Alteration of major vault protein in human glioblastoma and its relation with EGFR and PTEN status

Desmoplastic infantile astrocytoma with atypical phenotype, PTEN homozygous deletion and BRAF V600E mutation

Desmoplastic infantile astrocytoma (DIA) is rare, cystic and solid tumor of infants usually found in superficial cerebral hemispheres. Although DIA is usually benign, uncommon cases bearing malignant histological and aggressive clinical features have been described in the literature. We report a newborn patient who was diagnosed with a DIA and died postresection. Pathologic examination revealed that the main part of the tumor had benign features, but the internal region showed areas with a more aggressive appearance, with higher-proliferative cells, anaplastic GFAP positive cells with cellular polymorphism, necrosis foci, vascular hyperplasia with endothelial proliferation and microtrombosis. Genetic study, performed in both regions of the tumor, showed a BRAF V600E mutation and a homozygous deletion in PTEN, without changes in other relevant genes like EGFR, CDKN2A, TP53, NFKBIA, CDK4, MDM2 and PDGFRA. Although PTEN homozygous deletions are described in gliomas, the present case constitutes the first report of a PTEN mutation in a DIA, and this genetic feature may be related to the malignant behavior of a usually benign tumor. These genetic findings may point at the need of further and deeper genetic characterization of DIAs, in order to better understand the biology of this tumor and to obtain new prognostic approaches, a better clinical management and targeted therapies, especially in malignant cases of DIA.

Small but Powerful: The Human Vault RNAs as Multifaceted Modulators of Pro-Survival Characteristics and Tumorigenesis

Simple Summary

Small non-protein-coding RNAs have been recognized as valuable regulators of gene expression in all three domains of life. Particularly in multicellular organisms, ncRNAs-mediated gene expression control has evolved as a central principle of cellular homeostasis. Thus, it is not surprising that non-coding RNA misregulation has been linked to various diseases. Here, we review the contributions of the four human vault RNAs to cellular proliferation, apoptosis and cancer biology.

Abstract

The importance of non-coding RNAs for regulating gene expression has been uncovered in model systems spanning all three domains of life. More recently, their involvement in modulating signal transduction, cell proliferation, tumorigenesis and cancer progression has also made them promising tools and targets for oncotherapy. Recent studies revealed a class of highly conserved small ncRNAs, namely vault RNAs, as regulators of several cellular homeostasis mechanisms. The human genome encodes four vault RNA paralogs that share significant sequence and structural similarities, yet they seem to possess distinct roles in mammalian cells. The alteration of vault RNA expression levels has frequently been observed in cancer tissues, thus hinting at a putative role in orchestrating pro-survival characteristics. Over the last decade, significant advances have been achieved in clarifying the relationship between vault RNA and cellular mechanisms involved in cancer development. It became increasingly clear that vault RNAs are involved in controlling apoptosis, lysosome biogenesis and function, as well as autophagy in several malignant cell lines, most likely by modulating signaling pathways (e.g., the pro-survival MAPK cascade). In this review, we discuss the identified and known functions of the human vault RNAs in the context of cell proliferation, tumorigenesis and chemotherapy resistance.

Smurf1 silencing restores PTEN expression that ameliorates progression of human glioblastoma and sensitizes tumor cells to mTORC1/C2 inhibitor Torin1

Amplification of ubiquitin E3 ligase Smurf1 promotes degradation of PTEN leading to hyperactivation of the Akt/mTORC1 pathway. However, inhibitors of this pathway have not hitherto yielded promising results in clinical studies because of strong drug resistance. Here, we investigated Smurf1 expression in various glioblastoma (GB) cell lines and patient tissues. The therapeutic efficacy of Smurf1 silencing and Torin1 treatment was assessed in GB cells and orthotopic mouse model. We found Smurf1 loss elevates PTEN levels that interrupt the epidermal growth factor receptor pathway activity. Cotreatment with Smurf1 silencing and mTORC1/C2 inhibitor Torin1 remarkably decreased phosphorylation of Akt, and mTORC1 downstream targets 4EBP1 and S6K resulting in synergistic inhibitory effects. Smurf1 knockdown in orthotopic GB mouse model impaired tumor growth and enhanced cytotoxicity of Torin1. Together, these findings suggest a rational combination of Smurf1 inhibition and Torin1 as a promising new avenue to circumvent PI3K/Akt pathway-driven tumor progression and drug resistance.

