Role of Ets transcription factors in mammary gland development and oncogenesis

ETV4 mediates the wnt/β-catenin pathway through transcriptional activation of ANXA2 to promote hepatitis B virus-associated liver hepatocellular carcinoma progression

ETS variant 4 (ETV4) has been implicated in the development of various cancers. However, the molecular events mediated by ETV4 in liver cancer are poorly understood, especially in Hepatitis B virus (HBV)-associated liver hepatocellular carcinoma (LIHC). Here, we aimed to identify the target involved in ETV4-driven hepatocarcinogenesis. Bioinformatics analysis revealed that ETV4 was highly expressed in patients with HBV-associated LIHC, and HBV infection promoted the expression of ETV4 in LIHC cells. Inhibition of ETV4 repressed the proliferation, migration, invasion of LIHC cells and suppressed the secretion of HBV and the replication of HBV DNA. ANXA2 expression in LIHC patients was positively correlated with ETV4 expression. ChIP and dual-luciferase reporter assays revealed that ETV4 elevated the ANXA2 expression at the transcriptional level by binding to the ANXA2 promoter. Overexpression of ANXA2 reversed the inhibitory effect of sh-ETV4 on the malignant biological behaviors of HBV-infected LIHC cells by activating the Wnt/β-catenin pathway. In conclusion, ETV4 mediates the activation of Wnt/β-catenin pathway through transcriptional activation of ANXA2 expression to promote HBV-associated LIHC progression.

Expression of E26 transformation specific-1 (ETS-1) in tumour-infiltrating lymphocytes (TILs) is adverse prognostic factor in invasive breast cancer

AIM OF THE STUDY

The microenvironment depicts the relationship between tumour cells and immune response, and every insight into stromal lymphocytes could contribute to explain their role and activity. E26 transformation specific-1 (ETS-1) is a transcription factor that is active in cell proliferation. We analysed its immunohistochemical expression in tumour infiltrating lymphocytes (TILs) in invasive breast cancer and correlated its immunohistochemical score (IHS) to traditional predictive and prognostic factors and survival.

MATERIALS AND METHODS

The sample contains data of 121 patients with invasive breast cancer, not otherwise specified (NOS) who underwent mammectomy and lymphadenectomy in 2002 at the Clinical Hospital Centre Zagreb, Croatia. Paraffin blocks of the tumour tissue were collected from the pathological archive. Three representative areas of every patient were chosen and multiple tissue samples were made. Immunohistochemical staining with rabbit anti-ETS-1 (Novocastra, UK) and the ABC method was performed on a DAKO Autostainer. The expression of ETS-1 in stromal TILs was analysed on an Olympus 41 microscope. The IHS score was calculated and correlated with clinical and pathological parameters, as well as disease-free survival (DFS) and overall survival (OS).

RESULTS

In almost all patients (95%), some expression of ETS-1 in TILs was found. A moderate/high score of ETS-1 correlated with larger tumour size and higher histological grade, high proliferation index and low progesterone receptors (PgR). The patients with moderate/high ETS-1 expression in TILs had shorter DFS than patients with weak/negative ETS-1 expression.

CONCLUSION

In invasive breast cancer NOS, expression of ETS-1 in TILs is an adverse prognostic factor.

ETV4 transcription factor and MMP13 metalloprotease are interplaying actors of breast tumorigenesis

BACKGROUND

The ETS transcription factor ETV4 is involved in the main steps of organogenesis and is also a significant mediator of tumorigenesis and metastasis, such as in breast cancer. Indeed, ETV4 is overexpressed in breast tumors and is associated with distant metastasis and poor prognosis. However, the cellular and molecular events regulated by this factor are still misunderstood. In mammary epithelial cells, ETV4 controls the expression of many genes, MMP13 among them. The aim of this study was to understand the function of MMP13 during ETV4-driven tumorigenesis.

METHODS

Different constructs of the MMP13 gene promoter were used to study the direct regulation of MMP13 by ETV4. Moreover, cell proliferation, migration, invasion, anchorage-independent growth, and in vivo tumorigenicity were assayed using models of mammary epithelial and cancer cells in which the expression of MMP13 and/or ETV4 is modulated. Importantly, the expression of MMP13 and ETV4 messenger RNA was characterized in 456 breast cancer samples.

RESULTS

Our results revealed that ETV4 promotes proliferation, migration, invasion, and anchorage-independent growth of the MMT mouse mammary tumorigenic cell line. By investigating molecular events downstream of ETV4, we found that MMP13, an extracellular metalloprotease, was an ETV4 target gene. By overexpressing or repressing MMP13, we showed that this metalloprotease contributes to proliferation, migration, and anchorage-independent clonogenicity. Furthermore, we demonstrated that MMP13 inhibition disturbs proliferation, migration, and invasion induced by ETV4 and participates to ETV4-induced tumor formation in immunodeficient mice. Finally, ETV4 and MMP13 co-overexpression is associated with poor prognosis in breast cancer.

CONCLUSION

MMP13 potentiates the effects of the ETV4 oncogene during breast cancer genesis and progression.

Protein deregulation associated with breast cancer metastasis

Breast cancer is one of the most prevalent malignancies worldwide. It consists of a group of tumor cells that have the ability to grow uncontrollably, overcome replicative senescence (tumor progression) and metastasize within the body. Metastases are processes that consist of an array of complex gene dysregulation events. Although these processes are still not fully understood, the dysregulation of a number of key proteins must take place if the tumor cells are to disseminate and metastasize. It is now widely accepted that future effective and innovative treatments of cancer metastasis will have to encompass all the major components of malignant transformation. For this reason, much research is now being carried out into the mechanisms that govern the malignant transformation processes. Recent research has identified key genes involved in the development of metastases, as well as their mechanisms of action. A detailed understanding of the encoded proteins and their interrelationship generates the possibility of developing novel therapeutic approaches. This review will focus on a select group of proteins, often deregulated in breast cancer metastasis, which have shown therapeutic promise, notably, EMT, E-cadherin, Osteopontin, PEA3, Transforming Growth Factor Beta (TGF-β) and Ran.

