Frequent epigenetic inactivation of Wnt antagonist genes in breast cancer

BMP Stimulation Differentially Affects Phosphorylation and Protein Stability of β-Catenin in Breast Cancer Cell Lines

Increased expression and nuclear translocation of β-CATENIN is frequently observed in breast cancer, and it correlates with poor prognosis. Current treatment strategies targeting β-CATENIN are not as efficient as desired. Therefore, detailed understanding of β-CATENIN regulation is crucial. Bone morphogenetic proteins (BMP) and Wingless/Integrated (WNT) pathway crosstalk is well-studied for many cancer types including colorectal cancer, whereas it is still poorly understood for breast cancer. Analysis of breast cancer patient data revealed that BMP2 and BMP6 were significantly downregulated in tumors. Since mutation frequency in genes enhancing β-CATENIN protein stability is relatively low in breast cancer, we aimed to investigate whether decreased BMP ligand expression could contribute to a high protein level of β-CATENIN in breast cancer cells. We demonstrated that downstream of BMP stimulation, SMAD4 is required to reduce β-CATENIN protein stability through the phosphorylation in MCF7 and T47D cells. Consequently, BMP stimulation reduces β-CATENIN levels and prevents its nuclear translocation and target gene expression in MCF7 cells. Conversely, BMP stimulation has no effect on β-CATENIN phosphorylation or stability in MDA-MB-231 and MDA-MB-468 cells. Likewise, SMAD4 modulation does not alter the response of those cells, indicating that SMAD4 alone is insufficient for BMP-induced β-CATENIN phosphorylation. While our data suggest that considering BMP activity may serve as a prognostic marker for understanding β-CATENIN accumulation risk, further investigation is needed to elucidate the differential responsiveness of breast cancer cell lines.

Epigenetic modulation of antitumor immunity and immunotherapy response in breast cancer: biological mechanisms and clinical implications

Breast cancer (BC) is the most common non-skin cancer and the second leading cause of cancer death in American women. The initiation and progression of BC can proceed through the accumulation of genetic and epigenetic changes that allow transformed cells to escape the normal cell cycle checkpoint control. Unlike nucleotide mutations, epigenetic changes such as DNA methylation, histone posttranslational modifications (PTMs), nucleosome remodeling and non-coding RNAs are generally reversible and therefore potentially responsive to pharmacological intervention. Epigenetic dysregulations are critical mechanisms for impaired antitumor immunity, evasion of immune surveillance, and resistance to immunotherapy. Compared to highly immunogenic tumor types, such as melanoma or lung cancer, breast cancer has been viewed as an immunologically quiescent tumor which displays a relatively low population of tumor-infiltrating lymphocytes (TIL), low tumor mutational burden (TMB) and modest response rates to immune checkpoint inhibitors (ICI). Emerging evidence suggests that agents targeting aberrant epigenetic modifiers may augment host antitumor immunity in BC via several interrelated mechanisms such as enhancing tumor antigen presentation, activation of cytotoxic T cells, inhibition of immunosuppressive cells, boosting response to ICI, and induction of immunogenic cell death (ICD). These discoveries have established a highly promising basis for using combinatorial approaches of epigenetic drugs with immunotherapy as an innovative paradigm to improve outcomes of BC patients. In this review, we summarize the current understanding of how epigenetic processes regulate immune cell function and antitumor immunogenicity in the context of the breast tumor microenvironment. Moreover, we discuss the therapeutic potential and latest clinical trials of the combination of immune checkpoint blockers with epigenetic agents in breast cancer.

Nimbolide-based nanomedicine inhibits breast cancer stem-like cells by epigenetic reprogramming of DNMTs-SFRP1-Wnt/β-catenin signaling axis

Triple-negative breast cancer (TNBC) harbors a high percentage of breast cancer stem-like cells (BCSCs) that significantly contribute to poor prognosis, metastasis, and relapse of the disease. Thus, targeting BCSCs could be a promising approach to combat TNBC. In this context, we investigated nimbolide (Nim), a limonoid triterpenoid that has potent anticancer properties, but poor pharmacokinetics and low bioavailability limit its therapeutic application. So, to enhance the therapeutic potential of Nim, Nim-encapsulated poly(lactic-co-glycolic acid) (PLGA) nanoparticles (Nim NPs) were formulated and the anticancer stem cell (CSC) effects evaluated in vitro and in vivo. In vitro studies suggested that Nim NPs significantly inhibited several inherent characteristics of BCSCs, such as stemness, self-renewability, chemoresistance, epithelial-to-mesenchymal transition (EMT), and migration in comparison to native Nim. Next, the mechanism behind the anti-CSC effect of Nim was explored. Mechanistically, we found that Nim epigenetically restores tumor suppressor gene secreted frizzled-related protein 1 (SFRP1) expression by downregulating DNA methyltransferases (DNMTs), leading to Wnt/β-catenin signaling inhibition. Further, in vivo results demonstrated that Nim NPs showed enhanced anti-tumor and anti-metastatic effects compared to native Nim in two preclinical models without any systemic toxicity. Overall, these findings provide proof of concept that Nim-based phytonanomedicine can inhibit BCSCs by epigenetic reprogramming of the DNMTs-SFRP1-Wnt/β-catenin signaling axis.

Undifferentially Expressed CXXC5 as a Transcriptionally Regulatory Biomarker of Breast Cancer

This work hypothesizes that some genes undergo radically changed transcription regulations (TRs) in breast cancer (BC), but don't show differential expressions for unknown reasons. The TR of a gene is quantitatively formulated by a regression model between the expression of this gene and multiple transcription factors (TFs). The difference between the predicted and real expression levels of a gene in a query sample is defined as the mqTrans value of this gene, which quantitatively reflects its regulatory changes. This work systematically screens the undifferentially expressed genes with differentially expressed mqTrans values in 1036 samples across five datasets and three ethnic groups. This study calls the 25 genes satisfying the above hypothesis in at least four datasets as dark biomarkers, and the strong dark biomarker gene CXXC5 (CXXC Finger Protein 5) is even supported by all the five independent BC datasets. Although CXXC5 does not show differential expressions in BC, its transcription regulations show quantitative associations with BCs in diversified cohorts. The overlapping long noncoding RNAs (lncRNAs) may have contributed their transcripts to the expression miscalculations of dark biomarkers. The mqTrans analysis serves as a complementary view of the transcriptome-based detections of biomarkers that are ignored by many existing studies.

Secreted frizzled-related proteins: A promising therapeutic target for cancer therapy through Wnt signaling inhibition

The Wnt signaling system is a critical pathway that regulates embryonic development and adult homeostasis. Secreted frizzled-related proteins (SFRPs) are extracellular inhibitors of Wnt signaling that act by binding directly to Wnt ligands or Frizzled receptors. SFRPs can act as anti-Wnt agents and suppress cancer growth by blocking the action of Wnt ligands. However, SFRPs are often silenced by promoter methylation in cancer cells, resulting in hyperactivation of the Wnt pathway. Epigenetic modifiers can reverse this silencing and restore SFRPs expression. Despite the potential of SFRPs as a therapeutic target, the effects of SFRPs on tumor development remain unclear. Therefore, a review of the expression of various members of the SFRPs family in different cancers and their potential as therapeutic targets is warranted. This review aims to summarize the current knowledge of SFRPs in cancer, focusing on their expression patterns and their potential as novel therapeutic targets.

MEF2C and miR-194-5p: New Players in Triple Negative Breast Cancer Tumorigenesis

Among breast cancer (BC) subtypes, the most aggressive is triple negative BC (TNBC), which is prone to metastasis. We previously found that microRNA (miR)-194-5p is downregulated at the early stages of TNBC brain metastasis development. Additionally, the transcription factor myocyte enhancer factor 2 (MEF2)C, a bioinformatically predicted miR-194-5p target, was increasingly expressed throughout TNBC brain metastasis formation and disease severity. However, the contributions of these two players to malignant cells' features remain undetermined. This study aimed at disclosing the role of miR-194-5p and MEF2C in TNBC tumorigenesis. The transfection of 4T1 cells with a silencer for MEF2C or with a pre-miRNA for miR-194-5p was employed to study TNBC cells' phenotypic alterations regarding epithelial and mesenchymal markers, as well as migratory capability alterations. MEF2C-silenced cells presented a decline in both vimentin and cytokeratin expression, whereas the overexpression of miR-194-5p promoted an increase in cytokeratin and a reduction in vimentin, reflecting the acquisition of an epithelial phenotype. Both treatments reduced TNBC cells' migration. These results suggest that MEF2C may determine TNBC cells' invasive properties by partially determining the occurrence of epithelial-mesenchymal transition, while the overexpression of miR-194-5p promotes a decline in TNBC cells' aggressive behavior and reinforces this miRNA's role as a tumor suppressor in TNBC.