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Smurf1 ubiquitylates and degrades PTEN, leading to upregulating oncogenic pathways

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Loss of Smurf1 resensitizes tumor cells to mTOR inhibitor Torin1 in PTEN-wild type GB

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Smurf1 depletion with Torin1 has enhanced efficacy by inhibiting pho-4EBP1 and pho-S6K

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Smurf1 suppression with Torin1 is toxic to Rapamycin resistant GB cells

Silencing of ZFP36L2 increases sensitivity to temozolomide through G2/M cell cycle arrest and BAX mediated apoptosis in GBM cells

Despite the advancements in primary brain tumour diagnoses and treatments, the mortality rate remains high, particularly in glioblastoma (GBM). Chemoresistance, predominantly in recurrent cases, results in decreased mean survival of patients with GBM. We aimed to determine the chemosensitisation and oncogenic characteristics of zinc finger protein 36-like 2 (ZFP36L2) in LN18 GBM cells via RNA interference (RNAi) delivery. We conducted a meta-analysis of microarray datasets and RNAi screening using pooled small interference RNA (siRNA) to identify the druggable genes responsive to GBM chemosensitivity. Temozolomide-resistant LN18 cells were used to evaluate the effects of gene silencing on chemosensitisation to the sub-lethal dose (1/10 of the median inhibitory concentration [IC50]) of temozolomide. ZFP36L2 protein expression was detected by western blotting. Cell viability, proliferation, cell cycle and apoptosis assays were carried out using commercial kits. A human apoptosis array kit was used to determine the apoptosis pathway underlying chemosensitisation by siRNA against ZFP36L2 (siZFP36L2). Statistical analyses were performed using one-way analysis of variance; p > 0.05 was considered significant. The meta-analysis and RNAi screening identified ZFP36L2 as a potential marker of GBM. ZFP36L2 knockdown significantly induced apoptosis (p < 0.05). Moreover, ZFP36L2 inhibition led to increased cell cycle arrest and decreased cell proliferation. Downstream analysis showed that the sub-lethal dose of temozolomide and siZFP26L2 caused major upregulation of BCL2-associated X, apoptosis regulator (BAX). ZFP36L2 has oncogenic and chemosensitive characteristics and may play an important role in gliomagenesis through cell proliferation, cell cycle arrest and apoptosis. This suggests that RNAi combined with chemotherapy treatment such as temozolomide may be a potential GBM therapeutic intervention in the future.

The Vault Nanoparticle: A Gigantic Ribonucleoprotein Assembly Involved in Diverse Physiological and Pathological Phenomena and an Ideal Nanovector for Drug Delivery and Therapy

Simple Summary

In recent decades, a molecular complex referred to as vault nanoparticle has attracted much attention by the scientific community, due to its unique properties. At the molecular scale, it is a huge assembly consisting of 78 97-kDa polypeptide chains enclosing an internal cavity, wherein enzymes involved in DNA integrity maintenance and some small noncoding RNAs are accommodated. Basically, two reasons justify this interest. On the one hand, this complex represents an ideal tool for the targeted delivery of drugs, provided it is suitably engineered, either chemically or genetically; on the other hand, it has been shown to be involved in several cellular pathways and mechanisms that most often result in multidrug resistance. It is therefore expected that a better understanding of the physiological roles of this ribonucleoproteic complex may help develop new therapeutic strategies capable of coping with cancer progression. Here, we provide a comprehensive review of the current knowledge.

Abstract

The vault nanoparticle is a eukaryotic ribonucleoprotein complex consisting of 78 individual 97 kDa-“major vault protein” (MVP) molecules that form two symmetrical, cup-shaped, hollow halves. It has a huge size (72.5 × 41 × 41 nm) and an internal cavity, wherein the vault poly(ADP-ribose) polymerase (vPARP), telomerase-associated protein-1 (TEP1), and some small untranslated RNAs are accommodated. Plenty of literature reports on the biological role(s) of this nanocomplex, as well as its involvement in diseases, mostly oncological ones. Nevertheless, much has still to be understood as to how vault participates in normal and pathological mechanisms. In this comprehensive review, current understanding of its biological roles is discussed. By different mechanisms, vault’s individual components are involved in major cellular phenomena, which result in protection against cellular stresses, such as DNA-damaging agents, irradiation, hypoxia, hyperosmotic, and oxidative conditions. These diverse cellular functions are accomplished by different mechanisms, mainly gene expression reprogramming, activation of proliferative/prosurvival signaling pathways, export from the nucleus of DNA-damaging drugs, and import of specific proteins. The cellular functions of this nanocomplex may also result in the onset of pathological conditions, mainly (but not exclusively) tumor proliferation and multidrug resistance. The current understanding of its biological roles in physiological and pathological processes should also provide new hints to extend the scope of its exploitation as a nanocarrier for drug delivery.

