Introduction to the E2F family: protein structure and gene regulation

HBx promotes hepatocellular carcinoma progression by repressing the transcription level of miR-187-5p

HBV-associated hepatitis B virus x protein (HBx) plays multiple roles in the development of hepatocellular carcinoma. In our prior study, we discovered that miR-187-5p expression was inhibited by HBx. To investigate the underlying molecular mechanism of HBx-mediated miR-187-5p downregulation in hepatocellular carcinoma cells, effects of HBx and miR-187-5p on hepatoma carcinoma cell were observed, as well as their interactions. Through in vitro and in vivo experiments, we demonstrated that overexpression of miR-187-5p inhibited proliferation, migration, and invasion. Simultaneously, we observed a dysregulation in the expression of miR-187-5p in liver cancer cell lines, which may be attributed to transcriptional inhibition through the E2F1/FoxP3 axis. Additionally, we noted that HBx protein is capable of enhancing the expression of E2F1, a transcription factor that promotes the expression of FoxP3. In conclusion, our results suggest that the inhibitory effect of HBx on miR-187-5p is mediated through the E2F1/FoxP3 axis. As shown in this work, HBx promotes hepatoma carcinoma cell proliferation, migration, and invasion through the E2F1/FoxP3/miR-187 axis. It provides a theoretical basis for finding therapeutic targets that will help clinic treatment for HCC.

Expression and Prognostic Role of E2F2 in Hepatocellular Carcinoma

Introduction

Hepatocellular carcinoma (HCC) is a common clinical malignancy. Recent studies reported that E2F transcription factor 2 (E2F2) plays a significant role in tumor progression. However, its expression and biological function in HCC are still unclear. Therefore, we explored the relationship between E2F2 expression and tumor progression in HCC.

Methods

In this study, we utilized some online tools to explore the E2F2 expression in pan-carcinoma and HCC. The association of E2F2 expression with the clinical characteristics and prognosis of HCC was further studied. In addition, we explored the co-expressed genes of E2F2 and mined the positively/negatively corrected significant genes and excavated the possible functions. Meanwhile, the hub gene set was constructed based on protein-protein interaction (PPI) network, and the relationship between E2F2 and immunity was discovered.

Results

We observed that the expression level of E2F2 was generally upregulated in HCC. However, E2F2 expression was not significantly different between HCC and normal tissues in regard to the disease stage 4. Furthermore, we also observed the poor prognosis in patients with high E2F2 expression. The co-expressed genes of E2F2 were identified and further detected. Thereafter, we identified the positively/negatively corrected significant genes and constructed the hub gene network of E2F2 based on PPI network. We also found that E2F2 expression was positively correlated with the infiltration levels of CD4+ T, CD8+ T cells, macrophages, neutrophils, and dendritic cells.

Conclusion

Our findings suggested that E2F2 could be a potential prognostic factor for HCC, which could provide a therapeutic target for the molecular treatment of HCC.

Stress Relief Techniques: p38 MAPK Determines the Balance of Cell Cycle and Apoptosis Pathways

Protein signaling networks are formed from diverse and inter-connected cell signaling pathways converging into webs of function and regulation. These signaling pathways both receive and conduct molecular messages, often by a series of post-translation modifications such as phosphorylation or through protein-protein interactions via intrinsic motifs. The mitogen activated protein kinases (MAPKs) are components of kinase cascades that transmit signals through phosphorylation. There are several MAPK subfamilies, and one subfamily is the stress-activated protein kinases, which in mammals is the p38 family. The p38 enzymes mediate a variety of cellular outcomes including DNA repair, cell survival/cell fate decisions, and cell cycle arrest. The cell cycle is itself a signaling system that precisely controls DNA replication, chromosome segregation, and cellular division. Another indispensable cell function influenced by the p38 stress response is programmed cell death (apoptosis). As the regulators of cell survival, the BCL2 family of proteins and their dynamics are exquisitely sensitive to cell stress. The BCL2 family forms a protein-protein interaction network divided into anti-apoptotic and pro-apoptotic members, and the balance of binding between these two sides determines cell survival. Here, we discuss the intersections among the p38 MAPK, cell cycle, and apoptosis signaling pathways.

Emerging Roles of LncRNAs in the EZH2-regulated Oncogenic Network

Cancer is a life-threatening disease, but cancer therapies based on epigenetic mechanisms have made great progress. Enhancer of zeste homolog 2 (EZH2) is the key catalytic component of Polycomb repressive complex 2 (PRC2) that mediates the tri-methylation of lysine 27 on histone 3 (H3K27me3), a well-recognized marker of transcriptional repression. Mounting evidence indicates that EZH2 is elevated in various cancers and associates with poor prognosis. In addition, many studies revealed that EZH2 is also involved in transcriptional repression dependent or independent of PRC2. Meanwhile, long non-coding RNAs (lncRNAs) have been reported to regulate numerous and diverse signaling pathways in oncogenesis. In this review, we firstly discuss functional interactions between EZH2 and lncRNAs that determine PRC2-dependent and -independent roles of EZH2. Secondly, we summarize the lncRNAs regulating EZH2 expression at transcription, post-transcription and post-translation levels. Thirdly, we review several oncogenic pathways cooperatively regulated by lncRNAs and EZH2, including the Wnt/β-catenin and p53 pathways. In conclusion, lncRNAs play a key role in the EZH2-regulated oncogenic network with many fertile directions to be explored.

E2F1 regulates testicular descent and controls spermatogenesis by influencing WNT4 signaling

Cryptorchidism is the most common urologic birth defect in men and is a predisposing factor of male infertility and testicular cancer, yet the etiology remains largely unknown. E2F1 microdeletions and microduplications contribute to cryptorchidism, infertility and testicular tumors. Although E2f1 deletion or overexpression in mice causes spermatogenic failure, the mechanism by which E2f1 influences testicular function is unknown. This investigation revealed that E2f1-null mice develop cryptorchidism with severe gubernacular defects and progressive loss of germ cells resulting in infertility and, in rare cases, testicular tumors. It was hypothesized that germ cell depletion resulted from an increase in WNT4 levels. To test this hypothesis, the phenotype of a double-null mouse model lacking both Wnt4 and E2f1 in germ cells was analyzed. Double-null mice are fertile. This finding indicates that germ cell maintenance is dependent on E2f1 repression of Wnt4, supporting a role for Wnt4 in germ cell survival. In the future, modulation of WNT4 expression in men with cryptorchidism and spermatogenic failure due to E2F1 copy number variations may provide a novel approach to improve their spermatogenesis and perhaps their fertility potential after orchidopexy.

Genome-wide analysis of HOXC4 and HOXC6 regulated genes and binding sites in prostate cancer cells

Aberrant expression of HOXC6 and HOXC4 is commonly detected in prostate cancer. The high expression of these transcription factors is associated with aggressive prostate cancer and can predict cancer recurrence after treatment. Thus, HOXC4 and HOXC6 are clinically relevant biomarkers of aggressive prostate cancer. However, the molecular mechanisms by which these HOXC genes contribute to prostate cancer is not yet understood. To begin to address the role of HOXC4 and HOXC6 in prostate cancer, we performed RNA-seq analyses before and after siRNA-mediated knockdown of HOXC4 and/or HOXC6 and also performed ChIP-seq to identify genomic binding sites for both of these transcription factors. Our studies demonstrate that HOXC4 and HOXC6 co-localize with HOXB13, FOXA1 and AR, three transcription factors previously shown to contribute to the development of prostate cancer. We suggest that the aberrantly upregulated HOXC4 and HOXC6 proteins may compete with HOXB13 for binding sites, thus altering the prostate transcriptome. This competition model may be applicable to many different human cancers that display increased expression of a HOX transcription factor.

