WNT pathway and mammary carcinogenesis: loss of expression of candidate tumor suppressor gene SFRP1 in most invasive carcinomas except of the medullary type

Deciphering Stromal Changes between Metastatic and Non-metastatic Canine Mammary Carcinomas

Cancer-associated stroma (CAS) is widely recognized to influence development and progression of epithelial tumours including breast cancer. Canine mammary tumours (CMTs) such as simple canine mammary carcinomas represent valuable models for human breast cancer also with respect to stromal reprogramming. However, it remains unclear whether and how CAS changes in metastatic tumours compared to non-metastatic ones. To characterize stromal changes between metastatic and non-metastatic CMTs and identify potential drivers of tumour progression, we analysed CAS and matched normal stroma from 16 non-metastatic and 15 metastatic CMTs by RNA-sequencing of microdissected FFPE tissue. We identified 1438 differentially regulated genes between CAS and normal stroma, supporting previous results demonstrating stromal reprogramming in CMTs to be comparable with CAS in human breast cancer and validating deregulation of pathways and genes associated with CAS. Using primary human fibroblasts activated by treatment with TGFβ, we demonstrate some of the strongest expression changes to be conserved in fibroblasts across species. Furthermore, we identify 132 differentially expressed genes between CAS from metastatic and non-metastatic tumours, with strong changes in pathways including chemotaxis, regulation of apoptosis, immune response and TGFβ signalling and validate deregulation of several targets using RT-qPCR. Finally, we identify specific upregulation of COL6A5, F5, GALNT3, CIT and MMP11 in metastatic CAS, suggesting high stromal expression of these targets to be linked to malignancy and metastasis of CMTs. In summary, our data present a resource supporting further research into stromal changes of the mammary gland in relation to metastasis with implications for both canine and human mammary cancer.

A comprehensive review of stroke-related signaling pathways and treatment in western medicine and traditional Chinese medicine

This review provides insight into the complex network of signaling pathways and mechanisms involved in stroke pathophysiology. It summarizes the historical progress of stroke-related signaling pathways, identifying potential interactions between them and emphasizing that stroke is a complex network disease. Of particular interest are the Hippo signaling pathway and ferroptosis signaling pathway, which remain understudied areas of research, and are therefore a focus of the review. The involvement of multiple signaling pathways, including Sonic Hedgehog (SHH), nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE), hypoxia-inducible factor-1α (HIF-1α), PI3K/AKT, JAK/STAT, and AMPK in pathophysiological mechanisms such as oxidative stress and apoptosis, highlights the complexity of stroke. The review also delves into the details of traditional Chinese medicine (TCM) therapies such as Rehmanniae and Astragalus, providing an analysis of the recent status of western medicine in the treatment of stroke and the advantages and disadvantages of TCM and western medicine in stroke treatment. The review proposes that since stroke is a network disease, TCM has the potential and advantages of a multi-target and multi-pathway mechanism of action in the treatment of stroke. Therefore, it is suggested that future research should explore more treasures of TCM and develop new therapies from the perspective of stroke as a network disease.

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.

Wnt Signaling in the Breast: From Development to Disease

The Wnt cascade is a primordial developmental signaling pathway that plays a myriad of essential functions throughout development and adult homeostasis in virtually all animal species. Aberrant Wnt activity is implicated in embryonic and tissue morphogenesis defects, and several diseases, most notably cancer. The role of Wnt signaling in mammary gland development and breast cancer initiation, maintenance, and progression is far from being completely understood and is rather shrouded in controversy. In this review, we dissect the fundamental role of Wnt signaling in mammary gland development and adult homeostasis and explore how defects in its tightly regulated and intricated molecular network are interlinked with cancer, with a focus on the breast.

In Vitro Anti-cancer Effect of Crataegus oxyacantha Berry Extract on Hormone Receptor Positive and Triple Negative Breast Cancers via Regulation of Canonical Wnt Signaling Pathway

Breast cancer treatment strategy depends mainly on the receptor status. Our aim was to identify a herbal preparation, effective against breast cancer, irrespective of hormone sensitivity, and to understand its molecular mechanism. The rich antioxidant composition of hawthorn (Crataegus oxyacantha) makes it a promising anti-cancer drug candidate. Polyphenol-rich methanolic extract of C. oxyacantha berry (M.Co) was found to be cytotoxic on hormone receptor positive (MCF-7) and triple negative (MDA-MB-231) breast cancer cell lines, at a dose (75 μg/ml) safe on normal cells. It could effectively inhibit tumor cell proliferation and arrest cell cycle at G1/S transition in both cell lines. Molecular targets were selected from different levels of canonical Wnt signaling pathway (such as autocrine and antagonistic ligands, receptor, effector, cytoplasmic components, downstream targets, and pathway antagonist), since they are frequently found dysregulated in all breast cancers and their aberrant activation is associated with cancer stem cell expansion. M.Co could significantly downregulate the expression of Wnt pathway agonists and upregulate that of Wnt antagonists at transcriptional and translational levels, in both cell lines. To conclude, C. oxyacantha berry extract is effective against breast cancer irrespective of its hormone dependency, and cancer growth inhibition at stem cell level can be expected.

Wnt signaling and mammary stem cells

Wnt signaling is an important morphogenetic signaling pathway best known for its essential role in determining embryonic cell fates; it is often activated to re-specify fetal cells or to maintain the lineage flexibility of somatic stem cells. In this review, we consider the role of this pathway in the remarkable process of differentiation, growth and morphogenesis of the mammary gland during embryogenesis, ductal outgrowth and pregnancy. Specifically, mammary stem cells are compared with stem cells from other tissues, to identify commonalities and differences. Wnt signaling is known to be required to maintain the bipotent basal stem cell present in adult mammary ductal trees, however, the absence of this stem cell has little effect on growth or morphogenesis, and Wnt signaling is not induced during the ductal/alveolar expansion during pregnancy. The evidence for pre-determined hierarchies of mammary epithelial cells is reviewed, together with the role of signaling between mixtures of specified mammary epithelial cells in the maintenance of Wnt-dependent clonagenic stem cells. The dazzling variety of Wnt signaling components expressed by mammary epithelial cells is presented, along with some potential stromal sources of Wnt proteins that may be important starting points for the induction of plasticity in the epithelium.