HER2 and uPAR cooperativity contribute to metastatic phenotype of HER2-positive breast cancer

Human epidermal growth factor receptor type 2 (HER2)-positive breast carcinoma is highly aggressive and mostly metastatic in nature though curable/manageable in part by molecular targeted therapy. Recent evidence suggests a subtype of cells within HER2-positive breast tumors that concomitantly expresses the urokinase plasminogen activator receptor (uPAR) with inherent stem cell/mesenchymal-like properties promoting tumor cell motility and a metastatic phenotype. This HER-positive/uPAR-positive subtype may be partially responsible for the failure of HER2-targeted treatment strategies. Herein we discuss and substantiate the cumulative preclinical and clinical evidence on HER2-uPAR cooperativity in terms of gene co-amplification and/or mRNA/protein co-overexpression. We then propose a regulatory signaling model that we hypothesize to maintain upregulation and cooperativity between HER2 and uPAR in aggressive breast cancer. An improved understanding of the HER2/uPAR interaction in breast cancer will provide critical biomolecular information that may help better predict disease course and response to therapy.

Loss of a negative feedback loop involving pea3 and cyclin d2 is required for pea3-induced migration in transformed mammary epithelial cells

The Ets family transcription factor Pea3 (ETV4) is involved in tumorigenesis especially during the metastatic process. Pea3 is known to induce migration and invasion in mammary epithelial cell model systems. However, the molecular pathways regulated by Pea3 are still misunderstood. In the current study, using in vivo and in vitro assays, Pea3 increased the morphogenetic and tumorigenic capacity of mammary epithelial cells by modulating their cell morphology, proliferation, and migration potential. In addition, Pea3 overexpression favored an epithelial-mesenchymal transition (EMT) triggered by TGF-β1. During investigation for molecular events downstream of Pea3, Cyclin D2 (CCND2) was identified as a new Pea3 target gene involved in the control of cellular proliferation and migration, a finding that highlights a new negative regulatory loop between Pea3 and Cyclin D2. Furthermore, Cyclin D2 expression was lost during TGF-β1-induced EMT and Pea3-induced tumorigenesis. Finally, restored Cyclin D2 expression in Pea3-dependent mammary tumorigenic cells decreased cell migration in an opposite manner to Pea3. As such, these data demonstrate that loss of the negative feedback loop between Cyclin D2 and Pea3 contributes to Pea3-induced tumorigenesis.

IMPLICATIONS

This study reveals molecular insight into how the Ets family transcription factor Pea3 favors EMT and contributes to tumorigenesis via a negative regulatory loop with Cyclin D2, a new Pea3 target gene.

PDEF promotes luminal differentiation and acts as a survival factor for ER-positive breast cancer cells

Breast cancer is a heterogeneous disease and can be classified based on gene expression profiles that reflect distinct epithelial subtypes. We identify prostate-derived ETS factor (PDEF) as a mediator of mammary luminal epithelial lineage-specific gene expression and as a factor required for tumorigenesis in a subset of breast cancers. PDEF levels strongly correlate with estrogen receptor (ER)-positive luminal breast cancer, and PDEF transcription is inversely regulated by ER and GATA3. Furthermore, PDEF is essential for luminal breast cancer cell survival and is required in models of endocrine resistance. These results offer insights into the function of this ETS factor that are clinically relevant and may be of therapeutic value for patients with breast cancer treated with endocrine therapy.

Impaired c-src activation and motility defects in PEA3-null fibroblasts

Null mutations in the pea3 allele compromise the capacity of mammary tumors to metastasize in MMTV-Neu/ErbB2/HER2 transgenic mice, indicating a motility defect in PEA3-null cells. Cellular and biochemical analyses of established PEA3-null fibroblasts show impaired motility and aberrant localization of adhesion proteins in spreading cells. Our results show that PEA3-/- cells express normal levels of key adhesion components, but that spreading PEA3-null cells fail to activate c-src and to downregulate phospho-FAK(Y397), suggesting that focal adhesion signaling is impaired. Supporting this, biochemical analysis revealed that adhesion complex-associated proteins such as p130Cas failed to undergo tyrosine phosphorylation and dissociated from the adhesion complex with delayed kinetics. Overall our data show that the motility defects observed in PEA3-null cells are due to altered adhesion signaling.

NOTCH-1 and NOTCH-4 are novel gene targets of PEA3 in breast cancer: novel therapeutic implications

Introduction

Women with triple-negative breast cancer have the worst prognosis, frequently present with metastatic tumors and have few targeted therapy options. Notch-1 and Notch-4 are potent breast oncogenes that are overexpressed in triple-negative and other subtypes of breast cancer. PEA3, an ETS transcription factor, is also overexpressed in triple-negative and other breast cancer subtypes. We investigated whether PEA3 could be the critical transcriptional activator of Notch receptors in MDA-MB-231 and other breast cancer cells.

Methods

Real-time PCR and Western blot analysis were performed to detect Notch-1, Notch-2, Notch-3 and Notch-4 receptor expression in breast cancer cells when PEA3 was knocked down by siRNA. Chromatin immunoprecipitation was performed to identify promoter regions for Notch genes that recruited PEA3. TAM-67 and c-Jun siRNA were used to identify that c-Jun was necessary for PEA3 enrichment on the Notch-4 promoter. A Notch-4 luciferase reporter was used to confirm that endogenous PEA3 or AP-1 activated the Notch-4 promoter region. Cell cycle analysis, trypan blue exclusion, annexin V flow cytometry, colony formation assay and an in vivo xenograft study were performed to determine the biological significance of targeting PEA3 via siRNA, Notch signaling via a γ-secretase inhibitor, or both.