The novel non-immunological role and underlying mechanisms of B7-H3 in tumorigenesis

B7 homolog 3 (B7-H3) has been proven to be involved in tumorigenesis. An elucidation of its role and underlying mechanisms is essential to an understanding of tumorigenesis and the development of effective clinical applications. B7-H3 is abnormally overexpressed in many types of cancer and is generally associated with a poor clinical prognosis. B7-H3 inhibits the initiation of the "caspase cascade" by the Janus kinase/signal transducers and activators of transcription pathway to resist tumor cell apoptosis. B7-H3 accelerates malignant proliferation by attacking the checkpoint mechanism of the tumor cell cycle through the phosphatidylinositol 3-kinase and protein kinase B pathway. B7-H3 reprograms the metabolism of glucose and lipids and transforms the metabolic flux of tumor cells to promote tumorigenesis. B7-H3 induces abnormal angiogenesis by recruiting vascular endothelial growth factor and matrix metalloproteinase to tumor lesions. B7-H3 strongly promotes tumorigenesis through antiapoptotic, pro-proliferation, metabolism reprogramming, and pro-angiogenesis.

The Temporal Regulation of S Phase Proteins During G1

Successful DNA replication requires intimate coordination with cell-cycle progression. Prior to DNA replication initiation in S phase, a series of essential preparatory events in G₁ phase ensures timely, complete, and precise genome duplication. Among the essential molecular processes are regulated transcriptional upregulation of genes that encode replication proteins, appropriate post-transcriptional control of replication factor abundance and activity, and assembly of DNA-loaded protein complexes to license replication origins. In this chapter we describe these critical G₁ events necessary for DNA replication and their regulation in the context of both cell-cycle entry and cell-cycle progression.

Screening of potential therapy targets for prostate cancer using integrated analysis of two gene expression profiles

The aim of the present study was to analyze potential therapy targets for prostate cancer using integrated analysis of two gene expression profiles. First, gene expression profiles GSE38241 and GSE3933 were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs) between prostate cancer and normal control samples were identified using the Linear Models for Microarray Data package. Pathway enrichment analysis of DEGs was performed using Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes. Furthermore, protein-protein interaction (PPI) networks of DEGs were constructed, on the basis of the Search Tool for the Retrieval of Interacting Genes/Proteins database. The Molecular Complex Detection was utilized to perform module analysis of the PPI networks. In addition, transcriptional regulatory networks were constructed on the basis of the associations between transcription factors (TFs) and target genes. A total of 529 DEGs were identified, including 129 upregulated genes that were primarily associated with to the cell cycle. Additionally, 400 downregulated genes were identified, which were principally enriched in the pathways associated with vascular smooth muscle contraction and focal adhesion. Cell Division Cycle Associated 8, Cell Division Cycle 45, Ubiquitin Conjugating Enzyme E2 C and Thymidine Kinase 1 were identified as hub genes in the upregulated sub-network. Furthermore, the upregulated TF E2F, and the downregulated TF Early Growth Response 1, were identified to be critical in the transcriptional regulatory networks. The identified DEGs and TFs may have critical roles in the progression of prostate cancer, and may be used as target molecules for treating prostate cancer.

Functional Roles of E6 and E7 Oncoproteins in HPV-Induced Malignancies at Diverse Anatomical Sites

Approximately 200 human papillomaviruses (HPVs) infect human epithelial cells, of which the alpha and beta types have been the most extensively studied. Alpha HPV types mainly infect mucosal epithelia and a small group of these causes over 600,000 cancers per year worldwide at various anatomical sites, especially anogenital and head-and-neck cancers. Of these the most important is cervical cancer, which is the leading cause of cancer-related death in women in many parts of the world. Beta HPV types infect cutaneous epithelia and may contribute towards the initiation of non-melanoma skin cancers. HPVs encode two oncoproteins, E6 and E7, which are directly responsible for the development of HPV-induced carcinogenesis. They do this cooperatively by targeting diverse cellular pathways involved in the regulation of cell cycle control, of apoptosis and of cell polarity control networks. In this review, the biological consequences of papillomavirus targeting of various cellular substrates at diverse anatomical sites in the development of HPV-induced malignancies are highlighted.

Timing of transcription during the cell cycle: Protein complexes binding to E2F, E2F/CLE, CDE/CHR, or CHR promoter elements define early and late cell cycle gene expression

A central question in cell cycle control is how differential gene expression is regulated. Timing of expression is important for correct progression through the cell cycle. E2F, CDE, and CHR promoter sites have been linked to transcriptional repression in resting cells and activation during the cell cycle. Further, the DREAM complex binds CHR or CDE/CHR elements of G₂/M genes resulting in repression during G₀/G₁. Here, we show that DREAM also binds to E2F sites of S phase genes in quiescence and upon p53 activation. Furthermore, we describe a novel class of promoter sites, the CHR-like elements (CLE), which can support binding of DREAM to E2F elements. Activation of such S phase genes is achieved through binding of E2F1-3/DP complexes to E2F sites. In contrast, the activating MuvB complexes MMB and FOXM1-MuvB bind to CHR elements and mediate peak expression in G₂/M. In conclusion, data presented here in combination with earlier results leads us to propose a model that explains how DREAM can repress early cell cycle genes through E2F or E2F/CLE sites and late genes through CHR or CDE/CHR elements. Also p53-dependent indirect transcriptional repression through the p53-p21-Cyclin/CDK-DREAM-E2F/CLE/CDE/CHR pathway requires DREAM binding to E2F or E2F/CLE sites in early cell cycle genes and binding of DREAM to CHR or CDE/CHR elements of late cell cycle genes. Specific timing of activation is achieved through binding of E2F1-3/DP to E2F sites and MMB or FOXM1-MuvB complexes to CHR elements.

Functional development of the adult ovine mammary gland--insights from gene expression profiling

Background

The mammary gland is a dynamic organ that undergoes dramatic physiological adaptations during the transition from late pregnancy to lactation. Investigation of the molecular basis of mammary development and function will provide fundamental insights into tissue remodelling as well as a better understanding of milk production and mammary disease. This is important to livestock production systems and human health.

Here we use RNA-seq to identify differences in gene expression in the ovine mammary gland between late pregnancy and lactation.

Results

Between late pregnancy (135 days of gestation ± 2.4 SD) and lactation (15 days post partum ± 1.27 SD) 13 % of genes in the sheep genome were differentially expressed in the ovine mammary gland. In late pregnancy, cell proliferation, beta-oxidation of fatty acids and translation were identified as key biological processes. During lactation, high levels of milk fat synthesis were mirrored by enrichment of genes associated with fatty acid biosynthesis, transport and lipogenesis. Protein processing in the endoplasmic reticulum was enriched during lactation, likely in support of active milk protein synthesis. Hormone and growth factor signalling and activation of signal transduction pathways, including the JAK-STAT and PPAR pathways, were also differently regulated, indicating key roles for these pathways in functional development of the ovine mammary gland. Changes in the expression of epigenetic regulators, particularly chromatin remodellers, indicate a possible role in coordinating the large-scale transcriptional changes that appear to be required to switch mammary processes from growth and development during late pregnancy to synthesis and secretion of milk during lactation.

Conclusions

Coordinated transcriptional regulation of large numbers of genes is required to switch between mammary tissue establishment during late pregnancy, and activation and maintenance of milk production during lactation. Our findings indicate the remarkable plasticity of the mammary gland, and the coordinated regulation of multiple genes and pathways to begin milk production. Genes and pathways identified by the present study may be important for managing milk production and mammary development, and may inform studies of diseases affecting the mammary gland.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1947-9) contains supplementary material, which is available to authorized users.

One of the Mechanisms to Increase HSV-1 Uptake in HSV-1-Infected, Activated T Lymphocytes Is the Formation of Filopodia

OBJECTIVES

To explore the host transcription factor E2F-1 and/or any mechanisms that may support viral entry and its effect on the HSV-1 production in anti-CD3-activated Jurkat cells.

METHODS

The expressions of ICP4, HVEM and E2F-1 were studied using reverse transcription-PCR and Western blot. HSV-1 production was determined by plaque titration assay and HSV-1 DNA load was quantified by real-time PCR. The viral uptake was observed by electron microscopy.