MicroRNAs: The key players regulating the crosstalk between Hippo and Wnt/β-catenin pathways in breast cancer

Breast Cancer has the highest burden in females worldwide and is predicted to increase by many folds with increasing lifestyle related risk factors, genetic mutations, and an aging population. The Hippo signalling and Wnt signalling pathways were identified as important signal transducers involved in maintaining organ development, tissue homeostasis, cell proliferation and apoptosis. microRNAs are short nucleotide sequences which act as regulatory components driving signal transductions in most cancers and can serve as both diagnostic and prognostic markers. Several reports have implicated that deregulated Hippo as well as Wnt signalling mediated by miRNAs together drive tumorigenesis, metastases and chemoresistance in breast cancer. Recent evidences on a crosstalk between Hippo and Wnt components elucidated how these pathways might be synchronized to have overlapping functions to promote tumorigenesis. Since miRNAs are demonstrated to target most of the components in both the pathways, in this review, we talk about the crosstalk between Hippo and Wnt signalling pathways and the potential microRNAs that might regulate the interplay between the two pathways in breast cancer, which has not been explored earlier.

How epigenetics impacts on human diseases

Epigenetics is a rapidly growing field of biology that studies the changes in gene expression that are not due to alterations in the DNA sequence but rather the chemical modifications of DNA and its associated proteins. Epigenetic mechanisms can profoundly influence gene expression, cell differentiation, tissue development, and disease susceptibility. Understanding epigenetic changes is essential to elucidate the mechanisms underlying the increasingly recognized role of environmental and lifestyle factors in health and disease and the intergenerational transmission of phenotypes. Recent studies suggest epigenetics may be critical in various diseases, from cardiovascular disease and cancer to neurodevelopmental and neurodegenerative disorders. Epigenetic modifications are potentially reversible and could provide new therapeutic avenues for treating these diseases using epigenetic modulators. Moreover, epigenetics provide insight into disease pathogenesis and biomarkers for disease diagnosis and risk stratification. Nevertheless, epigenetic interventions have the potential for unintended consequences and may potentially lead to increased risks of unexpected outcomes, such as adverse drug reactions, developmental abnormalities, and cancer. Therefore, rigorous studies are essential to minimize the risks associated with epigenetic therapies and to develop safe and effective interventions for improving human health. This article provides a synthetic and historical view of the origin of epigenetics and some of the most relevant achievements.

Oncogenic Viruses and the Epigenome: How Viruses Hijack Epigenetic Mechanisms to Drive Cancer

Globally, viral infections substantially contribute to cancer development. Oncogenic viruses are taxonomically heterogeneous and drive cancers using diverse strategies, including epigenomic dysregulation. Here, we discuss how oncogenic viruses disrupt epigenetic homeostasis to drive cancer and focus on how virally mediated dysregulation of host and viral epigenomes impacts the hallmarks of cancer. To illustrate the relationship between epigenetics and viral life cycles, we describe how epigenetic changes facilitate the human papillomavirus (HPV) life cycle and how changes to this process can spur malignancy. We also highlight the clinical impact of virally mediated epigenetic changes on cancer diagnosis, prognosis, and treatment.

Analysis of endometrial carcinoma TCGA reveals differences in DNA methylation in tumors from Black and White women

OBJECTIVE

Racial disparities exist in cancer patients both in incidence and death rates. In endometrial cancer, Black patients are reported to have higher incidence of aggressive endometrial cancer subtypes and higher death rates than White women. To date, diagnostic and prognostic biomarkers associated with race-specific methylation driven genes have yet to be identified. The objective of this study was to explore DNA methylation patterns in endometrial tumor samples from White and Black women.

METHODS

Differentially methylated CpGs (DMCs) and differentially methylated regions (DMRs) were identified in White tumor samples compared to Black tumor samples using Endometrial Carcinoma (EC) methylation and clinical data from The Cancer Genome Atlas (TCGA). Survival analysis was performed using survival R package and results were visualized using Kaplan-Meier plots. To access the correlation between changes in methylation and gene expression, we downloaded raw RNA-sequencing by Expectation-Maximization (RSEM) counts data from The Cancer Genome Atlas (TCGA) using TCGABiolinks package (v2.18.0).

RESULTS

Our analysis revealed 704 differentially methylated CpGs in tumors from Black and White women. These differentially methylated genes showed strong negative correlation with gene expression and statistically significant enrichment in regulatory regions such as DNase I hypersensitivity sites (DHSs) and transcription factor binding sites (TFBSs). Increased variability in methylation occurred in genes such as the insulin signaling pathway in Black tumor samples.

CONCLUSION

By using two independent statistical method based on means (DMR, DMCs) and variances (DVCs) on the endometrial carcinoma TCGA data, we showed that endometrial tumors from Black women are hypomethylated and more hypervariable than tumors from White women. In-depth investigation of these methylation driven markers can aid in successful management of endometrial cancer disparities and improved overall survival in Black and White populations.

R-spondin-3 is an oncogenic driver of poorly differentiated invasive breast cancer

R-spondins (RSPOs) are influential signaling molecules that promote the Wnt/β-catenin pathway and self-renewal of stem cells. Currently, RSPOs are emerging as clinically relevant oncogenes, being linked to cancer development in multiple organs. Although this has instigated the rapid development and testing of therapeutic antibodies targeting RSPOs, functional evidence that RSPO causally drives cancer has focused primarily on the intestinal tract. Here, we assess the oncogenic capacity of RSPO in breast cancer in a direct fashion by generating and characterizing a novel mouse model with conditional Rspo3 expression in the mammary gland. We also address the prevalence of RSPO gene alterations in breast cancer patients. We found that a quarter of breast cancer patients harbor RSPO2/RSPO3 copy number amplifications, which are associated with lack of steroid hormone receptor expression and reduced patient survival. Foremost, we demonstrate the causal oncogenic capacity of RSPO3 in the breast, as conditional Rspo3 overexpression consistently drives the development of mammary adenocarcinomas in our novel Rspo3 breast cancer model. RSPO3-driven mammary tumors typically show poor differentiation, areas of epithelial-to-mesenchymal transition, and metastatic potential. Given the reported interplay in the Wnt/β-catenin pathway, we comparatively analyzed RSPO3-driven mouse mammary tumors versus classical WNT1-driven analogues. This revealed that RSPO3-driven tumors are distinct, as the poorly differentiated tumor morphology and metastatic potential were observed in RSPO3-driven tumorigenesis exclusively, further substantiated by differentiating gene expression profiles. Co-expression of Rspo3 and Wnt1 transduced mammary tumors with a mixed phenotype harboring morphological features characteristic of both transgenes. In summary, we report that a quarter of breast cancer patients harbor RSPO2/RSPO3 copy number gains, and these patients have a worse prognosis, whilst providing in vivo evidence that RSPO3 drives poorly differentiated invasive breast cancer in mice. Herewith, we establish RSPO3 as a driver of breast cancer with clinical relevance, proposing RSPO3 as a novel candidate target for therapy in breast cancer. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Epigenetic factors in breast cancer therapy

Epigenetic modifications are inherited differences in cellular phenotypes, such as cell gene expression alterations, that occur during somatic cell divisions (also, in rare circumstances, in germ line transmission), but no alterations to the DNA sequence are involved. Histone alterations, polycomb/trithorax associated proteins, short non-coding or short RNAs, long non—coding RNAs (lncRNAs), & DNA methylation are just a few biological processes involved in epigenetic events. These various modifications are intricately linked. The transcriptional potential of genes is closely conditioned by epigenetic control, which is crucial in normal growth and development. Epigenetic mechanisms transmit genomic adaptation to an environment, resulting in a specific phenotype. The purpose of this systematic review is to glance at the roles of Estrogen signalling, polycomb/trithorax associated proteins, DNA methylation in breast cancer progression, as well as epigenetic mechanisms in breast cancer therapy, with an emphasis on functionality, regulatory factors, therapeutic value, and future challenges.

