The pathology of EMT in mouse mammary tumorigenesis

Adaptive selection of p53 mutation metaplastic phenotypes in estrogen-independent progression of ER+ tumors: A mechanism for acquired resistance to hormonal therapy

Estrogen receptor positive (ER + ) subtypes of mammary adenocarcinoma comprise 79% of all breast cancer diagnosis and 67% of all breast cancer mortality. The paucity of models of ER + mammary cancer that mimic human disease and response to treatment has limited critical preclinical study of mechanisms and new therapies for ER + breast cancer. The Stat1 knockout, 129S6/SvEvTac-Stat1 tm1Rds ( Stat1 -/- ), females develop luminal type FoxA1 + , ER + , and PR + mammary carcinomas after prolonged latencies. Initial studies showed that a cell line derived from a Stat1-/- mammary carcinoma was tumorigenic in syngeneic mice, but non-tumorigenic in ovariectomized (Ovx) mice. Here, data shows that Ovx performed after SSM2 tumors establish growth results in ovarian hormone independent growth. The viable post-Ovx tumors were primarily composed of metaplastic CK14 + basal type cells with a high percentage p53 immunohistochemistry (IHC) positive "mutation pattern", rather than the original luminal type tumors with low percent "wild type" pattern p53. Comparing whole exome sequences of ER + Stat1 -/- mammary tumors before and after Ovx, revealed basal keratins, mesenchymal (EMT) phenotypes, and unique mutation profiles in genes, including Trp53 and Prlr, in the estrogen-independent tumors. Our experimental findings are consistent with the clinical evidence of tumor heterogeneity of ER + breast cancers in patients in recent whole genome sequencing studies. Similarly, spontaneous Stat1-/- tumors with high percentage p53 "mutation pattern" were more basaloid and grew rapidly after Ovx, while retaining high expression of ER and FoxA1. This study demonstrates that the STAT1 -/- , ER + estrogen dependent breast cancers can become resistant to through clonal selection of mammary cells comprised of metaplastic p53 + /CK14 + basaloid cells.

Benzophenone-3 alters expression of genes encoding vascularization and epithelial-mesenchymal transition functions during Trp53-null mammary tumorigenesis

Benzophenone-3 (also referred to as oxybenzone) is a putative endocrine disrupting chemical and common ingredient in sunscreens and other personal care products. We previously showed that benzophenone-3 was promotional for epithelial tumorigenesis in mice fed adult high-fat diet, while protective against the incidence of more aggressive spindle cell tumors in the same treatment group. In this study, we show that benzophenone-3 reduces epithelial to mesenchymal transition in the epithelial tumors of these mice. This reduction in epithelial to mesenchymal transition is associated with altered expression of several genes involved in regulation of angiogenesis and epithelial to mesenchymal transition. Among the genes altered in expression, Timp1 is of particular interest because benzophenone-3 suppressed both migration and Timp1 expression in a mammary tumor cell line that displays epithelial to mesenchymal transition characteristics. These alterations in gene expression plausibly stabilize the vasculature of epithelial carcinomas and contribute to benzophenone-3 promotion of epithelial tumors, while at the same time suppress epithelial to mesenchymal transition and suppress incidence of spindle cell tumors.

Fgf10/Fgfr2b Signaling in Mammary Gland Development, Homeostasis, and Cancer

Fibroblast growth factor 10 (Fgf10) is a secreted ligand acting via the Fibroblast growth factor receptor 2b (Fgfr2b). Fgf10/Fgfr2b signaling plays important roles both in the epithelium and in the mesenchyme during mammary gland development. Evidence in mice show that Fgf10 is critical for the induction of four out of five of the mammary placodes and for the formation of the white adipose tissue. Fgfr2b ligands also play important function in the maintenance of the terminal end buds, specialized structures at the tip of the ramified ducts during the postnatal phase of mammary gland development. Finally, in humans, FGF10 has been described to be expressed in 10% of the breast adenocarcinoma and activation of FGFR2b signaling correlates with a worse prognostic. Therefore, Fgf10 plays pleiotropic roles in both mammary gland development, homeostasis and cancer and elucidating its mechanism of action and cellular targets will be crucial to either enhance mammary gland development or to find innovative targets to treat aggressive breast cancer.

LncRNA FER1L4 induces apoptosis and suppresses EMT and the activation of PI3K/AKT pathway in osteosarcoma cells via inhibiting miR-18a-5p to promote SOCS5

Previous studies have determined that long non-coding RNA (lncRNA) Fer-1-like protein 4 (FER1L4) is suppressed in osteosarcoma (OS) and inhibits the tumorigenesis in a variety of cancer. However, the precise biological of FER1L4 in OS has not been cleared. The aim of this study is to investigate the roles and potential mechanisms of FER1L4 in apoptosis and epithelial-mesenchymal transition (EMT) in OS. In the present study, the levels of FER1L4 were decreased significantly in OS tissues and cell lines compared with non-tumorous tissues or hFOB1.19. Knockdown of FER1L4 in OS cells decreased the apoptosis rate, but increased the OS cell proliferation, upregulated the expression levels of CD133 and Nanog, as well as promoted Twist1 expression, increased the N-cadherin and Vimentin expression. In turn, the opposite trends were observed upon overexpression of FER1L4. In addition, the expression of PI3K, p-AKT (Ser470) and p-AKT (Thr308) was upregulated by siFER1L4, while decreased upon overexpression of FER1L4. MicroRNA (miRNA) -18a-5p, an osteosarcoma-promoting miRNA which was suggested a target of FER1L4 in osteosarcoma, was identified to be a functional target of FER1L4 on the regulating of cell apoptosis and EMT, presently. The effects of FER1L4 overexpression on the markers of cell apoptosis, proliferation, EMT, and stemness and PI3K/AKT signaling were all reversed by miR-18a-5p upregulation. Furthermore, the suppressor of cytokine signaling 5 (SOCS5) was confirmed a target gene of miR-18a-5p by luciferase gene reporter assay and SOCS5 suppression by miR-18a-5p attenuated the effects of FER1L4 overexpression on the OS cells apoptosis and the expressed levels of PI3K, AKT, Twist1, N-cadherin and Vimentin. In conclusion, our data indicated thatthe overexpression of FER1L4 promoted apoptosis and inhibited the EMT markers expression and PI3K/AKT signaling pathway activation in OS cells via downregulating miR-18a-5p to promote SOCS5.

miR-421 promotes apoptosis and suppresses metastasis of osteosarcoma cells via targeting LTBP2

Increasing evidence has confirmed that microRNAs (miRs) are involved in tumor development and progression. A previous study reported that miR-421 could serve as a diagnostic marker in patients with osteosarcoma (OS). The present study explored the potential roles of miR-421 in the regulation of cell proliferation, apoptosis, migration, invasion, and epithelial-mesenchymal transition of OS cells. Our results showed that miR-421 was upregulated in OS tissues and cell lines (MG63, U2OS, HOS, and Saos-2) compared with the corresponding adjacent tissues or human osteoblast cells hFOB1.19, while the latent transforming growth factor β-binding protein 2 (LTBP2) expression was reduced. In MG63 and U2OS cells, CCK8 assay displayed that cell proliferation was repressed by the miR-421 inhibitor, conversely increased by miR-421 mimics. Inhibition of miR-421 promoted cell apoptosis rate, caspase 3 activity, cleaved-caspase 3 (c-caspase 3) expression, and Bax/Bcl-2 ratio, restoration of miR-421 showed the opposite functions. Suppression of miR-421 blocked migration and invasion, whereas miR-421 overexpression promoted the migration and invasion of MG63 and U2OS cells. In addition, real-time polymerase chain reaction and Western blot analysis revealed that miR-421 negatively regulated E-cadherin expression, and positively regulated the expression of N-cadherin and vimentin. The luciferase reporter assay determined that miR-421 could target LTBP2-3'-UTR, and LTBP2 expression was regulated negatively by miR-421 both in mRNA and protein levels. Depletion of LTBP2 partly abolished the biological functions of miR-421 inhibitor in OS. In conclusion, miR-421 plays an oncogenic role in OS via targeting LTBP2, suggesting that miR-421 may be a potential therapeutic target against OS.