Results

Herein we provide new evidence for transcriptional regulation of Notch by PEA3 in breast cancer. PEA3 activates Notch-1 transcription in MCF-7, MDA-MB-231 and SKBr3 breast cancer cells. PEA3 activates Notch-4 transcription in MDA-MB-231 cells where PEA3 levels are endogenously high. In SKBr3 and BT474 breast cancer cells where PEA3 levels are low, overexpression of PEA3 increases Notch-4 transcripts. Chromatin immunoprecipitation confirmed the enrichment of PEA3 on Notch-1 and Notch-4 promoters in MDA-MB-231 cells. PEA3 recruitment to Notch-1 was AP-1-independent, whereas PEA3 recruitment to Notch-4 was c-JUN-dependent. Importantly, the combined inhibition of Notch signaling via a γ-secretase inhibitor (MRK-003 GSI) and knockdown of PEA3 arrested growth in the G₁ phase, decreased both anchorage-dependent and anchorage-independent growth and significantly increased apoptotic cells in vitro. Moreover, either PEA3 knockdown or MRK-003 GSI treatment significantly reduced tumor growth of MDA-MB-231 xenografts in vivo.

Conclusions

Taken together, the results from this study demonstrate for the first time that Notch-1 and Notch-4 are novel transcriptional targets of PEA3 in breast cancer cells. Targeting of PEA3 and/or Notch pathways might provide a new therapeutic strategy for triple-negative and possibly other breast cancer subtypes.

Minireview: steroid receptor coactivator-3: a multifarious coregulator in mammary gland metastasis

A member of the steroid receptor coactivator (SRC)/p160 family, SRC-3 acts as a coregulator for nuclear receptor (NR) and non-NR transcription factors. Such coregulator pleiotropy enables SRC-3 to influence a myriad of signaling networks that are essential for normal physiology and pathophysiology. Although SRC-3's proliferative role in primary tumor formation in the mammary gland is well established, a role for this oncogenic coregulator in tumor cell motility and invasion has only recently been elucidated. In the nucleus, SRC-3 is required for the execution of the epithelial-mesenchymal transition, a programming step which endows an immotile cancer cell with motile and invasive characteristics. Nuclear SRC-3 is also essential for proteolytic breakdown of the extracellular matrix by matrix-metalloproteinases, a process which enables primary tumor cell invasion into the surrounding stroma. At the plasma membrane, however, a truncated isoform of SRC-3 (SRC-3Δ4) serves as a signaling adaptor for the epidermal growth factor→focal adhesion kinase→c-Src signal transduction pathway, a signaling cascade that is central to growth factor-induced cell migration and invasion. Together, these studies underscore a pivotal role for SRC-3 not only as a proto-oncogene but also as a prometastatic factor during the early steps in the invasion-metastasis cascade. Beyond furnishing critical mechanistic insights into SRC-3's involvement in mammary tumor progression, these findings provide opportunities to develop new approaches for breast cancer diagnosis and intervention.

Transcript profiling of Elf5+/- mammary glands during pregnancy identifies novel targets of Elf5

Background

Elf5, an epithelial specific Ets transcription factor, plays a crucial role in the pregnancy-associated development of the mouse mammary gland. Elf5^−/− embryos do not survive, however the Elf5^+/− mammary gland displays a severe pregnancy-associated developmental defect. While it is known that Elf5 is crucial for correct mammary development and lactation, the molecular mechanisms employed by Elf5 to exert its effects on the mammary gland are largely unknown.

Principal Findings

Transcript profiling was used to investigate the transcriptional changes that occur as a result of Elf5 haploinsufficiency in the Elf5^+/− mouse model. We show that the development of the mouse Elf5^+/− mammary gland is delayed at a transcriptional and morphological level, due to the delayed increase in Elf5 protein in these glands. We also identify a number of potential Elf5 target genes, including Mucin 4, whose expression, is directly regulated by the binding of Elf5 to an Ets binding site within its promoter.

Conclusion

We identify novel transcriptional targets of Elf5 and show that Muc4 is a direct target of Elf5, further elucidating the mechanisms through which Elf5 regulates proliferation and differentiation in the mammary gland.

Social isolation reduces mammary development, tumor incidence, and expression of epigenetic regulators in wild-type and p53-heterozygotic mice

Chronic stress is associated with more rapid tumor progression, and recent evidence suggests that stress may contribute to social and ethnic disparities in the incidence and mortality of breast cancer. We evaluated the p53(+/-) FVB/N mouse as a model to investigate effects of chronic social stress on mammary gland development, gene expression, and tumorigenesis. We individually housed (IH) wild-type and p53(+/-) female FVB/N mice, starting at weaning. At 14 weeks of age, both wild-type and p53(+/-) IH mice showed strikingly reduced mammary development compared with group-housed (GH) controls, with IH mice having significantly fewer preterminal end buds. This morphologic difference was not reflected in levels of mammary transcripts for estrogen receptor-alpha or progestin receptor. However, IH increased levels of mRNA for the kisspeptin receptor in the medial preoptic area of the hypothalamus, associated with reduced duration of estrous cycles. Furthermore, IH altered mammary transcripts of genes associated with DNA methylation; transcripts for methyl-binding protein 2 and DNA methyltransferase 3b (DNMT3b), but not DNMT1 and DNMT3a, were reduced in IH compared with GH females. Interestingly, the glands of p53(+/-) females showed reduced expression of all these mediators compared with wild-type females. However, contrary to our initial hypothesis, IH did not increase mammary tumorigenesis. Rather, p53(+/-) GH females developed significantly more mammary tumors than IH mice. Together, these data suggest that social isolation initiated at puberty might confound studies of tumorigenesis by altering mammary development in mouse models.

