Oxford Nanopore direct-RNA sequencing, a third-generation sequencing technology, allows for the analysis of native RNA molecules in their natural cellular state. However, cellular RNA is predominantly composed of ribosomal RNA and transcripts from ubiquitously expressed housekeeping genes, which limits the coverage of transcripts from lowly expressed genes. To address this limitation, targeted sequencing can be employed to enrich read coverage by focusing specifically on genes of interest. Here, we present a step-by-step protocol for gene-specific RNA enrichment followed by Oxford Nanopore direct-RNA sequencing. The enrichment protocol utilizes biotinylated DNA capture probes complementary to the target gene. Following in-solution hybridization of probes to total RNA, a series of stringent washes is applied before elution of the enriched RNA sample. The protocol describes all steps from isolation of cellular total RNA to bioinformatic analyses of raw sequencing data. As a proof of concept, capture probes were designed to specifically enrich all RNA species encoded by the MYCN oncogene. The enrichment protocol successfully isolated RNAs from the MYCN gene, achieving a purification factor of 4.8 × 103. Direct-RNA sequencing of the enriched RNA sample revealed that 65% of the primary mapped reads aligned to MYCN transcripts. We also include a more thorough analysis of the most abundant non-target mapped reads and unmapped reads. This protocol proves to be highly effective in removing unwanted RNA species, delivering robust enrichment for the target gene, and significantly enhancing the efficiency of long-read direct-RNA sequencing.

Background Studies conducted in the last decades have revealed a role for the non-coding microRNAs (miRNAs) in cancer development and progression. Several miRNAs within the chromosome region 14q32, a region commonly deleted in cancers, are associated with poor clinical outcome in the childhood cancer neuroblastoma. We have previously identified miR-323a-3p from this region to be downregulated in chemotherapy treated neuroblastoma cells compared to pre-treatment cells from the same patients. Furthermore, in neuroblastoma tumors, this miRNA is downregulated in advanced stage 4 disease compared to stage 1–2. In this study, we attempt to delineate the unknown functional roles of miR-323a-3p in neuroblastoma. Methods Synthetic miRNA mimics were used to overexpress miR-323a-3p in neuroblastoma cell lines. To investigate the functional roles of miR-323a-3p, cell viability assay, flow cytometry, reverse transcription-quantitative polymerase chain reaction, luciferase reporter assay and western blot were conducted on the neuroblastoma cell lines Kelly, SH-SY5Y and SK-N-BE(2)-C. Results Ectopic expression of miR-323a-3p resulted in marked reduction of cell viability in Kelly, SH-SY5Y and SK-N-BE(2)-C by causing G1-cell cycle arrest in Kelly and SH-SY5Y and apoptosis in all the cell lines tested. Furthermore, mRNA and protein levels of signal transducer and activator of transcription 3 ( STAT3 ) were reduced upon miR-323a-3p overexpression. A direct binding of the miR-323a-3p to the 3′UTR of STAT3 was experimentally validated by luciferase reporter assay, where miR-323a-3p reduced luminescent signal from full length STAT3 3′UTR luciferase reporter, but not from a reporter with mutation in the predicted seed sequence. Conclusions miR-323a-3p inhibits growth of neuroblastoma cell lines through G1-cell cycle arrest and apoptosis, and the well-known oncogene STAT3 is a direct target of this miRNA.

PDF file - 62K, Differentially expressed miRNAs between MNA and nonMNA primary tumors

PDF file - 86K, Correlation between miRNA and Nmyc expression in NB cell lines

EDITORIAL article Front. Oncol., 30 November 2021Sec. Molecular and Cellular Oncology Volume 11 - 2021 | https://doi.org/10.3389/fonc.2021.803443

Neuroblastoma is a pediatric cancer of the developing sympathetic nervous system. High-risk neuroblastoma patients typically undergo an initial remission in response to treatment, followed by recurrence of aggressive tumors that have become refractory to further treatment. The need for biomarkers that can select patients not responding well to therapy in an early phase is therefore needed. In this study, we used next generation sequencing technology to determine the expression profiles in high-risk neuroblastoma cell lines established before and after therapy. Using partial least squares-discriminant analysis (PLS-DA) with least absolute shrinkage and selection operator (LASSO) and leave-one-out cross-validation, we identified a panel of 55 messenger RNAs and 17 long non-coding RNAs (lncRNAs) which were significantly altered in the expression between cell lines isolated from primary and recurrent tumors. From a neuroblastoma patient cohort, we found 20 of the 55 protein-coding genes to be differentially expressed in patients with unfavorable compared with favorable outcome. We further found a twofold increase or decrease in hazard ratios in these genes when comparing patients with unfavorable and favorable outcome. Gene set enrichment analysis (GSEA) revealed that these genes were involved in proliferation, differentiation and regulated by Polycomb group (PcG) proteins. Of the 17 lncRNAs, 3 upregulated (NEAT1, SH3BP5-AS1, NORAD) and 3 downregulated lncRNAs (DUBR, MEG3, DHRS4-AS1) were also found to be differentially expressed in favorable compared with unfavorable outcome. Moreover, using expression profiles on both miRNAs and mRNAs in the same cohort of cell lines, we found 13 downregulated and 18 upregulated experimentally observed miRNA target genes targeted by miR-21, -424 and -30e, -29b, -138, -494, -181a, -34a, -29b, respectively. The advantage of analyzing biomarkers in a clinically relevant neuroblastoma model system enables further studies on the effect of individual genes upon gene perturbation. In summary, this study identified several genes, which may aid in the prediction of response to therapy and tumor recurrence.

