Cell cycle regulation of NF-kappa b-binding activity in cells from human glioblastomas

Corylin inhibits the progression of Non-small cell lung cancer cells by regulating NF-κB signaling pathway via targeting p65

BACKGROUND

Lung cancer is characterized by high-risk and high mortality, among which non-small cell lung cancer (NSCLC) conquers a dominant position. Previous studies have reported that corylin has anti-inflammatory, anti-oxidant, and anti-tumor effects; however, its role in NSCLC cells remains unclear.

HYPOTHESIS

Corylin inhibits the progression of NSCLC cells.

METHODS

A lentivector NF-κB luciferase reporter was constructed by molecular cloning. Corylin was screened and identified as an NF-κB pathway inhibitor by luciferase reporter assay. Corylin inhibited the expression of NF-κB downstream genes, which was detected by qRT-PCR. The effect of corylin on NSCLC cells was detected by colony formation assay, cell apoptosis, cell proliferation, in vitro invasion, and cell scratch assay. Corylin inhibited p65 nuclear translocation and was detected by molecular docking, immunofluorescence assay, and Western blot analysis.

RESULTS

We constructed a lentiviral expression vector, containing an NF-κB luciferase reporter and established a stable A549 cell line for its expression. Using this cell line, corylin was screened and identified as an NF-κB pathway inhibitor. It was found that corylin inhibited the expression of NF-κB downstream genes and inhibited the proliferation and migration of NSCLC cells. Meanwhile, it was also found that corylin significantly reversed the increased proliferation of NSCLC cell lines induced by p65 overexpression. Molecular docking analysis showed that corylin could bind to p65 by hydrogen bonding. Further study showed that corylin inhibited the NF-κB signaling pathway by blocking p65 nuclear translocation.

CONCLUSIONS

Our study screened and identified corylin as an NF-κB inhibitor and elucidated the molecular mechanism by which corylin inhibits the growth of NSCLC cells. The present study provides a novel strategy for improving the prognosis and treatment of NSCLC patients.

An NF-κB- and Therapy-Related Regulatory Network in Glioma: A Potential Mechanism of Action for Natural Antiglioma Agents

High-grade gliomas are among the most aggressive malignancies, with significantly low median survival. Recent experimental research in the field has highlighted the importance of natural substances as possible antiglioma agents, also known for their antioxidant and anti-inflammatory action. We have previously shown that natural substances target several surface cluster of differentiation (CD) markers in glioma cells, as part of their mechanism of action. We analyzed the genome-wide NF-κB binding sites residing in consensus regulatory elements, based on ENCODE data. We found that NF-κB binding sites reside adjacent to the promoter regions of genes encoding CD markers targeted by antiglioma agents (namely, CD15/FUT4, CD28, CD44, CD58, CD61/SELL, CD71/TFRC, and CD122/IL2RB). Network and pathway analysis revealed that the markers are associated with a core network of genes that, altogether, participate in processes that associate tumorigenesis with inflammation and immune evasion. Our results reveal a core regulatory network that can be targeted in glioblastoma, with apparent implications in individuals that suffer from this devastating malignancy.

The Curcumin Analog C-150, Influencing NF-κB, UPR and Akt/Notch Pathways Has Potent Anticancer Activity In Vitro and In Vivo

C-150 a Mannich-type curcumin derivative, exhibited pronounced cytotoxic effects against eight glioma cell lines at micromolar concentrations. Inhibition of cell proliferation by C-150 was mediated by affecting multiple targets as confirmed at transcription and protein level. C-150 effectively reduced the transcription activation of NFkB, inhibited PKC-alpha which are constitutively over-expressed in glioblastoma. The effects of C-150 on the Akt/ Notch signaling were also demonstrated in a Drosophila tumorigenesis model. C-150 reduced the number of tumors in Drosophila with similar efficacy to mitoxantrone. In an in vivo orthotopic glioma model, C-150 significantly increased the median survival of treated nude rats compared to control animals. The multi-target action of C-150, and its preliminary in vivo efficacy would render this curcumin analogue as a potent clinical candidate against glioblastoma.