Role of Transglutaminase 2 in Migration of Tumor Cells and How Mouse Models Fit

A search for the "magic bullet", a molecule, the targeting abilities of which could stop the migration of tumor cells, is currently underway, but remains in the early stages. There are still many unknowns regarding the cell migration. The main approach is the employment of mouse models, that are sources of valuable information, but still cannot answer all of the questions. One of the molecules of interest is Transglutaminase 2 (TG2). It is a well-described molecule involved in numerous pathways and elevated in metastatic tumors. The question remains whether mice and humans can give the same answer considering TG2.

AKT-ions with a TWIST between EMT and MET

The transcription factor Twist is an important regulator of cranial suture during embryogenesis. Closure of the neural tube is achieved via Twist-triggered cellular transition from an epithelial to mesenchymal phenotype, a process known as epithelial-mesenchymal transition (EMT), characterized by a remarkable increase in cell motility. In the absence of Twist activity, EMT and associated phenotypic changes in cell morphology and motility can also be induced, albeit moderately, by other transcription factor families, including Snail and Zeb. Aberrant EMT triggered by Twist in human mammary tumour cells was first reported to drive metastasis to the lung in a metastatic breast cancer model. Subsequent analysis of many types of carcinoma demonstrated overexpression of these unique EMT transcription factors, which statistically correlated with worse outcome, indicating their potential as biomarkers in the clinic. However, the mechanisms underlying their activation remain unclear. Interestingly, increasing evidence indicates they are selectively activated by distinct intracellular kinases, thereby acting as downstream effectors facilitating transduction of cytoplasmic signals into nucleus and reprogramming EMT and mesenchymal-epithelial transition (MET) transcription to control cell plasticity. Understanding these relationships and emerging data indicating differential phosphorylation of Twist leads to complex and even paradoxical functionalities, will be vital to unlocking their potential in clinical settings.

Histological subtypes of mouse mammary tumors reveal conserved relationships to human cancers

Human breast cancer has been characterized by extensive transcriptional heterogeneity, with dominant patterns reflected in the intrinsic subtypes. Mouse models of breast cancer also have heterogeneous transcriptomes and we noted that specific histological subtypes were associated with particular subsets. We hypothesized that unique sets of genes define each tumor histological type across mouse models of breast cancer. Using mouse models that contained both gene expression data and expert pathologist classification of tumor histology on a sample by sample basis, we predicted and validated gene expression signatures for Papillary, EMT, Microacinar and other histological subtypes. These signatures predict known histological events across murine breast cancer models and identify counterparts of mouse mammary tumor types in subtypes of human breast cancer. Importantly, the EMT, Adenomyoepithelial, and Solid signatures were predictive of clinical events in human breast cancer. In addition, a pan-cancer comparison revealed that the histological signatures were active in a variety of human cancers such as lung, oral, and esophageal squamous tumors. Finally, the differentiation status and transcriptional activity implicit within these signatures was identified. These data reveal that within tumor histology groups are unique gene expression profiles of differentiation and pathway activity that stretch well beyond the transgenic initiating events and that have clear applicability to human cancers. As a result, our work provides a predictive resource and insights into possible mechanisms that govern tumor heterogeneity.

In vivo models in breast cancer research: progress, challenges and future directions

Research using animal model systems has been instrumental in delivering improved therapies for breast cancer, as well as in generating new insights into the mechanisms that underpin development of the disease. A large number of different models are now available, reflecting different types and stages of the disease; choosing which one to use depends on the specific research question(s) to be investigated. Based on presentations and discussions from leading experts who attended a recent workshop focused on in vivo models of breast cancer, this article provides a perspective on the many varied uses of these models in breast cancer research, their strengths, associated challenges and future directions. Among the questions discussed were: how well do models represent the different stages of human disease; how can we model the involvement of the human immune system and microenvironment in breast cancer; what are the appropriate models of metastatic disease; can we use models to carry out preclinical drug trials and identify pathways responsible for drug resistance; and what are the limitations of patient-derived xenograft models? We briefly outline the areas where the existing breast cancer models require improvement in light of the increased understanding of the disease process, reflecting the drive towards more personalised therapies and identification of mechanisms of drug resistance.

Tumorigenicity and Validity of Fluorescence Labelled Mesenchymal and Epithelial Human Oral Cancer Cell Lines in Nude Mice

Tumorigenicity and metastatic activity can be visually monitored in cancer cells that were labelled with stable fluorescence. The aim was to establish and validate local and distant spread of subcutaneously previously injected fluorescence transduced human tongue cancer cell lines of epithelial and mesenchymal phenotype in nude mice. A total of 32 four-week-old male athymic Balb/c nude mice were randomly allocated into 4 groups (n = 8). A single dose of 0.3 mL PBS containing 1 × 107 of four different cancer cell-lines (UM1, UM1-GFP, UM2, and UM2-RFP) was injected subcutaneously into the right side of their posterolateral back. Validity assessment of the labelled cancer cells' tumorigenicity was assessed by physical examination, imaging, and histology four weeks after the injection. The tumor take rate of cancer cells was similar in animals injected with either parental or transduced cancer cells. Transduced cancer cells in mice were easily detectable in vivo and after cryosection using fluorescent imaging. UM1 cells showed increased tumor take rate and mean tumor volume, presenting with disorganized histopathological patterns. Fluorescence labelled epithelial and mesenchymal human tongue cancer cell lines do not change in tumorigenicity or cell phenotype after injection in vivo.

Altered expression of epithelial-to-mesenchymal transition proteins in extraprostatic prostate cancer

Epithelial to mesenchymal transition (EMT) of cancer cells involves loss of epithelial polarity and adhesiveness, and gain of invasive and migratory mesenchymal behaviours. EMT occurs in prostate cancer (PCa) but it is unknown whether this is in specific areas of primary tumours. We examined whether any of eleven EMT-related proteins have altered expression or subcellular localisation within the extraprostatic extension component of locally advanced PCa compared with other localisations, and whether similar changes may occur in in vitro organotypic PCa cell cultures and in vivo PCa models. Expression profiles of three proteins (E-cadherin, Snail, and α-smooth muscle actin) were significantly different in extraprostatic extension PCa compared with intra-prostatic tumour, and 18/27 cases had an expression change of at least one of these three proteins. Of the three significantly altered EMT proteins in pT3 samples, one showed similar significantly altered expression patterns in in vitro organotypic culture models, and two in in vivo Pten-/- model samples. These results suggest that changes in EMT protein expression can be observed in the extraprostatic extension component of locally invasive PCa. The biology of some of these changes in protein expression may be studied in certain in vitro and in vivo PCa models.