RESULTS

In anti-CD3-activated Jurkat cells, there was a significant increase in the HSV-1 production. The expression of ICP4 mRNA after HSV-1 infection occurred 2 h prior to the synthesis of the ICP4 protein, which was significantly higher in activated than nonactivated T cells. There were no significant differences in the expressions of E2F-1 mRNA. The HVEM expression was positively correlated with the HSV-1 DNA in the activated T cells. From the electron micrograph, the formations of filopodia were observed only in HSV-1-infected, activated cells.

CONCLUSIONS

High expressions of viral receptor protein and filopodia formations are the key factors that enhance the HSV-1 entry into activated T lymphocytes, resulting in an increased production of the virus.

Deregulation of Rb-E2F1 axis causes chromosomal instability by engaging the transactivation function of Cdc20-anaphase-promoting complex/cyclosome

The E2F family of transcription factors regulates genes involved in various aspects of the cell cycle. Beyond the well-documented role in G1/S transition, mitotic regulation by E2F has also been reported. Proper mitotic progression is monitored by the spindle assembly checkpoint (SAC). The SAC ensures bipolar separation of chromosomes and thus prevents aneuploidy. There are limited reports on the regulation of the SAC by E2F. Our previous work identified the SAC protein Cdc20 as a novel transcriptional regulator of the mitotic ubiquitin carrier protein UbcH10. However, none of the Cdc20 transcription complex proteins have any known DNA binding domain. Here we show that an E2F1-DP1 heterodimer is involved in recruitment of the Cdc20 transcription complex to the UBCH10 promoter and in transactivation of the gene. We further show that inactivation of Rb can facilitate this transactivation process. Moreover, this E2F1-mediated regulation of UbcH10 influences mitotic progression. Deregulation of this pathway results in premature anaphase, chromosomal abnormalities, and aneuploidy. We conclude that excess E2F1 due to Rb inactivation recruits the complex of Cdc20 and the anaphase-promoting complex/cyclosome (Cdc20-APC/C) to deregulate the expression of UBCH10, leading to chromosomal instability in cancer cells.

Identification of cell cycle-regulated genes periodically expressed in U2OS cells and their regulation by FOXM1 and E2F transcription factors

Characterization of the cell cycle–regulated transcripts in U2OS cells yielded 1871 unique genes. FOXM1 targets were identified via ChIP-seq, and novel targets in G2/M and S phases were verified using a real-time luciferase assay. ChIP-seq data were used to map cell cycle transcriptional regulators of cell cycle–regulated gene expression in U2OS cells.

We identify the cell cycle–regulated mRNA transcripts genome-wide in the osteosarcoma-derived U2OS cell line. This results in 2140 transcripts mapping to 1871 unique cell cycle–regulated genes that show periodic oscillations across multiple synchronous cell cycles. We identify genomic loci bound by the G2/M transcription factor FOXM1 by chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-seq) and associate these with cell cycle–regulated genes. FOXM1 is bound to cell cycle–regulated genes with peak expression in both S phase and G2/M phases. We show that ChIP-seq genomic loci are responsive to FOXM1 using a real-time luciferase assay in live cells, showing that FOXM1 strongly activates promoters of G2/M phase genes and weakly activates those induced in S phase. Analysis of ChIP-seq data from a panel of cell cycle transcription factors (E2F1, E2F4, E2F6, and GABPA) from the Encyclopedia of DNA Elements and ChIP-seq data for the DREAM complex finds that a set of core cell cycle genes regulated in both U2OS and HeLa cells are bound by multiple cell cycle transcription factors. These data identify the cell cycle–regulated genes in a second cancer-derived cell line and provide a comprehensive picture of the transcriptional regulatory systems controlling periodic gene expression in the human cell division cycle.

The DREAM complex: master coordinator of cell cycle-dependent gene expression

The dimerization partner, RB-like, E2F and multi-vulval class B (DREAM) complex provides a previously unsuspected unifying role in the cell cycle by directly linking p130, p107, E2F, BMYB and forkhead box protein M1. DREAM mediates gene repression during the G0 phase and coordinates periodic gene expression with peaks during the G1/S and G2/M phases. Perturbations in DREAM complex regulation shift the balance from quiescence towards proliferation and contribute to the increased mitotic gene expression levels that are frequently observed in cancers with a poor prognosis.

The DREAM complex: master coordinator of cell cycle-dependent gene expression

The dimerization partner, RB-like, E2F and multi-vulval class B (DREAM) complex provides a previously unsuspected unifying role in the cell cycle by directly linking p130, p107, E2F, BMYB and forkhead box protein M1. DREAM mediates gene repression during the G0 phase and coordinates periodic gene expression with peaks during the G1/S and G2/M phases. Perturbations in DREAM complex regulation shift the balance from quiescence towards proliferation and contribute to the increased mitotic gene expression levels that are frequently observed in cancers with a poor prognosis.

Identifying molecular targets of lifestyle modifications in colon cancer prevention

One in four deaths in the United States is cancer-related, and colorectal cancer (CRC) is the second leading cause of cancer-associated deaths. Screening strategies are utilized but have not reduced disease incidence or mortality. In this regard, there is an interest in cancer preventive strategies focusing on lifestyle intervention, where specific etiologic factors involved in cancer initiation, promotion, and progression could be targeted. For example, exposure to dietary carcinogens, such as nitrosamines and polycyclic aromatic hydrocarbons influences colon carcinogenesis. Furthermore, dietary deficiencies could alter sensitivity to genetic damage and influence carcinogen metabolism contributing to CRC. High alcohol consumption increases the risk of mutations including the fact that acetaldehyde, an ethanol metabolite, is classified as a group 1 carcinogen. Tobacco smoke exposure is also a risk factor for cancer development; approximately 20% of CRCs are associated with smoking. Additionally, obese patients have a higher risk of cancer development, which is further supported by the fact that physical activity decreases CRC risk by 55%. Similarly, chronic inflammatory conditions also increase the risk of CRC development. Moreover, the circadian clock alters digestion and regulates other biochemical, physiological, and behavioral processes that could influence CRC. Taken together, colon carcinogenesis involves a number of etiological factors, and therefore, to create effective preventive strategies, molecular targets need to be identified and beleaguered prior to disease progression. With this in mind, the following is a comprehensive review identifying downstream target proteins of the above lifestyle risk factors, which are modulated during colon carcinogenesis and could be targeted for CRC prevention by novel agents including phytochemicals.

TNFα modulates Fibroblast Growth Factor Receptor 2 gene expression through the pRB/E2F1 pathway: identification of a non-canonical E2F binding motif

Interactions between epithelium and mesenchyme during wound healing are not fully understood, but Fibroblast Growth Factors (FGFs) and their receptors FGFRs are recognized as key elements. FGFR2 gene encodes for two splicing transcript variants, FGFR2-IIIb or Keratinocyte Growth Factor Receptor (KGFR) and FGFR2-IIIc, which differ for tissue localization and ligand specificity. Proinflammatory cytokines play an essential role in the regulation of epithelial-mesenchymal interactions, and have been indicated to stimulate FGFs production. Here we demonstrated that upregulation of FGFR2 mRNA and protein expression is induced by the proinflammatory cytokines Tumor Necrosis Factor-α, Interleukin-1β and Interleukin 2. Furthermore, we found that TNFα determines FGFR2 transcriptional induction through activation of pRb, mediated by Raf and/or p38 pathways, and subsequent release of the transcription factor E2F1. Experiments based on FGFR2 promoter serial deletions and site-directed mutagenesis allowed us to identify a minimal responsive element that retains the capacity to be activated by E2F1. Computational analysis indicated that this element is a non-canonical E2F responsive motif. Thus far, the molecular mechanisms of FGFR2 upregulation during wound healing or in pathological events are not known. Our data suggest that FGFR2 expression can be modulated by local recruitment of inflammatory cytokines. Furthermore, since alterations in FGFR2 expression have been linked to the pathogenesis of certain human cancers, these findings could also provide elements for diagnosis and potential targets for novel therapeutic approaches.

