β-Catenin Signaling Is a Critical Event in ErbB2-Mediated Mammary Tumor Progression

The roles of ncRNAs and histone-modifiers in regulating breast cancer stem cells

Cancer stem cells (CSCs), a subpopulation of cancer cells with ability of initiating tumorigenesis, exist in many kinds of tumors including breast cancer. Cancer stem cells contribute to treatment resistance and relapse. Conventional treatments only kill differentiated cancer cells, but spare CSCs. Combining conventional treatments with therapeutic drugs targeting to CSCs will eradicate cancer cells more efficiently. Studying the molecular mechanisms of CSCs regulation is essential for developing new therapeutic strategies. Growing evidences showed CSCs are regulated by non-coding RNA (ncRNA) including microRNAs and long non-coding RNAs (lncRNAs), and histone-modifiers, such as let-7, miR-93, miR-100, HOTAIR, Bmi-1 and EZH2. Herein we review the roles of microRNAs, lncRNAs and histone-modifiers especially Polycomb family proteins in regulating breast cancer stem cells (BCSCs).

Elevated β-catenin pathway as a novel target for patients with resistance to EGF receptor targeting drugs

There is a high death rate of lung cancer patients. Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are effective in some lung adenocarcinoma patients with EGFR mutations. However, a significant number of patients show primary and acquire resistance to EGFR-TKIs. Although the Akt kinase is commonly activated due to various resistance mechanisms, the key targets of Akt remain unclear. Here, we show that the Akt-β-catenin pathway may be a common resistance mechanism. We analyzed gene expression profiles of gefitinib-resistant PC9M2 cells that were derived from gefitinib-sensitive lung cancer PC9 cells and do not have known resistance mechanisms including EGFR mutation T790M. We found increased expression of Axin, a β-catenin target gene, increased phosphorylation of Akt and GSK3, accumulation of β-catenin in the cytoplasm/nucleus in PC9M2 cells. Both knockdown of β-catenin and treatment with a β-catenin inhibitor at least partially restored gefitinib sensitivity to PC9M2 cells. Lung adenocarcinoma tissues derived from gefitinib-resistant patients displayed a tendency to accumulate β-catenin in the cytoplasm. We provide a rationale for combination therapy that includes targeting of the Akt-β-catenin pathway to improve the efficacy of EGFR-TKIs.

The Internalization of Neurotensin by the Low-Affinity Neurotensin Receptors (NTSR2 and vNTSR2) Activates ERK 1/2 in Glioma Cells and Allows Neurotensin-Polyplex Transfection of tGAS1

Glioblastoma is the most malignant primary brain tumor and is very resistant to treatment; hence, it has a poor prognosis. Neurotensin receptor type 1 (NTSR1) plays a key role in cancer malignancy and has potential therapeutic applications. However, the presence and function of neurotensin (NTS) receptors in glioblastoma is not clearly established. RT-PCR assays showed that healthy (non-tumor) astroglial cells and C6 glioma cells express NTSR2 and its isoform (vNTSR2) rather than NTSR1. In glioma cells, NTS promotes the phosphorylation of extracellular signal-regulated kinases 1/2 (ERK 1/2), an effect that was completely abolished by blocking the internalization of the NTS/NTSR complex. We demonstrated pharmacologically that the internalization is dependent on the activation of NTSR2 receptors and it was prevented by levocabastine, a NTSR2 receptor antagonist. The internalization of NTSR2 and vNTSR2 was further demonstrated by its ability to mediate gene transfer (transfection) via the NTS-polyplex system. Expression of reporter transgenes and of the pro-apoptotic soluble form of growth arrest specific 1 (tGAS1) was observed in glioma cells. A significant reduction on the viability of C6 cells was determined when tGAS1 was transfected into glioma cells. Conversely, astroglial cells could neither internalize NTS nor activate ERK 1/2 and could not be transfected by the NTS-polyplex. These results demonstrate that the internalization process of NTSR2 receptors is a key regulator necessary to trigger the activation of the ERK 1/2. Our data support a new internalization pathway in glioma C6 cells that involve NTSR2/vNTSR2, which can be used to selectively transfer therapeutic genes using the NTS-polyplex system.