Synergistic therapeutic benefit by combining the antibody drug conjugate, depatux-m with temozolomide in pre-clinical models of glioblastoma with overexpression of EGFR

PURPOSE

Depatux-m is an antibody drug conjugate (ADC) that targets and inhibits growth of cancer cells overexpressing the epidermal growth factor receptor (EGFR) or the 2-7 deletion mutant (EGFRvIII) in tumor models in vitro and in vivo. Treatment of patients suffering from relapsed/refractory glioblastoma (GBM) with a combination of depatux-m and temozolomide (TMZ) tended to increase overall survival. As a first step to understand the nature of the interaction between the two drugs, we investigated whether the interaction was synergistic, additive or antagonistic.

METHODS

The efficacy of ADCs, antibodies, TMZ and radiation was tested in xenograft models of GBM, U-87MG and U-87MG EGFRvIII. Both models express EGFR. U-87MG EGFRvIII was transduced to express EGFRvIII. Changes in tumor volume, biomarkers of cell death and apoptosis after treatment were used to measure efficacy of the various treatments. Synergism of depatux-m and TMZ was verified in three-dimensional cultures of U-87MG and U-87MG EGFRvIII by the method of Chou and Talalay.

RESULTS

Combined with TMZ and radiotherapy (RT), depatux-m inhibited xenograft growth of U-87MG and U-87MG EGFRvIII more than either treatment with depatux-m or TMZ + RT. Durability of the response to depatux-m + TMZ + RT or depatux-m + TMZ was more pronounced in U-87MG EGFRvIII than in U-87MG. Efficacy of depatux-m + TMZ was synergistic in U-87MG EGFRvIII and additive in U-87MG.

CONCLUSION

Adding depatux-m enhances the efficacy of standard of care therapy in preclinical models of GBM. Durability of response to depatux-m + TMZ in vivo and synergy of the drug-drug interaction correlates with the amount of antigen expressed by the tumor cells.

Identification of New Genetic Clusters in Glioblastoma Multiforme: EGFR Status and ADD3 Losses Influence Prognosis

Glioblastoma multiforme (GB) is one of the most aggressive tumors. Despite continuous efforts to improve its clinical management, there is still no strategy to avoid a rapid and fatal outcome. EGFR amplification is the most characteristic alteration of these tumors. Although effective therapy against it has not yet been found in GB, it may be central to classifying patients. We investigated somatic-copy number alterations (SCNA) by multiplex ligation-dependent probe amplification in a series of 137 GB, together with the detection of EGFRvIII and FISH analysis for EGFR amplification. Publicly available data from 604 patients were used as a validation cohort. We found statistical associations between EGFR amplification and/or EGFRvIII, and SCNA in CDKN2A, MSH6, MTAP and ADD3. Interestingly, we found that both EGFRvIII and losses on ADD3 were independent markers of bad prognosis (p = 0.028 and 0.014, respectively). Finally, we got an unsupervised hierarchical classification that differentiated three clusters of patients based on their genetic alterations. It offered a landscape of EGFR co-alterations that may improve the comprehension of the mechanisms underlying GB aggressiveness. Our findings can help in defining different genetic profiles, which is necessary to develop new and different approaches in the management of our patients.

STAT3-PTTG11 abrogation inhibits proliferation and induces apoptosis in malignant glioma cells

Pituitary tumor transforming gene 1 (PTTG11) is abundantly expressed in glioma. Our previous study demonstrated that the downregulation of PTTG11 gene expression significantly inhibited the proliferation, migration and invasion ability, and increased the apoptosis of SHG44 glioma cells. However, the molecular mechanisms that regulate PTTG11 and its actions remain elusive. In the present study, CCK-8 and flow cytometry assays were used to assess the proliferation/viability and apoptosis, respectively, of the human glioma U251 cell line. STAT3-PTTG1 signals were further evaluated by western blotting. The findings of the present study revealed that STAT3 induced PTTG11 expression, which subsequently induced downstream c-Myc and Bcl-2 expression while inhibiting Bax expression, thereby promoting cell viability and inhibiting apoptosis. PTTG11 suppression via siRNA inhibited the viability and increased the apoptosis of glioma cells induced by the STAT3 activator S3I-201. c-Myc and Bcl-2 expression was suppressed by PTTG11 inhibition. The findings of the present study suggest that the STAT3-PTTG11 signaling pathway may play an important role in glioma progression by regulating cell proliferation and apoptosis.

