The AP-1 transcription factor regulates breast cancer cell growth via cyclins and E2F factors

COP1 and GSK3β cooperate to promote c-Jun degradation and inhibit breast cancer cell tumorigenesis

High abundance of c-Jun is detected in invasive breast cancer cells and aggressive breast tumor malignancies. Here, we demonstrate that a major cause of high c-Jun abundance in invasive breast cancer cells is prolonged c-Jun protein stability owing to poor poly-ubiquitination of c-Jun. Among the known c-Jun-targeting E3 ligases, we identified constitutive photomorphogenesis protein 1 (COP1) as an E3 ligase responsible for c-Jun degradation in less invasive breast cancer cells because depletion of COP1 reduced c-Jun poly-ubiquitination leading to the stabilization of c-Jun protein. In a panel of breast cancer cell lines, we observed an inverse association between the levels of COP1 and c-Jun. However, overexpressing COP1 alone was unable to decrease c-Jun level in invasive breast cancer cells, indicating that efficient c-Jun protein degradation necessitates an additional event. Indeed, we found that glycogen synthase kinase 3 (GSK3) inhibitors elevated c-Jun abundance in less invasive breast cancer cells and that GSK3β nonphosphorylable c-Jun-T239A mutant displayed greater protein stability and poorer poly-ubiquitination compared to the wild-type c-Jun. The ability of simultaneously enforced expression of COP1 and constitutively active GSK3β to decrease c-Jun abundance in invasive breast cancer cells allowed us to conclude that c-Jun is negatively regulated through the coordinated action of COP1 and GSK3β. Importantly, co-expressing COP1 and active GSK3β blocked in vitro cell growth/migration and in vivo metastasis of invasive breast cancer cells. Gene expression profiling of breast tumor specimens further revealed that higher COP1 expression correlated with better recurrence-free survival. Our study supports the notion that COP1 is a suppressor of breast cancer progression.

Knockdown of E2F2 inhibits tumorigenicity, but preserves stemness of human embryonic stem cells

Tumorigenicity of human pluripotent stem cells is a major threat limiting their application in cell therapy protocols. It remains unclear, however, whether suppression of tumorigenic potential can be achieved without critically affecting pluripotency. A previous study has identified hyperexpressed genes in cancer stem cells, among which is E2F2, a gene involved in malignant transformation and stem cell self-renewal. Here we tested whether E2F2 knockdown would affect the proliferative capacity and tumorigenicity of human embryonic stem cells (hESC). Transient E2F2 silencing in hESC significantly inhibited expression of the proto-oncogenes BMI1 and HMGA1, in addition to proliferation of hESC, indicated by a higher proportion of cells in G1, fewer cells in G2/M phase, and a reduced capacity to generate hESC colonies in vitro. Nonetheless, E2F2-silenced cells kept expression of typical pluripotency markers and displayed differentiation capacity in vitro. More importantly, E2F2 knockdown in hESC significantly inhibited tumor growth in vivo, which was considerably smaller than tumors generated from control hESC, although displaying typical teratoma traits, a major indicator of pluripotency retention in E2F2-silenced cells. These results suggest that E2F2 knockdown can inhibit hESC proliferation and tumorigenicity without significantly harming stemness, providing a rationale to future protocols aiming at minimizing risks related to therapeutic application of cells and/or products derived from human pluripotent cells.

CAPER, a novel regulator of human breast cancer progression

CAPER is an estrogen receptor (ER) co-activator that was recently shown to be involved in human breast cancer pathogenesis. Indeed, we reported increased expression of CAPER in human breast cancer specimens. We demonstrated that CAPER was undetectable or expressed at relatively low levels in normal breast tissue and assumed a cytoplasmic distribution. In contrast, CAPER was expressed at higher levels in ductal carcinoma in situ (DCIS) and invasive ductal carcinoma (IDC) specimens, where it assumed a predominantly nuclear distribution. However, the functional role of CAPER in human breast cancer initiation and progression remained unknown. Here, we used a lentiviral-mediated gene silencing approach to reduce the expression of CAPER in the ER-positive human breast cancer cell line MCF-7. The proliferation and tumorigenicity of MCF-7 cells stably expressing control or human CAPER shRNAs was then determined via both in vitro and in vivo experiments. Knockdown of CAPER expression significantly reduced the proliferation of MCF-7 cells in vitro. Importantly, nude mice injected with MCF-7 cells harboring CAPER shRNAs developed smaller tumors than mice injected with MCF-7 cells harboring control shRNAs. Mechanistically, tumors derived from mice injected with MCF-7 cells harboring CAPER shRNAs displayed reduced expression of the cell cycle regulators PCNA, MCM7, and cyclin D1, and the protein synthesis marker 4EBP1. In conclusion, knockdown of CAPER expression markedly reduced human breast cancer cell proliferation in both in vitro and in vivo settings. Mechanistically, knockdown of CAPER abrogated the activity of proliferative and protein synthesis pathways.

MicroRNA-206 induces G1 arrest in melanoma by inhibition of CDK4 and Cyclin D

Expression profiling of microRNAs in melanoma lesional skin biopsies compared with normal donor skin biopsies, as well as melanoma cell lines compared with normal melanocytes, revealed that hsa-miR-206 was down-regulated in melanoma (-75.4-fold, P = 1.7 × 10(-4)). MiR-206 has been implicated in a large number of cancers, including breast, lung, colorectal, ovarian, and prostate cancers; however, its role in tumor development remains largely unknown, its biologic function is poorly characterized, and its targets affecting cancer cells are largely unknown. MiR-206 reduced growth and migration/invasion of multiple melanoma cell lines. Bioinformatics identified cell cycle genes CDK2, CDK4, Cyclin C, and Cyclin D1 as strong candidate targets. Western blots and 3'UTR reporter gene assays revealed that miR-206 inhibited translation of CDK4, Cyclin D1, and Cyclin C. Additionally, hsa-miR-206 transfection induced G1 arrest in multiple melanoma cell lines. These observations support hsa-miR-206 as a tumor suppressor in melanoma and identify Cyclin C, Cyclin D1, and CDK4 as miR-206 targets.

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.

