Gene Summary

Gene:E2F5; E2F transcription factor 5
Aliases: E2F-5
Summary:The protein encoded by this gene is a member of the E2F family of transcription factors. The E2F family plays a crucial role in the control of cell cycle and action of tumor suppressor proteins and is also a target of the transforming proteins of small DNA tumor viruses. The E2F proteins contain several evolutionarily conserved domains that are present in most members of the family. These domains include a DNA binding domain, a dimerization domain which determines interaction with the differentiation regulated transcription factor proteins (DP), a transactivation domain enriched in acidic amino acids, and a tumor suppressor protein association domain which is embedded within the transactivation domain. This protein is differentially phosphorylated and is expressed in a wide variety of human tissues. It has higher identity to E2F4 than to other family members. Both this protein and E2F4 interact with tumor suppressor proteins p130 and p107, but not with pRB. Alternative splicing results in multiple variants encoding different isoforms. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:transcription factor E2F5
Source:NCBIAccessed: 15 March, 2017


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 15 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Ovarian Cancer
  • Papillomavirus Infections
  • MicroRNAs
  • E2F5 Transcription Factor
  • Transcription Factors
  • HeLa Cells
  • Cell Proliferation
  • Oligonucleotide Array Sequence Analysis
  • Biomarkers, Tumor
  • siRNA
  • RT-PCR
  • E2F4 Transcription Factor
  • Apoptosis
  • Cell Movement
  • Gene Expression Profiling
  • Polymerase Chain Reaction
  • Chromosome 8
  • ZAP-70 Protein-Tyrosine Kinase
  • Proteins
  • Cancer Gene Expression Regulation
  • E2F Transcription Factors
  • Tumor Suppressor Gene
  • Cell Cycle Proteins
  • Microarray Analysis
  • Promoter Regions
  • Down-Regulation
  • Oncogenes
  • Neoplasm Invasiveness
  • Signal Transduction
  • Western Blotting
  • Gene Knockdown Techniques
  • Transfection
  • rho GTP-Binding Proteins
  • Tumor Suppressor Proteins
  • Breast Cancer
  • Messenger RNA
  • Prostate Cancer
  • Repressor Proteins
  • DNA-Binding Proteins
Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (4)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: E2F5 (cancer-related)

Lu G, Sun Y, An S, et al.
MicroRNA-34a targets FMNL2 and E2F5 and suppresses the progression of colorectal cancer.
Exp Mol Pathol. 2015; 99(1):173-9 [PubMed] Related Publications
Colorectal cancer (CRC) is one of the most common malignancies. Increasing evidences indicate that dysregulation of miRNAs is a frequent event in CRC and contributes to the pathogenesis of CRC. In this study, we found that over-expression of miR-34a inhibited cell proliferation and invasion, induced a cell cycle arrest and triggered apoptosis, while knockdown of miR-34a showed the opposite effects. Moreover, ectopic miR-34a suppressed tumor growth and metastasis of CRC cells in vivo. FMNL2 and E2F5 were identified as direct targets of miR-34a. Reintroduction of FMNL2 or E2F5 without 3'UTR region reversed the inhibitory effects of miR-34a on cell proliferation and invasion. MiR-34a was down-regulated in CRC cells and inversely correlated with FMNL2 and E2F5 expressions. Our study suggests that miR-34a is an important tumor suppressor of CRC progression by targeting FMNL2 and E2F5, thus providing new insight into the molecular mechanisms underlying CRC progression and establishing a strong potential for the application of miR-34a as a novel therapeutic marker against CRC.

Cito L, Indovina P, Forte IM, et al.
pRb2/p130 localizes to the cytoplasm in diffuse gastric cancer.
J Cell Physiol. 2015; 230(4):802-5 [PubMed] Related Publications
pRb2/p130 is a key tumor suppressor, whose oncosuppressive activity has mainly been attributed to its ability to negatively regulate cell cycle by interacting with the E2F4 and E2F5 transcription factors. Indeed, pRb2/p130 has been found altered in various cancer types in which it functions as a valuable prognostic marker. Here, we analyzed pRb2/p130 expression in gastric cancer tissue samples of diffuse histotype, in comparison with their normal counterparts. We found a cytoplasmic localization of pRb2/p130 in cancer tissue samples, whereas, in normal counterparts, we observed the expected nuclear localization. pRb2/p130 cytoplasmic delocalization can lead to cell cycle deregulation, but considering the emerging involvement of pRb2/p130 in other key cellular processes, it could contribute to gastric tumorigenesis also through other mechanisms. Our data support the necessity of further investigations to verify the possibility of using pRb2/p130 as a biomarker or potential therapeutic target for diffuse gastric cancer.

Shike M, Doane AS, Russo L, et al.
The effects of soy supplementation on gene expression in breast cancer: a randomized placebo-controlled study.
J Natl Cancer Inst. 2014; 106(9) [PubMed] Free Access to Full Article Related Publications
BACKGROUND: There are conflicting reports on the impact of soy on breast carcinogenesis. This study examines the effects of soy supplementation on breast cancer-related genes and pathways.
METHODS: Women (n = 140) with early-stage breast cancer were randomly assigned to soy protein supplementation (n = 70) or placebo (n = 70) for 7 to 30 days, from diagnosis until surgery. Adherence was determined by plasma isoflavones: genistein and daidzein. Gene expression changes were evaluated by NanoString in pre- and posttreatment tumor tissue. Genome-wide expression analysis was performed on posttreatment tissue. Proliferation (Ki67) and apoptosis (Cas3) were assessed by immunohistochemistry.
RESULTS: Plasma isoflavones rose in the soy group (two-sided Wilcoxon rank-sum test, P < .001) and did not change in the placebo group. In paired analysis of pre- and posttreatment samples, 21 genes (out of 202) showed altered expression (two-sided Student's t-test, P < .05). Several genes including FANCC and UGT2A1 revealed different magnitude and direction of expression changes between the two groups (two-sided Student's t-test, P < .05). A high-genistein signature consisting of 126 differentially expressed genes was identified from microarray analysis of tumors. This signature was characterized by overexpression (>2-fold) of cell cycle transcripts, including those that promote cell proliferation, such as FGFR2, E2F5, BUB1, CCNB2, MYBL2, CDK1, and CDC20 (P < .01). Soy intake did not result in statistically significant changes in Ki67 or Cas3.
CONCLUSIONS: Gene expression associated with soy intake and high plasma genistein defines a signature characterized by overexpression of FGFR2 and genes that drive cell cycle and proliferation pathways. These findings raise the concerns that in a subset of women soy could adversely affect gene expression in breast cancer.

