Transcription factor E2F-1 acts as a growth-promoting factor and is associated with adverse prognosis in non-small cell lung carcinomas

MiRNA-329 targeting E2F1 inhibits cell proliferation in glioma cells

Background

MicroRNAs have recently emerged as key regulators of cancers, miR-329 located on 14q32.31 is one of down-regulated miRNAs in glioma, but the function and molecular mechanisms of miR-329 in determining the malignant phenotype of human glioma are elusive. This study therefore was conducted to investigate the role of miR-329 in biological behaviors of human glioma LN18 and T98G cell lines and its molecular mechanisms.

Methods

Nine patients with GBM were analyzed for the expression of miR-329 by quantitative RT–PCR. MiR-329 overexpression was established by transfecting miR-329 precursor into LN18 and T98G cells, and its effects on cell proliferation were studied using MTT assay, anchorage-independent growth ability assay, colony formation assays, Bromodeoxyuridine labeling and immunofluorescence.

The effects of miR-329 on cell cycle were studied by flow cytometry. The target of miR-329 was determined by luciferase assays. The regulation of miR-329 on Akt pathway was determined by western blot.

Results

The E2F1 was identified as the target of miR-329. Overexpression of miR-329 blocked G1/S transition in LN18 and T98G cell lines, dramatically suppressed cell proliferation and the ability of colony formation. MiR-329 significantly decreased the phosphorylation levels of intracellular kinases Akt and expression of cyclin D1, but the expression of p21 was upregulated, cell growth was suppressed by inhibiting E2F1-mediated Akt pathway.

Conclusions

MiR-329 may inhibit cell proliferation in human glioma cells through regulating E2F1-mediated suppression of Akt pathway.

E2F transcription factors and digestive system malignancies: How much do we know?

E2F family of transcription factors regulates various cellular functions related to cell cycle and apoptosis. Its individual members have traditionally been classified into activators and repressors, based on in vitro studies. However their contribution in human cancer is more complicated and difficult to predict. We review current knowledge on the expression of E2Fs in digestive system malignancies and its clinical implications for patient prognosis and treatment. E2F1, the most extensively studied member and the only one with prognostic value, exhibits a tumor-suppressing activity in esophageal, gastric and colorectal adenocarcinoma, and in hepatocellular carcinoma (HCC), whereas in pancreatic ductal adenocarcinoma and esophageal squamous cell carcinoma may function as a tumor-promoter. In the latter malignancies, E2F1 immunohistochemical expression has been correlated with higher tumor grade and worse patient survival, whereas in esophageal, gastric and colorectal adenocarcinomas is a marker of increased patient survival. E2F2 has only been studied in colorectal cancer, where its role is not considered significant. E2F4’s role in colorectal, gastric and hepatic carcinogenesis is tumor-promoting. E2F8 is strongly upregulated in human HCC, thus possibly contributing to hepatocarcinogenesis. Adenoviral transfer of E2F as gene therapy to sensitize pancreatic cancer cells for chemotherapeutic agents has been used in experimental studies. Other therapeutic strategies are yet to be developed, but it appears that targeted approaches using E2F-agonists or antagonists should take into account the tissue-dependent function of each E2F member. Further understanding of E2Fs’ contribution in cellular functions in vivo would help clarify their role in carcinogenesis.

Non-steroidal anti-inflammatory drugs decrease E2F1 expression and inhibit cell growth in ovarian cancer cells

Epidemiological studies have shown that the regular use of non-steroidal anti-inflammatory (NSAIDs) drugs is associated with a reduced risk of various cancers. In addition, in vitro and experiments in mouse models have demonstrated that NSAIDs decrease tumor initiation and/or progression of several cancers. However, there are limited preclinical studies investigating the effects of NSAIDs in ovarian cancer. Here, we have studied the effects of two NSAIDs, diclofenac and indomethacin, in ovarian cancer cell lines and in a xenograft mouse model. Diclofenac and indomethacin treatment decreased cell growth by inducing cell cycle arrest and apoptosis. In addition, diclofenac and indomethacin reduced tumor volume in a xenograft model of ovarian cancer. To identify possible molecular pathways mediating the effects of NSAID treatment in ovarian cancer, we performed microarray analysis of ovarian cancer cells treated with indomethacin or diclofenac. Interestingly, several of the genes found downregulated following diclofenac or indomethacin treatment are transcriptional target genes of E2F1. E2F1 was downregulated at the mRNA and protein level upon treatment with diclofenac and indomethacin, and overexpression of E2F1 rescued cells from the growth inhibitory effects of diclofenac and indomethacin. In conclusion, NSAIDs diclofenac and indomethacin exert an anti-proliferative effect in ovarian cancer in vitro and in vivo and the effects of NSAIDs may be mediated, in part, by downregulation of E2F1.

Bim, a proapoptotic protein, up-regulated via transcription factor E2F1-dependent mechanism, functions as a prosurvival molecule in cancer

Proapoptotic Bcl-2 homology 3-only protein Bim plays an important role in Bax/Bak-mediated cytochrome c release and apoptosis. Here, we provide evidence for a novel prosurvival function of Bim in cancer cells. Bim was constitutively overexpressed in multiple prostate and breast cancer cells as well as in primary tumor cells. Quantitative real time PCR analysis showed that Bim was transcriptionally up-regulated. We have identified eight endogenous E2F1-binding sites on the Bim promoter using in silico analysis. Luciferase assay demonstrated that Bim expression was E2F1-dependent as mutation of the E2F1-binding sites on the Bim promoter inhibited luciferase activities. In support, E2F1 silencing led to the loss of Bim expression in cancer cells. Bim primarily localized to mitochondrial and cytoskeleton-associated fractions. Bim silencing or microinjection of anti-Bim antibodies into the cell cytoplasm resulted in cell rounding, detachment, and subsequent apoptosis. We observed up-regulation of prosurvival proteins Bcl-xL and Mcl-1, which sequester Bim in cancer cells. In addition, a phosphorylated form of Bim was also elevated in cancer cells. These findings suggest that the constitutively overexpressed Bim may function as a prosurvival molecule in epithelial cancer cells, and phosphorylation and association with Bcl-xL/Mcl-1 block its proapoptotic functions.

Functional variants at the miRNA binding sites of the E2F1 gene and its mRNA expression

The transcription factor E2F1 is a key regulator of cell proliferation and apoptosis, and deregulated expression of E2F1 has been frequently found in a number of malignancies. Previous studies have indentified that E2F1 genetic 3' untranslated region (3'UTR) microRNA (miRNA) binding site variants are significantly associated with cancer risk; however, the roles of genetic variants in the E2F1 3'UTR in its post-transcriptional regulation have not been elucidated. Hence, using mRNA expression data from the HapMap online database, we analyzed the association between the variants at the miRNA binding sites of E2F1 and its mRNA expression. In the present study, we report the identification of 5 variants of putative miRNA binding sites in the E2F1 3'UTR by bioinformatic analysis. Among them, rs3213180 was found to be significantly associated with E2F1 expression in lymphoblastoid cell lines from the HapMap database (P=0.045); however, no significant association was demonstrated in this study for rs3213182 (P=0.345) and rs3213183 (P=0.402). This study demonstrated that rs3213180 may be a putative variant mediating the post-transcriptional regulation of the E2F1 target gene. In conclusion, 3'UTR polymorphism is significantly associated with E2F1 expression in lymphoblastoid cell lines. However, this finding requires validation in further functional analysis of the underlying mechanism involving E2F1 transcriptional activity associated with variants in the 3'UTR.