R-Spondins 2 and 3 Are Overexpressed in a Subset of Human Colon and Breast Cancers

Wnt signaling is activated in many cancer types, yet targeting the canonical Wnt pathway has been challenging for cancer therapy. The pathway might be effectively targeted at many levels depending on the mechanism by which it has become hyperactive. Recently, mouse genetic screens have found that R-spondins (RSPOs) act as oncogenes. Evidence includes recurrent genomic rearrangements that led to increased RSPO2 or RSPO3 expression in human colorectal adenocarcinomas, exclusive of APC mutations. RSPOs modulate Wnt signaling to promote epithelial cell proliferation and survival. These secreted proteins modulate Wnt signaling by binding to G-coupled receptors LGR4/5/6, ultimately inhibiting frizzled membrane clearance by RNF43 and ZNRF3. They also exert their function independent of leucine-rich repeat-containing, G protein-coupled receptors (LGRs) by binding to ZNRF3 and RNF43. This results in increased β-catenin concentration that, after translocation to the nucleus, acts as a transcriptional coactivator of genes necessary for proliferation and cell survival. In this article, we aimed to identify the role of RSPOs in colon and breast cancers by using in silico and in vitro studies. We found that expression of RSPO2 and RSPO3 at high levels characterized a subset of colorectal cancers (CRCs). RSPO2 expression was found to characterize a subset of triple-negative breast cancers. In both instances, increased expression of RSPOs was associated with an activated Wnt signaling gene expression profile. Furthermore, knockdown of RSPO2 decreased Wnt signaling and proliferation in human breast cancer cells. Our findings show and confirm that RSPO2 and RSPO3 expression is upregulated in a subset of colorectal adenocarcinomas and breast cancers and that both are attractive druggable oncoprotein targets against such cancers. We also describe novel fusion transcripts that occur in CRC.

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.

R-spondin 2 Drives Liver Tumor Development in a Yes-Associated Protein-Dependent Manner

Each year, more than 25,000 people succumb to liver cancer in the United States, and this neoplasm represents the second cause of cancer-related death globally. R-spondins (RSPOs) are secreted regulators of Wnt signaling that function in development and promote tissue stem cell renewal. In cancer, RSPOs 2 and 3 are oncogenes first identified by insertional mutagenesis screens in tumors induced by mouse mammary tumor virus and by transposon mutagenesis in the colonic epithelium of rodents. RSPO2 has been reported to be activated by chromosomal rearrangements in colorectal cancer and overexpressed in a subset of hepatocellular carcinoma. Using human liver tumor gene expression data, we first discovered that a subset of liver cancers were characterized by high levels of RSPO2 in contrast to low levels in adjacent nontumor tissue. To determine if RSPOs are capable of inducing liver tumors, we used an in vivo model from which we found that overexpression of RSPO2 in the liver promoted Wnt signaling, hepatomegaly, and enhanced liver tumor formation when combined with loss of transformation-related protein 53 (Trp53). Moreover, the Hippo/yes-associated protein (Yap) pathway has been implicated in many human cancers, influencing cell survival. Histologic and gene expression studies showed activation of Wnt/β-catenin and Hippo/Yap pathways following RSPO2 overexpression. We demonstrate that knockdown of Yap1 leads to reduced tumor penetrance following RSPO2 overexpression in the context of loss of Trp53. Conclusion: RSPO2 overexpression leads to tumor formation in the mouse liver in a Hippo/Yap-dependent manner. Overall, our results suggest a role for Yap in the initiation and progression of liver tumors and uncover a novel pathway activated in RSPO2-induced malignancies. We show that RSPO2 promotes liver tumor formation in vivo and in vitro and that RSPO2's oncogenic activity requires Hippo/Yap activation in hepatocytes. Both RSPO2 and YAP1 are suggested to represent novel druggable targets in Wnt-driven tumors of the liver.

Mycoplasma hyorhinis infection promotes gastric cancer cell motility via β-catenin signaling

Background

We previously identified that Mycoplasma hyorhinis infection promotes gastric cancer cell motility. The β‐catenin signaling pathway is critical to determining malignant cancer cell phenotypes; however, the association between M hyorhinis and the β‐catenin signaling pathway is unclear.

Methods

We performed subcellular fractionation and immunofluorescence staining to observe β‐catenin accumulation in the nucleus. The expression of downstream β‐catenin genes was detected by quantitative RT‐PCR. Gastric cancer cell motility was examined by transwell chamber migration and wound healing assays, and a co‐immunoprecipitation assay was used to detect the proteins associated with the membrane protein p37 of M hyorhinis.

Results

We found that M hyorhinis infection promoted nuclear β‐catenin accumulation and enhanced the expression of downstream β‐catenin genes. M hyorhinis‐promoted gastric cancer cell motility was counteracted by treatment with the β‐catenin inhibitor XAV939 or β‐catenin knockdown. We further detected a protein complex containing LRP6, GSK3β, and p37 in M hyorhinis‐infected cells. M hyorhinis also induced LRP6 phosphorylation in a GSK3β‐dependent fashion. Knockdown of LRP6 or GSK3β abolished M hyorhinis‐induced cell motility.

Conclusion

Our results reveal that the β‐catenin signaling pathway could be activated by M hyorhinis infection, thereby contributing to M hyorhinis‐induced gastric cancer cell motility.

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.

sFRP1 exerts effects on gastric cancer cells through GSK3β/Rac1‑mediated restraint of TGFβ/Smad3 signaling

Secreted frizzled-related protein 1 (sFRP1) is an inhibitor of canonical Wnt signaling; however, previous studies have determined a tumor-promoting function of sFRP1 in a number of different cancer types. A previous study demonstrated that sFRP1 overexpression was associated with an aggressive phenotype and the activation of transforming growth factor β (TGFβ) signaling. sFRP1 overexpression and sFRP1 knockdown cell models were established. Immunoblotting was conducted to examine the protein levels of the associated molecules. Immunofluorescence staining followed by confocal microscopy was performed to visualize the cytoskeleton alterations and subcellular localization of key proteins. sFRP1 overexpression restored glycogen synthase kinase 3β (GSK3β) activity, which activated Rac family small GTPase 1 (Rac1). GSK3β and Rac1 mediated the effect of sFRP1 on the positive regulation of cell growth and migration/invasion. Inhibition of GSK3β or Rac1 abolished the regulation of sFRP1 on TGFβ/SMAD family member 3 (Smad3) signaling and the aggressive phenotype; however, GSK3β or Rac1 overexpression increased cell migration/invasion and restrained Smad3 activity by preventing its nuclear translocation and limiting its transcriptional activity. The present study demonstrated a tumor-promoting function of sFRP1-overexpression by selectively activating TGFβ signaling in gastric cancer cells. GSK3β and Rac1 serve an important function in mediating the sFRP1-induced malignant alterations and signaling changes.

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.

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.

Identification of Differentially Expressed Genes in Prostatic Epithelium in Relation to Androgen Receptor CAG Repeat Length

The CAG repeat within exon 1 of the androgen receptor (AR) has been associated with the development of prostate cancer. The shorter number of glutamine residues in the protein has been associated with a higher transcriptional activity of the AR and increased relative risk for prostate cancer. In an attempt to identify differentially expressed genes in prostate cancer in relation to AR CAG repeat length variation, in this study we used total mRNA from normal and tumor tissues from 2 prostate cancer patients with AR alleles containing 19 and 26 CAG repeats to perform differential-display RT-PCR analysis. We were able to identify 48 different transcripts that showed homology to several known genes associated with different biological pathways. Among the differentially expressed genes, ATRX and SFRP1 were further validated by quantitative RT-PCR. The transcripts of both ATRX and SFRP1 genes proved to be down-regulated in most of the prostate tumors analyzed by quantitative RT-PCR. Hypermethylation of the promoter region of the SFRP1 gene was found in 17.5% (7/40) of the cases analyzed and was associated with the loss of SFRP1 expression (p=0.014). The differentially expressed genes identified in this study are implicated in several cellular pathways that, when up- or down-regulated, might play a role in the tumorigenic process of the prostate.