Shiozaki A, Nako Y, Ichikawa D, et al.
Role of the Na ⁺/K ⁺/2Cl⁻ cotransporter NKCC1 in cell cycle progression in human esophageal squamous cell carcinoma.
World J Gastroenterol. 2014; 20(22):6844-59 [PubMed] Free Access to Full Article Related Publications
AIM: To investigate the role of Na(+)/K(+)/2Cl(-) cotransporter 1 (NKCC1) in the regulation of genes involved in cell cycle progression and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC).
METHODS: An immunohistochemical analysis was performed on 68 primary tumor samples obtained from ESCC patients that underwent esophagectomy. NKCC1 expression in human ESCC cell lines was analyzed by Western blotting. Knockdown experiments were conducted using NKCC1 small interfering RNA, and the effects on cell cycle progression were analyzed. The gene expression profiles of cells were analyzed by microarray analysis.
RESULTS: Immunohistochemical staining showed that NKCC1 was primarily found in the cytoplasm of carcinoma cells and that its expression was related to the histological degree of differentiation of SCC. NKCC1 was highly expressed in KYSE170 cells. Depletion of NKCC1 in these cells inhibited cell proliferation via G2/M phase arrest. Microarray analysis identified 2527 genes with altered expression levels in NKCC1depleted KYSE170. Pathway analysis showed that the top-ranked canonical pathway was the G2/M DNA damage checkpoint regulation pathway, which involves MAD2L1, DTL, BLM, CDC20, BRCA1, and E2F5.
CONCLUSION: These results suggest that the expression of NKCC1 in ESCC may affect the G2/M checkpoint and may be related to the degree of histological differentiation of SCCs. We have provided a deeper understanding of the role of NKCC1 as a mediator and/or a biomarker in ESCC.

Ham S, Kim KH, Kwon TH, et al.
Luteolin induces intrinsic apoptosis via inhibition of E6/E7 oncogenes and activation of extrinsic and intrinsic signaling pathways in HPV-18-associated cells.
Oncol Rep. 2014; 31(6):2683-91 [PubMed] Related Publications
Luteolin, a flavonoid extracted from a number of plants with recognized anticancer, anti-inflammatory and anti-oxidative activities, inhibits angiogenic processes and modulates multidrug resistance. However, the efficacy and mechanisms of action of this flavonoid agent are still undergoing study. In order to elucidate whether luteolin exhibits an anticancer effect in cervical cancer cells, HeLa cells were incubated with luteolin and apoptosis was assessed by observing nuclear morphological changes, and performing Annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) staining. Cell cycle analysis, western blotting, RT-PCR and mitochondrial membrane potential measurements were also carried out. Luteolin showed a significant dose-dependent cytotoxic effect only in human papillomavirus (HPV)-positive cervical cancer cells, when compared to its effect on HPV-negative cervical cancer C33A cells. Expression levels of human papilloma virus E6 and E7 oncogenes were suppressed, those of related factors pRb and p53 were recovered and E2F5 was increased by luteolin treatment. Furthermore, luteolin enhanced the expression of death receptors and death receptor downstream factors such as Fas/FasL, DR5/TRAIL and FADD in HeLa cells, and activated caspase cascades. In particular, luteolin enhanced the activity of caspase-3 and -8 in a dose-dependent manner. Activation of caspase-3 induced caspase-8 activity and vice versa. Luteolin also induced mitochondrial membrane potential collapse and cytochrome c release, and inhibited Bcl-2 and Bcl-xL expression. In conclusion, luteolin exerts anticarcinogenic activity through inhibition of E6 and E7 expression and cross-activation of caspase-3 and -8. Taken together, these results suggest that luteolin induces inactivation of HPV-18 oncogene expression and apoptosis by activating the intrinsic and extrinsic pathways.

Subramanian M, Francis P, Bilke S, et al.
A mutant p53/let-7i-axis-regulated gene network drives cell migration, invasion and metastasis.
Oncogene. 2015; 34(9):1094-104 [PubMed] Free Access to Full Article Related Publications
Most p53 mutations in human cancers are missense mutations resulting in a full-length mutant p53 protein. Besides losing tumor suppressor activity, some hotspot p53 mutants gain oncogenic functions. This effect is mediated in part, through gene expression changes due to inhibition of p63 and p73 by mutant p53 at their target gene promoters. Here, we report that the tumor suppressor microRNA let-7i is downregulated by mutant p53 in multiple cell lines expressing endogenous mutant p53. In breast cancer patients, significantly decreased let-7i levels were associated with missense mutations in p53. Chromatin immunoprecipitation and promoter luciferase assays established let-7i as a transcriptional target of mutant p53 through p63. Introduction of let-7i to mutant p53 cells significantly inhibited migration, invasion and metastasis by repressing a network of oncogenes including E2F5, LIN28B, MYC and NRAS. Our findings demonstrate that repression of let-7i expression by mutant p53 has a key role in enhancing migration, invasion and metastasis.

Zou C, Li Y, Cao Y, et al.
Up-regulated MicroRNA-181a induces carcinogenesis in hepatitis B virus-related hepatocellular carcinoma by targeting E2F5.
BMC Cancer. 2014; 14:97 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Accumulating evidence showed that microRNAs are involved in development and progression of multiple tumors. Recent studies have found that miR-181a were dysregulated in several types of cancers, however, the function of miR-181a in hepatocellular carcinoma (HCC) remains unclear. In this study we assessed the potential association between miR-181a, HBV and HCC.
METHODS: The expression of miR-181a in HBV-expressing cells was determined by using qRT-PCR. Dual-Luciferase reporter Assay, qRT-PCR and western blot were performed to investigate the target genes of miR-181a. The effects of miR-181a on HCC proliferation were analyzed by MTS and colony formation assay. Tumor growth assay was used to analyze the effect of miR-181a on tumor formation.
RESULTS: HBV up-regulated miR-181a expression by enhancing its promoter activity. Overexpression of miR-181a in hepatoma cells promoted cell growth in vitro and tumor formation in vivo. Conversely, inhibition of miR-181a suppressed the proliferation of HBV-expressing cells. Mechanism investigation revealed that miR-181a inhibited the expression of transcription factor E2F5 by specifically targeting its mRNA 3'UTR. Moreover, E2F5 inhibition induced cell growth and rescued the suppressive effect of miR-181a inhibitor on the proliferation of SMMC-7721 cells. Interestingly, we also discovered that HBV could down-regulate E2F5 expression.
CONCLUSIONS: Those results strongly suggested that HBV down-regulated E2F5 expression, in part, by up-regulating the expression of miR-181a. Up-regulation of miR-181a by HBV in hepatoma cells may contribute to the progression of HCC possibly by targeting E2F5, suggesting miR-181a plays important role in HCC development.