Dysregulation of FURIN by prostaglandin-endoperoxide synthase 2 in lung epithelial NCI-H292 cells

Because proprotein convertases (PCSKs) activate growth factors and matrix metalloproteinase, these enzymes have been implicated in non-small cell lung cancer tumor progression and aggressiveness. Previous studies indicate that one PCSK member, FURIN is overexpressed in NSCLC, but little is known regarding the mechanisms driving PCSKs expression during malignant change. We sought to determine whether prostaglandin-endoperoxide synthase 2 (prostaglandin G/H synthase and cyclooxygenase) (PTGS2) (aka COX2), whose expression is also frequently increased in NSCLC, differentially regulates PCSK expression and activity between normal (NHBE) and NSCLC epithelial cells (NCI-H292, NCI-H441, A549). NSCLC cells exhibit significantly greater cell-associated and secreted PCSK activity as compared with NHBE. The heightened activity is consistent with increased FURIN, PCSK4, and PCSK6 protein in the NCSLC cells. Inhibition of PTGS2 activity using NS-398 and siRNA decreased FURIN mRNA, protein, activity along with cell proliferation in NCI-H292 cells but not NHBE cells. NSCLC also expressed elevated levels of the transcription factor E2F1. When NCI-H292 cells were transfected with E2F1 siRNA, both PTGS2 expression and PCSK activity were attenuated, arguing a pivotal role for E2F1 in the differential regulation of PCSKs by PTGS2. Our results highlight a novel role for PTGS2 in NSCLC and may provide a mechanism, whereby PTGS2 inhibitors suppress lung cancer cell growth.

The E2F transcription factor 1 transactives stathmin 1 in hepatocellular carcinoma

BACKGROUND

Through data mining the Stanford Microarray Database, the stathmin 1 (STMN1) transcript was found to be frequently upregulated in the hepatocellular carcinoma (HCC) with low alpha-fetoprotein level. The molecular mechanism of STMN1 upregulation in HCCs remained unclear.

METHODS

Quantitative RT-PCR, immunoblotting, immunohistochemistry, and transfection of expression or small hairpin RNA interference plasmids, chromatin immunoprecipitation (ChIP), and quantitative ChIP assays were performed in HCC specimens or 2 distinct HCC-derived cell lines. Dual luciferase assay and site-directed mutagenesis were applied to analyze the activities of STMN1 proximal promoter region.

RESULTS

STMN1 mRNA and proteins were significantly associated with several clinicopathological features. High STMN1 or E2F1 immunoexpression was predictive of poor overall survival (OS) rate (P < .01). In HCC-derived cell lines, E2F1 was elevated before STMN1 mRNA during the cell cycle. Exogenous expression of E2F1 or both transcription factor DP-1 (TFDP1) and E2F1 genes induced E2F1 and STMN1 mRNA (P < .01). Knockdown of the E2F1 gene suppressed E2F1 and STMN1 mRNA and E2F1 and STMN1 protein levels (P < .05). The promoter activity of STMN1 gene increased with overexpression of both E2F1 and TFDP1 genes (P < .05); however, it decreased when mutations were introduced in the E2F1-binding sites (P < .05).

CONCLUSIONS

Upregulation of E2F1 and STMN1 proteins associate with worse outcomes in patients with HCC. E2F1 significantly correlates with STMN1 protein level in HCC lesions and in vitro transactivation assays, suggesting that STMN1 gene is transactivated by the E2F1 protein.

Quantitative proteomics reveals regulation of karyopherin subunit alpha-2 (KPNA2) and its potential novel cargo proteins in nonsmall cell lung cancer

The process of nucleocytoplasmic shuttling is mediated by karyopherins. Dysregulated expression of karyopherins may trigger oncogenesis through aberrant distribution of cargo proteins. Karyopherin subunit alpha-2 (KPNA2) was previously identified as a potential biomarker for nonsmall cell lung cancer by integration of the cancer cell secretome and tissue transcriptome data sets. Knockdown of KPNA2 suppressed the proliferation and migration abilities of lung cancer cells. However, the precise molecular mechanisms underlying KPNA2 activity in cancer remain to be established. In the current study, we applied gene knockdown, subcellular fractionation, and stable isotope labeling by amino acids in cell culture-based quantitative proteomic strategies to systematically analyze the KPNA2-regulating protein profiles in an adenocarcinoma cell line. Interaction network analysis revealed that several KPNA2-regulating proteins are involved in the cell cycle, DNA metabolic process, cellular component movements and cell migration. Importantly, E2F1 was identified as a potential novel cargo of KPNA2 in the nuclear proteome. The mRNA levels of potential effectors of E2F1 measured using quantitative PCR indicated that E2F1 is one of the "master molecule" responses to KPNA2 knockdown. Immunofluorescence staining and immunoprecipitation assays disclosed co-localization and association between E2F1 and KPNA2. An in vitro protein binding assay further demonstrated that E2F1 interacts directly with KPNA2. Moreover, knockdown of KPNA2 led to subcellular redistribution of E2F1 in lung cancer cells. Our results collectively demonstrate the utility of quantitative proteomic approaches and provide a fundamental platform to further explore the biological roles of KPNA2 in nonsmall cell lung cancer.

Clinical significance of E2F1 protein expression in non-small cell lung cancer

BACKGROUND

The transcription factor E2F1 has been implicated in cell cycle control and DNA damage response. Paradoxically, E2F1 can promote apoptosis and function as tumor suppressor. In non-small cell lung cancer (NSCLC), there are conflicting data for clinical significance of E2F1 expression. In this study, we investigated the protein expression of E2F1 in patients with stage I-III NSCLC, and its correlation with clinical outcome.

RESULTS

56 paired adjacent non-tumor/tumor matched samples were prospectively obtained from patients undergoing surgery for stage I-III NSCLC at Taipei Veterans General Hospital. The protein expression of E2F1 was determined by Western blot analysis. The levels of E2F1 protein were significantly higher in tumor samples than in non-tumor lung specimens (P = 0.008). Overexpression of E2F1 was defined as a more than 2-fold expression in the tumorous sample compared with the corresponding nontumorous one, and was noted in 21 patients (37.5%). There was no significant difference in overall survival (P = 0.44) or probability of freedom from recurrence (P = 0.378) between patients with E2F1 overexpression vs. non-overexpressors. Additionally, there was no significant association between E2F1 overexpression and any clinicopathologic parameter such as histological type, stage, or angiolymphatic invasion of tumor.

CONCLUSION

E2F1 protein is frequently overexpressed in NSCLC. There is no correlation between E2F1 protein expression and clinical outcome such as survival and freedom from progression.

Dynamic network of transcription and pathway crosstalk to reveal molecular mechanism of MGd-treated human lung cancer cells

Recent research has revealed various molecular markers in lung cancer. However, the organizational principles underlying their genetic regulatory networks still await investigation. Here we performed Network Component Analysis (NCA) and Pathway Crosstalk Analysis (PCA) to construct a regulatory network in human lung cancer (A549) cells which were treated with 50 uM motexafin gadolinium (MGd), a metal cation-containing chemotherapeutic drug for 4, 12, and 24 hours. We identified a set of key TFs, known target genes for these TFs, and signaling pathways involved in regulatory networks. Our work showed that putative interactions between these TFs (such as ESR1/Sp1, E2F1/Sp1, c-MYC-ESR, Smad3/c-Myc, and NFKB1/RELA), between TFs and their target genes (such as BMP41/Est1, TSC2/Myc, APE1/Sp1/p53, RARA/HOXA1, and SP1/USF2), and between signaling pathways (such as PPAR signaling pathway and Adipocytokines signaling pathway). These results will provide insights into the regulatory mechanism of MGd-treated human lung cancer cells.

