REV3L confers chemoresistance to cisplatin in human gliomas: the potential of its RNAi for synergistic therapy

Enzymatic Processing of DNA-Protein Crosslinks

DNA-protein crosslinks (DPCs) represent a unique and complex form of DNA damage formed by covalent attachment of proteins to DNA. DPCs are formed through a variety of mechanisms and can significantly impede essential cellular processes such as transcription and replication. For this reason, anti-cancer drugs that form DPCs have proven effective in cancer therapy. While cells rely on numerous different processes to remove DPCs, the molecular mechanisms responsible for orchestrating these processes remain obscure. Having this insight could potentially be harnessed therapeutically to improve clinical outcomes in the battle against cancer. In this review, we describe the ways cells enzymatically process DPCs. These processing events include direct reversal of the DPC via hydrolysis, nuclease digestion of the DNA backbone to delete the DPC and surrounding DNA, proteolytic processing of the crosslinked protein, as well as covalent modification of the DNA-crosslinked proteins with ubiquitin, SUMO, and Poly(ADP) Ribose (PAR).

Leveraging the replication stress response to optimize cancer therapy

High-fidelity DNA replication is critical for the faithful transmission of genetic information to daughter cells. Following genotoxic stress, specialized DNA damage tolerance pathways are activated to ensure replication fork progression. These pathways include translesion DNA synthesis, template switching and repriming. In this Review, we describe how DNA damage tolerance pathways impact genome stability, their connection with tumorigenesis and their effects on cancer therapy response. We discuss recent findings that single-strand DNA gap accumulation impacts chemoresponse and explore a growing body of evidence that suggests that different DNA damage tolerance factors, including translesion synthesis polymerases, template switching proteins and enzymes affecting single-stranded DNA gaps, represent useful cancer targets. We further outline how the consequences of DNA damage tolerance mechanisms could inform the discovery of new biomarkers to refine cancer therapies.

Glioma stem cell signature predicts the prognosis and the response to tumor treating fields treatment

INTRODUCTION

Glioma stem cells (GSCs) play an important role in glioma recurrence and chemo-radiotherapy (CRT) resistance. Currently, there is a lack of efficient treatment approaches targeting GSCs. This study aimed to explore the potential personalized treatment of patients with GSC-enriched gliomas.

METHODS

Single-cell RNA sequencing (scRNA-seq) was used to identify the GSC-related genes. Then, machine learning methods were applied for clustering and validation. The least absolute shrinkage and selection operator (LASSO) and COX regression were used to construct the risk scores. Survival analysis was performed. Additionally, the incidence of chemo-radiotherapy resistance, immunotherapy status, and tumor treating field (TTF) therapy response were evaluated in high- and low-risk scores groups.

RESULTS

Two GSC clusters exhibited significantly different stemness indices, immune microenvironments, and genomic alterations. Based on GSC clusters, 11-gene GSC risk scores were constructed, which exhibited a high predictive value for prognosis. In terms of therapy, patients with high GSC risk scores had a higher risk of resistance to chemotherapy. TTF therapy can comprehensively inhibit the malignant biological characteristics of the high GSC-risk-score gliomas.

CONCLUSION

Our study constructed a GSC signature consisting of 11 GSC-specific genes and identified its prognostic value in gliomas. TTF is a promising therapeutic approach for patients with GSC-enriched glioma.

DNA Damage Tolerance Pathways in Human Cells: A Potential Therapeutic Target

DNA lesions arising from both exogenous and endogenous sources occur frequently in DNA. During DNA replication, the presence of unrepaired DNA damage in the template can arrest replication fork progression, leading to fork collapse, double-strand break formation, and to genome instability. To facilitate completion of replication and prevent the generation of strand breaks, DNA damage tolerance (DDT) pathways play a key role in allowing replication to proceed in the presence of lesions in the template. The two main DDT pathways are translesion synthesis (TLS), which involves the recruitment of specialized TLS polymerases to the site of replication arrest to bypass lesions, and homology-directed damage tolerance, which includes the template switching and fork reversal pathways. With some exceptions, lesion bypass by TLS polymerases is a source of mutagenesis, potentially contributing to the development of cancer. The capacity of TLS polymerases to bypass replication-blocking lesions induced by anti-cancer drugs such as cisplatin can also contribute to tumor chemoresistance. On the other hand, during homology-directed DDT the nascent sister strand is transiently utilised as a template for replication, allowing for error-free lesion bypass. Given the role of DNA damage tolerance pathways in replication, mutagenesis and chemoresistance, a more complete understanding of these pathways can provide avenues for therapeutic exploitation. A number of small molecule inhibitors of TLS polymerase activity have been identified that show synergy with conventional chemotherapeutic agents in killing cancer cells. In this review, we will summarize the major DDT pathways, explore the relationship between damage tolerance and carcinogenesis, and discuss the potential of targeting TLS polymerases as a therapeutic approach.

ATR inhibition reverses the resistance of homologous recombination deficient MGMTlow/MMRproficient cancer cells to temozolomide

The therapeutic efficacy of temozolomide (TMZ) is hindered by inherent and acquired resistance. Biomarkers such as MGMT expression and MMR proficiency are used as predictors of response. However, not all MGMTlow/-ve/MMRproficient patients benefit from TMZ treatment, indicating a need for additional patient selection criteria. We explored the role of ATR in mediating TMZ resistance and whether ATR inhibitors (ATRi) could reverse this resistance in multiple cancer lines. We observed that only 31% of MGMTlow/-ve/MMRproficient patient-derived and established cancer lines are sensitive to TMZ at clinically relevant concentrations. TMZ treatment resulted in DNA damage signaling in both sensitive and resistant lines, but prolonged G2/M arrest and cell death were exclusive to sensitive models. Inhibition of ATR but not ATM, sensitized the majority of resistant models to TMZ and resulted in measurable DNA damage and persistent growth inhibition. Also, compromised homologous recombination (HR) via RAD51 or BRCA1 loss only conferred sensitivity to TMZ when combined with an ATRi. Furthermore, low REV3L mRNA expression correlated with sensitivity to the TMZ and ATRi combination in vitro and in vivo. This suggests that HR defects and low REV3L levels could be useful selection criteria for enhanced clinical efficacy of an ATRi plus TMZ combination.