Activator protein-1 inhibition by 3-[(dodecylthiocarbonyl)methyl]-glutamaride impairs invasion and radiosensitizes osteosarcoma cells in vitro

Osteosarcoma (OS) is the most common primary malignant bone tumor. Despite advances in neoadjuvant multi-agent chemotherapy, the outcome of patients has not significantly improved in the last decades, making the search for more effective therapeutic agents imperative. In the present study, we explored the possibility of using activator protein-1 inhibition by 3-[(dodecylthiocarbonyl)methyl]-glutarimide (DTCM-g) as a new therapeutic strategy in two OS cell lines, HOS and MG-63. Our results showed that low concentrations (2.5, 5, 10, and 20 μg/mL) of the drug significantly decreased cell proliferation and clonogenic capacity, albeit it did not significantly induce cell death. DTCM-g also decreased cell invasiveness, and inhibited PDPN, MMP-2, TIMP1, and TIMP2 expressions. Moreover, our results showed that DTCM-g synergized with ionizing radiation in both cell lines while chemosensitized MG-63 cells to doxorubicin treatment. Even though additional laboratorial and preclinical tests are still needed to support our data, we demonstrate that DTCM-g inhibits growth in OS cells, increases the cytotoxicity of other commonly used agents, and may possess antimetastatic activity.

Fragment-based drug design and identification of HJC0123, a novel orally bioavailable STAT3 inhibitor for cancer therapy

Fragment-based drug design (FBDD) is a promising approach for the generation of lead molecules with enhanced activity and especially drug-like properties against therapeutic targets. Herein, we report the fragment-based drug design, systematic chemical synthesis and pharmacological evaluation of novel scaffolds as potent anticancer agents by utilizing six privileged fragments from known STAT3 inhibitors. Several new molecules such as compounds 5, 12, and 19 that may act as advanced chemical leads have been identified. The most potent compound 5 (HJC0123) has demonstrated to inhibit STAT3 promoter activity, downregulate phosphorylation of STAT3, increase the expression of cleaved caspase-3, inhibit cell cycle progression and promote apoptosis in breast and pancreatic cancer cells with low micromolar to nanomolar IC50 values. Furthermore, compound 5 significantly suppressed estrogen receptor (ER)-negative breast cancer MDA-MB-231 xenograft tumor growth in vivo (p.o.), indicating its great potential as an efficacious and orally bioavailable drug candidate for human cancer therapy.

p21-activated kinase-1 signaling regulates transcription of tissue factor and tissue factor pathway inhibitor

Tissue factor (TF) is a cell-surface glycoprotein responsible for initiating the coagulation cascade. Besides its role in homeostasis, studies have shown the implication of TF in embryonic development, cancer-related events, and inflammation via coagulation-dependent and -independent (signaling) mechanisms. Tissue factor pathway inhibitor (TFPI) plays an important role in regulating TF-initiated blood coagulation. Therefore, transcriptional regulation of TF expression and its physiological inhibitor TFPI would allow us to understand the critical step that controls many different processes. From a gene profiling study aimed at identifying differentially regulated genes between wild-type (WT) and p21-activated kinase 1-null (PAK1-KO) mouse embryonic fibroblasts (MEFs), we found TF and TFPI are differentially expressed in the PAK1-KO MEFs in comparison with wild-type MEFs. Based on these findings, we further investigated in this study the transcriptional regulation of TF and TFPI by PAK1, a serine/threonine kinase. We found that the PAK1·c-Jun complex stimulates the transcription of TF and consequently its procoagulant activity. Moreover, PAK1 negatively regulates the expression of TFPI and additionally contributes to increased TF activity. For the first time, this study implicates PAK1 in coagulation processes, through its dual transcriptional regulation of TF and its inhibitor.

The regulatory mechanism of the LY6K gene expression in human breast cancer cells

LY6K is a cancer biomarker and a therapeutic target that induces invasion and metastasis. However, the molecular mechanisms that determine human LY6K transcription are completely unknown. To elucidate the mechanisms involved in human LY6K gene regulation and expression, multiple cis-elements were predicted using TRANSFAC software, and the LY6K regulatory region was identified using the luciferase assay in the human LY6K gene promoter. We performed ChIP, EMSA, and supershift assays to investigate the transcription factor activity on the LY6K promoter, and the effect of a SNP and CpG site methylation on AP-1 transcription factor binding affinity. AP-1 and the CREB transcription factor bound to LY6K promoter within -550/-1, which was essential for LY6K expression, but only the AP-1 heterodimer, JunD, and Fra-1, modulates LY6K gene transcriptional level. A decrease in LY6K was associated with the SNP242 C allele, a polymorphic G/C-SNP at the 242 nucleotide in the LY6K promoter region (rs2585175), or methylation of the CpG site, which was closely located with the AP-1 site by interfering with binding of the AP-1 transcription factor to the LY6K promoter. Our findings reveal an important role for AP-1 activation in promoting LY6K gene expression that regulates cell mobility of breast cancer cells, whereas the SNP242 C allele or methylation of the CpG site may reduce the risk of invasion or metastasis by interfering AP-1 activation.

Toll-like receptor-9 agonists increase cyclin D1 expression partly through activation of activator protein-1 in human oral squamous cell carcinoma cells

Increasing evidence suggests that malignant transformation can result from chronic infection, and Toll-like receptors (TLRs) may play an important role in this process. We have previously reported that the increased expression of TLR-9 is associated with tumor cell proliferation in oral cancer. However, the mechanisms involved have not been elucidated. The aim of this study was to investigate whether CpG-oligodeoxynucleotides (CpG-ODN), a special TLR-9 agonist, is able to exert the proliferation-promoting effect in human oral squamous cell carcinoma (OSCC), and to explore the possible underlying molecular mechanism. Flow cytometry, MTT, and colony formation assay were used to evaluate cell proliferation and cell cycle distribution. The mRNA and protein levels were analyzed by quantitative RT-PCR and Western blot assay. Luciferase reporter gene, EMSA, and ChIP assays were used to detect the activity of activator protein-1 (AP-1) and nuclear factor-κB (NF-κB) in HB cells. Results showed that CpG-ODN could stimulate proliferation of HB cells in a dose- and time-dependent manner with a promoted G(1) /S cell cycle progression. Increased cyclin D1 expression was detected in the nuclear region after CpG-ODN treatment. Moreover, CpG-ODN promoted nuclear translocation and activation of AP-1, which appeared to be required for TLR-9-mediated cyclin D1 expression and subsequently cell proliferation, but seemed to have little impact on NF-κB activity. Our results indicate that CpG-ODN stimulates tumor cell proliferation through TLR-9-mediated AP-1-activated cyclin D1 expression in OSCC HB cells. Pharmacologic inhibition of the TLR-9/AP-1/cyclin D1 pathway may be a new therapeutic approach for prevention as well as treatment of OSCC.

