Suppression of Egr-1 transcription through targeting of the serum response factor by oncogenic H-Ras

CCT3-LINC00326 axis regulates hepatocarcinogenic lipid metabolism

OBJECTIVE

To better comprehend transcriptional phenotypes of cancer cells, we globally characterised RNA-binding proteins (RBPs) to identify altered RNAs, including long non-coding RNAs (lncRNAs).

DESIGN

To unravel RBP-lncRNA interactions in cancer, we curated a list of ~2300 highly expressed RBPs in human cells, tested effects of RBPs and lncRNAs on patient survival in multiple cohorts, altered expression levels, integrated various sequencing, molecular and cell-based data.

RESULTS

High expression of RBPs negatively affected patient survival in 21 cancer types, especially hepatocellular carcinoma (HCC). After knockdown of the top 10 upregulated RBPs and subsequent transcriptome analysis, we identified 88 differentially expressed lncRNAs, including 34 novel transcripts. CRISPRa-mediated overexpression of four lncRNAs had major effects on the HCC cell phenotype and transcriptome. Further investigation of four RBP-lncRNA pairs revealed involvement in distinct regulatory processes. The most noticeable RBP-lncRNA connection affected lipid metabolism, whereby the non-canonical RBP CCT3 regulated LINC00326 in a chaperonin-independent manner. Perturbation of the CCT3-LINC00326 regulatory network led to decreased lipid accumulation and increased lipid degradation in cellulo as well as diminished tumour growth in vivo.

CONCLUSIONS

We revealed that RBP gene expression is perturbed in HCC and identified that RBPs exerted additional functions beyond their tasks under normal physiological conditions, which can be stimulated or intensified via lncRNAs and affected tumour growth.

Nuclear-capture of endosomes depletes nuclear G-actin to promote SRF/MRTF activation and cancer cell invasion

Signals are relayed from receptor tyrosine kinases (RTKs) at the cell surface to effector systems in the cytoplasm and nucleus, and coordination of this process is important for the execution of migratory phenotypes, such as cell scattering and invasion. The endosomal system influences how RTK signalling is coded, but the ways in which it transmits these signals to the nucleus to influence gene expression are not yet clear. Here we show that hepatocyte growth factor, an activator of MET (an RTK), promotes Rab17- and clathrin-dependent endocytosis of EphA2, another RTK, followed by centripetal transport of EphA2-positive endosomes. EphA2 then mediates physical capture of endosomes on the outer surface of the nucleus; a process involving interaction between the nuclear import machinery and a nuclear localisation sequence in EphA2's cytodomain. Nuclear capture of EphA2 promotes RhoG-dependent phosphorylation of the actin-binding protein, cofilin to oppose nuclear import of G-actin. The resulting depletion of nuclear G-actin drives transcription of Myocardin-related transcription factor (MRTF)/serum-response factor (SRF)-target genes to implement cell scattering and the invasive behaviour of cancer cells.

Soluble Epoxide Hydrolase Inhibitors Regulate Ischemic Arrhythmia by Targeting MicroRNA-1

Background: Soluble epoxide hydrolase inhibitors (sEHis) inhibit the degradation of epoxyeicosatrienoic acids (EETs) in cells, and EETs have antiarrhythmic effects. Our previous experiments confirmed that t-AUCB, a preparation of sEHis, inhibited ischemic arrhythmia by negatively regulating microRNA-1 (miR-1), but its specific mechanism remained unclear. Aim: This study aimed to examine the role of serum response factor (SRF) and the PI3K/Akt/GSK3β pathway in t-AUCB-mediated regulation of miR-1 and the interaction between them. Methods/Results: We used SRF small interfering RNA (siSRF), SRF small hairpin (shSRF) RNA sequence adenovirus, PI3K/Akt/GSK3β pathway inhibitors, t-AUCB, and 14,15-EEZE (a preparation of EETs antagonists) to treat mouse cardiomyocytes overexpressing miR-1 and mice with myocardial infarction (MI). We found that silencing SRF attenuated the effects on miR-1 and its target genes KCNJ2 and GJA1 in the presence of t-AUCB, and inhibition of the PI3K/Akt/GSK3β pathway antagonized the effects of t-AUCB on miR-1, KCNJ2, and GJA1, which were associated with PI3Kα, Akt, and Gsk3β but not PI3Kβ or PI3Kγ. Moreover, the PI3K/Akt/GSK3β pathway was involved in the regulation of SRF by t-AUCB, and silencing SRF inhibited the t-AUCB-induced increases in Akt and Gsk3β phosphorylation. Conclusions: Both the SRF and the PI3K/Akt/GSK3β pathway are involved in the t-AUCB-mediated regulation of miR-1, and these factors interact with each other.

