Circ-E2F3 promotes cervical cancer progression by inhibiting microRNA-296-5p and increasing STAT3 nuclear translocation.

Circular RNA E2F transcription factor 3 (circ-E2F3) has been demonstrated to be differentially expressed in some diseases and cancers. However, the role of circ-E2F3 in cervical cancer (CC) progression remains unclear. Therefore, we aimed to elucidate the mechanism of circ-E2F3 regulation of CC progression. Circ-E2F3 expression was determined in CC samples, and its correlation with the clinicopathological characteristics of CC patients and cell biological processes was examined. The interaction among circ-E2F3, microRNA-296-5p (miR-296-5p), and signal transducer and activator of transcription 3 (STAT3) was analyzed by dual luciferase reporter gene and fluorescence in situ hybridization assays. Circ-E2F3-depleted CaSki cells were implanted into nude mice to verify the function of circ-E2F3 in vivo. Circ-E2F3 was upregulated in both CC tissues and cell lines, and this correlated with the clinicopathological features and poor prognosis of CC patients. Moreover, circ-E2F3 promoted the proliferation, invasion, and migration of CC cells and tumor growth in vivo. It was also observed that circ-E2F3 promoted the nuclear translocation of STAT3 through inhibition of miR-296-5p, thus affecting the expression of cyclin D1. Taken together, the key findings of our study demonstrate that circ-E2F3 induces inhibition of miR-296-5p, which triggers activation and nuclear translocation of STAT3 that then upregulates cyclin D1 expression.

Circular RNA circZNF292 regulates H2 O2 -induced injury in human lens epithelial HLE-B3 cells depending on the regulation of the miR-222-3p/E2F3 axis.

Circular RNAs (circRNAs) play important roles in the pathogenesis of age-related cataract (ARC). CircRNA zinc finger protein 292 (circZNF292, hsa_circ_0004058) is downregulated in ARC lens capsules. Here, we focused on its precise roles in oxidative stress underlying the pathogenesis of ARC. CircZNF292, microRNA (miR)-222-3p, and E2F transcription factor 3 (E2F3) were quantified by quantitative real-time polymerase chain reaction or western blot. Cell viability was assessed by the cell counting kit-8 assay. Cell cycle distribution and apoptosis were detected by flow cytometry. The activities of superoxide dismutase, catalase, and malondialdehyde were measured using the corresponding assay kit. Targeted correlations among circZNF292, miR-222-3p, and E2F3 were verified by the dual-luciferase reporter, RNA immunoprecipitation and RNA pull-down assays. Our data showed that circZNF292 was downregulated in ARC tissues and H2 O2 -treated human lens epithelial B3 (HLE-B3) cells. Increased expression of circZNF292 alleviated H2 O2 -induced cell viability suppression, apoptosis promotion, and oxidative stress enhancement. Mechanistically, circZNF292 directly targeted miR-222-3p, and circZNF292 regulated E2F3 expression through miR-222-3p. MiR-222-3p was a functional mediator of circZNF292 in modulating H2 O2 -induced injury in HLE-B3 cells. Furthermore, reduced level of miR-222-3p ameliorated H2 O2 -induced HLE-B3 cell damage by upregulating E2F3. Our present study demonstrated that increased expression of circZNF292 ameliorated H2 O2 -induced injury in HLE-B3 cells at least in part through the miR-222-3p/E2F3 axis, highlighting a novel insight into the involvement of circRNAs in the pathogenesis of ARC.

CircPRMT5 circular RNA promotes proliferation of colorectal cancer through sponging miR-377 to induce E2F3 expression.

CircPRTM5 is associated with cell proliferation and migration in many kinds of malignancies. However, the functions and mechanisms of CircPRTM5 in CRC progression remain unclear. We explored the role and the mechanisms of CircPRTM5 in the development of CRC. Tissues of CRC patients and matched adjacent non-tumour tissues were collected to evaluate the expression of CircPRTM5. The expression of CircPRTM5 in CRC tissues was significantly higher than that in adjacent tissues. The biological functions of CircPRTM5 in CRC were determined by overexpression and down-regulation of CircPRTM5 in CRC cells in vitro and in vivo. The results indicate that knockdown of CircPRTM5 can significantly inhibit the proliferation of CRC cells. The potential mechanisms of CircPRTM5 in CRC development were identified by RT-qPCR, Western blotting analysis and luciferase reporter assay. CircPRTM5 competitively regulates the expression of E2F3 by capillary adsorption of miR-377. CircPRMT5 regulates CRC proliferation by regulating the expression of E2F3, which affects the expression of the cell cycle-associated proteins cyclinD1 and CDK2. CircPRTM5 exerts critical regulatory role in CRC progression by sponging miR-377 to induce E2F3 expression.