ERBB2 triggers mammalian heart regeneration by promoting cardiomyocyte dedifferentiation and proliferation

The murine neonatal heart can regenerate after injury through cardiomyocyte (CM) proliferation, although this capacity markedly diminishes after the first week of life. Neuregulin-1 (NRG1) administration has been proposed as a strategy to promote cardiac regeneration. Here, using loss- and gain-of-function genetic tools, we explore the role of the NRG1 co-receptor ERBB2 in cardiac regeneration. NRG1-induced CM proliferation diminished one week after birth owing to a reduction in ERBB2 expression. CM-specific Erbb2 knockout revealed that ERBB2 is required for CM proliferation at embryonic/neonatal stages. Induction of a constitutively active ERBB2 (caERBB2) in neonatal, juvenile and adult CMs resulted in cardiomegaly, characterized by extensive CM hypertrophy, dedifferentiation and proliferation, differentially mediated by ERK, AKT and GSK3β/β-catenin signalling pathways. Transient induction of caERBB2 following myocardial infarction triggered CM dedifferentiation and proliferation followed by redifferentiation and regeneration. Thus, ERBB2 is both necessary for CM proliferation and sufficient to reactivate postnatal CM proliferative and regenerative potentials.

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

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

Pulmonary epithelial barrier function: some new players and mechanisms

The pulmonary epithelium serves as a barrier to prevent access of the inspired luminal contents to the subepithelium. In addition, the epithelium dictates the initial responses of the lung to both infectious and noninfectious stimuli. One mechanism by which the epithelium does this is by coordinating transport of diffusible molecules across the epithelial barrier, both through the cell and between cells. In this review, we will discuss a few emerging paradigms of permeability changes through altered ion transport and paracellular regulation by which the epithelium gates its response to potentially detrimental luminal stimuli. This review is a summary of talks presented during a symposium in Experimental Biology geared toward novel and less recognized methods of epithelial barrier regulation. First, we will discuss mechanisms of dynamic regulation of cell-cell contacts in the context of repetitive exposure to inhaled infectious and noninfectious insults. In the second section, we will briefly discuss mechanisms of transcellular ion homeostasis specifically focused on the role of claudins and paracellular ion-channel regulation in chronic barrier dysfunction. In the next section, we will address transcellular ion transport and highlight the role of Trek-1 in epithelial responses to lung injury. In the final section, we will outline the role of epithelial growth receptor in barrier regulation in baseline, acute lung injury, and airway disease. We will then end with a summary of mechanisms of epithelial control as well as discuss emerging paradigms of the epithelium role in shifting between a structural element that maintains tight cell-cell adhesion to a cell that initiates and participates in immune responses.

Mouse models of breast cancer

Breast cancer is the most common cause of cancer death in women worldwide. This malignancy is a complex disease, which is defined by an intrinsic heterogeneity on the histopathological and molecular level as well as response to therapy and outcome. In addition to classical histopathological features, breast cancer can be categorized into at least five major subtypes based on comprehensive gene expression profiling: luminal A, luminal B, basal-like, ERBB2-positive, and normal-like breast cancer. Genetically engineered mouse models can serve as tools to study the molecular underpinnings for this disease. Given the genetic complexity that drives the initiation and progression of individual breast cancer subtypes, it is evident that certain models can reflect only particular aspects of this malignancy. In this book chapter, we will primarily focus on advances in modeling breast cancer at defined stages of carcinogenesis using genetically engineered mice. We will discuss the ability as well as shortcomings of these models to faithfully recapitulate the spectrum of human breast cancer subtypes.