Mechanistic Analysis of an Extracellular Signal-Regulated Kinase 2-Interacting Compound that Inhibits Mutant BRAF-Expressing Melanoma Cells by Inducing Oxidative Stress

Constitutively active extracellular signal–regulated kinase (ERK) 1/2 signaling promotes cancer cell proliferation and survival. We previously described a class of compounds containing a 1,1-dioxido-2,5-dihydrothiophen-3-yl 4-benzenesulfonate scaffold that targeted ERK2 substrate docking sites and selectively inhibited ERK1/2-dependent functions, including activator protein-1–mediated transcription and growth of cancer cells containing active ERK1/2 due to mutations in Ras G-proteins or BRAF, Proto-oncogene B-RAF (Rapidly Acclerated Fibrosarcoma) kinase. The current study identified chemical features required for biologic activity and global effects on gene and protein levels in A375 melanoma cells containing mutant BRAF (V600E). Saturation transfer difference-NMR and mass spectrometry analyses revealed interactions between a lead compound (SF-3-030) and ERK2, including the formation of a covalent adduct on cysteine 252 that is located near the docking site for ERK/FXF (DEF) motif for substrate recruitment. Cells treated with SF-3-030 showed rapid changes in immediate early gene levels, including DEF motif–containing ERK1/2 substrates in the Fos family. Analysis of transcriptome and proteome changes showed that the SF-3-030 effects overlapped with ATP-competitive or catalytic site inhibitors of MAPK/ERK Kinase 1/2 (MEK1/2) or ERK1/2. Like other ERK1/2 pathway inhibitors, SF-3-030 induced reactive oxygen species (ROS) and genes associated with oxidative stress, including nuclear factor erythroid 2–related factor 2 (NRF2). Whereas the addition of the ROS inhibitor N-acetyl cysteine reversed SF-3-030–induced ROS and inhibition of A375 cell proliferation, the addition of NRF2 inhibitors has little effect on cell proliferation. These studies provide mechanistic information on a novel chemical scaffold that selectively regulates ERK1/2-targeted transcription factors and inhibits the proliferation of A375 melanoma cells through a ROS-dependent mechanism.

MiR-125b-2-3p associates with prognosis of ccRCC through promoting tumor metastasis via targeting EGR1

Clear cell renal cell carcinoma (ccRCC) is an aggressive tumor with frequent metastatic rate. In order to explore the mechanisms, we determined the roles of miR-125b-2-3p in metastatic ccRCC progression. In the study, both clinical and experimental evidences supported the critical role of miR-125b-2-3p in accelerating ccRCC metastasis. Elevated miR-125b-2-3p expression correlated with lymphatic invasion, distant metastasis and poor survival. Functional study showed that high miR-125b-2-3p expression significantly increased ccRCC cell migration in vitro and lung metastasis in vivo. Furthermore, we demonstrated that miR-125b-2-3p directly targeted EGR1, and miR-125b-2-3p accelerated ccRCC cell migration through down-regulating EGR1. Taken together, this study demonstrated that miR-125b-2-3p associates with ccRCC prognosis via promoting tumor metastasis through targeting EGR1.

Chemerin Reactivates PTEN and Suppresses PD-L1 in Tumor Cells via Modulation of a Novel CMKLR1-mediated Signaling Cascade

PURPOSE

Chemerin (retinoic acid receptor responder 2, RARRES2) is an endogenous leukocyte chemoattractant that recruits innate immune cells through its receptor, ChemR23. RARRES2 is widely expressed in nonhematopoietic tissues and often downregulated across multiple tumor types compared with normal tissue. Recent studies show that augmenting chemerin in the tumor microenvironment significantly suppresses tumor growth, in part, by immune effector cells recruitment. However, as tumor cells express functional chemokine/chemoattractant receptors that impact their phenotype, we hypothesized that chemerin may have additional, tumor-intrinsic effects.

EXPERIMENTAL DESIGN

We investigated the effect of exogenous chemerin on human prostate and sarcoma tumor lines. Key signaling pathway components were elucidated using qPCR, Western blotting, siRNA knockdown, and specific inhibitors. Functional consequences of chemerin treatment were evaluated using in vitro and in vivo studies.

RESULTS

We show for the first time that human tumors exposed to exogenous chemerin significantly upregulate PTEN expression/activity, and concomitantly suppress programmed death ligand-1 (PD-L1) expression. CMKLR1 knockdown abrogated chemerin-induced PTEN and PD-L1 modulation, exposing a novel CMKLR1/PTEN/PD-L1 signaling cascade. Targeted inhibitors suggested signaling was occurring through the PI3K/AKT/mTOR pathway. Chemerin treatment significantly reduced tumor migration, while significantly increasing T-cell-mediated cytotoxicity. Chemerin treatment was as effective as both PD-L1 knockdown and the anti-PD-L1 antibody, atezolizumab, in augmenting T-cell-mediated tumor lysis. Forced expression of chemerin in human DU145 tumors significantly suppressed in vivo tumor growth, and significantly increased PTEN and decreased PD-L1 expression.

CONCLUSIONS

Collectively, our data show a novel link between chemerin, PTEN, and PD-L1 in human tumor lines, which may have a role in improving T-cell-mediated immunotherapies.