Knockdown of DNA polymerase ζ relieved the chemoresistance of glioma via inhibiting the PI3K/AKT signaling pathway

Previous reports suggest that DNA polymerase ζ is highly expressed in glioma tissues. The present study aimed to investigate the roles of the REV7 subunit of DNA polymerase ζ in glioma cell chemoresistance and its underlying mechanisms. The bioinformatics method was used to compare the expression of REV7 in glioma and normal tissues. The expression of REV7 in glioma tumor samples and the adjacent tissue was examined by reverse transcription polymerase chain reaction. Moreover, an in vitro analysis using glioma cells was used to test the effects of REV7 siRNA on the proliferation and apoptosis of glioma cell line U251 cells, and the effect of REV7 siRNA on the sensitivity of the U251 cells to cisplatin was also explored. The expression of REV7 in glioma tumors was significantly increased. Moreover, the knockdown of REV7 in glioma cells decreased the proliferation and increased the apoptosis of U251 cells; moreover, REV7 siRNA also increased the sensitivity of U251 cells to cisplatin. Finally, REV7 may regulate the proliferation, apoptosis, and chemosensitivity of U251 cells by affecting phosphoinositide 3-kinase signaling. Our data suggest that REV7 is involved in the chemosensitivity of glioma cells and provides a theoretical basis for targeting DNA polymerase ζ to improve the sensitivity of glioma cells to chemotherapy.

Translesion DNA Synthesis and Reinitiation of DNA Synthesis in Chemotherapy Resistance

Many chemotherapy drugs block tumor cell division by damaging DNA. DNA polymerases eta (Pol η), iota (Pol ι), kappa (Pol κ), REV1 of the Y-family and zeta (Pol ζ) of the B-family efficiently incorporate nucleotides opposite a number of DNA lesions during translesion DNA synthesis. Primase-polymerase PrimPol and the Pol α-primase complex reinitiate DNA synthesis downstream of the damaged sites using their DNA primase activity. These enzymes can decrease the efficacy of chemotherapy drugs, contribute to the survival of tumor cells and to the progression of malignant diseases. DNA polymerases are promising targets for increasing the effectiveness of chemotherapy, and mutations and polymorphisms in some DNA polymerases can serve as additional prognostic markers in a number of oncological disorders.

RNA Interference Nanotherapeutics for Treatment of Glioblastoma Multiforme

Nucleic acid therapeutics for RNA interference (RNAi) are gaining attention in the treatment and management of several kinds of the so-called "undruggable" tumors via targeting specific molecular pathways or oncogenes. Synthetic ribonucleic acid (RNAs) oligonucleotides like siRNA, miRNA, shRNA, and lncRNA have shown potential as novel therapeutics. However, the delivery of such oligonucleotides is significantly hampered by their physiochemical (such as hydrophilicity, negative charge, and instability) and biopharmaceutical features (in vivo serum stability, fast renal clearance, interaction with extracellular proteins, and hindrance in cellular internalization) that markedly reduce their biological activity. Recently, several nanocarriers have evolved as suitable non-viral vectors for oligonucleotide delivery, which are known to either complex or conjugate with these oligonucleotides efficiently and also overcome the extracellular and intracellular barriers, thereby allowing access to the tumoral micro-environment for the better and desired outcome in glioblastoma multiforme (GBM). This Review focuses on the up-to-date advancements in the field of RNAi nanotherapeutics utilized for GBM treatment.

DNA polymerases in the risk and prognosis of colorectal and pancreatic cancers

Human cancers arise from the alteration of genes involved in important pathways that mainly affect cell growth and proliferation. DNA replication and DNA damages recognition and repair are among these pathways and DNA polymerases that take part in these processes are frequently involved in cancer onset and progression. For example, damaging alterations within the proofreading domain of replicative polymerases, often reported in patients affected by colorectal cancer (CRC), are considered risk factors and drivers of carcinogenesis as they can lead to the accumulation of several mutations throughout the genome. Thus, replicative polymerases can be involved in cancer when losses of their physiological functions occur. On the contrary, reparative polymerases are often involved in cancer precisely because of their physiological role. In fact, their ability to repair and bypass DNA damages, which confers genome stability, can also counteract the effect of most anticancer drugs. In addition, the altered expression can characterise some type of cancers, which exacerbates this aspect. For example, all of the DNA polymerases involved a damage bypass mechanism, known as translesion synthesis, with the only exception of polymerase theta, are downregulated in CRC. Conversely, in pancreatic ductal adenocarcinoma (PDAC), most of these polymerase result upregulated. This suggests that different types of cancer can rely on different reparative polymerases to acquire drug resistance. Here we will examine all of the aspects that link DNA polymerases with CRC and PDAC.

Association of variations in platinum resistance-related genes and prognosis in lung cancer patients

Purpose: We aimed to investigate the association of single-nucleotide polymorphisms (SNPs) in HMGB1, REV3L, and NFE2L2 with prognosis in lung cancer patients with platinum-based chemotherapy. Methods: We have recruited 348 lung cancer patients treated with platinum. Log-rank test and Cox regression analysis were used to assess overall survival (OS) and progression-free survival (PFS) among SNP genotypes. Results: The results revealed that patients carrying TC or CC genotype in REV3L rs462779 (HR=0.67, 95% CI=0.51-0.90, P=0.007) and AG or GG genotype in HMGB1 rs1045411 (HR=0.61, 95% CI=0.38-0.99, P=0.046) had a better overall survival. Additionally, carrying TC or TT genotype in rs462779 had a lower risk (OR=0.38, 95% CI=0.17-0.89, P=0.025) of lymph node metastasis, carrying AG or AA genotype in rs1045411 was significantly related to early T stage (OR=0.47, 95% CI=0.29-0.76, P=0.002). In stratified analysis, patients with TC or CC genotype in rs462779 were significantly associated with overall survival in male patients, never-smokers, patients with younger age (≤56), no family history of cancer, adenocarcinoma, advanced stage (stage III or IV), or ECOG PS 0-1. While patients with AG or GG genotype in rs1045411 were significantly associated with overall survival in patients with advanced stage (stage III or IV) or ECOG PS 0-1. Conclusion: Our results indicate that the TC or CC genotype in rs462779 and AG or GG genotype in rs1045411 are contributed to better overall survival. The REV3L rs462779 and HMGB1 rs1045411 may serve as prognosis markers in lung cancer patients with platinum-based chemotherapy.

S100A11 functions as novel oncogene in glioblastoma via S100A11/ANXA2/NF-κB positive feedback loop

Glioblastoma (GBM) is the most universal type of primary brain malignant tumour, and the prognosis of patients with GBM is poor. S100A11 plays an essential role in tumour. However, the role and molecular mechanism of S100A11 in GBM are not clear. Here, we found that S100A11 was up‐regulated in GBM tissues and higher S100A11 expression indicated poor prognosis of GBM patients. Overexpression of S100A11 promoted GBM cell growth, epithelial‐mesenchymal transition (EMT), migration, invasion and generation of glioma stem cells (GSCs), whereas its knockdown inhibited these activities. More importantly, S100A11 interacted with ANXA2 and regulated NF‐κB signalling pathway through decreasing ubiquitination and degradation of ANXA2. Additionally, NF‐κB regulated S100A11 at transcriptional level as a positive feedback. We also demonstrated the S100A11 on tumour growth in GBM using an orthotopic tumour xenografting. These data demonstrate that S100A11/ANXA2/NF‐κB positive feedback loop in GBM cells that promote the progression of GBM.