Pea3 transcription factors and wnt1-induced mouse mammary neoplasia

The role of the PEA3 subfamily of Ets transcription factors in breast neoplasia is controversial. Although overexpression of PEA3 (E1AF/ETV4), and of the related factors ERM (ETV5) and ER81 (ETV1), have been observed in human and mouse breast tumors, PEA3 factors have also been ascribed a tumor suppressor function. Here, we utilized the MMTV/Wnt1 mouse strain to further interrogate the role of PEA3 transcription factors in mammary tumorigenesis based on our previous observation that Pea3 is highly expressed in MMTV/Wnt1 mammary tumors. Pea3 expression in mouse mammary tissues was visualized using a Pea3^NLSlacZ reporter strain. In normal mammary glands, Pea3 expression is predominantly confined to myoepithelial cells. Wnt1 transgene expression induced marked amplification of this cell compartment in nontumorous mammary glands, accompanied by an apparent increase in Pea3 expression. The pattern of Pea3 expression in MMTV/Wnt1 mammary glands recapitulated the cellular profile of activated β-catenin/TCF signaling, which was visualized using both β-catenin immunohistochemistry and the β-catenin/TCF-responsive reporter Axin2^NLSlacZ. To test the requirement for PEA3 factors in Wnt1-induced tumorigenesis, we employed a mammary-targeted dominant negative PEA3 transgene, ΔNPEA3En. Expression of ΔNPEA3En delayed early-onset tumor formation in MMTV/Wnt1 virgin females (P = 0.03), suggesting a requirement for PEA3 factor function for Wnt1-driven tumor formation. Consistent with this observation, expression of the ΔNPEA3En transgene was profoundly reduced in mammary tumors compared to nontumorous mammary glands from bigenic MMTV/Wnt1, MMTV/ΔNPEA3En mice (P = 0.01). Our data provide the first description of Wnt1-mediated expansion of the Pea3-expressing myoepithelial compartment in nontumorous mammary glands. Consistent with this observation, mammary myoepithelium was selectively responsive to Wnt1. Together these data suggest the MMTV/Wnt1 strain as a potential model of basal breast cancer. Furthermore, this study provides evidence for a protumorigenic role of PEA3 factors in breast neoplasia, and supports targeting the PEA3 transcription factor family in breast cancer.

Osteopontin provides early proliferative drive and may be dependent upon aberrant c-myc signalling in murine intestinal tumours

Osteopontin is thought to play an important role in tumour metastasis. In a previous expression profiling study of murine intestinal adenomas, we found that Opn was up-regulated. We also found beta-catenin binding motifs in the Opn promoter implying that, contrary to current beliefs, induction of Opn may occur during early tumourigenesis. We studied 59 murine intestinal adenomas for Opn expression and every tumour showed up-regulation compared to normal mucosa confirming early deregulation in these tumours. To determine whether Opn makes a functional contribution to tumourigenesis, Opn was knocked down in the murine colorectal cancer cell line CMT93. Inhibition of Opn expression resulted in decreased cell numbers. To determine the mechanism of Opn induction in these tumours, the Opn promoter was cloned and each of the putative beta-catenin binding motifs was mutated. No major change in Opn promoter activity was observed thereby excluding Opn as a direct beta-catenin target gene. However, mutation of one of two putative c-myc binding sites in the Opn promoter led to near complete loss of promoter activity whilst mutation of one of four PEA3 binding sites led to a 50% reduction in promoter activity. We conclude that Opn deregulation is an early event in intestinal tumourigenesis which may promote tumour development by altering either proliferation or apoptosis to increase tumour cell numbers. Opn expression in the intestine is dependent on c-myc binding sites in the promoter. Since c-myc is a known beta-catenin target gene, deregulation of Opn may be a secondary effect of aberrant Wnt signalling.

FOG-1-mediated recruitment of NuRD is required for cell lineage re-enforcement during haematopoiesis

The transcriptional co-factor Friend of GATA1 (FOG-1) has been shown to interact with subunits of the nucleosome remodelling and histone deacetylase (NuRD) complex through a specific motif located at its N-terminus. To test the importance of FOG-1/NuRD interaction for haematopoiesis in vivo, we generated mice with a mutation that specifically disrupts FOG-1/NuRD interaction (FOG-1(R3K5A)). Homozygous FOG-1(R3K5A) mice were found to have splenomegaly, extramedullary erythropoiesis, granulocytosis and thrombocytopaenia secondary to a block in megakaryocyte maturation. FOG-1(R3K5A/R3K5A) megakaryocytes and erythroid progenitors expressed increased levels of GATA2, showing that FOG-1/NuRD interaction is required for the earlier described 'GATA Switch'. In addition, ablation of FOG-1/NuRD interaction led to inappropriate expression of mast cell and eosinophil-specific genes in the megakaryocyte and erythroid lineages. Chromatin immunoprecipitation experiments revealed that the NuRD complex was not properly recruited to a mast cell gene promoter in FOG-1(R3K5A/R3K5A) megakaryocytes, suggesting that FOG-1/NuRD interaction is required for the direct suppression of mast cell gene expression. Taken together, these results underscore the importance of the FOG-1/NuRD interaction for the re-enforcement of lineage commitment during erythropoiesis and megakaryopoiesis in vivo.

Lessons in signaling and tumorigenesis from polyomavirus middle T antigen

The small DNA tumor viruses have provided a very long-lived source of insights into many aspects of the life cycle of eukaryotic cells. In recent years, the emphasis has been on cancer-related signaling. Here we review murine polyomavirus middle T antigen, its mechanisms, and its downstream pathways of transformation. We concentrate on the MMTV-PyMT transgenic mouse, one of the most studied models of breast cancer, which permits the examination of in situ tumor progression from hyperplasia to metastasis.

Fgf-dependent Etv4/5 activity is required for posterior restriction of Sonic Hedgehog and promoting outgrowth of the vertebrate limb

Crosstalk between the fibroblast growth factor (FGF) and Sonic Hedgehog (Shh) pathways is critical for proper patterning and growth of the developing limb bud. Here, we show that FGF-dependent activation of the ETS transcription factors Etv4 and Etv5 contributes to proximal-distal limb outgrowth. Surprisingly, blockage of Etv activity in early distal mesenchyme also resulted in ectopic, anterior expansion of Shh, leading to a polydactylous phenotype. These data indicate an unexpected function for an FGF/Etv pathway in anterior-posterior patterning. FGF activity in the limb is not only responsible for maintaining posterior-specific Shh expression, but it also acts via Etvs to prevent inappropriate anterior expansion of Shh. This study identifies another level of genetic interaction between the orthogonal axes during limb development.