Newly synthesized podophyllotoxin derivative, LJ12, induces apoptosis and mitotic catastrophe in non-small cell lung cancer cells in vitro

Deoxypodophyllotoxin (DPT), an active compound isolated from a number of herbs and used in traditional medicine, has been reported to exhibit promising anti‑tumor activity. A newly synthesized derivative, N-(1-oxyl‑4'-demethyl-4-deoxyp odophyllic)-L‑methine-4'-piperazine carbamate (LJ12) may have improved antitumor activity and fewer side effects. The present study assessed the effect of LJ12 on cell viability, apoptosis, cell cycle distribution and mitotic catastrophe in A549 human lung cancer cells in vitro. The molecular mechanisms underlying the antitumor activity of LJ12 were also examined. The results demonstrated that LJ12 reduced A549 cell viability in a time‑ and dose‑dependent manner, with a lower half maximal inhibitory concentration of ~0.1 µM, compared with another known DPT derivative, etoposide (10 µM). Flow cytometric analysis showed that LJ12 induced tumor cell arrest at the G2/M phase of the cell cycle. The present study also observed an expected concomitant decrease in the numbers of cells cells in the G0/G1 and S phases. LJ12 was found to upregulate the protein expression levels of Cdc2 and Cyclin B1. Furthermore, LJ12 induced tumor cell apoptosis and the protein expression of B cell lymphoma‑2‑associated X protein, caspase‑3 and p53. The present study also observed the formation of giant, multinucleated cells, indicating that LJ12 induced mitotic catastrophe in the tumor cells. These results indicated that LJ12 has anti‑non‑small cell lung cancer activity in vitro. Further investigations aim to develop LJ12 as a therapeutic agent for the treatment of lung cancer.

Constitutively active Ras negatively regulates Erk MAP kinase through induction of MAP kinase phosphatase 3 (MKP3) in NIH3T3 cells

The Ras/Raf/MEK/Erk signaling pathway is important for regulation of cell growth, proliferation, differentiation, survival, and apoptosis in response to a variety of extracellular stimuli. Lack of Erk MAPK activation is observed in several cancer cells despite active activation of Ras. However, little is known about the modulation of Erk1/2 activity by active Ras. Here, we show that overexpression of active H-Ras (H-RasG12R) in NIH3T3 fibroblasts impaired FGF2-induced Erk1/2 phosphorylation, as compared to wild-type cells. Northern blot analysis revealed that prolonged expression of active Ras increased MAP kinase phosphatase 3 (MKP3) mRNA expression, a negative regulator of Erk MAPK. Inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway abrogated active Ras-induced up-regulation of MKP3 expression, leading to the rescue of Erk1/2 phosphorylation. Our results demonstrated that the Ras/Raf/MEK/Erk signaling cascade is negatively regulated by the PI3K/Akt dependent transcriptional activation of the MKP3 gene.

An Arf-Egr-C/EBPβ pathway linked to ras-induced senescence and cancer

Oncogene-induced senescence (OIS) protects normal cells from transformation by Ras, whereas cells lacking p14/p19(Arf) or other tumor suppressors can be transformed. The transcription factor C/EBPβ is required for OIS in primary fibroblasts but is downregulated by H-Ras(V12) in immortalized NIH 3T3 cells through a mechanism involving p19(Arf) loss. Here, we report that members of the serum-induced early growth response (Egr) protein family are also downregulated in 3T3(Ras) cells and directly and redundantly control Cebpb gene transcription. Egr1, Egr2, and Egr3 recognize three sites in the Cebpb promoter and associate transiently with this region after serum stimulation, coincident with Cebpb induction. Codepletion of all three Egrs prevented Cebpb expression, and serum induction of Egrs was significantly blunted in 3T3(Ras) cells. Egr2 and Egr3 levels were also reduced in Ras(V12)-expressing p19(Arf) null mouse embryonic fibroblasts (MEFs), and overall Egr DNA-binding activity was suppressed in Arf-deficient but not wild-type (WT) MEFs, leading to Cebpb downregulation. Analysis of human cancers revealed a strong correlation between EGR levels and CEBPB expression, regardless of whether CEBPB was increased or decreased in tumors. Moreover, overexpression of Egrs in tumor cell lines induced CEBPB and inhibited proliferation. Thus, our findings identify the Arf-Egr-C/EBPβ axis as an important determinant of cellular responses (senescence or transformation) to oncogenic Ras signaling.

Synthesis and evaluation of the apoptosis inducing and CT DNA interaction properties of a series of 4β-carbamoyl 4'-O-demethylepipodophyllotoxins

A series of carbamate derivatives of 4'-demethylepipodophyllotoxin have been synthesized, and their cytotoxicities against several human cancer cell lines, including HeLa, A549, HCT-8, and HL-60 cells, evaluated. Some of these compounds exhibited higher levels of cytotoxicity than the anticancer drug etoposide. 4β-4'-Demethylepipodophyllotoxin 1-(4-nitrophenyl) piperazinyl carbamate (19) was found to be the most potent compound of those synthesized in the current study, and induced cell cycle arrest in the G2/M phase in HeLa cells, which was accompanied by apoptosis. Furthermore, this compound activated the expression of Bax, p53 and caspase-3 in HeLa cells, leading to changes in the conformation of calf thymus DNA from the B-form to a more compact C-form.

Chromenylchalcones showing cytotoxicity on human colon cancer cell lines and in silico docking with aurora kinases

Due to toxicity problems, various plant-derived compounds have been screened to find the chemotherapeutic agents. As anticancer therapeutic agents, chalcones have advantages such as poor interaction with DNA and low risk of mutagenesity. Chromenones show anticancer activities too. Therefore, hybrids of chalcone and chromenone may be potent chemotherapeutic agents. We prepared 16 synthetic chromenylchalcones and applied a clonogenic long-term survival assay method for them on HCT116 human colorectal cancer cell lines. One of chromenylchalcones tested here, chromenylchalcone 11, showed IC50 of 93.1nM which can be competed with the IC50 values of well-known flavonoids such as catechin gallate and epicatechin gallate. Further biological experiments including cell cycle analysis, apoptosis assay, Western blot analysis, and immunofluorescent microscopy were carried out for this compound. In addition, in vitro kinases binding assay performed to explain its molecular mechanism demonstrated the compound inhibited aurora kinases. The binding modes between chromenylchalcone 11 and aurora kinases were elucidated using in silico docking experiments. These findings could be used for designing cancer therapeutic or preventive plant-derived chromenylchalcone agents.