Anti-cancer therapeutic strategies based on HGF/MET, EpCAM, and tumor-stromal cross talk

As an intelligent disease, tumors apply several pathways to evade the immune system. It can use alternative routes to bypass intracellular signaling pathways, such as nuclear factor-κB (NF-κB), Wnt, and mitogen-activated protein (MAP)/phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR). Therefore, these mechanisms lead to therapeutic resistance in cancer. Also, these pathways play important roles in the proliferation, survival, migration, and invasion of cells. In most cancers, these signaling pathways are overactivated, caused by mutation, overexpression, etc. Since numerous molecules share these signaling pathways, the identification of key molecules is crucial to achieve favorable consequences in cancer therapy. One of the key molecules is the mesenchymal-epithelial transition factor (MET; c-Met) and its ligand hepatocyte growth factor (HGF). Another molecule is the epithelial cell adhesion molecule (EpCAM), which its binding is hemophilic. Although both of them are involved in many physiologic processes (especially in embryonic stages), in some cancers, they are overexpressed on epithelial cells. Since they share intracellular pathways, targeting them simultaneously may inhibit substitute pathways that tumor uses to evade the immune system and resistant to therapeutic agents.

The crucial role of epigenetic regulation in breast cancer anti-estrogen resistance: Current findings and future perspectives

Breast cancer (BC) cell de-sensitization to Tamoxifen (TAM) or other selective estrogen receptor (ER) modulators (SERM) is a complex process associated with BC heterogeneity and the transformation of ER signalling. The most influential resistance-related mechanisms include modifications in ER expression and gene regulation patterns. During TAM/SERM treatment, epigenetic mechanisms can effectively silence ER expression and facilitate the development of endocrine resistance. ER status is efficiently regulated by specific epigenetic tools including hypermethylation of CpG islands within ER promoters, increased histone deacetylase activity in the ER promoter, and/or translational repression by miRNAs. Over-methylation of the ER α gene (ESR1) promoter by DNA methyltransferases was associated with poor prognosis and indicated the development of resistance. Moreover, BC progression and spreading were marked by transformed chromatin remodelling, post-translational histone modifications, and expression of specific miRNAs and/or long non-coding RNAs. Therefore, targeted inhibition of histone acetyltransferases (e.g. MYST3), deacetylases (e.g. HDAC1), and/or demethylases (e.g. lysine-specific demethylase LSD1) was shown to recover and increase BC sensitivity to anti-estrogens. Indicated as a powerful molecular instrument, the administration of epigenetic drugs can regain ER expression along with the activation of tumour suppressor genes, which can in turn prevent selection of resistant cells and cancer stem cell survival. This review examines recent advances in the epigenetic regulation of endocrine drug resistance and evaluates novel anti-resistance strategies. Underlying molecular mechanisms of epigenetic regulation will be discussed, emphasising the utilization of epigenetic enzymes and their inhibitors to re-program irresponsive BCs.

Functional regulations between genetic alteration-driven genes and drug target genes acting as prognostic biomarkers in breast cancer

Differences in genetic molecular features including mutation, copy number alterations and DNA methylation, can explain interindividual variability in response to anti-cancer drugs in cancer patients. However, identifying genetic alteration-driven genes and characterizing their functional mechanisms in different cancer types are still major challenges for cancer studies. Here, we systematically identified functional regulations between genetic alteration-driven genes and drug target genes and their potential prognostic roles in breast cancer. We identified two mutation and copy number-driven gene pairs (PARP1-ACSL1 and PARP1-SRD5A3), three DNA methylation-driven gene pairs (PRLR-CDKN1C, PRLR-PODXL2 and PRLR-SRD5A3), six gene pairs between mutation-driven genes and drug target genes (SLC19A1-SLC47A2, SLC19A1-SRD5A3, AKR1C3-SLC19A1, ABCB1-SRD5A3, NR3C2-SRD5A3 and AKR1C3-SRD5A3), and four copy number-driven gene pairs (ADIPOR2-SRD5A3, CASP12-SRD5A3, SLC39A11-SRD5A3 and GALNT2-SRD5A3) that all served as prognostic biomarkers of breast cancer. In particular, RARP1 was found to be upregulated by simultaneous copy number amplification and gene mutation. Copy number deletion and downregulated expression of ACSL1 and upregulation of SRD5A3 both were observed in breast cancers. Moreover, copy number deletion of ACSL1 was associated with increased resistance to PARP inhibitors. PARP1-ACSL1 pair significantly correlated with poor overall survival in breast cancer owing to the suppression of the MAPK, mTOR and NF-kB signaling pathways, which induces apoptosis, autophagy and prevents inflammatory processes. Loss of SRD5A3 expression was also associated with increased sensitivity to PARP inhibitors. The PARP1-SRD5A3 pair significantly correlated with poor overall survival in breast cancer through regulating androgen receptors to induce cell proliferation. These results demonstrate that genetic alteration-driven gene pairs might serve as potential biomarkers for the prognosis of breast cancer and facilitate the identification of combination therapeutic targets for breast cancers.

Identification and validation of plasma biomarkers for diagnosis of breast cancer in South Asian women

Breast cancer is the most common malignancy among women globally. Development of a reliable plasma biomarker panel might serve as a non-invasive and cost-effective means for population-based screening of the disease. Transcriptomic profiling of breast tumour, paired normal and apparently normal tissues, followed by validation of the shortlisted genes using TaqMan® Low density arrays and Quantitative real-time PCR was performed in South Asian women. Fifteen candidate protein markers and 3 candidate epigenetic markers were validated first in primary breast tumours and then in plasma samples of cases [N = 202 invasive, 16 DCIS] and controls [N = 203 healthy, 37 benign] using antibody array and methylation specific PCR. Diagnostic efficiency of single and combined markers was assessed. Combination of 6 protein markers (Adipsin, Leptin, Syndecan-1, Basic fibroblast growth factor, Interleukin 17B and Dickopff-3) resulted in 65% sensitivity and 80% specificity in detecting breast cancer. Multivariate diagnostic analysis of methylation status of SOSTDC1, DACT2, WIF1 showed 100% sensitivity and up to 91% specificity in discriminating BC from benign and controls. Hence, combination of SOSTDC1, DACT2 and WIF1 was effective in differentiating breast cancer [non-invasive and invasive] from benign diseases of the breast and healthy individuals and could help as a complementary diagnostic tool for breast cancer.

Validation of SFRP1 Promoter Hypermethylation in Plasma as a Prognostic Marker for Survival and Gemcitabine Effectiveness in Patients with Stage IV Pancreatic Adenocarcinoma

Simple Summary

Pancreatic adenocarcinoma (PDAC) is a disease with an incredibly grim prognosis. Most patients die within one year of receiving the diagnosis. There are currently very few tools to help the clinician decide between treatment options and evaluate prognosis at an individual level. The aim of the current study was to assess the effect of promoter hypermethylation of secreted frizzled-related protein 1 (phSFRP1) as an independent prognostic blood-based biomarker in gemcitabine-treated patients with advanced PDAC. The study was conducted as a combined discovery and validation study. Analysis in both cohorts confirmed that patients with phSFRP1 had overall poorer survival compared to those without hypermethylation. Thus, phSFRP1 shows promise as an independent prognostic biomarker in this patient group and can hopefully aid the clinician and patient find the correct balance between quantity and quality of life.

Abstract

No reliable predictive blood-based biomarkers are available for determining survival from pancreatic adenocarcinoma (PDAC). This combined discovery and validation study examines promoter hypermethylation (ph) of secreted frizzled-related protein 1 (SFRP1) in plasma-derived cell-free DNA as an independent prognostic marker for survival and Gemcitabine effectiveness in patients with stage IV PDAC. We conducted methylation-specific polymerase chain reaction analysis of the promoter region of the SFRP1 gene, based on bisulfite treatment. Survival was analyzed with Kaplan–Meier curves, log-rank test, and Cox regression. The discovery cohort included 40 patients, 25 receiving Gem. Gem-treated patients with phSFRP1 had a shorter median overall survival (mOS) (4.4 months) than unmethylated patients (11.6 months). Adjusted Cox-regression yielded a hazard rate (HR) of 3.48 (1.39–8.70). The validation cohort included 58 Gem-treated patients. Patients with phSFRP1 had a shorter mOS (3.2 months) than unmethylated patients (6.3 months). Adjusted Cox regression yielded an HR of 3.53 (1.85–6.74). In both cohorts, phSFRP1 was associated with poorer survival in Gem-treated patients. This may indicate that tumors with phSFRP1 are more aggressive and less sensitive to Gem treatment. This knowledge may facilitate tailored treatment of patients with stage IV PDAC. Further studies are planned to examine phSFRP1 in more intensive chemotherapy regimens.