Interplay between AP-1 and estrogen receptor α in regulating gene expression and proliferation networks in breast cancer cells

Estrogen receptor α (ERα) is a ligand-dependent transcription factor that plays an important role in breast cancer. Estrogen-dependent gene regulation by ERα can be mediated by interaction with other DNA-binding proteins, such as activator protein-1 (AP-1). The nature of such interactions in mediating the estrogen response in breast cancer cells remains unclear. Here we show that knockdown of c-Fos, a component of the transcription factor AP-1, attenuates the expression of 37% of all estrogen-regulated genes, suggesting that c-Fos is a fundamental factor for ERα-mediated transcription. Additionally, knockdown of c-Fos affected the expression of a number of genes that were not regulated by estrogen. Pathway analysis reveals that silencing of c-Fos downregulates an E2F1-dependent proproliferative gene network. Thus, modulation of the E2F1 pathway by c-Fos represents a novel mechanism by which c-Fos enhances breast cancer cell proliferation. Furthermore, we show that c-Fos and ERα can cooperate in regulating E2F1 gene expression by binding to regulatory elements in the E2F1 promoter. To start to dissect the molecular details of the cross talk between AP-1 and estrogen signaling, we identify a novel ERα/AP-1 target, PKIB (cAMP-dependent protein kinase inhibitor-β), which is overexpressed in ERα-positive breast cancer tissues. Knockdown of PKIB results in robust growth suppression of breast cancer cells. Collectively, our findings support c-Fos as a critical factor that governs estrogen-dependent gene expression and breast cancer proliferation programs.

In Silico Prediction for Regulation of Transcription Factors onTheir Shared Target Genes Indicates Relevant Clinical Implications in a Breast Cancer Population

Aberrant transcriptional activities have been documented in breast cancers. Studies often find some transcription factors to be inappropriately regulated and enriched in certain pathological states. The promoter regions of most target genes have binding sites for their transcription factors. An ample of evidence supports their combinatorial effect on their shared target gene expressions. Here, we used a new statistic method, bivariate CID, to predict combinatorial interaction activity between ERα and a transcription factor (E2F1or GATA3 or ERRα) in regulating target gene expression via four regulatory mechanisms. We identified gene sets in three signal transduction pathways perturbed in breast tumors: cell cycle, VEGF, and PDGFRB. Bivariate network analysis revealed several target genes previously implicated in tumor angiogenesis are among the predicted shared targets, including VEGFA, PDGFRB. In summary, our analysis suggests the importance for the multivariate space of an inferred ERα transcriptional regulatory network in breast cancer diagnostic and therapeutic development.

Activator protein 1 (AP-1) contributes to EpCAM-dependent breast cancer invasion

Introduction

EpCAM is a cell-surface glycoprotein that is overexpressed in the majority of epithelial carcinomas. However, the functional role of EpCAM in regulating cancer invasion remains controversial, and the mechanism(s) underlying EpCAM-mediated regulation of breast cancer invasion remain to be defined.

Methods

EpCAM expression was manipulated in breast cancer cell lines using RNA interference and cDNA expression constructs. Recombinant EpCAM was used to rescue EpCAM signaling following specific ablation of EpCAM. Protein and gene expression, invasion, transcription factor activity, and protein phosphorylation were measured using standard molecular biology techniques.

Results

In loss-of-function, and gain-of-function experiments we demonstrate that EpCAM expression is associated with increased breast cancer invasion in vitro and in vivo. We demonstrate further that specific ablation of EpCAM expression is associated with decreased activator protein-1 (AP-1) transcription factor activity. Phosphoprotein analyses confirm that specific ablation of EpCAM is associated with decreased phosphorylation of the AP-1 subunit c-Jun. Recombinant soluble extracellular EpCAM (rEpCAM) is able to rescue invasion, AP-1 transcription factor activity, and c-Jun phosphorylation in a dose-dependent fashion. Pharmacologic inhibitors, and constitutively active constructs of the c-Jun N-terminal kinase (JNK) signal transduction pathway, suggest that the impact of EpCAM expression on AP-1 transcription factor activity is mediated through the JNK pathway. In functional rescue experiments, forced expression of c-Jun rescues invasion in breast cancer cells following specific ablation of EpCAM.

Conclusions

These data demonstrate for the first time that EpCAM expression can influence the JNK/AP-1 signal transduction pathway, and suggest that modulation of AP-1 transcription factor activity contributes to EpCAM-dependent breast cancer invasion. These data have important implications for the design and application of molecular therapies targeting EpCAM.

The CDKN2A/CDKN2B/CDK4/CCND1 pathway is pivotal in well-differentiated and dedifferentiated liposarcoma oncogenesis: an analysis of 104 tumors

The MDM2 and CDK4 genes are the main targets of chromosome 12 amplification in well-differentiated and dedifferentiated liposarcomas. Nevertheless, around 10% of these tumors do not amplify CDK4. To find substitutive alterations of CDK4 amplification, we analyzed a large series of liposarcomas by array-CGH, real-time genomic PCR, gene expression array, and real-time RT-PCR. We demonstrate that an alteration in the CDKN2A/CDKN2B/CDK4/CCND1 pathway is present in almost all cases without CDK4 amplification, thereby confirming the pivotal role of this pathway in liposarcoma oncogenesis. Moreover, we show that cell cycle and differentiation are driven by a subtle and complex balance between members of this pathway. Finally, we demonstrate that in tumors without amplification/overexpression of CDK4, the chromosome 1q21-1q23 region is a preferential partner of chromosome 12 amplicon, suggesting that the mechanism of amplification is slightly different in this group of tumors.

P21-activated protein kinase (PAK2)-mediated c-Jun phosphorylation at 5 threonine sites promotes cell transformation

The oncoprotein c-Jun is one of the components of the activator protein-1 (AP-1) transcription factor complex. AP-1 regulates the expression of many genes and is involved in a variety of biological functions such as cell transformation, proliferation, differentiation and apoptosis. AP-1 activates a variety of tumor-related genes and therefore promotes tumorigenesis and malignant transformation. Here, we found that epidermal growth factor (EGF) induces phosphorylation of c-Jun by P21-activated kinase (PAK) 2. Our data showed that PAK2 binds and phosphorylates c-Jun at five threonine sites (Thr2, Thr8, Thr89, Thr93 and Thr286) in vitro and ex vivo. Knockdown of PAK2 in JB6 Cl41 (P+) cells had no effect on c-Jun phosphorylation at Ser63 or Ser73 but resulted in decreases in EGF-induced anchorage-independent cell transformation, proliferation and AP-1 activity. Mutation at all five c-Jun threonine sites phosphorylated by PAK2 decreased the transforming ability of JB6 cells. Knockdown of PAK2 in SK-MEL-5 melanoma cells also decreased colony formation, proliferation and AP-1 activity. These results indicated that PAK2/c-Jun signaling plays an important role in EGF-induced cell proliferation and transformation.