Synthesis and cytotoxic activity on human cancer cells of carbamate derivatives of 4β-(1,2,3-triazol-1-yl)podophyllotoxin

Carbamate derivatives of 4β-(1,2,3-triazol-1-yl)podophyllotoxin were synthesized by means of click chemistry, and their cytotoxicities against human cancer cell lines HL-60, A-549, HeLa, and HCT-8 were evaluated. Some compounds were more potent than the anticancer drug etoposide. 4'-O-Demethyl-4β-[(4-hydroxymethyl)-1,2,3-triazol-1-yl]-4-deoxypodophyllotoxin cyclopentyl carbamate, the most potent compound, induced cell cycle arrest in the G2/M phase accompanied by apoptosis in A-549 cells. Furthermore, this compound inhibited the formation of microtubules in A-549 cells and caused the inhibition of DNA topoisomerase-II.

Transcriptional regulation of the interleukin-11 gene by oncogenic Ras

Interleukin-11 (IL-11), which belongs to a class of IL6-type cytokines, plays an important role in inflammation, motility and invasion in cancer. The ras mutation is frequently found in human cancer, but little is known regarding the transcriptional activation of the IL-11 gene by the Ras signal pathway in tumour cells. In this study, we investigated the role of Ras in the regulation of IL-11 using two different cell model systems: mouse NIH3T3 cells over-expressing oncogenic Ras with a tet-on system and Capan-1 human pancreatic carcinoma cells harbouring a K-ras mutation. We found that IL-11 expression was up-regulated at the transcriptional level by oncogenic Ras. Activation of the AP-1 response element, located between -153 and -30 in the 5'-regulatory region of the IL-11 gene, was necessary for oncogenic Ras-induced IL-11 promoter activation. AP-1 proteins, including Fra-1 and Fra-2, were up-regulated through the Raf/MEK and phosphatidylinositol 3-kinase (PI3K)/Akt pathways by oncogenic Ras. Knockdown of Fra-1 by siRNA in NIH3T3 or Capan-1 cells strongly attenuated oncogenic Ras-induced IL-11 expression. Additionally, inhibition of JNK, p38 and Stat3 abrogated oncogenic Ras-induced IL-11 expression. These results suggest that both the PI3K and Raf pathways are necessary for the expression of IL-11 in oncogenic Ras-mutated cells, and that JNK, p38 and Stat3 also contribute to oncogenic Ras-induced IL-11 expression.

Imipramine activates glial cell line-derived neurotrophic factor via early growth response gene 1 in astrocytes

Recent evidence has suggested that deficits in glial plasticity contribute to the pathophysiology of depressive disorders. The present study explored early growth response 1 (EGR-1) transcriptional regulation of imipramine-induced glial cell line-derived neurotrophic factor (GDNF) expression in astrocytes. After we observed the induction of GDNF mRNA expression in rat astrocytes in response to imipramine, deletion mutant studies showed that the proximal region between -493 and -114 of the GDNF promoter, which contains three binding sites for EGR-1, was essential for maximal imipramine-induced activation of GDNF promoter. The dose-dependent upregulation of EGR-1 by imipramine, the activation of GDNF by the over-expression of EGR-1 without imipramine and the reduction in the imipramine-induced GDNF mRNA expression after silencing of endogenous EGR-1 demonstrated that EGR-1 is upregulated by imipramine to activate the GDNF promoter. Furthermore, imipramine-induced GDNF mRNA expression was strongly attenuated in primary astrocytes from Egr-1(-/-) mice, and the immunoreactivity to an anti-GDNF antibody in glial fibrillary acidic protein-positive cells was lower in imipramine-treated astrocytes from Egr-1(-/-) mice than in those from Egr-1(+/-) mice. To determine whether mitogen-activated protein kinases (MAPKs) were associated with imipramine-induced EGR-1 expression, we examined the induction of MAPK phosphorylation in response to imipramine. Pretreatment of rat primary astrocytes with the MAPK kinase inhibitor U0126 or the JNK inhibitor SP600125 strongly inhibited imipramine-stimulated EGR-1 expression. In conclusion, we found that imipramine induction of EGR-1 upregulated GDNF in astrocytes in a dose-dependent manner. This upregulation may occur through the MEK/ERK and JNK MAPK pathways, which suggests a new therapeutic mechanism of action for depressive disorders.