Sequestosome 1/p62 facilitates HER2-induced mammary tumorigenesis through multiple signaling pathways

Previous studies have shown that increased levels of the adaptor protein Sequestosome 1/p62 are observed in human breast cancers and significantly correlate with HER2 overexpression. However, the role of p62 in the pathophysiology of HER2-induced mammary tumorigenesis has not yet been investigated. In this study, we report that p62 facilitates HER2-mediated cell survival in both two-dimensional and three-dimensional cell culture and that HER2-induced cellular transformation requires p62, as well as NRF2, which is known to become stabilized by its release from Kelch-like ECH-associated protein 1 (KEAP1) via p62-KEAP1 interaction. In agreement with these results, genetic ablation of p62 delays HER2-induced mammary tumorigenesis in tumor cell allografts in nude mice, and in MMTV-Neu transgenic mice. We also report that ablation of p62 impairs AKT and β-catenin activation in association with PTEN (phosphatase and tensin homolog deleted on chromosome ten) accumulation, both in vitro and in vivo. Further in vivo studies suggest that loss of p62 also impairs NF-κB and NRF2 activation. Collectively, our results provide compelling evidence that p62 contributes to HER2-induced mammary tumorigenesis through multiple signaling pathways, including the PTEN/phosphoinositide-3-kinase/AKT axis, WNT/β-catenin signaling, the NF-κB pathway and the NRF2-KEAP1 axis, and offer novel insights into the potential role of p62 in the regulation of the tumor suppressor PTEN.

A germline mutation in the miR‑125a coding region reduces miR‑125a expression and is associated with human gastric cancer

MicroRNAs (miRNAs) are small non-coding RNAs that inhibit the expression of target protein-coding genes, most often at the post-transcriptional level. miRNAs are often found to be misregulated in human cancer and they can act as potent oncogenes or tumor suppressor genes. In this study, we found that a germline mutation in the miR-125a coding region is associated with human gastric cancer. This mutation reduced the expression of mature miR-125a and alleviated its inhibitory effect on erythroblastic leukemia viral oncogene homolog 2 (ERBB2) gene expression and on gastric tumor cell proliferation. Thus, the data of this study suggested that this germline mutation in pri‑miR-125a likely contributes to the genetic predisposition to gastric cancer by reducing the production of miR-125a, thereby interfering with the expression of miR-125a target genes.

HER2 mediated de novo production of TGFβ leads to SNAIL driven epithelial-to-mesenchymal transition and metastasis of breast cancer

HER2 is an important determinant of poor prognosis in breast cancer patients. Studies indicate that HER2 positive tumors are mostly resistant to therapy and have high metastatic potential however, the underlying mechanisms remain unknown. In this study, MDA-MB-231 and MCF-7 breast cancer cells with their HER2 overexpressing syngeneic variants were used to delineate the role of HER2 in EMT and metastasis. Our results demonstrated that HER2 overexpression increased the invasive potential of cells. Our results also showed that HER2 overexpression lead to the production of TGFβ resulting in the activation of TGFβ/SMAD signaling. Furthermore, activation of SNAIL, SLUG and ZEB-1, the transcriptional repressors of E-cadherin and increased mesenchymal characteristics were observed in high HER2 cells. Interestingly, EMT by HER2 was mediated through TGFβ. Intravenous injection of high HER2 MDA-MB-231 (HH) cells in athymic nude mice showed early and substantial metastasis as compared to the parent cells establishing the direct role of HER2 in metastasis. Our results showed that inhibition of HER2 mediated EMT by cucurbitacin B a triterpenoid, resulted in the suppression of brain metastasis of breast cancer cells. Taken together, our results identify a novel mechanism of HER2 in promoting breast cancer metastasis through de novo synthesis of TGFβ leading to EMT, an initial and essential step of metastasis.

A genomic analysis of mouse models of breast cancer reveals molecular features of mouse models and relationships to human breast cancer

INTRODUCTION

Genomic variability limits the efficacy of breast cancer therapy. To simplify the study of the molecular complexity of breast cancer, researchers have used mouse mammary tumor models. However, the degree to which mouse models model human breast cancer and are reflective of the human heterogeneity has yet to be demonstrated with gene expression studies on a large scale.

