ZFP36 expression impairs glioblastoma cell lines viability and invasiveness by targeting multiple signal transduction pathways

Identification of a miRNA multi-targeting therapeutic strategy in glioblastoma

Glioblastoma (GBM) is a deadly and the most common primary brain tumor in adults. Due to their regulation of a high number of mRNA transcripts, microRNAs (miRNAs) are key molecules in the control of biological processes and are thereby promising therapeutic targets for GBM patients. In this regard, we recently reported miRNAs as strong modulators of GBM aggressiveness. Here, using an integrative and comprehensive analysis of the TCGA database and the transcriptome of GBM biopsies, we identified three critical and clinically relevant miRNAs for GBM, miR-17-3p, miR-222, and miR-340. In addition, we showed that the combinatorial modulation of three of these miRNAs efficiently inhibited several biological processes in patient-derived GBM cells of all these three GBM subtypes (Mesenchymal, Proneural, Classical), induced cell death, and delayed tumor growth in a mouse tumor model. Finally, in a doxycycline-inducible model, we observed a significant inhibition of GBM stem cell viability and a significant delay of orthotopic tumor growth. Collectively, our results reveal, for the first time, the potential of miR-17-3p, miR-222 and miR-340 multi-targeting as a promising therapeutic strategy for GBM patients.

Tristetraprolin: A cytosolic regulator of mRNA turnover moonlighting as transcriptional corepressor of gene expression

Tristetraprolin (TTP) is a nucleocytoplasmic 326 amino acid protein whose sequence is characterized by possessing two CCCH-type zinc finger domains. In the cytoplasm TTP function is to promote the degradation of mRNAs that contain adenylate/uridylate-rich elements (AREs). Mechanistically, TTP promotes the recruitment of poly(A)-specific deadenylases and exoribonucleases. By reducing the half-life of about 10% of all the transcripts in the cell TTP has been shown to participate in multiple cell processes that include regulation of gene expression, cell proliferation, metabolic homeostasis and control of inflammation and immune responses. However, beyond its role in mRNA decay, in the cell nucleus TTP acts as a transcriptional coregulator by interacting with chromatin modifying enzymes. TTP has been shown to repress the transactivation of NF-κB and estrogen receptor suggesting the possibility that it participates in the transcriptional regulation of hundreds of genes in human cells and its possible involvement in breast cancer progression. In this review, we discuss the cytoplasmic and nuclear functions of TTP and the effect of the dysregulation of its protein levels in the development of human diseases. We suggest that TTP be classified as a moonlighting tumor supressor protein that regulates gene expression through two different mechanims; the decay of ARE-mRNAs and a transcriptional coregulatory function.

Tristetraprolin, a Potential Safeguard Against Carcinoma: Role in the Tumor Microenvironment

Tristetraprolin (TTP), a well-known RNA-binding protein, primarily affects the expression of inflammation-related proteins by binding to the targeted AU-rich element in the 3' untranslated region after transcription and subsequently mediates messenger RNA decay. Recent studies have focused on the role of TTP in tumors and their related microenvironments, most of which have referred to TTP as a potential tumor suppressor involved in regulating cell proliferation, apoptosis, and metastasis of various cancers, as well as tumor immunity, inflammation, and metabolism of the microenvironment. Elevated TTP expression levels could aid the diagnosis and treatment of different cancers, improving the prognosis of patients. The aim of this review is to describe the role of TTP as a potential safeguard against carcinoma.

Chemoprevention and therapeutic role of essential oils and phenolic compounds: Modeling tumor microenvironment in glioblastoma

Glioblastoma (GBM) is the most common primary tumor of the central nervous system. Current treatments available for GBM entails surgical resection followed by temozolomide chemotherapy and/or radiotherapy, which are associated with multidrug resistance and severe side effects. While this treatment could yield good results, in almost all cases, patients suffer from relapse, which leads to reduced survival rates. Thus, therapeutic approaches with improved efficiency and reduced off-target risks are needed to overcome these problems. Regarding this, natural products appear as a safe and attractive strategy as chemotherapeutic agents or adjuvants in the treatment of GBM. Besides the increasing role of natural compounds for chemoprevention of GBM, it has been proposed to prevent carcinogenesis and metastasis of GBM. Numerous investigations showed that natural products are able to inhibit proliferation and angiogenesis, to induce apoptosis, and to target GBM stem cells, which are associated with tumor development and recurrence. This review gives a timely and comprehensive overview of the current literature regarding chemoprevention and therapy of GBM by natural products with a focus on essential oils and phenolic compounds and their molecular mechanisms.