Dynamic, large-scale profiling of transcription factor activity from live cells in 3D culture

Background

Extracellular activation of signal transduction pathways and their downstream target transcription factors (TFs) are critical regulators of cellular processes and tissue development. The intracellular signaling network is complex, and techniques that quantify the activities of numerous pathways and connect their activities to the resulting phenotype would identify the signals and mechanisms regulating tissue development. The ability to investigate tissue development should capture the dynamic pathway activity and requires an environment that supports cellular organization into structures that mimic in vivo phenotypes. Taken together, our objective was to develop cellular arrays for dynamic, large-scale quantification of TF activity as cells organized into spherical structures within 3D culture.

Methodology/Principal Findings

TF-specific and normalization reporter constructs were delivered in parallel to a cellular array containing a well-established breast cancer cell line cultured in Matrigel. Bioluminescence imaging provided a rapid, non-invasive, and sensitive method to quantify luciferase levels, and was applied repeatedly on each sample to monitor dynamic activity. Arrays measuring 28 TFs identified up to 19 active, with 13 factors changing significantly over time. Stimulation of cells with β-estradiol or activin A resulted in differential TF activity profiles evolving from initial stimulation of the ligand. Many TFs changed as expected based on previous reports, yet arrays were able to replicate these results in a single experiment. Additionally, arrays identified TFs that had not previously been linked with activin A.

Conclusions/Significance

This system provides a method for large-scale, non-invasive, and dynamic quantification of signaling pathway activity as cells organize into structures. The arrays may find utility for investigating mechanisms regulating normal and abnormal tissue growth, biomaterial design, or as a platform for screening therapeutics.

Role of MSK1 in the malignant phenotype of Ras-transformed mouse fibroblasts

Activated by the RAS-MAPK signaling pathway, MSK1 is recruited to immediate-early gene (IEG) regulatory regions, where it phosphorylates histone H3 at Ser-10 or Ser-28. Chromatin remodelers and modifiers are then recruited by 14-3-3 proteins, readers of phosphoserine marks, leading to the occupancy of IEG promoters by the initiation-engaged form of RNA polymerase II and the onset of transcription. In this study, we show that this mechanism of IEG induction, initially elucidated in parental 10T1/2 murine fibroblast cells, applies to metastatic Hras1-transformed Ciras-3 cells. As the RAS-MAPK pathway is constitutively activated in Ciras-3 cells, MSK1 activity and phosphorylated H3 steady-state levels are elevated. We found that steady-state levels of the IEG products AP-1 and COX-2 were also elevated in Ciras-3 cells. When MSK1 activity was inhibited or MSK1 expression was knocked down in Ciras-3 cells, the induction of IEG expression and the steady-state levels of COX-2, FRA-1, and JUN were greatly reduced. Furthermore, MSK1 knockdown Ciras-3 cells lost their malignant phenotype, as reflected by the absence of anchorage-independent growth.

Trop2 expression contributes to tumor pathogenesis by activating the ERK MAPK pathway

Background

Trop2 is a cell-surface glycoprotein overexpressed by a variety of epithelial carcinomas with reported low to restricted expression in normal tissues. Expression of Trop2 has been associated with increased tumor aggressiveness, metastasis and decreased patient survival, but the signaling mechanisms mediated by Trop2 are still unknown. Here, we studied the effects murine Trop2 (mTrop2) exerted on tumor cellular functions and some of the signaling mechanisms activated by this oncogene.

Results

mTrop2 expression significantly increased tumor cell proliferation at low serum concentration, migration, foci formation and anchorage-independent growth. These in vitro characteristics translated to increased tumor growth in both subcutaneous and orthotopic pancreatic cancer murine models and also led to increased liver metastasis. mTrop2 expression also increased the levels of phosphorylated ERK1/2 mediating cell cycle progression by increasing the levels of cyclin D1 and cyclin E as well as downregulating p27. The activation of ERK was also observed in human pancreatic ductal epithelial cells and colorectal adenocarcinoma cells overexpressing human Trop2.

Conclusions

These findings demonstrate some of the pathogenic effects mediated by mTrop2 expression on cancer cells and the importance of targeting this cell surface glycoprotein. This study also provides the first indication of a molecular signaling pathway activated by Trop2 which has important implications for cancer cell growth and survival.

A dominant-negative c-jun mutant inhibits lung carcinogenesis in mice

Lung cancer is the leading cause of cancer mortality in the United States and worldwide. The identification of key regulatory and molecular mechanisms involved in lung tumorigenesis is therefore critical to increase our understanding of this disease and could ultimately lead to targeted therapies to improve prevention and treatment. Induction of members of the activator protein-1 (AP-1) transcription factor family has been described in human non-small cell lung carcinoma. Activation of AP-1 can either stimulate or repress transcription of multiple gene targets, ultimately leading to increased cell proliferation and inhibition of apoptosis. In the present study, we show induction of AP-1 in carcinogen-induced mouse lung tumors compared with surrounding normal lung tissue. We then used a transgenic mouse model directing conditional expression of the dominant-negative c-jun mutant TAM67 in lung epithelial cells to determine the effect of AP-1 inhibition on mouse lung tumorigenesis. Consistent with low AP-1 activity in normal lung tissue, TAM67 expression had no observed effects in adult mouse lung. TAM67 decreased tumor number and overall lung tumor burden in chemically induced mouse lung tumor models. The most significant inhibitory effect was observed on carcinoma burden compared with lower-grade lesions. Our results support the concept that AP-1 is a key regulator of mouse lung tumorigenesis, and identify AP-1-dependent transcription as a potential target to prevent lung tumor progression.

The role of neurofibromin in N-Ras mediated AP-1 regulation in malignant peripheral nerve sheath tumors

Plexiform neurofibromas commonly found in patients with Neurofibromatosis type I (NF1) have a 5% risk of being transformed into malignant peripheral nerve sheath tumors (MPNST). Germline mutations in the NF1 gene coding for neurofibromin, which is a Ras GTPase activating protein (RasGAP) and a negative regulator of Ras, result in an upregulation of the Ras pathway. We established a direct connection between neurofibromin deficiency and downstream effectors of Ras in cell lines from MPNST patients by demonstrating that knockdown of NF1 expression using siRNA in a NF1 wild type MPNST cell line, STS-26T, activates the Ras/ERK1,2 pathway and increases AP-1 binding and activity. We believe this is the first time the transactivation of AP-1 has been linked directly to neurofibromin deficiency in a disease relevant MPNST cell line. Previously, we have shown that N-Ras is constitutively activated in cell lines derived from independent MPNSTs from NF1 patients. We therefore sought to analyze the role of the N-Ras pathway in deregulating AP-1 transcriptional activity. We show that STS-26T clones conditionally expressing oncogenic N-Ras show increased phosphorylated ERK1,2 and phosphorylated JNK expression concomitant with increased AP-1 activity. MAP kinase pathways (ERK1,2 and JNK) were further examined in ST88-14, a neurofibromin-deficient MPNST cell line. The basal activity of ERK1,2 but not JNK was found to increase AP-1 activity. These experiments further confirmed the link between the loss of neurofibromin and increased activity of Ras/MAP kinase pathways and the activation of downstream transcriptional mechanisms in MPNSTs from NF1 patients.