Zhan L, Huang C, Meng XM, et al.
Promising roles of mammalian E2Fs in hepatocellular carcinoma.
Cell Signal. 2014; 26(5):1075-81 [PubMed] Related Publications
In mammalian cells, E2F family of transcription factors (E2Fs) traditionally modulates assorted cellular functions related to cell cycle progression, proliferation, apoptosis and differentiation. Eight members, E2F1 E2F8 have been recognized of this family so far, and the members of this family are generally divided into activator E2F (E2F1--E2F3a), repressor E2F (E2F3b--E2F5) and inhibitor E2F (E2F6--E2F8) subclasses based on their structur-e and function. Studies have showed that the mammalian E2F family members represent a recent evolutionary adaptation to malignancies besides hepatocellular carcinoma (HCC), and a growing body of evidence has validated that the individual members of the family develop a close relationship with HCC. E2F1 was identified to play overlapping roles in HCC, while E2F2--E2F8 (except E2F6 and E2F7) showed to be tumor-promoter in HCC. However, the mechanism underlying the mammalian E2Fs associated with HCC is still unknown and needs further research. The aim of this review is to sum up the collective knowledge of E2F family and the roles of each member of this family in HCC. Moreover, we will discuss some novel therapeutic target for HCC based on the complicated functions of mammalian E2Fs.

Yao YL, Wu XY, Wu JH, et al.
Effects of microRNA-106 on proliferation of gastric cancer cell through regulating p21 and E2F5.
Asian Pac J Cancer Prev. 2013; 14(5):2839-43 [PubMed] Related Publications
OBJECTIVE: To investigate the effects of miR-106b on malignant characteristics of gastric cancer cells, and explore possible mechanisms.
METHODS: Expression of miR-106b, p21 and E2F was determined by real-time PCR. Transfection with miR-106b mimics was conducted, and gastric cancer cells with miR-106b overexpression were obtained. Cells transfected with mimic mutants and those without transfection served as negative and blank controls, respectively. Flow cytometry and transwell assays were adopted to detect the effects of miR-106b overexpression on cell cycle, migration and invasion of gastric cancer cells.
RESULTS: . The expression of miR- 106b in gastric cancer cells was significantly higher than that in normal gastric mucosa cells. Furthermore, the expression level of miR-106b rose according to the degree of malignacy among the three GC cell strains (MKN- 45 > SGC-7901 > MKN-28). Overexpression of miR-106b shortened the G0/G1 phase and accelerated cell cycle progression, while reducing p21 and E2F5, without any significant effects on the capacity for migration and invasion of gastric cancer cells.
CONCLUSIONS: miR-106b may promote cell cycling of gastric cancer cells through regulation of p21 and E2F5 target gene expression.

Shiozaki A, Iitaka D, Ichikawa D, et al.
xCT, component of cysteine/glutamate transporter, as an independent prognostic factor in human esophageal squamous cell carcinoma.
J Gastroenterol. 2014; 49(5):853-63 [PubMed] Related Publications
BACKGROUND: xCT is a component of the cysteine/glutamate transporter, which plays a key role in glutathione synthesis. The objectives of the present study were to investigate the role of xCT in the regulation of genes involved in cell cycle progression and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC).
METHODS: xCT expression in human ESCC cell lines was analyzed by Western blotting and immunofluorescent staining. Knockdown experiments were conducted with xCT siRNA, and the effect on cell cycle was analyzed. The cells' gene expression profiles were analyzed by microarray analysis. An immunohistochemical analysis of 70 primary tumor samples obtained from ESCC patients that had undergone esophagectomy was performed.
RESULTS: xCT was highly expressed in TE13 and KYSE170 cells. In these cells, the knockdown of xCT using siRNA inhibited G1-S phase progression. Microarray analysis identified 1652 genes whose expression levels in TE13 cells were altered by the knockdown of xCT. Pathway analysis showed that the top-ranked canonical pathway was the G1/S checkpoint regulation pathway, which involves TP53INP1, CDKN1A, CyclinD1/cdk4, and E2F5. Immunohistochemical staining showed that xCT is mainly found in the nuclei of carcinoma cells, and that its expression is an independent prognostic factor.
CONCLUSIONS: These observations suggest that the expression of xCT in ESCC cells might affect the G1/S checkpoint and impact on the prognosis of ESCC patients. As a result, we have a deeper understanding of the role played by xCT as a mediator and/or biomarker in ESCC.

Zhao J, Wu XY, Ling XH, et al.
Analysis of genetic aberrations on chromosomal region 8q21-24 identifies E2F5 as an oncogene with copy number gain in prostate cancer.
Med Oncol. 2013; 30(1):465 [PubMed] Related Publications
The copy number gain of genes in chromosomal region 8q21-24 has been demonstrated to be associated with genesis and progression of prostate cancer (PCa). The aim of this study was to identify novel and effective molecular markers in this chromosomal region for PCa. The differentially expressed genes in PCa specimens were screened by gene microarray analysis, which was validated by RT-QPCR analysis. Then, the DNA qPCR analysis was carried out to detect the copy number changes of these differentially expressed genes. Moreover, the clinical significance of candidate markers (MYC and E2F5) in PCa were further determined. E2F5 and MYC were identified as candidate markers in PCa tissues and PCa cell lines. The DNA qPCR revealed the significant copy number gains of E2F5 and MYC in PCa tissues but not in PCa cell lines. In addition, Western blot analysis and immunohistochemical staining both found the significant higher expression of E2F5 and MYC proteins in PCa tissues than those in adjacent benign specimens (all P < 0.01). Moreover, the overexpression of E2F5 protein was significantly associated with a high Gleason score (P < 0.01), an advanced clinical stage (P = 0.01), a positive metastasis (P < 0.01) and PSA Failure (P < 0.01). The overexpression of MYC was more frequently found in PCa tissues with positive metastasis (P = 0.02) and PSA failure (P = 0.02). Interestingly, there was a close correlation in the expression level of MYC in PCa tissues with that of E2F5 (r ( s ) = 0.5, P ≤ 0.001). Our data offers the convincing evidence that the copy number gains of E2F5 and MYC may play an important role in genesis and progression of PCa. Especially, E2F5 may be a novel potential candidate marker for malignant PCa.