Tristetraprolin destabilizes NOX2 mRNA and protects dopaminergic neurons from oxidative damage in Parkinson's disease

Tristetraprolin (TTP), an RNA-binding protein encoded by the ZFP36 gene, is vital for neural differentiation; however, its involvement in neurodegenerative diseases such as Parkinson's disease (PD) remains unclear. To explore the role of TTP in PD, an in vitro 1-methyl-4-phenylpyridinium (MPP⁺ ) cell model and an in vivo 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) of PD were used. Transfection of small interfering (si)-TTP RNA upregulated pro-oxidative NOX2 expression and ROS formation, downregulated anti-oxidative GSH and SOD activity；si-TTP upregulated pro-apoptotic cleaved-caspase-3 expression, and downregulated antiapoptotic Bcl-2 expression; while overexpression (OE)-TTP lentivirus caused opposite effects. Through database prediction, luciferase experiment, RNA immunoprecipitation (RIP), and mRNA stability analysis, we evaluated the potential binding sites of TTP to 3'-untranslated regions (3'-UTR) of NOX2 mRNA. TTP affected the NOX2 luciferase activity by binding to two sites in the NOX2 3'-UTR. RIP-qPCR confirmed TTP binding to both sites, with a higher affinity for site-2. In addition, TTP reduced the NOX2 mRNA stability. si-NOX2 and antioxidant N-acetyl cysteine (NAC) reversed si-TTP-induced cell apoptosis. In MPTP-treated mice, TTP expression increased and was co-located with dopaminergic neurons. TTP also inhibited NOX2 and decreased the oxidative stress in vivo. In conclusion, TTP protects against dopaminergic oxidative injury by promoting NOX2 mRNA degradation in the MPP⁺ /MPTP model of PD, suggesting that TTP could be a potential therapeutic target for regulating the oxidative stress in PD.

The Tristetraprolin Family of RNA-Binding Proteins in Cancer: Progress and Future Prospects

Post-transcriptional regulation of gene expression plays a key role in cellular proliferation, differentiation, migration, and apoptosis. Increasing evidence suggests dysregulated post-transcriptional gene expression as an important mechanism in the pathogenesis of cancer. The tristetraprolin family of RNA-binding proteins (RBPs), which include Zinc Finger Protein 36 (ZFP36; commonly referred to as tristetraprolin (TTP)), Zinc Finger Protein 36 like 1 (ZFP36L1), and Zinc Finger Protein 36 like 2 (ZFP36L2), play key roles in the post-transcriptional regulation of gene expression. Mechanistically, these proteins function by binding to the AU-rich elements within the 3′-untranslated regions of their target mRNAs and, in turn, increasing mRNA turnover. The TTP family RBPs are emerging as key regulators of multiple biological processes relevant to cancer and are aberrantly expressed in numerous human cancers. The TTP family RBPs have tumor-suppressive properties and are also associated with cancer prognosis, metastasis, and resistance to chemotherapy. Herein, we summarize the various hallmark molecular traits of cancers that are reported to be regulated by the TTP family RBPs. We emphasize the role of the TTP family RBPs in the regulation of trait-associated mRNA targets in relevant cancer types/cell lines. Finally, we highlight the potential of the TTP family RBPs as prognostic indicators and discuss the possibility of targeting these TTP family RBPs for therapeutic benefits.