A target based approach identifies genomic predictors of breast cancer patient response to chemotherapy

Background

The efficacy of chemotherapy regimens in breast cancer patients is variable and unpredictable. Whether individual patients either achieve long-term remission or suffer recurrence after therapy may be dictated by intrinsic properties of their breast tumors including genetic lesions and consequent aberrant transcriptional programs. Global gene expression profiling provides a powerful tool to identify such tumor-intrinsic transcriptional programs, whose analyses provide insight into the underlying biology of individual patient tumors. For example, multi-gene expression signatures have been identified that can predict the likelihood of disease reccurrence, and thus guide patient prognosis. Whereas such prognostic signatures are being introduced in the clinical setting, similar signatures that predict sensitivity or resistance to chemotherapy are not currently clinically available.

Methods

We used gene expression profiling to identify genes that were co-expressed with genes whose transcripts encode the protein targets of commonly used chemotherapeutic agents.

Results

Here, we present target based expression indices that predict breast tumor response to anthracycline and taxane based chemotherapy. Indeed, these signatures were independently predictive of chemotherapy response after adjusting for standard clinic-pathological variables such as age, grade, and estrogen receptor status in a cohort of 488 breast cancer patients treated with adriamycin and taxotere/taxol.

Conclusions

Importantly, our findings suggest the practicality of developing target based indices that predict response to therapeutics, as well as highlight the possibility of using gene signatures to guide the use of chemotherapy during treatment of breast cancer patients.

The E2F6 repressor activates gene expression in myocardium resulting in dilated cardiomyopathy

The E2F/Rb pathway regulates cardiac growth and development and holds great potential as a therapeutic target. The E2F6 repressor is a unique E2F member that acts independently of pocket proteins. Forced expression of E2F6 in mouse myocardium induced heart failure and mortality, with severity of symptoms correlating to E2F6 levels. Echocardiography demonstrated a 37% increase (P<0.05) in left ventricular end-diastolic diameter and reduced ejection fraction (<40%, P<0.05) in young transgenic (Tg) mice. Microarray and qPCR analysis revealed a paradoxical increase in E2F-responsive genes, which regulate the cell cycle, without changes in cardiomyocyte cell number or size in Tg mice. Young adult Tg mice displayed a 75% (P<0.01) decrease in gap junction protein connexin-43, resulting in abnormal electrocardiogram including a 24% (P<0.05) increase in PR interval. Further, mir-206, which targets connexin-43, was up-regulated 10-fold (P<0.05) in Tg myocardium. The mitogen-activated protein kinase pathway, which regulates the levels of miR-206 and connexin-43, was activated in Tg hearts. Thus, deregulated E2F6 levels evoked abnormal gene expression at transcriptional and post-transcriptional levels, leading to cardiac remodeling and dilated cardiomyopathy. The data highlight an unprecedented role for the strict regulation of the E2F pathway in normal postnatal cardiac function.

Cyclin-dependent kinase inhibitor Cdkn2c regulates B cell homeostasis and function in the NZM2410-derived murine lupus susceptibility locus Sle2c1

Sle2c1 is an NZM2410- and NZB-derived lupus susceptibility locus that induces an expansion of the B1a cell compartment. B1a cells have a repertoire enriched for autoreactivity, and an expansion of this B cell subset occurs in several mouse models of lupus. A combination of genetic mapping and candidate gene analysis presents Cdkn2c, a gene encoding for cyclin-dependent kinase inhibitor p18(INK4c) (p18), as the top candidate gene for inducing the Slec2c1-associated expansion of B1a cells. A novel single nucleotide polymorphism in the NZB allele of the Cdkn2c promoter is associated with a significantly reduced Cdkn2c expression in the splenic B cells and peritoneal cavity B1a cells from Sle2c1-carrying mice, which leads to a defective G1 cell cycle arrest in splenic B cells and increased proliferation of peritoneal cavity B1a cells. As the cell cycle is differentially regulated in B1a and B2 cells, these results suggest that Cdkn2c plays a critical role in B1a cell self-renewal and that its impaired expression leads to an accumulation of these cells with high autoreactive potential.

E2F1 and KIAA0191 expression predicts breast cancer patient survival

BACKGROUND

Gene expression profiling of human breast tumors has uncovered several molecular signatures that can divide breast cancer patients into good and poor outcome groups. However, these signatures typically comprise many genes (~50-100), and the prognostic tests associated with identifying these signatures in patient tumor specimens require complicated methods, which are not routinely available in most hospital pathology laboratories, thus limiting their use. Hence, there is a need for more practical methods to predict patient survival.

METHODS

We modified a feature selection algorithm and used survival analysis to derive a 2-gene signature that accurately predicts breast cancer patient survival.

RESULTS

We developed a tree based decision method that segregated patients into various risk groups using KIAA0191 expression in the context of E2F1 expression levels. This approach led to highly accurate survival predictions in a large cohort of breast cancer patients using only a 2-gene signature.

CONCLUSIONS

Our observations suggest a possible relationship between E2F1 and KIAA0191 expression that is relevant to the pathogenesis of breast cancer. Furthermore, our findings raise the prospect that the practicality of patient prognosis methods may be improved by reducing the number of genes required for analysis. Indeed, our E2F1/KIAA0191 2-gene signature would be highly amenable for an immunohistochemistry based test, which is commonly used in hospital laboratories.

Small molecule regulators of Rb-E2F pathway as modulators of transcription

The retinoblastoma tumor suppressor protein, Rb, plays a major role in the regulation of mammalian cell cycle progression. It has been shown that Rb function is essential for the proper modulation of G1/S transition and inactivation of Rb contributes to deregulated cell proliferation. Rb exerts its cell cycle regulatory functions mainly by targeting the E2F family of transcription factors and Rb has been shown to physically interact with E2Fs 1, 2 and 3, repressing their transcriptional activity. Multiple genes involved in DNA synthesis and cell cycle progression are regulated by E2Fs, and Rb prevents their expression by inhibiting E2F activity, inducing growth arrest. It has been established that inactivation of Rb by phosphorylation, mutation, or by the interaction of viral oncoproteins leads to a release of the repression of E2F activity, facilitating cell cycle progression. Rb-mediated repression of E2F activity involves the recruitment of a variety of transcriptional co-repressors and chromatin remodeling proteins, including histone deacetylases, DNA methyltransferases and Brg1/Brm chromatin remodeling proteins. Inactivation of Rb by sequential phosphorylation events during cell cycle progression leads to a dissociation of these co-repressors from Rb, facilitating transcription. It has been found that small molecules that prevent the phosphorylation of Rb prevent the dissociation of certain co-repressors from Rb, especially Brg1, leading to the maintenance of Rb-mediated transcriptional repression and cell cycle arrest. Such small molecules have anti-cancer activities and will also act as valuable probes to study chromatin remodeling and transcriptional regulation.

Pattern of expression of the CREG gene and CREG protein in the mouse embryo

The cellular repressor of E1A-stimulated genes (CREG) is a secreted glycoprotein that inhibits cell proliferation and/or enhances differentiation. CREG is widely expressed in adult tissues such as the brain, heart, lungs, liver, intestines and kidneys in mice. We investigated the level of CREG expression during mouse embryogenesis and its distribution at 18.5 days post coitus (dpc) using immunohistochemical staining with diaminobenzidine, western blotting and reverse transcription-polymerase chain reaction. CREG expression was first detected in mouse embryos at 4.5 dpc. It was expressed at almost all stages up to 18.5 dpc. The level of CREG was found to increase gradually and was highest at 18.5 dpc. Western blotting showed that the CREG protein was expressed at higher levels in the brain, heart, intestines and kidneys than in the lungs and liver at 18.5 dpc. In 9.5 dpc embryos, CREG was expressed only in the endothelial cells of blood vessels, after the vascular lumen had formed. With advanced differentiation, vascular smooth muscle cells developed in the embryonic vascular structures; the expression of smooth muscle α-actin protein and CREG were positive and increased gradually in 10.5 dpc embryonic vessels. CREG expression in the embryonic blood vessels peaked at 15.5 dpc and was reduced slightly at 18.5 dpc. These results indicate that CREG is expressed during mouse embryogenesis and might participate in the differentiation of these organs during embryogenesis.