ATR mediates cisplatin resistance in 3D-cultured breast cancer cells via translesion DNA synthesis modulation

Tissue architecture and cell–extracellular matrix (cell–ECM) interaction determine the organ specificity; however, the influences of these factors on anticancer drugs preclinical studies are highly neglected. For considering such aspects, three-dimensional (3D) cell culture models are relevant tools for accurate analysis of cellular responses to chemotherapy. Here we compared the MCF-7 breast cancer cells responses to cisplatin in traditional two-dimensional (2D) and in 3D-reconstituted basement membrane (3D-rBM) cell culture models. The results showed a substantial increase of cisplatin resistance mediated by 3D microenvironment. This phenotype was independent of p53 status and autophagy activity and was also observed for other cellular models, including lung cancer cells. Such strong decrease on cellular sensitivity was not due to differences on drug-induced DNA damage, since similar levels of γ-H2AX and cisplatin–DNA adducts were detected under both conditions. However, the processing of these cisplatin-induced DNA lesions was very different in 2D and 3D cultures. Unlike cells in monolayer, cisplatin-induced DNA damage is persistent in 3D-cultured cells, which, consequently, led to high senescence induction. Moreover, only 3D-cultured cells were able to progress through S cell cycle phase, with unaffected replication fork progression, due to the upregulation of translesion (TLS) DNA polymerase expression and activation of the ATR-Chk1 pathway. Co-treatment with VE-821, a pharmacological inhibitor of ATR, blocked the 3D-mediated changes on cisplatin response, including low sensitivity and high TLS capacity. In addition, ATR inhibition also reverted induction of REV3L by cisplatin treatment. By using REV3L-deficient cells, we showed that this TLS DNA polymerase is essential for the cisplatin sensitization effect mediated by VE-821. Altogether, our results demonstrate that 3D-cell architecture-associated resistance to cisplatin is due to an efficient induction of REV3L and TLS, dependent of ATR. Thus co-treatment with ATR inhibitors might be a promising strategy for enhancement of cisplatin treatment efficiency in breast cancer patients.

Post-replication repair: Rad5/HLTF regulation, activity on undamaged templates, and relationship to cancer

The eukaryotic post-replication repair (PRR) pathway allows completion of DNA replication when replication forks encounter lesions on the DNA template and are mediated by post-translational ubiquitination of the DNA sliding clamp proliferating cell nuclear antigen (PCNA). Monoubiquitinated PCNA recruits translesion synthesis (TLS) polymerases to replicate past DNA lesions in an error-prone manner while addition of K63-linked polyubiquitin chains signals for error-free template switching to the sister chromatid. Central to both branches is the E3 ubiquitin ligase and DNA helicase Rad5/helicase-like transcription factor (HLTF). Mutations in PRR pathway components lead to genomic rearrangements, cancer predisposition, and cancer progression. Recent studies have challenged the notion that the PRR pathway is involved only in DNA lesion tolerance and have shed new light on its roles in cancer progression. Molecular details of Rad5/HLTF recruitment and function at replication forks have emerged. Mounting evidence indicates that PRR is required during lesion-less replication stress, leading to TLS polymerase activity on undamaged templates. Analysis of PRR mutation status in human cancers and PRR function in cancer models indicates that down regulation of PRR activity is a viable strategy to inhibit cancer cell growth and reduce chemoresistance. Here, we review these findings, discuss how they change our views of current PRR models, and look forward to targeting the PRR pathway in the clinic.

Exosomal transfer of long non-coding RNA SBF2-AS1 enhances chemoresistance to temozolomide in glioblastoma

Background

Acquired drug resistance is a constraining factor in clinical treatment of glioblastoma (GBM). However, the mechanisms of chemoresponsive tumors acquire therapeutic resistance remain poorly understood. Here, we aim to investigate whether temozolomide (TMZ) resistance of chemoresponsive GBM was enhanced by long non-coding RNA SBF2 antisense RNA 1 (lncRNA SBF2-AS1) enriched exosomes.

Method

LncSBF2-AS1 level in TMZ-resistance or TMZ-sensitive GBM tissues and cells were analyzed by qRT-PCR and FISH assays. A series of in vitro assay and xenograft tumor models were performed to observe the effect of lncSBF2-AS1 on TMZ-resistance in GBM. CHIP assay were used to investigate the correlation of SBF2-AS1 and transcription factor zinc finger E-box binding homeobox 1 (ZEB1). Dual-luciferase reporter, RNA immunoprecipitation (RIP), immunofluorescence and western blotting were performed to verify the relation between lncSBF2-AS1, miR-151a-3p and XRCC4. Comet assay and immunoblotting were performed to expound the effect of lncSBF2-AS1 on DNA double-stand break (DSB) repair. A series of in vitro assay and intracranial xenografts tumor model were used to determined the function of exosomal lncSBF2-AS1.

Result

It was found that SBF2-AS1 was upregulated in TMZ-resistant GBM cells and tissues, and overexpression of SBF2-AS1 led to the promotion of TMZ resistance, whereas its inhibition sensitized resistant GBM cells to TMZ. Transcription factor ZEB1 was found to directly bind to the SBF2-AS1 promoter region to regulate SBF2-AS1 level and affected TMZ resistance in GBM cells. SBF2-AS1 functions as a ceRNA for miR-151a-3p, leading to the disinhibition of its endogenous target, X-ray repair cross complementing 4 (XRCC4), which enhances DSB repair in GBM cells. Exosomes selected from temozolomide-resistant GBM cells had high levels of SBF2-AS1 and spread TMZ resistance to chemoresponsive GBM cells. Clinically, high levels of lncSBF2-AS1 in serum exosomes were associated with poor response to TMZ treatment in GBM patients.

Conclusion

We can conclude that GBM cells remodel the tumor microenvironment to promote tumor chemotherapy-resistance by secreting the oncogenic lncSBF2-AS1-enriched exosomes. Thus, exosomal lncSBF2-AS1 in human serum may serve as a possible diagnostic marker for therapy-refractory GBM.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1139-6) contains supplementary material, which is available to authorized users.