Withania somnifera Suppresses Tumor Growth of Intracranial Allograft of Glioma Cells

Gliomas are the most frequent type of primary brain tumor in adults. Their highly proliferative nature, complex cellular composition, and ability to escape therapies have confronted investigators for years, hindering the advancement toward an effective treatment. Agents that are safe and can be administered as dietary supplements have always remained priority to be most feasible for cancer therapy. Withania somnifera (ashwagandha) is an essential ingredient of Ayurvedic preparations and is known to eliminate cancer cells derived from a variety of peripheral tissues. Although our previous studies have addressed the in vitro anti-proliferative and differentiation-inducing properties of ashwagandha on neuronal cell lines, in vivo studies validating the same are lacking. While exploring the mechanism of its action in vitro, we observed that the ashwagandha water extract (ASH-WEX) induced the G2/M phase blockade and caused the activation of multiple pro-apoptotic pathways, leading to suppression of cyclin D1, bcl-xl, and p-Akt, and reduced the expression of polysialylated form of neural cell adhesion molecule (PSA-NCAM) as well as the activity of matrix metalloproteinases. ASH-WEX reduced the intracranial tumor volumes in vivo and suppressed the tumor-promoting proteins p-nuclear factor kappa B (NF-κB), p-Akt, vascular endothelial growth factor (VEGF), heat shock protein 70 (HSP70), PSA-NCAM, and cyclin D1 in the rat model of orthotopic glioma allograft. Reduction in glial fibrillary acidic protein (GFAP) and upregulation of mortalin and neural cell adhesion molecule (NCAM) expression specifically in tumor-bearing tissue further indicated the anti-glioma efficacy of ASH-WEX in vivo. Combining this enhanced understanding of the molecular mechanisms of ASH-WEX in glioma with in vivo model system offers new opportunities to develop therapeutic strategy for safe, specific, and effective formulations for treating brain tumors.

Biphasic effects of luteolin on interleukin-1β-induced cyclooxygenase-2 expression in glioblastoma cells

Success in developing therapeutic approaches to target brain tumor-associated inflammation in patients has been limited. Given that the inflammatory microenvironment is a hallmark signature of solid tumor development, anti-inflammatory targeting strategies have been envisioned as preventing glioblastoma initiation or progression. Consumption of foods from plant origin is associated with reduced risk of developing cancers, a chemopreventive effect that is, in part, attributed to their high content of phytochemicals with potent anti-inflammatory properties. We explored whether luteolin, a common flavonoid in many types of plants, may inhibit interleukin (IL)-1β function induction of the inflammation biomarker cyclooxygenase (COX)-2. We found that IL-1β triggered COX-2 expression in U-87 glioblastoma cells and synergized with luteolin to potentiate or inhibit that induction in a biphasic manner. Luteolin pretreatment of cells inhibited IL-1β-mediated phosphorylation of inhibitor of κB, nuclear transcription factor-κB (NF-κB) p65, extracellular signal-regulated kinase-1/2, and c-Jun amino-terminal kinase in a concentration-dependent manner. Luteolin also inhibited AKT phosphorylation and survivin expression, while it triggered both caspase-3 cleavage and expression of glucose-regulated protein 78. These effects were all potentiated by IL-1β, in part through increased nuclear translocation of NF-κB p65. Finally, luteolin was able to reduce IL-1 receptor gene expression, and treatment with IL-1 receptor antagonist or gene silencing of IL-1 receptor prevented IL-1β/luteolin-induced COX-2 expression. Our results document a novel adaptive cellular response to luteolin, which triggers anti-survival and anti-inflammatory mechanisms that contribute to the chemopreventive properties of this diet-derived molecule.