High-frequency deregulated expression of Wnt signaling pathway members in breast carcinomas

Purpose

Breast carcinoma is the most common malignancy and leading cause of cancer-related deaths in women worldwide including Saudi Arabia. Breast cancer in Saudi women develops at a much early age with median age of onset of 49 years compared to 62 years observed in patients from USA. Aberrations in wingless and integration site growth factor (Wnt) signaling pathway have been pathologically implicated in development of breast cancers and hence its role was examined in Saudi patients.

Materials and methods

We immunohistochemically examined various components of Wnt signaling pathway including β-catenin, tumor suppressor proteins, adenomatous polyposis coli (APC), and Axin, expression of naturally occurring pathway antagonists such as Dickkopf Wnt signaling pathway inhibitor 3 (DKK3), FRP2, and WIF1, as well as Wnt target cyclin D1 and c-Myc to establish if the pathway is constitutively activated in breast cancers arising in Saudi women.

Results

Cytoplasmic β-catenin, indicative of activation of the pathway, was observed in 24% of cases. Expression of APC and Axin, which are components of β-catenin destruction complex, was lost in 5% and 10% of tumors, respectively. Additionally, Wnt signaling inhibitors DKK3, FRP2, and Wnt inhibitory factor 1 (WIF1) were not expressed in 8%, 14%, and 5% breast tumors, respectively. Overall, accumulation of cytoplasmic β-catenin and downregulation of other Wnt pathway proteins (APC/Axin/DKK3/FRP2/WIF1) were found in approximately half of the breast cancers (47%) in our cohort. Consistent with this, analysis of Wnt target genes demonstrated moderate-to-strong expression of c-Myc in 58% and cyclin D1 in 50% of breast cancers. Deregulation of Wnt pathway was not associated with age of onset of the disease, tumor grade, and triple-negative status of breast cancers.

Conclusions

High level of deregulated expression of Wnt pathway proteins suggests its important role in pathogenesis of breast cancers arising in Saudi women who may benefit from development of therapeutic drugs targeting this pathway.

Molecular Signaling of Progesterone, Growth Hormone, Wnt, and HER in Mammary Glands of Dogs, Rodents, and Humans: New Treatment Target Identification

Mammary tumors are the most common form of neoplasia in the bitch. Female dogs are protected when they are spayed before the first estrus cycle, but this effect readily disappears and is already absent when dogs are spayed after the second heat. As the ovaries are removed during spaying, ovarian steroids are assumed to play an essential role in tumor development. The sensitivity toward tumor development is already present during early life, which may be caused by early mutations in stem cells during the first estrus cycles. Later on in life, tumors arise that are mostly steroid-receptor positive, although a small subset of tumors overexpressing human epidermal growth factor 2 (HER2) and some lacking estrogen receptor, progesterone receptor (PR), and HER2 (triple negative) are present, as is the situation in humans. Progesterone (P₄), acting through PR, is the major steroid involved in outgrowth of mammary tissue. PRs are expressed in two forms, the progesterone receptor A (PRA) and progesterone receptor B (PRB) isoforms derived from splice variants from a single gene. The dog and the whole family of canids have only a functional PRA isoform, whereas the PRB isoform, if expressed at all, is devoid of intrinsic biological activity. In human breast cancer, overexpression of the PRA isoform is related to more aggressive carcinomas making the dog a unique model to study PRA-related mammary cancer. Administration of P₄ to adult dogs results in local mammary expression of growth hormone (GH) and wing less-type mouse mammary tumor virus integration site family 4 (Wnt4). Both proteins play a role in activation of mammary stem cells. In this review, we summarize what is known on P₄, GH, and Wnt signaling in canine mammary cancer, how the family of HER receptors could interact with this signaling, and what this means for comparative and translational oncological aspects of human breast cancer development.

Breast Cancer: A Molecular and Redox Snapshot

SIGNIFICANCE

Breast cancer is a unique disease characterized by heterogeneous cell populations causing roadblocks in therapeutic medicine, owing to its complex etiology and primeval understanding of the biology behind its genesis, progression, and sustenance. Globocan statistics indicate over 1.7 million new breast cancer diagnoses in 2012, accounting for 25% of all cancer morbidities.

RECENT ADVANCES

Despite these dismal statistics, the introduction of molecular gene signature platforms, progressive therapeutic approaches in diagnosis, and management of breast cancer has led to more effective treatment strategies and control measures concurrent with an equally reassuring decline in the mortality rate.

CRITICAL ISSUES

However, an enormous body of research in this area is requisite as high mortality associated with metastatic and/or drug refractory tumors continues to present a therapeutic challenge. Despite advances in systemic chemotherapy, the median survival of patients harboring metastatic breast cancers continues to be below 2 years.

FUTURE DIRECTIONS

Hence, a massive effort to scrutinize and evaluate chemotherapeutics on the basis of the molecular classification of these cancers is undertaken with the objective to devise more attractive and feasible approaches to treat breast cancers and improve patients' quality of life. This review aims to summarize the current understanding of the biology of breast cancer as well as challenges faced in combating breast cancer, with special emphasis on the current battery of treatment strategies. We will also try and gain perspective from recent encounters on novel findings responsible for the progression and metastatic transformation of breast cancer cells in an endeavor to develop more targeted treatment options. Antioxid. Redox Signal. 25, 337-370.

MicroRNA-206 is differentially expressed in Brca1-deficient mice and regulates epithelial and stromal cell compartments of the mouse mammary gland

Depletion of Brca1 leads to defects in mouse mammary gland development and mammary tumors in humans and mice. To explore the role of microRNAs (miRNAs) in this process, we examined the mammary glands of MMTV-Cre Brca1^Co/Co mice for differential miRNA expression using a candidate approach. Several miRNAs were differentially expressed in mammary tissue at day 1 of lactation and in mammary epithelial cell lines in which Brca1 messenger RNA (mRNA) levels have been reduced. Functional studies revealed that several of these miRNAs regulate mammary epithelial cell function in vitro, including miR-206. Creation and analysis of MMTV-miR-206 transgenic mice showed no effect on lactational mammary development and no tumors, but indicates a role in mammary tissue remodeling in mature mice, potentially involving Igf-1 and Sfrp1. These results indicate the potential of miRNAs to mediate the consequences of Brca1 loss and suggest a novel function for miR-206.

Genetic Variants in the Wnt Signaling Pathway Are Not Associated with Survival Outcome of Non-Small Cell Lung Cancer in a Korean Population

Recently, genetic variants in the WNT signaling pathway have been reported to affect the survival outcome of Caucasian patients with early stage non-small cell lung cancer (NSCLC). We therefore attempted to determine whether these same WNT signaling pathway gene variants had similar impacts on the survival outcome of NSCLC patients in a Korean population. A total of 761 patients with stages I-IIIA NSCLC were enrolled in this study. Eight variants of WNT pathway genes were genotyped and their association with overall survival and disease-free survival were analyzed. None of the eight variants were significantly associated with overall survival or disease-free survival. There were no differences in survival outcome after stratifying the subjects according to age, gender, smoking status, and histological type. These results suggest that genetic variants in the WNT signaling pathway may not affect the survival outcome of NSCLC in a Korean population.