E2F-1 is overexpressed and pro-apoptotic in human hepatocellular carcinoma

E2F-1 is a transcription factor involved in DNA synthesis and repair, cell proliferation, and apoptosis. Hyposphorylated pRb represses E2F-1 action in early G1 phase, while in late G1, pRb hyperphosphorylation leads to E2F-1 release and activation. In vitro studies have shown that E2F-1 may act either as oncogene or as tumor suppressor gene. We evaluated immunohistochemical expression of E2F-1 protein in chronic viral liver disease and hepatocellular carcinoma (HCC) and correlated this with clinicopathological parameters, cell proliferation, apoptosis, and the expression of E2F-1-regulators, pRb, and phospho-pRb (Ser795). In liver biopsies from 30 patients with chronic viral hepatitis, including 22 with cirrhosis without HCC, and 57 with cirrhosis with HCC, E2F-1 expression was assessed by immunohistochemistry. In chronic hepatitis and cirrhosis, hepatocytes and cholangiocytes demonstrated mild cytoplasmic and/or nuclear membrane E2F-1 immunostaining. In contrast, all HCC (100 %) showed strong nuclear E2F-1 immunostaining, with or without membrane accentuation, while a minority demonstrated additional moderate cytoplasmic immunostaining. Abnormally low pRb and phospho-pRb expression was seen in 70 % and 67.9 % of HCC, respectively. In HCC, nuclear E2F-1 expression was inversely correlated with phospho-pRb expression (p = 0.001) and positively related to tumor apoptotic index (p = 0.025). No significant correlation was found between E2F-1 expression and patient demographics, HCC etiology, tumor grade, pRb, p53 expression, or cell proliferation. In conclusion, we show that the increased expression of E2F-1 protein in human HCC is correlated with enhanced tumor cell apoptosis supporting a pro-apoptotic role of E2F-1 in human HCC.

Detection of herplex simplex virus-1 and -2 in cardiac myxomas

The etiology of sporadic cardiac myxomas remains elusive. The tendency for these lesions to recur following resection, their immunopathological characteristics, along with their histological and molecular profile, may implicate the presence of an infective agent in this type of tumor. In this study, we investigated the presence of herpes simplex virus (HSV) DNA in a cohort of cardiac myxomas in a tertiary referral centre. Twenty-nine formalin-fixed paraffin-embedded (FFPE) sporadic cardiac myxomas were obtained, 17 of which were shown to be informative. These were compared to 19 macroscopically and microscopically normal heart tissue specimens. The detection of HSV-1 and -2 genomic sequences was achieved with the use of a combined nested PCR-Restriction Fragment Length Polymorphism methodology. The presence of HSV-1 and/or -2 DNA was demonstrated in 6 of 17 (35%) informative sporadic cardiac myxomas, whereas no HSV DNA was detected in normal heart tissues (P < 0.01). The existence of HSV-1/2 DNA in sporadic cardiac myxomas, along with its absence from normal heart tissues, reinforces the possibility that HSV infection might be involved in the development of these lesions. Our findings raise the point of anti-HSV medication postsurgically with a potential benefit in reducing the rate of recurrences.

Effects of E2F1-cyclin E1-E2 circuit down regulation in hepatocellular carcinoma cells

BACKGROUND

No effective therapy is available for hepatocellular carcinoma. To identify novel therapeutic strategies, we explored the effects of the depletion of E2F1, cyclin E1-E2 whose inter-relationships in hepatocellular carcinoma cell proliferation have never been defined.

METHODS

siRNA-mediated depletion of the targets was studied in the hepatocellular carcinoma cells HepG2, HuH7 and JHH6 characterized by high, medium and low hepatocyte differentiation grade, respectively; a model of normal human hepatocytes was also considered.

RESULTS

The depletion of each target mRNA reduced the levels of the other two mRNAs, thus demonstrating a close regulatory control, also confirmed by over-expression experiments. At the protein level, an exception to this trend was observed for cyclinE1 whose amount increased upon cyclin E2 (HepG2, HuH7, JHH6) and E2F1 (HepG2) depletion. In HepG2, reduced cyclinE1 proteolysis accounted for this observation. Additionally, cyclin E1-E2-E2F1 targeting decreased the levels of cyclin A2 mRNA and of the hyper-phosphorylated form of pRb thus leading to an S-phase cell decrease; migration was impaired as well. Finally, the model of human hepatocytes used was clearly less affected by target mRNAs depletion than hepatocellular carcinoma cells.

CONCLUSION

Our data provide novel mutual relationships amongst cyclin E1-E2-E2F1 and indicate their role in sustaining hepatocellular carcinoma cell proliferation/migration, validating the concept of an anti-cyclin E1-E2-E2F1 therapeutic approach for hepatocellular carcinoma.

A tri-marker proliferation index predicts biochemical recurrence after surgery for prostate cancer

Prostate cancer exhibits tremendous variability in clinical behavior, ranging from indolent to lethal disease. Better prognostic markers are needed to stratify patients for appropriately aggressive therapy. By expression profiling, we can identify a proliferation signature variably expressed in prostate cancers. Here, we asked whether one or more tissue biomarkers might capture that information, and provide prognostic utility. We assayed three proliferation signature genes: MKI67 (Ki-67; also a classic proliferation biomarker), TOP2A (DNA topoisomerase II, alpha), and E2F1 (E2F transcription factor 1). Immunohistochemical staining was evaluable on 139 radical prostatectomy cases (in tissue microarray format), with a median clinical follow-up of eight years. Each of the three proliferation markers was by itself prognostic. Notably, combining the three markers together as a “proliferation index” (0 or 1, vs. 2 or 3 positive markers) provided superior prognostic performance (hazard ratio = 2.6 (95% CI: 1.4–4.9); P = 0.001). In a multivariate analysis that included preoperative serum prostate specific antigen (PSA) levels, Gleason grade and pathologic tumor stage, the composite proliferation index remained a significant predictor (P = 0.005). Analysis of receiver-operating characteristic (ROC) curves confirmed the improved prognostication afforded by incorporating the proliferation index (compared to the clinicopathologic data alone). Our findings highlight the potential value of a multi-gene signature-based diagnostic, and define a tri-marker proliferation index with possible utility for improved prognostication and treatment stratification in prostate cancer.

The role of epigenetics in resistance to Cisplatin chemotherapy in lung cancer

Non-small cell lung cancer (NSCLC) is the most common cause of cancer related death in the world. Cisplatin and carboplatin are the most commonly used cytotoxic chemotherapeutic agents to treat the disease. These agents, usually combined with drugs such as gemcitabine or pemetrexed, induce objective tumor responses in only 20-30% of patients. Aberrant epigenetic regulation of gene expression is a frequent event in NSCLC. In this article we review the emerging evidence that epigenetics and the cellular machinery involved with this type of regulation may be key elements in the development of cisplatin resistance in NSCLC.

Predicting and preventing melanoma invasiveness: advances in clarifying E2F1 function

Malignant melanoma of the skin is one of the most aggressive human cancers with increasing incidence, despite efforts to improve primary prevention. In particular, the prognosis of patients at late stages of the disease has not significantly improved in the last three decades, because systemic therapies have proven disappointing. Thus, metastatic melanoma continues to be a daunting clinical problem. The increasingly high rates of lethal outcome associated with advanced melanoma rely on the acquisition of invasiveness, early metastatic dissemination of tumor cells from their primary sites, and generation of chemoresistance as a consequence of alteration of key molecules involved in the regulation of cell survival. Thus far, extensive studies have been conducted to understand the molecular mechanisms that drive tumor progression, but the specific requirements underlying the aggressive behavior are still widely unknown. Understanding the determinants of this process is key to unveiling its dynamics, especially those that promote invasiveness, and may open new routes for the development of therapeutic strategies that control metastatic spread, and eventually the prevention of life-threatening metastases. Here, we review recent advances on molecular aspects, particularly of E2F1 transcription factor function, in the context of patient data, and discuss the implications for targeting melanoma cells when they begin to invade and metastasize.