BEX2 has a functional interplay with c-Jun/JNK and p65/RelA in breast cancer

Background

We have previously demonstrated that BEX2 is differentially expressed in breast tumors and has a significant role in promoting cell survival and growth in breast cancer cells. BEX2 expression protects breast cancer cells against mitochondrial apoptosis and G1 cell cycle arrest. In this study we investigated the transcriptional regulation of BEX2 and feedback mechanisms mediating the cellular function of this gene in breast cancer.

Results

We found a marked induction of BEX2 promoter by c-Jun and p65/RelA using luciferase reporter assays in MCF-7 cells. Furthermore, we confirmed the binding of c-Jun and p65/RelA to the BEX2 promoter using a chromatin immunoprecipitation assay. Importantly, transfections of c-Jun or p65/RelA in MCF-7 cells markedly increased the expression of BEX2 protein. Overall, these results demonstrate that BEX2 is a target gene for c-Jun and p65/RelA in breast cancer. These findings were further supported by the presence of a strong correlation between BEX2 and c-Jun expression levels in primary breast tumors. Next we demonstrated that BEX2 has a feedback mechanism with c-Jun and p65/RelA in breast cancer. In this process BEX2 expression is required for the normal phosphorylation of p65 and IκBα, and the activation of p65. Moreover, it is necessary for the phosphorylation of c-Jun and JNK kinase activity in breast cancer cells. Furthermore, using c-Jun stable lines we showed that BEX2 expression is required for c-Jun mediated induction of cyclin D1 and cell proliferation. Importantly, BEX2 down-regulation resulted in a significant increase in PP2A activity in c-Jun stable lines providing a possible underlying mechanism for the regulatory effects of BEX2 on c-Jun and JNK.

Conclusions

This study shows that BEX2 has a functional interplay with c-Jun and p65/RelA in breast cancer. In this process BEX2 is a target gene for c-Jun and p65/RelA and in turn regulates the phosphorylation/activity of these proteins. These suggest that BEX2 is involved in a novel feedback mechanism with significant implications for the biology of breast cancer.

Microarray analysis of Shigella flexneri-infected epithelial cells identifies host factors important for apoptosis inhibition

Background

Shigella flexneri inhibits apoptosis in infected epithelial cells. In order to understand the pro-survival effects induced by the bacteria, we utilized apoptosis-specific microarrays to analyze the changes in eukaryotic gene expression in both infected and uninfected cells in the presence and absence of staurosporine, a chemical inducer of the intrinsic pathway of apoptosis. The goal of this research was to identify host factors that contribute to apoptosis inhibition in infected cells.

Results

The microarray analysis revealed distinct expression profiles in uninfected and infected cells, and these changes were altered in the presence of staurosporine. These profiles allowed us to make comparisons between the treatment groups. Compared to uninfected cells, Shigella-infected epithelial cells, both in the presence and absence of staurosporine, showed significant induced expression of JUN, several members of the inhibitor of apoptosis gene family, nuclear factor κB and related genes, genes involving tumor protein 53 and the retinoblastoma protein, and surprisingly, genes important for the inhibition of the extrinsic pathway of apoptosis. We confirmed the microarray results for a selection of genes using in situ hybridization analysis.

Conclusion

Infection of epithelial cells with S. flexneri induces a pro-survival state in the cell that results in apoptosis inhibition in the presence and absence of staurosporine. The bacteria may target these host factors directly while some induced genes may represent downstream effects due to the presence of the bacteria. Our results indicate that the bacteria block apoptosis at multiple checkpoints along both pathways so that even if a cell fails to prevent apoptosis at an early step, Shigella will block apoptosis at the level of caspase-3. Apoptosis inhibition is most likely vital to the survival of the bacteria in vivo. Future characterization of these host factors is required to fully understand how S. flexneri inhibits apoptosis in epithelial cells.

Computational discovery of miR-TF regulatory modules in human genome

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level. They play an important role in several biological processes such as cell development and differentiation. Similar to transcription factors (TFs), miRNAs regulate gene expression in a combinatorial fashion, i.e., an individual miRNA can regulate multiple genes, and an individual gene can be regulated by multiple miRNAs. The functions of TFs in biological regulatory networks have been well explored. And, recently, a few studies have explored miRNA functions in the context of gene regulation networks. However, how TFs and miRNAs function together in the gene regulatory network has not yet been examined. In this paper, we propose a new computational method to discover the gene regulatory modules that consist of miRNAs, TFs, and genes regulated by them. We analyzed the regulatory associations among the sets of predicted miRNAs and sets of TFs on the sets of genes regulated by them in the human genome. We found 182 gene regulatory modules of combinatorial regulation by miRNAs and TFs (miR-TF modules). By validating these modules with the Gene Ontology (GO) and the literature, it was found that our method allows us to detect functionally-correlated gene regulatory modules involved in specific biological processes. Moreover, our miR-TF modules provide a global view of coordinated regulation of target genes by miRNAs and TFs.

Emerging roles of ATF2 and the dynamic AP1 network in cancer

Cooperation among transcription factors is central for their ability to execute specific transcriptional programmes. The AP1 complex exemplifies a network of transcription factors that function in unison under normal circumstances and during the course of tumour development and progression. This Perspective summarizes our current understanding of the changes in members of the AP1 complex and the role of ATF2 as part of this complex in tumorigenesis.

Thioredoxin regulates cell cycle via the ERK1/2-cyclin D1 pathway

Thioredoxin (TRX) is a key component of redox regulation and has been indicated to play an essential role in cell survival and growth. Here, we investigated the molecular mechanism of TRX in the regulation of cell survival and growth by using RNA interference (RNAi) in A549 lung cancer and MCF7 breast cancer cells. TRX knockdown did not significantly increase the basal level of cell death without exposure to stress, but CDDP-induced cell death was enhanced. Meanwhile, TRX knockdown resulted in significant cell-cycle arrest at the G(1) phase. Cyclin D1 expression was reduced by TRX knockdown at the protein and mRNA levels. TRX knockdown caused suppression of activation of the cyclin D1 promoter through elements including AP-1. TRX knockdown also reduced the levels of phosphorylated ERK1/2 and the nuclear translocation of ERK 1/2 induced by EGF. These results suggest that TRX is an important regulator of the cell cycle in the G(1) phase via cyclin D1 transcription and the ERK/AP-1 signaling pathways.