Characterization of Spontaneous Mammary Tumors in Domestic Djungarian Hamsters (Phodopus sungorus)

Mammary tumors that spontaneously occurred in domestic Djungarian hamsters ( Phodopus sungorus) were histologically examined. Forty-five mammary tumors included 14 adenomas, 18 adenocarcinomas, 1 lipid-rich carcinoma, 2 adenoacanthomas, 2 malignant adenomyoepitheliomas, 1 benign mixed tumor, and 7 “balloon cell” carcinosarcomas. The latter 4 types were newly recognized neoplasms in Djungarian hamsters. The relatively high incidence of spontaneous mammary carcinosarcomas in domestic Djungarian hamsters is intriguing. Carcinosarcomas exhibited anomalous histological features made up of a mixture of glandular cells, polygonal cells (including “balloon cells”), and sarcomatous spindle cells in varying proportions. Transitional features from glandular cells to polygonal cells and subsequently to sarcomatous spindle cells were observed. Using immunohistochemistry, we observed that glandular cells exhibited an epithelial phenotype (cytokeratin(+)/vimentin(–)), spindle cells exhibited a mesenchymal phenotype (cytokeratin(–)/vimentin(+)), and polygonal cells exhibited an intermediate phenotype (cytokeratin(+)/vimentin(+)). Reduction or loss of β-catenin expression and gain of S100A4 expression were observed in polygonal and spindle cells. The polygonal cell population included a varying number of characteristic cells that were expanded by large intracytoplasmic vacuoles. Electron microscopy revealed that these “balloon cells” had large cytoplasmic lumens lined by microvilli. These observations suggest that epithelial-mesenchymal transition may account for the pathogenesis of mammary carcinosarcomas in Djungarian hamsters.

Mammary gland tumor promotion by chronic administration of IGF1 and the insulin analogue AspB10 in the p53R270H/⁺WAPCre mouse model

INTRODUCTION

Insulin analogues are structurally modified molecules with altered pharmaco-kinetic and -dynamic properties compared to regular human insulin used by diabetic patients. While these compounds are tested for undesired mitogenic effects, an epidemiological discussion is ongoing regarding an association between insulin analogue therapy and increased cancer incidence, including breast cancer. Standard in vivo rodent carcinogenesis assays do not pick up this possible increased carcinogenic potential.

METHODS

Here we studied the role of insulin analogues in breast cancer development. For this we used the human relevant mammary gland specific p53R270H/⁺WAPCre mouse model. Animals received life long repeated treatment with four different insulin (-like) molecules: normal insulin, insulin glargine, insulin X10 (AspB10) or insulin-like growth factor 1 (IGF1).

RESULTS

Insulin-like molecules with strong mitogenic signaling, insulin X10 and IGF1, significantly decreased the time for tumor development. Yet, insulin glargine and normal insulin, did not significantly decrease the latency time for (mammary gland) tumor development. The majority of tumors had an epithelial to mesenchymal transition phenotype (EMT), irrespective of treatment condition. Enhanced extracellular signaling related kinase (Erk) or serine/threonine kinase (Akt) mitogenic signaling was in particular present in tumors from the insulin X10 and IGF1 treatment groups.

CONCLUSIONS

These data indicate that insulin-like molecules with enhanced mitogenic signaling increase the risk of breast cancer development. Moreover, the use of a tissue specific cancer model, like the p53R270H/⁺WAPCre mouse model, is relevant to assess the intrinsic pro-carcinogenic potential of mitogenic and non-mitogenic biologicals such as insulin analogues.

Role of the host stroma in cancer and its therapeutic significance

Current cancer research focuses mainly upon the cancer cells in malignant tumours and is providing a growing database about aberrations in their genetic composition. However, tumours also contain non-cancerous host tissue, referred to as the stroma, which plays an active and indispensable role in tumour growth and influences the virulence of the neoplasm towards the host. Many cell types inhabit the stroma, amidst apparently inert fibrous and viscous matrix material, composed of complex polysaccharides, proteins and other molecules. Actually, all of these elements are in constant turnover, causing unpredictable evolution in the properties of the community. This article provides pathologic observations and data on reciprocal interactions between these stromal and neoplastic components of tumours and how they change during the course of the disease. Malignant progression depends upon dauntingly intricate communications between different specialised lineages within the cellular society, which enable rapid adaptation to changing circumstances. Opportunistic misuse of such communication networks enables tumour cells to recruit and incorporate adjacent normal stroma into their midst, so that they may grow, infiltrate and parasitise the host. The absolute dependency of primary tumours and metastases on their diverse stromal components for survival and their insatiable need to continuously recruit more stroma to support expansion, renders them vulnerable to strategies capable of disrupting the cellular interactions involved. This dependency is of critical importance for cancer therapy research, and proposed methods for turning this parasitic behaviour of tumours against themselves are suggested below.

Analysis of mouse model pathology: a primer for studying the anatomic pathology of genetically engineered mice

This primer of pathology is intended to introduce investigators to the structure (morphology) of cancer with an emphasis on genetically engineered mouse (GEM) models (GEMMs). We emphasize the necessity of using the entire biological context for the interpretation of anatomic pathology. Because the primary investigator is responsible for almost all of the information and procedures leading up to microscopic examination, they should also be responsible for documentation of experiments so that the microscopic interpretation can be rendered in context of the biology. The steps involved in this process are outlined, discussed, and illustrated. Because GEMMs are unique experimental subjects, some of the more common pitfalls are discussed. Many of these errors can be avoided with attention to detail and continuous quality assurance.

Epithelial mesenchymal transition in early invasive breast cancer: an immunohistochemical and reverse phase protein array study

Epithelial mesenchymal transition (EMT), as defined by loss of epithelial characteristics and gain of a mesenchymal phenotype, has been reported in vivo although the occurrence of events remains unclear. This study aims at exploration of EMT portraits of breast cancer (BC) with relevance to different molecular pathways, especially potential EMT triggers and BC molecular subtypes. Immunohistochemical (IHC) expression of markers/triggers of EMT was studied on a well-defined cohort of invasive non-lobular BC (n = 1,035), prepared as tissue microarrays. IHC panel of biomarkers included cadherins (cad; E-cad and N-cad), TGFβ1, PIK3CA, pAkt, and others. Reverse phase protein array (RPPA) was performed for quantitative analysis of proteins extracted from formalin fixed paraffin embedded tissues of a subset of cases from this cohort. Four combinatorial phenotypic groups representing cadherin switch were defined, including E-cad(+)/N-cad(-), E-cad(-)/N-cad(-), E-cad(+)/N-cad(+), and E-cad(-)/N-cad(+). Statistically significant association was noticed between these phenotypes and histological tumour grade, tumour type and size and NPI staging classes. The E-cad/N-cad switch occurred more frequently in the triple negative molecular class, both basal and non-basal, and in the HER2(+) subtype than in luminal BC. Significant outcome differences were observed between cadherin switch combinatorial groups regarding BCSS and DMFS (p < 0.001). Results of RPPA confirm those observed using IHC regarding differential expressions of EMT markers/triggers. EMT/cadherin switch programs in BC appear to occur in synergy with TGFβ1 and PIK3/Akt pathways activation. These data explain, at translational proteomic level, the molecular heterogeneity and in turn the varied clinical behaviour of BC molecular subtypes. RPPA is a promising high-throughput technique in monitoring subtle quantitative changes in protein expression in archival material.

