E2f3a and E2f3b contribute to the control of cell proliferation and mouse development

Histology Atlas of the Developing Mouse Placenta

The use of the mouse as a model organism is common in translational research. This mouse-human similarity holds true for placental development as well. Proper formation of the placenta is vital for development and survival of the maturing embryo. Placentation involves sequential steps with both embryonic and maternal cell lineages playing important roles. The first step in placental development is formation of the blastocyst wall (approximate embryonic days [E] 3.0-3.5). After implantation (∼E4.5), extraembryonic endoderm progressively lines the inner surface of the blastocyst wall (∼E4.5-5.0), forming the yolk sac that provides histiotrophic support to the embryo; subsequently, formation of the umbilical vessels (∼E8.5) supports transition to the chorioallantoic placenta and hemotrophic nutrition. The fully mature ("definitive") placenta is established by ∼E12.5. Abnormal placental development often leads to embryonic mortality, with the timing of death depending on when placental insufficiency takes place and which cells are involved. This comprehensive macroscopic and microscopic atlas highlights the key features of normal and abnormal mouse placental development from E4.5 to E18.5. This in-depth overview of a transient (and thus seldom-analyzed) developmental tissue should serve as a useful reference to aid researchers in identifying and describing mouse placental changes in engineered, induced, and spontaneous disease models.

Cell division cycle associated 8: A novel diagnostic and prognostic biomarker for hepatocellular carcinoma

The cell division cycle associated 8 (CDCA8) is a crucial component of the chromosome passenger complex (CPC). It has been implicated in the regulation of cell dynamic localization during mitosis. However, its role in hepatocellular carcinoma (HCC) is not clearly known. In this study, data of 374 patients with HCC were retrieved from the Cancer Genome Atlas (TCGA) database. Pan analysis of Gene Expression Profiling Interactive Analysis (GEPIA) database was performed to profile the mRNA expression of CDCA8 in HCC. Then, the Kaplan‐Meier plotter database was analysed to determine the prognostic value of CDCA8 in HCC. In addition, samples of tumour and adjacent normal tissues were collected from 88 HCC patients to perform immunohistochemistry (IHC), reverse transcription‐quantitative polymerase chain reaction (qRT‐PCR) and Western blotting. The results obtained from bioinformatic analyses were validated through CCK‐8 assay, EdU assay, colony formation assay, cell cycle assays and Western blotting experiments. Analysis of the Kaplan‐Meier plotter database showed that high expression of CDCA8 may lead to poor overall survival (OS, p = 4.06e‐05) in patients with HCC. For the 88 patients with HCC, we found that stages and grades appeared to be strongly linked with CDCA8 expression. Furthermore, the high expression of CDCA8 was found to be correlated with poor OS (p = 0.0054) and progression‐free survival (PFS, p = 0.0009). In vitro experiments revealed that inhibition of CDCA8 slowed cell proliferation and blocked the cell cycle at the G0/G1 phase. In vivo experiments demonstrated that inhibition of CDCA8 inhibited tumour growth. Finally, blockade of CDCA8 reduced the expression levels of cyclin A2, cyclin D1, CDK4, CDK6, Ki67 and PCNA. And, there is an interaction between CDCA8 and E2F1. In conclusion, this research demonstrates that CDCA8 may serve as a biomarker for early diagnosis and prognosis prediction of HCC patients. In addition, CDCA8 could be an effective therapeutic target in HCC.

Early 2 factor (E2F) transcription factors contribute to malignant progression and have clinical prognostic value in lower-grade glioma

Early 2 factor (E2F) genes encoding a family of transcription factors are significantly associated with apoptosis, metabolism, and angiogenesis in several tumor types. However, the biological functions of E2F transcription factors (E2Fs) and their potential involvement in the malignancy of lower-grade glioma (LGG) remain unclear. We explored the effects of the expression of eight E2F family members on the clinical characteristics of LGG based on the Chinese Glioma Genome Atlas (CGGA), The Cancer Genome Atlas (TCGA), and GSE16011 datasets. Two LGG subgroups were identified according to the consensus clustering of the eight E2Fs. We employed the least absolute shrinkage and selection operator (LASSO) Cox regression algorithm for further functional experiments and the development of a potential risk score. Two categories of patients with LGG were identified based on the median risk scores. We then developed a nomogram based on the results of the multivariate analysis. Real-time quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry were performed to validate the bioinformatics results. Our results indicated that E2F family members were significantly involved in the malignancy of LGG and might serve as effective prognostic biomarkers of the disease.

The Role and Clinical Implications of the Retinoblastoma (RB)-E2F Pathway in Gastric Cancer

Gastric cancer is the most common malignant tumor in the digestive tract, with very high morbidity and mortality in developing countries. The pathogenesis of gastric cancer is a complex biological process mediated by abnormal regulation of proto-oncogenes and tumor suppressor genes. Although there have been some in-depth studies on gastric cancer at the molecular level, the specific mechanism has not been fully elucidated. RB family proteins (including RB, p130, and p107) are involved in cell cycle regulation, a process that largely depends on members of the E2F gene family that encode transcriptional activators and repressors. In gastric cancer, inactivation of the RB-E2F pathway serves as a core transcriptional mechanism that drives cell cycle progression, and is regulated by cyclins, cyclin-dependent kinases, cyclin-dependent kinase inhibitors, p53, Helicobacter pylori and some other upstream molecules. The E2F proteins are encoded by eight genes (i.e. E2F1 to E2F8), each of which may play a specific role in gastric cancer. Interestingly, a single E2F such as E2F1 can activate or repress transcription, and enhance or inhibit cell proliferation, depending on the cell environment. Thus, the function of the E2F transcription factor family is very complex and needs further exploration. Importantly, the presence of H. pylori in stomach mucosa may affect the RB and p53 tumor suppressor systems, thereby promoting the occurrence of gastric cancer. This review aims to summarize recent research progress on important roles of the complex RB-E2F signaling network in the development and effective treatment of gastric cancer.

The Role of miR-210 in the Biological System: A Current Overview

BACKGROUND

MicroRNAs (miRNAs) represent a group of non-coding RNAs measuring 19-23 nucleotides in length and are recognized as powerful molecules that regulate gene expression in eukaryotic cells. miRNAs stimulate the post-transcriptional regulation of gene expression via direct or indirect mechanisms.

SUMMARY

miR-210 is highly upregulated in cells under hypoxia, thereby revealing its significance to cell endurance. Induction of this mRNA expression is an important feature of the cellular low-oxygen response and the most consistent and vigorous target of HIF. Key Message: miR-210 is involved in many cellular functions under the effect of HIF-1α, including the cell cycle, DNA repair, immunity and inflammation, angiogenesis, metabolism, and macrophage regulation. It also plays an important regulatory role in T-cell differentiation and stimulation.

The broken cycle: E2F dysfunction in cancer

The cyclin-dependent kinase (CDK)-RB-E2F axis forms the core transcriptional machinery driving cell cycle progression, dictating the timing and fidelity of genome replication and ensuring genetic material is accurately passed through each cell division cycle. The ultimate effectors of this axis are members of a family of eight distinct E2F genes encoding transcriptional activators and repressors. E2F transcriptional activity is tightly regulated throughout the cell cycle via transcriptional and translational regulation, post-translational modifications, protein degradation, binding to cofactors and subcellular localization. Alterations in one or more key components of this axis (CDKs, cyclins, CDK inhibitors and the RB family of proteins) occur in virtually all cancers and result in heightened oncogenic E2F activity, leading to uncontrolled proliferation. In this Review, we discuss the activities of E2F proteins with an emphasis on the newest atypical E2F family members, the specific and redundant functions of E2F proteins, how misexpression of E2F transcriptional targets promotes cancer and both current and developing therapeutic strategies being used to target this oncogenic pathway.