METHODS

To this end, we have built a database consisting of 1,172 mouse mammary tumor samples from 26 different major oncogenic mouse mammary tumor models.

RESULTS

In this dataset we identified heterogeneity within mouse models and noted a surprising amount of interrelatedness between models, despite differences in the tumor initiating oncogene. Making comparisons between models, we identified differentially expressed genes with alteration correlating with initiating events in each model. Using annotation tools, we identified transcription factors with a high likelihood of activity within these models. Gene signatures predicted activation of major cell signaling pathways in each model, predictions that correlated with previous genetic studies. Finally, we noted relationships between mouse models and human breast cancer at both the level of gene expression and predicted signal pathway activity. Importantly, we identified individual mouse models that recapitulate human breast cancer heterogeneity at the level of gene expression.

CONCLUSIONS

This work underscores the importance of fully characterizing mouse tumor biology at molecular, histological and genomic levels before a valid comparison to human breast cancer may be drawn and provides an important bioinformatic resource.

Suicide HSVtk gene delivery by neurotensin-polyplex nanoparticles via the bloodstream and GCV Treatment specifically inhibit the growth of human MDA-MB-231 triple negative breast cancer tumors xenografted in athymic mice

The human breast adenocarcinoma cell line MDA-MB-231 has the triple-negative breast cancer (TNBC) phenotype, which is an aggressive subtype with no specific treatment. MDA-MB-231 cells express neurotensin receptor type 1 (NTSR1), which makes these cells an attractive target of therapeutic genes that are delivered by the neurotensin (NTS)-polyplex nanocarrier via the bloodstream. We addressed the relevance of this strategy for TNBC treatment using NTS-polyplex nanoparticles harboring the herpes simplex virus thymidine kinase (HSVtk) suicide gene and its complementary prodrug ganciclovir (GCV). The reporter gene encoding green fluorescent protein (GFP) was used as a control. NTS-polyplex successfully transfected both genes in cultured MDA-MB-231 cells. The transfection was demonstrated pharmacologically to be dependent on activation of NTSR1. The expression of HSVtk gene decreased cell viability by 49% (P<0.0001) and induced apoptosis in cultured MDA-MB-231 cells after complementary GCV treatment. In the MDA-MB-231 xenograft model, NTS-polyplex nanoparticles carrying either the HSVtk gene or GFP gene were injected into the tumors or via the bloodstream. Both routes of administration allowed the NTS-polyplex nanoparticles to reach and transfect tumorous cells. HSVtk expression and GCV led to apoptosis, as shown by the presence of cleaved caspase-3 and Apostain immunoreactivity, and significantly inhibited the tumor growth (55-60%) (P<0.001). At the end of the experiment, the weight of tumors transfected with the HSVtk gene was 55% less than that of control tumors (P<0.05). The intravenous transfection did not induce apoptosis in peripheral organs. Our results offer a promising gene therapy for TNBC using the NTS-polyplex nanocarrier.

The expression of β-catenin in different subtypes of breast cancer and its clinical significance

The Wnt/β-catenin signaling pathway is implicated in mammary oncogenesis. Reports of β-catenin expression and its association with outcome in breast cancer are controversial. This study was performed to address the distribution of β-catenin expression in invasive breast cancer and the correlation between β-catenin expression and survival of breast cancer patients, and to determine whether β-catenin was specifically activated in any molecular subtypes. Immunohistochemistry was performed on a tissue microarray containing 169 invasive breast cancers to detect expression of β-catenin. One hundred thirty one of the 169 patients were followed up. Correlation between β-catenin expression and different molecular subtypes was determined using chi-square analysis. Overall survival (OS) was analyzed by Kaplan-Meier method with log-rank test. The invasive breast cancer displayed the different patterns of β-catenin expression from normal tissues with significantly increased cytoplasmic and nuclear staining of β-catenin. Aberrant β-catenin expression was observed in 109 in the 169 cases (64.50 %), and there was no difference in β-catenin expression in the four molecular subtypes. Furthermore, aberrant β-catenin expression was significantly associated with adverse outcome not only in the entire cohort but also in each of the different molecular subtypes. β-catenin activation is preferentially found and is associated with a poor clinical outcome in invasive breast cancer independent of molecular subtype.