Inducible and coupled expression of the polyomavirus middle T antigen and Cre recombinase in transgenic mice: an in vivo model for synthetic viability in mammary tumour progression

Introduction

Effective in vivo models of breast cancer are crucial for studying the development and progression of the disease in humans. We sought to engineer a novel mouse model of polyomavirus middle T antigen (PyV mT)-mediated mammary tumourigenesis in which inducible expression of this well-characterized viral oncoprotein is coupled to Cre recombinase (TetO-PyV mT-IRES-Cre recombinase or MIC).

Methods

MIC mice were crossed to the mouse mammary tumour virus (MMTV)-reverse tetracycline transactivator (rtTA) strain to generate cohorts of virgin females carrying one or both transgenes. Experimental (rtTA/MIC) and control (rtTA or MIC) animals were administered 2 mg/mL doxycycline beginning as early as eight weeks of age and monitored for mammary tumour formation, in parallel with un-induced controls of the same genotypes.

Results

Of the rtTA/MIC virgin females studied, 90% developed mammary tumour with complete penetrance to all glands in response to doxycycline and a T₅₀ of seven days post-induction, while induced or un-induced controls remained tumour-free after one year of induction. Histological analyses of rtTA/MIC mammary glands and tumour revealed that lesions followed the canonical stepwise progression of PyV mT tumourigenesis, from hyperplasia to mammary intraepithelial neoplasia/adenoma, carcinoma, and invasive carcinoma that metastasizes to the lung; at each of these stages expression of PyV mT and Cre recombinase transgenes was confirmed. Withdrawal of doxycycline from rtTA/MIC mice with end-stage mammary tumours led to rapid regression, yet animals eventually developed PyV mT-expressing and -non-expressing recurrent masses with varied tumour histopathologies.

Conclusions

We have successfully created a temporally regulated mouse model of PyV mT-mediated mammary tumourigenesis that can be used to study Cre recombinase-mediated genetic changes simultaneously. While maintaining all of the hallmark features of the well-established constitutive MMTV-PyV mT model, the utility of this strain derives from the linking of PyV mT and Cre recombinase transgenes; mammary epithelial cells are thereby forced to couple PyV mT expression with conditional ablation of a given gene. This transgenic mouse model will be an important research tool for identifying synthetic viable genetic events that enable PyV mT tumours to evolve in the absence of a key signaling pathway.

MMTV-Espl1 transgenic mice develop aneuploid, estrogen receptor alpha (ERα)-positive mammary adenocarcinomas

Separase, a protease encoded by the ESPL1 gene, cleaves the chromosomal cohesin during mitosis. Separase protein and transcripts are overexpressed in a wide range of human cancers (Meyer et al., Clin Cancer Res 2009; 15: 2703-2710). To investigate the physiological consequence of Separase overexpression in animals, we have generated a transgenic MMTVEspl1 mouse model that overexpresses Separase protein in the mammary glands. MMTV-Espl1 mice in a C57BL/6 genetic background develop aggressive, highly aneuploid, and estrogen receptor alpha positive (ERα+) mammary adenocarcinomas with an 80% penetrance. The mammary tumors caused by overexpression of Separase, alone or combined with p53 heterozygosity, in mammary epithelium mimic several aspects of the most aggressive forms of human breast cancer, including high levels of genetic instability, cell cycle defects, poor differentiation, distant metastasis, and metaplasia. Histopathologically, MMTV-Espl1 tumors are highly heterogeneous showing features of both luminal as well as basal subtypes of breast cancers, with aggressive disease phenotype. In addition to aneuploidy, Separase overexpression results in chromosomal instability (CIN) including premature chromatid separation (PCS), lagging chromosomes, anaphase bridges, micronuclei, centrosome amplification, multi nucleated cells, gradual accumulation of DNA damage, and progressive loss of tumor suppressors p53 and cadherin gene loci. These results suggest that Separase overexpressing mammary cells are not only susceptible to chromosomal missegregation-induced aneuploidy but also other genetic instabilities including DNA damage and loss of key tumor suppressor gene loci, which in combination can initiate tumorigenesis and disease progression.

Prolactin cooperates with loss of p53 to promote claudin-low mammary carcinomas

TP53 is one of the most commonly mutated genes in cancer. In breast cancer, it is mutated in about 40% of primary clinical tumors and is associated with poor survival. The mammotrophic hormone, prolactin (PRL), and/or its receptor are also expressed in many breast cancers, and accumulating epidemiologic data link PRL to breast cancer development and progression. Like TP53 mutations, evidence for PRL activity is evident across several molecular cancer subtypes, and elevated PRL expression and loss of p53 have been observed in some of the same clinical tumors. In order to examine the interaction of these factors, we used genetically modified mouse models of mammary-specific p53 loss and local overexpression of PRL. We demonstrated that mammary PRL decreased the latency of tumors in the absence of p53, and increased the proportion of triple-negative claudin-low carcinomas, which display similarities to human clinical metaplastic carcinomas. Moreover, PRL/p53(-/-) carcinomas displayed higher rates of proliferation and more aggressive behavior. Transcripts associated with cell cycle progression, invasion and stromal reactivity were differentially expressed in carcinomas that developed in the presence of elevated PRL. PRL/p53(-/-) carcinomas also exhibited selectively altered expression of activating protein-1 components, including higher levels of c-Jun and FosL1, which can drive transcription of many of these genes and the epithelial-mesenchymal transition. The ability of PRL to promote claudin-low carcinomas demonstrates that PRL can influence this subset of triple-negative breast cancers, which may have been obscured by the relative infrequency of this cancer subtype. Our findings suggest novel therapeutic approaches, and provide a preclinical model to develop possible agents.

Met synergizes with p53 loss to induce mammary tumors that possess features of claudin-low breast cancer

Triple-negative breast cancer (TNBC) accounts for ∼20% of cases and contributes to basal and claudin-low molecular subclasses of the disease. TNBCs have poor prognosis, display frequent mutations in tumor suppressor gene p53 (TP53), and lack targeted therapies. The MET receptor tyrosine kinase is elevated in TNBC and transgenic Met models (Met(mt)) develop basal-like tumors. To investigate collaborating events in the genesis of TNBC, we generated Met(mt) mice with conditional loss of murine p53 (Trp53) in mammary epithelia. Somatic Trp53 loss, in combination with Met(mt), significantly increased tumor penetrance over Met(mt) or Trp53 loss alone. Unlike Met(mt) tumors, which are histologically diverse and enriched in a basal-like molecular signature, the majority of Met(mt) tumors with Trp53 loss displayed a spindloid pathology with a distinct molecular signature that resembles the human claudin-low subtype of TNBC, including diminished claudins, an epithelial-to-mesenchymal transition signature, and decreased expression of the microRNA-200 family. Moreover, although mammary specific loss of Trp53 promotes tumors with diverse pathologies, those with spindloid pathology and claudin-low signature display genomic Met amplification. In both models, MET activity is required for maintenance of the claudin-low morphological phenotype, in which MET inhibitors restore cell-cell junctions, rescue claudin 1 expression, and abrogate growth and dissemination of cells in vivo. Among human breast cancers, elevated levels of MET and stabilized TP53, indicative of mutation, correlate with highly proliferative TNBCs of poor outcome. This work shows synergy between MET and TP53 loss for claudin-low breast cancer, identifies a restricted claudin-low gene signature, and provides a rationale for anti-MET therapies in TNBC.