5-Methoxyflavanone induces cell cycle arrest at the G2/M phase, apoptosis and autophagy in HCT116 human colon cancer cells

Natural flavonoids have diverse pharmacological activities, including anti-oxidative, anti-inflammatory, and anti-cancer activities. In this study, we investigated the molecular mechanism underlying the action of 5-methoxyflavanone (5-MF) which has a strong bioavailability and metabolic stability. Our results show that 5-MF inhibited the growth and clonogenicity of HCT116 human colon cancer cells, and that it activated DNA damage responses, as revealed by the accumulation of p53 and the phosphorylation of DNA damage-sensitive proteins, including ataxia-telangiectasia mutated (ATM) at Ser1981, checkpoint kinase 2 (Chk2) at Thr68, and histone H2AX at Ser139. 5-MF-induced DNA damage was confirmed in a comet tail assay. We also found that 5-MF increased the cleavage of caspase-2 and -7, leading to the induction of apoptosis. Pretreatment with the ATM inhibitor KU55933 enhanced 5-MF-induced γ-H2AX formation and caspase-7 cleavage. HCT116 cells lacking p53 (p53(-/-)) or p21 (p21(-/-)) exhibited increased sensitivity to 5-MF compared to wild-type cells. 5-MF further induced autophagy via an ERK signaling pathway. Blockage of autophagy with the MEK inhibitor U0126 potentiated 5-MF-induced γ-H2AX formation and caspase-2 activation. These results suggest that a caspase-2 cascade mediates 5-MF-induced anti-tumor activity, while an ATM/Chk2/p53/p21 checkpoint pathway and ERK-mediated autophagy act as a survival program to block caspase-2-mediated apoptosis induced by 5-MF.

Mutant p53 initiates a feedback loop that involves Egr-1/EGF receptor/ERK in prostate cancer cells

Early Growth Response-1 (Egr-1) is overexpressed in human prostate tumors and contributes to cancer progression. On the other hand, mutation of p53 is associated with advanced prostate cancer, as well as with metastasis and hormone independence.

This study shows that in prostate cell lines in culture, Egr-1 overexpression correlated with an alteration of p53 activity due to the expression of SV40-TAg or to a mutation in the TP53 gene. In cells containing altered p53 activity, Egr-1 expression was abolished upon pharmacological inhibition or RNAi silencing of p53. Although forced expression of wild-type p53 was not sufficient to trigger Egr-1 transcription, four different mutants of p53 were shown to induce Egr-1. Direct binding of p53 to the EGR1 promoter could not be detected. Instead, Egr-1 transcription was driven by the ERK1/2 pathway, since it was abrogated by specific inhibitors of MEK. Egr-1 increased the transcription of HB-EGF, amphiregulin and epiregulin, resulting in autocrine activation of the EGFR (epidermal growth factor receptor) and downstream MEK/ERK cascade. Thus, mutant p53 initiates a feedback loop that involves ERK1/2-mediated transactivation of Egr-1, which in turn increases the secretion of EGFR ligands and stimulates the EGFR signaling pathway. Finally, p53 may further regulate this feedback loop by altering the level of EGFR expression.

Egr-1 is necessary for fibroblast growth factor-2-induced transcriptional activation of the glial cell line-derived neurotrophic factor in murine astrocytes

Glial cell line-derived neurotrophic factor (Gdnf) promotes neurite outgrowth and survival of neuronal cells, but its transcriptional regulation is poorly understood. Here, we sought to investigate the mechanism underlying fibroblast growth factor-2 (FGF2) induction of Gdnf expression in astrocytes. We found that FGF2 stimulation of rat astrocytes induced expression of Egr-1 at a high level. Sequence analysis of the rat Gdnf gene identified three overlapping Egr-1-binding sites between positions -185 and -163 of the rat Gdnf promoter. Transfection studies using a series of deleted Gdnf promoters revealed that these Egr-1-binding sites are required for maximal activation of the Gdnf promoter by FGF2. Chromatin immunoprecipitation analysis indicated that Egr-1 binds to the Gdnf promoter. Furthermore, the induction of Gdnf expression by FGF2 is strongly attenuated both in C6 glioma cells stably expressing Egr-1-specific small interfering RNA and in primary cultured astrocytes from the Egr-1 knock-out mouse. Additionally, we found that stimulation of the ERK and JNK pathways by FGF2 is functionally linked to Gdnf expression through the induction of Egr-1. These data demonstrate that FGF2-induced Gdnf expression is mediated by the induction of Egr-1 through activation of the ERK and JNK/Elk-1 signaling pathways.

Efficient serum-free derivation of oligodendrocyte precursors from neural stem cell-enriched cultures

Oligodendrocytes derived in the laboratory from stem cells have been proposed as a treatment for acute and chronic injury to the central nervous system. Platelet-derived growth factor (PDGF) receptor alpha (PDGFRalpha) signaling is known to regulate oligodendrocyte precursor cell numbers both during development and adulthood. Here, we analyze the effects of PDGFRalpha signaling on central nervous system (CNS) stem cell-enriched cultures. We find that AC133 selection for CNS progenitors acutely isolated from the fetal cortex enriches for PDGF-AA-responsive cells. PDGF-AA treatment of fibroblast growth factor 2-expanded CNS stem cell-enriched cultures increases nestin(+) cell number, viability, proliferation, and glycolytic rate. We show that a brief exposure to PDGF-AA rapidly and efficiently permits the derivation of O4(+) oligodendrocyte-lineage cells from CNS stem cell-enriched cultures. The derivation of oligodendrocyte-lineage cells demonstrated here may support the effective use of stem cells in understanding fate choice mechanisms and the development of new therapies targeting this cell type.