Predicting malignant potential of gastrointestinal stromal tumors: Role of p16 and E2F1 expression

Altered expression of cell cycle regulatory proteins in GISTs (gastrointestinal stromal tumors) may be the mechanism for their diversity in clinical behavior. The use of these tumorigenetic and cell proliferative proteins may provide an alternative route for follow-up and treatment. The aim of this study was to determine the prognostic relevance of the E2F1 and p16 expression in GISTs. Tissues from 21 cases with GIST were collected retrospectively. Tumor grade was designated according to the consensus system. Immunohistochemistry was done with antibodies against Ki-67, p16, E2F1. For statistical analysis, Ki-67 proliferation index was evaluated in 2 categories: < or =10% and >10%, whereas p16 expression was scored as negative or positive. E2F1 expression cutoff values were tested for risk group variables as >5% and >10%. Correlation between the presence of necrosis, Ki-67 proliferation index, p16, E2F1 expression and the risk grade was determined by Spearman correlation test. Sensitivity and specificity were determined by Fisher exact test with P < or =0.05 considered as significant. High E2F1 expression (over 10%) and high Ki-67 proliferation index (over 10%) correlated significantly with increasing risk grade. There was also a significant correlation between the presence of necrosis and high-risk grade. No correlation was found between the risk grade and p16 expression. Our results suggest that in addition to high Ki-67 proliferation index, high E2F1 expression may also be a useful predictive marker for malignant potential of GISTs.

miRNA-331-3p directly targets E2F1 and induces growth arrest in human gastric cancer

Deregulation of E2F1 activity is characteristic of gastric tumorigenesis, which involves in complex molecular mechanisms. microRNA is one of the post-transcriptional regulators for gene expression. Here, we report a member of miR-331 family, miR-331-3p, which was decreased in some kinds of malignancies. However, the biological function of miR-331-3p on gastric cancer is largely unknown. In this study, we screened the expressing levels of miR-331-3p and E2F1 in gastric cancer cell lines. We transfected precursor or inhibitor of miR-331-3p into gastric cancer cells. As results, miR-331-3p is down-regulated in all gastric cancer cell lines by real-time PCR. Over-expression of miR-331-3p blocked G1/S transition on SGC-7901 and AGS cell lines. Introduction of miR-331-3p dramatically suppressed the ability of colony formation and cell growth in vitro by interfering E2F1 activity. Our data highlight an important role of miR-331-3p in cell cycle control by targeting 3'-UTR of cell cycle-related molecule E2F1. We concluded that miR-331-3p is a potential tumor suppressor in gastric cancer. Restoring miR-331-3p in gastric cancer cells revealed potential application in gastric cancer therapy.

Overexpression of the JmjC histone demethylase KDM5B in human carcinogenesis: involvement in the proliferation of cancer cells through the E2F/RB pathway

BACKGROUND

Although an increasing number of histone demethylases have been identified and biochemically characterized, their biological functions largely remain uncharacterized, particularly in the context of human diseases such as cancer. We investigated the role of KDM5B, a JmjC histone demethylase, in human carcinogenesis. Quantitative RT-PCR and microarray analyses were used to examine the expression profiles of histone demethylases in clinical tissue samples. We also examined the functional effects of KDM5B on the growth of cancer cell lines treated with small interfering RNAs (siRNAs). Downstream genes and signal cascades induced by KDM5B expression were identified from Affymetrix Gene Chip experiments, and validated by real-time PCR and reporter assays. Cell cycle-dependent characteristics of KDM5B were identified by immunofluorescence and FACS.

RESULTS

Quantitative RT-PCR analysis confirmed that expression levels of KDM5B are significantly higher in human bladder cancer tissues than in their corresponding non-neoplastic bladder tissues (P < 0.0001). The expression profile analysis of clinical tissues also revealed up-regulation of KDM5B in various kinds of malignancies. Transfection of KDM5B-specific siRNA into various bladder and lung cancer cell lines significantly suppressed the proliferation of cancer cells and increased the number of cells in sub-G1 phase. Microarray expression analysis indicated that E2F1 and E2F2 are downstream genes in the KDM5B pathway.

CONCLUSIONS

Inhibition of KDM5B may affect apoptosis and reduce growth of cancer cells. Further studies will explore the pan-cancer therapeutic potential of KDM5B inhibition.

Role of cell cycle regulators in lung carcinogenesis

Cellular division is an ordered, tightly regulated process involving multiple checkpoints that assess extracellular growth signals, cell size and DNA integrity. Progression throughout the cell cycle is based on the activation of different CDK-cyclin complexes that prevent cells from entering into a new phase until thay have successfully complete the previous one. In addition, a series of cell cycle checkpoints are designed to preserve genome integrity and chromosomal stability. Neoplastic lung cells develop the ability to bypass several of these checkpoints, and tumor cell proliferation is frequently associated with genetic or epigenetic alterations in key regulators of the cell cycle. The goal of this review is to summarize the knowledge about the dysregulation of major cell cycle regulators in lung cancer pathogenesis and to discuss the use of these proteins as targets for therapeutic intervention.

E2F1 in melanoma progression and metastasis

Metastases are responsible for cancer deaths, but the molecular alterations leading to tumor progression are unclear. Overexpression of the E2F1 transcription factor is common in high-grade tumors that are associated with poor patient survival. To investigate the association of enhanced E2F1 activity with aggressive phenotype, we performed a gene-specific silencing approach in a metastatic melanoma model. Knockdown of endogenous E2F1 via E2F1 small hairpin RNA (shRNA) expression increased E-cadherin expression of metastatic SK-Mel-147 melanoma cells and reduced their invasive potential but not their proliferative activity. Although growth rates of SK-Mel-147 and SK-Mel-103 xenograft tumors expressing E2F1 shRNA or control shRNA were similar, mice implanted with cells expressing E2F1 shRNA had a smaller area of metastases per lung than control mice (n = 3 mice per group; 5% vs 46%, difference = 41%, 95% confidence interval = 15% to 67%; P = .01; one-way analysis of variance). We identified epidermal growth factor receptor as a direct target of E2F1 and demonstrated that inhibition of receptor signaling abrogates E2F1-induced invasiveness, emphasizing the importance of the E2F1-epidermal growth factor receptor interaction as a driving force in melanoma progression that may serve as a paradigm for E2F1-induced metastasis in other human cancers.

Emerging roles of E2Fs in cancer: an exit from cell cycle control

Mutations of the retinoblastoma tumour suppressor gene (RB1) or components regulating the RB pathway have been identified in almost every human malignancy. The E2F transcription factors function in cell cycle control and are intimately regulated by RB. Studies of model organisms have revealed conserved functions for E2Fs during development, suggesting that the cancer-related proliferative roles of E2F family members represent a recent evolutionary adaptation. However, given that some human tumours have concurrent RB1 inactivation and E2F amplification and overexpression, we propose that there are alternative tumour-promoting activities for the E2F family, which are independent of cell cycle regulation.

Modulation of the E2F1-driven cancer cell fate by the DNA damage response machinery and potential novel E2F1 targets in osteosarcomas

Osteosarcoma is the most common primary bone cancer. Mutations of the RB gene represent the most frequent molecular defect in this malignancy. A major consequence of this alteration is that the activity of the key cell cycle regulator E2F1 is unleashed from the inhibitory effects of pRb. Studies in animal models and in human cancers have shown that deregulated E2F1 overexpression possesses either "oncogenic" or "oncosuppressor" properties, depending on the cellular context. To address this issue in osteosarcomas, we examined the status of E2F1 relative to cell proliferation and apoptosis in a clinical setting of human primary osteosarcomas and in E2F1-inducible osteosarcoma cell line models that are wild-type and deficient for p53. Collectively, our data demonstrated that high E2F1 levels exerted a growth-suppressing effect that relied on the integrity of the DNA damage response network. Surprisingly, induction of p73, an established E2F1 target, was also DNA damage response-dependent. Furthermore, a global proteome analysis associated with bioinformatics revealed novel E2F1-regulated genes and potential E2F1-driven signaling networks that could provide useful targets in challenging this aggressive neoplasm by innovative therapies.