Functional Polymorphisms in DNA Repair Genes Are Associated with Sporadic Colorectal Cancer Susceptibility and Clinical Outcome

DNA repair processes are involved in both the onset and treatment efficacy of colorectal cancer (CRC). A change of a single nucleotide causing an amino acid substitution in the corresponding protein may alter the efficiency of DNA repair, thus modifying the CRC susceptibility and clinical outcome. We performed a candidate gene approach in order to analyze the association of non-synonymous single nucleotide polymorphisms (nsSNPs) in the genes covering the main DNA repair pathways with CRC risk and clinical outcome modifications. Our candidate polymorphisms were selected according to the foremost genomic and functional prediction databases. Sixteen nsSNPs in 12 DNA repair genes were evaluated in cohorts from the Czech Republic and Austria. Apart from the tumor-node-metastasis (TNM) stage, which occurred as the main prognostic factor in all of the performed analyses, we observed several significant associations of different nsSNPs with survival and clinical outcomes in both cohorts. However, only some of the genes (REV3L, POLQ, and NEIL3) were prominently defined as prediction factors in the classification and regression tree analysis; therefore, the study suggests their association for patient survival. In summary, we provide observational and bioinformatics evidence that even subtle alterations in specific proteins of the DNA repair pathways may contribute to CRC susceptibility and clinical outcome.

Mechanisms of DNA Damage Tolerance: Post-Translational Regulation of PCNA

DNA damage is a constant source of stress challenging genomic integrity. To ensure faithful duplication of our genomes, mechanisms have evolved to deal with damage encountered during replication. One such mechanism is referred to as DNA damage tolerance (DDT). DDT allows for replication to continue in the presence of a DNA lesion by promoting damage bypass. Two major DDT pathways exist: error-prone translesion synthesis (TLS) and error-free template switching (TS). TLS recruits low-fidelity DNA polymerases to directly replicate across the damaged template, whereas TS uses the nascent sister chromatid as a template for bypass. Both pathways must be tightly controlled to prevent the accumulation of mutations that can occur from the dysregulation of DDT proteins. A key regulator of error-prone versus error-free DDT is the replication clamp, proliferating cell nuclear antigen (PCNA). Post-translational modifications (PTMs) of PCNA, mainly by ubiquitin and SUMO (small ubiquitin-like modifier), play a critical role in DDT. In this review, we will discuss the different types of PTMs of PCNA and how they regulate DDT in response to replication stress. We will also cover the roles of PCNA PTMs in lagging strand synthesis, meiotic recombination, as well as somatic hypermutation and class switch recombination.

MicroRNA‑29a enhances cisplatin sensitivity in non‑small cell lung cancer through the regulation of REV3L

Cisplatin-based chemotherapy may greatly enhance patient prognosis; however, chemotherapy resistance remains an obstacle to curing patients with non-small cell lung cancer (NSCLC). The aim of the present study was to explore the microRNAs (miRs) that could regulate cisplatin sensitivity and provide a potential treatment method for cisplatin resistance in clinical. Results from the present study revealed that miR-29a overexpression enhanced and miR-29a inhibition reduced the sensitivity of two NSCLC cell lines, A549 and H1650, to cisplatin treatment. In addition, reduced miR-29a expression levels were observed in cisplatin-resistant A549 cells (A549rCDDP), and increased expression of miR-29a augmented cisplatin-induced inhibition of proliferation and apoptosis in A549rCDDP cells. These data indicated that miR-29a expression may be involved in the development of cisplatin resistance. miR-29a was revealed to negatively regulate REV3-like DNA-directed polymerase ζ catalytic subunit (REV3L) expression in both A549 and H1650 cells; elevated expression of REV3L in A549rCDDP cells was also detected. REV3L encodes the catalytic subunit of DNA polymerase ζ and was hypothesized, based on results from the online tool TargetScan 7.1, to be a target gene of miR-29a; this was confirmed with a dual luciferase assay. Cells treated with a very low concentration of cisplatin exhibited a significant reduction in proliferation and cell cycle arrest at the G2/M phase in REV3L-knockdown as well as in miR-29a-upregulated A549 cells. Notably, reduced miR-29a expression and an increase in REV3L mRNA expression were observed in tumor tissues from patients with NSCLC. Additionally, a negative correlation between miR-29a and REV3L mRNA expression levels in tumor tissues from patients with NSCLC was observed; low expression of miR-29a and high expression of REV3L were closely associated with an advanced tumor-node-metastasis classification. The results of the present study suggested a pivotal role of miR-29a in mediating NSCLC cell sensitivity towards cisplatin through the regulation of REV3L.

pH-Responsive Cross-Linked Low Molecular Weight Polyethylenimine as an Efficient Gene Vector for Delivery of Plasmid DNA Encoding Anti-VEGF-shRNA for Tumor Treatment

RNA interference (RNAi) is a biological process through which gene expression can be inhibited by RNA molecules with high selectivity and specificity, providing a promising tool for tumor treatment. Two types of molecules are often applied to inactivate target gene expression: synthetic double stranded small interfering RNA (siRNA) and plasmid DNA encoding short hairpin RNA (shRNA). Vectors with high transfection efficiency and low toxicity are essential for the delivery of siRNA and shRNA. In this study, TDAPEI, the synthetic derivative of low-molecular-weight polyethylenimine (PEI), was cross-linked with imine bonds by the conjugation of branched PEI (1.8 kDa) and 2,5-thiophenedicarboxaldehyde (TDA). This biodegradable cationic polymer was utilized as the vector for the delivery of plasmid DNA expressing anti-VEGF-shRNA. Compared to PEI (25 kDa), TDAPEI had a better performance since experimental results suggest its higher transfection efficiency as well as lower toxicity both in cell and animal studies. TDAPEI did not stimulate innate immune response, which is a significant factor that should be considered in vector design for gene delivery. All the results suggested that TDAPEI delivering anti-VEGF-shRNA may provide a promising method for tumor treatment.

DNA repair pathways and cisplatin resistance: an intimate relationship

The main goal of chemotherapeutic drugs is to induce massive cell death in tumors. Cisplatin is an antitumor drug widely used to treat several types of cancer. Despite its remarkable efficiency, most tumors show intrinsic or acquired drug resistance. The primary biological target of cisplatin is genomic DNA, and it causes a plethora of DNA lesions that block transcription and replication. These cisplatin-induced DNA lesions strongly induce cell death if they are not properly repaired or processed. To counteract cisplatin-induced DNA damage, cells use an intricate network of mechanisms, including DNA damage repair and translesion synthesis. In this review, we describe how cisplatin-induced DNA lesions are repaired or tolerated by cells and focus on the pivotal role of DNA repair and tolerance mechanisms in tumor resistance to cisplatin. In fact, several recent clinical findings have correlated the tumor cell status of DNA repair/translesion synthesis with patient response to cisplatin treatment. Furthermore, these mechanisms provide interesting targets for pharmacological modulation that can increase the efficiency of cisplatin chemotherapy.