The Pea3 Ets transcription factor regulates differentiation of multipotent progenitor cells during mammary gland development

The Pea3 Ets transcription factor is overexpressed in breast tumors suggesting that it plays a role in mammary oncogenesis. However, the normal biological function of Pea3 in the mammary gland is not known. Here we report that Pea3 was expressed in the epithelium of the mouse mammary anlagen commensurate with their genesis, and at later times in the nipple and mammary ducts of female embryos. In adult mice Pea3 transcripts peaked at the onset of puberty and early pregnancy, times of active epithelial cell proliferation and differentiation. Pea3 was expressed in all progenitor cap cells and rare body cells of terminal end buds, and in the myoepithelial cells of ducts and alveoli. Analyses of the mammary glands of Pea3-null mice during puberty revealed an increased number of terminal end buds and an increased fraction of proliferating progenitor cells within these structures compared to their wild type littermates. Tissue transplant experiments demonstrated that these phenotypes were intrinsic to the Pea3-null mammary epithelium. During pregnancy, mammary glands isolated from Pea3-null females had impaired alveolar development as revealed by a decreased fraction of alveolar structures. We performed in vitro colony forming assays of mammary epithelial cells and discovered that loss of Pea3 altered the distribution of specific multipotent progenitor cells. Double-immunofluorescence confirmed that multipotential progenitors co-expressing markers of the myoepithelial and luminal epithelial lineage were amplified in the mammary glands of Pea3-null mice by comparison to their wild type counterparts. We propose that Pea3 functions in multipotential progenitors to regulate their lineage-specific differentiation potential.

Ets-1 upregulates HER2-induced MMP-1 expression in breast cancer cells

The human epidermal growth factor receptor-2 (HER2) plays an important role in breast cancer. Enhanced Ets-1 activity has recently been shown to be associated with breast cancer pathogenesis. To test the role of Ets-1 in breast cancer cells in relation to the expression of HER2 and MMP-1, we transiently overexpressed Ets-1 and/or HER2 in MCF-7 breast cancer cells and comprehensively searched for genes related to HER2 and Ets-1 using cDNA microarray analysis. The expression of matrix metalloproteinase (MMP) genes was enhanced by the overexpression of HER2/Ets-1. We analyzed the relationship between HER2-induced MMP-1 expression and the transcription factor Ets-1, which has significant activity in breast cancer pathogenesis. Our results demonstrate that HER2-induced MMP-1 expression is positively regulated by Ets-1 in breast cancer cells. This study confirms that Ets-1 is a downstream effector of oncogenic HER2, associated with MMP-1.

Reduced tumorigenesis in mouse mammary cancer cells following inhibition of Pea3- or Erm-dependent transcription

Pea3 and Erm are transcription factors expressed in normal developing branching organs such as the mammary gland. Deregulation of their expression is generally associated with tumorigenesis and particularly breast cancer. By using RNA interference (RNAi) to downregulate the expression of Pea3 and/or Erm in a mammary cancer cell line, we present evidence for a role of these factors in proliferation, migration and invasion capacity of cancer cells. We have used different small interfering RNAs (siRNAs) targeting pea3 and erm transcripts in transiently or stably transfected cells, and assessed the physiological behavior of these cells in in vitro assays. We also identified an in vivo alteration of tumor progression after injection of cells that overexpress pea3 and/or erm short hairpin RNAs (shRNAs) in immunodeficient mice. Using transcriptome profiling in Pea3- or Erm-targeted cells, two largely independent gene expression programs were identified on the basis of their shared phenotypic modifications. A statistically highly significant part of both sets of target genes had previously been already associated with the cellular signaling pathways of the ;proliferation, migration, invasion' class. These data provide the first evidence, by using endogenous knockdown, for pivotal and complementary roles of Pea3 and Erm transcription factors in events crucial to mammary tumorigenesis, and identify sets of downstream target genes whose expression during tumorigenesis is regulated by these transcription factors.

ETS-family genes in pancreatic development

ETS-family factors play major roles in development and cancer, notably as critical targets for extra-cellular signaling pathways, including MAPK-signaling. Given the presently limited knowledge on the role of ETS-factors in pancreatic development, we here sought to characterize all 26 individual members of the ETS-family in relation to pancreatic development using a combination of genomics, RT-PCR, and histological techniques. This analysis uncovers 22 ETS family genes displaying select spatial and temporal expression patterns in the developing pancreas. Highly specific expression of ETS-family components is observed in pancreatic progenitor cells or the associated embryonic mesenchyme. Other members are linked to the differentiation of more mature pancreatic cells, including exocrine and endocrine cell types. We find that two members of the Etv subfamily, Etv4 and Etv5, are expressed in cells proximal to pancreatic mesenchyme, and, furthermore, induced in FGF10-arrested pancreatic progenitors suggesting that these factors mediate mesenchymal-to-epithelial signaling.

ETS transcription factors in endocrine systems

E26 transformation-specific (ETS) transcription factors have become increasingly recognized as key regulators of differentiation, hormone responses and tumorigenesis in endocrine organs and target tissues. The ETS family is highly diverse, consisting of both transcription activators and repressors that mediate growth factor signaling and regulate gene expression through combinatorial interactions with multiple protein partners on composite DNA elements. ETS proteins have a role in the endocrine system in establishing pituitary-specific gene expression, mammary gland development and cancers of the breast, prostate and reproductive organs.

Antitumor activity of an Ets protein, PEA3, in breast cancer cell lines MDA-MB-361DYT2 and BT474M1

Polyomavirus enhancer activator 3 (PEA3) is a member of the Ets family of transcription factors. We demonstrated in a previous study that, by downregulating the HER-2/neu oncogene at the transcriptional level, PEA3 can inhibit the growth and development into tumors of HER-2/neu-overexpressing ovarian cancer cells. Here, we establish stable clones of the human breast cancer cell line MDA-MB-361DYT2 that express PEA3 under the control of a tetracycline-inducible promoter. Ectopic expression of PEA3 in this cell line inhibited cell growth and resulted in cell cycle accumulation in the G1 phase. We demonstrate that expression of PEA3 in an orthotopic breast cancer model inhibited tumor growth and prolonged the survival of tumor-bearing mice. In a parallel experiment with another breast cancer cell line, BT474M1, we were unable to obtain stable PEA3-inducible transfectants, suggesting that PEA3 may exert a strong growth inhibition effect in this cell line. Indeed, PEA3 coupled with the liposome SN2 demonstrated therapeutic effects in mice bearing tumors induced by BT474M1. These results provide evidence for the antitumor activity of PEA3 in human breast cancers.