Somatic copy number alterations are associated with EGFR amplification and shortened survival in patients with primary glioblastoma

Glioblastoma (GBM) is the most common malignant primary tumor of the central nervous system. With no effective therapy, the prognosis for patients is terrible poor. It is highly heterogeneous and EGFR amplification is its most frequent molecular alteration.

In this light, we aimed to examine the genetic heterogeneity of GBM and to correlate it with the clinical characteristics of the patients. For that purpose, we analyzed the status of EGFR and the somatic copy number alterations (CNAs) of a set of tumor suppressor genes and oncogenes.

Thus, we found GBMs with high level of EGFR amplification, low level and with no EGFR amplification. Highly amplified tumors showed histological features of aggressiveness. Interestingly, accumulation of CNAs, as a measure of tumor mutational burden, was frequent and significantly associated to shortened survival. EGFR-amplified GBMs displayed both a higher number of concrete CNAs and a higher global tumor mutational burden than their no EGFR-amplified counterparts. In addition to genetic changes previously described in GBM, we found PARK2 and LARGE1 CNAs associated to EGFR amplification. The set of genes analyzed allowed us to explore relevant signaling pathways on GBM. Both PARK2 and LARGE1 are related to receptor tyrosine kinase/PI3K/PTEN/AKT/mTOR-signaling pathway. Finally, we found an association between the molecular pathways altered, EGFR amplification and a poor outcome.

Our results underline the potential interest of categorizing GBM according to their EGFR amplification level and the usefulness of assessing the tumor mutational burden. These approaches would open new knowledge possibilities related to GBM biology and therapy.

Characterization of a new glioblastoma cell line, GB-val4, with unusual TP53 mutation

A novel cell line derived from a human glioblastoma (GB), named GB-val4, has been established and characterized. GB-val4 cells were hyperdiploid, with many numerical and structural chromosomal rearrangements. The cell line did not show mutations in IDH1/IDH2 genes or EGFR amplification, but it presented two missense mutations in TP53, which imply a very low p53 protein activity within the cell line. Cells also had gain of TP73 copies, hypermethylation of APC, CASP8 and RASSF1, increased expression of ARF1, CDH1 and NF-κB and decreased expression of CDKN2A. Tumorigenity was demonstrated by transplant of GB-val4 cells into athymic nude mice, where solid tumors were grown. Interestingly, a high percentage of GB-val4 cells presented expression of GSC markers CD133 or CD44. These GSC markers were increased in neurosphere cultures, which better mimic solid tumor conditions and maintain the genetic features of the tumor cells. In this study, we aimed to define the characteristics of this novel cell line and its applications in human cancer research. With its genetic features and a poor p53 activity, GB-val4 cells resemble GB tumors. Moreover, the important presence of GSCs in adherent cultures and especially in neurosphere cultures makes GB-val4 an attractive tool to study cancer stem cells, deepen in the knowledge the molecular pathways of GB and develop new therapeutic strategies for patients with these tumors.

A fast and straightforward procedure for vault nanoparticle purification and the characterization of its endocytic uptake

BACKGROUND

Vaults are eukaryotic ribonucleoprotein particles composed of up 78 copies of the 97 kDa major vault protein that assembles into a barrel-like, "nanocapsule" enclosing poly(ADP-ribose) polymerase, telomerase-associated protein-1 and small untranslated RNAs. Overall, the molecular mass of vault particles amounts to about 13 MDa. Although it has been implicated in several cellular functions, its physiological roles remain poorly understood. Also, the possibility to exploit it as a nanovector for drug delivery is currently being explored in several laboratories.

METHODS

Using the baculovirus expression system, vaults were expressed and purified by a dialysis step using a 1 MDa molecular weight cutoff membrane and a subsequent size exclusion chromatography. Purity was assessed by SDS-PAGE, transmission electron microscopy and dynamic light scattering. Particle's endocytic uptake was monitored by flow cytometry and confocal microscopy.

RESULTS

The purification protocol here reported is far simpler and faster than those currently available and lead to the production of authentic vault. We then demonstrated its clathrin-mediated endocytic uptake by normal fibroblast and glioblastoma, but not carcinoma cell lines. In contrast, no significant caveolin-mediated endocytosis was detected.