Arsenic trioxide inhibits viability and induces apoptosis through reactivating the Wnt inhibitor secreted frizzled related protein-1 in prostate cancer cells

Background

Growing evidence suggests that arsenic trioxide (As₂O₃) induces apoptosis and inhibits tumor cell growth in prostate cancer (PCa), although details of the mechanism are still inconclusive. We investigated the antitumor effect of As₂O₃ in human PCa cell lines LNCaP and PC3 and the underlying mechanisms by focusing on the Wnt signaling pathway.

Methods

The effect of As₂O₃ on the viability and apoptosis of PCa cells was investigated by cholecystokinin-8 and flow cytometry. The expression of the related proteins in the Wnt signaling pathway and the downstream target genes of the Wnt signaling pathway was examined by Western blot and quantitative real-time PCR assay. The methylation status of the SFRP1 gene promoter was assessed by bisulfite sequencing.

Results

As₂O₃ inhibited the viability of PCa cells and induced apoptosis of PCa cells in a dose-dependent manner. The protein level of phosphoglycogen synthase kinase-3β was upregulated, whereas the protein level of β-catenin and the mRNA levels of c-MYC, MMP-7, and COX-2 were downregulated in a dose-dependent manner in PCa cells treated with As₂O₃. In addition, As₂O₃ upregulated the protein and mRNA levels of secreted frizzled related protein-1, and increased the demethylation of the SFRP1 gene promoter.

Conclusion

Our results suggest that As₂O₃ may inhibit cell viability and induce apoptosis through reactivating the Wnt inhibitor secreted frizzled related protein-1 in both androgen-dependent and -independent human PCa.

Characterization of a beta-catenin nuclear localization defect in MCF-7 breast cancer cells

Beta-catenin plays a key role in transducing Wnt signals from the plasma membrane to the nucleus. Here we characterize an unusual subcellular distribution of beta-catenin in MCF-7 breast cancer cells, wherein beta-catenin localizes to the cytoplasm and membrane but atypically did not relocate to the nucleus after Wnt treatment. The inability of Wnt or the Wnt agonist LiCl to induce nuclear localization of beta-catenin was not due to defective nuclear transport, as the transport machinery was intact and ectopic GFP-beta-catenin displayed rapid nuclear entry in living cells. The mislocalization is explained by a shift in the retention of beta-catenin from nucleus to cytoplasm. The reduced nuclear retention is caused by unusually low expression of lymphoid enhancer factor/T-cell factor (LEF/TCF) transcription factors. The reconstitution of LEF-1 or TCF4 expression rescued nuclear localization of beta-catenin in Wnt treated cells. In the cytoplasm, beta-catenin accumulated in recycling endosomes, golgi and beta-COP-positive coatomer complexes. The peripheral association with endosomes diminished after Wnt treatment, potentially releasing β-catenin into the cytoplasm for nuclear entry. We propose that in MCF-7 and perhaps other breast cancer cells, beta-catenin may contribute to cytoplasmic functions such as ER-golgi transport, in addition to its transactivation role in the nucleus.

Aberrant DNA methylation impacts gene expression and prognosis in breast cancer subtypes

DNA methylation has a substantial impact on gene expression, affecting the prognosis of breast cancer (BC) patients dependent on molecular subtypes. In this study, we investigated the prognostic relevance of the expression of genes reported as aberrantly methylated, and the link between gene expression and DNA methylation in BC subtypes. The prognostic value of the expression of 144 aberrantly methylated genes was evaluated in ER+/HER2-, HER2+, and ER-/HER2- molecular BC subtypes, in a meta-analysis of two large transcriptomic cohorts of BC patients (n = 1,938 and n = 1,640). The correlation between gene expression and DNA methylation in distinct gene regions was also investigated in an independent dataset of 104 BCs. Survival and Pearson correlation analyses were computed for each gene separately. The expression of 48 genes was significantly associated with BC prognosis (p < 0.05), and 32 of these prognostic genes exhibited a direct expression-methylation correlation. The expression of several immune-related genes, including CD3D and HLA-A, was associated with both relapse-free survival (HR = 0.42, p = 3.5E-06; HR = 0.35, p = 1.7E-08) and overall survival (HR = 0.50, p = 5.5E-04; HR = 0.68, p = 4.5E-02) in ER-/HER2- BCs. On the overall, the distribution of both positive and negative expression-methylation correlation in distinct gene regions have different effects on gene expression and prognosis in BC subtypes. This large-scale meta-analysis allowed the identification of several genes consistently associated with prognosis, whose DNA methylation could represent a promising biomarker for prognostication and clinical stratification of patients with distinct BC subtypes.

The Discovery of Novel Biomarkers Improves Breast Cancer Intrinsic Subtype Prediction and Reconciles the Labels in the METABRIC Data Set

BACKGROUND

The prediction of breast cancer intrinsic subtypes has been introduced as a valuable strategy to determine patient diagnosis and prognosis, and therapy response. The PAM50 method, based on the expression levels of 50 genes, uses a single sample predictor model to assign subtype labels to samples. Intrinsic errors reported within this assay demonstrate the challenge of identifying and understanding the breast cancer groups. In this study, we aim to: a) identify novel biomarkers for subtype individuation by exploring the competence of a newly proposed method named CM1 score, and b) apply an ensemble learning, as opposed to the use of a single classifier, for sample subtype assignment. The overarching objective is to improve class prediction.

METHODS AND FINDINGS

The microarray transcriptome data sets used in this study are: the METABRIC breast cancer data recorded for over 2000 patients, and the public integrated source from ROCK database with 1570 samples. We first computed the CM1 score to identify the probes with highly discriminative patterns of expression across samples of each intrinsic subtype. We further assessed the ability of 42 selected probes on assigning correct subtype labels using 24 different classifiers from the Weka software suite. For comparison, the same method was applied on the list of 50 genes from the PAM50 method.

CONCLUSIONS

The CM1 score portrayed 30 novel biomarkers for predicting breast cancer subtypes, with the confirmation of the role of 12 well-established genes. Intrinsic subtypes assigned using the CM1 list and the ensemble of classifiers are more consistent and homogeneous than the original PAM50 labels. The new subtypes show accurate distributions of current clinical markers ER, PR and HER2, and survival curves in the METABRIC and ROCK data sets. Remarkably, the paradoxical attribution of the original labels reinforces the limitations of employing a single sample classifiers to predict breast cancer intrinsic subtypes.