Notch-1 activates estrogen receptor-alpha-dependent transcription via IKKalpha in breast cancer cells

Approximately 80% of breast cancers express the estrogen receptor-alpha (ERalpha) and are treated with anti-estrogens. Resistance to these agents is a major cause of mortality. We have shown that estrogen inhibits Notch, whereas anti-estrogens or estrogen withdrawal activate Notch signaling. Combined inhibition of Notch and estrogen signaling has synergistic effects in ERalpha-positive breast cancer models. However, the mechanisms whereby Notch-1 promotes the growth of ERalpha-positive breast cancer cells are unknown. Here, we demonstrate that Notch-1 increases the transcription of ERalpha-responsive genes in the presence or absence of estrogen via a novel chromatin crosstalk mechanism. Our data support a model in which Notch-1 can activate the transcription of ERalpha-target genes via IKKalpha-dependent cooperative chromatin recruitment of Notch-CSL-MAML1 transcriptional complexes (NTC) and ERalpha, which promotes the recruitment of p300. CSL binding elements frequently occur in close proximity to estrogen-responsive elements (EREs) in the human and mouse genomes. Our observations suggest that a hitherto unknown Notch-1/ERalpha chromatin crosstalk mediates Notch signaling effects in ERalpha-positive breast cancer cells and contributes to regulate the transcriptional functions of ERalpha itself.

Systematic identification of transcription factors associated with patient survival in cancers

Background

Aberrant activation or expression of transcription factors has been implicated in the tumorigenesis of various types of cancer. In spite of the prevalent application of microarray experiments for profiling gene expression in cancer samples, they provide limited information regarding the activities of transcription factors. However, the association between transcription factors and cancers is largely dependent on the transcription regulatory activities rather than mRNA expression levels.

Results

In this paper, we propose a computational approach that integrates microarray expression data with the transcription factor binding site information to systematically identify transcription factors associated with patient survival given a specific cancer type. This approach was applied to two gene expression data sets for breast cancer and acute myeloid leukemia. We found that two transcription factor families, the steroid nuclear receptor family and the ATF/CREB family, are significantly correlated with the survival of patients with breast cancer; and that a transcription factor named T-cell acute lymphocytic leukemia 1 is significantly correlated with acute myeloid leukemia patient survival.

Conclusion

Our analysis identifies transcription factors associating with patient survival and provides insight into the regulatory mechanism underlying the breast cancer and leukemia. The transcription factors identified by our method are biologically meaningful and consistent with prior knowledge. As an insightful tool, this approach can also be applied to other microarray cancer data sets to help researchers better understand the intricate relationship between transcription factors and diseases.

Homeobox gene HOPX is epigenetically silenced in human uterine endometrial cancer and suppresses estrogen-stimulated proliferation of cancer cells by inhibiting serum response factor

HOPX (homeodomain only protein X) is a newly identified homeobox gene whose loss of expression has been reported for several types of neoplasm. Although we found most human uterine endometrial cancers (HEC) defective in HOPX expression, genetic mutations in the HOPX gene were undetectable. As is the case with several tumor suppressor genes, the promoter region of HOPX is densely methylated in HEC tissue samples obtained by laser capture microdissection. HOPX mRNA and protein levels were reduced in the majority of samples, and this correlated with hypermethylation of the HOPX promoter. Forced expression of HOPX resulted in a partial block in cell proliferation, in vivo tumorigenicity and c-fos gene expression in HEC and MCF7 cells in response to 17beta-estradiol (E(2)) stimulation. Analysis of the serum response element (SRE) of c-fos gene promoter showed that the effect of HOPX expression is associated with inhibition of E(2)-induced c-fos activation through the serum response factor (SRF) motif. Knockdown of HOPX in immortalized human endometrial cells resulted in accelerated proliferation. Our study indicates that transcriptional silencing of HOPX results from hypermethylation of the HOPpromoter, which leads to HEC development.

Effect of lapatinib on the development of estrogen receptor-negative mammary tumors in mice

Lapatinib, a selective orally available inhibitor of epidermal growth factor receptor (EGFR) and ErbB2 receptor tyrosine kinases, is a promising agent for the treatment of breast cancer. We examined the effect of lapatinib on the development of mammary tumors in MMTV-erbB2 transgenic mice, which express wild-type ErbB2 under the control of the mouse mammary tumor virus promoter and spontaneously develop estrogen receptor (ER)-negative and ErbB2-positive mammary tumors by 14 months of age. Mice were treated from age 3 months to age 15 months with vehicle (n = 17) or lapatinib (30 or 75 mg/kg body weight; n = 16 mice per group) by oral gavage twice daily (6 d/wk). All statistical tests were two-sided. By 328 days after the start of treatment, all 17 (100%) of the vehicle-treated mice vs five (31%) of the 16 mice treated with high-dose lapatinib developed mammary tumors (P < .001). Among MMTV-erbB2 mice treated for 5 months (n = 20 mice per group), those treated with lapatinib had fewer premalignant lesions and noninvasive cancers in their mammary glands than those treated with vehicle (P = .02). Lapatinib also effectively blocked epidermal growth factor-induced signaling through the EGFR and ErbB2 receptors, suppressed cyclin D1 and epiregulin mRNA expression, and stimulated p27 mRNA expression in human mammary epithelial cells and in mammary epithelial cells from mice treated for 5 months with high-dose lapatinib. Thus, cyclin D1, epiregulin, and p27 may represent useful biomarkers of lapatinib response in patients. These data suggest that lapatinib is a promising agent for the prevention of ER-negative breast cancer.