Kim SG, Kim AS, Jeong JH, et al.
4-hexylresorcinol stimulates the differentiation of SCC-9 cells through the suppression of E2F2, E2F3 and Sp3 expression and the promotion of Sp1 expression.
Oncol Rep. 2012; 28(2):677-81 [PubMed] Related Publications
The dormancy-inducing factors of bacteria inhibit tumor cell growth. In the present study, we evaluated the antitumor effects of the dormancy-inducing factor 4-hexylresorcinol (4-HR) using real-time cell electronic sensing (RT-CES) in SCC-9 cells (tongue squamous cell carcinoma cells). Treatment with 4-HR suppressed the growth of SCC-9 cells in a dose-dependent manner. We used a DNA microarray to identify genes that showed a significant change in expression upon 4-HR administration in SCC-9 cells. Among the differentially expressed genes, the protein expression of several cell proliferation related factors, including E2F1, E2F2, E2F3, E2F4, E2F5, E2F6, Sp1 and Sp3, were determined by western blot analyses. Treatment with 4-HR strongly suppressed E2F2 and slightly suppressed E2F3 but did not change the expression of E2F1, E2F4, E2F5 and E2F6 relative to no treatment. Furthermore, 4-HR increased Sp1 expression in a dose-dependent manner and decreased Sp3 expression. Therefore, the ratio of Sp1 to Sp3, an important driving force of epithelial cell differentiation, was drastically increased. Consistent with this observation, 4-HR increased the expression of the epithelial cell differentiation markers involucrin and keratin 10. Together, our results indicate that 4-HR induces the differentiation of SCC-9 via the modulation of the E2F-mediated signaling pathway.

Bomben R, Gobessi S, Dal Bo M, et al.
The miR-17∼92 family regulates the response to Toll-like receptor 9 triggering of CLL cells with unmutated IGHV genes.
Leukemia. 2012; 26(7):1584-93 [PubMed] Related Publications
Chronic lymphocytic leukemia (CLL) cells from clinically aggressive cases have a greater capacity to respond to external microenvironmental stimuli, including those transduced through Toll-like-receptor-9 (TLR9). Concomitant microRNA and gene expression profiling in purified CLL cells (n=17) expressing either unmutated (UM) or mutated (M) IGHV genes selected microRNAs from the miR-17∼92 family as significantly upregulated and in part responsible for modifications in the gene expression profile of UM CLL cells stimulated with the TLR9 agonist CpG. Notably, the stable and sustained upregulation of miR-17∼92 microRNAs by CpG was preceded by a transient induction of the proto-oncogene MYC. The enforced expression of miR-17, a major member from this family, reduced the expression of the tumor suppressor genes E2F5, TP53INP1, TRIM8 and ZBTB4, and protected cells from serum-free-induced apoptosis (P ≤ 0.05). Consistently, transfection with miR-17∼92 family antagomiRs reduced Bromo-deoxy-uridine incorporation in CpG-stimulated UM CLL cells. Finally, miR-17 expression levels, evaluated in 83 CLL samples, were significantly higher in UM (P=0.03) and ZAP-70(high) (P=0.02) cases. Altogether, these data reveal a role for microRNAs of the miR-17∼92 family in regulating pro-survival and growth-promoting responses of CLL cells to TLR9 triggering. Overall, targeting of this pathway may represent a novel therapeutic option for management of aggressive CLL.

Donzelli S, Fontemaggi G, Fazi F, et al.
MicroRNA-128-2 targets the transcriptional repressor E2F5 enhancing mutant p53 gain of function.
Cell Death Differ. 2012; 19(6):1038-48 [PubMed] Free Access to Full Article Related Publications
p53 mutations have profound effects on non-small-cell lung cancer (NSCLC) resistance to chemotherapeutic treatments. Mutant p53 proteins are usually expressed at high levels in tumors, where they exert oncogenic functions. Here we show that p53R175H, a hotspot p53 mutant, induces microRNA (miRNA)-128-2 expression. Mutant p53 binds to the putative promoter of miR128-2 host gene, ARPP21, determining a concomitant induction of ARPP21 mRNA and miR-128-2. miR-128-2 expression in lung cancer cells inhibits apoptosis and confers increased resistance to cisplatin, doxorubicin and 5-fluorouracyl treatments. At the molecular level, miR-128-2 post-transcriptionally targets E2F5 and leads to the abrogation of its repressive activity on p21(waf1) transcription. p21(waf1) protein localizes to the cytoplasmic compartment, where it exerts an anti-apoptotic effect by preventing pro-caspase-3 cleavage. This study emphasizes miRNA-128-2 role as a master regulator in NSCLC chemoresistance.

Hwang SJ, Suh MJ, Yoon JH, et al.
Identification of characteristic molecular signature of Müllerian inhibiting substance in human HPV-related cervical cancer cells.
Int J Oncol. 2011; 39(4):811-20 [PubMed] Related Publications
Müllerian inhibiting substance (MIS), also known as anti-Müllerian hormone (AMH), is a member of the transforming growth factor-β (TGF-β) superfamily that plays an important role in the mesenchymal-epithelial interaction, cell growth and proliferation, extracellular matrix production and tissue remodeling. Previously, we demonstrated that MIS suppressed ovarian cancer cell growth and suggested large-scale genetic elements that could be responsible for anti-neoplastic effects of MIS on ovarian cancer cells. In this study, we demonstrated the expression of MIS type II receptor (MISRII) in the human papillomavirus (HPV)-16-related cervical cancer cell lines CaSki and SiHa, and a non-HPV-related cervical cancer cell line, C33A. We also showed that MIS inhibited growth of cervical cancer cells, and induced cellular apoptosis of C33A. In addition, we identified a characteristic molecular signature of MIS in CaSki cells by using whole genome expression analysis. Of the 1,690 genes that showed significant expression changes by MIS, 21 genes were related to cell cycle; 13 genes to apoptosis; and 52 genes to the cancer pathway. On performing a search for cell cycle pathways in the KEGG pathway database, several gene expressions at the G1/S checkpoint were found. In particular, the expression of p16 and p107 increased and that of E2F2 and E2F3 decreased at an early stage, whereas the expression of E2F4 and E2F5 decreased at a later stage after MIS treatment. These data suggest that MIS produces activity against HPV16-related cervical cancers in vitro, and MIS may also be an effective targeted therapy for HPV16-related cervical cancer. Genetic data obtained here could be useful in determining the treatment strategy of MISR-expressing cervical tumors in the future.