Diagnostic value of SFRP1 as a favorable predictive and prognostic biomarker in patients with prostate cancer

Growing genetic and molecular biological evidence suggests that the disruption of balance between Secreted Frizzled-Related Protein-1 (SFRP1) and β-catenin plays an important role in the initiation and development of multiple cancers. The aim of this study was to examine whether the expression of SFRP1 and β-catenin is associated with the clinical-pathologic features of patients with prostate cancer (PCa), and to evaluate their potential roles as predictive and prognostic biomarkers. In this study, a total of 61 patients with PCa and 10 patients with benign prostatic hyperplasia were included, and we showed that the expression of SFRP1 and β-catenin was correlated with the Gleason score, survival rate and response for endocrine therapy of PCa. The survival rates of PCa patients with low SFRP1 expression (P = 0.016) or high β-catenin expression (P = 0.004) were significantly poorer. A negative correlation (r = -0.275, P = 0.032) between SFRP1 and β-catenin was observed by Chi-square test. Multivariate analysis suggested that SFRP1 (hazard ratio, 0.429; 95% confidence intervals, 0.227–0.812; P = 0.009) may serve as an independent predictive and prognostic factor for PCa. We also showed that the protein and mRNA levels of SFRP1 in androgen-dependent PCa cell line LNCaP were significantly higher than those in androgen-independent PCa cell lines DU145 and PC3. However, the protein level of β-catenin in LNCaP cells was significantly lower than that in DU145 and PC3 cells, and no significant difference of β-catenin mRNA level was observed in LNCaP, DU145 and PC3 cells. Bisulfite sequencing PCR assay revealed significantly lower methylation level of SFRP1 promoter in LNCaP cells than that in DU145 and PC3 cells. Taken together, these findings suggest that SFRP1, which expression inversely correlates with that of β-catenin, is a favorable predictive and prognostic biomarker.

Identification of coexistence of DNA methylation and H3K27me3 specifically in cancer cells as a promising target for epigenetic therapy

Alterations of epigenetic modifications are promising targets for cancer therapy, and several epigenetic drugs are now being clinically utilized. At the same time, individual epigenetic modifications have physiological functions in normal cells, and cancer cell specificity is considered difficult to achieve using a drug against a single epigenetic modification. To overcome this limitation, a combination of epigenetic modifications specifically or preferentially present in cancer cells is a candidate target. In this study, we aimed to demonstrate (i) the presence of a cancer cell-specific combination of epigenetic modifications by focusing on DNA methylation and trimethylation of histone H3 lysine 27 (H3K27me3) and (ii) the therapeutic efficacy of a combination of DNA demethylation and EZH2 inhibition. Analyses of DNA methylation and H3K27me3 in human colon, breast and prostate cancer cell lines revealed that 24.7±4.1% of DNA methylated genes had both DNA methylation and H3K27me3 (dual modification) in cancer cells, while it was 11.8±7.1% in normal cells. Combined treatment with a DNA demethylating agent, 5-aza-2'-deoxycytidine (5-aza-dC) and an EZH2 inhibitor, GSK126, induced marked re-expression of genes with the dual modification, including known tumor-suppressor genes such as IGFBP7 and SFRP1, and showed an additive inhibitory effect on growth of cancer cells in vitro. Finally, an in vivo combined treatment with 5-aza-dC and GSK126 inhibited growth of xenograft tumors more efficiently than a single treatment with 5-aza-dC. These results showed that the dual modification exists specifically in cancer cells and is a promising target for cancer cell-specific epigenetic therapy.

Differential expression of centrosome regulators in Her2+ breast cancer cells versus non-tumorigenic MCF10A cells

Centrosome amplification (CA) amongst particular breast cancer subtypes (Her2+ subtype) is associated with genomic instability and aggressive tumor phenotypes. However, changes in signaling pathways associated with centrosome biology have not been fully explored in subtype specific models. Novel centrosome regulatory genes that are selectively altered in Her2+ breast cancer cells are of interest in discerning why CA is more prevalent in this subtype. To determine centrosome/cell cycle genes that are altered in Her2+ cells that display CA (HCC1954) versus non-tumorigenic cells (MCF10A), we carried out a gene microarray. Expression differences were validated by real-time PCR and Western blotting. After the microarray validation, we pursued a panel of upregulated and downregulated genes based on novelty/relevance to centrosome duplication. Functional experiments measuring CA and BrdU incorporation were completed after genetic manipulation of targets (TTK, SGOL1, MDM2 and SFRP1). Amongst genes that were downregulated in HCC1954 cells, knockdown of MDM2 and SFRP1 in MCF10A cells did not consistently induce CA or impaired BrdU incorporation. Conversely, amongst upregulated genes in HCC1954 cells, knockdown of SGOL1 and TTK decreased CA in breast cancer cells, while BrdU incorporation was only altered by SGOL1 knockdown. We also explored the Kaplan Meier Plot resource and noted that MDM2 and SFRP1 are positively associated with relapse free survival in all breast cancer subtypes, while TTK is negatively correlated with overall survival of Luminal A patients. Based on this functional screen, we conclude that SGOL1 and TTK are important modulators of centrosome function in a breast cancer specific model.

The Wnt antagonist sFRP1 as a favorable prognosticator in human biliary tract carcinoma

Inactivation of Secreted Frizzled-Related Protein-1 (SFRP1) and overexpression of β-catenin play important roles in the development and progression of a wide range of malignancies. We sought to determine whether the expression of SFRP1 and β-catenin correlates with clinicopathologic parameters in human biliary tract cancer (BTC) and to evaluate the potential roles of these proteins as prognostic indicators. The expression of SFRP1 and β-catenin in 78 patients with BTC and 36 control patients as investigated by immunohistochemistry. A wide variety of statistical parameters were assessed to determine the association between these proteins and the occurrence, clinical features, and overall survival rate in BTC.SFRP1 and β-catenin had an inverse correlation (r = -0.636, P<0.0001) as assessed by Spearman rank analysis, with 52 (66.7%) of the BTC samples negative for SFRP1 expression and 53 (68.0%) positive for β-catenin expression. Expression of each protein was associated with the histological type and lymph node invasion of BTC. A significantly poorer overall survival rate was observed for patients with low SFRP1 expression (P<0.0001) or high β-catenin expression (P = 0.007). SFRP1 expression (P<0.0001), β-catenin expression (P<0.01) and histological type (P<0.01) were correlated with overall survival rate as assessed by univariate analysis; while multivariate analysis suggested that SFRP1 (hazard ratio, 10.514; 95% confidence intervals, 2.381-39.048; P<0.0001) may serve as an independent prognostic factor for BTC. Collectively, these results demonstrate that SFRP1 is a favorable prognostic factor for human BTC and that its expression inversely correlates with that of β-catenin.

Hyperpolarized (3)He diffusion MRI and histology of secreted frizzled related protein-1 (SFRP1) deficient lungs in a Murine model

Secreted frizzled related protein-1 (SFRP1) plays a key role in many diverse processes, including embryogenesis, tissue repair, bone formation, and tumor genesis. Previous studies have shown the effects of the SFRP1 gene on lung development using the SFRP1 knockout mouse model via histological and physiological studies. In this study, the feasibility of ADC (acquired via HP (3)He) to detect altered lung structure in the SFRP1 knockout (SFRP1(-/-)) mice was investigated, and compared to analysis by histology. This study consisted of two groups, the wild-type (WT) mice and the knockout (KO) mice with n=6 mice for each group. (3)He ADC MRI and histology were performed on all of the animals. The global Lm values of WT and KO mice were 35.0±0.8μm and 38.4±3.8μm, respectively, which translated to an increase of 9.58% in the Lm of KO mice. The mean global ADCs for the WT and KO mice were 0.12±0.01cm(2)/s and 0.13±0.01cm(2)/s, respectively, which equated to a relative increase of 8.0% in the KO mice compared to the WT mice. In the sub-analysis of the anterior, medial and posterior lung regions, Lm increased by 10.50%, 6.66% and 11.84% in the KO mice, respectively, whereas the differences in ADC between the two groups in the anterior, medial, and posterior regions were 7.3%, 8.3%, and 4.6%, respectively. These results suggest that HP MRI measurements can be used as a suitable substitute for histology to obtain valuable information about lung geometry non-invasively. This technique is also advantageous as regional measurements can be performed, which can identify lung destruction more precisely. Most importantly, this approach extends far beyond the specific pathology analyzed in this study, as it can be applied to many other pathological conditions in the lung tissue, as well to many other embryonic studies.