Toxoplasma Controls Host Cyclin E Expression through the Use of a Novel MYR1-Dependent Effector Protein, HCE1

Toxoplasma gondii is an obligate intracellular parasite that establishes a favorable environment in the host cells in which it replicates. We have previously reported that it uses MYR-dependent translocation of dense granule proteins to elicit a key set of host responses related to the cell cycle, specifically, E2F transcription factor targets, including cyclin E. We report here the identification of a novel Toxoplasma effector protein that is exported from the parasitophorous vacuole in a MYR1-dependent manner and localizes to the host's nucleus. Parasites lacking this inducer of host cyclin E (HCE1) are unable to modulate E2F transcription factor target genes and exhibit a substantial growth defect. Immunoprecipitation of HCE1 from infected host cells showed that HCE1 efficiently binds elements of the cyclin E regulatory complex, namely, DP1 and its partners E2F3 and E2F4. Expression of HCE1 in Neospora caninum, or in uninfected human foreskin fibroblasts (HFFs), showed localization of the expressed protein to the host nuclei and strong cyclin E upregulation. Thus, HCE1 is a novel effector protein that is necessary and sufficient to impact the E2F axis of transcription, resulting in co-opting of host functions to the advantage of ToxoplasmaIMPORTANCE Like most Apicomplexan parasites, Toxoplasma gondii has the remarkable ability to invade and establish a replicative niche within another eukaryotic cell, in this case, any of a large number of cell types in almost any warm-blooded animals. Part of the process of establishing this niche is the export of effector proteins to co-opt host cell functions in favor of the parasite. Here we identify a novel effector protein, HCE1, that the parasites export into the nucleus of human cells, where it modulates the expression of multiple genes, including the gene encoding cyclin E, one of the most crucial proteins involved in controlling when and whether a human cell divides. We show that HCE1 works through binding to specific transcription factors, namely, E2F3, E2F4, and DP1, that normally carefully regulate these all-important pathways. This represents a new way in which these consummately efficient infectious agents co-opt the human cells that they so efficiently grow within.

A Mild PUM1 Mutation Is Associated with Adult-Onset Ataxia, whereas Haploinsufficiency Causes Developmental Delay and Seizures

Certain mutations can cause proteins to accumulate in neurons, leading to neurodegeneration. We recently showed, however, that upregulation of a wild-type protein, Ataxin1, caused by haploinsufficiency of its repressor, the RNA-binding protein Pumilio1 (PUM1), also causes neurodegeneration in mice. We therefore searched for human patients with PUM1 mutations. We identified eleven individuals with either PUM1 deletions or de novo missense variants who suffer a developmental syndrome (Pumilio1-associated developmental disability, ataxia, and seizure; PADDAS). We also identified a milder missense mutation in a family with adult-onset ataxia with incomplete penetrance (Pumilio1-related cerebellar ataxia, PRCA). Studies in patient-derived cells revealed that the missense mutations reduced PUM1 protein levels by ∼25% in the adult-onset cases and by ∼50% in the infantile-onset cases; levels of known PUM1 targets increased accordingly. Changes in protein levels thus track with phenotypic severity, and identifying posttranscriptional modulators of protein expression should identify new candidate disease genes.

Critical Roles of E2F3 in Growth and Musculo-skeletal Phenotype in Mice

E2F3, a member of the E2F family, plays a critical role in cell cycle and proliferation by targeting downstream, retinoblastoma (RB) a tumor suppressor family protein. The purpose of this study, was to investigate the role and function of E2F3 in vivo. We examined phenotypic abnormalities, by deletion of the E2f3 gene in mice. Complete ablation of the E2F3 was fully penetrant, in the pure C57BL/6N background. The E2f3^{+/ -} mouse embryo developed normally without fatal disorder. However, they exhibited reduced body weight, growth retardation, skeletal imperfection, and poor grip strength ability. Findings suggest that E2F3 has a pivotal role in muscle and bone development, and affect normal mouse growth.

The role of E2F8 in the human placenta

Recent studies have reported that E2F transcription factor (E2F) 8, an atypical E2F transcription factor, serves a critical role in promoting the growth and development of the murine placenta. However, the function of E2F8 in the human placenta remains unknown. Invasion of extravillous trophoblasts (EVTs) into the maternal decidua is known to be important for the development of the human placenta. To investigate the role of E2F8 in human placental development, E2F8 localisation was examined in the human placenta and E2F8 mRNA expression was detected in primary cultured EVTs. The human EVT cell line, HTR‑8/SVneo, was divided into two groups and treated separately, one with retrovirus expressing short hairpin (sh)‑RNA against E2F8 (shE2F8 cells) and the other with non‑target control shRNA (shControl cells). The cell functions, including cell cycle, proliferation, invasion and adhesion, were compared between the shE2F8 and shControl cells. A histological examination revealed that E2F8 was localised in the decidua cells, EVTs, and cytotrophoblasts in the placenta. E2F8 mRNA was confirmed to be expressed in cultured primary EVTs. No significant difference was observed in the cell cycle, proliferation or adhesion between the shE2F8 and shControl cells. The invasive ability was ~2‑fold higher in the shE2F8 cells when compared with the shControl cells (P<0.01). Production of matrix metalloproteinase‑1 was significantly increased in the shE2F8 cells when compared with the shControl cells (P<0.05). Taken together, E2F8 is present in the EVTs of the human placenta, but, unlike murine placenta, it may suppress the invasiveness of EVTs. E2F8 was also present in cytotrophoblasts in cell columns, which have no invasive ability and differentiate into EVTs. In conclusion, E2F8 also exists in the human placenta, and its function may be different from that in the murine placenta, although further investigation is required.

A comprehensive spatial-temporal transcriptomic analysis of differentiating nascent mouse lens epithelial and fiber cells

Elucidation of both the molecular composition and organization of the ocular lens is a prerequisite to understand its development, function, pathology, regenerative capacity, as well as to model lens development and disease using in vitro differentiation of pluripotent stem cells. Lens is comprised of the anterior lens epithelium and posterior lens fibers, which form the bulk of the lens. Lens fibers differentiate from lens epithelial cells through cell cycle exit-coupled differentiation that includes cellular elongation, accumulation of crystallins, cytoskeleton and membrane remodeling, and degradation of organelles within the central region of the lens. Here, we profiled spatiotemporal expression dynamics of both mRNAs and non-coding RNAs from microdissected mouse nascent lens epithelium and lens fibers at four developmental time points (embryonic [E] day 14.5, E16.5, E18.5, and P0.5) by RNA-seq. During this critical time window, multiple complex biosynthetic and catabolic processes generate the molecular and structural foundation for lens transparency. Throughout this developmental window, 3544 and 3518 genes show consistently and significantly greater expression in the nascent lens epithelium and fibers, respectively. Comprehensive data analysis confirmed major roles of FGF-MAPK, Wnt/β-catenin, PI3K/AKT, TGF-β, and BMP signaling pathways and revealed significant novel contributions of mTOR, EIF2, EIF4, and p70S6K signaling in lens formation. Unbiased motif analysis within promoter regions of these genes with consistent expression changes between epithelium and fiber cells revealed an enrichment for both established (e.g. E2Fs, Etv5, Hsf4, c-Maf, MafG, MafK, N-Myc, and Pax6) transcription factors and a number of novel regulators of lens formation, such as Arntl2, Dmrta2, Stat5a, Stat5b, and Tulp3. In conclusion, the present RNA-seq data serves as a comprehensive reference resource for deciphering molecular principles of normal mammalian lens differentiation, mapping a full spectrum of signaling pathways and DNA-binding transcription factors operating in both lens compartments, and predicting novel pathways required to establish lens transparency.