Dar AA, Majid S, de Semir D, et al.
miRNA-205 suppresses melanoma cell proliferation and induces senescence via regulation of E2F1 protein.
J Biol Chem. 2011; 286(19):16606-14 [PubMed] Free Access to Full Article Related Publications
MicroRNAs (miRNAs) regulate gene expression by repressing translation or directing sequence-specific degradation of complementary mRNA. Here, we report that expression of miR-205 is significantly suppressed in melanoma specimens when compared with nevi and is correlated inversely with melanoma progression. miRNA target databases predicted E2F1 and E2F5 as putative targets. The expression levels of E2F1 and E2F5 were correlated inversely with that of miR-205 in melanoma cell lines. miR-205 significantly suppressed the luciferase activity of reporter plasmids containing the 3'-UTR sequences complementary to either E2F1 or E2F5. Overexpression of miR-205 in melanoma cells reduced E2F1 and E2F5 protein levels. The proliferative capacity of melanoma cells was suppressed by miR-205 and mediated by E2F-regulated AKT phosphorylation. miR-205 overexpression resulted in induction of apoptosis, as evidenced by increased cleaved caspase-3, poly-(ADP-ribose) polymerase, and cytochrome c release. Stable overexpression of miR-205 suppressed melanoma cell proliferation, colony formation, and tumor cell growth in vivo and induced a senescence phenotype accompanied by elevated expression of p16INK4A and other markers for senescence. E2F1 overexpression in miR-205-expressing cells partially reversed the effects on melanoma cell growth and senescence. These results demonstrate a novel role for miR-205 as a tumor suppressor in melanoma.

Thomsen R, Christensen DB, Rosborg S, et al.
Analysis of HP1α regulation in human breast cancer cells.
Mol Carcinog. 2011; 50(8):601-13 [PubMed] Related Publications
The three mammalian HP1 proteins, HP1α/CBX5, HP1β/CBX1, and HPγ/CBX3, are involved in chromatin packing and gene regulation. The HP1α protein is down-regulated in invasive compared to non-invasive breast cancer cells and HP1α is a suppressor of cell migration and invasion. In this report, we examined the background for HP1α protein down-regulation in invasive breast cancer cells. We identified a strict correlation between HP1α down-regulation at the protein level and the mRNA level. The HP1α mRNA down-regulation in invasive cancer cells was not caused by mRNA destabilization. Chromatin immunoprecipitation analysis of the HP1α gene showed a decrease in the histone mark for transcriptional activity H3-K36 tri-methylation and RNA polymerase II in invasive breast cancer cells which correlated with a decreased abundance of basal transcription factors at the HP1α promoter. E2F transcription factors regulate HP1α transcription and we identified that E2F5 depletion increased HP1α expression in invasive breast cancer cells. Finally, we have characterized two HP1α mRNA isoforms and both HP1α mRNA isoforms were down-regulated to a similar extend at the transcriptional level in invasive breast cancer cells. Collectively the presented results show that HP1α down-regulation in invasive breast cancer cells is primary a transcriptional effect and demonstrates a novel set of mechanisms involved in HP1α transcriptional regulation. The finding that HP1α is down-regulated primarily at the transcriptional level provides a new insight for the further elucidation of the detailed molecular mechanisms causing the HP1α down-regulation in invasive breast cancer cells.

Jiang Y, Yim SH, Xu HD, et al.
A potential oncogenic role of the commonly observed E2F5 overexpression in hepatocellular carcinoma.
World J Gastroenterol. 2011; 17(4):470-7 [PubMed] Free Access to Full Article Related Publications
AIM: To explore the expression pattern of E2F5 in primary hepatocellular carcinomas (HCCs) and elucidate the roles of E2F5 in hepatocarcinogenesis.
METHODS: E2F5 expression was analyzed in 120 primary HCCs and 29 normal liver tissues by immunohistochemistry analysis. E2F5-small interfering RNA was transfected into HepG2, an E2F5-overexpressed HCC cell line. After E2F5 knockdown, cell growth capacity and migrating potential were examined.
RESULTS: E2F5 was significantly overexpressed in primary HCCs compared with normal liver tissues (P = 0.008). The E2F5-silenced cells showed significantly reduced proliferation (P = 0.004). On the colony formation and soft agar assays, the number of colonies was significantly reduced in E2F5-silenced cells (P = 0.004 and P = 0.009, respectively). E2F5 knockdown resulted in the accumulation of G0/G1 phase cells and a reduction of S phase cells. The number of migrating/invading cells was also reduced after E2F5 knockdown (P = 0.021).
CONCLUSION: To our knowledge, this is the first evidence that E2F5 is commonly overexpressed in primary HCC and that E2F5 knockdown significantly repressed the growth of HCC cells.

Fokas E, You A, Juricko J, et al.
Genetic alterations after carbon ion irradiation in human lung adenocarcinoma cells.
Int J Oncol. 2011; 38(1):161-8 [PubMed] Related Publications
The aim of this study was to investigate the difference in gene expression profiles of human lung adenocarcinoma cells and identify genes whose expression is altered by heavy ions but not X-rays. The lung adenocarcinoma cell line A549 was irradiated with carbon ion beams and X-rays using biologically equivalent doses (2 Gy and 6 Gy, respectively). The transcriptional profiling was determined with a high density cDNA microarray containing 11.800 genes, and genetic network and gene ontology analysis was performed. The changes in selected genes involved were validated by quantitative real-time polymerase chain reaction (qRT-PCR). The microarray analysis identified 49 mapped, network-eligible genes, the expression level of which was altered by carbon ions but not by X-rays. From these, 29 were upregulated while 20 genes were downregulated 4 h post-irradiation with carbon ions in A549 cells, as compared to the control. Among these, three genes (CCND2, RARG and E2F5) were involved in the aryl hydrocarbon receptor signalling and G1/S cell cycle checkpoint pathways. The microarray data were corroborated by qRT-PCR analysis of the selected genes (p<0.05). Our findings provide information on the genetic signature of carbon ions in human lung adenocarcinoma cells and add to the understanding of the complicated molecular response to carbon ion irradiation.