Protein expression profiles and prognostic value of E2F family members in clear cell renal cell carcinoma.

The derangement of the cell cycle facilitates uncontrolled cell proliferation and acquisition of genetic alterations favorable for malignancy. However, the protein expression profiles of E2 F family cell cycle regulators in clear cell renal cell carcinoma (ccRCC) have not yet been thoroughly investigated. In this study, we aimed to examine the protein expression profiles and prognostic value of E2 F1, E2 F3, and E2 F4 in ccRCC cases. The immunohistochemical expression of E2 F1, E2 F3, and E2 F4 was quantitatively scored in 180 ccRCC tumor tissues and 79 normal kidney tissues. The prognostic implications of these E2 F members were determined. We found that ccRCC tumor cells showed higher nuclear expression of E2 F1, E2 F3 and E2 F4 than normal kidney samples. High E2 F1 and E2 F3 expression in tumor cells was associated with poor prognostic factors of ccRCC, whereas high E2 F4 correlated with beneficial prognostic factors. High expression of E2 F1 and E2 F3 in tumor cells was correlated with a poor overall and recurrence-free survival, while high E2 F4 expression did not. In conclusion, E2 F1, E2 F3 and E2 F4 may function as oncogenes during tumorigenesis of ccRCC, although they contribute to the progression of ccRCC in different ways. Additional studies are required to clarify the conflicting role of E2 F4 in the tumor evolution of ccRCC.

RNA N6-methyladenosine modification participates in miR-660/E2F3 axis-mediated inhibition of cell proliferation in gastric cancer.

Increasing evidence has shown that dysregulation of mircoRNA (miRNA) is linked to the development and progression of human cancer, including gastric cancer (GC). In the current study, by analysing the GEO database (GSE78091), we found that miR-660 was significantly downregulated in GC. Consistently, quantitative real-time PCR (qRT-PCR) results showed that miR-660 was dramatically decreased in GC tissues and cell lines. Importantly, low miR-660 expression was closely related to larger tumor size (P = 0.008), lymph node metastasis (P = 0.006), advanced TNM stage (P = 0.029), and poor outcome (P = 0.023). Ectopic expression of miR-660 inhibited proliferation of MGC-803 and AGS cells and induced apoptosis. Further mechanism experiments suggested that the well-known oncogene E2F3 (E2F transcription factor 3) was a downstream target of miR-660. Overexpression of miR-660 reduced the activity of E2F3 by directly binding to the 3221˜3226 region of E2F3 3`-UTR, and there was a strong negative correlation between the expression of miR-660 and E2F3 in GC tissues (r = - 0.648, P < 0.001). Furthermore, E2F3 overexpression abrogated the anti-proliferation effect of miR-660 in GC cell lines. Of note, we found an N6-methyladenosine (m6A) motif at the 3063˜3067 region of E2F3 3`-UTR, and this m6A-modified motif was required for the interaction between miR-660 and E2F3 3`-UTR. Collectively, our findings reveal the compelling role of m6A in GC and highlight the regulatory function of the miR-660/E2F3 pathway in GC progression.

MiR-194-5p inhibits cell migration and invasion in bladder cancer by targeting E2F3.

PURPOSE: MicroRNA (miR)-194-5p is downregulated in bladder cancer (BC), but its role in BC has not been determined mechanistically. METHODS: The expression levels of miR-194-5p and E2F transcription factor 3 (E2F3) were determined by means of quantitative reverse transcription and polymerase chain reaction in BC specimens. In addition, T24 BC cells were transfected with a miR-194-5p mimic, a miR-194-5p inhibitor, or E2F3 small interfering (si)RNA, and the level of E2F3 protein expressed by these cells was assessed by western blotting. A dual luciferase reporter assay was applied to verify the binding site between miR-194-5p and the 3' untranslated region of E2F3. Transwell assays were performed to examine cell migration and invasion. RESULTS: Dysregulation of miR-194-5p in BC was closely associated with node metastasis and differentiation. In BC specimens and cell lines, miR-194-5p mRNA was downregulated, while E2F3 mRNA was upregulated. Overexpression of miR-194-5p suppressed the expression of E2F3 mRNA and protein. By regulating E2F3, miR-194-5p inhibited cell migration and invasion in BC. Treatment of BC cells with E2F3 siRNA had the same effect as did overexpression of miR-194-5p. CONCLUSIONS: MiR-194-5p directly targets E2F3 and inhibits cell migration and invasion in BC.