SRC-induced disassembly of adherens junctions requires localized phosphorylation and degradation of the rac activator tiam1

The Rac activator Tiam1 is required for adherens junction (AJ) maintenance, and its depletion results in AJ disassembly. Conversely, the oncoprotein Src potently induces AJ disassembly and epithelial-mesenchymal transition (EMT). Here, we show that Tiam1 is phosphorylated on Y384 by Src. This occurs predominantly at AJs, is required for Src-induced AJ disassembly and cell migration, and creates a docking site on Tiam1 for Grb2. We find that Tiam1 is associated with ERK. Following recruitment of the Grb2-Sos1 complex, ERK becomes activated and triggers the localized degradation of Tiam1 at AJs, likely involving calpain proteases. Furthermore, we demonstrate that, in human tumors, Y384 phosphorylation positively correlates with Src activity, and total Tiam1 levels are inversely correlated. Thus, our data implicate Tiam1 phosphorylation and consequent degradation in Src-mediated EMT and resultant cell motility and establish a paradigm for regulating local concentrations of Rho-GEFs.

E2F1 overexpression correlates with thymidylate synthase and survivin gene expressions and tumor proliferation in non small-cell lung cancer

PURPOSE

We investigated the clinical significance of E2F1 gene expression in relation to its target genes, thymidylate synthase (TS) and Survivin, in case of non-small-cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

One hundred twenty-seven cases of resected NSCLC were analyzed. Quantitative reverse transcription-PCR was done to evaluate the gene expression of E2F1, TS, and Survivin. Immunohistochemistry was done to investigate the protein expression of E2F1, TS, and Survivin. The Ki-67 proliferation index and the apoptotic index using the terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling method were also evaluated.

RESULTS

E2F1 gene expression significantly correlated with the Ki-67 proliferation index (r = 0.487; P < 0.0001), although no correlation was observed between E2F1 gene expression and the apoptotic index. With regard to E2F1 target genes, E2F1 gene expression significantly correlated with TS gene expression (r = 0.709; P < 0.0001) and Survivin gene expression (r = 0.403; P < 0.0001). The overall survival rate was significantly lower in patients with high-E2F1 tumors than in those with low-E2F1 tumors (P = 0.0027), especially among patients with stage II to III NSCLCs (P = 0.0188). A Cox regression analysis showed that the E2F1 status was a significant prognostic factor for NSCLC patients (hazard ratio, 2.052; P = 0.0261).

CONCLUSIONS

The present study revealed that E2F1 gene expression correlates with TS and Survivin gene expressions and tumor proliferation. During the progression of NSCLC, E2F1 overexpression could produce more aggressive tumors with a high proliferation rate and chemoresistance.

p110 CUX1 cooperates with E2F transcription factors in the transcriptional activation of cell cycle-regulated genes

The transcription factor p110 CUX1 was shown to stimulate cell proliferation by accelerating entry into S phase. As p110 CUX1 can function as a transcriptional repressor or activator depending on promoter context, we investigated its mechanism of transcriptional activation using the DNA polymerase alpha gene promoter as a model system. Linker-scanning analysis revealed that a low-affinity E2F binding site is required for transcriptional activation. Moreover, coexpression with a dominant-negative mutant of DP-1 suggested that endogenous E2F factors are indeed needed for p110-mediated activation. Tandem affinity purification, coimmunoprecipitation, chromatin immunoprecipitation, and reporter assays indicated that p110 CUX1 can engage in weak protein-protein interactions with E2F1 and E2F2, stimulate their recruitment to the DNA polymerase alpha gene promoter, and cooperate with these factors in transcriptional activation. On the other hand, in vitro assays suggested that the interaction between CUX1 and E2F1 either is not direct or is regulated by posttranslational modifications. Genome-wide location analysis revealed that targets common to p110 CUX1 and E2F1 included many genes involved in cell cycle, DNA replication, and DNA repair. Comparison of the degree of enrichment for various E2F factors suggested that binding of p110 CUX1 to a promoter will favor the specific recruitment of E2F1, and to a lesser extent E2F2, over E2F3 and E2F4. Reporter assays on a subset of common targets confirmed that p110 CUX1 and E2F1 cooperate in their transcriptional activation. Overall, our results show that p110 CUX1 and E2F1 cooperate in the regulation of many cell cycle genes.

Age-specific differences in oncogenic pathway deregulation seen in human breast tumors

Purpose

To define the biology driving the aggressive nature of breast cancer arising in young women.

Experimental Design

Among 784 patients with early stage breast cancer, using prospectively-defined, age-specific cohorts (young ≤45 years; older ≥65 years), 411 eligible patients (n = 200≤45 years; n = 211≥65 years) with clinically-annotated Affymetrix microarray data were identified. GSEA, signatures of oncogenic pathway deregulation and predictors of chemotherapy sensitivity were evaluated within the two age-defined cohorts.

Results

In comparing deregulation of oncogenic pathways between age groups, a higher probability of PI3K (p = 0.006) and Myc (p = 0.03) pathway deregulation was observed in breast tumors arising in younger women. When evaluating unique patterns of pathway deregulation, a low probability of Src and E2F deregulation in tumors of younger women, concurrent with a higher probability of PI3K, Myc, and β-catenin, conferred a worse prognosis (HR = 4.15). In contrast, a higher probability of Src and E2F pathway activation in tumors of older women, with concurrent low probability of PI3K, Myc and β-catenin deregulation, was associated with poorer outcome (HR = 2.7). In multivariate analyses, genomic clusters of pathway deregulation illustrate prognostic value.

Conclusion

Results demonstrate that breast cancer arising in young women represents a distinct biologic entity characterized by unique patterns of deregulated signaling pathways that are prognostic, independent of currently available clinico-pathologic variables. These results should enable refinement of targeted treatment strategies in this clinically challenging situation.

Gene amplification is a relatively frequent event leading to ZBTB7A (Pokemon) overexpression in non-small cell lung cancer

ZBTB7A (Pokemon) is a member of the POK family of transcriptional repressors. Its main function is the suppression of the p14ARF tumour suppressor gene. Although ZBTB7A expression has been found to be increased in various types of lymphoma, there are no reports dealing with its expression in solid tumours. Given that p14(ARF) inhibits MDM2, the main negative regulator of p53, we hypothesized that overexpression of ZBTB7A could lead indirectly to p53 inactivation. To this end, we examined the status of ZBTB7A and its relationship with tumour kinetics (proliferation and apoptosis) and nodal members of the p53 network in a panel of 83 non-small cell lung carcinomas (NSCLCs). We observed, in the majority of the samples, prominent expression of ZBTB7A in the cancerous areas compared to negligible presence in the adjacent normal tissue elements. Gene amplification (two- to five-fold) was found in 27.7% of the cases, denoting its significance as a mechanism driving ZBTB7A overproduction in NSCLCs. In the remaining non-amplified group of carcinomas, analysis of the mRNA and protein expression patterns suggested that deregulation at the transcriptional and post-translational level accounts for ZBTB7A overexpression. Proliferation was associated with ZBTB7A expression (p = 0.033) but not apoptosis. The association with proliferation was reflected in the positive correlation between ZBTB7A expression and tumour size (p = 0.018). The overexpression of ZBTB7A in both p53 mutant and p53 wild-type cases, implies either a synergistic effect or that ZBTB7A exerts its oncogenic properties independently of the p14(ARF)-MDM2-p53 axis. The concomitant expression of ZBTB7A with p14(ARF) (p = 0.039), instead of the anticipated inverse relation, supports the latter notion. In conclusion, regardless of the pathway followed, the distinct expression of ZBTB7A in cancerous areas and the association with proliferation and tumour size pinpoints a role for this novel cell cycle regulator in the pathogenesis of lung cancer.

Overexpression of E2F1 in clear cell renal cell carcinoma: a potential impact of erroneous regulation by thyroid hormone nuclear receptors

We show here that the promoter of E2F1 gene, encoding one of the key regulators of cell proliferation, is overly active in the presence of low amounts of triiodothyronine (T3) and in the presence of mutant thyroid hormone receptor. We also show that T3-thyroid hormone receptor pathway of regulation of molecular processes is disturbed in clear cell renal cell carcinoma (ccRCC) on several levels, including overexpression of thyroid hormone receptors and the disturbance of their binding to DNA and to the hormone. In comparison to the cancer-free kidneys and peritumoral respective control tissues, E2F1 mRNA and protein levels are significantly increased in cancer tissues. A significant correlation between E2F1 mRNA and protein levels has been found in both control types and ccRCCs. No correlation was observed between the amount of E2F1 mRNA and the amount of thyroid hormone receptors or their DNA or T3 binding activity, suggesting that the function of thyroid hormone receptors could be markedly disturbed in both tumor and peritumoral cells. In summary, we show that ccRCC is characterized by the overexpression of E2F1, which is likely a result of a deregulated control of T3-dependent molecular processes.