Teissier S, Pang CL, Thierry F
The E2F5 repressor is an activator of E6/E7 transcription and of the S-phase entry in HPV18-associated cells.
Oncogene. 2010; 29(36):5061-70 [PubMed] Related Publications
High-risk papillomavirus type 18 (HPV18) is one of the less represented HPV types in low-grade lesions of the anogenital tract, whereas it occupies the second place in cervical cancer, where it can be found in 16% of the cases worldwide, after HPV16 present in 54% of them. These epidemiological data indicate that HPV18 infection is more prone to carcinogenic progression. The main oncogenic proteins, E6 and E7 of HPV18, are functionally comparable to the homologous proteins of the other high-risk viruses, including HPV16. In this work, we investigated the possibility that the higher oncogenic potential of HPV18 might be due to transcriptional regulation of the E6/E7 oncogenes. By comparing the E6/E7 promoter and enhancer sequences of the mucosal HPV genomes, we identified E2F binding sites specific for HPV18. The E2F family of transcription factors contains activators (E2F1-3) and repressors (E2F4-8) that regulate the transcription of S-phase and mitotic genes and thereby have a crucial role in cell-cycle progression. Surprisingly, we identified E2F5 as a direct activator of HPV18 E6/E7 transcription by sequential silencing of E2F members in HeLa cells. In addition, we could show that E2F5 positively regulates S-phase entry in HeLa cells and that this activation of the cell cycle by a member of the E2F repressor family is specific for HPV18-expressing cells. Diverting the function of E2F5 from a cell-cycle repressor into an activator might contribute to the higher oncogenic potential of HPV18 when compared with other high-risk HPV types.

Kothandaraman N, Bajic VB, Brendan PN, et al.
E2F5 status significantly improves malignancy diagnosis of epithelial ovarian cancer.
BMC Cancer. 2010; 10:64 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Ovarian epithelial cancer (OEC) usually presents in the later stages of the disease. Factors, especially those associated with cell-cycle genes, affecting the genesis and tumour progression for ovarian cancer are largely unknown. We hypothesized that over-expressed transcription factors (TFs), as well as those that are driving the expression of the OEC over-expressed genes, could be the key for OEC genesis and potentially useful tissue and serum markers for malignancy associated with OEC.
METHODS: Using a combination of computational (selection of candidate TF markers and malignancy prediction) and experimental approaches (tissue microarray and western blotting on patient samples) we identified and evaluated E2F5 transcription factor involved in cell proliferation, as a promising candidate regulatory target in early stage disease. Our hypothesis was supported by our tissue array experiments that showed E2F5 expression only in OEC samples but not in normal and benign tissues, and by significantly positively biased expression in serum samples done using western blotting studies.
RESULTS: Analysis of clinical cases shows that of the E2F5 status is characteristic for a different population group than one covered by CA125, a conventional OEC biomarker. E2F5 used in different combinations with CA125 for distinguishing malignant cyst from benign cyst shows that the presence of CA125 or E2F5 increases sensitivity of OEC detection to 97.9% (an increase from 87.5% if only CA125 is used) and, more importantly, the presence of both CA125 and E2F5 increases specificity of OEC to 72.5% (an increase from 55% if only CA125 is used). This significantly improved accuracy suggests possibility of an improved diagnostics of OEC. Furthermore, detection of malignancy status in 86 cases (38 benign, 48 early and late OEC) shows that the use of E2F5 status in combination with other clinical characteristics allows for an improved detection of malignant cases with sensitivity, specificity, F-measure and accuracy of 97.92%, 97.37%, 97.92% and 97.67%, respectively.
CONCLUSIONS: Overall, our findings, in addition to opening a realistic possibility for improved OEC diagnosis, provide an indirect evidence that a cell-cycle regulatory protein E2F5 might play a significant role in OEC pathogenesis.

Dominguez-Brauer C, Brauer PM, Chen YJ, et al.
Tumor suppression by ARF: gatekeeper and caretaker.
Cell Cycle. 2010; 9(1):86-9 [PubMed] Related Publications
ARF is a vital tumor suppressor and its loss contributes significantly to cancer. The frequency in which ARF is mutated, deleted or silenced is second to the loss of p53. The most documented and widely accepted activity of ARF is mediated through its activation of the p53 transcriptional program by inhibiting MDM2 function. However, several lines of evidence have surfaced demonstrating that ARF possesses p53-independent functions. One of these p53-independent functions is ARF's regulation of the E2F family. The E2F/DP transcription factor is critical for cell cycle progression. The balance between activator and repressor E2Fs regulates the expression of E2F target genes and thus cell proliferation as well as other cellular functions such as checkpoint, chromosome assembly and repair. Through its ability to bind directly to DP1, ARF can cause dissociation of both activator and repressor E2Fs. While the regulation of the activator E2Fs is related to cell cycle arrest, there is evidence that the regulation of the repressors, E2F4 and E2F5, is significant in maintaining genomic stability.

Rückert F, Joensson P, Saeger HD, et al.
Functional analysis of LOXL2 in pancreatic carcinoma.
Int J Colorectal Dis. 2010; 25(3):303-11 [PubMed] Related Publications
OBJECTIVES: Lysyl oxidase-like 2 (LOXL2) plays a part in epithelial-mesenchymal transition (EMT) by stabilizing the transcription factor SNAI1. Previous studies showed that LOXL2 is one of the most highly and specifically upregulated genes in pancreatic cancer. LOXL2 was also found to be strongly upregulated in the secretome of established pancreatic cancer cell lines. To get more insight into the aggressive growth and infiltrating nature of pancreatic cancer, we evaluated the functional role of LOXL2 in pancreatic cancer cells.
METHODS: Gene inhibition by small interfering RNAs was used to silence LOXL2 in pancreatic cancer cell lines MiaPaCa-2 and Panc1. Cell death, proliferation, and morphology of transfected cells were determined. Cell characteristics under cell stress and gemcitabine treatment were analyzed. Gene expression analysis of transfected cells by DNA microarray was used to understand the processes of chemosensitization.
RESULTS: Silencing of LOXL2 in pancreatic cancer cells resulted in an augmented sensitivity toward gemcitabine treatment, with significantly elevated cell death and reduced viable cells. However, transfection had no direct effect on morphology or growth pattern of Mia PaCa-2 and Panc1 cell lines. Gene expression analysis identified among others the transcription factor E2F5 as possible target of LOXL2.
CONCLUSIONS: Gene inhibition of the EMT regulatory gene LOXL2 resulted in a distinct sensitization toward gemcitabine. Additionally, gene expression analysis showed a role for LOXL2 in the regulation of different transcription factors associated with invasion and metastasis. Our results suggest that the improved response toward chemotherapy in LOLX2-silenced pancreatic cancer cells is possibly mediated by the transcription factor E2F5.