Enrichment of Aldolase C Correlates with Low Non-Mutated IDH1 Expression and Predicts a Favorable Prognosis in Glioblastomas

The aldolases family is one of the main enzymes involved in the process of glycolysis. Aldolase C (ALDOC), which belongs to the aldolase family, is found in normal brain tissue and is responsible for the repair of injured tissue. However, the role of ALDOC in glioblastoma remains unclear. In this study, we data-mined in silico databases to evaluate aldolase family members’ mRNA expression in glioblastoma patient cohorts for determining its prognostic values. After that, we also performed immunohistochemical stain (IHC) analysis to evaluate protein expression levels of ALDOC in glioblastoma tissues. From The Cancer Genome Atlas (TCGA) database analyses, higher mRNA expression levels in normal brain tissue compared to glioblastoma was observed. In addition, compared to low-grade glioma, ALDOC expression was significantly downregulated in high-grade glioblastoma. Besides, the expression level of ALDOC was associated with molecular subtypes of glioblastomas and recurrent status in several data sets. In contrast, aldolase A (ALDOA) and aldolase B (ALDOB) revealed no significant prognostic impacts in the glioblastoma cohorts. Furthermore, we also proved that ALDOC mRNA and protein expression inversely correlated with non-mutated IDH1 expressions in glioblastoma patient cohorts. Additionally, the concordance of low ALDOC and high non-mutated IDH1 expressions predicted a stronger poor prognosis in glioblastoma patients compared to each of above tests presented alone. The plausible ALDOC and IDH1 regulatory mechanism was further elucidated. Our results support high ALDOC expression in glioblastomas that might imply the mutated status of IDH1, less possibility of mesenchymal subtype, and predict a favorable prognosis.

Musashi-1 Enhances Glioblastoma Migration by Promoting ICAM1 Translation

Glioblastoma multiforme (GBM) is a lethal brain tumor with a mean survival time of 1 year. One major reason for therapeutic failure is that GBM cells have an extraordinary capacity to invade normal brain tissue beyond the surgical margin, accounting for the lack of treatment efficacy. GBM cells that can infiltrate into the healthy brain possess tumor properties of stemness and invasion, and previous studies demonstrate that Musashi-1 (MSI1), a neural stem cell marker, plays an important role in the maintenance of stem cell status, cellular differentiation, and tumorigenesis in cancers. By analyzing neuronal progenitor cell markers and stemness genes, we predicted that MSI1 might be an important factor in GBM pathogenesis. Because inflammation aids in the proliferation and survival of malignant cells, the inflammatory microenvironment also promotes GBM invasion, and intercellular adhesion molecule-1 (ICAM1), a member of the immunoglobulin superfamily, is involved in inflammation. Our results indicate that the above phenomena are likely due to MSI1 upregulation, which occurred simultaneously with higher expression of ICAM1 in GBM cells. Indeed, MSI1 knockdown effectively suppressed ICAM1 expression and blocked GBM cell motility and invasion, whereas overexpressing ICAM1 reversed these effects. According to RNA immunoprecipitation assays, MSI1-mediated mRNA interactions promote ICAM1 translation. Finally, immunohistochemical analysis showed MSI1 and ICAM-1 to be coexpressed at high levels in GBM tissues. Thus, the MSI1/ICAM1 pathway plays an important role in oncogenic resistance, including increased tumor invasion, and MSI1/ICAM1 may be a target for GBM treatment.

Roles of Tristetraprolin in Tumorigenesis

Genetic loss or mutations in tumor suppressor genes promote tumorigenesis. The prospective tumor suppressor tristetraprolin (TTP) has been shown to negatively regulate tumorigenesis through destabilizing the messenger RNAs of critical genes implicated in both tumor onset and tumor progression. Regulation of TTP has therefore emerged as an important issue in tumorigenesis. Similar to other tumor suppressors, TTP expression is frequently downregualted in various human cancers, and its low expression is correlated with poor prognosis. Additionally, disruption in the regulation of TTP by various mechanisms results in the inactivation of TTP protein or altered TTP expression. A recent study showing alleviation of Myc-driven lymphomagenesis by the forced expression of TTP has shed light on new therapeutic avenues for cancer prevention and treatment through the restoration of TTP expression. In this review, we summarize key oncogenes subjected to the TTP-mediated mRNA degradation, and discuss how dysregulation of TTP can contribute to tumorigenesis. In addition, the control mechanism underlying TTP expression at the posttranscriptional and posttranslational levels will be discussed.

