Transcription Of E2F1 Gene Research Articles

Expression of E2F1 Gene in Acute Leukemia and Its Clinical Significance

To investigate the expression of E2F1 gene in patients with acute leukemia(AL) and its clinical significance. Seventy-two AL patients treated in March 2015 -March 2016 in our hospital were selected, and 24 healthy people were selected as controls. RT-PCR and Western blot were applied to determine the level of E2F1 gene transcription and expression, and the statistical analysis was performed to reveal the clinical value of E2F1 gene. The relative expression levels of E2F1 gene and protein in bone marrow of AL patients was higher than that in control group (P<0.05). The levels of WBC, β2-MG and LDH in the patients with high expression of E2F1 gene were higher than those in patients with low expression of E2F1 gene(P<0.05), but the E2F1 gene expression did not correlate with sex, fever, fatigue, bone marrow blast ratio, peripheral blood blasts ratio (P>0.05). The complete remission (CR) of patients with low expression of E2F1 was significantly higher than that of patients with high expression of E2F1(P<0.05). And the drug resistance in the patients with low expression of E2F1 gene was lower than that of patients with high expression of E2F1 gene (P<0.05). The expression level of E2F1 gene decreased significantly in patients with symptomatic remission after treatment (P<0.05). The expression levels of E2F1 gene in M1, M2 and M5 patients decreased significantly after treatment (P<0.05). Kaplan-Meier survival analysis showed that OS and DFS in the patients with low expression of E2F1 gene were higher than those in patients with high expression (P<0.05). Multivariate Cox regression analysis showed that the age and E2F1 gene were the independent influencing factors of OS (P<0.05); the sex and E2F1 gene were the dependent factors of DFS (P<0.05). The expression level of E2F1 gene in patients with AL has been found to be higher, the higher level of E2F1 gene closely relates with AL patients, E2F1 gene can be used as a biological target for the clinical treatment of AL.

Collapsin response mediator protein 3 deacetylates histone H4 to mediate nuclear condensation and neuronal death

CRMP proteins play critical regulatory roles during semaphorin-mediated neurite outgrowth, neuronal differentiation and death. Albeit having a high degree of structure and sequence resemblance to that of liver dihydropyrimidinase, purified rodent brain CRMPs do not hydrolyze dihydropyrimidinase substrates. Here we found that mouse CRMP3 has robust histone H4 deacetylase activity. During excitotoxicity-induced mouse neuronal death, calpain-cleaved, N-terminally truncated CRMP3 undergoes nuclear translocation to cause nuclear condensation through deacetylation of histone H4. CRMP3-mediated deacetylation of H4 leads to de-repression of the E2F1 gene transcription and E2F1-dependent neuronal death. These studies revealed a novel mechanism of CRMP3 in neuronal death. Together with previous well established bodies of literature that inhibition of histone deacetylase activity provides neuroprotection, we envisage that inhibition of CRMP3 may represent a novel therapeutic approach towards excitotoxicity-induced neuronal death.

Abstract 1252: Interacting role of the androgen receptor and the corepressor Alien in the proliferation inhibition of prostate cancer cells