The role of R-spondin proteins in cancer biology

R-spondin (RSPO) proteins constitute a family of four secreted glycoproteins (RSPO1-4) that have appeared as multipotent signaling ligands. The best-known molecular function of RSPOs lie within their capacity to agonize the Wnt/β-catenin signaling pathway. As RSPOs act upon cognate receptors LGR4/5/6 that are typically expressed by stem cells and progenitor cells, RSPO proteins importantly potentiate Wnt/β-catenin signaling especially within these proliferative stem cell compartments. Since multiple organs express LGR4/5/6 receptors and RSPO ligands within their stem cell niches, RSPOs can exert an influential role in stem cell regulation throughout the body. Inherently, over the last decade a multitude of reports implicated the deregulation of RSPOs in cancer development. First, RSPO2 and RSPO3 gene fusions with concomitant enhanced expression have been identified in colon cancer patients, and proposed as an alternative driver of Wnt/β-catenin hyperactivation that earmarks cancer in the colorectal tract. Moreover, the causal oncogenic capacity of RSPO3 overactivation has been demonstrated in the mouse intestine. As a paradigm organ in this field, most of current knowledge about RSPOs in cancer is derived from studies in the intestinal tract. However, RSPO gene fusions as well as enhanced RSPO expression have been reported in multiple additional cancer types, affecting different organs that involve divergent stem cell hierarchies. Importantly, the emerging oncogenic role of RSPO and its potential clinical utility as a therapeutic target have been recognized and investigated in preclinical and clinical settings. This review provides a survey of current knowledge on the role of RSPOs in cancer biology, addressing the different organs implicated, and of efforts made to explore intervention opportunities in cancer cases with RSPO overrepresentation, including the potential utilization of RSPO as novel therapeutic target itself.

Different properties of mammary carcinogenesis induced by two chemical carcinogens, DMBA and PhIP, in heterozygous BALB/c Trp53 knockout mice

Chemical carcinogens, such as 7,12-dimethylbenz[a]anthracene (DMBA) and 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), are known to induce mammary carcinomas in mice and rats. In the present study, the phenotypic and genotypic characteristics of carcinogen-induced mammary carcinogenesis in heterozygous BALB/c tumor protein p53 (Trp53) knockout mice were examined with reference to published data surrounding human breast cancer. A significantly accelerated induction of mammary carcinomas was observed following a single dose of DMBA (50 mg/kg of body weight at 7 weeks of age), and a modest acceleration was induced by PhIP (50 mg/kg of body weight) administered by gavage 6 times/2 weeks from 7 weeks of age. DMBA-induced mammary carcinomas were histopathologically characterized by distinct biphasic structures with luminal and myoepithelial cells, as well as a frequent estrogen receptor expression, and PhIP-induced carcinomas with solid/microacinar structures consisted of pleomorphic cells. Of note, DMBA-induced mammary carcinomas were characterized by a HRas proto-oncogene (Hras) mutation at codon 61, and gene/protein expression indicating MAPK stimulation. PhIP-induced lesions were suspected to be caused by different molecular mechanisms, including Wnt/β-catenin signaling and/or gene mutation-independent PI3K/AKT signaling activation. In conclusion, the present mouse mammary carcinogenesis models, induced by a combination of genetic and exogenous factors, may be utilized (such as the DMBA-induced model with Trp53 gene function deficiency as a model of adenomyoepithelioma, characterized by distinct biphasic cell constituents and Hras mutations), but PhIP-induced models are required to further analyze the genetic/epigenetic mechanisms promoting mammary carcinomas.

Silencing of KIF18B restricts proliferation and invasion and enhances the chemosensitivity of breast cancer via modulating Akt/GSK-3β/β-catenin pathway

Kinesin family member 18B (KIF18B) is a new tumor-associated protein that contributes to the carcinogenesis of multiple malignancies. However, the detailed relevance of KIF18B in breast cancer has not been fully elucidated. This work aimed was to evaluate a possible relationship between KIF18B and breast cancer progression. Our findings show KIF18B is increased in breast cancer and demonstrate that high KIF18B level predicts a reduced survival rate. Cellular functional studies revealed that knockdown of KIF18B markedly reduces the proliferation, invasion, and epithelial-mesenchymal transition of breast cancer cells and enhances their chemosensitivity toward doxorubicin. Further studies showed that KIF18B modulates the level of phospho-Akt, phospho-glycogen synthase kinase-3β, and β-catenin. Notably, suppression of Akt abolished KIF18B-overexpression-induced increases in activation of Wnt/β-catenin pathway. In addition, re-expression of β-catenin reversed KIF18B-silencing-induced cancer-promoting effect. In vivo animal experiments elucidated that knockdown of KIF18B significantly weakened the tumorigenicity of breast cancer cells. Taken together, data of this study illustrate that KIF18B exerts a potential cancer-promoting function in breast cancer via enhancement of Wnt/β-catenin pathway through modulation of the Akt/GSK-3β axis.

A pan-cancer analysis of CpG Island gene regulation reveals extensive plasticity within Polycomb target genes

CpG Island promoter genes make up more than half of human genes, and a subset regulated by Polycomb-Repressive Complex 2 (PRC2+-CGI) become DNA hypermethylated and silenced in cancer. Here, we perform a systematic analysis of CGI genes across TCGA cancer types, finding that PRC2+-CGI genes are frequently prone to transcriptional upregulation as well. These upregulated PRC2+-CGI genes control important pathways such as Epithelial-Mesenchymal Transition (EMT) and TNFα-associated inflammatory response, and have greater cancer-type specificity than other CGI genes. Using publicly available chromatin datasets and genetic perturbations, we show that transcription factor binding sites (TFBSs) within distal enhancers underlie transcriptional activation of PRC2+-CGI genes, coinciding with loss of the PRC2-associated mark H3K27me3 at the linked promoter. In contrast, PRC2-free CGI genes are predominantly regulated by promoter TFBSs which are common to most cancer types. Surprisingly, a large subset of PRC2+-CGI genes that are upregulated in one cancer type are also hypermethylated/silenced in at least one other cancer type, underscoring the high degree of regulatory plasticity of these genes, likely derived from their complex regulatory control during normal development.

Epigenetic mechanisms in breast cancer therapy and resistance

The majority of breast cancers express the estrogen receptor (ERα) and agents targeting this pathway represent the main treatment modality. Endocrine therapy has proven successful in the treatment of hormone-responsive breast cancer since its early adoption in the 1940s as an ablative therapy. Unfortunately, therapeutic resistance arises, leading to disease recurrence and relapse. Recent studies increased our understanding in how changes to the chromatin landscape and deregulation of epigenetic factors orchestrate the resistant phenotype. Here, we will discuss how the epigenome is an integral determinant in hormone therapy response and why epigenetic factors are promising targets for overcoming clinical resistance.

Endocrine therapy has been the mainstay for hormone responsive breast cancer treatment. Here, Garcia-Martinez and colleagues discuss epigenetic mechanisms regulating ER + breast cancer and endocrine therapy resistance, and highlight approaches to rewire the cancer epigenome to improve targeted therapies for this cancer.

Protein arginine methyltransferase 5 (PRMT5) activates WNT/β-catenin signalling in breast cancer cells via epigenetic silencing of DKK1 and DKK3

Protein arginine methyltransferase 5 (PRMT5) activity is dysregulated in many aggressive cancers and its enhanced levels are associated with increased tumour growth and survival. However, the role of PRMT5 in breast cancer remains underexplored. In this study, we show that PRMT5 is overexpressed in breast cancer cell lines, and that it promotes WNT/β-CATENIN proliferative signalling through epigenetic silencing of pathway antagonists, DKK1 and DKK3, leading to enhanced expression of c-MYC, CYCLIN D1 and SURVIVIN. Through chromatin immunoprecipitation (ChIP) studies, we found that PRMT5 binds to the promoter region of WNT antagonists, DKK1 and DKK3, and induces symmetric methylation of H3R8 and H4R3 histones. Our findings also show that PRMT5 inhibition using a specific small molecule inhibitor, compound 5 (CMP5), reduces PRMT5 recruitment as well as methylation of H3R8 and H4R3 histones in the promoter regions of DKK1 and DKK3, which consequently results in reduced expression CYCLIN D1 and SURVIVIN. Furthermore, CMP5 treatment either alone or in combination with 5-Azacytidine and Trichostatin A restored expression of DKK1 and DKK3 in TNBCs. PRMT5 inhibition also altered the growth characteristics of breast cancer cells and induced their death. Collectively, these results show that PRMT5 controls breast cancer cell growth through epigenetic silencing of WNT/β-CATENIN pathway antagonists, DKK1 and DKK3, resulting in up-regulation of WNT/β-CATENIN proliferative signalling.