Inflammation and Hras signaling control epithelial-mesenchymal transition during skin tumor progression

Epithelial-mesenchymal transition (EMT) is thought to be an important, possibly essential, component of the process of tumor dissemination and metastasis. About 20%-30% of Hras mutant mouse skin carcinomas induced by chemical initiation/promotion protocols have undergone EMT. Reduced exposure to TPA-induced chronic inflammation causes a dramatic reduction in classical papillomas and squamous cell carcinomas (SCCs), but the mice still develop highly invasive carcinomas with EMT properties, reduced levels of Hras and Egfr signaling, and frequent Ink4/Arf deletions. Deletion of Hras from the mouse germline also leads to a strong reduction in squamous tumor development, but tumors now acquire activating Kras mutations and exhibit more aggressive metastatic properties. We propose that invasive carcinomas can arise by different genetic and biological routes dependent on exposure to chronic inflammation and possibly from different target cell populations within the skin. Our data have implications for the use of inhibitors of inflammation or of Ras/Egfr pathway signaling for prevention or treatment of invasive cancers.

Ink4a/Arf(-/-) and HRAS(G12V) transform mouse mammary cells into triple-negative breast cancer containing tumorigenic CD49f(-) quiescent cells

Intratumoral heterogeneity within individual breast tumors is a well-known phenomenon that may contribute to drug resistance. This heterogeneity is dependent on several factors, such as types of oncogenic drivers and tumor precursor cells. The purpose of our study was to engineer a mouse mammary tumor model with intratumoral heterogeneity by using defined genetic perturbations. To achieve this, we used mice with knockout (−/−) of Ink4a/Arf, a tumor suppressor locus; these mice are known to be susceptible to non-mammary tumors such as fibrosarcoma. To induce mammary tumors, we retrovirally introduced an oncogene, HRAS(G12V), into Ink4a/Arf^−/− mammary cells in vitro, and those cells were inoculated into syngeneic mice mammary fat pads. We observed 100% tumorigenesis. The tumors formed were negative for estrogen receptor, progesterone receptor, and HER2. Further, they had pathological features similar to those of human triple-negative breast cancer (e.g. pushing borders, central necrosis). The tumors were found to be heterogeneous and included two subpopulations: CD49f⁻ quiescent cells and CD49f⁺ cells. Contrary to our expectation, CD49f⁻ quiescent cells had high tumor-initiating potential and CD49f⁺ cells had relatively low tumor-initiating potential. Gene expression analysis revealed that CD49f⁻ quiescent cells overexpressed epithelial-to-mesenchymal transition-driving genes, reminiscent of tumor-initiating cells and claudin-low breast cancer. Our animal model with intratumoral heterogeneity, derived from defined genetic perturbations, allows us to test novel molecular targeted drugs in a setting that mimics the intratumoral heterogeneity of human triple-negative breast cancer.

Spontaneous Adenosquamous Carcinoma with Rapid Growth and EMT-like Changes in the Mammary Gland of a Young Adult Female BALB/c Mouse

This study histopathologically and immunohistochemically investigated a spontaneously occurring single mass subcutaneously located in the left lower abdomen of a female BALB/cAJcl-nu/+ mouse at 10 weeks of age. The mass was about 20 × 15 × 10 mm in size after formalin fixation; nevertheless, it was not detected by clinical observations at 9 weeks of age. H&E staining revealed the tumor origin was epithelial and probably arose from the mammary gland, and the tumor cells demonstrated a squamous, acinar or polyhedral/basal pattern. A cell kinetics analysis revealed that many of the tumor cells of the squamous, acinar or polyhedral/basal component were positive for PCNA and cyclin D1, although there were a few of TUNEL-positive tumor cells in all of the components. An epithelial/mesenchymal analysis demonstrated that most of the tumor cells of the squamous and acinar components contained keratin and E-cadherin; however, most of the tumor cells of the polyhedral/basal component were less or very weakly positive for these markers. The tumor cells of the squamous component were negative for vimentin and SMA; however, many of the tumor cells of the polyhedral/basal component exhibited vimentin. In addition, expression of SMA was confirmed in some tumor cells of the acinar and basal components. Based on the microscopic and immunohistochemical characterizations, the tumor was diagnosed to be adenosquamous carcinoma that originated from the mammary gland with rapid growth, and the tumor cells demonstrated epithelial-mesenchymal transition-like changes.

Proliferative and nonproliferative lesions of the rat and mouse mammary, Zymbal's, preputial, and clitoral glands

The mammary gland of laboratory rodents is an important organ for the evaluation of effects of xenobiotics, especially those that perturb hormonal homeostasis or are potentially carcinogenic. Mammary gland cancer is a leading cause of human mortality and morbidity worldwide and is a subject of major research efforts utilizing rodent models. Zymbal's, preputial, and clitoral glands are standard tissues that are evaluated in animal models that enable human risk assessment of xenobiotics. A widely accepted and utilized international harmonization of nomenclature for mammary, Zymbal's, preputial, and clitoral gland lesions in laboratory animals will improve diagnostic alignment among regulatory and scientific research organizations and enrich international exchanges of information among toxicologists and pathologists.

Cooperativity of Rb, Brca1, and p53 in malignant breast cancer evolution

Breast cancers that are "triple-negative" for the clinical markers ESR1, PGR, and HER2 typically belong to the Basal-like molecular subtype. Defective Rb, p53, and Brca1 pathways are each associated with triple-negative and Basal-like subtypes. Our mouse genetic studies demonstrate that the combined inactivation of Rb and p53 pathways is sufficient to suppress the physiological cell death of mammary involution. Furthermore, concomitant inactivation of all three pathways in mammary epithelium has an additive effect on tumor latency and predisposes highly penetrant, metastatic adenocarcinomas. The tumors are poorly differentiated and have histologic features that are common among human Brca1-mutated tumors, including heterogeneous morphology, metaplasia, and necrosis. Gene expression analyses demonstrate that the tumors share attributes of both Basal-like and Claudin-low signatures, two molecular subtypes encompassed by the broader, triple-negative class defined by clinical markers.

Py2T murine breast cancer cells, a versatile model of TGFβ-induced EMT in vitro and in vivo

Introduction

Increasing evidence supports a role of an epithelial to mesenchymal transition (EMT) process in endowing subsets of tumor cells with properties driving malignant tumor progression and resistance to cancer therapy. To advance our understanding of the underlying mechanisms, we sought to generate a transplantable cellular model system that allows defined experimental manipulation and analysis of EMT in vitro and at the same time recapitulates oncogenic EMT in vivo.