NDRG2 suppresses cell proliferation through down-regulation of AP-1 activity in human colon carcinoma cells

Recently, the anti-tumor activity of N-myc downstream-regulated gene 2 (NDRG2) was elucidated, but the molecular mechanism of how NDRG2 works as a tumor suppressor is not well known. To determine the function of NDRG2 as a tumor suppressor, we established stable cell lines expressing NDRG2 protein or its mutant forms, and studied their effects on tumor cell growth. Interestingly, constitutive expression of wild-type NDRG2 induced the growth retardation of SW620 colon carcinoma cells. Introduction of NDRG2 into SW620 cells induced the decrease of c-Jun phosphorylation at Ser63, followed by the attenuation of activator protein-1 (AP-1) function as a transcriptional activator. Subsequently, the down-regulation of cyclin D1, which is known as a major target for AP-1 transcription activator, resulted in cell cycle arrest at G1/S phase. Additionally, treatment of NDRG2-siRNA on NDRG2-expressing cells has induced the recovery of c-Jun phosphorylation and cyclin D1 expression. Cell proliferation of those cells was also increased compared with untreated cells. NDRG2 mutants of which the phosphorylation sites at C-terminal region were removed by deletion or site-directed mutagenesis have shown no effect on cyclin D1 expression and could not induce cell growth retardation. In conclusion, NDRG2 modulates intracellular signals to control cell cycle through the regulation of cyclin D1 expression via phosphorylation pathway.

Extracellular superoxide dismutase is a growth regulatory mediator of tissue injury recovery

Extracellular superoxide dismutase (SOD3) gene therapy has been shown to attenuate tissue damages and to improve the recovery of the tissue injuries, but the cellular events delivering the therapeutic response of the enzyme are not well defined. In the current work, we overexpressed SOD3 in rat hindlimb ischemia model to study the signal transduction and injury healing following the sod3 gene transfer. The data suggest a novel sod3 gene transfer-derived signal transduction cascade through Ras-Mek-Erk mitogenic pathway leading to activation of AP1 and CRE transcription factors, increased vascular endothelial growth factor (VEGF)-A and cyclin D1 expression, increased cell proliferation, and consequently improved metabolic functionality of the injured tissue. Increased cell proliferation could explain the improved metabolic performance and the healing of the tissue damages after the sod3 gene transfer. The present data is a novel description of the molecular mechanism of SOD3-mediated recovery of tissue injury and suggests a new physiological role for SOD3 as a Ras regulatory molecule in signal transduction.

Comparison of molecular strategies for breast cancer virotherapy using oncolytic adenovirus

Oncolytic viruses are regulated by the tumor phenotype to replicate and lyse cancer cells selectively. To identify optimal strategies for breast cancer we compared five adenoviruses with distinct regulatory mechanisms: Ad-dl922-947 (targets G1-S checkpoint); Ad-Onyx-015 and Ad-Onyx-017 (target p53/mRNA export); Ad-vKH1 (targets Wnt pathway), and AdEHE2F (targets estrogen receptor/G1-S checkpoint/hypoxic signaling). The quantity of virus required to kill 50% of breast cancer cells after 6 days (EC(50), plaque-forming units per cell) was measured. The most potent virus was Ad-dl922-947 (EC(50), 0.01-5.4 in SkBr3, MDA-231, MDA-468, MCF7, and ZR75.1 cells), followed by wild-type (Ad-WT; EC(50), 0.3-5.5) and AdEHE2F (EC(50), 1.4-3.9). Ad-vKH1 (EC(50), 7.2-72.1), Ad-Onyx-017 (EC(50), 8.4-167), and Ad-Onyx-015 (EC(50), 17.7-377) showed less activity. Most viruses showed limited cytotoxicity in normal human cells, including breast epithelium MCF10A (EC(50), >722) and fibroblasts (EC(50), >192) and only moderate cytotoxicity in normal microvascular endothelial cells (HMVECs; EC(50), 42.8-149), except Ad-dl922-947, which was active in HMVECs (EC(50), 1.6). After injection into MDA-231 xenografts, Ad-WT, AdEHE2F, and Ad-dl922-947 showed replication, assessed by hexon staining and quantitative polymerase chain reaction measurement of viral DNA, and significantly inhibited tumor growth, leading to extended survival. After intravenous injection Ad-dl922-947 showed DNA replication (233% of the injected dose was measured in liver after 3 days) whereas AdEHE2F did not. Overall, AdEHE2F showed the best combination of low toxicity in normal cells and high activity in breast cancer in vitro and in vivo, suggesting that molecular targeting using estrogen response elements, hypoxia response elements, and a dysregulated G1-S checkpoint is a promising strategy for virotherapy of breast cancer.

Cytokines and myelination in the central nervous system

Myelin abnormalities that reflect damage to developing and mature brains are often found in neurological diseases with evidence of inflammatory infiltration and microglial activation. Many cytokines are virtually undetectable in the uninflamed central nervous system (CNS), so that their rapid induction and sustained elevation in immune and glial cells contributes to dysregulation of the inflammatory response and neural cell homeostasis. This results in aberrant neural cell development, cytotoxicity, and loss of the primary myelin-producing cells of the CNS, the oligodendrocytes. This article provides an overview of cytokine and chemokine activity in the CNS with relevance to clinical conditions of neonatal and adult demyelinating disease, brain trauma, and mental disorders with observed white matter defects. Experimental models that mimic human disease have been developed in order to study pathogenic and therapeutic mechanisms, but have shown mixed success in clinical application. However, genetically altered animals, and models of CNS inflammation and demyelination, have offered great insight into the complexities of neuroimmune interactions that impact oligodendrocyte function. The intracellular signaling pathways of selected cytokines have also been highlighted to illustrate current knowledge of receptor-mediated events. By learning to interpret the actions of cytokines and by improving methods to target appropriate predictors of disease risk selectively, a more comprehensive understanding of altered immunoregulation will aid in the development of advanced treatment options for patients with inflammatory white matter disorders.

A chemical compound commonly used to inhibit PKR, {8-(imidazol-4-ylmethylene)-6H-azolidino[5,4-g] benzothiazol-7-one}, protects neurons by inhibiting cyclin-dependent kinase

Activation of the double-stranded RNA-dependent protein kinase (PKR) has been implicated in the pathogenesis of several neurodegenerative diseases. We find that a compound widely used as a pharmacological inhibitor of this enzyme, referred to as PKR inhibitor (PKRi), {8-(imidazol-4-ylmethylene)-6H-azolidino[5,4-g]benzothiazol-7-one}, protects against the death of cultured cerebellar granule and cortical neurons. PKRi also prevents striatal neurodegeneration and improves behavioral outcomes in a chemically induced mouse model of Huntington's disease. Surprisingly, PKRi fails to block the phosphorylation of eIF2alpha, a downstream target of PKR, and does not reduce the autophosphorylation of PKR enzyme immunoprecipitated from neurons. Furthermore, neurons lacking PKR are fully protected from apoptosis by PKRi, demonstrating that neuroprotection by this compound is not mediated by PKR inhibition. Using in vitro kinase assays we investigated whether PKRi affects any other protein kinase. These analyses demonstrated that PKRi has no major inhibitory effect on pro-apoptotic kinases such as the c-Jun N-terminal kinases, the p38 MAP kinases and the death-associated protein kinases, or on other kinases including c-Raf, MEK1, MKK6 and MKK7. PKRi does, however, inhibit the activity of certain cyclin-dependent kinases (CDKs), including CDK1, CDK2 and CDK5 both in vitro and in low potassium-treated neurons. Consistent with its inhibitory action on mitotic CDKs, the treatment of HT-22 and HEK293T cell lines with PKRi sharply reduces the rate of cell cycle progression. Taken together with the established role of CDK activation in the promotion of neurodegeneration, our results suggest that PKRi exerts its neuroprotective action by inhibiting CDK.