Epigenetic Modulation of SPCA2 Reverses Epithelial to Mesenchymal Transition in Breast Cancer Cells

Simple Summary

The triple receptor negative breast cancer subtype, or TNBC, currently has no tailored treatment options. TNBC is highly metastatic, associated with high patient mortality, and disproportionately occurs in Black/African American women where it contributes to racial disparities in health outcomes. Therefore, we focused on new therapeutic approaches to TNBC. We discovered that levels of the Calcium-ATPase SPCA2 are abnormally low in TNBC and that these low levels correlate with poor survival prognosis in patients. Previously, we showed that recombinant SPCA2 prevented TNBC cells from acquiring aggressive “mesenchymal” properties associated with metastasis both in vitro and in vivo. These findings motivated us to search for drugs that turn the SPCA2 gene back on in TNBC cells. In this study, we show that histone deacetylase inhibitors increase SPCA2 levels, activate Ca²⁺ signaling and convert cancer cells to a less aggressive “epithelial” state. These findings could lead to new treatment options for TNBC.

Abstract

The secretory pathway Ca²⁺-ATPase SPCA2 is a tumor suppressor in triple receptor negative breast cancer (TNBC), a highly aggressive molecular subtype that lacks tailored treatment options. Low expression of SPCA2 in TNBC confers poor survival prognosis in patients. Previous work has established that re-introducing SPCA2 to TNBC cells restores basal Ca²⁺ signaling, represses mesenchymal gene expression, mitigates tumor migration in vitro and metastasis in vivo. In this study, we examined the effect of histone deacetylase inhibitors (HDACi) in TNBC cell lines. We show that the pan-HDACi vorinostat and the class I HDACi romidepsin induce dose-dependent upregulation of SPCA2 transcript with concurrent downregulation of mesenchymal markers and tumor cell migration characteristic of epithelial phenotype. Silencing SPCA2 abolished the ability of HDACi to reverse epithelial to mesenchymal transition (EMT). Independent of ATPase activity, SPCA2 elevated resting Ca²⁺ levels to activate downstream components of non-canonical Wnt/Ca²⁺ signaling. HDACi treatment led to SPCA2-dependent phosphorylation of CAMKII and β-catenin, turning Wnt signaling off. We conclude that SPCA2 mediates the efficacy of HDACi in reversing EMT in TNBC by a novel mode of non-canonical Wnt/Ca²⁺ signaling. Our findings provide incentive for screening epigenetic modulators that exploit Ca²⁺ signaling pathways to reverse EMT in breast tumors.

Wnt signaling in breast cancer: biological mechanisms, challenges and opportunities

Wnt signaling is a highly conserved signaling pathway that plays a critical role in controlling embryonic and organ development, as well as cancer progression. Genome-wide sequencing and gene expression profile analyses have demonstrated that Wnt signaling is involved mainly in the processes of breast cancer proliferation and metastasis. The most recent studies have indicated that Wnt signaling is also crucial in breast cancer immune microenvironment regulation, stemness maintenance, therapeutic resistance, phenotype shaping, etc. Wnt/β-Catenin, Wnt-planar cell polarity (PCP), and Wnt-Ca2+ signaling are three well-established Wnt signaling pathways that share overlapping components and play different roles in breast cancer progression. In this review, we summarize the main findings concerning the relationship between Wnt signaling and breast cancer and provide an overview of existing mechanisms, challenges, and potential opportunities for advancing the therapy and diagnosis of breast cancer.

Expression and methylation of Dickkopf-1 in the pathogenesis and malignant transformation of oral submucous fibrosis

BACKGROUND

Dickkopf-1 is an inhibitor of the Wnt/β-catenin pathway, but the role of Dickkopf-1 in oral submucous fibrosis remains unclear. We evaluated the protein expression and gene methylation levels of dickkopf-1 to determine the mechanism underlying abnormal Wnt/β-catenin pathway activation.

METHODS

Healthy mucosa, oral submucous fibrosis, oral squamous cell carcinoma, and cancer-adjacent tissues were collected. The expression and promoter methylation levels of dickkopf-1 were analyzed.

RESULTS

The expression levels of dickkopf-1 in oral submucous fibrosis and oral squamous cell carcinoma tissues were lower than those in healthy and cancer-adjacent tissues. The methylation levels of the dickkopf-1 gene in oral submucous fibrosis and oral squamous cell carcinoma tissues were higher than those in healthy and cancer-adjacent tissues. Dickkopf-1 expression was negatively correlated with dickkopf-1 gene methylation.

CONCLUSIONS

High dickkopf-1 methylation levels in oral submucous fibrosis and oral squamous cell carcinoma tissues may decrease dickkopf-1 expression, which may induce an abnormal activation of the Wnt/β-catenin pathway and oral submucous fibrosis pathogenesis.

Contribution of the Low-Density Lipoprotein Receptor Family to Breast Cancer Progression

The low-density lipoprotein receptor (LDLR) family comprises 14 single-transmembrane receptors sharing structural homology and common repeats. These receptors specifically recognize and internalize various extracellular ligands either alone or complexed with membrane-spanning co-receptors that are then sorted for lysosomal degradation or cell-surface recovery. As multifunctional endocytic receptors, some LDLR members from the core family were first considered as potential tumor suppressors due to their clearance activity against extracellular matrix-degrading enzymes. LDLRs are also involved in pleiotropic functions including growth factor signaling, matricellular proteins, and cell matrix adhesion turnover and chemoattraction, thereby affecting both tumor cells and their surrounding microenvironment. Therefore, their roles could appear controversial and dependent on the malignancy state. In this review, recent advances highlighting the contribution of LDLR members to breast cancer progression are discussed with focus on (1) specific expression patterns of these receptors in primary cancers or distant metastasis and (2) emerging mechanisms and signaling pathways. In addition, potential diagnosis and therapeutic options are proposed.

Klotho and the Treatment of Human Malignancies

Klotho was first discovered as an anti-ageing protein linked to a number of age-related disease processes, including cardiovascular, renal, musculoskeletal, and neurodegenerative conditions. Emerging research has also demonstrated a potential therapeutic role for Klotho in cancer biology, which is perhaps unsurprising given that cancer and ageing share similar molecular hallmarks. In addition to functioning as a tumour suppressor in numerous solid tumours and haematological malignancies, Klotho represents a candidate therapeutic target for patients with these diseases, the majority of whom have limited treatment options. Here, we examine contemporary evidence evaluating the anti-neoplastic effects of Klotho and describe the modulation of downstream oncogenic signalling pathways, including Wnt/β-catenin, FGF, IGF1, PIK3K/AKT, TGFβ, and the Unfolded Protein Response. We also discuss possible approaches to developing therapeutic Klotho and consider technological advances that may facilitate the delivery of Klotho through gene therapy.

WHSC1 promotes wnt/β-catenin signaling in a FoxM1-dependent manner facilitating proliferation, invasion and epithelial-mesenchymal transition in breast cancer

Objectives: Wolf-Hirschhorn syndrome candidate gene-1 (WHSC1) is highly expressed in various malignant tumors. We investigated the correlation and regulatory pathway of WHSC1 in the progression of breast cancer (BC).Methods: The expression and distribution of WHSC1 in the BC tissues and cell lines were determined by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and immunohistochemical staining. Spearman correlation analysis demonstrated the correlation between WHSC1 high expression level and the clinical characteristics of BC patients. The effects of WHSC1 on the proliferation, apoptosis, migration and invasion of BC cells were analyzed by cell transfection, MTT, colony formation, scratch assay, and transwell. Furthermore, the expression of Forkhead box M1 (FoxM1) and the location of β-catenin were detected by qRT-PCR and western blot.Results: Firstly, WHSC1 expression was up-regulated in BC tissues and cell lines. The high expression of WHSC1 in BC is associated with the tumor size (p = 0.027), metastasis (p = 0.018) and pathological stages (p = 0.025) of the BC patients. The knockdown of WHSC1 inhibited the growth, proliferation migration, invasion and EMT of BC cell lines. Furthermore, WHSC1 could promote the expression of FoxM1 in BC cells and tissues. WHSC1 enhanced the expression of FoxM1, and promoted the nuclear localization of β-catenin, and thus activated the downstream genes expression of Wnt/β-catenin signaling pathway to regulate the development of BC.Conclusion: In summary, our study elucidates the correlation and specific regulatory mechanism between WHSC1 and the progression of BC, thus implying that WHSC1 may function as molecular diagnosis, prognosis and molecular targeted therapy of BC.