Infection by agnoprotein-negative mutants of polyomavirus JC and SV40 results in the release of virions that are mostly deficient in DNA content

BACKGROUND

Human polyomavirus JC (JCV) is the etiologic agent of a brain disease, known as progressive multifocal leukoencephalopathy (PML). The JCV genome encodes a small multifunctional phospho-protein, agnoprotein, from the late coding region of the virus, whose regulatory functions in viral replication cycle remain elusive. In this work, the functional role of JCV and SV40 agnoproteins in virion release was investigated using a point mutant (Pt) of each virus, where the ATG codon of agnoprotein was mutated to abrogate its expression.

RESULTS

Analysis of both viral protein expression and replication using Pt mutant of each virus revealed that both processes were substantially down-regulated in the absence of agnoprotein compared to wild-type (WT) virus. Complementation studies in cells, which are constitutively expressing JCV agnoprotein and transfected with the JCV Pt mutant genome, showed an elevation in the level of viral DNA replication near to that observed for WT. Constitutive expression of large T antigen was found to be not sufficient to compensate the loss of agnoprotein for efficient replication of neither JCV nor SV40 in vivo. Examination of the viral release process for both JCV and SV40 Pt mutants showed that viral particles are efficiently released from the infected cells in the absence of agnoprotein but were found to be mostly deficient in viral DNA content.

CONCLUSIONS

The results of this study provide evidence that agnoprotein plays an important role in the polyomavirus JC and SV40 life cycle. Infection by agnoprotein-negative mutants of both viruses results in the release of virions that are mostly deficient in DNA content.

NFκB/p53 crosstalk-a promising new therapeutic target

The transcription factors p53 and NFκB determine cellular fate and are involved in the pathogenesis of most-if not all-cancers. The crosstalk between these transcription factors becomes increasingly appreciated as an important mechanism operative during all stages of tumorigenesis, metastasis, and immunological surveillance. In this review, we summarize molecular mechanisms regulating cross-signaling between p53 and NFκB proteins and how dysregulated interactions between p53 and NFκB family members contribute to oncogenesis. We furthermore analyze how such signaling modules represent targets for the design of novel intervention strategies using established compounds and powerful combination therapies.

Cross talk between stimulated NF-kappaB and the tumor suppressor p53

Nuclear factor-kappaB (NF-kappaB) and p53 critically determine cancer development and progression. Defining the cross talk between these transcription factors can expand our knowledge on molecular mechanisms of tumorigenesis. Here, we show that induction of replicational stress activates NF-kappaB p65 and triggers its interaction with p53 in the nucleus. Experiments with knockout cells show that p65 and p53 are both required for enhanced NF-kappaB activity during S-phase checkpoint activation involving ataxia-telangiectasia mutated and checkpoint kinase-1. Accordingly, the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) also triggers formation of a transcriptionally active complex containing nuclear p65 and p53 on kappaB response elements. Gene expression analyses revealed that, independent of NF-kappaB activation in the cytosol, TNF-induced NF-kappaB-directed gene expression relies on p53. Hence, p53 is unexpectedly necessary for NF-kappaB-mediated gene expression induced by atypical and classical stimuli. Remarkably, data from gain- and loss-of function approaches argue that anti-apoptotic NF-kappaB p65 activity is constitutively evoked by a p53 hot-spot mutant frequently found in tumors. Our observations suggest explanations for the outstanding question why p53 mutations rather than p53 deletions arise in tumors of various origins.

Critical parameters determining standard radiotherapy treatment outcome for glioblastoma multiforme: a computer simulation

The aim of this paper is to investigate the most critical parameters determining radiotherapy treatment outcome in terms of tumor cell kill for glioblastoma multiforme tumors by using an already developed simulation model of in vivo tumor response to radiotherapy.