Roles of CREB-binding protein (CBP)/p300 in respiratory epithelium tumorigenesis

CREB-binding protein (CBP) and its homologue p300 are transcriptional co-activators of various sequence-specific transcription factors that are involved in a wide array of cellular activities, such as DNA repair, cell growth, differentiation and apoptosis. Several studies have suggested that CBP and p300 might be considered as tumour suppressors, with their prominent role being the cross-coupling of distinct gene expression patterns in response to various stimuli. They exert their actions mainly via acetylation of histones and other regulatory proteins (e.g. p53). A major paradox in CBP/p300 function is that they seem capable of contributing to various opposed cellular processes. Respiratory epithelium tumorigenesis represents a complex process of multi-step accumulations of a gamut of genetic and epigenetic aberrations. Transcription modulation through the alternate formation of activating and repressive complexes is the ultimate converging point of these derangements, and CBP/p300 represents key participants in this interplay. Thus, illumination of their molecular actions and interactions could reveal new potential targets for pharmacological interventions in respiratory epithelium carcinogenesis.

Significance of E2F-1 overexpression in epithelial ovarian cancer

E2F-1 is a downstream regulator of the Rb pathway and is a transcription factor that plays a key role in the control of cell cycle progression. Deregulation of E2F-1 expression and Rb pathway is involved in carcinogenesis. The aim of this study was to evaluate E2F-1 expression and Rb pathway alteration and to elucidate their correlation with clinical and pathologic parameters in epithelial ovarian cancer (EOC). We investigated overexpression of E2F-1 and alterations of p16(INK4a), cyclin D1, CDK4, and pRb using immunohistochemistry and tissue microarray methods in 72 EOC patients. Overexpression of E2F-1 was detected in 45.8% of samples. The overall abnormal expression frequencies of p16(INK4a), cyclin D1, CDK4, and pRb were 33.3%, 11.1%, 12.5%, and 38.9%, respectively. E2F-1 overexpression was not associated with alteration of the Rb pathway. E2F-1 overexpression was correlated with FIGO stage, histologic grade, and mitotic index; it was a valuable prognostic variable along with FIGO stage in the multivariated analysis. The results suggest that E2F-1 has a growth-promoting effect in EOC and that E2F-1 overexpression may provide a useful prognostic indicator for EOC.

TGFbeta regulates the expression and activities of G2 checkpoint kinases in human myeloid leukemia cells

Transforming Growth Factor-beta (TGFbeta) is known to be a negative regulator of G1 cyclin/cdk activity. It is not clear whether TGFbeta has any effect on G2 checkpoint kinases. We have found that TGFbeta downregulated the expression of several G2 checkpoint kinases including cdc2, cyclin B1, and cdc25c without causing cell accumulation in G2/M phases in two human leukemia cell lines. The inhibition was time-dependent with a maximal inhibition being observed by 24h for cyclin B1 and cdc2 and by 48h for cdc25c. The inhibition was not a result of G1 arrest but a direct effect of TGFbeta which downregulates their expression at mRNA level. In proliferating cells, there was a significant formation of cdc2-pRb complexes, which was decreased to 30% of control levels by 48h after initiating TGFbeta treatment. Cdc2 showed a marked kinase activity on GST-Rb protein in proliferating cells detected by in vitro kinase assay, which was downregulated in response to TGFbeta. In addition, TGFbeta caused a rapid and transient dephosphorylation of cdc2 (Tyr15) and cdc25c (Ser216) for about 2-3h before a dramatic decrease of both molecules by 48h. Taken together, our data suggest that TGFbeta has a direct inhibitory effect on G2 checkpoint kinases, which is regulated at mRNA level. The transient activation of cdc2 and cdc25c and subsequent inhibition of cdc2, cyclin B1, and cdc25c could amplify TGFbeta-induced G1 arrest and growth inhibition.

Clinical relevance of E2F family members in ovarian cancer--an evaluation in a training set of 77 patients

PURPOSE

The major obstacle in treating ovarian cancer is the rapid development of platinum resistance during therapy. Deregulation of members of the E2F family of transcription factors is crucially involved in carcinogenesis and probably in mechanisms underlying platinum resistance. We therefore investigated the relevance of the whole set of E2F family members in predicting clinical outcome and their significance in predicting platinum resistance.

EXPERIMENTAL DESIGN

Real-time PCR of all E2F family members was done from 77 ovarian carcinomas, defined as our training set, and 8 healthy control samples. The correlation with clinicopathologic characteristics, platinum resistance, and survival was investigated. Furthermore, the cross-talk of E2F family members was assessed for its value in predicting survival and platinum resistance.

RESULTS

The proliferation-promoting E2F1 and E2F2 were associated with grade 3 tumors and residual disease >2 cm in diameter after initial surgery. Survival analyses showed low expression of E2F1 or E2F2 to be significantly associated with favorable disease-free and overall survival (E2F1, P = 0.039 and 0.047, respectively; E2F2, P = 0.009 and 0.006, respectively). In contrast, high expression of inhibiting E2F4 or E2F7 predicted favorable disease-free and overall survival (E2F4, P = 0.047 and 0.042, respectively; E2F7, P = 0.048 and 0.042, respectively). A high E2F2 to E2F4 ratio was the most valuable prognostic variable for disease-free survival in multivariate analysis (hazard ratio, 6.494; P = 0.002). Tumors considered platinum resistant were associated with lower E2F4 and E2F7 expression (P = 0.012 and 0.009, respectively) compared with platinum-sensitive tumors. Again, ratios of E2F1 or E2F2 to E2F7 were the most favorable variables in predicting platinum resistance.

CONCLUSIONS

We here show that deregulation of both proliferation-promoting and proliferation-inhibiting E2F transcription factors and their cross-talk is crucially involved in the tumor biology of ovarian cancer and influences clinical outcome. Furthermore, down-regulation of E2F7 may contribute to mechanisms underlying platinum resistance, and calculation of ratios of proliferation-promoting E2F1 to E2F7 could serve as a putative predictor of platinum resistance.

Expression of the E2F family of transcription factors and its clinical relevance in ovarian cancer

The E2F family of transcription factors plays a pivotal role in the regulation of cellular proliferation. On the basis of sequence homology and function, eight distinct members of E2F transcription factors (E2F-1 to E2F-8) have been distinguished to date. The regulation of E2F transcription factors is closely associated with the function of the retinoblastoma family of tumor suppressors (RB pathway). In the last decade various alterations of distinct components of the RB-E2F pathway were found to be associated with tumor progression. However, no data on the role of E2F family members are available in tumor biology of ovarian cancer. Here we describe an expression study of E2F transcription factors in various human ovarian cancer cell lines; its clinical relevance was examined in a training set of 77 ovarian cancer patients. Expression levels of E2F-1, E2F-2, and E2F-8 were elevated in all the ovarian cancer cell lines studied when compared with human peritoneal mesothelial cells (HPMCs). Interestingly, EGF treatment showed a time-dependent upregulation of the activating transcription factor E2F-3 and a simultaneous increase of DP-1, the heterodimeric partner of E2F-3. High expression of E2F-1, E2F-2, and E2F-8 was found to be associated with histopathologic grade 3 tumors and residual tumor over 2 cm in diameter after primary debulking surgery in ovarian cancer patients. Taken together, these data suggest that the proliferation-promoting E2F transcription factors E2F-1 and especially E2F-2 play a pivotal role in tumor biology of ovarian cancer and may be candidates for specific therapeutic targets.