Genome-Wide Analysis of Methylation-Driven Genes and Identification of an Eight-Gene Panel for Prognosis Prediction in Breast Cancer

BACKGROUND

Aberrant DNA methylation is a crucial epigenetic regulator that is closely related to the occurrence and development of various cancers, including breast cancer (BC). The present study aimed to identify a novel methylation-based prognosis biomarker panel by integrally analyzing gene expression and methylation patterns in BC patients.

METHODS

DNA methylation and gene expression data of breast cancer (BRCA) were downloaded from The Cancer Genome Atlas (TCGA). R packages, including ChAMP, SVA, and MethylMix, were applied to identify the unique methylation-driven genes. Subsequently, these genes were subjected to Metascape for GO analysis. Univariant Cox regression was used to identify survival-related genes among the methylation-driven genes. Robust likelihood-based survival modeling was applied to define the prognosis markers. An independent data set (GSE72308) was used for further validation of our risk score system.

RESULTS

A total of 879 DNA methylation-driven genes were identified from 765 BC patients. In the discovery cohort, we identified 50 survival-related methylation-driven genes. Finally, we built an eight-methylation-driven gene panel that serves as prognostic predictors.

CONCLUSIONS

Our analysis of transcriptome and methylome variations associated with the survival status of BC patients provides a further understanding of basic biological processes and a basis for the genetic etiology in BC.

Downregulation of SFRP1 is a protumorigenic event in hepatoblastoma and correlates with beta-catenin mutations

Background

Hepatoblastoma (HB) and pediatric hepatocellular carcinoma (HCC) are the most common malignant liver tumors in childhood. Both tumor types exhibit genetic and epigenetic alterations in the WNT/β-catenin signaling pathway, which is a key regulator of liver progenitor cells in embryonic development. The tumors demonstrate a high rate of β-catenin mutations and gene expression changes of several WNT antagonists. However, the role of the WNT inhibitory factor secreted frizzled-related protein 1 (SFRP1) has not been addressed in pediatric liver cancer so far.

Results

In our study, we investigated the gene expression level, DNA methylation status and functional relevance of SFRP1 in HB cell lines and in pediatric liver tumor patient samples. SFRP1 was downregulated due to DNA promoter methylation in all tested HB cell lines. Overexpression of SFRP1 in HB cell lines diminished tumor cell proliferation, colony formation and migration potential. In addition, the SFRP1-expressing HB cell lines showed reduced WNT/β-catenin signaling pathway activity and decreased expression of WNT target genes. To evaluate the utility of SFRP1 as a biomarker in pediatric liver cancer, we determined the gene expression level and DNA methylation status of SFRP1 in 45 pediatric liver tumor patient samples. The correlation analysis of different clinical parameters and tumor characteristics revealed a significant correlation of reduced SFRP1 expression with the presence of mutant β-catenin. The methylation status of SFRP1 was furthermore associated to a pediatric liver tumor type with HCC-like characteristics, TERT mutations and an older age at diagnosis.

Conclusion

Altogether, our data demonstrate that the epigenetic suppression of the WNT/β-catenin antagonist SFRP1 has an important impact on the malignant behavior of HB cells. Although SFRP1 methylation is a common event in HCC-like pediatric liver tumors, its potential as a prognostic or diagnostic biomarker needs to be further investigated.

Electronic supplementary material

The online version of this article (10.1007/s00432-020-03182-1) contains supplementary material, which is available to authorized users.

Aberrant WNT/CTNNB1 Signaling as a Therapeutic Target in Human Breast Cancer: Weighing the Evidence

WNT signaling is crucial for tissue morphogenesis during development in all multicellular animals. After birth, WNT/CTNNB1 responsive stem cells are responsible for tissue homeostasis in various organs and hyperactive WNT/CTNNB1 signaling is observed in many different human cancers. The first link between WNT signaling and breast cancer was established almost 40 years ago, when Wnt1 was identified as a proto-oncogene capable of driving mammary tumor formation in mice. Since that discovery, there has been a dedicated search for aberrant WNT signaling in human breast cancer. However, much debate and controversy persist regarding the importance of WNT signaling for the initiation, progression or maintenance of different breast cancer subtypes. As the first drugs designed to block functional WNT signaling have entered clinical trials, many questions about the role of aberrant WNT signaling in human breast cancer remain. Here, we discuss three major research gaps in this area. First, we still lack a basic understanding of the function of WNT signaling in normal human breast development and physiology. Second, the overall extent and precise effect of (epi)genetic changes affecting the WNT pathway in different breast cancer subtypes are still unknown. Which underlying molecular and cell biological mechanisms are disrupted as a result also awaits further scrutiny. Third, we survey the current status of targeted therapeutics that are aimed at interfering with the WNT pathway in breast cancer patients and highlight the importance and complexity of selecting the subset of patients that may benefit from treatment.

Epigenetic heterogeneity in cancer

Phenotypic and functional heterogeneity is one of the hallmarks of human cancers. Tumor genotype variations among tumors within different patients are known as interpatient heterogeneity, and variability among multiple tumors of the same type arising in the same patient is referred to as intra-patient heterogeneity. Subpopulations of cancer cells with distinct phenotypic and molecular features within a tumor are called intratumor heterogeneity (ITH). Since Nowell proposed the clonal evolution of tumor cell populations in 1976, tumor heterogeneity, especially ITH, was actively studied. Research has focused on the genetic basis of cancer, particularly mutational activation of oncogenes or inactivation of tumor-suppressor genes (TSGs). The phenomenon of ITH is commonly explained by Darwinian-like clonal evolution of a single tumor. Despite the monoclonal origin of most cancers, new clones arise during tumor progression due to the continuous acquisition of mutations. It is clear that disruption of the "epigenetic machinery" plays an important role in cancer development. Aberrant epigenetic changes occur more frequently than gene mutations in human cancers. The epigenome is at the intersection of the environment and genome. Epigenetic dysregulation occurs in the earliest stage of cancer. The current trend of epigenetic therapy is to use epigenetic drugs to reverse and/or delay future resistance to cancer therapies. A majority of cancer therapies fail to achieve durable responses, which is often attributed to ITH. Epigenetic therapy may reverse drug resistance in heterogeneous cancer. Complete understanding of genetic and epigenetic heterogeneity may assist in designing combinations of targeted therapies based on molecular information extracted from individual tumors.

Exosomal miR-196a-1 promotes gastric cancer cell invasion and metastasis by targeting SFRP1

Aim: To investigate the role of exosomal miRNAs on gastric cancer (GC) metastasis. Materials & methods: miRNA expression profiles of exosomes with distinct invasion potentials were analyzed using miRNA microarray and validated by quantitative real-time PCR. In vitro and in vivo experiments assessed the role of exosomal miR-196a-1 in GC's metastasis. Results: High expression level of exosomal miR-196a-1 expression was significantly associated with poor survival in GC. Exosomes that contained miR-196a-1 were secreted from high-invasive GC cells. Ectopic miR-196a-1 expression promoted invasion of low-invasive GC cells by targeting SFRP1. Conclusion: miR-196a-1 was delivered from high-invasive GC into low-invasive GC cells via exosomes and promoted metastasis to the liver in vitro and in vivo.

miR-221/222 activate the Wnt/β-catenin signaling to promote triple-negative breast cancer

Triple-negative breast cancer (TNBC), characterized by the lack of expression of the estrogen receptor, the progesterone receptor, and the human epidermal growth factor receptor 2, is an aggressive form of cancer that conveys unpredictable and poor prognosis due to limited treatment options and lack of effective targeted therapies. Wnt/β-catenin signaling is hyperactivated in TNBC, which promotes the progression of TNBC. However, the molecular mechanism of Wnt/β-catenin activation in TNBC remains unknown. Here, we report the drastic overexpression of miR-221/222 in all of four TNBC cell lines and TNBC primary tumor samples from patients. Furthermore, we demonstrate by both ex vivo and xenograft experiments that inhibiting miR-221/222 expression in a TNBC cell line (MDA-MB-231) suppresses its proliferation, viability, epithelial-to-mesenchymal transition, and migration; whereas expressing miR-221/222 in a non-TNBC line (MCF7) promotes all of the above cancer properties. miR-221/222 achieve so by directly repressing multiple negative regulators of the Wnt/β-catenin signaling pathway, including WIF1, SFRP2, DKK2, and AXIN2, to activate the pathway. Notably, the level of miR-221/222 expression is inversely correlated whereas that of WIF1, DKK2, SFRP2, and AXIN2 expression is positively correlated with the patient survival. Last, we show that anti-miR-221/222 significantly increases apoptotic cells with tamoxifen/Wnt3a treatment but not with cyclophosphamide/Wnt3a treatment. These results demonstrate that miR-221/222 activate the Wnt/β-catenin signaling to promote the aggressiveness and TNBC properties of breast cancers, and thus reveal a new prospect for TNBC treatment.