Polyploidy in tissue homeostasis and regeneration

Polyploid cells, which contain multiple copies of the typically diploid genome, are widespread in plants and animals. Polyploidization can be developmentally programmed or stress induced, and arises from either cell-cell fusion or a process known as endoreplication, in which cells replicate their DNA but either fail to complete cytokinesis or to progress through M phase entirely. Polyploidization offers cells several potential fitness benefits, including the ability to increase cell size and biomass production without disrupting cell and tissue structure, and allowing improved cell longevity through higher tolerance to genomic stress and apoptotic signals. Accordingly, recent studies have uncovered crucial roles for polyploidization in compensatory cell growth during tissue regeneration in the heart, liver, epidermis and intestine. Here, we review current knowledge of the molecular pathways that generate polyploidy and discuss how polyploidization is used in tissue repair and regeneration.

Expression patterns of E2F transcription factors and their potential prognostic roles in breast cancer

E2Fs, as a family of pivotal transcription factors, have been implicated in multiple biological functions in human cancer; however, the expression and prognostic significance of E2Fs in breast cancer remains unknown. In the present study, the mRNA expression patterns of E2Fs in breast cancer were investigated with Oncomine and The Cancer Genome Atlas data. Prognostic values of E2Fs for patients with breast cancer were determined using the Kaplan-Meier plotter database. The results strongly indicated that E2F1, E2F2, E2F3, E2F5, E2F7 and E2F8 were overexpressed in patients with breast cancer, whereas E2F4 and E2F6 exhibited no expression difference between patients with cancer and healthy controls. In survival analyses, elevated E2F1, E2F3, E2F5, E2F7 and E2F8 expression levels were significantly associated with lower overall survival, relapse-free survival (RFS), distant metastasis-free survival (DMFS) or post-progression survival for patients with breast cancer. Furthermore, high expression of E2F4 indicated improved RFS but reduced DMFS. Subgroup analyses based on four clinicopathological factors further revealed that E2Fs were associated with the prognosis of patients with breast cancer in an estrogen receptor-, progesterone receptor-, human epidermal growth factor 2- and lymph node status-specific manner. These data indicated that E2Fs may serve as promising biomarkers and therapeutic targets for breast cancer.

Functional characterization of E2F3b in human HepG2 liver cancer cell line

E2F3 is a transcription factor that has been shown to be overexpressed in hepatocellular carcinoma (HCC). It is well-known that the E2F3 gene encodes two proteins E2F3a and E2F3b. Therefore, the functions of the two distinct isoforms need to be clarified separately. To characterize the function of E2F3b in HCC, the effects of ectopic expression of E2F3b on cell proliferation, cell cycle, apoptosis and gene expression were investigated. E2F3b promoted G1/S phase transition and markedly increased cell proliferation, but had minor effect on apoptosis. Microarray analyses identified 366 differentially expressed genes (171 upregulated and 195 downregulated) in E2F3b- overexpressing cells. Differential expression of 16 genes relevant to cell cycle and cell proliferation were further verified by real-time PCR. Six genes, including CDC2, CCNE1, ARF, MAP4K2, MUSK, and PAX2 were confirmed to be upregulated by more than twofold; one gene, CCNA2 was validated to be downregulated by more than twofold. We also confirmed that E2F3b increased the protein levels of both cyclin E and Arf but did not affect cyclin D1 protein. These results suggest that E2F3b functions as an important promoter for cell proliferation and plays important roles in transcriptional regulation in HepG2 liver cancer cells.

Determination of the physiological and pathological roles of E2F3 in adult tissues

While genetically engineered mice have made an enormous contribution towards the elucidation of human disease, it has hitherto not been possible to tune up or down the level of expression of any endogenous gene. Here we describe compound genetically modified mice in which expression of the endogenous E2f3 gene may be either reversibly elevated or repressed in adult animals by oral administration of tetracycline. This technology is, in principle, applicable to any endogenous gene, allowing direct determination of both elevated and reduced gene expression in physiological and pathological processes. Applying this switchable technology to the key cell cycle transcription factor E2F3, we demonstrate that elevated levels of E2F3 drive ectopic proliferation in multiple tissues. By contrast, E2F3 repression has minimal impact on tissue proliferation or homeostasis in the majority of contexts due to redundancy of adult function with E2F1 and E2F2. In the absence of E2F1 and E2F2, however, repression of E2F3 elicits profound reduction of proliferation in the hematopoietic compartments that is rapidly lethal in adult animals.

Knockdown of E2F3 Inhibits Proliferation, Migration, and Invasion and Increases Apoptosis in Glioma Cells

E2F3a, as a member of the E2F family, is essential for cell division associated with the progression of many cancers. However, the biological effect of E2F3a on glioma is not understood as well. To investigate the functional mechanism of E2F3a in glioma, we examined the expression of E2F3a in glioma tissue and cell lines. We found that E2F3a was upregulated in glioma tissue compared with adjacent tissue, and this was associated with a poor survival rate. E2F3a was highly expressed in glioma cell lines compared with normal HEB cell lines. Knockdown of E2F3a significantly inhibited cell proliferation, promoted G0/G1 phase arrest, elevated apoptosis rates, and suppressed cell migration and invasion. However, overexpression of E2F3a markedly promoted cell proliferation, migration, and invasion and inhibited apoptosis. Moreover, in vivo studies showed that knockdown of E2F3a expression dramatically inhibited U373 tumor growth in a nude mouse model. Results of real-time PCR and Western blot showed that the depletion of E2F3a upregulated the expression levels of cell apoptosis-related proteins and downregulated migration-related proteins. Conversely, E2F3a overexpression downregulated the expression levels of cell apoptosis-related proteins and upregulated migration-related proteins. In conclusion, our results highlight the importance of E2F3a in glioma and provide new insights into the diagnostics and therapeutics of gliomas.

Comparative proteomics of paired vocal fold and oral mucosa fibroblasts

Injuries of the vocal folds frequently heal with scar formation, which can have lifelong detrimental impact on voice quality. Current treatments to prevent or resolve scars of the vocal fold mucosa are highly unsatisfactory. In contrast, the adjacent oral mucosa is mostly resistant to scarring. These differences in healing tendency might relate to distinct properties of the fibroblasts populating oral and vocal fold mucosae. We thus established the in vitro cultivation of paired, near-primary vocal fold fibroblasts (VFF) and oral mucosa fibroblasts (OMF) to perform a basic cellular characterization and comparative cellular proteomics. VFF were significantly larger than OMF, proliferated more slowly, and exhibited a sustained TGF-β1-induced elevation of pro-fibrotic interleukin 6. Cluster analysis of the proteomic data revealed distinct protein repertoires specific for VFF and OMF. Further, VFF displayed a broader protein spectrum, particularly a more sophisticated array of factors constituting and modifying the extracellular matrix. Conversely, subsets of OMF-enriched proteins were linked to cellular proliferation, nuclear events, and protection against oxidative stress. Altogether, this study supports the notion that fibroblasts sensitively adapt to the functional peculiarities of their respective anatomical location and presents several molecular targets for further investigation in the context of vocal fold wound healing.