Methodology/Results

We have established a stable murine breast cancer cell line (Py2T) from a breast tumor of an MMTV-PyMT transgenic mouse. Py2T cells display a metastable epithelial phenotype characterized by concomitant expression of luminal and basal cytokeratins and sheet migration. Exposure of Py2T cells to transforming growth factor β (TGFβ) in vitro induces reversible EMT accompanied by downregulation of E-cadherin and upregulation of mesenchymal markers, including EMT transcription factors, and a gain in single cell motility and invasiveness. Py2T cells give rise to tumors after orthotopic injection into syngeneic FVB/N mice. Notably, transplantation of epithelial Py2T cells results in the formation of invasive primary tumors with low to absent E-cadherin expression, indicating that the cells undergo EMT-like changes in vivo. This process appears to at least in part depend on TGFβ signaling, since tumors formed by Py2T cells expressing a dominant-negative version of TGFβ receptor widely maintain their epithelial differentiation status.

Conclusions/Significance

Together, the data demonstrate that the Py2T cell line represents a versatile model system to study the EMT process in vitro and in vivo. The observation that Py2T cells give rise to tumors and collectively undergo EMT-like changes in vivo highlights the suitability of the Py2T model system as a tool to study tumor-related EMT. In particular, Py2T cells may serve to corroborate recent findings relating EMT to cancer cell stemness, to therapy resistance and to tumor recurrence.

Trypsin-2 enhances carcinoma invasion by processing tight junctions and activating ProMT1-MMP

Enhanced proteolysis and altered tight junction (TJ) proteins associate with carcinoma invasion. We hypothesized that trypsin-2, a tumor-associated serine proteinase, induces tongue carcinoma invasion by activating pro-membrane type-1 matrix metalloproteinase (MT1-MMP) and disturbing the TJs. The effects of invasion were analyzed using trypsin-2 over-expressing human tongue squamous cell carcinoma cells (Try2-HSC-3) in vitro and in vivo. The invasion of Try2-HSC-3 cells was increased in mouse xenografts and human organotypic model. Trypsin-2 activated proMT1-MMP, as well as altered the expression of TJ protein claudin-7. In conclusion, trypsin-2 over-expression enhanced tongue carcinoma cell invasion by various genetic and proteolytic mechanisms.

Lunatic fringe deficiency cooperates with the Met/Caveolin gene amplicon to induce basal-like breast cancer

Basal-like breast cancers (BLBC) express a luminal progenitor gene signature. Notch receptor signaling promotes luminal cell fate specification in the mammary gland, while suppressing stem cell self-renewal. Here we show that deletion of Lfng, a sugar transferase that prevents Notch activation by Jagged ligands, enhances stem/progenitor cell proliferation. Mammary-specific deletion of Lfng induces basal-like and claudin-low tumors with accumulation of Notch intracellular domain fragments, increased expression of proliferation-associated Notch targets, amplification of the Met/Caveolin locus, and elevated Met and Igf-1R signaling. Human BL breast tumors, commonly associated with JAGGED expression, elevated MET signaling, and CAVEOLIN accumulation, express low levels of LFNG. Thus, reduced LFNG expression facilitates JAG/NOTCH luminal progenitor signaling and cooperates with MET/CAVEOLIN basal-type signaling to promote BLBC.

Comparative oncogenomics identifies breast tumors enriched in functional tumor-initiating cells

The claudin-low subtype is a recently identified rare molecular subtype of human breast cancer that expresses low levels of tight and adherens junction genes and shows high expression of epithelial-to-mesenchymal transition (EMT) genes. These tumors are enriched in gene expression signatures derived from human tumor-initiating cells (TICs) and human mammary stem cells. Through cross-species analysis, we discovered mouse mammary tumors that have similar gene expression characteristics as human claudin-low tumors and were also enriched for the human TIC signature. Such claudin-low tumors were similarly rare but came from a number of distinct mouse models, including the p53 null transplant model. Here we present a molecular characterization of 50 p53 null mammary tumors compared with other mouse models and human breast tumor subtypes. Similar to human tumors, the murine p53 null tumors fell into multiple molecular subtypes, including two basal-like, a luminal, a claudin-low, and a subtype unique to this model. The claudin-low tumors also showed high gene expression of EMT inducers, low expression of the miR-200 family, and low to absent expression of both claudin 3 and E-cadherin. These murine subtypes also contained distinct genomic DNA copy number changes, some of which are similarly altered in their cognate human subtype counterpart. Finally, limiting dilution transplantation revealed that p53 null claudin-low tumors are highly enriched for TICs compared with the more common adenocarcinomas arising in the same model, thus providing a unique preclinical mouse model to investigate the therapeutic response of TICs.

TGFβ and BMP-2 regulate epicardial cell invasion via TGFβR3 activation of the Par6/Smurf1/RhoA pathway

Coronary vessel development requires transfer of mesothelial cells to the heart surface to form the epicardium where some cells subsequently undergo epithelial-mesenchymal transformation (EMT) and invade the subepicardial matrix. Tgfbr3(-/-) mice die due to failed coronary vessel formation associated with decreased epicardial cell invasion but the mediators downstream of TGFβR3 are not well described. TGFβR3-dependent endocardial EMT stimulated by either TGFβ2 or BMP-2 requires activation of the Par6/Smurf1/RhoA 1pathway where Activin Receptor Like Kinase (ALK5) signals Par6 to act downstream of TGFβ to recruit Smurf1 to target RhoA for degradation to regulate apical-basal polarity and tight junction dissolution. Here we asked if this pathway was operant in epicardial cells and if TGFβR3 was required to access this pathway. Targeting of ALK5 in Tgfbr3(+/+) cells inhibited loss of epithelial character and invasion. Overexpression of wild-type (wt) Par6, but not dominant negative (dn) Par6, induced EMT and invasion while targeting Par6 by siRNA inhibited EMT and invasion. Overexpression of Smurf1 and dnRhoA induced loss of epithelial character and invasion. Targeting of Smurf1 by siRNA or overexpression of constitutively active (ca) RhoA inhibited EMT and invasion. In Tgfbr3(-/-) epicardial cells which have a decreased ability to invade collagen gels in response to TGFβ2, overexpression of wtPar6, Smurf1, or dnRhoA had a diminished ability to induce invasion. Overexpression of TGFβR3 in Tgfbr3(-/-) cells, followed by siRNA targeting of Par6 or Smurf1, diminished the ability of TGFβR3 to rescue invasion demonstrating that the Par6/Smurf1/RhoA pathway is activated downstream of TGFβR3 in epicardial cells.

Critical and reciprocal regulation of KLF4 and SLUG in transforming growth factor β-initiated prostate cancer epithelial-mesenchymal transition

Epithelial-mesenchymal transition (EMT) is implicated in various pathological processes within the prostate, including benign prostate hyperplasia (BPH) and prostate cancer progression. However, an ordered sequence of signaling events initiating carcinoma-associated EMT has not been established. In a model of transforming growth factor β (TGFβ)-induced prostatic EMT, SLUG is the dominant regulator of EMT initiation in vitro and in vivo, as demonstrated by the inhibition of EMT following Slug depletion. In contrast, SNAIL depletion was significantly less rate limiting. TGFβ-stimulated KLF4 degradation is required for SLUG induction. Expression of a degradation-resistant KLF4 mutant inhibited EMT, and furthermore, depletion of Klf4 was sufficient to initiate SLUG-dependent EMT. We show that KLF4 and another epithelial determinant, FOXA1, are direct transcriptional inhibitors of SLUG expression in mouse and human prostate cancer cells. Furthermore, self-reinforcing regulatory loops for SLUG-KLF4 and SLUG-FOXA1 lead to SLUG-dependent binding of polycomb repressive complexes to the Klf4 and Foxa1 promoters, silencing transcription and consolidating mesenchymal commitment. Analysis of tissue arrays demonstrated decreased KLF4 and increased SLUG expression in advanced-stage primary prostate cancer, substantiating the involvement of the EMT signaling events described in model systems.

