patients (AUC 0.780, 95% CI, 0.699-0.862, 50.0% sensitivity, and 90.7% specificity in the training cohort; AUC 0.745, 95% CI, 0.626-0.865, 53.8% sensitivity, and 84.9% specificity in the validation cohort). Furthermore, the levels of serum DKK-1 or DKK-1 autoantibody after surgical resection were lower, respectively, compared with the corresponding preoperative samples (P < 0.05). Our results suggest that measurement of DKK-1 combined with DKK-1 autoantibodies is a potentially valuable tool for the early detection of ESCC.

Characterizing the activation of the Wnt signaling pathway in hilar cholangiocarcinoma using a tissue microarray approach

Hilar cholangiocarcinoma (HCCA) is an invasive hepatic malignancy that is difficult to biopsy; therefore, novel markers of HCCA prognosis are needed. Here, the level of canonical Wnt activation in patients with HCCA, intrahepatic cholangiocarcinoma (IHCC), and congenital choledochal cysts (CCC) was compared to understand the role of Wnt signaling in HCCA. Pathology specimens from HCCA (n=129), IHCC (n=31), and CCC (n=45) patients were used to construct tissue microarrays. Wnt2, Wnt3, β-catenin, TCF4, c-Myc, and cyclin D1 were detected by immunohistochemistry. Parallel correlation analysis was used to analyze differences in protein levels between the HCCA, IHCC, and CCC groups. Univariate and multivariate analyses were used to determine independent predictors of successful resection and prognosis in the HCCA group. The protein levels of Wnt2, β-catenin, TCF4, c-Myc, and cyclin D1 were significantly higher in HCCA compared to IHHC or CCC. Wnt signaling activation (Wnt2+, Wnt3+, nuclear β-catenin+, nuclear TCF4+) was significantly greater in HCCA tissues than CCC tissues. Univariable analyses indicated that expression of cyclin D1 as well as Wnt signaling activation, and partial Wnt activation (Wnt2+ or Wnt3+ and nuclear β-catenin+ or nuclear TCF4+) predicted successful resection, but only cyclin D1 expression remained significant in multivariable analyses. Only partial Wnt activation was an independent predictor of survival time. Proteins in the canonical Wnt signaling pathway were present at higher levels in HCCA and correlated with tumor resecility and patient prognosis. These results suggest that Wnt pathway analysis may be a useful marker for clinical outcome in HCCA.

Ubiquitin-Dependent Turnover of MYC Antagonizes MYC/PAF1C Complex Accumulation to Drive Transcriptional Elongation

MYC is an unstable protein, and its turnover is controlled by the ubiquitin system. Ubiquitination enhances MYC-dependent transactivation, but the underlying mechanism remains unresolved. Here we show that MYC proteasomal turnover is dispensable for loading of RNA polymerase II (RNAPII). In contrast, MYC turnover is essential for recruitment of TRRAP, histone acetylation, and binding of BRD4 and P-TEFb to target promoters, leading to phosphorylation of RNAPII and transcriptional elongation. In the absence of histone acetylation and P-TEFb recruitment, MYC associates with the PAF1 complex (PAF1C) through a conserved domain in the MYC amino terminus ("MYC box I"). Depletion of the PAF1C subunit CDC73 enhances expression of MYC target genes, suggesting that the MYC/PAF1C complex can inhibit transcription. Because several ubiquitin ligases bind to MYC via the same domain ("MYC box II") that interacts with TRRAP, we propose that degradation of MYC limits the accumulation of MYC/PAF1C complexes during transcriptional activation.

Newly Constructed Network Models of Different WNT Signaling Cascades Applied to Breast Cancer Expression Data

INTRODUCTION

WNT signaling is a complex process comprising multiple pathways: the canonical β-catenin-dependent pathway and several alternative non-canonical pathways that act in a β-catenin-independent manner. Representing these intricate signaling mechanisms through bioinformatic approaches is challenging. Nevertheless, a simplified but reliable bioinformatic WNT pathway model is needed, which can be further utilized to decipher specific WNT activation states within e.g. high-throughput data.