Elevated E2F1 inhibits transcription of the androgen receptor in metastatic hormone-resistant prostate cancer

Activation of E2F transcription factors, through disruption of the retinoblastoma (Rb) tumor-suppressor gene, is a key event in the development of many human cancers. Previously, we showed that homozygous deletion of Rb in a prostate tissue recombination model exhibits increased E2F activity, activation of E2F-target genes, and increased susceptibility to hormonal carcinogenesis. In this study, we examined the expression of E2F1 in 667 prostate tissue cores and compared it with the expression of the androgen receptor (AR), a marker of prostate epithelial differentiation, using tissue microarray analysis. We show that E2F1 expression is low in benign and localized prostate cancer, modestly elevated in metastatic lymph nodes from hormone-naïve patients, and significantly elevated in metastatic tissues from hormone-resistant prostate cancer patients (P = 0.0006). In contrast, strong AR expression was detected in benign prostate (83%), localized prostate cancer (100%), and lymph node metastasis (80%), but decreased to 40% in metastatic hormone-resistant prostate cancer (P = 0.004). Semiquantitative reverse transcription-PCR analysis showed elevated E2F1 mRNA levels and increased levels of the E2F-target genes dihyrofolate reductase and proliferating cell nuclear antigen in metastatic hormone-independent prostate cancer cases compared with benign tissues. To identify a role of E2F1 in hormone-independent prostate cancer, we examined whether E2F1 can regulate AR expression. We show that exogenous expression of E2F1 significantly inhibited AR mRNA and AR protein levels in prostate epithelial cells. E2F1 also inhibited an AR promoter-luciferase construct that was dependent on the transactivation domain of E2F1. Furthermore, using chromatin immunoprecipitation assays, we show that E2F1 and the pocket protein family members p107 and p130 bind to the AR promoter in vivo. Taken together, these results show that elevated E2F1, through its ability to repress AR transcription, may contribute to the progression of hormone-independent prostate cancer.

Centrosome abnormalities are frequently observed in non-small-cell lung cancer and are associated with aneuploidy and cyclin E overexpression

Centrosome abnormalities are observed in human cancers and have been associated with aneuploidy, a driving force in tumour progression. However, the exact pathways that tend to cause centrosome abnormalities have not been fully elucidated in human tumours. Using a series of 68 non-small-cell lung carcinomas and an array of in vitro experiments, the relationship between centrosome abnormalities, aneuploidy, and the status of key G1 to S-phase transition cell-cycle molecules, involved in the regulation of centrosome duplication, was investigated. Centrosome amplification and structural abnormalities were common (53%), were strongly related to aneuploidy, and, surprisingly, were even seen in adjacent hyperplastic regions, suggesting the possibility that these are early lesions in lung carcinogenesis. Cyclin E and E2F1 overexpression, but not p53 mutation, was observed to correlate with centrosome abnormalities in vivo (p = 0.029 and p = 0.015, respectively). This was further strengthened by the observation that cyclin E was specifically present in the nucleus and/or cytoplasm of the cells that contained centrosome aberrations. The cytoplasmic cyclin E signal may be attributed, in part, to the presence of truncated low-molecular-weight isoforms of cyclin E. In order to isolate the effect of cyclin E on the appearance of centrosome abnormalities, a U2OS tetracycline-repressible cyclin E cell line that has a normal centrosome profile by default was used. With this system, it was confirmed in vitro that persistent cyclin E overexpression is sufficient to cause the appearance of centrosome abnormalities.

E2F1 suppresses skin carcinogenesis via the ARF-p53 pathway

The E2F1 transcription factor, which is deregulated in most human cancers by mutations in the p16-cyclin D-Rb pathway, has both oncogenic and tumor-suppressive properties. This is dramatically illustrated by the phenotype of an E2F1 transgenic mouse model that spontaneously develops tumors in the skin and other epithelial tissues but is resistant to papilloma formation when subjected to a two-stage carcinogenesis protocol. Here, this E2F1 transgenic model was used to further explore the tumor-suppressive property of E2F1. Transgenic expression of E2F1 was found to inhibit ras-driven skin carcinogenesis at the promotion stage independent of the type of promoting agent used. E2F1 transgenic epidermis displayed increased expression of p19(ARF), p53, and p21(Cip1). Inactivation of either p53 or Arf in E2F1 transgenic mice restored sensitivity to two-stage skin carcinogenesis. While Arf inactivation impaired tumor suppression and p21 induction by E2F1, it did not reduce the level of apoptosis observed in E2F1 transgenic mice. Based on these findings, we propose that E2F1 suppresses ras-driven skin carcinogenesis through a nonapoptotic mechanism involving ARF and p53.

Immunohistochemical detection of retinoblastoma protein and E2 promoter-binding factor-1 in ameloblastomas

BACKGROUND

To clarify the roles of cell cycle regulation in oncogenesis and cytodifferentiation of odontogenic tumors, expression of retinoblastoma protein (RB) and E2 promoter-binding factor-1 (E2F-1) was analyzed in ameloblastomas as well as in tooth germs.

METHODS

Tissue specimens of 10 tooth germs, 40 benign ameloblastomas, and five malignant ameloblastomas were examined immunohistochemically with the use of antibodies against RB, E2F-1, and phosphorylated RB. Ki-67 antigen immunostaining was made as a marker of cell proliferation.

RESULTS

Immunohistochemical reactivity for RB, E2F-1, phosphorylated RB, and Ki-67 was detected in the nuclei of odontogenic epithelial cells near the basement membrane in tooth germs and benign and malignant ameloblastomas. The number of cells positive for phosphorylated RB was nearly equal to or slightly less than the number of cells positive for RB or E2F-1. The number of Ki-67-positive cells was slightly more than the numbers of cell positive for RB, E2F-1, or phosphorylated RB. The levels of immunoreactivity for RB, E2F-1, phosphorylated RB, and Ki-67 were slightly higher in benign and malignant ameloblastomas than in tooth germs. Plexiform ameloblastomas showed significantly higher expression of RB than follicular ameloblastomas. Ki-67 immunoreactivity was significantly higher in ameloblastic carcinomas than in metastasizing ameloblastomas.

CONCLUSION

Similar immunoreactivity for RB, E2F-1, phosphorylated RB, and Ki-67 in tooth germs and ameloblastomas indicated cellular expression of phosphorylated RB and active-free E2F-1 in both normal and neoplastic odontogenic tissues. Expression of RB, E2F-1, and phosphorylated RB was considered to be involved in cell proliferation and differentiation of odontogenic epithelium via control of the cell cycle.

Role of cell-cycle regulators in lung cancer

Lung cancer is the leading cause of cancer death worldwide. Histologically, 80% of lung cancers are classified as non-small-cell lung cancer (NSCLC), and the remaining 20% as small-cell lung cancer (SCLC). Lung carcinoma is the result of molecular changes in the cell, resulting in the deregulation of pathways controlling normal cellular growth, differentiation, and apoptosis. This review summarizes some of the most recent findings about the role of cell-cycle proteins in lung cancer pathogenesis and progression.

Stabilization of E2F1 protein by MDM2 through the E2F1 ubiquitination pathway

Although previous studies suggested that the tumorigenicity of mouse double minute 2 (MDM2) was due to its negative regulation of p53, the p53-independent interactions may be equally as important. During recent studies utilizing MDM2 inhibitors, we noted that E2F transcription factor 1 (E2F1) was down regulated upon inhibition of MDM2, regardless of the p53 status of the cancer. The present study investigated the mechanisms responsible for the MDM2-mediated increase in E2F1 expression. MDM2 prolongs the half-life of the E2F1 protein by inhibiting its ubiquitination. MDM2 displaces SCF(SKP2), the E2F1 E3 ligase. Direct binding between MDM2 and E2F1 is necessary for the negative effects of MDM2 on E2F1 ubiquitination, and deletion of the MDM2 nuclear localization signal does not result in loss of the ability to increase the E2F1 protein level. The downregulation of E2F1 upon MDM2 inhibition was not due to either pRB or p14(Arf). In addition, E2F1 was responsible for at least part of the inhibition of cell proliferation induced by MDM2 knockdown. In conclusion, the present study provides evidence that stabilization of the E2F1 protein is likely another p53-independent component of MDM2-mediated tumorigenesis. More knowledge about the MDM2-E2F1 interaction may be helpful in developing novel anticancer therapies.