Secreted frizzled related proteins: Implications in cancers

The Wnt (wingless-type) signaling pathway plays an important role in embryonic development, tissue homeostasis, and tumor progression becaluse of its effect on cell proliferation, migration, and differentiation. Secreted frizzled-related proteins (SFRPs) are extracellular inhibitors of Wnt signaling that act by binding directly to Wnt ligands or to Frizzled receptors. In recent years, aberrant expression of SFRPs has been reported to be associated with numerous cancers. As gene expression of SFRP members is often lost through promoter hypermethylation, inhibition of methylation through the use of epigenetic modifying agents could renew the expression of SFRP members and further antagonize deleterious Wnt signaling. Several reports have described epigenetic silencing of these Wnt signaling antagonists in various human cancers, suggesting their possible role as tumor suppressors. SFRP family members thus come across as potential tools in combating Wnt-driven tumorigenesis. However, little is known about SFRP family members and their role in different cancers. This review comprehensively covers all the available information on the role of SFRP molecules in various human cancers.

Suppression of Wnt signaling by the miR-29 family is mediated by demethylation of WIF-1 in non-small-cell lung cancer

Wnt inhibitory factor-1 (WIF-1) silencing induced by promoter hypermethylation is a common mechanism of aberrant activation of the Wnt signaling pathway in non-small-cell lung cancer (NSCLC). However, the activity of regulators associated with the methylation of the WIF-1 gene remains unclear. Here, we investigated the role of three DNA methyltransferases (DNMT1, DNMT3A and DNMT3B) in the expression of WIF-1. The three DNMTs were up-regulated in NSCLC tumor tissues and suppression of DNMT3A and DNMT3B restored the expression of WIF-1 in NSCLC cells. The miR-29 family (miR-29a, -29b, and -29c), which negatively regulates DNMT3A and DNMT3B, was examined in association with the Wnt/β-catenin signaling pathway. A positive correlation between the expression of WIF-1 and that of MiR-29s was observed in NSCLC tissues. Methylation-specific PCR and Western blotting indicated that miR-29s positively regulate WIF-1 expression by inhibiting the methylation of its promoter. Furthermore, miR-29 overexpression downregulated β-catenin expression, inhibited cell proliferation and induced apoptosis. The expression of miR-29a and miR-29b was partially regulated by DNMT3A and DNMT3B in a positive feedback loop. Taken together, our findings show that miR-29s suppress the Wnt signaling pathway through demethylation of WIF-1 in NSCLC.

Expression of SFRP Family Proteins in Human Keratoconus Corneas

We investigated the expression of the secreted frizzled-related proteins (SFRPs) in keratoconus (KC) and control corneas. KC buttons (∼8 mm diameter) (n = 15) and whole control corneas (n = 7) were fixed in 10% formalin or 2% paraformaldehyde and subsequently paraffin embedded and sectioned. Sections for histopathology were stained with hematoxylin and eosin, or Periodic Acid Schiff's reagent. A series of sections was also immunolabelled with SFRP 1 to 5 antibodies, visualised using immunofluorescence, and examined with a Zeiss LSM700 scanning laser confocal microscope. Semi-quantitative grading was used to compare SFRP immunostaining in KC and control corneas. Overall, KC corneas showed increased immunostaining for SFRP1 to 5, compared to controls. Corneal epithelium in all KC corneas displayed heterogeneous moderate to strong immunoreactivity for SFRP1 to 4, particularly in the basal epithelium adjacent to cone area. SFRP3 and 5 were localised to epithelial cell membranes in KC and control corneas, with increased SFRP3 cytoplasmic expression observed in KC. Strong stromal expression of SFRP5, including extracellular matrix, was seen in both KC and control corneas. In control corneas we observed differential expression of SFRP family proteins in the limbus compared to more central cornea. Taken together, our results support a role for SFRPs in maintaining a healthy cornea and in the pathogenesis of epithelial and anterior stromal disruption observed in KC.

Association of single nucleotide polymorphisms in Wnt signaling pathway genes with breast cancer in Saudi patients

Breast cancer is a complex heterogeneous disease involving genetic and epigenetic alterations in genes encoding proteins that are components of various signaling pathways. Candidate gene approach have identified association of genetic variants in the Wnt signaling pathway genes and increased susceptibility to several diseases including breast cancer. Due to the rarity of somatic mutations in key genes of Wnt pathway, we investigated the association of genetic variants in these genes with predisposition to breast cancers. We performed a case-control study to identify risk variants by examining 15 SNPs located in 8 genes associated with Wnt signaling. Genotypic analysis of individual locus showed statistically significant association of five SNPs located in β-catenin, AXIN2, DKK3, SFRP3 and TCF7L2 with breast cancers. Increased risk was observed only with the SNP in β-catenin while the other four SNPs conferred protection against breast cancers. Majority of these associations persisted after stratification of the cases based on estrogen receptor status and age of on-set of breast cancer. The rs7775 SNP in exon 6 of SFRP3 gene that codes for either arginine or glycine exhibited very strong association with breast cancer, even after Bonferroni's correction. Apart from these five variants, rs3923086 in AXIN2 and rs3763511 in DKK4 that did not show any association in the overall population were significantly associated with early on-set and estrogen receptor negative breast cancers, respectively. This is the first study to utilize pathway based approach to identify association of risk variants in the Wnt signaling pathway genes with breast cancers. Confirmation of our findings in larger populations of different ethnicities would provide evidence for the role of Wnt pathway as well as screening markers for early detection of breast carcinomas.

The way Wnt works: components and mechanism

The canonical Wnt/β-catenin pathway is an ancient and evolutionarily conserved signaling pathway that is required for the proper development of all metazoans, from the basal demosponge Amphimedon queenslandica to humans. Misregulation of Wnt signaling is implicated in many human diseases, making this pathway an intense area of research in industry as well as academia. In this review, we explore our current understanding of the molecular steps involved in the transduction of a Wnt signal. We will focus on how the critical Wnt pathway component, β-catenin, is in a "futile cycle" of constant synthesis and degradation and how this cycle is disrupted upon pathway activation. We describe the role of the Wnt pathway in major human cancers and in the control of stem cell self-renewal in the developing organism and in adults. Finally, we describe well-accepted criteria that have been proposed as evidence for the involvement of a molecule in regulating the canonical Wnt pathway.