MiR-210 protects cardiomyocytes from OGD/R injury by inhibiting E2F3.

OBJECTIVE: To detect the change in miRNA-210 expression of cardiomyocytes under hypoxia/reoxygenation status. Also, the effect of miR-210 on the apoptosis of cardiomyocytes induced by oxygen-glucose deprivation/reperfusion (OGD/R) and its mechanism through establishing the OGD/R injury model of primary cardiomyocytes in this experiment were investigated. MATERIALS AND METHODS: The cell model of OGD/R injury was established. The cell apoptosis in each group was detected by methyl thiazolyl tetrazolium (MTT) assay and detection of Caspase-3 activity. The change in miR-210 expression in each group was detected by Real-time fluorescence quantitative polymerase chain reaction (PCR). The high-expression and low-expression miR-210 models were established through the transient transfection of miR-210 mimic and inhibitor to detect the relevant indexes of cell apoptosis. At the same time, changes in mRNA and protein expressions of E2F3 were detected by RT-PCR and Western blotting, respectively. The E2F3 overexpression vector was constructed, and the overexpression vector plasmid and miR-210 mimic were jointly transfected into the cells to detect the relevant indexes of cell apoptosis. RESULTS: After OGD/R treatment, the activity of Caspase-3 was increased, the survival of cardiomyocytes was significantly inhibited and the expression level of miR-210 was up-regulated in OGD/R injury. Transfection of miR-210 mimic for miR-210 overexpression could alleviate the OGD/R-induced cardiomyocyte injury, while the decrease of miR-210 expression could aggravate the apoptosis of cardiomyocytes. In addition, the high expression of miR-210 could inhibit the protein expression of E2F3, and co-transfection of E2F3 plasmid and miR-210 mimic could reverse the inhibiting effect of miR-210 on the apoptosis of cardiomyocytes. CONCLUSIONS: We confirmed that miR-210 can inhibit the OGD/R-induced apoptosis of cardiomyocytes, and miR-210, as an upstream factor, plays a protective role in cardiomyocytes through directly inhibiting the protein expression of its target gene E2F3.

MicroRNA-152 Suppresses Human Osteosarcoma Cell Proliferation and Invasion by Targeting E2F Transcription Factor 3.

MicroRNA-152 (miR-152) expression has been reported to be downregulated in osteosarcoma (OS). However, the role of miR-152 in OS is not well documented. In the present study, we aimed to explore the function and underlying mechanism of miR-152 in OS. We found that miR-152 was underexpressed in OS tissues and cell lines. Decreased miR-152 was inversely correlated with lymph node metastasis and advanced clinical stage. Overexpression of miR-152 significantly inhibited cell proliferation, colony formation, migration, and invasion of OS cells. Bioinformatics analyses showed that miR-152 directly targeted E2F transcription factor 3 (E2F3), as further confirmed by a dual-luciferase reporter assay. E2F3 expression was upregulated and inversely correlated with miR-152 expression level in human OS tissues. Moreover, the inhibitory effects of miR-152 on OS growth and invasion were attenuated by E2F3 overexpression. Taken together, our findings indicated that miR-152 reduced OS growth and invasion by targeting E2F3 and provided new evidence of miR-152 as a potential therapeutic target for OS.

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

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

Rb knockdown accelerates bladder cancer progression through E2F3 activation.

Bladder cancer is one of the most common cancers diagnosed in the world and leads to significant mortality and morbidity among affected patients. The retinoblastoma (Rb) protein is a main tumor suppressor, controlling cellular responses to potentially oncogenic stimulation. E2F3 was invariably disrupted in different human cancers for its central role in the control of cellular proliferation. Here, we investigated how Rb is integrated to control bladder cancer progression through E2F3 and p53 regulation. The results exhibit that Rb expression is lower in patients with bladder tumor, while E2F3 level is high. Rb knockdown enhanced bladder tumor cell proliferation and migration, aggravated with p53 silence. Interestingly, Rb silence results in E2F3, Myc and mTOR signaling pathway activation, contributing to bladder cancer cell proliferation and apoptosis suppression mainly through caspase-3 inhibition in vitro and in vivo. Immunohistochemical analysis revealed that Rb is highly expressed in normal bladder cells, but was repressed in tumor tissues of the bladder completely, suggesting a possible role of Rb as a tumor suppressor.

miR-34c plays a role of tumor suppressor in HEC­1-B cells by targeting E2F3 protein.