RESULTS

In order to build such a model, we collected, parsed, and curated available WNT signaling knowledge from different pathway databases. The data were assembled to construct computationally suitable models of different WNT signaling cascades in the form of directed signaling graphs. This resulted in four networks representing canonical WNT signaling, non-canonical WNT signaling, the inhibition of canonical WNT signaling and the regulation of WNT signaling pathways, respectively. Furthermore, these networks were integrated with microarray and RNA sequencing data to gain deeper insight into the underlying biology of gene expression differences between MCF-7 and MDA-MB-231 breast cancer cell lines, representing weakly and highly invasive breast carcinomas, respectively. Differential genes up-regulated in the MDA-MB-231 compared to the MCF-7 cell line were found to display enrichment in the gene set originating from the non-canonical network. Moreover, we identified and validated differentially regulated modules representing canonical and non-canonical WNT pathway components specific for the aggressive basal-like breast cancer subtype.

CONCLUSIONS

In conclusion, we demonstrated that these newly constructed WNT networks reliably reflect distinct WNT signaling processes. Using transcriptomic data, we shaped these networks into comprehensive modules of the genes implicated in the aggressive basal-like breast cancer subtype and demonstrated that non-canonical WNT signaling is important in this context. The topology of these networks can be further refined in the future by integration with complementary data such as protein-protein interactions, in order to gain greater insight into signaling processes.

Effects of Low-Dose Bisphenol A on DNA Damage and Proliferation of Breast Cells: The Role of c-Myc

BACKGROUND

Humans are exposed to low-dose bisphenol A (BPA) through plastic consumer products and dental sealants containing BPA. Although a number of studies have investigated the mammary gland effects after high-dose BPA exposure, the study findings differ. Furthermore, there has been a lack of mechanistic studies.

OBJECTIVE

The objective of this study was to investigate the effect and the mechanism of low-dose BPA in mammary gland cells.

METHODS

We evaluated DNA damage following BPA exposure using the comet assay and immunofluorescence staining, and used cell counting and three-dimensional cultures to evaluate effects on proliferation. We examined the expressions of markers of DNA damage and cell-cycle regulators by immunoblotting and performed siRNA-mediated gene silencing to determine the role of c-Myc in regulating BPA's effects.

RESULTS

Low-dose BPA significantly promoted DNA damage, up-regulated c-Myc and other cell-cycle regulatory proteins, and induced proliferation in parallel in estrogen receptor-α (ERα)-negative mammary cells. Silencing c-Myc diminished these BPA-induced cellular events, suggesting that c-Myc is essential for regulating effects of BPA on DNA damage and proliferation in mammary cells.

CONCLUSIONS

Low-dose BPA exerted c-Myc-dependent genotoxic and mitogenic effects on ERα-negative mammary cells. These findings provide significant evidence of adverse effects of low-dose BPA on mammary cells.

N-Methyl-N-nitrosourea as a mammary carcinogenic agent

The administration of chemical carcinogens is one of the most commonly used methods to induce tumors in several organs in laboratory animals in order to study oncologic diseases of humans. The carcinogen agent N-methyl-N-nitrosourea (MNU) is the oldest member of the nitroso compounds that has the ability to alkylate DNA. MNU is classified as a complete, potent, and direct alkylating compound. Depending on the animals' species and strain, dose, route, and age at the administration, MNU may induce tumors' development in several organs. The aim of this manuscript was to review MNU as a carcinogenic agent, taking into account that this carcinogen agent has been frequently used in experimental protocols to study the carcinogenesis in several tissues, namely breast, ovary, uterus, prostate, liver, spleen, kidney, stomach, small intestine, colon, hematopoietic system, lung, skin, retina, and urinary bladder. In this paper, we also reviewed the experimental conditions to the chemical induction of tumors in different organs with this carcinogen agent, with a special emphasis in the mammary carcinogenesis.

The network of pluripotency, epithelial-mesenchymal transition, and prognosis of breast cancer

Breast cancer is the leading female cancer in terms of prevalence. Progress in molecular biology has brought forward a better understanding of its pathogenesis that has led to better prognostication and treatment. Subtypes of breast cancer have been identified at the genomic level and guide therapeutic decisions based on their biology and the expected benefit from various interventions. Despite this progress, a significant percentage of patients die from their disease and further improvements are needed. The cancer stem cell theory and the epithelial-mesenchymal transition are two comparatively novel concepts that have been introduced in the area of cancer research and are actively investigated. Both processes have their physiologic roots in normal development and common mediators have begun to surface. This review discusses the associations of these networks as a prognostic framework in breast cancer.