Neuroblastoma is the most common diagnosed tumor in infants and the second most common extracranial tumor of childhood. The survival rate of patients with high-risk neuroblastoma is still very low despite intensive multimodal treatments. Therefore, new treatment strategies are needed. In recent years, miRNA-based anticancer therapy has received growing attention. Advances in this novel treatment strategy strongly depends on the identification of candidate miRNAs with broad-spectrum antitumor activity. Here, we identify miR-193b as a miRNA with tumor suppressive properties. We show that miR-193b is expressed at low levels in neuroblastoma cell lines and primary tumor samples. Introduction of miR-193b mimics into nine neuroblastoma cell lines with distinct genetic characteristics significantly reduces cell growth in vitro independent of risk factors such as p53 functionality or MYCN amplification. Functionally, miR-193b induces a G1 cell cycle arrest and cell death in neuroblastoma cell lines by reducing the expression of MYCN, Cyclin D1 and MCL-1, three important oncogenes in neuroblastoma of which inhibition has shown promising results in preclinical testing. Therefore, we suggest that miR-193b may represent a new candidate for miRNA-based anticancer therapy in neuroblastoma.

Abnormal increases in nucleolar size and number caused by dysregulation of ribosome biogenesis has emerged as a hallmark in the majority of spontaneous cancers. The observed ribosome hyperactivity can be directly induced by the MYC transcription factors controlling the expression of RNA and protein components of the ribosome. Neuroblastoma, a highly malignant childhood tumor of the sympathetic nervous system, is frequently characterized by MYCN gene amplification and high expression of MYCN and c-MYC signature genes. Here, we show a strong correlation between high-risk disease, MYCN expression, poor survival, and ribosome biogenesis in neuroblastoma patients. Treatment of neuroblastoma cells with quarfloxin or CX-5461, two small molecule inhibitors of RNA polymerase I, suppressed MycN expression, induced DNA damage, and activated p53 followed by cell cycle arrest or apoptosis. CX-5461 repressed the growth of established MYCN-amplified neuroblastoma xenograft tumors in nude mice. These findings suggest that inhibition of ribosome biogenesis represent new therapeutic opportunities for children with high-risk neuroblastomas expressing high levels of Myc.

High-risk neuroblastoma is the most aggressive form of cancer in children. The estimated survival of children with high-risk neuroblastoma is 40-50% compared with low and intermediate risk neuroblastoma, which is >98 and 90-95%, respectively. In addition, patients with high-risk neuroblastoma often experience relapse following intensive treatments with standard chemotherapeutic drugs. Therefore alternative strategies are required to address this problem. MicroRNAs (miRNAs/miRs) are small, endogenously expressed non-coding RNAs, which when deregulated have been demonstrated to serve significant roles in the tumorigenesis of a number of different types of cancer. Results from a previous deep sequencing study identified 22 downregulated miRNAs from the 14q32 miRNA cluster differentially expressed in neuroblastoma cell lines isolated from 6 patients at diagnosis and at relapse following intensive treatments. miR-376c-3p is one of the 22 miRNAs that was downregulated in the majority of the cell lines isolated from patients post treatment. The present study employed reverse transcription-quantitative polymerase chain reaction (RT-qPCR) to quantify the basic expression of miR-376c-3p in 6 neuroblastoma cell lines. The functional role of miR-376c-3p in the neuroblastoma cell lines was evaluated by alamar blue-cell viability and propidium iodide-flow cytometric assays. In addition, luciferase reporter assays, RT-qPCR and western blotting were performed to identify and quantify the targets of miR-376c-3p in neuroblastoma cell lines. Ectopic expression of miR-376c-3p led to significant inhibition of cell viability and G1-cell cycle arrest in multiple neuroblastoma cell lines by reducing the expression of cyclin D1, an oncogene critical for neuroblastoma pathogenesis. The results of the present study provide novel insights into the functional role of miR-376c-3p and suggest new approaches for the treatment of neuroblastoma.