Curcumin suppresses growth and chemoresistance of human glioblastoma cells via AP-1 and NFκB transcription factors

Malignant gliomas are a debilitating class of brain tumors that are resistant to radiation and chemotherapeutic drugs, contributing to the poor prognosis associated with these tumors. Over-expression of transcription factors such as NFkappaB and AP-1 contribute to the enhanced glioma survival, radioresistance, and chemoresistance. Curcumin, which may inhibit these pathways, was therefore investigated for a potential therapeutic role in glioma. The effect of curcumin on glioma survival was investigated in human (T98G, U87MG, and T67) and rat (C6) glioma cell lines. The ability of curcumin to overcome glioma cell radioresistance and chemoresistance was also explored. Curcumin reduced cell survival in a p53- and caspase-independent manner, an effect correlated with the inhibition of AP-1 and NFkappaB signaling pathways via prevention of constitutive JNK and Akt activation. Curcumin-sensitized glioma cells to several clinically utilized chemotherapeutic agents (cisplatin, etoposide, camptothecin, and doxorubicin) and radiation, effects correlated with reduced expression of bcl-2 and IAP family members as well as DNA repair enzymes (MGMT, DNA-PK, Ku70, Ku80, and ERCC-1). These findings support a role for curcumin as an adjunct to traditional chemotherapy and radiation in the treatment of brain cancer.

Activation of early gene transcription in polyomavirus BK by human immunodeficiency virus type 1 Tat

Polyomavirus BK (BKV) is a serious problem for immunocompromised patients, where latent virus can enter into the lytic cycle causing cytolytic destruction of host cells. BKV infects >80% of the population worldwide during childhood and then remains in a latent state in the kidney. In the context of immunosuppression in kidney transplant patients, reactivation of the viral early promoter (BKV(E)) results in production of T antigen, enabling virus replication and transition from latency to the lytic phase, causing polyomavirus-associated nephropathy. Reactivation of BKV can also cause complications such as nephritis, atypical retinitis and haemorrhagic cystitis in AIDS patients. Here, the effects of human immunodeficiency virus type 1 (HIV-1) proteins Tat and Vpr on BKV transcription were investigated and it was demonstrated that Tat dramatically stimulated BKV(E). Site-directed mutagenesis analysis of potential Tat-responsive transcriptional motifs complemented by an electrophoretic mobility shift assay (EMSA) showed that Tat activated BKV(E) by inducing binding of the NF-kappaB p65 subunit to a kappaB motif near the 3' end of BKV(E). In addition, a sequence within the 5' UTR of BKV(E) transcripts (BKV(E)-TAR) was identified that is identical to the HIV-1 transactivation response (TAR) element. The BKV(E)-TAR sequence bound TAT in RNA EMSA assays and deletion of the BKV(E)-TAR sequence eliminated Tat transactivation of BKV(E) transcription. Thus, Tat positively affected BKV(E) transcription by a dual mechanism and this may be important in diseases involving BKV reactivation in AIDS patients.

Human polyomavirus JCV late leader peptide region contains important regulatory elements

Transcription is a complex process that relies on the cooperative interaction between sequence-specific factors and the basal transcription machinery. The strength of a promoter depends on upstream or downstream cis-acting DNA elements, which bind transcription factors. In this study, we investigated whether DNA elements located downstream of the JCV late promoter, encompassing the late leader peptide region, which encodes agnoprotein, play regulatory roles in the JCV lytic cycle. For this purpose, the entire coding region of the leader peptide was deleted and the functional consequences of this deletion were analyzed. We found that viral gene expression and replication were drastically reduced. Gene expression also decreased from a leader peptide point mutant but to a lesser extent. This suggested that the leader peptide region of JCV might contain critical cis-acting DNA elements to which transcription factors bind and regulate viral gene expression and replication. We analyzed the entire coding region of the late leader peptide by a footprinting assay and identified three major regions (region I, II and III) that were protected by nuclear proteins. Further investigation of the first two protected regions by band shift assays revealed a new band that appeared in new infection cycles, suggesting that viral infection induces new factors that interact with the late leader peptide region of JCV. Analysis of the effect of the leader peptide region on the promoter activity of JCV by transfection assays demonstrated that this region has a positive and negative effect on the large T antigen (LT-Ag)-mediated activation of the viral early and late promoters, respectively. Furthermore, a partial deletion analysis of the leader peptide region encompassing the protected regions I and II demonstrated a significant down-regulation of viral gene expression and replication. More importantly, these results were similar to that obtained from a complete deletion of the late leader peptide region, indicating the critical importance of these two protected regions in JCV regulation. Altogether, these findings suggest that the late leader peptide region contains important regulatory elements to which transcription factors bind and contribute to the JCV gene regulation and replication.