Epithelial-mesenchymal transition in development and cancer: role of phosphatidylinositol 3' kinase/AKT pathways

Epithelial-mesenchymal transition (EMT) is an important process during development by which epithelial cells acquire mesenchymal, fibroblast-like properties and show reduced intercellular adhesion and increased motility. Accumulating evidence points to a critical role of EMT-like events during tumor progression and malignant transformation, endowing the incipient cancer cell with invasive and metastatic properties. Several oncogenic pathways (peptide growth factors, Src, Ras, Ets, integrin, Wnt/beta-catenin and Notch) induce EMT and a critical molecular event is the downregulation of the cell adhesion molecule E-cadherin. Recently, activation of the phosphatidylinositol 3' kinase (PI3K)/AKT axis is emerging as a central feature of EMT. In this review, we discuss the role of PI3K/AKT pathways in EMT during development and cancer with a focus on E-cadherin regulation. Interactions between PI3K/AKT and other EMT-inducing pathways are presented, along with a discussion of the therapeutic implications of modulating EMT in order to achieve cancer control.

Prognostic value of ERM gene expression in human primary breast cancers

We measured the expression of ERM gene, a nuclear transcription factor belonging to the ets family, in a series of 364 unselected primary breast cancers from patients who underwent locoregional surgery in the Centre Oscar Lambret between May 1989 and December 1991. The expression of ERM was quantified with a real-time one-step reverse transcription-PCR assay based on the 5'-nuclease activity of the TaqDNA polymerase and with an Abi Prism 7700 Sequence Detector System (Applied Biosystems, Courtaboeuf, France). ERM was positively correlated (Spearman test) to epidermal growth factor receptor (EGFR; P < 0.001, r = 0.296) and to histoprognostic grading (P = 0.044, r = 0.112), whereas it was negatively correlated to estradiol receptors (P = 0.019, r = -0.124), HER3 (c-erbB-3; P = 0.01, r = -0.135), and HER4 (c-erbB-4; P = 0.003, r = -0.154). Using the chi2 test, a positive relationship was found between the expression of ERM and EGFR (chi2 = 7.795, P = 0.007). In overall survival studies, Cox univariate analyses demonstrated a prognostic value of ERM (P = 0.006; risk ratio, 2.95) besides the classical prognostic factors histoprognostic grading, node involvement, tumor size, estradiol receptors, progesterone receptors, EGFR, HER3, and HER4. In multivariate analyses, ERM preserved its prognostic value (P = 0.004; risk ratio, 3.779) together with histoprognostic grading, tumor size, estradiol receptors, and progesterone receptors. In relapse-free survival studies, univariate analyses demonstrated that histoprognostic grading, node involvement, tumor size, and HER4 were prognostic factors. These parameters, except histoprognostic grading, retained their prognostic value in multivariate analyses. This study demonstrates for the first time that ERM gene expression is an independent adverse prognostic factor for overall survival in breast cancer patients.

Associations and Interactions between Ets-1 and Ets-2 and Coregulatory Proteins, SRC-1, AIB1, and NCoR in Breast Cancer

PURPOSE

Associations between p160 coactivator proteins and the development of resistance to endocrine treatment have been described. We hypothesized that nuclear receptor coregulatory proteins may interact with nonsteroid receptors. We investigated the mitogen-activated protein kinase-activated transcription factors, Ets, as possible interaction proteins for the coactivators SRC-1 and AIB1 and the corepressor NCoR in human breast cancer.

EXPERIMENTAL DESIGN

Expression and coexpression of Ets and the coregulatory proteins was investigated using immunohistochemistry and immunofluorescence in a cohort of breast tumor patients (N = 134). Protein expression, protein-DNA interactions and protein-protein interactions were assessed using Western blot, electromobility shift, and coimmunoprecipitation analysis, respectively.

RESULTS

Ets-1 and Ets-2 associated with reduced disease-free survival (P < 0.0292, P < 0.0001, respectively), whereas NCoR was a positive prognostic indicator (P < 0.0297). Up-regulation of Ets-1 protein expression in cell cultures derived from patient tumors in the presence of growth factors associated with tumor grade (P < 0.0013; n = 28). In primary breast tumor cell cultures and in the SKBR3 breast cell line, growth factors induced interaction between Ets and their DNA response element, induced recruitment of coactivators to the transcription factor-DNA complex, and up-regulated protein expression of HER2. Ets-1 and Ets-2 interacted with the coregulators under basal conditions, and growth factors up-regulated Ets-2 interaction with SRC-1 and AIB1. Coexpression of Ets-2 and SRC-1 significantly associated with the rate of recurrence and HER expression, compared with patients who expressed Ets-2 but not SRC-1 (P < 0.0001 and P < 0.0001, respectively).

CONCLUSIONS

These data describe associations and interactions between nonsteroid transcription factors and coregulatory proteins in human breast cancer.

Expression of the Ets transcription factor Erm is regulated through a conventional PKC signaling pathway in the Molt4 lymphoblastic cell line

Erm, a member of the PEA3 group within the Ets family of transcription factors, is expressed in murine and human lymphocytes. Here, we show that in the human Molt4 lymphoblastic cell line, the erm gene expression is regulated by the conventional PKC (cPKC) pathway. To better characterize the molecular mechanism by which cPKC regulates Erm transcription in Molt4 cells, we tested proximal promoter deletions of the human gene, and identified a specific cPKC-regulated region between positions -420 and -115 upstream of the first exon.