Abstract Androgen receptor (AR) plays a central role in normal prostate growth and in prostate cancer development. The goal of this study was to identify negative regulatory factor(s) that contribute to proliferation inhibition of prostate cancer cells. The biphasic proliferation pattern of LNCaP human prostate cancer cells at low versus high androgen concentrations was utilized to examine regulatory factors involved in AR-mediated regulation of E2F1 gene transcription. E2F1 is a key cell cycle regulatory transcription factor and an important proliferation stimulator of prostate cancer cells. LNCaP cells are known to be stimulated by ≤ 1 nM androgen, while the cells are arrested at G1/S at high androgen (≥10 nM). Quantitative RT-PCR revealed increased expression of E2F1 and E2F1 target genes (such as cyclin A and the antiapoptotic protein Bcl2) in LNCaP cells treated with 0.1nM R1881 (a synthetic androgen). This up regulation was markedly reduced at the 50 nM R1881 treatment condition. The E2F1 promoter activity showed a similar biphasic regulation by low versus high androgen. Functional analysis of deleted E2F1 promoter fragments identified an androgen responsive region (ARR) in the E2F1 upstream promoter. Chromatin immunoprecipitation (ChIP) of LNCaP cells treated with 0.1nM R1881 showed co-recruitment of AR and the p160 coactivator SRC3 to the ARR in parallel to E2F1 gene induction and increased cell proliferation. AR and SRC3 occupancy at ARR was abrogated by 50 nM R1881 treatment, in parallel to de-induction of E2F1 gene expression. Proliferation inhibition at 50 nM R1881 and loss of AR occupancy at ARR was prevented by SRC3 over expression. Reciprocally, proliferation stimulation by 0.1nM R1881 was lost in SRC3-silenced cells. In further novel findings, we show that the corepressor protein Alien (also known as TRIP15) strongly interacted with AR at 50 nM R1881, while interaction of AR with Alien was much weaker at 0.1 nM R1881. Androgen dose-dependent differential interaction between AR and Alien was demonstrated by co-immunoprecipitation and GST pull down assays of LNCaP cell nuclear extracts. Alien was absent constitutively from ARR in the E2F1 promoter at all conditions (i.e. LNCaP cells treated with vehicle, 0.1 nM R1881 or 50 nM R1881). This suggests that Alien interacts with AR in the nucleoplasm, not in a chromatin environment of the E2F1 promoter. Stable knockdown of Alien prevented proliferation inhibition of LNCaP cells at 50 nM R1881. We conclude that the corepressor Alien/TRIP15 negatively regulates proliferation of prostate cancer cells by sequestering AR in the nucleoplasm, which in turn leads to interference with E2F1 gene induction by androgen-activated AR. In ongoing studies we are utilizing a xenograft tumor model in immune-compromised mice to validate the inhibitory role of the corepressor Alien/TRIP15 in the proliferation of human prostate cancer cells in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1252.

E2F1 transcription is induced by genotoxic stress through ATM/ATR activation

E2F1, a member of the E2F family of transcription factors, plays a critical role in controlling both cell cycle progression and apoptotic cell death in response to DNA damage and oncogene activation. Following genotoxic stresses, E2F1 protein is stabilized by phosphorylation and acetylation driven to its accumulation. The aim of the present work was to examine whether the increase in E2F1 protein levels observed after DNA damage is only a reflection of an increase in E2F1 protein stability or is also the consequence of enhanced transcription of the E2F1 gene. The data presented here demonstrates that UV light and other genotoxics induce the transcription of E2F1 gene in an ATM/ATR dependent manner, which results in increasing E2F1 mRNA and protein levels. After genotoxic stress, transcription of cyclin E, an E2F1 target gene, was significantly induced. This induction was the result of two well-differentiated effects, one of them dependent on de novo protein synthesis and the other on the protein stabilization. Our results strongly support a transcriptional effect of DNA damaging agents on E2F1 expression. The results presented herein uncover a new mechanism involving E2F1 in response to genotoxic stress.

HDAC‐3 Participates in the Repression of e2f‐Dependent Gene Transcription in Primary Differentiated Neurons

Activation of e2f-1 gene expression is an event that has been now established in many models of neuronal apoptosis. Accumulated E2F-1 protein has also been observed in post mortem brains obtained from patients suffering from different neurodegenerative diseases. We have previously shown in primary neuronal cultures that e2f-1 gene transcription was actively repressed in neuroprotective conditions through HDAC-dependent regulation on the E2F-responsive elements (E2F-REs) located in the e2f-1 gene promoter. Here, we further investigated the protein complex bound to these sites by gel shift analysis. We found that the specific protein binding to E2F-REs is altered in apoptotic conditions compared to neuroprotective conditions, suggesting that the proteic constituents of the complex are likely to be modified upon apoptosis onset. Indeed, Western blot analysis showed a time-dependent degradation of the Rb/E2F binding protein HDAC-3 during apoptosis, a degradation that is caspase-dependent. Altogether, these data point to HDAC-3 as a good candidate involved in the active e2f-1 repression necessary for neuroprotection.

PKC/Raf/MEK/ERK signaling pathway modulates native-LDL-induced E2F-1 gene expression and endothelial cell proliferation.