Nuclear factor-kB signaling pathway constitutively activated in esophageal squamous cell carcinoma cell lines and inhibition of growth of cells by small interfering RNA

Although constitutive nuclear factor (NF)-kappaB activation has been reported in many human tumors, the role of the NF-kappaB pathway in esophageal squamous cell carcinoma (ESCC) has not been known. In this study, NF-kappaB pathway in two ESCC cell lines was investigated using immunocytochemistry, Western blot and reverse transcription-polymerase chain reaction. The activation of NF-kappaB DNA binding was determined by electrophoretic mobility-shift assay. RNA interference was used to specifically inhibit the expression of p65. Growth of cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The results showed that p50, p65, IkappaBalpha p-IkappaBalpha and IkappaB kinase beta were expressed and mainly localized in the cytoplasm. Reverse transcription-polymerase chain reaction results showed the constitutive expressions of p50, p65 and IkappaBalpha mRNA in the two ESCC cell lines. Furthermore, the nuclear extracts revealed that p50 and p65 translocated to the nucleus had DNA-binding activity. Finally, small interfering RNA of p65 decreased the expression of p65, and the viability of cells transfected with p65 small interfering RNA was significantly suppressed at the same concentration of 5-fluorouracil (P < 0.05) compared to untransfected cells. The results of this study showed that there was the constitutively activated NF-kB signaling pathway in the ESCC cell lines. RNA interference targeting at p65 increased the sensitivity of the ESCC cell lines to 5-fluorouracil, suggesting that NF-kappaB might be a good target for cancer treatment.

Phosphorylation mutants of JC virus agnoprotein are unable to sustain the viral infection cycle

Many eukaryotic and viral regulatory proteins are known to undergo posttranslational modifications including phosphorylation, which plays a critical role in many aspects of cell function. Previous studies from our and other laboratories indicated that the JC virus (JCV) late regulatory protein, agnoprotein, plays an important role in the JCV life cycle. Agnoprotein contains several potential phosphorylation sites, including Ser7, Ser11, and Thr21, which are potential targets for the serine/threonine-specific protein kinase C (PKC). In this study, we investigated the functional significance of these phosphorylation sites for the activity of agnoprotein. In vitro and in vivo kinase assays demonstrated that agnoprotein is a target for phosphorylation by PKC. In addition, each of the PKC phosphorylation sites was mutated to Ala singly and in combination, and the effects of these mutations on the JCV life cycle were analyzed. Although the expression of each mutant agnoprotein was detectable during the infection cycle, virus containing each of these mutations failed to propagate. These results contrast with those obtained with an agnoprotein start codon point (Pt) mutant where agnoprotein expression was completely inhibited. The Pt mutant was viable but replicates less efficiently than the wild type (WT). Moreover, conservative substitutions at PKC phosphorylation sites (Ser7, Ser11, and Thr21 to Asp) resulted in a viable virus, which further demonstrate the importance of these sites on agnoprotein function. Further analysis of the mutants by viral release assay and electron microscopy studies revealed that viral particles were efficiently released from infected cells and morphologically indistinguishable from those of WT but were deficient in DNA content. This may account for the defective propagation of the mutants. These results imply that phosphorylated forms of agnoprotein may have essential functions in the viral life cycle and serve as potential targets for therapeutic interventions to limit JCV propagation and JCV-induced diseases.