The E2F-1 associated retinoblastoma-susceptibility gene product is modified by O-GlcNAc

The retinoblastoma-susceptibility gene product (pRB) is a classical tumor suppressor. pRB regulates a number of cellular processes including proliferation, differentiation, and apoptosis. One of the essential mechanisms by which pRB, and the related p107 and p130 family members, act is through its interactions with the E2F class of transcription factors. E2F-1 transcription is necessary for entry into S-phase during the cell-cycle. pRB binds E2F-1 and represses transcription via recruitment of a histone deacetylase complex and by preventing co-activator complexes from binding E2F-1. Current dogma suggests that phosphorylation of pRB during mid- to late-G1 leads to release of E2F-1 and E2F-1 dependent transcriptional activation of essential S-phase genes. Here we show that pRB, and the related p107 protein, are modified by O-linked β-N-acetylglucosamine (O-GlcNAc) in an in vitro transcription/translation system. Furthermore, we show in vivo that pRB is more heavily glycosylated in G1 of the cell-cycle when pRB is known to be in an active, hypophosphorylated state. Finally, we demonstrate that E2F-1 associated pRB is modified by O-GlcNAc. These studies suggest that regulation of pRB function(s) may be controlled by dynamic O-GlcNAc modification, as well as phosphorylation.

The anticancer effect of probiotic Bacillus polyfermenticus on human colon cancer cells is mediated through ErbB2 and ErbB3 inhibition

A wealth of data implicates that ErbB receptors have essential roles in tumor development. Probiotic bacteria are known to exert an anticancer activity in animal studies. Bacillus polyfermenticus (B.P.), a probiotic bacterium, has been clinically used for a variety of gastrointestinal disorders in East Asia. Here, we investigated the effect of B.P. on the growth of tumors and its putative mechanism of actions. Conditioned medium of B.P. cultures (B.P. CM) inhibited the growth of human colon cancer cells including HT-29, DLD-1 and Caco-2 cells. Moreover, B.P. CM suppressed colony formation of HT-29 cells cultured on soft agar and reduced carcinogen-induced colony formation of normal colonocytes. Furthermore, data from the mouse xenograft model of human colon cancer cells showed reduced tumor size in B.P. CM-injected mice when compared to E. coli conditioned medium-injected mice. Exposure of B.P. CM to HT-29 cells for 24 hr, 48 hr and 2 weeks reduced ErbB2 and ErbB3 protein expression as well as mRNA levels. Moreover, cyclin D1 expression that is required for ErbB-dependent cell transformation was decreased by B.P. CM. Furthermore, transcription factor E2F-1 that regulates cyclin D1 expression was also decreased by B.P. CM. These results show that B.P. inhibits tumor growth and its anticancer activity occurs, at least in part, through suppressing ErbB2 and ErbB3. Taken together, our study suggests that this probiotic may be clinically used as a prophylactic treatment to prevent colon cancer development.

Regulation of vascular endothelial growth factor receptors by Rb and E2F1: role of acetylation

E2F transcription factors regulate a variety of cellular processes, but their role in angiogenesis is not clear. We find that many genes involved in angiogenesis such as FLT-1, KDR, and angiopoietin 2 have potential E2F1 binding sites in their promoter. Chromatin immunoprecipitation (ChIP) assays showed that E2F1 can associate with these promoters and the recruitment of E2F1 was enhanced upon vascular endothelial growth factor (VEGF) stimulation with concomitant dissociation of Rb, leading to the transcriptional activation of these promoters. Transient transfection experiments showed that these promoters were induced by E2F1 and repressed by Rb, whereas depletion of E2F1 decreased their expression. The increased binding of E2F1 to these promoters upon VEGF stimulation correlated with the acetylation of histones and E2F1; this required VEGF receptor function, as seen in ChIP-re-ChIP experiments. This suggests the existence of a positive feedback loop regulating E2F1 acetylation and VEGF receptor expression. Acetylation associated with VEGF signaling seems to be predominantly mediated by P300/CBP-associated factor, and the depletion of histone acetyl transferases disrupted the formation of angiogenic tubules. These results suggest a novel role for E2F1 and acetylation in the angiogenic process.

E2F in vivo binding specificity: comparison of consensus versus nonconsensus binding sites

We have previously shown that most sites bound by E2F family members in vivo do not contain E2F consensus motifs. However, differences between in vivo target sites that contain or lack a consensus E2F motif have not been explored. To understand how E2F binding specificity is achieved in vivo, we have addressed how E2F family members are recruited to core promoter regions that lack a consensus motif and are excluded from other regions that contain a consensus motif. Using chromatin immunoprecipitation coupled with DNA microarray analysis (ChIP-chip) assays, we have shown that the predominant factors specifying whether E2F is recruited to an in vivo binding site are (1) the site must be in a core promoter and (2) the region must be utilized as a promoter in that cell type. We have tested three models for recruitment of E2F to core promoters lacking a consensus site, including (1) indirect recruitment, (2) looping to the core promoter mediated by an E2F bound to a distal motif, and (3) assisted binding of E2F to a site that weakly resembles an E2F motif. To test these models, we developed a new in vivo assay, termed eChIP, which allows analysis of transcription factor binding to isolated fragments. Our findings suggest that in vivo (1) a consensus motif is not sufficient to recruit E2Fs, (2) E2Fs can bind to isolated regions that lack a consensus motif, and (3) binding can require regions other than the best match to the E2F motif.

Regulation of Sp1 by cell cycle related proteins

Sp1 transcription factor regulates the expression of multiple genes, including the Sp1 gene itself. We analyzed the ability of different cell cycle regulatory proteins to interact with Sp1 and to affect Sp1 promoter activity. Using an antibody array, we observed that CDK4, SKP2, Rad51, BRCA2 and p21 could interact with Sp1 and we confirmed these interactions by co-immunoprecipitation. CDK4, SKP2, Rad51, BRCA2 and p21 also activated the Sp1 promoter. Among the known Sp1-interacting proteins, E2F-DP1, Cyclin D1, Stat3 and Rb activated the Sp1 promoter, whereas p53 and NF kappaB inhibited it. The proteins that regulated Sp1 gene expression were shown by positive chromatin immunoprecipitation to be bound to the Sp1 promoter. Moreover, SKP2, BRCA2, p21, E2F-DP1, Stat3, Rb, p53 and NF kappaB had similar effects on an artificial promoter containing only Sp1 binding sites. Transient transfections of CDK4, Rad51, E2F-DP1, p21 and Stat3 increased mRNA expression from the endogenous Sp1 gene in HeLa cells whereas overexpression of NF kappaB, and p53 decreased Sp1 mRNA levels. p21 expression from a stably integrated inducible promoter in HT1080 cells activated Sp1 expression at the promoter and mRNA levels, but at the same time it decreased Sp1 protein levels due to the activation of Sp1 degradation. The observed multiple effects of cell cycle regulators on Sp1 suggest that Sp1 may be a key mediator of cell cycle associated changes in gene expression.

Interferon-inducible Ifi200-family genes in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is the prototype of complex autoimmune diseases. Studies have suggested that genetic, hormonal, and environmental factors contribute to the development of the disease. Interestingly, several recent studies involving SLE patients and mouse models of the disease have suggested a role for interferon (IFN)-stimulated genes (ISGs) in the development of SLE. One family of ISGs is the Ifi200-family, which includes mouse (Ifi202a, Ifi202b, Ifi203, Ifi204, and Ifi205) and human (IFI16, MNDA, AIM2, and IFIX) genes. The mouse genes cluster between serum amyloid P-component (Apcs) and alpha-spectrin (Spna-1) genes on chromosome 1 and the human genes cluster in syntenic region 1q23. The Ifi200-family genes encode structurally and functionally related proteins (the p200-family proteins). Increased expression of certain p200-family proteins in cells is associated with inhibition of cell proliferation, modulation of apoptosis, and cell differentiation. Our studies involving generation of B6.Nba2 congenic mice, coupled with gene expression analyses, identified the Ifi202 as a candidate lupus-susceptibility gene. Importantly, recent studies using different mouse models of SLE have suggested that increased expression of Ifi202 gene (encoding p202 protein) in immune cells contributes to lupus susceptibility. Consistent with a functional role for the p202 protein in lupus susceptibility, increased levels of IFI16 protein in human SLE patients are associated with the diseases. This review summarizes recent findings concerning the regulation and role of p200-family proteins in the development of SLE.