CONCLUSIONS

These results provide the first evidence for an intrinsic propensity of the vault complex to undergo endocytic uptake cultured eukaryotic cells.

GENERAL SIGNIFICANCE

The newly developed purification procedure will greatly facilitate any investigation based on the use of the vault particle as a natural nanocarrier. Its clathrin-mediated endocytic uptake observed in normal and in some tumor cell lines sheds light on its physiological role.

Modulation of the Vault Protein-Protein Interaction for Tuning of Molecular Release

Vaults are naturally occurring ovoid nanoparticles constructed from a protein shell that is composed of multiple copies of major vault protein (MVP). The vault-interacting domain of vault poly(ADP-ribose)-polymerase (INT) has been used as a shuttle to pack biomolecular cargo in the vault lumen. However, the interaction between INT and MVP is poorly understood. It is hypothesized that the release rate of biomolecular cargo from the vault lumen is related to the interaction between MVP and INT. To tune the release of molecular cargos from the vault nanoparticles, we determined the interactions between the isolated INT-interacting MVP domains (iMVP) and wild-type INT and compared them to two structurally modified INT: 15-amino acid deletion at the C terminus (INTΔC15) and histidine substituted at the interaction surface (INT/DSA/3 H) to impart a pH-sensitive response. The apparent affinity constants determined using surface plasmon resonance (SPR) biosensor technology are 262 ± 4 nM for iMVP/INT, 1800 ± 160 nM for iMVP/INTΔC15 at pH 7.4. The INT/DSA/3 H exhibits stronger affinity to iMVP (K_Dapp = 24 nM) and dissociates at a slower rate than wild-type INT at pH 6.0.

Natural Products as Chemopreventive Agents by Potential Inhibition of the Kinase Domain in ErbB Receptors

Small molecules found in natural products provide therapeutic benefits due to their pharmacological or biological activity, which may increase or decrease the expression of human epidermal growth factor receptor (HER), a promising target in the modification of signaling cascades involved in excessive cellular growth. In this study, in silico molecular protein-ligand docking protocols were performed with AutoDock Vina in order to evaluate the interaction of 800 natural compounds (NPs) from the NatProd Collection (http://www.msdiscovery.com/natprod.html), with four human HER family members: HER1 (PDB: 2ITW), HER2 (PDB: 3PP0), HER3 (PDB: 3LMG) and HER4 (PDB: 2R4B). The best binding affinity values (kcal/mol) for docking pairs were obtained for HER1-podototarin (−10.7), HER2-hecogenin acetate (−11.2), HER3-hesperidin (−11.5) and HER4-theaflavin (−10.7). The reliability of the theoretical calculations was evaluated employing published data on HER inhibition correlated with in silico binding calculations. IC₅₀ values followed a significant linear relationship with the theoretical binding Affinity data for HER1 (R = 0.656, p < 0.0001) and HER2 (R = 0.543, p < 0.0001), but not for HER4 (R = 0.364, p > 0.05). In short, this methodology allowed the identification of several NPs as HER inhibitors, being useful in the discovery and design of more potent and selective anticancer drugs.

Search for KPNA7 cargo proteins in human cells reveals MVP and ZNF414 as novel regulators of cancer cell growth

Karyopherin alpha 7 (KPNA7) belongs to a family of nuclear import proteins that recognize and bind nuclear localization signals (NLSs) in proteins to be transported to the nucleus. Previously we found that KPNA7 is overexpressed in a subset of pancreatic cancer cell lines and acts as a critical regulator of growth in these cells. This characteristic of KPNA7 is likely to be mediated by its cargo proteins that are still mainly unknown. Here, we used protein affinity chromatography in Hs700T and MIA PaCa-2 pancreatic cancer cell lines and identified 377 putative KPNA7 cargo proteins, most of which were known or predicted to localize to the nucleus. The interaction was confirmed for two of the candidates, MVP and ZNF414, using co-immunoprecipitation, and their transport to the nucleus was hindered by siRNA based KPNA7 silencing. Most importantly, silencing of MVP and ZNF414 resulted in marked reduction in Hs700T cell growth. In conclusion, these data uncover two previously unknown human KPNA7 cargo proteins with distinct roles as novel regulators of pancreatic cancer cell growth, thus deepening our understanding on the contribution of nuclear transport in cancer pathogenesis.