MicroRNA-340 inhibits the proliferation and promotes the apoptosis of colon cancer cells by modulating REV3L

DNA Directed Polymerase Zeta Catalytic Subunit (REV3L) has recently emerged as an important oncogene. Although the expressions of REV3L are similar in normal and cancer cells, several mutations in REV3L have been shown to play important roles in cancer. These mutations cause proteins misfolding and mislocalization, which in turn alters their interactions and biological functions. miRNAs play important regulatory roles during the progression and metastasis of several human cancers. This study was undertaken to determine how changes in the location and interactions of REV3L regulate colon cancer progression. REV3L protein mislocalization confirmed from the immunostaining results and the known interactions of REV3L was found to be broken as seen from the PLA assay results. The mislocalized REV3L might interact with new proteins partners in the cytoplasm which in turn may play role in regulating colon cancer progression. hsa-miR-340 (miR-340), a microRNA down-regulated in colon cancer, was used to bind to and downregulate REV3L, and found to control the proliferation and induce the apoptosis of colon cancer cells (HCT-116 and DLD-1) via the MAPK pathway. Furthermore, this down-regulation of REV3L also diminished colon cancer cell migration, and down-regulated MMP-2 and MMP-9. Combined treatment of colon cancer cells with miR-340 and 5-FU enhanced the inhibitory effects of 5-FU. In addition, in vivo experiments conducted on nude mice revealed tumor sizes were smaller in a HCT-116-miR-340 injected group than in a HCT-116-pCMV injected group. Our findings suggest mutations in REV3L causes protein mislocalization to the cytoplasm, breaking its interaction and is believed to form new protein interactions in cytoplasm contributing to colon cancer progression. Accordingly, microRNA-340 appears to be a good candidate for colon cancer therapy.

Cytoplasmic RAP1 mediates cisplatin resistance of non-small cell lung cancer

Cytotoxic chemotherapy agents (e.g., cisplatin) are the first-line drugs to treat non-small cell lung cancer (NSCLC) but NSCLC develops resistance to the agent, limiting therapeutic efficacy. Despite many approaches to identifying the underlying mechanism for cisplatin resistance, there remains a lack of effective targets in the population that resist cisplatin treatment. In this study, we sought to investigate the role of cytoplasmic RAP1, a previously identified positive regulator of NF-κB signaling, in the development of cisplatin resistance in NSCLC cells. We found that the expression of cytoplasmic RAP1 was significantly higher in high-grade NSCLC tissues than in low-grade NSCLC; compared with a normal pulmonary epithelial cell line, the A549 NSCLC cells exhibited more cytoplasmic RAP1 expression as well as increased NF-κB activity; cisplatin treatment resulted in a further increase of cytoplasmic RAP1 in A549 cells; overexpression of RAP1 desensitized the A549 cells to cisplatin, and conversely, RAP1 depletion in the NSCLC cells reduced their proliferation and increased their sensitivity to cisplatin, indicating that RAP1 is required for cell growth and has a key mediating role in the development of cisplatin resistance in NSCLC cells. The RAP1-mediated cisplatin resistance was associated with the activation of NF-κB signaling and the upregulation of the antiapoptosis factor BCL-2. Intriguingly, in the small portion of RAP1-depleted cells that survived cisplatin treatment, no induction of NF-κB activity and BCL-2 expression was observed. Furthermore, in established cisplatin-resistant A549 cells, RAP1 depletion caused BCL2 depletion, caspase activation and dramatic lethality to the cells. Hence, our results demonstrate that the cytoplasmic RAP1–NF-κB–BCL2 axis represents a key pathway to cisplatin resistance in NSCLC cells, identifying RAP1 as a marker and a potential therapeutic target for cisplatin resistance of NSCLC.

Structural insight into inhibition of REV7 protein interaction revealed by docking, molecular dynamics and MM/PBSA studies

The inhibitors of the REV7/REV3L protein interaction bind to the two pockets of REV7 divided by the ‘safety-belt’ structure, as revealed by computational modeling.

DNA polymerases in the mitochondria: A critical review of the evidence

Since 1970, the DNA polymerase gamma (PolG) has been known to be the DNA polymerase responsible for replication and repair of mitochondrial DNA, and until recently it was generally accepted that this was the only polymerase present in mitochondria. However, recent data has challenged that opinion, as several polymerases are now proposed to have activity in mitochondria. To date, their exact role of these other DNA polymerases is unclear and the amount of evidence supporting their role in mitochondria varies greatly. Further complicating matters, no universally accepted standards have been set for definitive proof of the mitochondrial localization of a protein. To gain an appreciation of these newly proposed DNA polymerases in the mitochondria, we review the evidence and standards needed to establish the role of a polymerase in the mitochondria. Employing PolG as an example, we established a list of criteria necessary to verify the existence and function of new mitochondrial proteins. We then apply this criteria towards several other putative mitochondrial polymerases. While there is still a lot left to be done in this exciting new direction, it is clear that PolG is not acting alone in mitochondria, opening new doors for potential replication and repair mechanisms.

Co-inhibition of pol θ and HR genes efficiently synergize with cisplatin to suppress cisplatin-resistant lung cancer cells survival

Cisplatin exert its anticancer effect by creating intrastrand and interstrand DNA cross-links which block DNA replication and is a major drug used to treat lung cancer. However, the main obstacle of the efficacy of treatment is drug resistance. Here, we show that expression of translesion synthesis (TLS) polymerase Q (POLQ) was significantly elevated by exposure of lung cancer cells A549/DR (a cisplatin-resistant A549 cell line) to cisplatin. POLQ expression correlated inversely with homologous recombination (HR) activity. Co-depletion of BRCA2 and POLQ by siRNA markedly increased sensitivity of A549/DR cells to cisplatin, which was accompanied with impairment of double strand breaks (DSBs) repair reflected by prominent cell cycle checkpoint response, increased chromosomal aberrations and persistent colocalization of p-ATM and 53BP1 foci induced by cisplatin. Thus, co-knockdown of POLQ and HR can efficiently synergize with cisplatin to inhibit A549/DR cell survival by inhibiting DNA DSBs repair. Similar results were observed in A549/DR cells co-depleted of BRCA2 and POLQ following BMN673 (a PARP inhibitor) treatment. Importantly, the sensitization effects to cisplatin and BMN673 in A549/DR cells by co-depleting BRCA2 and POLQ was stronger than those by co-depleting BRCA2 and other TLS factors including POLH, REV3, or REV1. Our results indicate that there is a synthetic lethal relationship between pol θ-mediated DNA repair and HR pathways. Pol θ may be considered as a novel target for lung cancer therapy.