RasV12-mediated down-regulation of CCAAT/enhancer binding protein beta in immortalized fibroblasts requires loss of p19Arf and facilitates bypass of oncogene-induced senescence

The transcription factor CCAAT/enhancer binding protein beta (C/EBPbeta) is involved in cellular responses to oncogenic and physiologic Ras signals. C/EBPbeta is required for premature senescence of primary mouse fibroblasts induced by expression of H-Ras(V12), demonstrating its role in oncogene-induced senescence. Here, we have investigated the mechanisms by which Ras inhibits proliferation of normal cells but transforms immortalized cells. We show that oncogenic Ras down-regulates C/EBPbeta expression in NIH 3T3 cells, which are immortalized by a deletion of the CDKN2A locus and, therefore, lack the p16(Ink4a) and p19(Arf) tumor suppressors. Ras(V12)-induced silencing of C/EBPbeta occurred at the mRNA level and involved both the Raf-mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase-ERK and phosphatidylinositol 3-kinase signaling pathways. Oncogenic Ras decreased C/EBPbeta expression in Ink4a/Arf(-/-) mouse embryo fibroblasts (MEF) but increased C/EBPbeta levels in wild-type MEFs. C/EBPbeta down-regulation in NIH 3T3 cells was reversed by expression of p19(Arf), but not of p53 or p16(Ink4a), highlighting a critical role for p19(Arf) in sustaining C/EBPbeta levels. Ectopic expression of p34 C/EBPbeta (LAP) inhibited Ras(V12)-mediated transformation of NIH 3T3 cells, suppressed their tumorigenicity in nude mice, and reactivated expression of the proapoptotic Fas receptor, which is also down-regulated by Ras. Our findings indicate that Cebpb gene silencing eliminates a growth inhibitory transcription factor that would otherwise restrain oncogenesis. We propose that C/EBPbeta is part of a p53-independent, p19(Arf)-mediated network that enforces Ras-induced cell cycle arrest and tumor suppression in primary fibroblasts.

Thalidomide inhibits leukemia cell invasion and migration by upregulation of early growth response gene 1

Thalidomide has been shown to exert its antitumor activity through the significant effects on microenvironment and immunomodulatory properties. In this study, 10 microM thalidomide treatment markedly increased the expression of the early growth response gene 1 (Egr-1) at both mRNA and protein levels in HL-60 leukemic cells. Thalidomide treatment significantly decreased the invasive cells number through Matrigel and human umbilical vein endothelial cells when compared with the controls. Moreover, the inhibitory effects could be markedly abolished by Egr-1 gene silencing with siRNA technology. Our data indicated thalidomide could suppress leukemia cell invasion and migration by upregulation of Egr-1, suggesting a novel mechanism of thalidomide in the treatment of leukemia. Further investigations are needed to explore the detailed mechanism of Egr-1 induction by thalidomide and the downstream pathways involved in the regulation of leukemia cell invasion.

PTEN regulation by Akt-EGR1-ARF-PTEN axis

The PTEN tumour suppressor gene is induced by the early growth response 1 (EGR1) transcription factor, which also transactivates p53, p73, and p300/CBP as well as other proapoptotic and anti-cancer genes. Here, we describe a novel Akt-EGR1-alternate reading frame (ARF)-PTEN axis, in which PTEN activation in vivo requires p14ARF-mediated sumoylation of EGR1. This modification is dependent on the phosphorylation of EGR1 at S350 and T309 by Akt, which promotes interaction of EGR1 with ARF at K272 in its repressor domain by the ARF/Ubc9/SUMO system. EGR1 sumoylation is decreased by ARF reduction, and no EGR1 sumoylation is detected in ARF(-/-) mice, which also exhibit reduced amounts of PTEN. Our model predicts that perturbation of any of the clinically important tumour suppressors, PTEN, EGR1, and ARF, will cause some degree of dysfunction of the others. These results also explain the known negative feedback regulation by PTEN on its own synthesis through PI3 kinase inhibition.

p21 Waf1/Cip1 expression by curcumin in U-87MG human glioma cells: role of early growth response-1 expression

Curcumin, a natural compound, is a well-known chemopreventive agent with potent anticarcinogenic activity in a wide variety of tumor cells. Curcumin inhibits cancer cell proliferation in part by suppressing cyclin D1 and inducing expression of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). Both p53-dependent and p53-independent mechanisms regulate p21(Waf1/Cip1) expression, but the mechanism by which curcumin regulates p21(Waf1/Cip1) expression remains unknown. Here, we report that transcription of the p21(Waf1/Cip1) gene is activated by early growth response-1 (Egr-1) independently of p53 in response to curcumin treatment in U-87MG human glioblastoma cells. Egr-1 is a transcription factor that helps regulate differentiation, growth, and apoptosis in many cell types. Egr-1 expression is induced by curcumin through extracellular signal-regulated kinase (ERK) and c-Jun NH(2)-terminal kinase (JNK), but not the p38, mitogen-activated protein kinase (MAPK) pathways, which mediate the transactivation of Elk-1. Transient expression of Egr-1 enhanced curcumin-induced p21(Waf1/Cip1) promoter activity, whereas suppression of Egr-1 expression by small interfering RNA abrogated the ability of curcumin to induce p21(Waf1/Cip1) promoter activity. In addition, stable knockdown of Egr-1 expression in U-87MG cells suppressed curcumin-induced p21 expression. Our results indicate that ERK and JNK MAPK/Elk-1/Egr-1 signal cascade is required for p53-independent transcriptional activation of p21(Waf1/Cip1) in response to curcumin in U-87MG human glioblastoma cells.