ESX induces transformation and functional epithelial to mesenchymal transition in MCF-12A mammary epithelial cells

ESX is an epithelial-restricted member of a large family of transcription factors known as the Ets family. ESX expression has been shown to be correlated with Her2/neu proto-oncogene amplification in highly aggressive breast cancers and induced by Her2/neu in breast cell lines, but its role in tumorigenesis is unknown. Previously, we have shown that ESX enhances breast cell survival in colony-formation assays. In order to determine whether ESX can act as a transforming gene, we stably transfected MCF-12A human mammary epithelial cells with the ESX expression vector, pCGN2-HA-ESX. The MCF-12A cell line is immortalized, but nontransformed, and importantly, these cells fail to express endogenous ESX protein. We used pCGN2-HA-Ets-2 and pSVRas expression vectors as positive controls for transformation. Like HA-Ets-2 and V12-Ras, stable expression of ESX induced EGF-independent proliferation, serum-independent MAPK phosphorylation and growth in soft agar. Additionally, stable ESX expression conferred increased cell adhesion, motility and invasion in two-dimensional and transwell filter assays, and an epithelial to mesenchymal morphological transition. In three-dimensional cultures, parental and vector control (pCGN2) cells formed highly organized duct-like structures with evidence of cell polarity, ECM adhesion-dependent proliferation and cell survival, and lack of cellular invasion into surrounding matrix. Remarkably, the ESX stable cells formed solid, disorganized structures, with lack of cell polarity, loss of adhesion junctions and cytokeratin staining and loss of dependence on ECM adhesion for cell proliferation and survival. In addition, ESX cells invaded the surrounding matrix, indicative of a transformed and metastatic phenotype. Taken together, these data show that ESX expression alone confers a transformed and in vitro metastatic phenotype to otherwise normal MCF-12A cells.

Transcriptional control of the cell cycle in mammary gland development and tumorigenesis

Over the past several years it has become increasingly evident that normal development and cancer share many properties. Both processes involve alterations in cell proliferation and differentiation, cell death, neovascularization, and cell motility and invasion. Thus, genes involved in normal development are frequently utilized in neoplasia. During development, numerous transcriptional regulatory mechanisms are used to ensure tight control over cellular proliferation. In this review we focus on a number of transcription factor families (homeobox, STAT, and Ets), and on inhibitors of transcription factors (Id), which have been implicated in controlling the cell cycle not only in normal mammary gland development but also in breast tumorigenesis.

Immortalization of epididymal epithelium in transgenic mice expressing simian virus 40 T antigen: characterization of cell lines and regulation of the polyoma enhancer activator 3

In the present study epididymal epithelium was immortalized in transgenic mice by expressing simian virus 40 T antigen under a 5.0-kb mouse glutathione peroxidase 5 promoter (GPX5-Tag1). Epididymal tumorigenesis was associated with an increase in c-Myc expression, and a marked decrease in B-Myc expression, with a 500-fold lower level in the GPX5-Tag1 caput epididymis compared with wild-type caput. Furthermore, B-Myc was undetectable in the immortalized corpus and cauda epididymis. Hence, it is possible that the normally high B-Myc expression in the epididymis is one of the factors contributing to the highly resistant nature of epididymis toward immortalization. Morphologically different epithelial cell lines were generated from the immortalized epididymides, and the cells expressed several genes typical for epididymal epithelium, such as mouse epididymal 1, mouse epididymal protein 9, androgen and estrogen receptors, anion exchangers 2 and 4, retinoic acid receptor alpha, and polyoma enhancer activator 3 (PEA3). This indicated the differentiated status of the cells and their usefulness for analyzing epididymal gene expression in vitro. As PEA3 is considered to be one of the transcription factors responsible for epididymal gene expression, we further studied its regulation in epididymal cells in vitro. The data showed that PEA3 mRNA expression is regulated in the epididymis via protein kinase A and ERK signaling cascades. Inhibiting protein kinase A resulted in up-regulation and inhibiting ERK resulted in down-regulation of PEA3 mRNA, whereas no significant effect on PEA3 expression was found by modulating the protein kinase C, stress-activated p38, phosphoinositol 3-kinase and p70 S6 kinase cascades.

Changes in the expression of many Ets family transcription factors and of potential target genes in normal mammary tissue and tumors

Interfering with Ets transcription factor function reverses multiple aspects of the transformed phenotype of mouse or human tumor cells. However, the unknown number of individual Ets factors expressed in any cellular context and the similar DNA binding specificities of Ets family members complicates the identification of those that mediate transformation. By utilizing quantitative PCR assays for 25 mouse Ets factors, we analyzed the expression of essentially the entire Ets family in normal mammary tissue, mammary-related cell lines, and mammary tumors. In normal mammary tissue, 24 Ets factors were expressed. Even clonal derived cell lines expressed 14-20 Ets members. The most abundant Ets factor mRNAs measured in normal mammary tissue were Elk4, Elf1, and Ets2. Subtractive analysis of mammary tissue identified which Ets factors were predominantly expressed in the myeloid/lymphoid or epithelial cell compartments. Comparison of Ets factor expression in normal mammary tissue and mammary tumors identified significantly elevated expression of Pse/PDEF, Ese2/Elf5, Ese3/Ehf, TEL/Etv6, and Elf2/NERF in mammary tumors and confirmed previously reported alterations in expression of Ese1/Elf3 and the PEA3 subfamily. Expression of 13 Ets target genes, implicated in various aspects of tumor progression, was also analyzed. Altered expression of particular Ets target genes was significantly correlated with particular Ets factors (e.g. maspin and Ese2), suggesting specific in vivo regulatory roles. Together, this comprehensive analysis revealed unexpectedly diverse Ets family gene expression, characterized novel Ets factor changes in mammary tumors, and implicated specific Ets factors in the regulation of multiple genes involved in mammary tumor progression.