FOXC2 expression links epithelial-mesenchymal transition and stem cell properties in breast cancer

Resistance to chemotherapy and metastases are the major causes of breast cancer-related mortality. Moreover, cancer stem cells (CSC) play critical roles in cancer progression and treatment resistance. Previously, it was found that CSC-like cells can be generated by aberrant activation of epithelial-mesenchymal transition (EMT), thereby making anti-EMT strategies a novel therapeutic option for treatment of aggressive breast cancers. Here, we report that the transcription factor FOXC2 induced in response to multiple EMT signaling pathways as well as elevated in stem cell-enriched factions is a critical determinant of mesenchymal and stem cell properties, in cells induced to undergo EMT- and CSC-enriched breast cancer cell lines. More specifically, attenuation of FOXC2 expression using lentiviral short hairpin RNA led to inhibition of the mesenchymal phenotype and associated invasive and stem cell properties, which included reduced mammosphere-forming ability and tumor initiation. Whereas, overexpression of FOXC2 was sufficient to induce CSC properties and spontaneous metastasis in transformed human mammary epithelial cells. Furthermore, a FOXC2-induced gene expression signature was enriched in the claudin-low/basal B breast tumor subtype that contains EMT and CSC features. Having identified PDGFR-β to be regulated by FOXC2, we show that the U.S. Food and Drug Administration-approved PDGFR inhibitor, sunitinib, targets FOXC2-expressing tumor cells leading to reduced CSC and metastatic properties. Thus, FOXC2 or its associated gene expression program may provide an effective target for anti-EMT-based therapies for the treatment of claudin-low/basal B breast tumors or other EMT-/CSC-enriched tumors.

Wnt signaling in mammary glands: plastic cell fates and combinatorial signaling

The mouse mammary gland is an outstanding developmental model that exemplifies the activities of many of the effector pathways known to organize mammalian morphogenesis; furthermore, there are well-characterized methods for the specific genetic manipulation of various mammary epithelial cell components. Among these signaling pathways, Wnt signaling has been shown to generate plasticity of fate determination, expanding the genetic programs available to cells in the mammary lineage. It is responsible first for the appearance of the mammary fate in embryonic ectoderm and then for maintaining bi-potential basal stem cells in adult mammary ductal trees. Recent technical developments have led to the separate analysis of various mammary epithelial cell subpopulations, spurring the investigation of Wnt-dependent interactions. Although Wnt signaling was shown to be oncogenic for mouse mammary epithelium even before being identified as the principle oncogenic driver for gut epithelium, conclusive data implicating this pathway as a tumor driver for breast cancer lag behind, and we examine potential reasons.

Paracrine signaling by progesterone

Steroid hormones coordinate and control the development and function of many organs and are implicated in many pathological processes. Progesterone signaling, in particular, is essential for several important female reproductive functions. Physiological effects of progesterone are mediated by its cognate receptor, expressed in a subset of cells in target tissues. Experimental evidence has accumulated that progesterone acts through both cell intrinsic as well as paracrine signaling mechanisms. By relegating the hormonal stimulus to paracrine signaling cascades the systemic signal gets amplified locally and signaling reaches different cell types that are devoid of hormone receptors. Interestingly, distinct biological responses to progesterone in different target tissues rely on several tissue-specific and some common paracrine factors that coordinate biological responses in different cell types. Evidence is forthcoming that the intercellular signaling pathways that control development and physiological functions are important in tumorigenesis.

MENA is a transcriptional target of the Wnt/beta-catenin pathway

Wnt/β-catenin signalling pathway plays important roles in embryonic development and carcinogenesis. Overactivation of the pathway is one of the most common driving forces in major cancers such as colorectal and breast cancers. The downstream effectors of the pathway and its regulation of carcinogenesis and metastasis are still not very well understood. In this study, which was based on two genome-wide transcriptomics screens, we identify MENA (ENAH, Mammalian enabled homologue) as a novel transcriptional target of the Wnt/β-catenin signalling pathway. We show that the expression of MENA is upregulated upon overexpression of degradation-resistant β-catenin. Promoters of all mammalian MENA homologues contain putative binding sites for Tcf4 transcription factor – the primary effector of the Wnt/β-catenin pathway and we demonstrate functionality of these Tcf4-binding sites using luciferase reporter assays and overexpression of β-catenin, Tcf4 and dominant-negative Tcf4. In addition, lithium chloride-mediated inhibition of GSK3β also resulted in increase in MENA mRNA levels. Chromatin immunoprecipitation showed direct interaction between β-catenin and MENA promoter in Huh7 and HEK293 cells and also in mouse brain and liver tissues. Moreover, overexpression of Wnt1 and Wnt3a ligands increased MENA mRNA levels. Additionally, knock-down of MENA ortholog in D. melanogaster eyeful and sensitized eye cancer fly models resulted in increased tumor and metastasis formations. In summary, our study identifies MENA as novel nexus for the Wnt/β-catenin and the Notch signalling cascades.

Small molecule antagonists of the Wnt/β-catenin signaling pathway target breast tumor-initiating cells in a Her2/Neu mouse model of breast cancer

Background

Recent evidence suggests that human breast cancer is sustained by a minor subpopulation of breast tumor-initiating cells (BTIC), which confer resistance to anticancer therapies and consequently must be eradicated to achieve durable breast cancer cure.

Methods/Findings

To identify signaling pathways that might be targeted to eliminate BTIC, while sparing their normal stem and progenitor cell counterparts, we performed global gene expression profiling of BTIC- and mammary epithelial stem/progenitor cell- enriched cultures derived from mouse mammary tumors and mammary glands, respectively. Such analyses suggested a role for the Wnt/Beta-catenin signaling pathway in maintaining the viability and or sustaining the self-renewal of BTICs in vitro. To determine whether the Wnt/Beta-catenin pathway played a role in BTIC processes we employed a chemical genomics approach. We found that pharmacological inhibitors of Wnt/β-catenin signaling inhibited sphere- and colony-formation by primary breast tumor cells and primary mammary epithelial cells, as well as by tumorsphere- and mammosphere-derived cells. Serial assays of self-renewal in vitro revealed that the Wnt/Beta-catenin signaling inhibitor PKF118–310 irreversibly affected BTIC, whereas it functioned reversibly to suspend the self-renewal of mammary epithelial stem/progenitor cells. Incubation of primary tumor cells in vitro with PKF118–310 eliminated their capacity to subsequently seed tumor growth after transplant into syngeneic mice. Administration of PKF118–310 to tumor-bearing mice halted tumor growth in vivo. Moreover, viable tumor cells harvested from PKF118–310 treated mice were unable to seed the growth of secondary tumors after transplant.

Conclusions

These studies demonstrate that inhibitors of Wnt/β-catenin signaling eradicated BTIC in vitro and in vivo and provide a compelling rationale for developing such antagonists for breast cancer therapy.

Small molecule antagonists of the Wnt/β-catenin signaling pathway target breast tumor-initiating cells in a Her2/Neu mouse model of breast cancer

BACKGROUND

Recent evidence suggests that human breast cancer is sustained by a minor subpopulation of breast tumor-initiating cells (BTIC), which confer resistance to anticancer therapies and consequently must be eradicated to achieve durable breast cancer cure.