Disruption of mutually negative regulatory feedback loop between interferon-inducible p202 protein and the E2F family of transcription factors in lupus-prone mice

Studies have identified IFN-inducible Ifi202 gene as a lupus susceptibility gene (encoding p202 protein) in mouse models of lupus disease. However, signaling pathways that regulate the Ifi202 expression in cells remain to be elucidated. We found that steady-state levels of Ifi202 mRNA and protein were high in mouse embryonic fibroblasts (MEFs) from E2F1 knockout (E2F1(-/-)) and E2F1 and E2F2 double knockout (E2F1(-/-)E2F2(-/-)) mice than isogenic wild-type MEFs. Moreover, overexpression of E2F1 in mouse fibroblasts decreased expression of p202. Furthermore, expression of E2F1, but not E2F4, transcription factor in mouse fibroblasts repressed the activity of 202-luc-reporter in promoter-reporter assays. Interestingly, the E2F1-mediated transcriptional repression of the 202-luc-reporter was independent of p53 and pRb expression. However, the repression was dependent on the ability of E2F1 to bind DNA. We have identified a potential E2F DNA-binding site in the 5'-regulatory region of the Ifi202 gene, and mutations in this E2F DNA-binding site reduced the E2F1-mediated transcriptional repression of 202-luc-reporter. Because p202 inhibits the E2F1-mediated transcriptional activation of genes, we compared the expression of E2F1 and its target genes in splenic cells from lupus-prone B6.Nba2 congenic mice, which express increased levels of p202, with age-matched C57BL/6 mice. We found that increased expression of Ifi202 in the congenic mice was associated with inhibition of E2F1-mediated transcription and decreased expression of E2F1 and its target genes that encode proapoptotic proteins. Our observations support the idea that increased Ifi202 expression in certain strains of mice contributes to lupus susceptibility in part by inhibiting E2F1-mediated functions.

A comprehensive ChIP-chip analysis of E2F1, E2F4, and E2F6 in normal and tumor cells reveals interchangeable roles of E2F family members

Using ChIP-chip assays (employing ENCODE arrays and core promoter arrays), we examined the binding patterns of three members of the E2F family in five cell types. We determined that most E2F1, E2F4, and E2F6 binding sites are located within 2 kb of a transcription start site, in both normal and tumor cells. In fact, the majority of promoters that are active (as defined by TAF1 or POLR2A binding) in GM06990 B lymphocytes and Ntera2 carcinoma cells were also bound by an E2F. This very close relationship between E2F binding sites and binding sites for general transcription factors in both normal and tumor cells suggests that a chromatin-bound E2F may be a signpost for active transcription initiation complexes. In general, we found that several E2Fs bind to a given promoter and that there is only modest cell type specificity of the E2F family. Thus, it is difficult to assess the role of any particular E2F in transcriptional regulation, due to extreme redundancy of target promoters. However, Ntera2 carcinoma cells were exceptional in that a large set of promoters were bound by E2F6, but not by E2F1 or E2F4. It has been proposed that E2F6 contributes to gene silencing by recruiting enzymes involved in methylating histone H3. To test this hypothesis, we created Ntera2 cell lines harboring shRNAs to E2F6. We found that reduction of E2F6 only induced minimal alteration of the transcriptome of Ntera2 transcriptome. Our results support the concept of functional redundancy in the E2F family and suggest that E2F6 is not critical for histone methylation.

Proteomic analysis of the E2F1 response in p53-negative cancer cells: new aspects in the regulation of cell survival and death

E2F1 is an essential transcription factor that regulates cell-cycle progression and apoptosis. Overexpression of E2F1 sensitizes neoplastic cells to apoptosis and leads to tumor growth suppression, making it an interesting target for anticancer therapy. Use of E2F1 as a therapeutic, however, requires a detailed knowledge of the mechanisms by which it controls cellular proliferation and apoptosis, and of other potential E2F1 activities. In this study, a differential proteome analysis was performed to identify proteins associated with E2F1 activity in inducible p53-deficient Saos-2ERE2F1 osteosarcoma cells. 2-DE revealed a distinct protein profile at 32 h after E2F1 activation. Thirty-three proteins were reproducibly identified as either up-regulated or down-regulated. Proteins were identified by MALDI-MS. They included hitherto unknown E2F1 target proteins of cytoskeletal origin, chaperones, enzymes, proteasomal proteins, and several heterogeneous nuclear ribonucleoproteins, suggesting its role in the ER-stress response, protein degradation, and modulation of pre-mRNA splicing. Protein analysis-derived results were verified by Western blot using representative protein candidates. Thirteen identified proteins were the products of genes known to be cancer related. Thus, proteome analysis provides new information about the complexity of E2F1 activities in human cancer cells that may be considered when using E2F1 as a drug.

Necdin and E2F4 are modulated by rosiglitazone therapy in diabetic human adipose and muscle tissue

To identify novel pathways mediating molecular mechanisms of thiazolidinediones (TZDs) in humans, we assessed gene expression in adipose and muscle tissue from six subjects with type 2 diabetes before and after 8 weeks of treatment with rosiglitazone. mRNA was analyzed using Total Gene Expression Analysis (TOGA), an automated restriction-based cDNA display method with quantitative analysis of PCR products. The expression of cell cycle regulatory transcription factors E2F4 and the MAGE protein necdin were similarly altered in all subjects after rosiglitazone treatment. E2F4 expression was decreased by 10-fold in muscle and 2.5-fold in adipose tissue; necdin was identified in adipose tissue only and increased 1.8-fold after TZD treatment. To determine whether changes were related to an effect of the drug or adipogenesis, we evaluated the impact of rosiglitazone and differentiation independently in 3T3-L1 adipocytes. While treatment of differentiated adipocytes with rosiglitazone did not alter E2F4 or necdin, expression of both genes was significantly altered during differentiation. Differentiation was associated with increased cytosolic localization of E2F4. Moreover, necdin overexpression potently inhibited adipocyte differentiation and cell cycle progression. These data suggest that changes in necdin and E2F4 expression after rosiglitazone exposure in humans are associated with altered adipocyte differentiation and may contribute to improved insulin sensitivity in humans treated with TZDs.

JPO1/CDCA7, a novel transcription factor E2F1-induced protein, possesses intrinsic transcriptional regulator activity

JPO1/CDCA7 was originally identified as a c-Myc-responsive gene that participates in neoplastic transformation. Here, we report the identification of JPO1/CDCA7 as a direct transcriptional target of transcription factor E2F1. We demonstrated that overexpression of E2F1 by adenoviral-mediated gene transfer upregulated JPO1/CDCA7 mRNA expression in human cells. Analysis of human and mouse JPO1/CDCA7 promoter constructs showed that an E2F-responsive sequence was necessary for E2F1-induced activation of the JPO1/CDCA7 gene transcription. Among the members of the E2F family, E2F1 to E2F4, but not E2F5 or E2F6, activated the JPO1/CDCA7 reporter construct. Chromatin immunoprecipitation analysis demonstrated that E2F1, E2F2, and E2F4 specifically bound to an E2F-responsive sequence of the human JPO1/CDCA7 gene. Like JPO2/R1, which has a homologous transcriptional regulator domain, the C-terminal cysteine-rich region of JPO1/CDCA7 protein induced transcriptional activity in a mammalian one-hybrid assay. Taken together, our results suggest that JPO1/CDCA7 is a unique transcription regulator whose expression is activated by E2F1 as well as c-Myc.