A Comprehensive Review on the Genetic Regulation of Cisplatin-induced Nephrotoxicity

Cisplatin (CDDP) is a well-known antineoplastic drug which has been extensively utilized over the last decades in the treatment of numerous kinds of tumors. However, CDDP induces a wide range of toxicities in a dose-dependent manner, among which nephrotoxicity is of particular importance. Still, the mechanism of CDDP-induced renal damage is not completely understood; moreover, the knowledge about the role of microRNAs (miRNAs) in the nephrotoxic response is still unknown. miRNAs are known to interact with the representative members of a diverse range of regulatory pathways (including postnatal development, proliferation, inflammation and fibrosis) and pathological conditions, including kidney diseases: polycystic kidney diseases (PKDs), diabetic nephropathy (DN), kidney cancer, and drug-induced kidney injury. In this review, we shed light on the following important aspects: (i) information on genes/proteins and their interactions with previously known pathways engaged with CDDP-induced nephrotoxicity, (ii) information on newly discovered biomarkers, especially, miRNAs for detecting CDDP-induced nephrotoxicity and (iii) information to improve our understanding on CDDP. This information will not only help the researchers belonging to nephrotoxicity field, but also supply an indisputable help for oncologists to better understand and manage the side effects induced by CDDP during cancer treatment. Moreover, we provide up-to-date information about different in vivo and in vitro models that have been utilized over the last decades to study CDDP-induced renal injury. Taken together, this review offers a comprehensive network on genes, miRNAs, pathways and animal models which will serve as a useful resource to understand the molecular mechanism of CDDP-induced nephrotoxicity.

The Error-Prone DNA Polymerase κ Promotes Temozolomide Resistance in Glioblastoma through Rad17-Dependent Activation of ATR-Chk1 Signaling

The acquisition of drug resistance is a persistent clinical problem limiting the successful treatment of human cancers, including glioblastoma (GBM). However, the molecular mechanisms by which initially chemoresponsive tumors develop therapeutic resistance remain poorly understood. In this study, we report that Pol κ, an error-prone polymerase that participates in translesion DNA synthesis, was significantly upregulated in GBM cell lines and tumor tissues following temozolomide treatment. Overexpression of Pol κ in temozolomide-sensitive GBM cells conferred resistance to temozolomide, whereas its inhibition markedly sensitized resistant cells to temozolomide in vitro and in orthotopic xenograft mouse models. Mechanistically, depletion of Pol κ disrupted homologous recombination (HR)-mediated repair and restart of stalled replication forks, impaired the activation of ATR-Chk1 signaling, and delayed cell-cycle re-entry and progression. Further investigation of the relationship between Pol κ and temozolomide revealed that Pol κ inactivation facilitated temozolomide-induced Rad17 ubiquitination and proteasomal degradation, subsequently silencing ATR-Chk1 signaling and leading to defective HR repair and the reversal of temozolomide resistance. Moreover, overexpression of Rad17 in Pol κ-depleted GBM cells restored HR efficiency, promoted the clearance of temozolomide-induced DNA breaks, and desensitized cells to the cytotoxic effects of temozolomide observed in the absence of Pol κ. Finally, we found that Pol κ overexpression correlated with poor prognosis in GBM patients undergoing temozolomide therapy. Collectively, our findings identify a potential mechanism by which GBM cells develop resistance to temozolomide and suggest that targeting the DNA damage tolerance pathway may be beneficial for overcoming resistance. Cancer Res; 76(8); 2340-53. ©2016 AACR.

Association of polymorphisms in translesion synthesis genes with prognosis of advanced non-small-cell lung cancer patients treated with platinum-based chemotherapy

BACKGROUND AND OBJECTIVES

Translesion synthesis (TLS) polymerases enable cells to bypass or overcome DNA damage during DNA replication and contributes to genomic instability and cancer. Inhibition of the expression of TLS genes enhances the sensitivity of cancer cells to cisplatin. This study aimed to investigate the relationship between single nucleotide polymorphisms (SNPs) in the TLS genes and clinical outcome of advanced non-small-cell lung cancer (NSCLC) patients treated with platinum-based chemotherapy.

METHODS

A total of 16 SNPs were genotyped and analyzed in 302 advanced NSCLC patients (discovery set), and the results were further validated in additional 428 NSCLC patients (validation set).

RESULTS

Analyses revealed significant associations of two SNPs, rs3213801 and rs3792136, with overall survival, with the lowest combined P values of 0.003 and 0.016, respectively. These effects also remained in stratification analyses by clinical variables. Furthermore, the number of risk genotypes of the two SNPs showed a cumulative effect on overall survival (P = 0.03).

CONCLUSIONS

Genetic polymorphisms in the TLS genes might serve as potential predictive biomarkers of prognosis of advanced NSCLC patients treated with platinum-based chemotherapy.

Human REV3 DNA Polymerase Zeta Localizes to Mitochondria and Protects the Mitochondrial Genome

To date, mitochondrial DNA polymerase γ (POLG) is the only polymerase known to be present in mammalian mitochondria. A dogma in the mitochondria field is that there is no other polymerase present in the mitochondria of mammalian cells. Here we demonstrate localization of REV3 DNA polymerase in the mammalian mitochondria. We demonstrate localization of REV3 in the mitochondria of mammalian tissue as well as cell lines. REV3 associates with POLG and mitochondrial DNA and protects the mitochondrial genome from DNA damage. Inactivation of Rev3 leads to reduced mitochondrial membrane potential, reduced OXPHOS activity, and increased glucose consumption. Conversely, inhibition of the OXPHOS increases expression of Rev3. Rev3 expression is increased in human primary breast tumors and breast cancer cell lines. Inactivation of Rev3 decreases cell migration and invasion, and localization of Rev3 in mitochondria increases survival and the invasive potential of cancer cells. Taken together, we demonstrate that REV3 functions in mammalian mitochondria and that mitochondrial REV3 is associated with the tumorigenic potential of cells.

c-Myc-miR-29c-REV3L signalling pathway drives the acquisition of temozolomide resistance in glioblastoma

Resistance to temozolomide poses a major clinical challenge in glioblastoma multiforme treatment, and the mechanisms underlying the development of temozolomide resistance remain poorly understood. Enhanced DNA repair and mutagenesis can allow tumour cells to survive, contributing to resistance and tumour recurrence. Here, using recurrent temozolomide-refractory glioblastoma specimens, temozolomide-resistant cells, and resistant-xenograft models, we report that loss of miR-29c via c-Myc drives the acquisition of temozolomide resistance through enhancement of REV3L-mediated DNA repair and mutagenesis in glioblastoma. Importantly, disruption of c-Myc/miR-29c/REV3L signalling may have dual anticancer effects, sensitizing the resistant tumours to therapy as well as preventing the emergence of acquired temozolomide resistance. Our findings suggest a rationale for targeting the c-Myc/miR-29c/REV3L signalling pathway as a promising therapeutic approach for glioblastoma, even in recurrent, treatment-refractory settings.