METHODS/FINDINGS

To identify signaling pathways that might be targeted to eliminate BTIC, while sparing their normal stem and progenitor cell counterparts, we performed global gene expression profiling of BTIC- and mammary epithelial stem/progenitor cell- enriched cultures derived from mouse mammary tumors and mammary glands, respectively. Such analyses suggested a role for the Wnt/Beta-catenin signaling pathway in maintaining the viability and or sustaining the self-renewal of BTICs in vitro. To determine whether the Wnt/Beta-catenin pathway played a role in BTIC processes we employed a chemical genomics approach. We found that pharmacological inhibitors of Wnt/β-catenin signaling inhibited sphere- and colony-formation by primary breast tumor cells and primary mammary epithelial cells, as well as by tumorsphere- and mammosphere-derived cells. Serial assays of self-renewal in vitro revealed that the Wnt/Beta-catenin signaling inhibitor PKF118-310 irreversibly affected BTIC, whereas it functioned reversibly to suspend the self-renewal of mammary epithelial stem/progenitor cells. Incubation of primary tumor cells in vitro with PKF118-310 eliminated their capacity to subsequently seed tumor growth after transplant into syngeneic mice. Administration of PKF118-310 to tumor-bearing mice halted tumor growth in vivo. Moreover, viable tumor cells harvested from PKF118-310 treated mice were unable to seed the growth of secondary tumors after transplant.

CONCLUSIONS

These studies demonstrate that inhibitors of Wnt/β-catenin signaling eradicated BTIC in vitro and in vivo and provide a compelling rationale for developing such antagonists for breast cancer therapy.

Use of integrative epigenetic and cytogenetic analyses to identify novel tumor-suppressor genes in malignant melanoma

The objective of this study was to identify novel tumor-suppressor genes in melanoma, using an integrative genomic approach. Data from: (i) earlier reports of DNA loss and gain in malignant melanoma accompanied by comparative genomic hybridization high-definition array data of the entire human genome; (ii) microarray expression data from melanoma-derived cell lines identifying genes with significantly increased expression due to methylation using a pharmacologic demethylating strategy; and (iii) publicly available RNA expression microarray data of primary tumors and benign nevi were integrated using statistical tools to define a population of candidate tumor-suppressor genes. Twenty-seven genes were identified in areas of deletion that demonstrated diminished expression in primary melanomas relative to benign nevi and were significantly increased in expression by 5-Aza treatment. Seven genes of these 27 genes demonstrated methylation and deletion in a validation cohort of 14 separate primary tumors. These were: CHRDL1, SFRP1, TMEM47, LPL, RARRES1, PLCXD1, and KOX15. All of these genes demonstrated growth-suppressive properties with transfection into melanoma-derived cell lines. Seven putative tumor-suppressor genes in malignant melanoma were identified using a novel integrative technique.

Mammary development and breast cancer: the role of stem cells

The mammary gland is a highly regenerative organ that can undergo multiple cycles of proliferation, lactation and involution, a process controlled by stem cells. The last decade much progress has been made in the identification of signaling pathways that function in these stem cells to control self-renewal, lineage commitment and epithelial differentiation in the normal mammary gland. The same signaling pathways that control physiological mammary development and homeostasis are also often found deregulated in breast cancer. Here we provide an overview on the functional and molecular identification of mammary stem cells in the context of both normal breast development and breast cancer. We discuss the contribution of some key signaling pathways with an emphasis on Notch receptor signaling, a cell fate determination pathway often deregulated in breast cancer. A further understanding of the biological roles of the Notch pathway in mammary stem cell behavior and carcinogenesis might be relevant for the development of future therapies.

Rad6B acts downstream of Wnt signaling to stabilize β-catenin: Implications for a novel Wnt/β-catenin target

BACKGROUND

Aberrant Wnt/β-catenin signaling is associated with breast cancer even though genetic mutations in Wnt signaling components are rare. We have previously demonstrated that Rad6B, an ubiquitin conjugating enzyme, stabilizes β-catenin via polyubiqutin modifications that render β-catenin insensitive to proteasomal degradation. Rad6B is a transcriptional target of β-catenin, creating a positive feedback loop between Rad6B expression and β-catenin activation.

METHODS

To isolate subpopulations expressing high or low Rad6B levels, we transfected MDA-MB-231 or WS-15 human breast cancer cells with ZsGreen fluorescent reporter vector in which the expression of ZsGreen was placed under the control of Rad6B promoter. ZsGreenhigh and ZsGreenlow subpopulations, reflective of high and low Rad6B promoter activity, respectively, were isolated by FACS. To determine the relevance of Wnt signaling in Rad6B-mediated β-catenin stabilization/activation, the ZsGreenhigh cells were transfected with signaling-defective Wnt coreceptor LRP6Δ173. Rad6B expression and promoter activity were determined by RT-PCR, Western blot and Rad6B promoter-mediated luciferase assays. β-catenin levels and transcriptional activity were determined by Western blot and TOP/FOP Flash reporter assays. Tumor formation and morphologies of ZsGreenlow, ZsGreenhigh, and ZsGreenhigh/LRP6Δ173 cells compared to unsorted vector controls were evaluated in nude mice. Expression of Wnt signaling related genes was profiled using the Wnt signaling pathway RT2 Profiler PCR arrays.

RESULTS

ZsGreenhigh subpopulations showed high Rad6B expression and Rad6B promoter activity as compared to ZsGreenlow cells. ZsGreenhigh (high Rad6B expressors) also showed elevated β-catenin levels and TOP/Flash activity. Inhibiting Wnt signaling in the high Rad6B expressors decreased ZsGreen fluorescence, Rad6B gene expression, β-catenin levels and TOP/Flash activity. Tumors derived from high Rad6B expressors were predominantly composed of cells with epithelial mesenchymal transition (EMT) phenotype as compared to control tumors that were composed of both cuboidal and EMT-type cells. Tumors derived from low Rad6B expressors lacked EMT phenotype. Inhibition of LRP6 function in the high Rad6B expressors abrogated the EMT phenotype. Gene expression profiling showed upregulation of several Wnt signaling pathway regulators in high Rad6B expressors that were downregulated by interference of Wnt signaling with mutant LRP6 or by Rad6B silencing.

CONCLUSIONS

These data reveal a functional link between the canonical Wnt pathway and Rad6B in β-catenin activation and breast cancer progression.

Wnt and mammary stem cells: hormones cannot fly wingless

The mammary stem cell and its local microenvironment are central for the maintenance of proper tissue homeostasis during normal development. Defining the hierarchical organization of the epithelial subtypes in the mammary gland and the molecular pathways guiding their development has begun to provide a framework for understanding how cancer stem cells sustain the progression and heterogeneity of breast cancers. The Wnt pathway plays a fundamental role in multiple adult stem cells, as well as in orchestrating proper mammary gland development and maintenance. These processes are intricately guided by the influence of systemic hormones and local factors. Alterations in Wnt signaling can skew the homeostatic balance of the mammary epithelium to drive malignant progression; however, complexities of Wnt pathway components present a challenge in understanding their physiological function.