EAPP, a novel E2F binding protein that modulates E2F-dependent transcription

E2F transcription factors play an essential role in cell proliferation and apoptosis and their activity is frequently deregulated in human cancers. In a yeast two-hybrid screen we identified a novel E2F-binding protein. Due to its strong phosphorylation we named it EAPP (e2F-associated phosphoprotein). EAPP is localized in the nucleus and interacts with E2F-1, E2F-2, and E2F-3, but not with E2F-4. Examination of a number of human cell lines revealed that EAPP levels are elevated in most transformed cells. Moreover, EAPP mRNA was detected in all investigated human tissues in varying amounts. EAPP is present throughout the cell cycle but disappears during mitosis. In transfection assays with reporters controlled by either an artificial E2F-dependent promoter or the murine thymidine kinase promoter, EAPP increased the activation caused by E2F-1 but not by E2F-4. Surprisingly, the promoter of the p14(ARF) gene, which was also activated by E2F-1, became repressed by EAPP. Overexpression of EAPP in U2OS cells resulted in a significant increase of cells in S-phase, whereas RNAi-mediated knock down of EAPP reduced the fraction of cells in S-phase. Taken together, these data suggest that EAPP modulates E2F-regulated transcription, stimulates proliferation, and may be involved in the malignant transformation of cells.

Onychin inhibits proliferation of vascular smooth muscle cells by regulating cell cycle

AIM

To investigate the effects of onychin on the proliferation of cultured rat artery vascular smooth muscle cells (VSMCs) in the presence of 10% new-born calf serum (NCS).

METHODS

Rat VSMCs were incubated with onychin 150 micromol/L or genistein 10 micromol/L in the presence of 10% NCS for 24 h. The proliferation of VSMCs was measured by cell counting and MTS/PMS colorimetric assays. Cell cycle progression was evaluated by flow cytometry. Retinoblastoma (Rb) phosphorylation, and expression of cyclin D1 and cyclin E were measured by Western blot assays. The tyrosine phosphorylation of ERK1/2 was examined by immunoprecipitation techniques using anti-phospho-tyrosine antibodies.

RESULTS

The proliferation of VSMCs was accelerated significantly in the presence of 10% NCS. Onychin reduced the metabolic rate of MTS and the cell number of VSMCs in the presence of 10% NCS in a dose-dependent manner. Flow cytometry analysis revealed that the G1-phase fraction ratio in the onychin group was higher than that in the 10% NCS group (85.2% vs 70.0%, P<0.01), while the S-phase fraction ratio in the onychin group was lower than that in 10% NCS group (4.3% vs 16.4%, P<0.01). Western blot analysis showed that onychin inhibited Rb phosphorylation and reduced the expression of cyclin D1 and cyclin E. The effects of onychin on proliferation, the cell cycle and the expression of cyclins in VSMCs were similar to those of genistein, an inhibitor of tyrosine kinase. Furthermore immunoprecipitation studies showed that both onychin and genistein markedly inhibited the tyrosine phosphorylation of ERK1/2 induced by 10% NCS.

CONCLUSION

Onychin inhibits the proliferation of VSMCs through G1 phase cell cycle arrest by decreasing the tyrosine phosphorylation of ERK1/2, and the expression of cyclin D1 and cyclin E, and sequentially inhibiting Rb phosphorylation.

Solution NMR structure of the C-terminal domain of the human protein DEK

The chromatin-associated protein DEK was first identified as a fusion protein in patients with a subtype of acute myelogenous leukemia. It has since become associated with diverse human ailments ranging from cancers to autoimmune diseases. Despite much research effort, the biochemical basis for these clinical connections has yet to be explained. We have identified a structural domain in the C-terminal region of DEK [DEK(309-375)]. DEK(309-375) implies clinical importance because it can reverse the characteristic abnormal DNA-mutagen sensitivity in fibroblasts from ataxia-telangiectasia (A-T) patients. We determined the solution structure of DEK(309-375) by nuclear magnetic resonance spectroscopy, and found it to be structurally homologous to the E2F/DP transcription factor family. On the basis of this homology, we tested whether DEK(309-375) could bind DNA and identified the DNA-interacting surface. DEK presents a hydrophobic surface on the side opposite the DNA-interacting surface. The structure of the C-terminal region of DEK provides insights into the protein function of DEK.

Inhibitory Effect of TIS7 on Sp1-C/EBPα Transcription Factor Module Activity

The transcription factors C/EBPalpha and Sp1 functionally interact to induce expression of specific genes during myeloid and epithelial cell differentiation. The C/EBPalpha-Sp1 transcription factor "module" binds to enhancer elements within the upstream regulatory sequences of target genes. In our previous study we identified mouse TPA inducible sequence 7 (TIS7) as a novel co-repressor in epithelial cells undergoing loss of polarity. Increased levels of TIS7 down-regulate the transcription of a specific set of genes. Using bioinformatic analysis we identified a common binding site for the C/EBPalpha-Spl transcription factor module within the upstream regulatory regions of TIS7-regulated genes. The inhibitory effect of TIS7 on C/EBPalpha-Sp1-mediated transcription was confirmed by reporter assays. Our data showed that the TIS7 effect was mediated through specific interference with Sp1 transcriptional activity. Furthermore, TIS7 prevented formation of a complex between Sp1 protein and its consensus DNA binding site. Data presented here further specify the mechanism of action of the transcriptional co-repressor TIS7 as well as document the strength of a bioinformatic approach for the prediction and analysis of transcription factor modules.

Interactions between human cytomegalovirus IE1-72 and cellular p107: functional domains and mechanisms of up-regulation of cyclin E/cdk2 kinase activity

Previous work has demonstrated that the human cytomegalovirus IE1-72 protein is able to bind to the N terminus of p107, and IE1-72 alone is sufficient for alleviation of p107-mediated cell growth suppression. However, the mechanism of this alleviation is unclear. Here, we show that IE1-72 can alleviate p107 inhibition of cyclin E/cdk2 kinase activity. We cotransfected various IE1-72 and p107 constructs into C33A cells and demonstrated that IE1-72 could activate the kinase activity of cyclin E/cdk2. Conversely, IE2-86 did not activate this activity, suggesting that the interaction between p107 and IE1-72 and the subsequent kinase activation are specific. By the use of a series of deletion and point mutants of IE1-72 and p107, we observed that a mutation of the loop region of helix-loop-helix-turn-helix in exon 3 of IE1-72 as well as a mutation of the leucine zipper-2 region in exon 4 of IE1-72 abolished binding to p107. In addition, these two IE1-72 mutants did not alleviate p107 inhibition of cyclin E/cdk2 kinase activity and also failed to alleviate p107 inhibition of the E2F-responsive promoter. Meanwhile, deletion of the N-terminal aa 1 to 175 of p107 abolished both p107 binding with IE1-72 and p107 inhibition of cyclin E/cdk2 kinase activity. This result confirms that the N-terminus aa 1 to 175 region of p107 is a common region where both IE1-72 protein and cyclin E/cdk2 bind. We propose a mechanism in which binding of IE1-72 to p107 displaces cyclin E/cdk2 from p107. Once released from p107, cyclin E/cdk2 is able to function as an active kinase.

Human papillomaviruses: targeting differentiating epithelial cells for malignant transformation

Human papillomavirus (HPV) infections play a crucial role in the pathogenesis of cervical neoplasia. Insights into the mechanisms by which HPV infection can, in a small numbers of cases, result in malignancy, comes from the observation that three proteins encoded by high-risk genital HPVs, E6, E7 and to a lesser extent E5, target factors that control the cell cycle and proliferation. These interactions result in abrogation of cell cycle control, chromosomal alterations, telomerase activation, and eventual cell immortalization. In this review, we discuss the functions of E6, E7, and E5 proteins that are most relevant to the malignant progression of HPV-transformed cells.