RNA interferences targeting the Fanconi anemia/BRCA pathway upstream genes reverse cisplatin resistance in drug-resistant lung cancer cells

BACKGROUND

Cisplatin is one of the most commonly used chemotherapy agent for lung cancer. The therapeutic efficacy of cisplatin is limited by the development of resistance. In this study, we test the effect of RNA interference (RNAi) targeting Fanconi anemia (FA)/BRCA pathway upstream genes on the sensitivity of cisplatin-sensitive (A549 and SK-MES-1) and -resistant (A549/DDP) lung cancer cells to cisplatin.

RESULT

Using small interfering RNA (siRNA), knockdown of FANCF, FANCL, or FANCD2 inhibited function of the FA/BRCA pathway in A549, A549/DDP and SK-MES-1 cells, and potentiated sensitivity of the three cells to cisplatin. The extent of proliferation inhibition induced by cisplatin after knockdown of FANCF and/or FANCL in A549/DDP cells was significantly greater than in A549 and SK-MES-1 cells, suggesting that depletion of FANCF and/or FANCL can reverse resistance of cisplatin-resistant lung cancer cells to cisplatin. Furthermore, knockdown of FANCL resulted in higher cisplatin sensitivity and dramatically elevated apoptosis rates compared with knockdown of FANCF in A549/DDP cells, indicating that FANCL play an important role in the repair of cisplatin-induced DNA damage.

CONCLUSION

Knockdown of FANCF, FANCL, or FANCD2 by RNAi could synergize the effect of cisplatin on suppressing cell proliferation in cisplatin-resistant lung cancer cells through inhibition of FA/BRCA pathway.

Exploiting the Fanconi Anemia Pathway for Targeted Anti-Cancer Therapy

Genome instability, primarily caused by faulty DNA repair mechanisms, drives tumorigenesis. Therapeutic interventions that exploit deregulated DNA repair in cancer have made considerable progress by targeting tumor-specific alterations of DNA repair factors, which either induces synthetic lethality or augments the efficacy of conventional chemotherapy and radiotherapy. The study of Fanconi anemia (FA), a rare inherited blood disorder and cancer predisposition syndrome, has been instrumental in understanding the extent to which DNA repair defects contribute to tumorigenesis. The FA pathway functions to resolve blocked replication forks in response to DNA interstrand cross-links (ICLs), and accumulating knowledge of its activation by the ubiquitin-mediated signaling pathway has provided promising therapeutic opportunities for cancer treatment. Here, we discuss recent advances in our understanding of FA pathway regulation and its potential application for designing tailored therapeutics that take advantage of deregulated DNA ICL repair in cancer.

Resistance to therapy in BRCA2 mutant cells due to loss of the nucleosome remodeling factor CHD4

BRCA-associated cancers are sensitive to DNA-damaging agents such as cisplatin, but the efficacy of cisplatin is limited by the development of resistance. Guillemette et al. performed a genome-wide short hairpin (shRNA) screen and found that loss of the nucleosome remodeling factor CHD4 conferred cisplatin resistance. Cisplatin-resistant clones lacking genetic reversion of BRCA2 show de novo loss of CHD4 expression in vitro. BRCA2 mutant ovarian cancers with reduced CHD4 expression correlate with shorter progression-free survival and shorter overall survival.

Hereditary cancers derive from gene defects that often compromise DNA repair. Thus, BRCA-associated cancers are sensitive to DNA-damaging agents such as cisplatin. The efficacy of cisplatin is limited, however, by the development of resistance. One cisplatin resistance mechanism is restoration of homologous recombination (HR), which can result from BRCA reversion mutations. However, in BRCA2 mutant cancers, cisplatin resistance can occur independently of restored HR by a mechanism that remains unknown. Here we performed a genome-wide shRNA screen and found that loss of the nucleosome remodeling factor CHD4 confers cisplatin resistance. Restoration of cisplatin resistance is independent of HR but correlates with restored cell cycle progression, reduced chromosomal aberrations, and enhanced DNA damage tolerance. Suggesting clinical relevance, cisplatin-resistant clones lacking genetic reversion of BRCA2 show de novo loss of CHD4 expression in vitro. Moreover, BRCA2 mutant ovarian cancers with reduced CHD4 expression significantly correlate with shorter progression-free survival and shorter overall survival. Collectively, our findings indicate that CHD4 modulates therapeutic response in BRCA2 mutant cancer cells.

REV3L, a promising target in regulating the chemosensitivity of cervical cancer cells

REV3L, the catalytic subunit of DNA Polymerase ζ (Polζ), plays a significant role in the DNA damage tolerance mechanism of translesion synthesis (TLS). The role of REV3L in chemosensitivity of cervical cancer needs exploration. In the present study, we evaluated the expression of the Polζ protein in paraffin-embedded tissues using immunohistochemistry and found that the expression of Polζ in cervical cancer tissues was higher than that in normal tissues. We then established some cervical cancer cell lines with REV3L suppression or overexpression. Depletion of REV3L suppresses cell proliferation and colony formation of cervical cancer cells through G₁ arrest, and REV3L promotes cell proliferation and colony formation of cervical cancer cells by promoting G₁ phase to S phase transition. The suppression of REV3L expression enhanced the sensitivity of cervical cancer cells to cisplatin, and the overexpression of REV3L conferred resistance to cisplatin as evidenced by the alteration of apoptosis rates, and significantly expression level changes of anti-apoptotic proteins B-cell lymphoma 2 (Bcl-2), myeloid cell leukemia sequence 1 (Mcl-1) and B-cell lymphoma-extra large (Bcl-xl) and proapoptotic Bcl-2-associated x protein (Bax). Our data suggest that REV3L plays an important role in regulating cervical cancer cellular response to cisplatin, and thus targeting REV3L may be a promising way to alter chemosensitivity in cervical cancer patients.