Combined effects of radiotherapy and endostatin gene therapy in melanoma tumor model

PEgr-Endostatin-EGFP plasmid was constructed to investigate its expression properties induced by ionizing irradiation and the effect of pEgr-Endostatin-EGFP gene-radiotherapy on melanoma tumor-bearing mice. The pEgr-Endostatin-EGFP plasmid was transfected into B16 cell line with liposome. The expression property of endostatin was investigated by RT-PCR and that of EGFP was detected by flow cytometry. Tumor-bearing mice were treated by the plasmid injection and 2 Gy X-irradiation of three fractions. Tumor growth was observed for 18 days after treatment. Change of tumor capillary formation was measured with histochemistry assay at the end of the experiment. The expression of GFP in B16 melanoma cells was detected after X-irradiation with 0.05-20 Gy. Time-course studies showed that the expression of GFP in B16 cells reached its peak at 8 h after irradiation with 2 Gy. The injection of pEgr-Endostatin-EGFP recombinant plasmid into the implanted B16 melanoma in C57BL/6J mice followed by local X-irradiation could significantly inhibit tumor growth with inhibition of intratumor micro-vessel density. The inhibitory effect of pEgr-Endostatin-EGFP gene-radiotherapy on the growth of B16 melanoma is correlated with the marked decrease of intratumoral vascularization. The present data point to the potential of an anti-angiogenic approach in gene-radiotherapy of cancer.

Promoter-independent regulation of vimentin expression in mammary epithelial cells by val(12)ras and TGFbeta

The 1,029 series of mammary epithelial cell lines (D6, GP+E, r3 and r3T) are progressively more transformed: the latter two by val(12)ras. These cell lines respond to TGFbeta by undergoing early events of epithelial-mesenchymal transition (EMT), including morphological changes and redistribution of E-cadherin. Tumors formed by r3T cells in the choroid of the eye express vimentin, a late marker of EMT, possibly in response to TGFbeta. In vitro, vimentin expression is induced in all the cell lines by TGFbeta treatment, whereas cytokeratin expression is only slightly affected. Surprisingly, ras transformation results in a 10-fold suppression of vimentin expression. Neither suppression of vimentin by ras transformation nor induction by TGFbeta is mediated by the vimentin promoter in r3T cells. In transient transfection assays, several human vimentin promoter constructs are more active in the low-expressing r3T cell line than in the vimentin-expressing mesenchymal cell line NIH3T3. In the r3T cells, there is no effect of TGFbeta treatment for 9 days on the activity of either promoter. Azacytidine treatment does not affect vimentin expression in either NIH3T3 or r3T, suggesting that promoter methylation is not the mechanism of suppression by ras. Finally, the half-life of the vimentin mRNA is similar in both the r3T cells and NIH3T3 cells. We conclude that the suppression of vimentin expression by ras, and the relief of this suppression by TGFbeta, occurs in a promoter-independent fashion, possibly through sequences in the first or second intron.

Amitriptyline induces early growth response-1 gene expression via ERK and JNK mitogen-activated protein kinase pathways in rat C6 glial cells

Astrocytes play important roles in guiding the construction of the nervous system, controlling extracellular ions and neurotransmitters, and regulating CNS synaptogenesis. Egr-1 is a transcription factor involved in neuronal differentiation and astrocyte cell proliferation. In this study, we investigated whether the tricyclic antidepressant (TCA) amitriptyline induces Egr-1 expression in astrocytes using rat C6 glioma cells as a model. We found that amitriptyline increased the expression of Egr-1 in a dose- and time-dependent manner. The amitriptyline-induced Egr-1 expression was mediated through serum response elements (SREs) in the Egr-1 promoter. SREs were activated by the Ets-domain transcription factor Elk-1 through the ERK and JNK mitogen-activated protein (MAP) kinase pathways. The inhibition of the ERK and JNK MAP kinase signals attenuated amitriptyline-induced transactivation of Gal4-Elk-1 and Egr-1 promoter activity. Our findings suggest that the induction of Egr-1 expression in astrocytes may be required to attain the therapeutic effects of antidepressant drugs.

Tamoxifen-induced activation of p21Waf1/Cip1 gene transcription is mediated by Early Growth Response-1 protein through the JNK and p38 MAP kinase/Elk-1 cascades in MDA-MB-361 breast carcinoma cells

Tamoxifen (TAM) is a synthetic non-steroidal anti-estrogen compound that is widely used as an effective chemotherapeutic agent for treatment and prevention of breast cancer. Unfortunately, prolonged treatment with TAM causes TAM-responsive tumors to become TAM resistant through an as-yet-unknown mechanism. To develop novel anti-breast cancer agents that are therapeutically superior to TAM, we must first fully understand the biological effects of TAM. In this study, we found that TAM treatment of MDA-MB-361 breast cancer cells activated p21Waf1/Cip1 gene transcription independently of p53. Furthermore, TAM-induced p21Waf1/Cip1 promoter activity was enhanced by transient expression of the gene encoding Early Growth Response-1 (Egr-1) protein, a transcription factor that plays an important role in cell growth and differentiation. The TAM-induced p21Waf1/Cip1 promoter activity was blocked by the expression of small interfering RNA (siRNA) targeted to Egr-1 mRNA. In addition, induction of Egr-1 expression by TAM occurred at the transcriptional level via Ets-domain transcription factor Elk-1 through the JNK and p38 mitogen-activated protein (MAP) kinase pathways. Inhibition of the JNK and p38 MAP kinase signals inhibited Egr-1-mediated p21Waf1/Cip1 promoter activity. We conclude that TAM stimulation of p21Waf1/Cip1 gene transcription in MDA-MB-361 cells depends largely on Elk-1-mediated Egr-1 expression induced by activation of the JNK and p38 MAP kinase pathways.