Morphological and Immunohistochemical Characterization of Sarcomatous Tumors in Wild-Type and Genetically Engineered Mice

Malignant soft tissue tumors are commonly observed in wild-type and gene-targeted mice. These tumors have different degrees of differentiation, cellularity, cellular atypia, nuclear pleomorphism, normal and abnormal mitosis, and giant tumor cells with enlarged polylobulated nuclei. They are often diagnosed as pleomorphic sarcoma, undifferentiated sarcoma, fibrosarcoma, malignant fibrous histiocytoma, sarcoma, or sarcoma, not otherwise specified. Pleomorphic sarcomas have no morphological differentiation toward a differentiated mesenchymal or other tumor type in hematoxylin and eosin–stained sections. With the use of immunohistochemistry, human and mouse, tumors associated with these broad nonspecific diagnoses can often be demonstrated to be of a specific cellular lineage. With mouse models being used to delineate the molecular mechanisms, pathogenesis, and cellular origin of human sarcomas, it will be necessary to correlate the morphological and cellular lineage and the molecular profiles of the pleomorphic tumors associated with these mouse models. The results presented here show that with the use of immunohistochemistry, the cellular lineage of many mouse tumors with pleomorphic features can be determined.

The H4 histamine receptor agonist, clobenpropit, suppresses human cholangiocarcinoma progression by disruption of epithelial mesenchymal transition and tumor metastasis

Cholangiocarcinoma (CCA) is a biliary cancer arising from damaged bile ducts. Epithelial-mesenchymal transition (EMT) occurs as epithelial cells begin to resemble mesenchymal cells leading to increased invasion potential as the extracellular matrix (ECM) degrades. Histamine exerts its effects by way of four receptors (H1-H4 HRs). Clobenpropit, a potent H4HR agonist, inhibits mammary adenocarcinoma growth. We have shown that (1) cholangiocytes and CCA cells express H1-H4 HRs and (2) the H3HR decreases CCA proliferation. We evaluated the effects of clobenpropit on CCA proliferation, invasion, EMT phenotypes, and ECM degradation. In vitro, we used CCA cell lines to study proliferation, signaling pathways, and the morphological invasive potential. Gene and protein expression of the hepatobiliary epithelial markers CK-7, CK-8, and CK-19, the focal contact protein paxillin, and the mesenchymal markers fibronectin, s100A4, and vimentin were evaluated. Cell invasion across an ECM layer was quantitated and matrix metalloproteinase-1, -2, -3, -9, and -11 gene and protein expression was examined. Evaluation of the specific role of H4HR was performed by genetic knockdown of the H3HR and overexpression of H4HR. Proliferation was evaluated by proliferating cellular nuclear antigen immunoblotting. In vivo, xenograft tumors were treated with either vehicle or clobenpropit for 39 days. Tumor volume was recorded every other day. Clobenpropit significantly decreased CCA proliferation by way of a Ca(2+) -dependent pathway and altered morphological development and invasion. Loss of H3HR expression or overexpression of H4HR significantly decreased CCA proliferation. In vivo, clobenpropit inhibited xenograft tumor growth compared with controls.

CONCLUSION

Modulation of H4HR by clobenpropit disrupts EMT processes, ECM breakdown, and invasion potential and decreases tumor growth. Interruption of tumorigenesis and invasion by histamine may add to therapeutic advances for CCAs.

Three interrelated themes in current breast cancer research: gene addiction, phenotypic plasticity, and cancer stem cells

Recent efforts to understand breast cancer biology involve three interrelated themes that are founded on a combination of clinical and experimental observations. The central concept is gene addiction. The clinical dilemma is the escape from gene addiction, which is mediated, in part, by phenotypic plasticity as exemplified by epithelial-to-mesenchymal transition and mesenchymal-to-epithelial transition. Finally, cancer stem cells are now recognized as the basis for minimal residual disease and malignant progression over time. These themes cooperate in breast cancer, as induction of epithelial-to-mesenchymal transition enhances self-renewal and expression of cancer stem cells, which are believed to facilitate tumor resistance.

Heterogeneity in MYC-induced mammary tumors contributes to escape from oncogene dependence

A hallmark of human cancer is heterogeneity, reflecting the complex series of changes resulting in the activation of oncogenes coupled with inactivation of tumor suppressor genes. Breast cancer is no exception and indeed, many studies have revealed considerable complexity and heterogeneity in the population of primary breast tumors and substantial changes in a recurrent breast tumor that has acquired metastatic properties and drug resistance. We have made use of a Myc-inducible transgenic mouse model of breast cancer in which elimination of Myc activity following tumor development initially leads to a regression of a subset of tumors generally followed by de novo Myc-independent growth. We have observed that tumors that grow independent of Myc expression have gene profiles that are distinct from the primary tumors with characteristics indicative of an epithelial-mesenchymal transition (EMT) phenotype. Phenotypic analyses of Myc-independent tumors confirm the acquisition of an EMT phenotype suggested to be associated with invasive and migratory properties in human cancer cells. Further genomic analyses reveal mouse mammary tumors growing independent of myc have a higher probability of exhibiting a gene signature similar to that observed for human 'tumor-initiating' cells. Collectively, the data reveal genetic alterations that underlie tumor progression and an escape from Myc-dependent growth in a transgenic mouse model that can provide insights to what occurs in human cancers as they acquire drug resistance and metastatic properties.

Metastasis Update: Human Prostate Carcinoma Invasion via Tubulogenesis

This paper proposes that human prostate carcinoma primarily invades as a cohesive cell collective through a mechanism similar to embryonic tubulogenesis, instead of the popular epithelial-mesenchymal transformation (EMT) model. Evidence supporting a tubulogenesis model is presented, along with suggestions for additional research. Additionally, observations documenting cell adhesion molecule changes in tissue and stromal components are reviewed, allowing for comparisons between the current branching morphogenesis models and the tubulogenesis model. Finally, the implications of this model on prevailing views of therapeutic and diagnostic strategies for aggressive prostatic disease are considered.

Elevated PI3K signaling drives multiple breast cancer subtypes

Most human breast tumors have mutations that elevate signaling through a key metabolic pathway that is induced by insulin and a number of growth factors. This pathway serves to activate an enzyme known as phosphatidylinositol 3' kinase (PI3K) as well as to regulate proteins that signal in response to lipid products of PI3K. The specific mutations that activate this pathway in breast cancer can occur in genes coding for tyrosine kinase receptors, adaptor proteins linked to PI3K, catalytic and regulatory subunits of PI3K, serine/threonine kinases that function downstream of PI3K, and also phosphatidylinositol 3' phosphatase tumor suppressors that function to antagonize this pathway. While each genetic change results in net elevation of PI3K pathway signaling, and all major breast cancer subtypes show pathway activation, the specific mutation(s) involved in any one tumor may play an important role in defining tumor subtype, prognosis and even sensitivity to therapy. Here, we describe mouse models of breast cancer with elevated PI3K signaling, and how they may be used to guide development of novel therapeutics.