BIOLOGICAL SIGNIFICANCE

Mammalian vocal folds are a unique but delicate tissue. A considerable fraction of people is affected by voice problems, yet many of the underlying vocal fold pathologies are sparsely understood at the molecular level. One such pathology is vocal fold scarring - the tendency of vocal fold injuries to heal with scar formation -, which represents a clinical problem with highly suboptimal treatment modalities. This study employed proteomics to obtain comprehensive insight into the protein repertoire of vocal fold fibroblasts, which are the cells that predominantly synthesize the extracellular matrix in both physiological and pathophysiological conditions. Protein profiles were compared to paired fibroblasts from the oral mucosa, a neighboring tissue that is remarkably resistant to scarring. Bioinformatic analyses of the data revealed a number of pathways as well as single proteins (e.g. ECM-remodeling factors, transcription factors, enzymes) that were significantly different between the two fibroblast types. Thereby, this study has revealed novel interesting molecular targets which can be analyzed in the future for their impact on vocal fold wound healing.

miR‑34a suppresses proliferation and induces apoptosis of human lens epithelial cells by targeting E2F3

microRNA (miRNA) is abnormally expressed in numerous diseases, and it was intimately associated with cell proliferation and apoptosis. However, the mechanism by which miRNAs control cataractogenesis remains unclear. In the current study, it was demonstrated that miR-34a was highly expressed in the cataractous lens by stem-loop reverse transcription-quantitative polymerase chain reaction. Trying to investigate the role of miR-34a in human lens epithelial cells, miR-34a mimics were transfected into SRA01/04 cells, and this suppressed proliferation and induced apoptosis. Subsequently, E2F3 was confirmed as a direct target of miR-34a. Downregulation of E2F3 by small interfering (si) RNA siE2F3 resulted in proliferation inhibition and apoptosis of SRA01/04 cells. Furthermore, it was demonstrated that miR-34a and siE2F3 downregulated E2F3 expression at a protein level. In summary, the current study demonstrated that miR-34a suppressed the proliferation and induced apoptosis of SRA01/04 cells by downregulating E2F3. These observations provide novel insights with potential therapeutic applications for the treatment of cataracts.

E2f4 and E2f5 are essential for the development of the male reproductive system

The E2F transcription factors are primarily implicated in the regulation of entry and exit from the cell cycle. However, in vivo studies have established additional roles for E2Fs during organ development and homeostasis. With the goal of addressing the intestinal requirements of E2f4 and E2f5, we crossed mice carrying Vil-cre, E2f4 conditional and E2f5 germline alleles. E2f4 deletion had no detectable effect on intestinal development. However, E2f4f/f;E2f5+/-;Vil-cre males, but not E2f4f/f;Vil-cre littermates, were unexpectedly sterile. This defect was not due to defective spermatogenesis. Instead, the seminiferous tubules and rete testes showed significant dilation, and spermatozoa accumulated aberrantly in the rete testis and efferent ducts. Our data show that these problems result from defective efferent ducts, a tissue whose primary function is to concentrate sperm through fluid absorption. First, Vil-cre expression, and consequent E2F4 loss, was specific to the efferent ducts and not other reproductive tract tissues. Second, the E2f4f/f;E2f5+/-;Vil-cre efferent ducts had completely lost multiciliated cells and greatly reduced levels of critical absorptive cell proteins: aquaporin1, a water channel protein, and clusterin, an endocytic marker. Collectively, the observed testis phenotypes suggest a fluid flux defect. Remarkably, we observed rete testis dilation prior to the normal time of seminiferous fluid production, arguing that the efferent duct defects promote excessive secretory activity within the reproductive tract. Finally, we also detect key aspects of these testis defects in E2f5-/- mice. Thus, we conclude that E2f4 and E2f5 display overlapping roles in controlling the normal development of the male reproductive system.

Silencing of E2F3 suppresses tumor growth of Her2+ breast cancer cells by restricting mitosis

The E2F transcriptional activators E2F1, E2F2 and E2F3a regulate many important cellular processes, including DNA replication, apoptosis and centrosome duplication. Previously, we demonstrated that silencing E2F1 or E2F3 suppresses centrosome amplification (CA) and chromosome instability (CIN) in Her2+ breast cancer cells without markedly altering proliferation. However, it is unknown whether and how silencing a single E2F activator, E2F3, affects malignancy of human breast cancer cells. Thus, we injected HCC1954 Her2+ breast cancer cells silenced for E2F3 into mammary fat pads of immunodeficient mice and demonstrated that loss of E2F3 retards tumor growth. Surprisingly, silencing of E2F3 led to significant reductions in mitotic indices relative to vector controls, while the percentage of cells undergoing S phase were not affected. Nek2 is a mitotic kinase commonly upregulated in breast cancers and a critical regulator of Cdk4- or E2F-mediated CA. In this report, we found that Nek2 overexpression rescued back the CA caused by silencing of shE2F3. However, the effects of Nek2 overexpression in affecting tumor growth rates of shE2F3 and shE2F3; GFP cells were inconclusive. Taken together, our results indicate that E2F3 silencing decreases mammary tumor growth by reducing percentage of cells undergoing mitosis.

E2F1 transcription factor and its impact on growth factor and cytokine signaling

E2F1 is a transcription factor involved in cell cycle regulation and apoptosis. The transactivation capacity of E2F1 is regulated by pRb. In its hypophosphorylated form, pRb binds and inactivates DNA binding and transactivating functions of E2F1. The growth factor stimulation of cells leads to activation of CDKs (cyclin dependent kinases), which in turn phosphorylate Rb and hyperphosphorylated Rb is released from E2F1 or E2F1/DP complex, and free E2F1 can induce transcription of several genes involved in cell cycle entry, induction or inhibition of apoptosis. Thus, growth factors and cytokines generally utilize E2F1 to direct cells to either fate. Furthermore, E2F1 regulates expressions of various cytokines and growth factor receptors, establishing positive or negative feedback mechanisms. This review focuses on the relationship between E2F1 transcription factor and cytokines (IL-1, IL-2, IL-3, IL-6, TGF-beta, G-CSF, LIF), growth factors (EGF, KGF, VEGF, IGF, FGF, PDGF, HGF, NGF), and interferons (IFN-α, IFN-β and IFN-γ).

The Spectrum of E2F in Liver Disease--Mediated Regulation in Biology and Cancer

Uncoordinated cell growth is one of the fundamental concepts in carcinogenesis and occurs secondary to dysregulation of the cell cycle. The E2Fs are a large family of transcription factors and are key regulators of the cell cycle. The activation of E2Fs is intimately regulated by retinoblastoma 1 (RB1). The RB pathway has been implicated in almost every human malignancy. Recently there have been exciting developments in the E2F field using animal models to better understand the role of E2Fs in vivo. Genetic mouse models have proven essential in implicating E2Fs in hepatocellular carcinoma (HCC) and liver disease. In this review, the general structure and function of E2Fs as well as the role for E2Fs in the development of HCC and liver disease is evaluated. Specifically, what is known about E2Fs in human disease is explored in depth, and future directions are discussed.

MiR-34a Inhibits Viability and Invasion of Human Papillomavirus-Positive Cervical Cancer Cells by Targeting E2F3 and Regulating Survivin

OBJECTIVE

Previous studies confirmed that high-risk human papillomavirus (HR-HPV) infection is a risk factor of cervical cancer, and the infection was associated with significantly reduced miR-34a expression during carcinogenesis. However, the downstream targets of miR-34a and their roles are still not well understood. This study explored the regulative role of miR-34a on E2F3 and survivin expression and the viability and invasion of HPV-positive cervical cancer cells.

METHODS

MiR-34a and survivin expression in 56 cases of HR-HPV-positive patients, 28 cases of HR-HPV-negative patients, and 28 normal cases without HR-HPV infections were measured. Human papillomavirus-18-positive HeLa cervical cancer cells and HPV-16-positive SiHa cells were used to explore the effect of miR-34a on cell viability and invasion. The molecular target of miR-34a was also explored in cervical cancer cells.

RESULTS

The results showed that miR-34a overexpression could inhibit HPV-positive cancer cell viability, whereas its downregulation promoted cell viability. E2F3 is a direct target of miR-34a in HPV-positive cervical cancer cells. By targeting E2F3, miR-34a could regulate the expression of survivin. Thus, through regulating E2F3 and survivin, miR-34a could reduce the viability and invasion of HPV-positive cervical cancer cells.

CONCLUSIONS

This study confirmed a novel miR-34a-E2F3-survivin axis in the tumor suppressor role of miR-34a in cervical cancer.