Hormone-induced modifications of the chromatin structure surrounding upstream regulatory regions conserved between the mouse and rabbit whey acidic protein genes

The upstream regulatory regions of the mouse and rabbit whey acidic protein (WAP) genes have been used extensively to target the efficient expression of foreign genes into the mammary gland of transgenic animals. Therefore both regions have been studied to elucidate fully the mechanisms controlling WAP gene expression. Three DNase I-hypersensitive sites (HSS0, HSS1 and HSS2) have been described upstream of the rabbit WAP gene in the lactating mammary gland and correspond to important regulatory regions. These sites are surrounded by variable chromatin structures during mammary-gland development. In the present study, we describe the upstream sequence of the mouse WAP gene. Analysis of genomic sequences shows that the mouse WAP gene is situated between two widely expressed genes (Cpr2 and Ramp3). We show that the hypersensitive sites found upstream of the rabbit WAP gene are also detected in the mouse WAP gene. Further, they encompass functional signal transducer and activator of transcription 5-binding sites, as has been observed in the rabbit. A new hypersensitive site (HSS3), not specific to the mammary gland, was mapped 8 kb upstream of the rabbit WAP gene. Unlike the three HSSs described above, HSS3 is also detected in the liver, but similar to HSS1, it does not depend on lactogenic hormone treatments during cell culture. The region surrounding HSS3 encompasses a potential matrix attachment region, which is also conserved upstream of the mouse WAP gene and contains a functional transcription factor Ets-1 (E26 transformation-specific-1)-binding site. Finally, we demonstrate for the first time that variations in the chromatin structure are dependent on prolactin alone.

Function of PEA3 Ets transcription factors in mammary gland development and oncogenesis

The Ets gene families of mice and man currently comprise 27 genes that encode sequence-specific transcription factors. Ets proteins share an approximately 85 amino acid structurally conserved ETS DNA binding domain. Genetic analyses in model organisms suggest roles for Ets proteins in embryonic development and various adult physiological processes. Chromosomal translocations involving several ETS genes are associated with Ewing's sarcomas and leukemias, whereas the overexpression of some ETS genes is linked with numerous malignancies, including breast cancer. Indeed PEA3, ETS-1, PDEF, and ELF-3 transcripts have all been reported to be elevated in human breast tumors. Some of the ETS genes that are overexpressed in human breast tumors are also overexpressed in mouse models of this disease. Notably, pea3, as well as its close paralogs er81 and erm, which comprise the pea3 subfamily of ets genes, are coordinately overexpressed in mouse mammary tumors. Genetic analyses in mice reveal required roles for one or more of the PEA3 subfamily Ets proteins in the initiation and progression of mouse mammary tumors. The pea3 subfamily genes are normally expressed in the primitive epithelium of mouse mammary buds during embryogenesis, and these three genes are expressed in epithelial progenitor cells during postnatal mammary gland development. Loss-of-function mutations in the mouse pea3 gene results in increased numbers of terminal end buds and an increased fraction of proliferating cells in these structures, suggesting a role for PEA3 in progenitor cell renewal or terminal differentiation. Taken together these observations suggest that the PEA3 subfamily proteins play key regulatory roles in both mammary gland development and oncogenesis.

The epithelial-specific ETS transcription factor ESX/ESE-1/Elf-3 modulates breast cancer-associated gene expression

Several members of the ETS family of transcription factors contribute to tumorigenesis in many different tissues, including breast epithelium. The ESX gene is an epithelial-specific Ets member that is particularly relevant to breast cancer. ESX is amplified in early breast cancers, it is overexpressed in human breast ductal carcinoma in situ, and there may be a positive feedback loop between the HER2/neu proto-oncogene and ESX. Despite this progress in our understanding of ESX, its ability to regulate tumor-related gene expression and to modulate breast cell survival, remain unknown. Here we show that HA-ESX stimulates the collagenase and HER2/neu promoters, but fails to activate an intact stromelysin promoter. However, HA-ESX activates, in a dose-dependent manner, a heterologous promoter containing eight copies of the Ets binding site derived from the stromelysin gene (p8Xpal-CAT). Analysis of the ability of constructs encoding nine Ets family members to activate the HER2/neu promoter revealed three patterns of gene activation: (1) no effect or repressed promoter activity (Elk-1 and NET); (2) intermediate activity (ER81, GABP, ESX, and HA-Ets-2); and, (3) maximal activity (Ets-1, VP-16-Ets-1, and EHF). Based on these observations, we also determined whether ESX is capable of conferring a survival phenotype upon immortalized, but nontransformed and ESX negative MCF-12A human breast cells. Using a colony formation assay, we found that HA-ESX and HA-Ets-2, mediated MCF-12A cell survival rates that approached those generated by oncogenic V12 Ras, whereas empty vector resulted in negligible colony formation. By contrast, in immortalized and transformed T47D breast cancer cells, which express both HER2/neu and ESX, we found that antisense and dominant-negative HA-ESX inhibited T47D colony formation, whereas control vector allowed formation of many colonies. These results are significant because they show that HA-ESX is able to differentially activate several malignancy-associated gene promoters, and that ESX expression is required for cellular survival of nontransformed MCF-12A and transformed T47D human mammary cells.

Cyclooxygenase-2 is overexpressed in HER-2/neu-positive breast cancer: evidence for involvement of AP-1 and PEA3

Markedly increased levels of cyclooxygenase-2 (COX-2) mRNA, protein, and prostaglandin E(2) synthesis were detected in HER-2/neu-transformed human mammary epithelial cells (184B5/HER) compared with its nontransformed partner cell line (184B5). HER-2/neu stimulated COX-2 transcription via the Ras --> Raf --> MAPK pathway. The inductive effects of HER-2/neu were mediated, in part, by enhanced binding of AP-1 (c-Jun, c-Fos, and ATF-2) to the cyclic AMP-response element (-59/-53) of the COX-2 promoter. The potential contribution of the transcription factor PEA3 was also investigated. Elevated levels of PEA3 were detected in 184B5/HER cells. A PEA3 site (-75/-72) was identified juxtaposed to the cyclic AMP-response element. HER-2/neu-mediated activation of the COX-2 promoter was blocked by mutagenizing the PEA3 site or overexpressing antisense to PEA3. To determine whether HER-2/neu status was also a determinant of COX-2 expression in vivo, we compared levels of COX-2 protein in HER-2/neu-positive and -negative human breast cancers. Increased amounts of COX-2 were detected in HER-2/neu-positive tumors. Taken together, these results suggest that closely spaced PEA3 and cyclic AMP-response elements are required for HER-2/neu-mediated induction of COX-2 transcription. The clear relationship between HER-2/neu status and COX-2 expression in human breast tumors suggests that this mechanism is likely to be operative in vivo.