Endometrial carcinoma (EC) is a common malignancy of the female genital tract with a poor prognosis. It has been reported that miR-34c is significantly reduced in EC, but research concerning its function in EC is rare. In the present study, the expression of miR-34c was upregulated in the EC cell line, HEC-1-B, by transfecting the cells with hsa-miR-34c-5p mimics. Then, after determining the transfection efficiency by RT-qPCR, we analyzed the effects of miR-34c on the HEC-1-B cells. We found that overexpression of miR-34c significantly inhibited cell proliferation, colony formation, migration and invasion and induced cell cycle arrest and apoptosis. Finally, western blot analysis demonstrated that the expression of E2F3 was reduced after upregulation of the expression of miR-34c in the HEC-1-B cells, and the effects of miR-34c are likely associated with the reduction in E2F3 protein. In conclusion, our study demonstrated that miR-34c plays a role of tumor suppressor in HEC-1-B cells, and E2F3 protein may be a target of miR-34c.

Global epigenetic regulation of microRNAs in multiple myeloma.

Epigenetic changes frequently occur during tumorigenesis and DNA hypermethylation may account for the inactivation of tumor suppressor genes in cancer cells. Studies in Multiple Myeloma (MM) have shown variable DNA methylation patterns with focal hypermethylation changes in clinically aggressive subtypes. We studied global methylation patterns in patients with relapsed/refractory MM and found that the majority of methylation peaks were located in the intronic and intragenic regions in MM samples. Therefore, we investigated the effect of methylation on miRNA regulation in MM. To date, the mechanism by which global miRNA suppression occurs in MM has not been fully described. In this study, we report hypermethylation of miRNAs in MM and perform confirmation in MM cell lines using bisulfite sequencing and methylation-specific PCR (MSP) in the presence or absence of the DNA demethylating agent 5-aza-2'-deoxycytidine. We further characterized the hypermethylation-dependent inhibition of miR-152, -10b-5p and -34c-3p which was shown to exert a putative tumor suppressive role in MM. These findings were corroborated by the demonstration that the same miRNAs were down-regulated in MM patients compared to healthy individuals, alongside enrichment of miR-152-, -10b-5p, and miR-34c-3p-predicted targets, as shown at the mRNA level in primary MM cells. Demethylation or gain of function studies of these specific miRNAs led to induction of apoptosis and inhibition of proliferation as well as down-regulation of putative oncogene targets of these miRNAs such as DNMT1, E2F3, BTRC and MYCBP. These findings provide the rationale for epigenetic therapeutic approaches in subgroups of MM.

Control of glutamine metabolism by the tumor suppressor Rb.

Retinoblastoma (Rb) protein is a tumor suppressor that is dysregulated in a majority of human cancers. Rb functions to inhibit cell cycle progression in part by directly disabling the E2F family of cell cycle-promoting transcription factors. Because the de novo synthesis of multiple glutamine-derived anabolic precursors is required for cell cycle progression, we hypothesized that Rb also may directly regulate proteins involved in glutamine metabolism. We examined glutamine metabolism in mouse embryonic fibroblasts (MEFs) isolated from mice that have triple knock-outs (TKO) of all three Rb family members (Rb-1, Rbl1 and Rbl2) and found that loss of global Rb function caused a marked increase in (13)C-glutamine uptake and incorporation into glutamate and tricarboxylic acid cycle (TCA) intermediates in part via upregulated expression of the glutamine transporter ASCT2 and the activity of glutaminase 1 (GLS1). The Rb-controlled transcription factor E2F-3 altered glutamine uptake by direct regulation of ASCT2 mRNA and protein expression, and E2F-3 was observed to associate with the ASCT2 promoter. We next examined the functional consequences of the observed increase in glutamine uptake and utilization and found that glutamine exposure potently increased oxygen consumption, whereas glutamine deprivation selectively decreased ATP concentration in the Rb TKO MEFs but not the wild-type (WT) MEFs. In addition, TKO MEFs exhibited elevated production of glutathione from exogenous glutamine and had increased expression of gamma-glutamylcysteine ligase relative to WT MEFs. Importantly, this metabolic shift towards glutamine utilization was required for the proliferation of Rb TKO MEFs but not for the proliferation of the WT MEFs. Last, addition of the TCA cycle intermediate α-ketoglutarate to the Rb TKO MEFs reversed the inhibitory effects of glutamine deprivation on ATP, GSH levels and viability. Taken together, these studies demonstrate that the Rb/E2F cascade directly regulates a major energetic and anabolic pathway that is required for neoplastic growth.