PIM2 interacts with tristetraprolin and promotes breast cancer tumorigenesis

Tristetraprolin (TTP) is an AU‐rich element‐binding protein that regulates mRNA stability and plays important roles in cancer. The mechanisms by which TTP is regulated in breast cancer are poorly understood. Using multiple biochemical approaches, we found that proviral insertion in murine lymphomas 2 (PIM2) is a novel binding partner of TTP. Interestingly, PIM2 decreased TTP protein levels independent of its kinase activity. PIM2 instead targeted TTP protein for degradation via the ubiquitin‐proteasome pathway. Furthermore, immunohistochemical staining showed that PIM2 and TTP protein levels were negatively correlated in human breast cancer samples. Indeed, PIM2 overexpression de‐repressed TTP‐mediated inhibition of breast cancer cell proliferation and migration in vitro and promoted breast tumor xenograft growth in vivo. These findings demonstrate an important role for the PIM2‐TTP complex in breast cancer tumorigenesis, suggesting that PIM2 may represent a potential therapeutic target for breast cancer treatment.

Musashi-1 promotes chemoresistant granule formation by PKR/eIF2α signalling cascade in refractory glioblastoma

Musashi-1 (MSI1), one of the RNA-binding proteins, is abundantly found not only in neural stem cells but also in several cancer tissues and has been reported to act as a positive regulator of cancer progression. Growing evidence indicates that PKR and eIF2α play pivotal roles in the stimulation of stress granule formation as well as in the subsequent translation modulation in response to stressful conditions; however, little is known about whether MSI1 is involved in this PKR/eIF2α cancer stem cell-enhancing machinery. In this study, we demonstrated that MSI1 promotes human glioblastoma multiforme (GBM) stem cells and enhances chemoresistance when exposed to sublethal stress. The overexpression of MSI1 leads to a protective effect in mitigating drug-induced cell death, thus facilitating the formation of chemoresistant stress granules (SGs) in response to arsenic trioxide (ATO) treatment. SG components, such as PKR and eIF2α, were dominantly activated and assembled, while ATO was engaged. The activated PKR and eIF2α contribute to the downstream enhancement of stem cell genes, thereby promoting the progression of GBM. The silencing of MSI1 or PKR both obviously withdrew the phenomena. Taken together, our findings indicate that MSI1 plays a leading role in stress granule formation that grants cancer stem cell properties and chemoresistant stress granules in GBM, in response to stressful conditions via the PKR/eIF2α signalling cascade.

Loss of ZFP36 expression in colorectal cancer correlates to wnt/ ß-catenin activity and enhances epithelial-to-mesenchymal transition through upregulation of ZEB1, SOX9 and MACC1

The mRNA-destabilizing protein ZFP36 has been previously described as a tumor suppressor whose expression is lost during colorectal cancer development. In order to evaluate its role in this disease, we restored ZFP36 expression in different cell contexts, showing that the presence of this protein impairs the epithelial-to-mesenchymal transition (EMT) and induces a higher susceptibility to anoikis. Consistently, we found that ZFP36 inhibits the expression of three key transcription factors involved in EMT: ZEB1, MACC1 and SOX9. Finally, we observed for the first time that its expression negatively correlates with the activity of Wnt/β-catenin pathway, which is constitutively activated in colorectal cancer. This evidence provides a clue on the mechanism leading to the loss of ZFP36 in CRC.