Assessing the diagnostic value of serum Dickkopf-related protein 1 levels in cancer detection: a case-control study and meta-analysis

BACKGROUND

This study aimed to summarize the potential diagnostic value of serum DKK1 levels in cancer detection.

MATERIALS AND METHODS

Serum DKK1 was measured using enzyme-linked immunosorbent assay in a case-control study. Then we performed a meta-analysis and the pooled sensitivity, specificity, diagnostic odds ratio, and summary receiver operating characteristic (sROC) curves were used to evaluate the overall test performance.

RESULTS

Serum DKK1 levels were found to be significantly upregulated in gastric cancer as compared to controls. ROC curve analysis revealed an AUC of 0.636, indicating the test has the potential to diagnose cancer with poor accuracy. The summary estimates of the pooled sensitivity, specificity and diagnostic odds ratio in meta-analysis were 0.55 with a 95% confidence interval (CI) (0.53-0.57), 0.86 (95%CI, 0.84-0.88) and 12.25 (95%CI, 5.31-28.28), respectively. The area under the sROC was 0.85. Subgroup analysis revealed that the diagnostic accuracy of serum DKK1 in lung cancer (sensitivity: 0.69 with 95%CI, 0.66-0.74; specificity: 0.95 with 95%CI, 0.92-0.97; diagnostic odds ratio: 44.93 with 95%CI, 26.19-77.08) was significantly higher than for any other cancer.

CONCLUSIONS

Serum DKK1 might be useful as a noninvasive method for confirmation of cancer diagnosis, particularly in the case of lung cancer.

Musashi1 regulates survival of hepatoma cell lines by activation of Wnt signalling pathway

BACKGROUND & AIMS

Musashi1 (MSI1) belongs to the RNA-binding protein (RBP) family, with functions as translational activator or suppressor of specifically bound mRNA. However, its function in hepatocellular carcinoma (HCC) has been deeply unexplored. Here, we investigated the role of MSI1 for proliferation and tumourigenesis in HCC.

METHODS

The expression of MSI1 in HCC tissues was examined by immunohistochemistry and western blotting. The effects of MSI1 overexpression and silencing on cell proliferation, cell viability, tumoursphere and tumour formation of HCC were explored.

RESULTS

In this study, we initially reported that MSI1 was upregulated in HCC. Overexpression of MSI1 in HepG2 cell lines resulted in significantly promoted cell growth, tumour formation and cell cycle progression. Consistently, knockdown of MSI1 in Huh7 cell lines remarkably inhibited cell growth and tumour formation, and caused cell cycle arrest at the G1/S transition. Dual-luciferase assays indicated that MSI1 activated Wnt signal pathway, and APC and DKK1 were direct targets of MSI1.

CONCLUSION

Taken together, these findings indicate that an oncogenic role of MSI1 in HCC may be through modulation of cell growth and cell cycle by activating Wnt pathway via direct downregulation of APC and DKK1.

β-catenin regulates c-Myc and CDKN1A expression in breast cancer cells

We previously reported that the Wnt pathway is preferentially activated in basal-like breast cancer. However, the mechanisms by which the Wnt pathway regulates down-stream targets in basal-like breast cancer, and the biological significance of this regulation, are poorly understood. In this study, we found that c-Myc is highly expressed in the basal-like subtype by microarray analyses and immunohistochemical staining. After silencing β-catenin using siRNA, c-Myc expression was decreased in non-basal-like breast cancer cells. In contrast, c-Myc mRNA and protein expression were up-regulated in the basal-like breast cancer cell lines. Decreased c-Myc promoter activity was observed after inhibiting β-catenin by siRNA in non-basal-like breast cancer cells; however, inhibition of β-catenin or over-expression of dominant-negative LEF1 had no effect on c-Myc promoter activity in basal-like breast cancer cell lines. In addition, CDKN1A mRNA and p21 protein expression were significantly increased in all breast cancer cell lines upon β-catenin silencing. Interestingly, inhibiting β-catenin expression alone did not induce apoptosis in breast cancer cell lines despite c-Myc regulation, but we observed a modest increase of cells in the G1 phase of the cell cycle and decrease of cells in S phase upon β-catenin silencing. Our findings suggest that the regulation of c-Myc in breast cancer cells is dependent on the molecular subtype, and that β-catenin-mediated regulation of c-Myc and p21 may control the balance of cell death and proliferation in breast cancer.