Umemura S, Shirane M, Takekoshi S, et al.
Overexpression of E2F-5 correlates with a pathological basal phenotype and a worse clinical outcome.
Br J Cancer. 2009; 100(5):764-71 [PubMed] Free Access to Full Article Related Publications
The purpose of the present study is to identify genes that contribute to cell proliferation or differentiation of breast cancers independent of signalling through the oestrogen receptor (ER) or human epidermal growth factor receptor 2 (HER2). An oligonucleotide microarray assayed 40 tumour samples from ER(+)/HER2(-), ER(+)/HER2(+), ER(-)/HER2(+), and ER(-)/HER2(-) breast cancer tissues. Quantitative reverse transcriptase PCR detected overexpression of a cell cycle-related transcription factor, E2F-5, in ER-negative breast cancers, and fluorescence in situ hybridisation detected gene amplification of E2F-5 in 5 out of 57 (8.8%) breast cancer samples. No point mutations were found in the DNA-binding or DNA-dimerisation domain of E2F-5. Immunohistochemically, E2F-5-positive cancers correlated with a higher Ki-67 labelling index (59.5%, P=0.001) and higher histological grades (P=0.049). E2F-5-positive cancers were found more frequently in ER(-)/progesterone receptor (PgR)(-)/HER2(-) cancer samples (51.9%, P=0.0049) and in breast cancer samples exhibiting a basal phenotype (56.0%, P=0.0012). Disease-free survival in node-negative patients with E2F-5-positive cancers was shorter than for patients with E2F-5-negative cancers. In conclusion, we identify, for the first time, a population of breast cancer cells that overexpress the cell cycle-related transcription factor, E2F-5. This E2F-5-positive breast cancer subtype was associated with an ER(-)/PgR(-)/HER2(-) status, a basal phenotype, and a worse clinical outcome.

Gandellini P, Folini M, Longoni N, et al.
miR-205 Exerts tumor-suppressive functions in human prostate through down-regulation of protein kinase Cepsilon.
Cancer Res. 2009; 69(6):2287-95 [PubMed] Related Publications
Limited information is available concerning the expression and role of microRNAs in prostate cancer. In this study, we investigated the involvement of miR-205 in prostate carcinogenesis. Significantly lower miR-205 expression levels were found in cancer than in normal prostate cell lines as well as in tumor compared with matched normal prostate tissues, with a particularly pronounced reduction in carcinomas from patients with local-regionally disseminated disease. Restoring the expression of miR-205 in prostate cancer cells resulted in cell rearrangements consistent with a mesenchymal-to-epithelial transition, such as up-regulation of E-cadherin and reduction of cell locomotion and invasion, and in the down-regulation of several oncogenes known to be involved in disease progression (i.e., interleukin 6, caveolin-1, EZH2). Our evidence suggests that these events are driven by the concurrent repression of specific predicted miR-205 targets, namely N-chimaerin, ErbB3, E2F1, E2F5, ZEB2, and protein kinase Cepsilon. Strikingly, the latter seemed to play a direct role in regulating epithelial-to-mesenchymal transition. In fact, its down-regulation led to a cell phenotype largely reminiscent of that of cells ectopically expressing miR-205. Overall, we showed for the first time that miR-205 exerts a tumor-suppressive effect in human prostate by counteracting epithelial-to-mesenchymal transition and reducing cell migration/invasion, at least in part through the down-regulation of protein kinase Cepsilon.

Arvanitis DA, Spandidos DA
Deregulation of the G1/S phase transition in cancer and squamous intraepithelial lesions of the uterine cervix: a case control study.
Oncol Rep. 2008; 20(4):751-60 [PubMed] Related Publications
High-risk types of HPV express the oncoproteins, E6 and E7, that can inactivate TP53 and RB1, respectively, and thus take control of both cell cycle and apoptosis. Herein, the mRNA expression profiles of 24 G1/S checkpoint genes were analysed in cancer and squamous intraepithelial lesions (SIL) of the uterine cervix. In total 35 squamous cervical carcinomas, 26 high-grade SIL (HSIL), 33 low-grade SIL (LSIL) tissues, and 28 normal uterine cervix specimens as controls were assessed by RT-PCR. Five genes were found to be upregulated only in tumours, RBL2, E2F2, CDK6, CCNE1 and MYC; eight in tumours and HSILs, E2F1, E2F3, E2F5, CCND1, CDK2, CDKN1B, PCNA and POLA, and five in tumours, HSILs and LSILs, TP53, E2F4, CDKN1A, CDKN2A and DHFR. MDM2 was found to be upregulated in SIL, while RBL1 was found to be downregulated in all three groups of cases. TP73 exhibited lower levels in carcinomas; however, its exon 13-containing isoforms were increased and exon 2-containing isoforms were reduced in both cancer and HSIL. Three genes, RB1, CDK4 and CDKN2D, did not exhibit any significant alteration in gene expression. Hierarchical clustering revealed that this set of G1/S checkpoint genes was able to discriminate the total 122 samples into groups of disease and non-disease with only 8 exceptions (6.6%). Our data suggest that deregulation of G1/S phase transition in cervical carcinogenesis is a progressive process. Certain clusters of genes are activated very early in pre-cancerous SILs while others are activated later, during malignant transformation. The ability of this array of markers to identify disease status suggests that it could be used for diagnostic purposes.