Association of E2F3 expression with clinicopathological features of Wilms' tumors.

PURPOSE: The transcription factor E2F3 plays an important role in controlling cell cycle progression and proliferation, and is overexpressed in various human cancers. The present study was undertaken to examine the expression of E2F3 and investigate its relevance in clinical and pathological features of pediatric Wilms' tumors. METHODS: Twenty-six Wilms' tumor samples collected at the First Affiliated Hospital of Harbin Medical University underwent immunohistochemical staining for E2F3 protein expression by measuring the percentage of E2F3-positive cells and integrated optical density (IOD), and quantitative real-time polymerase chain reaction (qRT-PCR) for E2F3 mRNA expression. RESULTS: The expression of E2F3 protein and mRNA was detectable in all the Wilms' tumor samples with big variations (The average percentage of positive cells was 30.2%±23.5%, range 0.3%-75.6%; average IOD was 6.61×10(4)±3.92×10(4), range 2.32×10(4)-13.84×10(4); average relative mRNA unit was 0.54±0.38, range 0.03-1.31), but not in fetal kidney tissues. Wilms' tumors with aggressive features, such as higher stage, unfavorable histology and higher risk level, expressed higher levels of E2F3 protein and mRNA. CONCLUSIONS: The preliminary data indicate that E2F3 is frequently expressed in pediatric Wilms' tumors examined in the present study. E2F3 expression may be associated with Wilms' tumors, particularly those that have more aggressive features. However, further studies are needed to validate these pilot observations and to clarify the functional and mechanistic significance of this association.

Elevated miR-34c-5p mediates dermal fibroblast senescence by ultraviolet irradiation.

Previous studies showed that several miRNAs can regulate pathways involved in UVB-induced premature senescence and response to ultraviolet irradiation. It has also been reported that miR-34c-5p may be involved in senescence-related mechanisms. We propose that miR-34c-5p may play a crucial role in senescence of normal human primary dermal fibroblasts. Here, we explored the roles of miR-34c-5p in UVB-induced premature senescence on dermal fibroblasts. MiR-34c-5p expression was increased in dermal fibroblasts after repeated subcytotoxic UVB treatments. Underexpression of miR-34c-5p in dermal fibroblasts led to a marked delay of many senescent phenotypes induced by repeated UVB treatments. Furthermore, underexpression of miR-34c-5p in dermal fibroblasts can antagonize the alteration of G1-arrested fibroblasts. Moreover, E2F3, which can inactivate p53 pathway and play a role in cell cycle progression, is a down-stream target of miR-34c-5p. Forced down-expression of miR-34c-5p decreased the expression of UVB-SIPS induced P21 and P53 at both mRNA and protein levels. Our data demonstrated that down-regulation of miR-34c-5p can protect human primary dermal fibroblasts from UVB-induced premature senescence via regulations of some senescence-related molecules.

miR-449b inhibits the proliferation of SW1116 colon cancer stem cells through downregulation of CCND1 and E2F3 expression.

Colorectal cancer is one of the leading causes of cancer-related mortality worldwide. Cancer stem cells are cell populations with stem cell nature presenting in tumor tissues and are the root of tumor formation and metastasis. CCND1 and E2F3 play important roles in cell cycle regulation. The 3'UTRs of CCND1 and E2F3 contain miR-449 binding sites. By transfecting pre-miR-449b and inhibiting miR-449b, we found that cell cycle, cell proliferation ability and cell cycle regulatory protein expression levels of colon cancer stem cells were altered. The correlation between CCND1, E2F3 and miR-449b showed that miR-449b could downregulate CCND1 and E2F3 expression. This, in turn, reduced the proliferative ability of colon cancer stem cells. These data suggest that miR-449b plays a tumor-suppressive role in colon cancer stem cells.

E2F3b over-expression in ovarian carcinomas and in BRCA1 haploinsufficient fallopian tube epithelium.