BACKGROUND:In recent years, evidence has accumulated indicating that both normal and cancer cells communicate via the release and delivery of macromolecules packed into extracellular membrane vesicles.MATERIALS AND METHODS:We isolated nano-sized extracellular vesicles from MYCN-amplified neuroblastoma cell lines using ultracentrifugation and exosome precipitation (Exoquick) protocols. These vesicles were characterized by transmission electron microscopy (TEM), nanoparticle tracking analysis and western blotting. Exosomal miRNA profiles were obtained using a reverse transcription-polymerase chain reaction (RT-PCR) ready-to-use panel measuring a total of 742 miRNAs.RESULTS:In this study, we showed that MYCN-amplified neuroblastoma cell lines secrete populations of miRNAs inside small exosome-like vesicular particles. These particles were shown to be taken-up by recipient cells. By profiling the miRNA content, we demonstrated high expression of a group of established oncomirs in exosomes from two MYCN-amplified neuroblastoma cell lines. Despite the fact that other studies have demonstrated the ability of exosomal miRNAs both to repress mRNA targets and to stimulate Toll-like receptor-8 (TLR8) signaling in recipient cells, we did not observe these effects with exosomes from MYCN-amplified neuroblastoma cells. However, functional enrichment analysis reveals that mRNA targets of highly expressed exosomal miRNAs are associated with a range of cellular and molecular functions related to cell growth and cell death.CONCLUSION:MYCN-amplified neuroblastoma cell lines secrete exosome-like particles containing oncogenic miRNAs. This work showed for the first time that neuroblastoma cells secrete exosome-like particles containing miRNAs with potential roles in cancer progression. These findings indicate a new way for MYCN-amplified neuroblastoma cells to interact with the tumor environment.

The DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) is commonly overexpressed in cancers and is implicated in the development of chemoresistance. The use of drugs inhibiting MGMT has been hindered by their haematologic toxicity and inefficiency. As a different strategy to inhibit MGMT we investigated cellular regulators of MGMT expression in multiple cancers. Here we show a significant correlation between Wnt signalling and MGMT expression in cancers with different origin and confirm the findings by bioinformatic analysis and immunofluorescence. We demonstrate Wnt-dependent MGMT gene expression and cellular co-localization between active β-catenin and MGMT. Pharmacological or genetic inhibition of Wnt activity downregulates MGMT expression and restores chemosensitivity of DNA-alkylating drugs in mouse models. These findings have potential therapeutic implications for chemoresistant cancers, especially of brain tumours where the use of temozolomide is frequently used in treatment.

Neuroblastoma is a pediatric cancer of the developing sympathetic nervous system. High risk neuroblastoma patients typically undergo an initial remission in response to treatment, followed by recurrence of aggressive tumors that have become refractory to further treatment. Recent works have underlined the involvement of microRNAs (miRNAs) in neuroblastoma development and evolution of drug resistance. In this study we have used deep sequencing technology to identify miRNAs differentially expressed in neuroblastoma cell lines isolated from 6 patients at diagnosis and at relapse after intensive treatments. This approach revealed a panel of 42 differentially expressed miRNAs, 8 of which were upregulated and 34 were downregulated. Most strikingly, the 14q32 miRNA clusters encode 22 of the downregulated miRNAs. Reduced expression of 14q32 miRNAs in tumors associated with poor prognosis factors was confirmed in a cohort consisting of 226 primary neuroblastomas. In order to gain insight into the nature of the genes that may be affected by the differentially expressed miRNAs we utilized Ingenuity Pathway Analysis (IPA). This analysis revealed several biological functions and canonical pathways associated with cancer progression and drug resistance. The results of this study contribute to the identification of miRNAs involved in the complex processes of surviving therapeutic treatment and developing drug resistance in neuroblastoma.

The MYCN oncogene is frequently amplified in neuroblastoma and is associated with aggressive disease and treatment failure. MYCN induces expression of different miRNAs, which are posttranscriptional regulators of gene expression with established roles in neuroblastoma development. In this study, we show that MYCN -amplified cell lines not only express miRNAs with functions inside the cell, but also secrete populations of miRNAs inside small vesicular structures called exosomes, with the ability to shuttle to other cells. We have isolated and characterised exosomes from MYCN amplified cell lines, and here demonstrate their ability to be taken up by other cells. By profiling the miRNA expression, we demonstrate high expression of a group of established on comirs in exosomes from two MYCN- amplified cell lines. Despite the fact that other studies have demonstrated the ability of exosomal miRNAs to regulate their targets in recipient cells, we did not observe this with exosomes from MYCN -amplified cells. However, exosomes were able to induce in vitro angiogenic tube formation, suggesting that they can have tumorigenic properties. These new findings reveal a potential new way for MYCN -amplified neuroblastoma cells to interact with their environment.

The MYC genes are the most frequently activated oncogenes in human tumors and are hence attractive therapeutic targets. MYCN amplification leads to poor clinical outcome in childhood neuroblastoma, yet strategies to modulate the function of MYCN do not exist. Here we show that 10058-F4, a characterized c-MYC/Max inhibitor, also targets the MYCN/Max interaction, leading to cell cycle arrest, apoptosis, and neuronal differentiation in MYCN-amplified neuroblastoma cells and to increased survival of MYCN transgenic mice. We also report the discovery that inhibition of MYC is accompanied by accumulation of intracellular lipid droplets in tumor cells as a direct consequence of mitochondrial dysfunction. This study expands on the current knowledge of how MYC proteins control the metabolic reprogramming of cancer cells, especially highlighting lipid metabolism and the respiratory chain as important pathways involved in neuroblastoma pathogenesis. Together our data support direct MYC inhibition as a promising strategy for the treatment of MYC-driven tumors.