MicroRNA-27b up-regulated by human papillomavirus 16 E7 promotes proliferation and suppresses apoptosis by targeting polo-like kinase2 in cervical cancer

The infection with high-risk human papillomavirus is linked to cervical cancer, nevertheless, the role of miRNAs regulated by HPV oncogenes in cancer progression remain largely unknown. Here, we knocked down endogenous E6/E7 in HPV16-positive CaSki cell lines, screened differences in miRNA expression profile with control using miRNA array. 38 miRNAs were down-regulated and 6 miRNAs were up-regulated in the E6/E7 silenced CaSki cells (>2-fold changes with P <0.05). The levels of miR-27b, miR-20a, miR-24, miR-93, and miR-106b were verified by qPCR in E6/E7 silenced CaSki and SiHa cells. MiR-27b, up-regulated by E7, promoted CaSki and SiHa cell proliferation and invasion, inhibit paclitaxel-induced apoptosis. Dual-luciferase experiment confirmed miR-27b down-regulated its target gene PLK2 through the “seed regions”. The tumor suppressor PLK2 inhibited SiHa cell proliferation, reduced cell viability, and promoted paclitaxel/cisplatin -induced apoptosis. Furthermore, DGCR8 was found to mediate the up-regulation of miR-27b by HPV16 E7. Our study demonstrated that HPV16 E7 could increase DGCR8 to promote the generation of miR-27b, which accelerated cell proliferation and inhibited paclitaxel-induced cell apoptosis through down-regulating PLK2. These findings provide an insight into the interaction network of viral oncogene, miR-27b and PLK2, and support the potential strategies using antisense nucleic acid of miR-27b for therapy of cervical cancer in the future.

Low tristetraprolin expression promotes cell proliferation and predicts poor patients outcome in pancreatic cancer

Tristetraprolin (also known as TTP, TIS11, ZFP36, and Nup475) is a well-characterized tumor suppressor that is down-regulated in several tumor types. In the current study, we found that TTP expression was markedly reduced in pancreatic cancer samples as compared to matched normal tissues. Low TTP level was associated with age (P=0.037), tumor size (P=0.008), tumor differentiation (P=0.004), postoperative T stage (pT stage, P<0.001), postoperative N stage (pN stage, P=0.008) and TNM stage (P<0.001). Moreover, low TTP expression predicted reduced survival rates and poor patient outcome. We also found that TTP impairs pancreatic cancer cell proliferation both in vivo and in vitro. Fluorescence Activated Cell Sorting (FACS) assay showed that TTP over-expression both increases apoptosis and decreases proliferation in pancreatic cancer cells. RNA-sequencing analysis showed that TTP over-expression downregulates several tumor-related factors, including Pim-1 and IL-6. Our findings indicate that TTP could serve as a potential prognostic indicator in pancreatic cancer.

Interaction with Pyruvate Kinase M2 Destabilizes Tristetraprolin by Proteasome Degradation and Regulates Cell Proliferation in Breast Cancer

Pyruvate kinase M2 (PKM2), which is predominantly expressed in most cancers, plays a key role in the Warburg effect. However, how PKM2 functions as a tumor supportive protein has not been fully elucidated. Here, we identified tristetraprolin (TTP), an AU-rich, element-binding protein that regulates mRNA stability, as a new binding partner of PKM2. Our data reveal that PKM2 suppresses TTP protein levels by promoting its phosphorylation, ubiquitination, and proteasome degradation, reducing its mRNA turnover ability and ultimately impairing cell viability in breast cancer cells. The p38/mitogen-activated protein kinase (MAPK) pathway might be involved in PKM2-mediated TTP degradation, while treatment with the p38 inhibitor or siRNA abolished PKM2-induced TTP protein degradation. These findings demonstrate that PKM2-TTP association is crucial for regulating breast cancer cell proliferation and is therefore a potential therapeutic target in cancer.

RNA binding proteins as regulators of immune cell biology

Sequence-specific RNA binding proteins (RBP) are important regulators of the immune response. RBP modulate gene expression by regulating splicing, polyadenylation, localization, translation and decay of target mRNAs. Increasing evidence suggests that RBP play critical roles in the development, activation and function of lymphocyte populations in the immune system. This review will discuss the post-transcriptional regulation of gene expression by RBP during lymphocyte development, with particular focus on the Tristetraprolin family of RBP.