Haploinsufficiency of EGR1, a candidate gene in the del(5q), leads to the development of myeloid disorders

Loss of a whole chromosome 5 or a deletion of the long arm, del(5q), is a recurring abnormality in myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML). To identify a leukemia-related gene on chromosome 5, we previously delineated a 970-kb segment of 5q31 that is deleted in all patients examined, and prepared a transcript map of this region. EGR1 is a candidate tumor suppressor gene within the commonly deleted segment of 5q, and encodes a zinc finger transcription factor. To test the hypothesis that loss of function of Egr1 is an initiating event in the pathogenesis of AML/MDS, Egr1-deficient mice were treated with a potent DNA alkylating agent, N-ethyl-nitrosourea (ENU), to induce secondary cooperating mutations. Egr1(+/-) and Egr1(-/-) mice treated with ENU developed immature T-cell lymphomas (CD4(+), CD8(+)) or a myeloproliferative disorder (MPD) at increased rates and with shorter latencies than that of wild-type littermates. The MPD was characterized by an elevated white blood cell count, anemia, and thrombocytopenia with ineffective erythropoiesis. Biallelic mutations of Egr1 were not observed in MPDs in Egr1(+/-) mice. Our data suggest that haploinsufficiency for Egr1 plays a role in murine leukemogenesis, and in the development of AML/MDS characterized by abnormalities of chromosome 5.

The cytoskeleton-associated PDZ-LIM protein, ALP, acts on serum response factor activity to regulate muscle differentiation

In this report, an antisense RNA strategy has allowed us to show that disruption of ALP expression affects the expression of the muscle transcription factors myogenin and MyoD, resulting in the inhibition of muscle differentiation. Introduction of a MyoD expression construct into ALP-antisense cells is sufficient to restore the capacity of the cells to differentiate, illustrating that ALP function occurs upstream of MyoD. It is known that MyoD is under the control of serum response factor (SRF), a transcriptional regulator whose activity is modulated by actin dynamics. A dramatic reduction of actin filament bundles is observed in ALP-antisense cells and treatment of these cells with the actin-stabilizing drug jasplakinolide stimulates SRF activity and restores the capacity of the cells to differentiate. Furthermore, we show that modulation of ALP expression influences SRF activity, the level of its coactivator, MAL, and muscle differentiation. Collectively, these results suggest a critical role of ALP on muscle differentiation, likely via cytoskeletal regulation of SRF.

K-RasG12D expression induces hyperproliferation and aberrant signaling in primary hematopoietic stem/progenitor cells

Defining how cancer-associated mutations perturb signaling networks in stem/progenitor populations that are integral to tumor formation and maintenance is a fundamental problem with biologic and clinical implications. Point mutations in RAS genes contribute to many cancers, including myeloid malignancies. We investigated the effects of an oncogenic Kras(G12D) allele on phosphorylated signaling molecules in primary c-kit(+) lin(-/low) hematopoietic stem/progenitor cells. Comparison of wild-type and Kras(G12D) c-kit(+) lin(-/low) cells shows that K-Ras(G12D) expression causes hyperproliferation in vivo and results in abnormal levels of phosphorylated STAT5, ERK, and S6 under basal and stimulated conditions. Whereas Kras(G12D) cells demonstrate hyperactive signaling after exposure to granulocyte-macrophage colony-stimulating factor, we unexpectedly observe a paradoxical attenuation of ERK and S6 phosphorylation in response to stem cell factor. These studies provide direct biochemical evidence that cancer stem/progenitor cells remodel signaling networks in response to oncogenic stress and demonstrate that multi-parameter flow cytometry can be used to monitor the effects of targeted therapeutics in vivo. This strategy has broad implications for defining the architecture of signaling networks in primary cancer cells and for implementing stem cell-targeted interventions.

Suppression of PTEN expression during aggregation with retinoic acid in P19 mouse embryonal carcinoma cells

Apoptosis is thought to be involved in the maintenance of cellular homeostasis, as well as various pathological processes. However, little information is available about the regulation of apoptosis during the aggregation stage of P19 embryonal carcinoma (EC) cells. Here we report that aggregation-induced apoptosis is markedly attenuated by treatment with retinoic acid (RA). PTEN (phosphatase and tensin homolog deleted on chromosome 10) expression was down-regulated during the aggregation phase of P19 EC cells in the presence, but not in the absence, of RA. Suppression of PTEN expression during the aggregation was accompanied by increased phosphorylation of serine/threonine kinase Akt and glycogen synthase kinase-3beta (GSK-3beta). Our results suggest that RA attenuates the induction of apoptosis during the aggregation phase of P19 EC cells, probably by suppressing PTEN expression.