Lassmann S, Weis R, Makowiec F, et al.
Array CGH identifies distinct DNA copy number profiles of oncogenes and tumor suppressor genes in chromosomal- and microsatellite-unstable sporadic colorectal carcinomas.
J Mol Med (Berl). 2007; 85(3):293-304 [PubMed] Related Publications
DNA copy number changes represent molecular fingerprints of solid tumors and are as such relevant for better understanding of tumor development and progression. In this study, we applied genome-wide array comparative genomic hybridization (aCGH) to identify gene-specific DNA copy number changes in chromosomal (CIN)- and microsatellite (MIN)-unstable sporadic colorectal cancers (sCRC). Genomic DNA was extracted from microdissected, matching normal colorectal epithelium and invasive tumor cells of formalin-fixed and paraffin-embedded tissues of 22 cases with colorectal cancer (CIN = 11, MIN = 11). DNA copy number changes were determined by aCGH for 287 target sequences in tumor cell DNAs, using pooled normal DNAs as reference. aCGH data of tumor cell DNAs was confirmed by fluorescence in situ hybridization (FISH) for three genes on serial tissues as those used for aCGH. aCGH revealed DNA copy number changes previously described by metaphase CGH (gains 7, 8q, 13q, and 20q; losses 8p, 15q, 18q, and 17p). However, chromosomal regions 20q, 13q, 7, and 17p were preferentially altered in CIN-type tumors and included DNA amplifications of eight genes on chromosome 20q (TOP1, AIB1, MYBL2, CAS, PTPN1, STK15, ZNF217, and CYP24), two genes on chromosome 13q (BRCA2 and D13S25), and three genes on chromosome 7 (IL6, CYLN2, and MET) as well as DNA deletions of two genes on chromosome 17p (HIC1 and LLGL1). Finally, additional CIN-tumor-associated DNA amplifications were identified for EXT1 (8q24.11) and MYC (8q24.12) as well as DNA deletions for MAP2K5 (15q23) and LAMA3 (18q11.2). In contrast, distinct MIN-tumor-associated DNA amplifications were detected for E2F5 (8p22-q21.3), GARP (11q13.5-q14), ATM (11q22.3), KAL (Xp22.3), and XIST (Xq13.2) as well as DNA deletions for RAF1 (3p25), DCC (18q21.3), and KEN (21q tel). aCGH revealed distinct DNA copy number changes of oncogenes and tumor suppressor genes in CIN- and MIN-type sporadic colorectal carcinomas. The identified candidate genes are likely to have distinct functional roles in the carcinogenesis and progression of CIN- and MIN-type sporadic CRCs and may be involved in the differential response of CIN- and MIN-type tumor cells to (adjuvant) therapy, such as 5-fluorouracil.

Valladares A, Hernández NG, Gómez FS, et al.
Genetic expression profiles and chromosomal alterations in sporadic breast cancer in Mexican women.
Cancer Genet Cytogenet. 2006; 170(2):147-51 [PubMed] Related Publications
Breast cancer is the second-leading cause of death among Mexican women >35 years of age. At the molecular level, changes in many genetic pathways have been reported to be associated with this neoplasm. To analyze these changes, we determined gene expression profiles and chromosomal structural alterations in tumors from Mexican women. We obtained mRNA to identify expression profiles with microarray technology, and DNA to determine amplifications and deletions, in 10 fresh sporadic breast tumor biopsies without treatment, as well as in 10 nonaffected breast tissues. Expression profiles were compared with genetic changes observed by comparative genomic hybridization (CGH). We compared the expression profiles against the structural alterations from the studied genes by means of microarrays; at least 17 of these genes correlated with DNA copy number alterations. We found that the following genes were overexpressed: LAMC1, PCTK3, CCNC, CCND1, FGF3, PCTK2, L1CAM, BGN, and PLXNB3 (alias PLEXR). Underexpressed genes included CASP9, FGR, TP73, HSPG2, and ERCC1; genes turned off included FRAP1, EPHA2 (previously ECK), IL12A, E2F5, TNFRSF10B, TNFRSF10A, EFNB3, and BCL2. The results will allow us, in the near future, to outline genes that could serve as diagnostic, prognostic, or target therapy markers for the Mexican population.

Reimer D, Sadr S, Wiedemair A, et al.
Heterogeneous cross-talk of E2F family members is crucially involved in growth modulatory effects of interferon-gamma and EGF.
Cancer Biol Ther. 2006; 5(7):771-6 [PubMed] Related Publications
There is growing evidence that deregulation of E2F transcription factors is causatively involved in the patho-physiology of various tumors. However, no data on the role of E2F family members in tumor biology of ovarian cancer are available. We here describe an expression study of all known E2F transcription factors and their coactivators DP-1 and DP-2 in various human ovarian cancer cell lines and the breast cancer cell line T47D and their involvement in pathways affected by interferon-gamma and EGF. A significant overexpression of the proliferation-promoting E2F1 and especially E2F2 points to a pivotal role in modulating the uncontrolled proliferation in ovarian cancer cells. Of special note is the fact that interferon-gamma treatment did not only caused a reduction of the proliferation-promoting transcription factors E2F1 and E2F2, but also increased the inhibiting transcription factors E2F4 and E2F5, thus underlining the importance of an E2F cross-talk in the anti-proliferative function of interferon-gamma. Moreover, an increase in DP-1 and E2F3 is probably involved in the proliferation-enhancing effect of EGF. Our study provides a new insight in the crucial role of E2F cross-talk, especially the role of the inhibiting transcription factors E2F4 and E2F5, in the tumor biology of cancer and its possible usefulness as targets in anti-cancer therapy.

Lu Z, Luo RZ, Peng H, et al.
Transcriptional and posttranscriptional down-regulation of the imprinted tumor suppressor gene ARHI (DRAS3) in ovarian cancer.
Clin Cancer Res. 2006; 12(8):2404-13 [PubMed] Related Publications
PURPOSE: ARHI expression is lost or markedly down-regulated in the majority of ovarian cancers. The mechanism by which ARHI is down-regulated in ovarian cancers is still not clear. Our previous reports indicated that ARHI promoter activity was reduced in ovarian cancer cells, due in part to the effects of negative regulatory transcription factor(s).
EXPERIMENTAL DESIGN AND RESULTS: We now show that E2F1 and E2F4, but not E2F2, E2F3, or E2F5, bind to the ARHI promoter and repress its activity in ovarian cancer cells. Consistent with this observation, immunochemical staining of cell lines and of 364 samples of ovarian cancer tissue show that the expression of E2F1 and E2F4 proteins is much higher in ovarian cancer cells than in normal ovarian epithelial cells, and that increased expression of E2Fs was negatively correlated with ARHI expression (P < 0.05). Mutation of the putative E2F binding site in the ARHI promoter reversed this inhibitory effect and significantly increased ARHI promoter activity. In addition to the effects of transcriptional regulation, ARHI mRNA also exhibited a significantly reduced half-life in ovarian cancer cells when compared with that in normal ovarian epithelial cells (P < 0.01), suggesting posttranscriptional regulation of ARHI expression. ARHI mRNA contains AU-rich elements (ARE) in the 3'-untranslated region. We have found that these AREs interact with HuR, an ARE-binding protein that stabilizes bound mRNAs, possibly contributing to the rapid turnover of ARHI mRNA. Finally, reduced HuR ARE binding activity was observed in ovarian cancer cells when compared with normal ovarian surface epithelium.
CONCLUSIONS: Taken together, our data suggest that ARHI expression is regulated at both the transcriptional and the posttranscriptional levels, contributing to the dramatic decrease in ARHI expression in ovarian cancers.

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