The interactions of low-density lipoprotein (LDL) with the endothelium are thought to play a major role in the development of atherosclerosis. Due to this reason, the molecular sequelae of events resulting from native LDL (N-LDL) interaction with human endothelial cells (HECs) are largely under investigation. Here, we report that the exposure of serum-free HECs to different concentrations of N-LDL-cholesterol (LDL-chol) elicited a time- and dose-dependent induction of DNA synthesis. The exposure of serum-free HECs to N-LDL was able to elicit a time- and dose-dependent increase of protein kinase C (PKC) activity that, along with the activation of the Raf/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway, leads to an increase in E2F-1 gene expression. In addition, the treatment of HECs with N-LDL was also able to induce both E2F-1 gene transcription and protein expression. These N-LDL-aroused responses were dramatically counteracted by PKC inhibition or down regulation. Similarly to what observed for Raf/MEK/ERK activation and E2F-1 gene expression, the inhibition of PKC as well as its down regulation, significantly lowered the DNA synthesis induced by N-LDL in serum-free HECs. These results suggest that the activation of PKC/Raf/MEK/ERK-mediated events controlling E2F-1 gene expression by N-LDL may represent an important mechanism in the regulation of HECs proliferation during normal and pathological processes.

Modulation of E2F Activity via Signaling through Surface IgM and CD40 Receptors in WEHI-231 B Lymphoma Cells

Stimulation of the phenotypically immature B cell lymphoma WEHI-231 with anti-IgM induces G1 arrest followed by apoptotic cell death, which can be reversed by stimulation via the CD40 receptor. Here, we show that cells expressing bcl-xL (WEHI-bcl-xL) arrest at G0/G1 following culture with anti-IgM but do not undergo apoptosis. These arrested cells can be induced to reenter the cell cycle by ligation of CD40. We have therefore used these cells as a model to study the regulation of the transcription factor E2F, which is critically involved in transit through the cell cycle. We found that anti-IgM treatment induces the appearance of an inhibitory DNA binding complex containing the pRB-related pocket protein p130 together with E2F and a concomitant decrease in "free" E2F, consisting of E2F1 and its partner DP1; these effects were reversed following stimulation via CD40. These changes in free E2F levels were regulated by changes in E2F1 gene transcription, which is at least partly a result of control of E2F1 promoter activity through its E2F binding sites. Transient transfection experiments showed that either E2F1 or the viral oncoprotein E1A, which sequesters pocket proteins, including p130, overcame anti-IgM-induced cell cycle arrest in WEHI-bcl-xL. Taken together, these results indicate that in WEHI-231 sIgM ligation induces the accumulation of hypophosphorylated p130 with consequent inhibition of E2F1 gene transcription and cell cycle arrest. Conversely, ligation of CD40 causes hyperphosphorylation of p130, thereby releasing the repression of E2F1 and other E2F-regulated genes, enabling the cells to reenter the cycle. These results, therefore, provide novel insights into the mechanisms whereby antigen receptors on immature B cells deliver inhibitory signals (leading to negative selection of self-reactive B cells) and how these signals can be modulated by positive signals generated via CD40.

Carbon Monoxide Controls the Proliferation of Hypoxic Vascular Smooth Muscle Cells

Excess vascular smooth muscle cell (VSMC) proliferation and contractility are key events in the pathophysiology of vascular disorders induced by hypoxia. We have recently reported that carbon monoxide (CO), produced by VSMC under conditions of hypoxia, can be a modulator of cGMP levels in both endothelial and smooth muscle cells. In this respect, some of the physiologic effects of CO in the vasculature parallel those of nitric oxide (NO), a well characterized regulator of vascular tone. We report here that under hypoxia, VSMC-derived CO is an important regulator of VSMC proliferation. Inhibiting CO formation or scavenging CO with hemoglobin increased VSMC proliferation in response to serum or to mitogens such as endothelin, whereas increasing CO production or exposing cells to exogenous CO lead to a markedly attenuated growth response. The effects of CO on VSMC proliferation correlated with changes in E2F-1 expression, the prototype member of a family of transcription factors that participate in the control of cell cycle progression. CO significantly suppressed E2F-1 expression, whereas, removal of CO from the cultures with hemoglobin lead to increased E2F-1 gene transcription, mRNA, and protein production as well as mRNA levels of c-myc, a target gene of E2F-1. Moreover, the actions of CO were mediated by the second messenger molecule, cGMP. Limiting VSMC growth by increasing the release of CO may represent a key event in the body's compensatory responses to hypoxia.