Association between SFRP promoter hypermethylation and different types of cancer: A systematic review and meta-analysis

Abnormal methylation of secreted frizzled-related proteins (SFRPs) has been observed in various human cancer types. The loss of SFRP gene expression induces the activation of the Wnt pathway and is a vital mechanism for tumorigenesis and development. The aim of the present systematic review was to assess the association between SFRP methylation and cancer risk. A meta-analysis was systematically conducted to assess the clinicopathological significance of SFRP methylation in cancer risk. The Cochrane Library, PubMed and Web of Science databases were comprehensively searched, and 83 publications with a total of 21,612 samples were selected for the meta-analysis. The pooled odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were calculated to evaluate the degree of associations between SFRP promoter methylation and cancer risk. Subgroup analysis, meta regression and sensitivity analysis were used to identify the potential sources of heterogeneity. SFRP1, SFRP2, SFRP4 and SFRP5 hypermethylation was significantly associated with cancer risk, with ORs of 8.48 (95% CI, 6.26-11.49), 8.21 (95% CI, 6.20-10.88), 11.41 (95% CI, 6.42-20.30) and 6.34 (95% CI, 3.86-10.42), respectively. SFRP2 methylation was significantly associated with differentiation in colorectal cancer (OR, 2.16; 95% CI, 1.02-4.56). The results of the present study demonstrated that SFRP methylation may contribute to carcinogenesis, especially in certain cancer types, including hepatocellular carcinoma and colorectal cancer.

The MMTV-Wnt1 murine model produces two phenotypically distinct subtypes of mammary tumors with unique therapeutic responses to an EGFR inhibitor

The Wnt gene family encodes an evolutionarily conserved group of proteins that regulate cell growth, differentiation and stem cell self-renewal. Aberrant Wnt signaling in human breast tumors has been proposed as a driver of tumorigenesis, especially in the basal-like tumor subtype where canonical Wnt signaling is both enriched and predictive of poor clinical outcomes. The development of effective Wnt-based therapeutics, however, has been slowed in part by a limited understanding of the context-dependent nature with which these aberrations influence breast tumorigenesis. We previously reported that MMTV-Wnt1 mice, an established model for studying Wnt signaling in breast tumors, develop two subtypes of tumors by gene expression classification: Wnt1-Early^Ex and Wnt1-Late^Ex Here, we extend this initial observation and show that Wnt1-Early^Ex tumors exhibit high expression of canonical Wnt, non-canonical Wnt, and EGFR signaling pathway signatures. Therapeutically, Wnt1-Early^Ex tumors showed a dynamic reduction in tumor volume when treated with an EGFR inhibitor. Wnt1-Early^Ex tumors had primarily Cd49f^pos/Epcam^neg FACS profiles, but it was not possible to serially transplant these tumors into wild-type FVB female mice. Conversely, Wnt1-Late^Ex tumors had a bloody gross pathology, which was highlighted by the presence of 'blood lakes' identified by H&E staining. These tumors had primarily Cd49f^pos/Epcam^pos FACS profiles, but also contained a secondary Cd49f^pos/Epcam^neg subpopulation. Wnt1-Late^Ex tumors were enriched for activating Hras1 mutations and were capable of reproducing tumors when serially transplanted into wild-type FVB female mice. This study definitively shows that the MMTV-Wnt1 mouse model produces two phenotypically distinct subtypes of mammary tumors that differ in multiple biological aspects including sensitivity to an EGFR inhibitor.

Sfrp3 modulates stromal-epithelial crosstalk during mammary gland development by regulating Wnt levels

Mammary stroma is essential for epithelial morphogenesis and development. Indeed, postnatal mammary gland (MG) development is controlled locally by the repetitive and bi-directional cross-talk between the epithelial and the stromal compartment. However, the signalling pathways involved in stromal–epithelial communication are not entirely understood. Here, we identify Sfrp3 as a mediator of the stromal–epithelial communication that is required for normal mouse MG development. Using Drosophila wing imaginal disc, we demonstrate that Sfrp3 functions as an extracellular transporter of Wnts that facilitates their diffusion, and thus, their levels in the boundaries of different compartments. Indeed, loss of Sfrp3 in mice leads to an increase of ductal invasion and branching mirroring an early pregnancy state. Finally, we observe that loss of Sfrp3 predisposes for invasive breast cancer. Altogether, our study shows that Sfrp3 controls MG morphogenesis by modulating the stromal-epithelial cross-talk during pubertal development.

The signalling pathways regulating how the mammary gland stroma interacts with the epithelia to then regulate gland development are unclear. Here, the authors identify Sfrp3 as regulating stroma communication via Wnts, on deletion, this increases ductal invasion and initiates an early pregnancy state.

Correlation between SFRP1 expression and clinicopathological parameters in patients with triple-negative breast cancer

Aim: Breast cancer is a heterogeneous disease with distinct molecular and clinical behavior demanding reliable biomarkers, especially in triple-negative breast cancer (TNBC). This study seeks to improve the understanding of SFRP1 as a potential biomarker in breast cancer focusing on TNBC. Materials & methods: SFRP1 expression was investigated via immunohistochemistry with two anti-SFRP1-antibodies on tissue-microarrays of 376 invasive breast cancers. Results: Statistical analysis revealed a highly significant association between TNBC (n = 36) and SFRP1 expression (p < 0.001). SFRP1 expression was significantly associated with younger age, higher tumor stage, size and grade. Conclusion: SFRP1 expression is strongly correlated with TNBC on protein level. Associations with age and tumor grade support the role of SFRP1 as a biomarker for chemotherapy response in TNBC.

UHRF1 depletion and HDAC inhibition reactivate epigenetically silenced genes in colorectal cancer cells

BACKGROUND

Ubiquitin-like protein containing PHD and RING finger domains 1 (UHRF1) is a major regulator of epigenetic mechanisms and is overexpressed in various human malignancies. In this study, we examined the involvement of UHRF1 in aberrant DNA methylation and gene silencing in colorectal cancer (CRC).

RESULTS

CRC cell lines were transiently transfected with siRNAs targeting UHRF1, after which DNA methylation was analyzed using dot blots, bisulfite pyrosequencing, and Infinium HumanMethylation450 BeadChip assays. Gene expression was analyzed using RT-PCR and gene expression microarrays. Depletion of UHRF1 rapidly induced genome-wide DNA demethylation in CRC cells. Infinium BeadChip assays and bisulfite pyrosequencing revealed significant demethylation across entire genomic regions, including CpG islands, gene bodies, intergenic regions, and repetitive elements. Despite the substantial demethylation, however, UHRF1 depletion only minimally reversed CpG island hypermethylation-associated gene silencing. By contrast, the combination of UHRF1 depletion and histone deacetylase (HDAC) inhibition reactivated the silenced genes and strongly suppressed CRC cell proliferation. The combination of UHRF1 depletion and HDAC inhibition also induced marked changes in the gene expression profiles such that cell cycle-related genes were strikingly downregulated.

CONCLUSIONS

Our results suggest that (i) maintenance of DNA methylation in CRC cells is highly dependent on UHRF1; (ii) UHRF1 depletion rapidly induces DNA demethylation, though it is insufficient to fully reactivate the silenced genes; and (iii) dual targeting of UHRF1 and HDAC may be an effective new therapeutic strategy.

Gap Junctions and Wnt Signaling in the Mammary Gland: a Cross-Talk?

Connexins (Cxs), the building blocks of gap junctions (GJs), exhibit spatiotemporal patterns of expression and regulate the development and differentiation of the mammary gland, acting via channel-dependent and channel-independent mechanisms. Impaired Cx expression and localization are reported in breast cancer, suggesting a tumor suppressive role for Cxs. The signaling events that mediate the role of GJs in the development and tumorigenesis of the mammary gland remain poorly identified. The Wnt pathways, encompassing the canonical or the Wnt/β-catenin pathway and the noncanonical β-catenin-independent pathway, also play important roles in those processes. Indeed, aberrant Wnt signaling is associated with breast cancer. Despite the coincident roles of Cxs and Wnt pathways, the cross-talk in the breast tissue is poorly defined, although this is reported in a number of other tissues. Our previous studies revealed a channel-independent role for Cx43 in inducing differentiation or suppressing tumorigenesis of mammary epithelial cells by acting as a negative regulator of the Wnt/β-catenin pathway. Here, we provide a brief overview of mammary gland development, with emphasis on the role of Cxs in development and tumorigenesis of this tissue. We also discuss the role of Wnt signaling in similar contexts, and review the literature illustrating interplay between Cxs and Wnt pathways.

