The molecular and functional characterization of E2F-5 transcription factor

Competing endogenous RNA (ceRNA) cross talk and language in ceRNA regulatory networks: A new look at hallmarks of breast cancer

Breast cancer (BC) is the most frequently occurring malignancy in women worldwide. Despite the substantial advancement in understanding the molecular mechanisms and management of BC, it remains the leading cause of cancer death in women. One of the main reasons for this obstacle is that we have not been able to find the Achilles heel for the BC as a highly heterogeneous disease. Accumulating evidence has revealed that noncoding RNAs (ncRNAs), play key roles in the development of BC; however, the involving of complex regulatory interactions between the different varieties of ncRNAs in the development of this cancer has been poorly understood. In the recent years, the newly discovered mechanism in the RNA world is "competing endogenous RNA (ceRNA)" which proposes regulatory dialogues between different RNAs, including long ncRNAs (lncRNAs), microRNAs (miRNAs), transcribed pseudogenes, and circular RNAs (circRNAs). In the latest BC research, various studies have revealed that dysregulation of several ceRNA networks (ceRNETs) between these ncRNAs has fundamental roles in establishing the hallmarks of BC development. And it is thought that such a discovery could open a new window for a better understanding of the hidden aspects of breast tumors. Besides, it probably can provide new biomarkers and potential efficient therapeutic targets for BC. This review will discuss the existing body of knowledge regarding the key functions of ceRNETs and then highlights the emerging roles of some recently discovered ceRNETs in several hallmarks of BC. Moreover, we propose for the first time the "ceRnome" as a new term in the present article for RNA research.

SNHG16 contributes to breast cancer cell migration by competitively binding miR-98 with E2F5

Long noncoding RNAs (lncRNAs) have been proved to play important roles in cellular processes of cancer, including the development, proliferation, and migration of cancer cells. In the present study, we demonstrated small nucleolar RNA host gene 16 (SNHG16) as an oncogene on cell migration in breast cancer. Expression levels of SNHG16 were found to be frequently higher in breast cancer tissues than in the paired noncancerous tissues. Gain- and loss-of-function studies proved that SNHG16 significantly promoted breast cancer cell migration. We predicted SNHG16 as a competitive endogenous RNA (ceRNA) of E2F transcription factor 5 protein (E2F5) via competition for the shared miR-98 through bioinformatics analysis, and proved this regulation using relative quantitative real-time PCR (qRT-PCR), western blot, RNA immunoprecipitation (RIP) assay and luciferase reporter assay. In addition, we identified a positive correlation between SNHG16 and E2F5 in breast cancer tissues. Furthermore, we demonstrated that forced expression of miR-98 could partially abrogate SNHG16-mediated increase of breast cancer cells migration, suggesting that SNHG16 promoted cell migration in a miR-98 dependent manner. Taken together, our findings indicated that SNHG16 induces breast cancer cell migration by competitively binding miR-98 with E2F5, and SNHG16 can serve as a potential therapeutic target for breast cancer treatment.

Genome-wide profiling of long non-coding RNA expression patterns in the EGFR-TKI resistance of lung adenocarcinoma by microarray

Mutations in the epidermal growth factor receptor (EGFR) make lung adenocarcinoma cells sensitive to EGFR tyrosine kinase inhibitors (TKIs). Long-term cancer therapy may cause the occurrence of acquired resistance to EGFR TKIs. Long non-coding RNAs (lncRNAs) play important roles in tumor formation, tumor metastasis and the development of EGFR-TKI resistance in lung cancer. To gain insight into the molecular mechanisms of EGFR-TKI resistance, we generated an EGFR-TKI-resistant HCC827-8-1 cell line and analyzed expression patterns by lncRNA microarray and compared it with its parental HCC827 cell line. A total of 1,476 lncRNA transcripts and 1,026 mRNA transcripts were dysregulated in the HCC827‑8-1 cells. The expression levels of 7 chosen lncRNAs were validated by real-time quantitative PCR. As indicated by functional analysis, several groups of lncRNAs may be involved in the bio-pathways associated with EGFR-TKI resistance through their cis- and/or trans‑regulation of protein-coding genes. Thus, lncRNAs may be used as novel candidate biomarkers and potential targets in EGFR-TKI therapy in the future.