Myofibroblast-derived SFRP1 as potential inhibitor of colorectal carcinoma field effect

Epigenetic changes of stromal-epithelial interactions are of key importance in the regulation of colorectal carcinoma (CRC) cells and morphologically normal, but genetically and epigenetically altered epithelium in normal adjacent tumor (NAT) areas. Here we demonstrated retained protein expression of well-known Wnt inhibitor, secreted frizzled-related protein 1 (SFRP1) in stromal myofibroblasts and decreasing epithelial expression from NAT tissues towards the tumor. SFRP1 was unmethylated in laser microdissected myofibroblasts and partially hypermethylated in epithelial cells in these areas. In contrast, we found epigenetically silenced myofibroblast-derived SFRP1 in CRC stroma. Our results suggest that the myofibroblast-derived SFRP1 protein might be a paracrine inhibitor of epithelial proliferation in NAT areas and loss of this signal may support tumor proliferation in CRC.

WNT signaling: an emerging mediator of cancer cell metabolism?

WNT signaling was discovered in tumor models and has been recognized as a regulator of cancer development and progression for over 3 decades. Recent work has highlighted a critical role for WNT signaling in the metabolic homeostasis of mammals, where its misregulation has been heavily implicated in diabetes. While the majority of WNT metabolism research has focused on nontransformed tissues, the role of WNT in cancer metabolism remains underinvestigated. Cancer is also a metabolic disease where oncogenic signaling pathways regulate energy production and macromolecular synthesis to fuel rapidly proliferating tumors. This review highlights the emerging evidence for WNT signaling in the reprogramming of cancer cell metabolism and examines the role of these signaling pathways as mediators of tumor bioenergetics.

Loss of the multifunctional RNA-binding protein RBM47 as a source of selectable metastatic traits in breast cancer

The mechanisms through which cancer cells lock in altered transcriptional programs in support of metastasis remain largely unknown. Through integrative analysis of clinical breast cancer gene expression datasets, cell line models of breast cancer progression, and mutation data from cancer genome resequencing studies, we identified RNA binding motif protein 47 (RBM47) as a suppressor of breast cancer progression and metastasis. RBM47 inhibited breast cancer re-initiation and growth in experimental models. Transcriptome-wide HITS-CLIP analysis revealed widespread RBM47 binding to mRNAs, most prominently in introns and 3′UTRs. RBM47 altered splicing and abundance of a subset of its target mRNAs. Some of the mRNAs stabilized by RBM47, as exemplified by dickkopf WNT signaling pathway inhibitor 1, inhibit tumor progression downstream of RBM47. Our work identifies RBM47 as an RNA-binding protein that can suppress breast cancer progression and demonstrates how the inactivation of a broadly targeted RNA chaperone enables selection of a pro-metastatic state.

DOI:http://dx.doi.org/10.7554/eLife.02734.001

Tumors form when mistakes in the genes of a single cell allow it to multiply uncontrollably. Sometimes further mutations in genes allow the cancerous cells to escape from the tumor, enter the bloodstream and start a second cancer elsewhere in the body. However, many of the genetic changes behind this process, which is called metastasis, are poorly understood—especially those changes in genes that occur rarely, but can still help the cancer to spread.

Vanharanta, Marney et al. have looked at data on which genes are switched ‘on’ or ‘off’ in metastatic breast cancer cells. A gene called RBM47 was often switched off in these cells, and patients with a low level of RBM47 tended to have a poor clinical outcome.

To test the function of the gene, Vanharanta, Marney et al. switched on RBM47 in cancer cells that had spread from the breast to either the lungs or the brain, and then injected these cells into mice. Few of these cells were able to invade lung and brain tissues in the mice. However, switching off the RBM47 gene in breast cancer cells had the opposite effect; these cells invaded the lungs of mice more efficiently.

RBM47 encodes a protein that sticks to molecules of messenger RNA: molecules that transport the instructions encoded in DNA to the machinery that builds proteins. Vanharanta, Marney et al. found that the wild-type RBM47 protein increased the levels of 102 different messenger RNA molecules, but decreased the levels of another 92. Further experiments showed that RBM47 also slows the rate at which messenger RNA molecules are broken down inside cells: this results in the accumulation of proteins that slow down the growth of tumors. Without RBM47, tumor growth is unleashed. Further work is needed to test if increasing RBM47 activity could be used as a new treatment for some types of cancer.