P27kip1 regulates the cell cycle arrest and survival of activated T lymphocytes in response to interleukin-2 withdrawal

The majority of activated T lymphocytes undergo cell death at the end of a primary immune response, while a minority survive as memory cells. The mechanisms that control the decision between these two fates are unknown. In the present study we examined the response of activated T cells to interleukin-2 (IL-2) withdrawal. Within hours, the percentage of T lymphocytes in cell cycle showed a steady decrease, while the percentage arrested in G1 increased proportionally. Deprivation of IL-2 resulted in upregulation of the cell cycle inhibitor p27kip1. Comparison with resting T-cell populations revealed that the highest expression of p27kip1 occurs in activated T cells undergoing cell cycle arrest following IL-2 withdrawal. T cells deficient in p27kip1 expression showed an impaired ability to undergo cell cycle arrest in response to IL-2 deprivation. Moreover, T cells deficient in p27kip1 showed significantly more apoptosis after IL-2 withdrawal. Collectively, this study demonstrates that p27kip1 regulates both the cell cycle arrest and the apoptosis of antigen-specific T lymphocytes.

Gene expression changes in response to E2F1 activation

The p16/RB/E2F regulatory pathway, which controls transit through the G1 restriction point of the cell cycle, is one of the most frequent targets of genetic alterations in human cancer. Any of these alterations results in the deregulated expression of the transcription factor E2F, one of the key mediators of cell cycle progression. Under these conditions, E2F1 also participates in the induction of apoptosis by a p53-dependent pathway, and independently of p53. Recently, we identified the p53-homolog p73 as a first direct target of p53-independent apoptosis. Here, we used a cDNA microarray to screen an inducible E2F1-expressing Saos-2 cell line for E2F1 target genes. Expression analysis by cDNA microarray and RT-PCR revealed novel E2F1 target genes involved in E2F1-regulated cellular functions such as cell cycle control, DNA replication and apoptosis. In addition, the identification of novel E2F1 target genes participating in the processes of angiogenesis, invasion and metastasis supports the view that E2F1 plays a central role in many aspects of cancer development. These results provide new insight into the role of E2F1 in tumorigenesis as a basis for the development of novel anti-cancer therapeutics.

Nucleocytoplasmic shuttling of p130/RBL2: novel regulatory mechanism

The retinoblastoma-related pocket proteins pRb, p107, and p130 are implicated in the control of cell proliferation, differentiation, and transformation. The function of pocket proteins is in part mediated by their ability to inhibit specific E2F transcription factors. The transcriptional activity of E2Fs is controlled by alteration of their nucleocytoplasmic localization during the cell cycle. p130 was observed to shuttle between the nucleus and cytoplasm in a heterokaryon fusion assay, suggesting the presence of nuclear and cytoplasmic localization signals. Two independent nuclear localization signals (NLS) that could target reporter proteins to the nucleus in transient transfection and microinjection experiments were identified in the C terminus of p130. In addition to the C-terminal NLS, the intact pocket domain of p130 itself was sufficient for nuclear translocation. Moreover, an additional functional NLS was mapped within the unique Loop region of p130. An N-terminal domain that conferred cytoplasmic localization was identified. Removal of the entire N terminus did not affect the ability of p130 to interact with E2F and to induce growth arrest. A model suggesting that the activity of pRb family members can be regulated by intracellular trafficking of the proteins is proposed.

The proliferative and apoptotic activities of E2F1 in the mouse retina

The E2F1 transcription factor controls cell proliferation and apoptosis. E2F1 activity is negatively regulated by the retinoblastoma (RB) protein. To study how inactivation of Rb and dysregulated E2F1 affects the developing retina, we analysed wild-type and Rb(-/-) embryonic retinas and retinal transplants and we established transgenic mice expressing human E2F1 in retinal photoreceptor cells under the regulation of the IRBP promoter (TgIRBPE2F1). A marked increase in cell proliferation and apoptosis was observed in the retinas of Rb(-/-) mice and TgIRBPE2F1 transgenic mice. In the transgenic mice, photoreceptor cells formed rosette-like arrangements at postnatal days 9 through 28. Complete loss of photoreceptors followed in the TgIRBPE2F1 mice but not in the Rb(-/-) retinal transplants. Both RB-deficient and E2F1-overexpressing photoreceptor cells expressed rhodopsin, a marker of terminal differentiation. Loss of p53 partially reduced the apoptosis and resulted in transient hyperplasia of multiple cell types in the TgIRBPE2F1 retinas at postnatal day 6. Our findings support the concept that cross-talk occurs between different retinal cell types and that multiple genetic pathways must become dysregulated for the full oncogenic transformation of neuronal retinal cells.

Cloning and characterization of a novel transcription factor involved in cellular proliferation arrest: PATF

Cell cycle withdrawal involves several transcription factors such as E2Fs members that play a key role in cell growth control. Here we describe a novel putative bZIP transcription factor isolated from the retina and involved in neuronal proliferation arrest at the terminal differentiation: PATF (Proliferation Arrest Transcription Factor). We show that PATF associates with E2F4 protein and interacts with the E2F consensus site. PATF expression increases with establishment of quiescent state. Furthermore, the nuclear PATF localization like E2F4, depends on cell growth arrest. The decrease of PATF amount, using a retroviral antisense strategy, results in pursued neuroretina cell mitosis. Our results indicate that PATF could be a new molecular signal implicated in the final neuronal cell cycle withdrawal.

Molecular cloning and characterization of a novel mouse epidermal differentiation gene and its promoter

The transcription factor E2F1 is an important regulator of cell proliferation, apoptosis, and differentiation. A novel mouse gene (Eig3) was originally identified as up-regulated in E2F1-overexpressing keratinocytes by the rapid analysis of gene expression technique. An apparently full-length cDNA and a 2.8-kb genomic fragment containing the entire gene have been cloned. Sequence comparisons suggest that Eig3 is homologous to a human epidermal differentiation gene, XP5, and belongs to a family of at least 10 murine genes that are related to the small proline-rich genes involved in skin differentiation. Eig3 was expressed in adult mouse stomach and epidermis and overexpressed in keratinocytes transgenic for E2F1 or E2F4, but not in c-myc transgenics. Interestingly, Eig3 expression was highly increased in mouse skin papillomas but not in squamous carcinomas. Since there is no E2F consensus binding sequence in the promoter or first intron of Eig3, E2F regulation may be indirect.

Mre11 complex and DNA replication: linkage to E2F and sites of DNA synthesis

We show that the Mre11 complex associates with E2F family members via the Nbs1 N terminus. This association and Nbs1 phosphorylation are correlated with S-phase checkpoint proficiency, whereas neither is sufficient individually for checkpoint activation. The Nbs1 E2F interaction occurred near the Epstein-Barr virus origin of replication as well as near a chromosomal replication origin in the c-myc promoter region and was restricted to S-phase cells. The Mre11 complex colocalized with PCNA at replication forks throughout S phase, both prior to and coincident with the appearance of nascent DNA. These data suggest that the Mre11 complex suppresses genomic instability through its influence on both the regulation and progression of DNA replication.

c-Myc is a critical target for c/EBPalpha in granulopoiesis

CCAAT/enhancer binding protein alpha (C/EBPalpha) is an integral factor in the granulocytic developmental pathway, as myeloblasts from C/EBPalpha-null mice exhibit an early block in differentiation. Since mice deficient for known C/EBPalpha target genes do not exhibit the same block in granulocyte maturation, we sought to identify additional C/EBPalpha target genes essential for myeloid cell development. To identify such genes, we used both representational difference analysis and oligonucleotide array analysis with RNA derived from a C/EBPalpha-inducible myeloid cell line. From each of these independent screens, we identified c-Myc as a C/EBPalpha negatively regulated gene. We mapped an E2F binding site in the c-Myc promoter as the cis-acting element critical for C/EBPalpha negative regulation. The identification of c-Myc as a C/EBPalpha target gene is intriguing, as it has been previously shown that down-regulation of c-Myc can induce myeloid differentiation. Here we show that stable expression of c-Myc from an exogenous promoter not responsive to C/EBPalpha-mediated down-regulation forces myeloblasts to remain in an undifferentiated state. Therefore, C/EBPalpha negative regulation of c-Myc is critical for allowing early myeloid precursors to enter a differentiation pathway. This is the first report to demonstrate that C/EBPalpha directly affects the level of c-Myc expression and, thus, the decision of myeloid blasts to enter into the granulocytic differentiation pathway.