Increase of miR-199a-5p by protoporphyrin IX, a photocatalyzer, directly inhibits E2F3, sensitizing mesenchymal tumor cells to anti-cancer agents

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related deaths. Protoporphyrin IX (PPIX) has been used for photodynamic therapy. Mesenchymal cancer cells adapt to tumor microenvironments for growth and metastasis possibly in association with miRNA dysregulation. In view of the effect of PPIX on cancer-related genes, and its potential to inhibit tumor growth and migration/invasion, this study investigated whether PPIX enables mesenchymal liver tumor to restore dysregulated miRNAs, and if so, whether it sensitizes the cancer cells to chemotherapy. In addition, we explored new target(s) of the miRNA(s) that contribute to the anti-cancer effects. Of the ten miRNAs predicted by the 3′-UTR of HIF-1α mRNA, PPIX treatment increased miR-199a-5p, leading to the inhibition of E2F3 expression which is upregulated in mesenchymal liver tumor. miR-199a-5p levels were downregulated in HCC with E2F3 overexpression. An approach modulating epithelial-mesenchymal transition provided the expected changes in miR-199a-5p and E2F3 in vivo. PPIX prevented tumor cell growth and migration/invasion, and had a synergistic anti-cancer effect when combined with chemotherapeutics. In a xenograft model, PPIX treatment decreased overall growth and average tumor volume, which paralleled E2F3 inhibition. Overall, PPIX inhibited growth advantage and migratory ability of cancer cells and sensitized mesenchymal liver tumor cells to chemotherapeutics.

E2F Transcription Factors Control the Roller Coaster Ride of Cell Cycle Gene Expression

Initially, the E2F transcription factor was discovered as a factor able to bind the adenovirus E2 promoter and activate viral genes. Afterwards it was shown that E2F also binds to promoters of nonviral genes such as C-MYC and DHFR, which were already known at that time to be important for cell growth and DNA metabolism, respectively. These findings provided the first clues that the E2F transcription factor might be an important regulator of the cell cycle. Since this initial discovery in 1987, several additional E2F family members have been identified, and more than 100 targets genes have been shown to be directly regulated by E2Fs, the majority of these are important for controlling the cell cycle. The progression of a cell through the cell cycle is accompanied with the increased expression of a specific set of genes during one phase of the cell cycle and the decrease of the same set of genes during a later phase of the cell cycle. This roller coaster ride, or oscillation, of gene expression is essential for the proper progression through the cell cycle to allow accurate DNA replication and cell division. The E2F transcription factors have been shown to be critical for the temporal expression of the oscillating cell cycle genes. This review will focus on how the oscillation of E2Fs and their targets is regulated by transcriptional, post-transcriptional and post-translational mechanism in mammals, yeast, flies, and worms. Furthermore, we will discuss the functional impact of E2Fs on the cell cycle progression and outline the consequences when E2F expression is disturbed.

Coordinate regulation of residual bone marrow function by paracrine trafficking of AML exosomes

We recently demonstrated that acute myeloid leukemia (AML) cell lines and patient-derived blasts release exosomes that carry RNA and protein; following an in vitro transfer, AML exosomes produce proangiogenic changes in bystander cells. We reasoned that paracrine exosome trafficking may have a broader role in shaping the leukemic niche. In a series of in vitro studies and murine xenografts, we demonstrate that AML exosomes downregulate critical retention factors (Scf, Cxcl12) in stromal cells, leading to hematopoietic stem and progenitor cell (HSPC) mobilization from the bone marrow. Exosome trafficking also regulates HSPC directly, and we demonstrate declining clonogenicity, loss of CXCR4 and c-Kit expression, and the consistent repression of several hematopoietic transcription factors, including c-Myb, Cebp-β and Hoxa-9. Additional experiments using a model of extramedullary AML or direct intrafemoral injection of purified exosomes reveal that the erosion of HSPC function can occur independent of direct cell-cell contact with leukemia cells. Finally, using a novel multiplex proteomics technique, we identified candidate pathways involved in the direct exosome-mediated modulation of HSPC function. In aggregate, this work suggests that AML exosomes participate in the suppression of residual hematopoietic function that precedes widespread leukemic invasion of the bone marrow directly and indirectly via stromal components.

Transcriptional control of stem cell fate by E2Fs and pocket proteins

E2F transcription factors and their regulatory partners, the pocket proteins (PPs), have emerged as essential regulators of stem cell fate control in a number of lineages. In mammals, this role extends from both pluripotent stem cells to those encompassing all embryonic germ layers, as well as extra-embryonic lineages. E2F/PP-mediated regulation of stem cell decisions is highly evolutionarily conserved, and is likely a pivotal biological mechanism underlying stem cell homeostasis. This has immense implications for organismal development, tissue maintenance, and regeneration. In this article, we discuss the roles of E2F factors and PPs in stem cell populations, focusing on mammalian systems. We discuss emerging findings that position the E2F and PP families as widespread and dynamic epigenetic regulators of cell fate decisions. Additionally, we focus on the ever expanding landscape of E2F/PP target genes, and explore the possibility that E2Fs are not simply regulators of general ‘multi-purpose’ cell fate genes but can execute tissue- and cell type-specific gene regulatory programs.

Tissue-specific targeting of cell fate regulatory genes by E2f factors

Cell cycle proteins are important regulators of diverse cell fate decisions, and in this capacity have pivotal roles in neurogenesis and brain development. The mechanisms by which cell cycle regulation is integrated with cell fate control in the brain and other tissues are poorly understood, and an outstanding question is whether the cell cycle machinery regulates fate decisions directly or instead as a secondary consequence of proliferative control. Identification of the genes targeted by E2 promoter binding factor (E2f) transcription factors, effectors of the pRb/E2f cell cycle pathway, will provide essential insights into these mechanisms. We identified the promoter regions bound by three neurogenic E2f factors in neural precursor cells in a genome-wide manner. Through bioinformatic analyses and integration of published genomic data sets we uncovered hundreds of transcriptionally active E2f-bound promoters corresponding to genes that control cell fate processes, including key transcriptional regulators and members of the Notch, fibroblast growth factor, Wnt and Tgf-β signaling pathways. We also demonstrate a striking enrichment of the CCCTC binding factor transcription factor (Ctcf) at E2f3-bound nervous system-related genes, suggesting a potential regulatory co-factor for E2f3 in controlling differentiation. Finally, we provide the first demonstration of extensive tissue specificity among E2f target genes in mammalian cells, whereby E2f3 promoter binding is well conserved between neural and muscle precursors at genes associated with cell cycle processes, but is tissue-specific at differentiation-associated genes. Our findings implicate the cell cycle pathway as a widespread regulator of cell fate genes, and suggest that E2f3 proteins control cell type-specific differentiation programs by regulating unique sets of target genes. This work significantly enhances our understanding of how the cell cycle machinery impacts cell fate and differentiation, and will importantly drive further discovery regarding the mechanisms of cell fate control and transcriptional regulation in the brain, as well as in other tissues.

E2F activators signal and maintain centrosome amplification in breast cancer cells

Centrosomes ensure accurate chromosome segregation by directing spindle bipolarity. Loss of centrosome regulation results in centrosome amplification, multipolar mitosis and aneuploidy. Since centrosome amplification is common in premalignant lesions and breast tumors, it is proposed to play a central role in breast tumorigenesis, a hypothesis that remains to be tested. The coordination between the cell and centrosome cycles is of paramount importance to maintain normal centrosome numbers, and the E2Fs may be responsible for regulating these cycles. However, the role of E2F activators in centrosome amplification is unclear. Because E2Fs are deregulated in Her2(+) cells displaying centrosome amplification, we addressed whether they signal this abnormal process. Knockdown of E2F1 or E2F3 in Her2(+) cells decreased centrosome amplification without significantly affecting cell cycle progression, whereas the overexpression of E2F1, E2F2, or E2F3 increased centrosome amplification in MCF10A mammary epithelial cells. Our results revealed that E2Fs affect the expression of proteins, including Nek2 and Plk4, known to influence the cell/centrosome cycles and mitosis. Downregulation of E2F3 resulted in cell death and delays/blocks in cytokinesis, which was reversed by Nek2 overexpression. Nek2 overexpression enhanced centrosome amplification in Her2(+) breast cancer cells silenced for E2F3, revealing a role for the E2F activators in maintaining centrosome amplification in part through Nek2.