A method for analyzing censored survival phenotype with gene expression data

BACKGROUND

Survival time is an important clinical trait for many disease studies. Previous works have shown certain relationship between patients' gene expression profiles and survival time. However, due to the censoring effects of survival time and the high dimensionality of gene expression data, effective and unbiased selection of a gene expression signature to predict survival probabilities requires further study.

METHOD

We propose a method for an integrated study of survival time and gene expression. This method can be summarized as a two-step procedure: in the first step, a moderate number of genes are pre-selected using correlation or liquid association (LA). Imputation and transformation methods are employed for the correlation/LA calculation. In the second step, the dimension of the predictors is further reduced using the modified sliced inverse regression for censored data (censorSIR).

RESULTS

The new method is tested via both simulated and real data. For the real data application, we employed a set of 295 breast cancer patients and found a linear combination of 22 gene expression profiles that are significantly correlated with patients' survival rate.

CONCLUSION

By an appropriate combination of feature selection and dimension reduction, we find a method of identifying gene expression signatures which is effective for survival prediction.

Targeting the activator protein 1 transcription factor for the prevention of estrogen receptor-negative mammary tumors

The oncogene erbB2 is overexpressed in 20% to 30% human breast cancers and is most commonly overexpressed in estrogen receptor (ER)-negative breast cancers. Transgenic mice expressing erbB2 develop ER-negative mammary tumors, mimicking human breast carcinogenesis. Previously, we have shown that activator protein 1 (AP-1) regulates proliferation of ER-negative breast cancer cells. We hypothesized that blockade of AP-1 in mouse mammary epithelial cells will suppress ER-negative tumorigenesis induced by erbB2. Trigenic erbB2 mice were generated by crossing a bigenic pUHD-Tam67/MMTV-rtTA mouse to a MMTV-erbB2 mouse. The resulting trigenic mice develop tumors and express a doxycycline-inducible c-Jun dominant negative mutant (Tam67) in the mammary glands. In vivo AP-1 blockade by Tam67 expression started delayed mammary tumor formation in MMTV-erbB2 mice by more than 11 weeks. By 52 weeks of age, 100% (18 of 18) of the untreated animals had developed mammary tumors, whereas 56% (9 of 16) of the doxycycline-treated trigenic mice developed tumors. In addition, the tumors that arose in the AP-1-blocked erbB2 mice failed to express Tam67. Twenty-five percent of the doxycycline-treated MMTV-erbB2 mice survived more than 72 weeks of age without developing mammary tumors. Examination of normal-appearing mammary glands from these mice showed that AP-1 blockade by Tam67 also significantly prevents the development of premalignant lesions in these glands. The expression of erbB2 either in normal mammary tissue or in mammary tumors was not altered. Our results show that blocking the AP-1 signaling in mammary cells suppresses erbB2-induced transformation, and show that the AP-1 transcription factor is a critical transducer of erbB2. These results provide a scientific rationale to develop targeted drugs that inhibit AP-1 to prevent the development of ER-negative breast cancer.

ETV6-NTRK3 fusion oncogene initiates breast cancer from committed mammary progenitors via activation of AP1 complex

To better understand the cellular origin of breast cancer, we developed a mouse model that recapitulates expression of the ETV6-NTRK3 (EN) fusion oncoprotein, the product of the t(12;15)(p13;q25) translocation characteristic of human secretory breast carcinoma. Activation of EN expression in mammary tissues by Wap-Cre leads to fully penetrant, multifocal malignant breast cancer with short latency. We provide genetic evidence that, in nulliparous Wap-Cre;EN females, committed alveolar bipotent or CD61(+) luminal progenitors are targets of tumorigenesis. Furthermore, EN transforms these otherwise transient progenitors through activation of the AP1 complex. Given the increasing relevance of chromosomal translocations in epithelial cancers, such mice serve as a paradigm for the study of their genetic pathogenesis and cellular origins, and generation of preclinical models.

Paradoxical antiproliferative effect by a murine mammary tumor-derived epithelial cell line

BACKGROUND

Despite significant advancement in breast cancer therapy, there is a great need for a better understanding of the mechanisms involved in breast carcinogenesis and progression, as well as of the role of epigenetic contributions from stromal cells in mammary tumorigenesis. In this study, we isolated and characterized murine mammary tumor-derived epithelial and myofibroblast cell lines, and investigated the in vitro and in vivo effect of cellular soluble factors produced by the epithelial cell line on tumor cells.

METHODS

Morphology, immunophenotype, cytogenetics, invasiveness, and tumorigenicity of epithelial (LM-234ep) and myofibroblast (LM-234mf) cell lines isolated from two murine mammary adenocarcinomas with common ancestor were studied. The in vitro effects of LM-234ep conditioned medium on proliferation, cell cycle distribution, and expression of cell cycle proteins, were investigated in LM-234mf cells, mouse melanoma cells (B16-F10), and human cervical adenocarcinoma cells (HeLa). The in vivo anti-tumor activity of LM-234ep conditioned media was evaluated in subcutaneous tumors formed in nude mice by B16-F10 and HeLa cells.

RESULTS

LM-234ep cells were found to be cytokeratin positive and hipertriploid, whereas LM-234mf cells were alpha-smooth muscle actin positive and hypohexaploid. Chromosome aberrations were found in both cases. Only LM-234mf revealed to be invasive in vitro and to secrete active MMP-2, though neither of the cell types were able to produce progressing tumors. LM-234ep-derived factors were able to inhibit the in vitro growth of LM-234mf, B16-F10, and HeLa cells, inducing cell cycle arrest in G0/G1 phase. The administration of LM-234ep conditioned medium inhibited the growth of B16-F10 and HeLa tumors in nude mice.

CONCLUSION

Our data suggest the existence of epithelial cell variants with tumor suppressive properties within mammary tumors. To our knowledge, this is the first report showing antiproliferative and antineoplastic activities induced by tumor-derived epithelial cells.