Wnt signaling in human and mouse breast cancer: Focusing on Wnt ligands, receptors and antagonists

Wnt proteins, a group of secreted glycoproteins, mainly combine with receptors Frizzled (FZD) and/or low-density-lipoprotein receptor-related proteins 5/6 (LRP5/6), initiating β-catenin-dependent and -independent signaling pathways. These pathways, which can be regulated by some secreted antagonists such as secreted Frizzled-related proteins (SFRP) and dickkopf-related protein (DKK), play a critical role in embryo development and adult homeostasis. Overactivation of Wnt signaling has been implicated in some human diseases including cancer. Wnt transgenic mice provide convincing evidence that Wnt signaling is involved in breast cancer initiation and progression, which is further strengthened by observations on human clinical breast cancer patients and studies on in vitro cultured human breast cancer cells. This review focuses on the roles of Wnt ligands, receptors and antagonists in breast cancer development instead of molecules or signaling transactivating β-catenin independent on Wnt upstream components.

SFRP1 Promoter Methylation and Renal Carcinoma Risk: A Systematic Review and Meta-Analysis

BACKGROUND/AIM

Epigenetic inactivation of tumor suppressor genes is an important molecular mechanism in the formation and development of human tumors. The purpose of our study was to evaluate the correlation between the methylation level of the secreted frizzled-related protein 1 (SFRP1) gene and the risk of renal cell carcinoma (RCC).

METHODS

The relevant literature was searched in detail in several electronic databases. The methodological heterogeneity was analyzed by meta-regression and subgroup analyses. The odds ratios (ORs) and their corresponding 95% confidence intervals (CIs) were calculated to summarize the dichotomous outcomes of our meta-analysis.

RESULTS

The ten included articles contained 535 RCC samples and 475 normal controls. The results demonstrated that the methylation level of the SFRP1 promoter region was significantly correlated with an increased incidence of RCC (OR=13.72; 95% CI: 6.01-31.28; P=0.000). Furthermore, the eligible studies that had sufficient clinical data about the RCC cases were included in the analysis, and the results indicated that the frequency of SFRP1 promoter methylation was associated with a higher histological grade (P=0.000), tumor stage (P=0.033), tumor size (≥5 cm; P=0.029), and distant metastasis (P=0.047).

CONCLUSION

Our results indicate that the methylation level of the SFRP1 promoter region is increased in patients with RCC compared to normal controls and might be involved in the occurrence and development of RCC. Additional well-designed studies are needed to further verify our conclusions.

Breast cancer stem cells: Features, key drivers and treatment options

The current view is that breast cancer is a stem cell disease characterized by the existence of cancer cells with stem-like features and tumor-initiating potential. These cells are made responsible for tumor dissemination and metastasis. Common therapies by chemotherapeutic drugs fail to eradicate these cells and rather increase the pool of cancer stem cells in tumors, an effect that may increase the likelyhood of recurrence. Fifteen years after the first evidence for a small stem-like subpopulation playing a major role in breast cancer initiation has been published a large body of knowledge has been accumulated regarding the signaling cascades and proteins involved in maintaining stemness in breast cancer. Differences in the stem cell pool size and in mechanisms regulating stemness in the different breast cancer subtypes have emerged. Overall, this knowledge offers new approaches to intervene with breast cancer stem cell activity. New options are particularly needed for the treatment of triple-negative breast cancer subtype, which is particularly rich in cancer stem cells and is also the subtype for which specific therapies are still not available.

DKK1 and Kremen Expression Predicts the Osteoblastic Response to Bone Metastasis

Bone metastasis is a complication of advanced breast and prostate cancer. Tumor-secreted Dickkopf homolog 1 (DKK1), an inhibitor of canonical Wnt signaling and osteoblast differentiation, was proposed to regulate the osteoblastic response to metastatic cancer in bone. The objectives of this study were to compare DKK1 expression with the in vivo osteoblastic response in a panel of breast and prostate cancer cell lines, and to discover mechanisms that regulate cancer DKK1 expression. DKK1 expression was highest in MDA-MB-231 and PC3 cells that produce osteolytic lesions, and hence a suppressed osteoblastic response, in animal models of bone metastasis. LnCaP, C4-2B, LuCaP23.1, T47D, ZR-75-1, MCF-7, ARCaP and ARCaP_M cancer cells that generate osteoblastic, mixed or no bone lesions had the lowest DKK1 expression. The cell lines with negligible expression, LnCaP, C4-2B and T47D, exhibited methylation of the DKK1 promoter. Canonical Wnt signaling activity was then determined and found in all cell lines tested, even in the MDA-MB-231 and PC3 cell lines despite sizeable amounts of DKK1 protein expression expected to block canonical Wnt signaling. A mechanism of DKK1 resistance in the osteolytic cell lines was investigated and determined to be at least partially due to down-regulation of the DKK1 receptors Kremen1 and Kremen2 in the MDA-MB-231 and PC3 cell lines. Combined DKK1 and Kremen expression in cancer cells may serve as predictive markers of the osteoblastic response of breast and prostate cancer bone metastasis.

Dickkopf-related protein 2 induces G0/G1 arrest and apoptosis through suppressing Wnt/β-catenin signaling and is frequently methylated in breast cancer

Dickkopf-related protein 2 (DKK2) is one of the antagonists of Wnt/β-catenin signaling, with its downregulation reported in multiple cancers. However, how DKK2 contributes to breast tumorigenesis remains unclear. We examined its expression and promoter methylation in 10 breast tumor cell lines, 98 primary tumors, and 21 normal breast tissues. Compared with normal tissues, DKK2 was frequently silenced in breast cell lines (7/8). DKK2 promoter methylation was detected in 77.8% of cell lines and 86.7% of breast tumors; while rarely detected in normal breast tissues (19%), indicating common DKK2 methylation in breast cancer. Ectopic expression of DKK2 changed breast tumor cell morphology, inhibited cell proliferation and colony formation by inducing G0/G1 cell cycle arrest and apoptosis, and suppressed tumor cell migration by reversing epithelial-mesenchymal transition (EMT) and downregulating stem cell markers. Moreover, restored expression of DKK2 in MCF7 cells disrupted the microtube formation of human umbilical vein endothelial cells on Matrigel®. In vivo, the growth of MDA-MB-231 cells in nude mice was markedly decreased after stable expression of DKK2. DKK2 suppressed canonical Wnt/β-catenin signaling by inhibiting β-catenin activity with decreased active β-catenin protein. Thus, our findings demonstrate that DKK2 functions as a tumor suppressor through inhibiting cell proliferation and inducing apoptosis via regulating Wnt signaling during breast tumorigenesis.

Dishevelled: A masterful conductor of complex Wnt signals

The Dishevelled gene was first identified in Drosophila mutants with disoriented hair and bristle polarity [1-3]. The Dsh gene (Dsh/Dvl, in Drosophila and vertebrates respectively) gained popularity when it was discovered that it plays a key role in segment polarity during early embryonic development in Drosophila [4]. Subsequently, the vertebrate homolog of Dishevelled genes were identified in Xenopus (Xdsh), mice (Dvl1, Dvl2, Dvl3), and in humans (DVL1, DVL2, DVL3) [5-10]. Dishevelled functions as a principal component of Wnt signaling pathway and governs several cellular processes including cell proliferation, survival, migration, differentiation, polarity and stem cell renewal. This review will revisit seminal discoveries and also summarize recent advances in characterizing the role of Dishevelled in both normal and pathophysiological settings.

Dickkopf homolog 3 (DKK3): A candidate for detection and treatment of cancers?

Wnt signaling is an evolutionary highly conserved pathway that is modulated by several inhibitors and activators, and plays a key role in numerous physiological processes. One of the extracellular Wnt inhibitors is the DKK (Dickkopf Homolog) family which has four members (Dkk1-4) and a unique Dkk3-related gene, Dkkl1 (soggy). DKK3 is a divergent member of the DKK protein family. Evidence suggests that DKK3 may serve as a potential therapeutic target in several types of human cancers. We review here the biological role of DKK3 as a tumor suppressor gene (TSG) or oncogene, and its correlation with various miRNAs. In addition, we discuss the role of polymorphisms and promoter methylation of the DKK3 gene, and of its expression in regulating cancer cell proliferation. Finally, we propose that DKK3 may be considered as both a biomarker and a therapeutic target in different cancers.