Inactivation of Rb and E2f8 synergizes to trigger stressed DNA replication during erythroid terminal differentiation

Rb is critical for promoting cell cycle exit in cells undergoing terminal differentiation. Here we show that during erythroid terminal differentiation, Rb plays a previously unappreciated and unorthodox role in promoting DNA replication and cell cycle progression. Specifically, inactivation of Rb in erythroid cells led to stressed DNA replication, increased DNA damage, and impaired cell cycle progression, culminating in defective terminal differentiation and anemia. Importantly, all of these defects associated with Rb loss were exacerbated by the concomitant inactivation of E2f8. Gene expression profiling and chromatin immunoprecipitation (ChIP) revealed that Rb and E2F8 cosuppressed a large array of E2F target genes that are critical for DNA replication and cell cycle progression. Remarkably, inactivation of E2f2 rescued the erythropoietic defects resulting from Rb and E2f8 deficiencies. Interestingly, real-time quantitative PCR (qPCR) on E2F2 ChIPs indicated that inactivation of Rb and E2f8 synergizes to increase E2F2 binding to its target gene promoters. Taken together, we propose that Rb and E2F8 collaborate to promote DNA replication and erythroid terminal differentiation by preventing E2F2-mediated aberrant transcriptional activation through the ability of Rb to bind and sequester E2F2 and the ability of E2F8 to compete with E2F2 for E2f-binding sites on target gene promoters.

E2F inhibition synergizes with paclitaxel in lung cancer cell lines

The CDK/Rb/E2F pathway is commonly disrupted in lung cancer, and thus, it is predicted that blocking the E2F pathway would have therapeutic potential. To test this hypothesis, we have examined the activity of HLM006474 (a small molecule pan-E2F inhibitor) in lung cancer cell lines as a single agent and in combination with other compounds. HLM006474 reduces the viability of both SCLC and NSCLC lines with a biological IC₅₀ that varies between 15 and 75 µM, but with no significant difference between the groups. Combination of HLM006474 with cisplatin and gemcitabine demonstrate little synergy; however, HLM006474 synergizes with paclitaxel. Surprisingly, we discovered that brief treatment of cells with HLM006474 led to an increase of E2F3 protein levels (due to de-repression of these promoter sites). Since paclitaxel sensitivity has been shown to correlate with E2F3 levels, we hypothesized that HLM006474 synergy with paclitaxel may be mediated by transient induction of E2F3. To test this, H1299 cells were depleted of E2F3a and E2F3b with siRNA and treated with paclitaxel. Assays of proliferation showed that both siRNAs significantly reduced paclitaxel sensitivity, as expected. Taken together, these results suggest that HLM006474 may have efficacy in lung cancer and may be useful in combination with taxanes.

Endocycles: a recurrent evolutionary innovation for post-mitotic cell growth

In endoreplication cell cycles, known as endocycles, cells successively replicate their genomes without segregating chromosomes during mitosis and thereby become polyploid. Such cycles, for which there are many variants, are widespread in protozoa, plants and animals. Endocycling cells can achieve ploidies of >200,000 C (chromatin-value); this increase in genomic DNA content allows a higher genomic output, which can facilitate the construction of very large cells or enhance macromolecular secretion. These cells execute normal S phases, using a G1-S regulatory apparatus similar to the one used by mitotic cells, but their capability to segregate chromosomes has been suppressed, typically by downregulation of mitotic cyclin-dependent kinase activity. Endocycles probably evolved many times, and the various endocycle mechanisms found in nature highlight the versatility of the cell cycle control machinery.

MiR-215 modulates gastric cancer cell proliferation by targeting RB1

Growing evidence indicates that miRNAs play critical roles in tumorigenesis and cancer progression. Here, we report that miR-215 is significantly up-regulated in gastric cancer tissues from either gastrectomy or gastroscopy. Receiver Operator Characteristic (ROC) curve analysis indicated that miR-215 may be a candidate biomarker for gastric cancer diagnosis. Inhibition of miR-215 significantly suppressed gastric cancer cell proliferation possibly via G1 arrest. Further analyses indicated that miR-215 was able to target retinoblastoma tumor-suppressor gene 1 (RB1) through its 3'-UTR in gastric cancer cells. These data suggest that frequently up-regulated miR-215 in gastric cancer may influence cell proliferation by targeting RB1.

Involvement of down-regulated E2F3 in Hirschsprung's disease

BACKGROUND/PURPOSE

Hirschsprung's disease (HSCR) is a common cause of neonatal bowel obstruction characterized by the absence of ganglion cells in the colon. Impaired migration of the neural crest cells (NCCs) has been implicated as one of the main causes of HSCR. E2F3, a member in the E2F family, which plays a crucial role in the control of the cell cycle is correlated with neuron migration. However, the function of E2F3 in the development of the enteric nervous system still remains unknown. This study aims to reveal the correlation of E2F3 in the progress of HSCR.

METHODS

By using reverse transcriptase polymerase chain reaction (RT-PCR) and western blot assay, we investigated levels of E2F3 expression in 58 HSCR patients, both in the aganglionic bowel segment and the normal ganglionic segment, and in 39 unrelated controls. By in vitro assays, we used the siRNA method to knock-down the level of E2F3 expression in 293T cell lines. Furthermore, transwell assay was used to detect cell migration ability.

RESULTS

Aberrant lower expression level of E2F3 was detected in the HSCR-S segment compared with the control group by RT-PCR and western blot assay. Besides, down-regulated E2F3 could suppress the cell migration.

CONCLUSIONS

This is the first study showing the down-regulation of E2F3 in HSCR, bringing new insight to the mechanism of the impaired migration of neural crest cells.

Evidence that Igf2 down-regulation in postnatal tissues and up-regulation in malignancies is driven by transcription factor E2f3

Insulin-like growth factor 2 (IGF2) is an important fetal growth factor. Its expression is dramatically down-regulated in multiple organs after birth but is frequently up-regulated in cancers. The mechanisms that drive down-regulation of IGF2 in postnatal tissues or the up-regulation in malignancy are unclear. We found evidence that E2F transcription factor 3 (E2F3) drives these changes in expression. E2f3 mRNA expression, protein expression, and binding to the Igf2 promoter all decreased with age postnatally in multiple mouse organs. In late juvenile hepatocytes, restoration of high E2f3 expression restored high Igf2 expression, indicating a causal relationship, but this induction did not occur in fetal hepatocytes, which already have high E2f3 and Igf2 expression. Transient expression of E2f3 in both HEK293 cells and in late juvenile hepatocytes were able to activate reporter constructs containing the mouse Igf2 promoter P2, which includes consensus E2F-binding sites. In humans, microarray data revealed declines in E2F3 and IGF2 expression with age similar to the mouse. In addition, E2F3-overexpressing human prostate and bladder cancers showed increased IGF2 expression, and levels of E2F3 and IGF2 mRNA in these cancers were positively correlated. Taken together, the findings suggest that down-regulation of E2f3 with age helps drive the dramatic decline in Igf2 expression in postnatal organs, and E2F3 overexpression in human cancers induces IGF2 overexpression.

miR-141 contributes to fetal growth restriction by regulating PLAG1 expression

Background

Fetal growth restriction (FGR) is an important but poorly understood condition of pregnancy, which results in significant fetal, neonatal and long-term morbidity and mortality. Novel research has suggested that altered miRNA expression in the plasma and placenta is associated with adverse pregnancy. We hypothesized that aberrant expression of microRNA-141 (miR-141) in the placenta is associated with FGR. Additionally, expression levels of predicted target genes of miR-141 were also analyzed in placental tissues of FGR and normal controls.