ZFP36 stabilizes RIP1 via degradation of XIAP and cIAP2 thereby promoting ripoptosome assembly

Background

ZFP36 is an mRNA binding protein that exerts anti-tumor activity in glioblastoma by triggering cell death, associated to an increase in the stability of the kinase RIP1.

Methods

We used cell death assays, size exclusion chromatography, Co-Immunoprecipitation, shRNA lentivectors and glioma neural stem cells to determine the effects of ZFP36 on the assembly of a death complex containing RIP1 and on the induction of necroptosis.

Results

Here we demonstrate that ZFP36 promotes the assembly of the death complex called Ripoptosome and induces RIP1-dependent death. This involves the depletion of the ubiquitine ligases cIAP2 and XIAP and leads to the association of RIP1 to caspase-8 and FADD. Moreover, we show that ZFP36 controls RIP1 levels in glioma neural stem cell lines.

Conclusions

We provide a molecular mechanism for the tumor suppressor role of ZFP36, and the first evidence for Ripoptosome assembly following ZFP36 expression. These findings suggest that ZFP36 plays an important role in RIP1-dependent cell death in conditions where IAPs are depleted.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1388-5) contains supplementary material, which is available to authorized users.

Tristetraprolin inhibits the growth of human glioma cells through downregulation of urokinase plasminogen activator/urokinase plasminogen activator receptor mRNAs

Urokinase plasminogen activator (uPA) and urokinase plasminogen activator receptor (uPAR) play a major role in the infiltrative growth of glioblastoma. Downregulatoion of the uPA and uPAR has been reported to inhibit the growth glioblastoma. Here, we demonstrate that tristetraprolin (TTP) inhibits the growth of U87MG human glioma cells through downregulation of uPA and uPAR. Our results show that expression level of TTP is inversely correlated with those of uPA and uPAR in human glioma cells and tissues. TTP binds to the AU-rich elements within the 3' untranslated regions of uPA and uPAR and overexpression of TTP decreased the expression of uPA and uPAR through enhancing the degradation of their mRNAs. In addition, overexpression of TTP inhibited the growth and invasion of U87MG cells. Our findings implicate that TTP can be used as a promising therapeutic target to treat human glioma.

PIM kinases: an overview in tumors and recent advances in pancreatic cancer

The PIM kinases represent a family of serine/threonine kinases, which is composed of three different members (PIM1, PIM2 and PIM3). Aberrant expression of PIM kinases is observed in variety of tumors, including pancreatic cancer. The PIM kinases play pivotal roles in the regulation of cell cycle, apoptosis, properties of stem cells, metabolism, autophagy, drug resistance and targeted therapy. The roles of PIM kinases in pancreatic cancer include the regulation of proliferation, apoptosis, cell cycle, formation, angiogenesis and prediction prognosis. Blocking the activities of PIM kinases could prevent pancreatic cancer development. PIM kinases may be a novel target for cancer therapy.

Steering tumor progression through the transcriptional response to growth factors and stroma

Tumor progression can be understood as a collaborative effort of mutations and growth factors, which propels cell proliferation and matrix invasion, and also enables evasion of drug-induced apoptosis. Concentrating on EGFR, we discuss downstream signaling and the initiation of transcriptional events in response to growth factors. Specifically, we portray a wave-like program, which initiates by rapid disappearance of two-dozen microRNAs, followed by an abrupt rise of immediate early genes (IEGs), relatively short transcripts encoding transcriptional regulators. Concurrent with the fall of IEGs, some 30-60 min after stimulation, a larger group, the delayed early genes, is up-regulated and its own fall overlaps the rise of the final wave of late response genes. This late wave persists and determines long-term phenotype acquisition, such as invasiveness. Key regulatory steps in the orderly response to growth factors provide a trove of potential oncogenes and tumor suppressors.