Quantitative metric profiles capture three-dimensional temporospatial architecture to discriminate cellular functional states

BACKGROUND

Computational analysis of tissue structure reveals sub-visual differences in tissue functional states by extracting quantitative signature features that establish a diagnostic profile. Incomplete and/or inaccurate profiles contribute to misdiagnosis.

METHODS

In order to create more complete tissue structure profiles, we adapted our cell-graph method for extracting quantitative features from histopathology images to now capture temporospatial traits of three-dimensional collagen hydrogel cell cultures. Cell-graphs were proposed to characterize the spatial organization between the cells in tissues by exploiting graph theory wherein the nuclei of the cells constitute the nodes and the approximate adjacency of cells are represented with edges. We chose 11 different cell types representing non-tumorigenic, pre-cancerous, and malignant states from multiple tissue origins.

RESULTS

We built cell-graphs from the cellular hydrogel images and computed a large set of features describing the structural characteristics captured by the graphs over time. Using three-mode tensor analysis, we identified the five most significant features (metrics) that capture the compactness, clustering, and spatial uniformity of the 3D architectural changes for each cell type throughout the time course. Importantly, four of these metrics are also the discriminative features for our histopathology data from our previous studies.

CONCLUSIONS

Together, these descriptive metrics provide rigorous quantitative representations of image information that other image analysis methods do not. Examining the changes in these five metrics allowed us to easily discriminate between all 11 cell types, whereas differences from visual examination of the images are not as apparent. These results demonstrate that application of the cell-graph technique to 3D image data yields discriminative metrics that have the potential to improve the accuracy of image-based tissue profiles, and thus improve the detection and diagnosis of disease.

Prostate epithelial Pten/TP53 loss leads to transformation of multipotential progenitors and epithelial to mesenchymal transition

Loss of PTEN and loss of TP53 are common genetic aberrations occurring in prostate cancer. PTEN and TP53 contribute to the regulation of self-renewal and differentiation in prostate progenitors, presumptive tumor initiating cells for prostate cancer. Here we characterize the transformed phenotypes resulting from deletion of the Pten and TP53 tumor suppressors in prostate epithelium. Using the PB-Cre4(+)Pten(fl/fl)TP53(fl/fl) model of prostate cancer, we describe the histological and metastatic properties of primary tumors, transplanted primary tumor cells, and clonal cell lines established from tumors. Adenocarcinoma was the major primary tumor type that developed, which progressed to lethal sarcomatoid carcinoma at approximately 6 months of age. In addition, basal carcinomas and prostatic urothelial carcinomas were observed. We show that tumor heterogeneity resulted, at least in part, from the transformation of multipotential progenitors. CK8+ luminal epithelial cells were capable of undergoing epithelial to mesenchymal transition in vivo to sarcomatoid carcinomas containing osseous metaplasia. Metastasis rarely was observed from primary tumors, but metastasis to lung and lymph nodes occurred frequently from orthotopic tumors initiated from a biphenotypic clonal cell line. Androgen deprivation influenced the differentiated phenotypes of metastases. These data show that one functional consequence of Pten/TP53 loss in prostate epithelium is lineage plasticity of transformed cells.

Metastasis suppressor genes at the interface between the environment and tumor cell growth

The molecular mechanisms and genetic programs required for cancer metastasis are sometimes overlapping, but components are clearly distinct from those promoting growth of a primary tumor. Every sequential, rate-limiting step in the sequence of events leading to metastasis requires coordinated expression of multiple genes, necessary signaling events, and favorable environmental conditions or the ability to escape negative selection pressures. Metastasis suppressors are molecules that inhibit the process of metastasis without preventing growth of the primary tumor. The cellular processes regulated by metastasis suppressors are diverse and function at every step in the metastatic cascade. As we gain knowledge into the molecular mechanisms of metastasis suppressors and cofactors with which they interact, we learn more about the process, including appreciation that some are potential targets for therapy of metastasis, the most lethal aspect of cancer. Until now, metastasis suppressors have been described largely by their function. With greater appreciation of their biochemical mechanisms of action, the importance of context is increasingly recognized especially since tumor cells exist in myriad microenvironments. In this chapter, we assemble the evidence that selected molecules are indeed suppressors of metastasis, collate the data defining the biochemical mechanisms of action, and glean insights regarding how metastasis suppressors regulate tumor cell communication to-from microenvironments.

Deletion of the proline-rich region of the murine metastasis susceptibility gene Brd4 promotes epithelial-to-mesenchymal transition- and stem cell-like conversion

The bromodomain-containing chromatin-modifying factor BRD4 is an inherited susceptibility gene for breast cancer progression and metastasis, but its functionality in these settings has yet to be explored. Here we show that deletion of either of the BRD4 bromodomains had modest effects on the metastatic suppression ability of BRD4. In contrast, expression of the natural short isoform of BRD4 that truncates the protein after the SEED domain restored progression and metastatic capacity. Unexpectedly, deletion of the proline-rich region induced mesenchymal-like conversion and acquisition of cancer stem cell-like properties, which are mediated by the carboxy-terminal P-TEFb binding domain. Deletion of this proline-rich region also induced a gene expression signature that predicted poor outcome in human breast cancer data sets and that overlapped G3 grade human breast tumors. Thus our findings suggest that BRD4 may be altering the predisposition of tumors to undergo conversion to a more de-differentiated or primitive state during metastatic progression.

Breast cancer stem cells: treatment resistance and therapeutic opportunities

The clinical and pathologic heterogeneity of human breast cancer has long been recognized. Now, molecular profiling has enriched our understanding of breast cancer heterogeneity and yielded new prognostic and predictive information. Despite recent therapeutic advances, including the HER2-specific agent, trastuzumab, locoregional and systemic disease recurrence remain an ever-present threat to the health and well being of breast cancer survivors. By definition, disease recurrence originates from residual treatment-resistant cells, which regenerate at least the initial breast cancer phenotype. The discovery of the normal breast stem cell has re-ignited interest in the identity and properties of breast cancer stem-like cells and the relationship of these cells to the repopulating ability of treatment-resistant cells. The cancer stem cell model of breast cancer development contrasts with the clonal evolution model, whereas the mixed model draws on features of both. Although the origin and identity of breast cancer stem-like cells is contentious, treatment-resistant cells survive and propagate only because aberrant and potentially druggable signaling pathways are recruited. As a means to increase the rates of breast cancer cure, several approaches to specific targeting of the treatment-resistant cell population exist and include methods for addressing the problem of radioresistance in particular.

Molecular and functional imaging of invasion and metastasis: windows into the metastatic cascade

The ability of cancer cells to invade, metastasize, and form distant colonies, is one of the key characteristics that confers lethality to cancer. Metastatic cancer cells typically become refractory to treatment. The metastatic cascade is a multi-step process that is governed by events within the cancer cell, the tumor microenvironment, and the distant environments that are invaded and colonized by the cancer cells. Noninvasive imaging techniques are facilitating a close examination of the stepwise journey of the cancer cell from the primary tumor to the distant metastatic site. Here we have discussed the metastatic process, and how molecular and functional imaging of cancer are providing new insights into the metastatic cascade that can be exploited for treatment of metastatic disease.