A phase 1-2, prospective, double blind, randomized study of the safety and efficacy of Sulfasalazine for the treatment of progressing malignant gliomas: study protocol of [ISRCTN45828668]

Background

The prognosis of patients suffering from WHO grade 3 and 4 astrocytic glioma remains poor despite surgery, radiation therapy and the use of current chemotherapy regimen. Indeed, the median survival of glioblastoma multiforme (WHO grade 4) patients is at best 14.6 month with only 26.5 percents of the patients still alive after 2 years and the median survival of anaplastic astrocytomas (WHO grade 3) is 19.2 month. Recent evidence suggests that the transcription factor NF-kappaB is constitutively expressed in malignant gliomas and that its inhibition by drugs like Sulfasalazine may block the growth of astrocytic tumors in vitro and in experimental models of malignant gliomas.

Design

ULg_GBM_04/1 is a prospective, randomized, double blind single-center phase 1–2 study. A total of twenty patients with progressive malignant glioma despite surgery, radiation therapy and a first line of chemotherapy will be recruited and assigned to four dosage regimen of Sulfasalazine. This medication will be taken orally t.i.d. at a daily dose of 1.5–3–4 or 6 g, continuously until complete remission, evidence of progression or drug intolerance. Primary endpoints are drug safety in the setting of malignant gliomas and tumor response as measured according to MacDonald's criteria. An interim analysis of drug safety will be conducted after the inclusion of ten patients. The complete evaluation of primary endpoints will be conducted two years after the enrolment of the last patient or after the death of the last patient should this occur prematurely.

Discussion

The aim of this study is to evaluate the safety and efficacy of Sulfasalazine as a treatment for recurring malignant gliomas. The safety and efficacy of this drug are analyzed as primary endpoints. Overall survival and progression-free survival are secondary endpoint.

EPO receptor-mediated ERK kinase and NF-kappaB activation in erythropoietin-promoted differentiation of astrocytes

Erythropoietin (EPO), a hematopoietic factor, is also required for normal brain development, and its receptor is localized in brain. Therefore, it is possible that EPO could act as a neurotropic factor inducing differentiation of neurons. In the present study, we investigated whether EPO can promote differentiation of neuronal stem cells into astrocytes. In primary culture of cortical neuronal stem cells isolated from post neonatal (Day 1) rat brain, EPO dose (0.1-10U/ml) dependently promoted initiation of morphological differentiation of astrocyte and expression of an astrocyte marker protein, glial fibrillary acidic protein (GFAP). Expression of EPO receptor was also increased during morphological differentiation of astrocytes. EPO-induced increased morphological differentiation of astrocytes and GFAP expression were reduced by treatment with anti-EPO and EPO receptor antibodies. Since our previous study showed that activation of MAPK family and transcription factors is differentially involved in neuronal cell differentiation, we further determined the activation of MAP kinase family and NF-kappaB during morphological differentiation of astrocytes. Concomitant with the progression of the morphological differentiation of astrocytes, ERK(2) but not JNK(1) and p38 MAPK as well as NF-kappaB were activated. However, in the presence of PD98,059, an inhibitor of ERK, and salicylic acid, an NF-kappaB inhibitor, the EPO-induced morphological differentiation of astrocytes and expression of FGAP and EPO receptor were reduced. Conversely, treatment with anti-EPO and EPO receptor antibodies also reduced EPO-induced ERK(2) and NF-kappaB activation. These data demonstrate that EPO can promote differentiation of neuronal stem cells into astrocytes in an EPO receptor dependent manner, and this effect may be associated with the activation of ERK kinase and NF-kappaB pathway.