Oncogenes as novel targets for cancer therapy (part III): transcription factors

This is the third paper in a four-part serial review on potential therapeutic targeting of oncogenes. The previous parts described the involvement of oncogenes in different aspects of cancer growth and development, and considered the new technologies responsible for the advancement of oncogene identification, target validation, and drug design. Because of such advances, new specific and more efficient therapeutic agents can be developed for cancer. This part of the review continues the exploration of various oncogenes that we have grouped within seven categories: growth factors, tyrosine kinases, intermediate signaling molecules, transcription factors, cell cycle regulators, DNA damage repair genes, and genes involved in apoptosis. Part one discussed growth factors and tyrosine kinases and part two discussed intermediate signaling molecules. This portion of the review covers transcription factors and the various strategies being used to inhibit their expression or decrease their activities.

Increased E2F-1 expression via tumour cell proliferation and decreased apoptosis are correlated with adverse prognosis in patients with squamous cell carcinoma of the oesophagus

BACKGROUND

The retinoblastoma (Rb) pathway, which governs cell cycle progression, is frequently genetically altered in cancer, causing deregulated expression of the E2F-1 transcription factor, which promotes DNA synthesis and cell cycle progression. Recent studies show that E2F-1 also participates in apoptosis induction in a p53 dependent or independent manner. Despite its crucial role and paradoxical effects on cell turnover, the function of E2F-1 in human cancer is unclear.

AIMS

To evaluate E2F-1 expression using immunohistochemistry in 43 surgically resected oesophageal squamous cell carcinoma (OSCC) specimens.

METHODS

This study analysed the association of E2F-1 with tumour cell proliferation and apoptosis and the upstream regulators modulating these processes, and its impact on patient outcome. Tumour cell proliferation and apoptosis were assessed as percentage of MIB-1 positive or apoptotic cells (MIB-1 labelling index (MI) and apoptotic index (AI)), respectively.

RESULTS

Entire specimens showed abnormal expression of one or more upstream regulators of pRb/E2F-1. Although E2F-1 positivity was not associated with the expression of upstream regulators, it showed a linear and positive correlation with MI but not AI. Patients with high MI, low AI, or high E2F-1 positivity had significantly shorter recurrence free survival. By multivariate analysis, high MI and low AI were independently associated with recurrence free survival, but E2F-1 was not.

CONCLUSIONS

Increased cell proliferation and decreased apoptosis are associated with adverse prognosis in patients with OSCC. Although E2F-1 remains a controversial prognostic factor, its expression was closely associated with tumour cell proliferation and might influence clinical outcome, mainly via cell cycle progression.

Inhibitors of histone deacetylases target the Rb-E2F1 pathway for apoptosis induction through activation of proapoptotic protein Bim

Inhibitors of histone deacetylases (HDACIs) are a new generation of anticancer agents that selectively kill tumor cells. However, the molecular basis for their tumor selectivity is not well understood. We investigated the effects of HDACIs on the oncogenic Rb-E2F1 pathway, which is frequently deregulated in human cancers. Here, we report that cancer cells with elevated E2F1 activity, caused either by enforced E2F1 expression, or by E1A oncogene expression, are highly susceptible to HDACI-induced cell death. This E2F1-mediated apoptosis is neither p53- nor p73-dependent but proceeds through selective induction of proapoptotic BH3-only protein Bim. We show that Bim is a direct target of E2F1 and that HDAC inhibition promotes the recruitment of E2F1 to the Bim promoter. Moreover, silencing of Bim by specific small interfering RNA (siRNA) effectively abolishes the E2F1-mediated cell death sensitization to HDACIs. These findings suggest that the oncogenic E2F1 pathway participates in HDACIs-induced apoptosis in cancer cells and underscore the importance of Bim as a key mediator of oncogene-induced apoptosis. Our study provides an important insight into the molecular mechanism of tumor selectivity of HDACIs and predicts that, clinically, HDACIs will be more effective in tumors with high E2F1 activity.

Expression of apoptosome pathway-related transcripts in non-small cell lung cancer

PURPOSE

Tumour cells killing by cytotoxic therapies largely depends on triggering the intrinsic apoptosome-mediated caspase activation pathway but it had never been evaluated whether the expression of transcripts encoding the core components of apoptosome pathway is altered in non-small cell lung carcinoma (NSCLC).

METHODS

We investigated the expression status of several apoptosome pathway-related transcripts including Apaf-1, procaspase-9, -3, -6, -7 and Smac in tumour and lung tissue samples from 65 surgically treated NSCLC patients and in 10 NSCLC cell lines with using real time RT-PCR.

RESULTS

NSCLC tissues and cell lines showed significantly increased expression of procaspase-9, -3, -6 and Smac mRNAs as compared to the lungs and expression of these transcripts was simultaneously upregulated in a subset of NSCLCs belonging to different histopathological type, grade and stage categories. The expression of procaspase-7 mRNA in NSCLC tissues and cell lines and lungs was not significantly different. By contrast, the expression of Apaf-1 mRNA was frequently downregulated in the tumours as compared to matched lungs. Nevertheless, the examined NSCLC cell lines showed significantly higher expression of Apaf-1 mRNA than the lungs. The expression of Apaf-1, procaspase-9 and -6 mRNAs was higher in lung adenocarcinomas as compared to squamous cell lung carcinomas but the expression levels of the studied apoptosome pathway-related transcripts in the tumours were independent of tumour's grade and stage.

CONCLUSIONS

The results of the present study suggest that there is a subgroup of NSCLCs, which may be intrinsically primed for apoptosis through upregulated expression of transcripts encoding the apoptosome pathway components.

Involvement of E2F transcription factor family in cancer

The E2F family of transcription factors is a central modulator of important cellular events, including cell cycle progression, apoptosis and DNA damage response. The role of E2F family members in various human malignancies is yet unclear and may provide vital clues to the diagnosis, prognosis and therapy of cancer patients. In this review we provide a brief but concise overview of E2F function and its putative role in the most common human tumour types.

Prognostic Role of E2F1 and Members of the CDKN2A Network in Gastrointestinal Stromal Tumors

PURPOSE

The aim of the current study was to examine the prognostic relevance of the CDKN2A tumor suppressor pathway in gastrointestinal stromal tumors (GIST).

EXPERIMENTAL DESIGN

We determined the mRNA expression of p1(INK4A), p14(ARF), CDK4, RB1, MDM2, TP53, and E2F1 by quantitative reverse transcription-PCR in 38 cases of GISTs and correlated the findings with clinicopathologic factors, including mutation analysis of KIT and PDGFRA.

RESULTS

The k-means cluster analysis yielded three prognostic subgroups of GISTs with distinct mRNA expression patterns of the CDKN2A pathway. GISTs with low mRNA expression of the CDKN2A transcripts p16(INK4A) and p14(ARF) but high mRNA expression of CDK4, RB1, MDM2, TP53, and E2F1 were associated with aggressive clinical behavior and unfavorable prognosis, whereas GISTs with a low mRNA expression of CDK4, RB1, MDM2, TP53, and E2F1 were not. GISTs with a moderate to high mRNA expression of all examined genes also seemed to be associated with unfavorable prognosis. Regarding mutation analysis, we found significant differences in the KIT/PDGFRA genotype among the three clusters. Univariate analysis revealed high expression of E2F1 to be associated with mitotic count, proliferation rate, KIT mutation, and aggressive clinical behavior. These findings on mRNA level could be confirmed by immunohistochemistry.

CONCLUSION

Our findings implicate differential regulation schemes of the CDKN2A tumor suppressor pathway converging to up-regulation of E2F1 as the critical link to increased cell proliferation and adverse prognosis of GISTs.