Walleye dermal sarcoma virus: expression of a full-length clone or the rv-cyclin (orf a) gene is cytopathic to the host and human tumor cells

Walleye dermal sarcoma virus (WDSV) is etiologically associated with a skin tumor, walleye dermal sarcoma (WDS), which develops in the fall and regresses in the spring. WDSV genome contains, in addition to gag, pol and env, three open reading frames (orfs) designated orf a (rv-cyclin), orf b and orf c. Unintegrated linear WDSV provirus DNA isolated from infected tumor cells was used to construct a full-length WDSV provirus clone pWDSV, while orf a was cloned into pSVK3 to construct the expression vector porfA. Stable co-transfection of a walleye cell line (W12) with pWDSV and pcDNA3 generated fewer and smaller G418-resistant colonies compared to the control. By Northern blot analysis, several small transcripts (2.8, 1.8, 1.2, and 0.8 kb) were detected using a WDSV LTR-specific probe. By RT-PCR and Southern blot analysis, three cDNAs (2.4, 1.6 and 0.8 kb) were identified, including both orf a and orf b messenger. Furthermore stable co-transfection of both a human lung adenocarcinoma cell line (SPC-A-1) and a cervical cancer cell line (HeLa) with pcDNA3 and ether porfA or pWDSV also generated fewer and smaller G418-resistant colonies. We conclude that expression of the full-length WDSV clone or the orf a gene inhibits the host fish and human tumor cell growth, and Orf A protein maybe a potential factor which contributes to the seasonal tumor development and regression. This is the first fish provirus clone that has been expressed in cell culture system, which will provide a new in vitro model for tumor research and oncotherapy study.

Identification and expression analysis of two zebrafish E2F5 genes during oogenesis and development

During the process of screening genes that are preferentially expressed in zebrafish germ cells, we isolated an E2F family member zE2F5b, which is a truncated isoform of zebrafish E2F5a. The E2F transcription factors are thought to play an essential role in cell cycle progression. Reverse transcription polymerase chain reaction and whole mount in situ hybridization analyses have demonstrated that both zE2F5a and zE2F5b mRNAs are predominantly expressed in stage I and II oocytes. In early development, the two zE2F5 transcripts are expressed by many parts of the embryo and are then restricted to the brain area. Interestingly, zE2F5b mRNA is detected later in the lens and optic tectum while zE2F5a mRNA is absent. Our data suggests that E2F5 may play important roles in zebrafish brain, eye and ovarian development.

The C. elegans E2F- and DP-related proteins are required for embryonic asymmetry and negatively regulate Ras/MAPK signaling

Early C. elegans embryos exhibit protein asymmetries that allow rapid diversification of cells. Establishing these asymmetries requires the novel protein MEX-5. We show that mutations in the efl-1 and dpl-1 genes cause defects in protein localization resembling defects caused by mutations in mex-5. efl-1 and dpl-1 encode homologs of vertebrate E2F and DP proteins that regulate transcription as a heterodimer. efl-1 and dpl-1 mutants have elevated levels of activated Map kinase in oocytes. Their mutant phenotype and that of mex-5 mutants can be suppressed by reducing Ras/Map kinase signaling. We propose this signaling pathway has a role in embryonic asymmetry and that EFL-1/DPL-1 control the level of Map kinase activation.