DOI:http://dx.doi.org/10.7554/eLife.02734.002

Pim-2 kinase is an important target of treatment for tumor progression and bone loss in myeloma

Pim-2 kinase is overexpressed in multiple myeloma (MM) cells to enhance their growth and survival, and regarded as a novel therapeutic target in MM. However, the impact of Pim-2 inhibition on bone disease in MM remains unknown. We demonstrated here that Pim-2 expression was also upregulated in bone marrow stromal cells and MC3T3-E1 preosteoblastic cells in the presence of cytokines known as the inhibitors of osteoblastogenesis in MM, including interleukin-3 (IL-3), IL-7, tumor necrosis factor-α, transforming growth factor-β (TGF-β) and activin A, as well as MM cell conditioned media. The enforced expression of Pim-2 abrogated in vitro osteoblastogenesis by BMP-2, which suggested Pim-2 as a negative regulator for osteoblastogenesis. Treatment with Pim-2 short-interference RNA as well as the Pim inhibitor SMI-16a successfully restored osteoblastogenesis suppressed by all the above inhibitory factors and MM cells. The SMI-16a treatment potentiated BMP-2-mediated anabolic signaling while suppressing TGF-β signaling. Furthermore, treatment with the newly synthesized thiazolidine-2,4-dione congener, 12a-OH, as well as its prototypic SMI-16a effectively prevented bone destruction while suppressing MM tumor growth in MM animal models. Thus, Pim-2 may have a pivotal role in tumor progression and bone loss in MM, and Pim-2 inhibition may become an important therapeutic strategy to target the MM cell-bone marrow interaction.

The activation of the WNT signaling pathway is a Hallmark in neurofibromatosis type 1 tumorigenesis

PURPOSE

The hallmark of neurofibromatosis type 1 (NF1) is the onset of dermal or plexiform neurofibromas, mainly composed of Schwann cells. Plexiform neurofibromas can transform into malignant peripheral nerve sheath tumors (MPNST) that are resistant to therapies.

EXPERIMENTAL DESIGN

The aim of this study was to identify an additional pathway in the NF1 tumorigenesis. We focused our work on Wnt signaling that is highly implicated in cancer, mainly in regulating the proliferation of cancer stem cells. We quantified mRNAs of 89 Wnt pathway genes in 57 NF1-associated tumors including dermal and plexiform neurofibromas and MPNSTs. Expression of two major stem cell marker genes and five major epithelial-mesenchymal transition marker genes was also assessed. The expression of significantly deregulated Wnt genes was then studied in normal human Schwann cells, fibroblasts, endothelial cells, and mast cells and in seven MPNST cell lines.

RESULTS

The expression of nine Wnt genes was significantly deregulated in plexiform neurofibromas in comparison with dermal neurofibromas. Twenty Wnt genes showed altered expression in MPNST biopsies and cell lines. Immunohistochemical studies confirmed the Wnt pathway activation in NF1-associated MPNSTs. We then confirmed that the knockdown of NF1 in Schwann cells but not in epithelial cells provoked the activation of Wnt pathway by functional transfection assays. Furthermore, we showed that the protein expression of active β-catenin was increased in NF1-silenced cell lines. Wnt pathway activation was strongly associated to both cancer stem cell reservoir and Schwann-mesenchymal transition.

CONCLUSION

We highlighted the implication of Wnt pathway in NF1-associated tumorigenesis.

Secreted Frizzled-related protein potentiation versus inhibition of Wnt3a/β-catenin signaling