We have previously shown that the E2F3 oncogene is up-regulated as part of a "preneoplastic expression profile" in fallopian tube epithelium (FTE) of women with BRCA1 mutations. We studied E2F3 expression in FTE and carcinomas of women with BRCA1 or BRCA2 mutations or wildtype for both genes. Significantly more foci of TP53 positive cells in histologically normal FTE from women with BRCA1 mutations but not in wildtype or BRCA2 mutated individuals had E2F3 protein overexpression relative to adjacent normal FTE, which occurred in the context of focally increased proliferation, potentially explaining the increased neoplastic potential of tubal TP53 foci in women with BRCA1 mutations. To assess mechanisms of E2F3 deregulation in ovarian or tubal carcinogenesis, we studied E2F3 and its two isoforms E2F3a and E2F3b in wild-type ovarian carcinomas and ovarian carcinomas associated with germline BRCA1 and BRCA2 mutations. The expression of E2F3b, but not E2F3a, was correlated with the expression of BRCA1 in all three genetic groups. In primary cultures of FTE from women with BRCA1 mutation or wildtype for BRCA1 and BRCA2, siRNA-induced BRCA1 deficiency led to increased E2F3b but not E2F3a expression. Our results suggest that E2F3b and BRCA1 are functionally connected, and BRCA1 haploinsufficiency in normal FTE may lead to up-regulation of E2F3b and increased proliferation before the development of intraepithelial neoplasia. These data support that E2F3b up-regulation is an important preneoplastic event in FTE from BRCA1 mutation carriers.

4-hexylresorcinol stimulates the differentiation of SCC-9 cells through the suppression of E2F2, E2F3 and Sp3 expression and the promotion of Sp1 expression.

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.

E2F3a is critically involved in epidermal growth factor receptor-directed proliferation in ovarian cancer.

We describe for the first time a new integral molecular pathway, linking transcription factor E2F3a to epidermal growth factor receptor (EGFR) activation in ovarian cancer cells. Investigations on the role of E2F family members in EGFR-mediated mitogenic signaling revealed that E2F3a was selectively upregulated following EGFR activation, whereas all other E2F family members remained unaffected. In contrast, EGF treatment of healthy ovarian surface epithelial and mesothelial cells yielded a selective upregulation of proliferation-promoting E2F1 and E2F2 without influencing E2F3a expression. In ovarian cancer cell lines, the extent of EGF-induced proliferative stimulus was closely related to the magnitude of E2F3a increase, and proliferation inhibition by E2F3a knockdown was not overcome by EGF exposure. Furthermore, the EGFR-E2F3a axis was found to be signal transducer and activator of transcription 1/3 dependent and the ratio of IFN-regulatory factor (IRF)-1 to IRF-2 was shown to be determinative for E2F3a control. In a pilot study on 32 primary ovarian cancer specimens, a highly significant correlation between activated EGFR and E2F3a expression was disclosed. This new integral pathway in the EGFR-driven mitogenic cell response, which through its key player E2F3a was found to be essential in triggering proliferation in ovarian cancer cells, provides new insights into EGFR signaling and could represent the basis for appealing new therapeutic approaches in ovarian cancer.

Identification of novel posttranscriptional targets of the BCR/ABL oncoprotein by ribonomics: requirement of E2F3 for BCR/ABL leukemogenesis.

Several RNA binding proteins (RBPs) have been implicated in the progression of chronic myelogenous leukemia (CML) from the indolent chronic phase to the aggressively fatal blast crisis. In the latter phase, expression and function of specific RBPs are aberrantly regulated at transcriptional or posttranslational levels by the constitutive kinase activity of the BCR/ABL oncoprotein. As a result, altered expression/function of RBPs leads to increased resistance to apoptotic stimuli, enhanced survival, growth advantage, and differentiation arrest of CD34+ progenitors from patients in CML blast crisis. Here, we identify the mRNAs bound to the hnRNP-A1, hnRNP-E2, hnRNP-K, and La/SSB RBPs in BCR/ABLtransformed myeloid cells. Interestingly, we found that the mRNA encoding the transcription factor E2F3 associates to hnRNP-A1 through a conserved binding site located in the E2F3 3' untranslated region (UTR). E2F3 levels were up-regulated in CML-BCCD34+ in a BCR/ABL kinase- and hnRNP-A1 shuttling-dependent manner. Moreover, by using shRNA-mediated E2F3 knock-down and BCR/ABL-transduced lineage-negative bone marrow cells from E2F3+/+ and E2F3-/- mice, we show that E2F3 expression is important for BCR/ABL clonogenic activity and in vivo leukemogenic potential. Thus, the complexity of the mRNA/RBP network, together with the discovery of E2F3 as an hnRNP-A1-regulated factor, outlines the relevant role played by RBPs in posttranscriptional regulation of CML development and progression.