Methodology/Principal Findings

Using quantitative real time PCR, we analyzed the expression level of miR-141 and its target genes in placentas of FGR pregnancies (n = 21) and normal controls (n = 34). Western blot was used to detect the protein expression level of the target genes of miR-141. MiR-141 showed significant up regulation in FGR and significant down regulation of its targets, i.e. E2F transcription factor 3 (E2F3) protein, pleiomorphic adenoma gene 1 (PLAG1) mRNA and protein. Moreover, a positive correlation was found between PLAG1 and insulin-like growth factor 2 (IGF2) expression levels (Spearman r = 0.56, p<0.0001). MiR-141 yields an AUC of 0.83 with 88.5% sensitivity and 71.7% specificity for separating FGR from normal controls. This study indicates that miR-141 may be diagnostically important in FGR.

Conclusions/Significance

Our results indicate that aberrant high expression level of miR-141 might play important roles in the pathogenesis of FGR by suppressing E2F3 and PLAG1. We propose that miR-141 may participate in a miR-141-PLAG1-IGF2 network relating to FGR development. These findings may provide new targets via miR-141 in diagnosis and therapy of FGR in the future.

Endoreplication

Developmentally programmed polyploidy occurs by at least four different mechanisms, two of which (endoreduplication and endomitosis) involve switching from mitotic cell cycles to endocycles by the selective loss of mitotic cyclin-dependent kinase (CDK) activity and bypassing many of the processes of mitosis. Here we review the mechanisms of endoreplication, focusing on recent results from Drosophila and mice.

Tripartite motif containing 28 (Trim28) can regulate cell proliferation by bridging HDAC1/E2F interactions

BACKGROUND

Trim28 appears up-regulated in many cancers.

RESULTS

In early stage lung tumors high Trim28 correlates with increased overall survival and Trim28 reduces cell proliferation in model lung cancer cell lines through E2F interactions.

CONCLUSION

Trim28 may have a tumor suppressing role in the early stages of lung cancer.

SIGNIFICANCE

These results suggest a complex role for Trim28 in lung cancer. Trim28 is a poorly understood transcriptional co-factor with pleiotropic biological activities. Although Trim28 mRNA is found in many studies to be up-regulated in both lung and breast cancer tissues relative to normal adjacent tissue, we found that within a panel of early-stage lung adenocarcinomas high levels of Trim28 protein correlate with better overall survival. This surprising observation suggests that Trim 28 may have anti-proliferative activity within tumors. To test this hypothesis, we used shRNAi to generate Trim28-knockdown breast and lung cancer cell lines and found that Trim28 depletion led to increased cell proliferation. Likewise, overexpression of Trim28 led to decreased cell proliferation. Confocal microscopy indicated co-localization of E2F3 and E2F4 with Trim28 within the cell nucleus, and co-immunoprecipitation assays demonstrated that Trim28 can bind both E2F3 and E2F4. Trim28 overexpression inhibited the transcriptional activity of E2F3 and E2F4, whereas Trim28 deficiency enhanced their activity. Co-immunoprecipitations further indicated that Trim28 bridges an interaction between E2Fs 3 and 4 and HDAC1. Promoter-reporter assays demonstrated that the ability of HDAC1 to repress E2F3 and E2F4-driven transcription is dependent on Trim28. Trim28 depletion increased E2F3 and E2F4 DNA binding activity, as measured by chromatin-immunoprecipitation (ChIP) assays while simultaneously reducing HDAC1 binding. Finally, ChIP-ReChIP experiments demonstrated that Trim/E2F complexes exist on several E2F-regulated promoters. Taken together, these results suggest that Trim28 has anti-proliferative activity in lung cancers via repression of members of the E2F family that are critical for cell proliferation.

Curtailing overexpression of E2F3 in breast cancer using siRNA (E2F3)-based gene silencing

BACKGROUND AND AIMS

The E2F3 transcription factor claims its role in controlling cell cycle progression. As reported earlier, nuclear E2F3 overexpression leads to development of bladder and prostate cancer in humans. Accordingly, the present investigation has been designed to assess to what extent E2F3 would be overexpressed in breast cancer. The aim of this study was to emphasize that the levels of E2F3 are increased in breast cancer and highlights the efficacy of siRNA targeted to E2F3.

METHODS

To investigate the expression level of E2F3 and the progression of breast tumors, quantitative real-time PCR analysis was carried out. Western blotting analysis was performed to measure its counterparts, namely, E2F3a and E2F3b.

RESULTS

In the novel axis of E2F3, a large set of 11 breast cancer cell lines were identified to have the property of overexpression. Furthermore, the small interfering RNA (siRNA) developed against E2F3 significantly blocked the expression of the E2F3 in the selected breast cancer cell lines. Thus, the present findings authenticate the efficiency of siRNA (E2F3) to fight against breast cancer; hence, the siRNA mediated E2F3 gene silencing knockdown the E2F3.

CONCLUSIONS

This in vitro study demonstrates that E2F3 is a newly identified diagnostic and potential therapeutic target in breast cancer. Outcomes of this study affirm that siRNA for E2F3 facilitates the silencing of E2F3 overexpression and fights against breast cancer. Therefore, it plays a vital role as an alternative for diagnosis and clinical outcome for the treatment of breast cancer.

E2F1 loss induces spontaneous tumour development in Rb-deficient epidermis

The specific ablation of Rb1 gene in epidermis (Rb(F/F);K14cre) promotes proliferation and altered differentiation but does not produce spontaneous tumour development. These phenotypic changes are associated with increased expression of E2F members and E2F-dependent transcriptional activity. Here, we have focused on the possible dependence on E2F1 gene function. We have generated mice that lack Rb1 in epidermis in an inducible manner (Rb(F/F);K14creER(TM)). These mice are indistinguishable from those lacking pRb in this tissue in a constitutive manner (Rb(F/F);K14cre). In an E2F1-null background (Rb(F/F);K14creER(TM); and E2F1(-/-) mice), the phenotype due to acute Rb1 loss is not ameliorated by E2F1 loss, but rather exacerbated, indicating that pRb functions in epidermis do not rely solely on E2F1. On the other hand, Rb(F/F);K14creER(TM);E2F1(-/-) mice develop spontaneous epidermal tumours of hair follicle origin with high incidence. These tumours, which retain a functional p19(arf)/p53 axis, also show aberrant activation of β-catenin/Wnt pathway. Gene expression studies revealed that these tumours display relevant similarities with specific human tumours. These data demonstrate that the Rb/E2F1 axis exerts essential functions not only in maintaining epidermal homoeostasis, but also in suppressing tumour development in epidermis, and that the disruption of this pathway may induce tumour progression through specific alteration of developmental programs.

Atypical E2F repressors and activators coordinate placental development

The evolutionarily ancient arm of the E2f family of transcription factors consisting of the two atypical members E2f7 and E2f8 is essential for murine embryonic development. However, the critical tissues, cellular processes, and molecular pathways regulated by these two factors remain unknown. Using a series of fetal and placental lineage-specific cre mice, we show that E2F7/E2F8 functions in extraembryonic trophoblast lineages are both necessary and sufficient to carry fetuses to term. Expression profiling and biochemical approaches exposed the canonical E2F3a activator as a key family member that antagonizes E2F7/E2F8 functions. Remarkably, the concomitant loss of E2f3a normalized placental gene expression programs, corrected placental defects, and fostered the survival of E2f7/E2f8-deficient embryos to birth. In summary, we identified a placental transcriptional network tightly coordinated by activation and repression through two distinct arms of the E2F family that is essential for extraembryonic cell proliferation, placental development, and fetal viability.