Selection of personalized patient therapy through the use of knowledge-based computational models that identify tumor-driving signal transduction pathways

Increasing knowledge about signal transduction pathways as drivers of cancer growth has elicited the development of "targeted drugs," which inhibit aberrant signaling pathways. They require a companion diagnostic test that identifies the tumor-driving pathway; however, currently available tests like estrogen receptor (ER) protein expression for hormonal treatment of breast cancer do not reliably predict therapy response, at least in part because they do not adequately assess functional pathway activity. We describe a novel approach to predict signaling pathway activity based on knowledge-based Bayesian computational models, which interpret quantitative transcriptome data as the functional output of an active signaling pathway, by using expression levels of transcriptional target genes. Following calibration on only a small number of cell lines or cohorts of patient data, they provide a reliable assessment of signaling pathway activity in tumors of different tissue origin. As proof of principle, models for the canonical Wnt and ER pathways are presented, including initial clinical validation on independent datasets from various cancer types.

Nek2 and Plk4: prognostic markers, drivers of breast tumorigenesis and drug resistance

The Nek2 and Plk4 kinases serve as crucial regulators of mitotic processes such as the centrosome duplication cycle and spindle assembly. Deregulation of these processes can trigger chromosome instability and aneuploidy, which are hallmarks of many solid tumors, including breast cancer. Emerging data from the literature illustrated various functions of Nek2 in breast cancer models, with compelling evidence of its prognostic value in breast tumors. The two kinases control distinct steps in the centrosome-centriole cycle and their dysregulation lead to centrosome amplification, marked by the presence of more than two centrosomes within the cell. We found single or composite overexpression of these kinases in breast tumor samples, regardless of subtype, which strongly associated with poor prognosis. Interestingly, in a panel of established cell lines, both kinases are highly expressed in Her2-positive breast cancer cells exhibiting centrosome amplification and trastuzumab resistance. In summary, it appears that Nek2 and Plk4 might synergize to promote breast tumorigenesis and may also be involved in tamoxifen and trastuzumab resistance.

Mammary cells with active Wnt signaling resist ErbB2-induced tumorigenesis

Aberrant activation of Wnt signaling is frequent in human malignancies. In normal epithelial tissues, including the breast, Wnt signaling is active only in a subset of cells, but it is unknown whether this subset of Wnt signaling-active cells is at increased risk of carcinogenesis. We created transgenic mice (TOP-tva) in which the synthetic Wnt-responsive promoter TOP controlled the gene encoding TVA, which confers susceptibility to infection by the retroviral vector RCAS. Thus, only cells in which Wnt signaling is active will express tva and be targeted by RCAS. Surprisingly, we found that RCAS-mediated delivery of cDNA encoding a constitutively activated version of ErbB2 (HER2/Neu) into the small number of TVA+ mammary epithelial cells in TOP-tva mice failed to induce tumor, while the same virus readily induced mammary tumors after it was delivered into a comparable number of cells in our previously reported mouse line MMTV-tva, whose tva is broadly expressed in mammary epithelium. Furthermore, we could not even detect any early lesions or infected cells in TOP-tva mice at the time of necropsy. Therefore, we conclude that the Wnt pathway-active cell subset in the normal mammary epithelium does not evolve into tumors following ErbB2 activation–rather, they apparently die due to apoptosis, an anticancer “barrier” that we have reported to be erected in some mammary cells followed ErbB2 activation. In accord with these mouse model data, we found that unlike the basal subtype, ErbB2+ human breast cancers rarely involve aberrant activation of Wnt signaling. This is the first report of a defined sub-population of mammalian cells that is “protected” from tumorigenesis by a potent oncogene, and provides direct in vivo evidence that mammary epithelial cells are not equal in their response to oncogene-initiated transformation.