Systematic review of protein biomarkers of invasive behavior in glioblastoma

Glioblastoma (GBM) is an aggressive and incurable brain tumor with a grave prognosis. Recurrence is inevitable even with maximal surgical resection, in large part because GBM is a highly invasive tumor. Invasiveness also contributes to the failure of multiple cornerstones of GBM therapy, including radiotherapy, temozolomide chemotherapy, and vascular endothelial growth factor blockade. In recent years there has been significant progress in the identification of protein biomarkers of invasive phenotype in GBM. In this article, we comprehensively review the literature and survey a broad spectrum of biomarkers, including proteolytic enzymes, extracellular matrix proteins, cell adhesion molecules, neurodevelopmental factors, cell signaling and transcription factors, angiogenic effectors, metabolic proteins, membrane channels, and cytokines and chemokines. In light of the marked variation seen in outcomes in GBM patients, the systematic use of these biomarkers could be used to form a framework for better prediction, prognostication, and treatment selection, as well as the identification of molecular targets for further laboratory investigation and development of nascent, directed therapies.

CPEB1 regulates the expression of MTDH/AEG-1 and glioblastoma cell migration

Cytoplasmic polyadenylation element-binding protein 1 (CPEB1) is an mRNA-binding protein present in both neurons and glia. CPEB1 is capable of both repressing mRNA translation and activating it depending upon its phosphorylation state. CPEB1-bound mRNAs are held in translational dormancy until CPEB1 is phosphorylated, leading to the cytoplasmic polyadenylation of the bound mRNA that triggers translation. Here, we show that CPEB1 can bind to and regulate translation of the mRNA-encoding metadherin (MTDH, also known as AEG-1 and Lyric) in the rat glioblastoma cell line CNS1. MTDH/AEG-1 is being revealed as a critical signaling molecule in tumor progression, playing roles in invasion, metastasis, and chemoresistance. By using a mutant of CPEB1 that cannot be phosphorylated (thereby holding target mRNAs in translational arrest), we show that inhibiting CPEB1-mediated translation blocks MTDH/AEG-1 expression in vitro and inhibits glioblastomas tumor growth in vivo. CPEB1-mediated translation is likely to impact several signaling pathways that may promote tumor progression, but we present evidence suggesting a role in directed cell migration in glioblastoma cells. In addition, reporter mRNA containing CPEB1-binding sites is transported to the leading edge of migrating cells and translated, whereas the same mRNA with point mutations in the binding sites is synthesized perinuclearly. Our findings show that CPEB1 is hyperactive in rat glioblastoma cells and is regulating an important cohort of mRNAs whose increased translation is fueling the progression of tumor proliferation and dispersal in the brain. Thus, targeting CPEB1-mediated mRNA translation might be a sound therapeutic approach.

Cell of origin determines clinically relevant subtypes of MLL-rearranged AML

Mixed lineage leukemia (MLL)-fusion proteins can induce acute myeloid leukemias (AMLs) from either hematopoietic stem cells (HSCs) or granulocyte-macrophage progenitors (GMPs), but it remains unclear whether the cell of origin influences the biology of the resultant leukemia. MLL-AF9-transduced single HSCs or GMPs could be continuously replated, but HSC-derived clones were more likely than GMP-derived clones to initiate AML in mice. Leukemia stem cells derived from either HSCs or GMPs had a similar immunophenotype consistent with a maturing myeloid cell (LGMP). Gene expression analyses demonstrated that LGMP inherited gene expression programs from the cell of origin including high-level Evi-1 expression in HSC-derived LGMP. The gene expression signature of LGMP derived from HSCs was enriched in poor prognosis human MLL-rearranged AML in three independent data sets. Moreover, global 5'-mC levels were elevated in HSC-derived leukemias as compared with GMP-derived leukemias. This mirrored a difference seen in 5'-mC between MLL-rearranged human leukemias that are either EVI1 positive or EVI1 negative. Finally, HSC-derived leukemias were more resistant to chemotherapy than GMP-derived leukemias. These data demonstrate that the cell of origin influences the gene expression profile, the epigenetic state and the drug response in AML, and that these differences can account for clinical heterogeneity within a molecularly defined group of leukemias.