Dysregulation of cyclin E gene expression in human cytomegalovirus-infected cells requires viral early gene expression and is associated with changes in the Rb-related protein p130

We have previously shown that many cell cycle regulatory gene products are markedly affected by infection of primary fibroblasts with human cytomegalovirus (HCMV) (F. M. Jault, J. M. Jault, F. Ruchti, E. A. Fortunato, C. Clark, J. Corbeil, D. D. Richman, and D. H. Spector, J. Virol. 69:6697-6704, 1995). One of these proteins, cyclin E, is a key determinant of cell cycle progression during G(1), and its mRNA levels are significantly increased in HCMV-infected fibroblasts (B. S. Salvant, E. A. Fortunato, and D. H. Spector, J. Virol. 72:3729-3741, 1998). To determine the molecular basis of this effect, we have examined the events that occur at the endogenous cyclin E promoter during the course of infection. In vivo dimethyl sulfate footprinting of the cyclin E promoter revealed several regions of protection and hypersensitivity that were unique to infected cells. In accord with this observation, we find that the virus-induced cyclin E transcripts initiate downstream of the start site identified in mock-infected cells, in regions where these newly appearing protected and hypersensitive sites occur. Viral gene expression is required for this induction. However, the viral immediate-early proteins IE1-72 and IE2-86, either alone or in combination, cannot induce expression of the endogenous cyclin E. The virus must progress past the immediate-early phase and express an early gene product(s) for activation of cyclin E expression. Moreover, IE1-72 does not appear to be required, as infection of cells with an HCMV mutant containing a deletion in the IE1-72 gene leads to full upregulation of cyclin E expression. Using electrophoretic mobility shift assays with infected cell extracts and a region of the cyclin E promoter that includes two previously defined E2F sites as the probe, we detected the appearance of an infection-specific banding pattern. One of the infection-specific bands contained the proteins E2F-4, DP-1, and p130, which were maintained in the infected cells as uniquely phosphorylated species. These results suggest that an altered E2F-4-DP-1-p130 complex along with viral early gene expression may play a role in the transcriptional regulation of cyclin E mRNA during HCMV infection.

Differential regulation of E2F transcription factors by p53 tumor suppressor protein

The cell cycle is under the control of various positive and negative regulators. Two such regulators are the E2F family of transcription factors and the p53 tumor suppressor protein. While E2F proteins are implicated in promoting the S phase of the cell cycle, p53 has the potential to arrest cells in G1 phase and thereby prevent entry into S phase. Because they perform seemingly opposite functions in the control of cell growth, a possibility of functional interactions between E2F and p53 was investigated. It was found that p53 specifically inhibited activated transcription by E2F-5 but not by E2F-1. Investigation into the mechanism of action established that heterodimer formation and the DNA-binding steps were not significantly inhibited by p53. However, the transcriptional activation step of E2F-5 activity, as examined by using a Gal4 DNA-binding domain chimera, was specifically inhibited by p53. Interestingly, p53 could also inhibit transcriptional activation by E2F-4 but not by E2F-2 or E2F-3. The results indicate that p53 differentially regulates the activities of two subclasses (E2F-1/-2/-3 vs. E2F-4/-5) of E2F transcription factors. Detailed analysis using a two-hybrid approach in mammalian cells indicated lack of physical interaction between p53 and E2F-5, DP-1, or E2F-1. Reciprocal analysis revealed that whereas E2F-1 dramatically inhibited p53-activated transcription, E2F-5 or DP-1 did not. Thus, nonreciprocal functional interactions exist between various members of the E2F family of transcription factors and p53 tumor suppressor protein. The complex interplay between various positive and negative regulators of cell growth, such as E2F and p53 proteins, may be crucial in determining the ultimate outcome in terms of cell cycle arrest, cell growth, or apoptosis.

Regulation of E2F: a family of transcription factors involved in proliferation control

Members of the E2F family of transcription factors are key participants in orchestration of the cell cycle, cell growth arrest and apoptosis. Therefore, an understanding of the regulation of E2F activity is essential for an understanding of the control of cellular proliferation. E2F activity is regulated by the retinoblastoma family of tumor suppressors and by multiple other mechanisms. This review will describe our current knowledge of these mechanisms which together constitute a highly complex network by which the cell cycle and cellular proliferation can be controlled.