Dysregulation of microRNA-34a expression in head and neck squamous cell carcinoma promotes tumor growth and tumor angiogenesis

BACKGROUND

MicroRNAs (miRs) are small non-coding RNAs that play an important role in cancer development where they can act as oncogenes or as tumor-suppressors. miR-34a is a tumor-suppressor that is frequently downregulated in a number of tumor types. However, little is known about the role of miR-34a in head and neck squamous cell carcinoma (HNSCC).

METHODS AND RESULTS

miR-34a expression in tumor samples, HNSCC cell lines and endothelial cells was examined by real time PCR. Lipofectamine-2000 was used to transfect miR-34a in HNSCC cell lines and human endothelial cells. Cell-proliferation, migration and clonogenic survival was examined by MTT, Xcelligence system, scratch assay and colony formation assay. miR-34a effect on tumor growth and tumor angiogenesis was examined by in vivo SCID mouse xenograft model. Our results demonstrate that miR-34a is significantly downregulated in HNSCC tumors and cell lines. Ectopic expression of miR-34a in HNSCC cell lines significantly inhibited tumor cell proliferation, colony formation and migration. miR-34a overexpression also markedly downregulated E2F3 and survivin levels. Rescue experiments using microRNA resistant E2F3 isoforms suggest that miR-34a-mediated inhibition of cell proliferation and colony formation is predominantly mediated by E2F3a isoform. In addition, tumor samples from HNSCC patients showed an inverse relationship between miR-34a and survivin as well as miR-34a and E2F3 levels. Overexpression of E2F3a completely rescued survivin expression in miR-34a expressing cells, thereby suggesting that miR-34a may be regulating survivin expression via E2F3a. Ectopic expression of miR-34a also significantly inhibited tumor growth and tumor angiogenesis in a SCID mouse xenograft model. Interestingly, miR-34a inhibited tumor angiogenesis by blocking VEGF production by tumor cells as well as directly inhibiting endothelial cell functions.

CONCLUSIONS

Taken together, these findings suggest that dysregulation of miR-34a expression is common in HNSCC and modulation of miR34a activity might represent a novel therapeutic strategy for the treatment of HNSCC.

Concomitant inactivation of Rb and E2f8 in hematopoietic stem cells synergizes to induce severe anemia

The retinoblastoma (Rb) tumor suppressor plays important roles in regulating hematopoiesis, particularly erythropoiesis. In an effort to understand whether Rb function can be mediated by E2F transcription factors in a BM-derived hematopoietic system in mice, we uncovered a functional synergy between Rb and E2F8 to promote erythropoiesis and to prevent anemia. Specifically, whereas Mx1-Cre-mediated inactivation of Rb or E2f8 in hematopoietic stem cells only led to mild erythropoietic defects, concomitant inactivation of both genes resulted in marked ineffective erythropoiesis and mild hemolysis, leading to severe anemia despite the presence of enhanced extramedullary erythropoiesis. Interestingly, although ineffective erythropoiesis was already present in the RbΔ/Δ mice and exacerbated in the RbΔ/Δ;E2f8Δ/Δ mice, hemolysis was exclusively manifested in the double-knockout mice. Using an adoptive transfer system and an erythroid-specific knockout system, we have shown that the synergy of Rb and E2f8 deficiency in triggering severe anemia is intrinsic to the erythroid lineage. Surprisingly, concomitant inactivation of Rb and E2f7, a close family member of E2f8, did not substantially worsen the erythropoietic defect resulted from Rb deficiency. The results of the present study reveal the specificity of E2F8 in mediating Rb function in erythropoiesis and suggest critical and overlapping roles of Rb and E2f8 in maintaining normal erythropoiesis and in preventing hemolysis.

Genome-wide analyses of Nkx2-1 binding to transcriptional target genes uncover novel regulatory patterns conserved in lung development and tumors

The homeodomain transcription factor Nkx2-1 is essential for normal lung development and homeostasis. In lung tumors, it is considered a lineage survival oncogene and prognostic factor depending on its expression levels. The target genes directly bound by Nkx2-1, that could be the primary effectors of its functions in the different cellular contexts where it is expressed, are mostly unknown. In embryonic day 11.5 (E11.5) mouse lung, epithelial cells expressing Nkx2-1 are predominantly expanding, and in E19.5 prenatal lungs, Nkx2-1-expressing cells are predominantly differentiating in preparation for birth. To evaluate Nkx2-1 regulated networks in these two cell contexts, we analyzed genome-wide binding of Nkx2-1 to DNA regulatory regions by chromatin immunoprecipitation followed by tiling array analysis, and intersected these data to expression data sets. We further determined expression patterns of Nkx2-1 developmental target genes in human lung tumors and correlated their expression levels to that of endogenous NKX2-1. In these studies we uncovered differential Nkx2-1 regulated networks in early and late lung development, and a direct function of Nkx2-1 in regulation of the cell cycle by controlling the expression of proliferation-related genes. New targets, validated in Nkx2-1 shRNA transduced cell lines, include E2f3, Cyclin B1, Cyclin B2, and c-Met. Expression levels of Nkx2-1 direct target genes identified in mouse development significantly correlate or anti-correlate to the levels of endogenous NKX2-1 in a dosage-dependent manner in multiple human lung tumor expression data sets, supporting alternative roles for Nkx2-1 as a transcriptional activator or repressor, and direct regulator of cell cycle progression in development and tumors.

Epstein-Barr virus downregulates microRNA 203 through the oncoprotein latent membrane protein 1: a contribution to increased tumor incidence in epithelial cells

The Epstein-Barr virus (EBV) is highly associated with nasopharyngeal carcinoma (NPC), and it regulates some microRNAs (miRNAs) that are involved in the development of cancer. The role of EBV in the deregulation of cellular miRNAs and how this affects the progression of NPC remain to be investigated. An analysis of the miRNA profile in an EBV-infected cell line revealed that miRNA 203 (miR-203) was downregulated. miR-203 is expressed specifically in epithelial cells. This downregulation of miR-203 was further verified and functionally analyzed. miR-203 was downregulated substantially in epithelial cells and NPC tissues that were latently infected with EBV. Downregulation of miR-203 also occurred during the early stage of EBV infection. Furthermore, the viral oncoprotein, latent membrane protein 1 (LMP1), was responsible for downregulation of miR-203. Removal of the latent EBV genome or suppression of LMP1 resulted in restoration of miR-203 expression. EBV-LMP1 mediated the downregulation of miR-203 at the primary transcript level. E2F3 and CCNG1 were identified as target genes of miR-203. Ectopic expression of miR-203 inhibited EBV-induced S-phase entry and transformation in vivo. Overexpression of the targets overcame the effects of miR-203 mimics on the cell cycle, and the expression of target genes in tumor models was inhibited by miR-203. Inhibitors of Jun N-terminal protein kinase (JNK) and NF-κB blocked miR-203 downregulation. These results imply that EBV promotes malignancy by downregulating cellular miR-203, which contributes to the etiology of NPC.

Network calisthenics: control of E2F dynamics in cell cycle entry

Stimulation of quiescent mammalian cells with mitogens induces an abrupt increase in E2F1-3 expression just prior to the onset of DNA synthesis, followed by a rapid decline as replication ceases. This temporal adaptation in E2F facilitates a transient pattern of gene expression that reflects the ordered nature of DNA replication. The challenge to understand how E2F dynamics coordinate molecular events required for high-fidelity DNA replication has great biological implications. Indeed, precocious, prolonged, elevated or reduced accumulation of E2F can generate replication stress that culminates in either arrest or death. Accordingly, temporal characteristics of E2F are regulated by several network modules that include feedforward and autoregulatory loops. In this review, we discuss how these network modules contribute to "shaping" E2F dynamics in the context of mammalian cell cycle entry.