In vitro and in vivo activity of the nuclear factor-kappaB inhibitor sulfasalazine in human glioblastomas

Glioblastomas, the most common primary brain cancers, respond poorly to current treatment modalities and carry a dismal prognosis. In this study, we demonstrated that the transcription factor nuclear factor (NF)-kappaB is constitutively activated in glioblastoma surgical samples, primary cultures, and cell lines and promotes their growth and survival. Sulfasalazine, an anti-inflammatory drug that specifically inhibits the activation of NF-kappaB, blocked the cell cycle and induced apoptosis in several glioblastoma cell lines and primary cultures, as did gene therapy with a vector encoding a super-repressor of NF-kappaB. In vivo, sulfasalazine also significantly inhibited the growth of experimental human glioblastomas in nude mice brains. Given the documented safety of sulfasalazine in humans, these results may lead the way to a new class of glioma treatment.

Functional interaction between JC virus late regulatory agnoprotein and cellular Y-box binding transcription factor, YB-1

Human polyomavirus JC virus (JCV) is a causative agent of progressive multifocal leukoencephalopathy which results from lytic infection of glial cells. Although significant progress has been made in understanding the regulation of JCV gene transcription, the mechanism(s) underlying the viral lytic cycle remains largely unknown. We recently reported that the JCV late auxiliary Agnoprotein may have a regulatory role in JCV gene transcription and replication. Here, we investigated its regulatory function in viral gene transcription through its physical and functional interaction with YB-1, a cellular transcription factor which contributes to JCV gene expression in glial cells. Time course studies revealed that Agnoprotein is first detected at day 3 postinfection and that its level increased during the late stage of the infection cycle. Agnoprotein is mainly localized to the cytoplasmic compartment of the infected cell, with high concentrations found in the perinuclear region. While the position of Agnoprotein throughout the infection cycle remained relatively unaltered, the subcellular distribution of YB-1 between the cytoplasm and nucleus changed. Results from coimmunoprecipitation and glutathione S-transferase pull-down experiments revealed that Agnoprotein physically interacts with YB-1 and that the amino-terminal region of Agnoprotein, between residues 1 and 36, is critical for this association. Further investigation of this interaction by functional assays demonstrated that Agnoprotein negatively regulates YB-1-mediated gene transcription and that the region corresponding to residues 1 to 36 of Agnoprotein is important for the observed regulatory event. Taken together, these data demonstrate that the interaction of the viral late regulatory Agnoprotein and cellular Y-box binding factor YB-1 modulates transcriptional activity of JCV promoters.

Growth inhibition of glioblastoma cells by human Pur(alpha)

Pur(alpha) is a multifunctional DNA- and RNA-binding protein implicated in a variety of biological events including transcription and replication. Further, this protein has the ability to form a complex with several cellular proteins which are important for cell proliferation including the transcription factor, E2F-1. Pur(alpha) has a modular structure highlighted by alternating three basic aromatic class I and two acidic leucine-rich class II repeats in the central region of the protein. Here, we demonstrate that ectopic overexpression of Pur(alpha) suppresses proliferation of a variety of transformed and tumor cells including human glioblastoma. By utilizing various deletion mutants of Pur(alpha) in colony formation assay, we identified the region spanning the first class II repeat (residues 107-131) and the second class I repeat (residues 148-170) of Pur(alpha) which participate in growth inhibitory action of Pur(alpha). Results from protein transduction experiments using the synthetic peptides representing residues 109-131 and 123-154 of Pur(alpha) in fusion with the arginine rich domain of HIV-1 Tat revealed cellular internalization and nuclear appearance of the Tat-Pur(alpha) fusion peptide after 2 h and its detection in nuclei up to 24 h after treatment. Glioblastoma cells treated with Tat-Pur(alpha) (109-131) and Tat-Pur(alpha) (123-154) exhibited 41 and 47% decrease, respectively, in proliferation. Altogether these results illustrate the efficacy of Pur(alpha) in suppressing glioblastoma cell growth and provide evidence for the potential use of this protein and its derivative(s) in blocking proliferation of tumor cells.