Wnt signaling regulates a variety of cellular processes during embryonic development and in the adult. Many of these activities are mediated by the Frizzled family of seven-pass transmembrane receptors, which bind Wnts via a conserved cysteine-rich domain (CRD). Secreted Frizzled-related proteins (sFRPs) contain an amino-terminal, Frizzled-like CRD and a carboxyl-terminal, heparin-binding netrin-like domain. Previous studies identified sFRPs as soluble Wnt antagonists that bind directly to Wnts and prevent their interaction with Frizzleds. However, subsequent observations suggested that sFRPs and Frizzleds form homodimers and heterodimers via their respective CRDs, and that sFRPs can stimulate signal transduction. Here, we present evidence that sFRP1 either inhibits or enhances signaling in the Wnt3a/β-catenin pathway, depending on its concentration and the cellular context. Nanomolar concentrations of sFRP1 increased Wnt3a signaling, while higher concentrations blocked it in HEK293 cells expressing a SuperTopFlash reporter. sFRP1 primarily augmented Wnt3a/β-catenin signaling in C57MG cells, but it behaved as an antagonist in L929 fibroblasts. sFRP1 enhanced reporter activity in L cells that were engineered to stably express Frizzled 5, though not Frizzled 2. This implied that the Frizzled expression pattern could determine the response to sFRP1. Similar results were obtained with sFRP2 in HEK293, C57MG and L cell reporter assays. CRDsFRP1 mimicked the potentiating effect of sFRP1 in multiple settings, contradicting initial expectations that this domain would inhibit Wnt signaling. Moreover, CRDsFRP1 showed little avidity for Wnt3a compared to sFRP1, implying that the mechanism for potentiation by CRDsFRP1 probably does not require an interaction with Wnt protein. Together, these findings demonstrate that sFRPs can either promote or suppress Wnt/β-catenin signaling, depending on cellular context, concentration and most likely the expression pattern of Fzd receptors.

AP4 is a mediator of epithelial-mesenchymal transition and metastasis in colorectal cancer

The basic helix-loop-helix transcription factor AP4/TFAP4/AP-4 is encoded by a c-MYC target gene and displays up-regulation concomitantly with c-MYC in colorectal cancer (CRC) and numerous other tumor types. Here a genome-wide characterization of AP4 DNA binding and mRNA expression was performed using a combination of microarray, genome-wide chromatin immunoprecipitation, next-generation sequencing, and bioinformatic analyses. Thereby, hundreds of induced and repressed AP4 target genes were identified. Besides many genes involved in the control of proliferation, the AP4 target genes included markers of stemness (LGR5 and CD44) and epithelial-mesenchymal transition (EMT) such as SNAIL, E-cadherin/CDH1, OCLN, VIM, FN1, and the Claudins 1, 4, and 7. Accordingly, activation of AP4 induced EMT and enhanced migration and invasion of CRC cells. Conversely, down-regulation of AP4 resulted in mesenchymal-epithelial transition and inhibited migration and invasion. In addition, AP4 induction was required for EMT, migration, and invasion caused by ectopic expression of c-MYC. Inhibition of AP4 in CRC cells resulted in decreased lung metastasis in mice. Elevated AP4 expression in primary CRC significantly correlated with liver metastasis and poor patient survival. These findings imply AP4 as a new regulator of EMT that contributes to metastatic processes in CRC and presumably other carcinomas.

Parathyroid hormone-related protein inhibits DKK1 expression through c-Jun-mediated inhibition of β-catenin activation of the DKK1 promoter in prostate cancer

Prostate cancer (PCa)bone metastases are unique in that majority of them induce excessive mineralized bone matrix, through undefined mechanisms, as opposed to most other cancers that induce bone resorption. Parathyroid hormone-related protein (PTHrP) is produced by PCa cells and intermittent PTHrP exposure has bone anabolic effects, suggesting that PTHrP could contribute to the excess bone mineralization. Wnts are bone-productive factors produced by PCa cells, and the Wnt inhibitor Dickkopfs-1 (DKK1) has been shown to promote PCa progression. These findings, in conjunction with the observation that PTHrP expression increases and DKK1 expression decreases as PCa progresses, led to the hypothesis that PTHrP could be a negative regulator of DKK1 expression in PCa cells and, hence, allow the osteoblastic activity of Wnts to be realized. To test this, we first demonstrated that PTHrP downregulated DKK1 mRNA and protein expression. We then found through multiple mutated DKK1 promoter assays that PTHrP, through c-Jun activation, downregulated the DKK1 promoter through a transcription factor (TCF) response element site. Furthermore, chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that PTHrP mediated this effect through inducing c-Jun to bind to a transcriptional activator complex consisting of β-catenin, which binds the most proximal DKK1 promoter, the TCF response element. Together, these results demonstrate a novel signaling linkage between PTHrP and Wnt signaling pathways that results in downregulation of a Wnt inhibitor allowing for Wnt activity that could contribute the osteoblastic nature of PCa.