Eukaryotic DNA polymerase ζ

This review focuses on eukaryotic DNA polymerase ζ (Pol ζ), the enzyme responsible for the bulk of mutagenesis in eukaryotic cells in response to DNA damage. Pol ζ is also responsible for a large portion of mutagenesis during normal cell growth, in response to spontaneous damage or to certain DNA structures and other blocks that stall DNA replication forks. Novel insights in mutagenesis have been derived from recent advances in the elucidation of the subunit structure of Pol ζ. The lagging strand DNA polymerase δ shares the small Pol31 and Pol32 subunits with the Rev3-Rev7 core assembly giving a four subunit Pol ζ complex that is the active form in mutagenesis. Furthermore, Pol ζ forms essential interactions with the mutasome assembly factor Rev1 and with proliferating cell nuclear antigen (PCNA). These interactions are modulated by posttranslational modifications such as ubiquitination and phosphorylation that enhance translesion synthesis (TLS) and mutagenesis.

miR-25 promotes glioma cell proliferation by targeting CDKN1C

MicroRNAs (miRNA) have oncogenic or tumor-suppressive roles in the development and growth of human glioma. Glioma development is also associated with alteration in the activities and expression of cell cycle regulators, and miRNAs are emerging as important regulators of cell cycle progression. Here, we show that miR-25 is overexpressed in 91% of examined human glioma tissues and 4 out of 6 human glioma cell lines. MiR-25 increases cell proliferation in two independent glioma cell lines. Ectopic expression of miR-25 was found to reduce CDKN1C protein levels by directly targeting its 3'-untranslated region (UTR). Notably, ablation of endogenous miR-25 rescued CDKN1C expression and significantly decreased glioma cell proliferation by facilitating normal cell cycle progression. Our clinical investigation found CDKN1C and miR-25 levels were inversely correlated. Lastly, downregulation of CDKN1 by siRNA blocked the activity of miR-25 on promoting glioma cell proliferation. Overall, our results for the first time show an oncogenic role of miR-25 in human glioma by targeting CDKN1C and that miR-25 could potentially be a therapeutic target for glioma intervention.

Dendrimer-PLGA based multifunctional immuno-nanocomposite mediated synchronous and tumor selective delivery of siRNA and cisplatin: potential in treatment of hepatocellular carcinoma

The in-house synthesized PLK-1 siRNA and cisplatin loaded innovative dendrimer-PLGA immuno-nanocomposite bears the capacity of delivering both the cargos simultaneously to the same liver cancer cell in a targeted manner.

Crosstalk between translesion synthesis, Fanconi anemia network, and homologous recombination repair pathways in interstrand DNA crosslink repair and development of chemoresistance

Bifunctional alkylating and platinum based drugs are chemotherapeutic agents used to treat cancer. These agents induce DNA adducts via formation of intrastrand or interstrand (ICL) DNA crosslinks, and DNA lesions of the ICL type are particularly toxic as they block DNA replication and/or DNA transcription. However, the therapeutic efficacies of these drugs are frequently limited due to the cancer cell's enhanced ability to repair and tolerate these toxic DNA lesions. This ability to tolerate and survive the DNA damage is accomplished by a set of specialized low fidelity DNA polymerases called translesion synthesis (TLS) polymerases since high fidelity DNA polymerases are unable to replicate the damaged DNA template. TLS is a crucial initial step in ICL repair as it synthesizes DNA across the lesion thus preparing the damaged DNA template for repair by the homologous recombination (HR) pathway and Fanconi anemia (FA) network, processes critical for ICL repair. Here we review the molecular features and functional roles of TLS polymerases, discuss the collaborative interactions and cross-regulation of the TLS DNA damage tolerance pathway, the FA network and the BRCA-dependent HRR pathway, and the impact of TLS hyperactivation on development of chemoresistance. Finally, since TLS hyperactivation results from overexpression of Rad6/Rad18 ubiquitinating enzymes (fundamental components of the TLS pathway), increased PCNA ubiquitination, and/or increased recruitment of TLS polymerases, the potential benefits of selectively targeting critical components of the TLS pathway for enhancing anti-cancer therapeutic efficacy and curtailing chemotherapy-induced mutagenesis are also discussed.

Expression and prognostic significance of TCTN1 in human glioblastoma

Background

Glioblastoma (GBM) is the most common and lethal intracranial malignancy in adults, with dismal prognosis despite multimodal therapies. Tectonic family member 1 (TCTN1) is a protein involved in a diverse range of developmental processes, yet its functions in GBM remain unclear. This study aims to investigate expression profile, prognostic value and effects of TCTN1 gene in GBM.

Methods

Protein levels of TCTN1 were assessed by immunohistochemical staining using a tissue microarray constructed by a Chinese cohort of GBM patients (n = 110), and its mRNA expression was also detected in a subset of this cohort. Kaplan-Meier analysis and Cox regression were performed to estimate the prognostic significance of TCTN1. Similar analyses were also conducted in another two independent cohorts: The Cancer Genome Atlas (TCGA) cohort (n = 528) and the Repository for Molecular Brain Neoplasia Data (REMBRANDT) cohort (n = 228). For the TCGA cohort, the relationships between TCTN1 expression, clinical outcome, molecular subtypes and genetic alterations were also analysed. Furthermore, proliferation of TCTN1 overexpressed or silenced GBM cells was determined by CCK-8 assays.

Results

As discovered in three independent cohorts, both mRNA and protein levels of TCTN1 expression were markedly elevated in human GBMs, and higher TCTN1 expression served as an independent prognostic factor predicting poorer prognosis of GBM patients. Additionally, in the TCGA cohort, TCTN1 expression was dramatically decreased in patients within the proneural subtype compared to other subtypes, and significantly influenced by the status of several genetic aberrations such as CDKN2A/B deletion, EGFR amplification, PTEN deletion and TP53 mutation. The prognostic value of TCTN1 was more pronounced in proneural and mesenchymal subtypes, and was also affected by several genetic alterations particularly PTEN deletion. Furthermore, overexpression of TCTN1 significantly promoted proliferation of GBM cells, while its depletion evidently hampered cell growth.

Conclusions

TCTN1 is elevated in human GBMs and predicts poor clinical outcome for GBM patients, which is associated with molecular subtypes and genetic features of GBMs. Additionally, TCTN1 expression impacts GBM cell proliferation. Our results suggest for the first time that TCTN1 may serve as a novel prognostic factor and a potential therapeutic target for GBM.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0288-9) contains supplementary material, which is available to authorized users.

VAMP8 facilitates cellular proliferation and temozolomide resistance in human glioma cells

BACKGROUND

Malignant glioma is a common and lethal primary brain tumor in adults. Here we identified a novel oncoprotein, vesicle-associated membrane protein 8 (VAMP8), and investigated its roles in tumorigenisis and chemoresistance in glioma.

METHODS

The expression of gene and protein were determined by quantitative PCR and Western blot, respectively. Histological analysis of 282 glioma samples and 12 normal controls was performed by Pearson's chi-squared test. Survival analysis was performed using the log-rank test and Cox proportional hazards regression. Cell proliferation and cytotoxicity assay were conducted using Cell Counting Kit-8. Autophagy was detected by confocal microscopy and Western blot.

RESULTS

VAMP8 was significantly overexpressed in human glioma specimens and could become a potential novel prognostic and treatment-predictive marker for glioma patients. Overexpression of VAMP8 promoted cell proliferation in vitro and in vivo, whereas knockdown of VAMP8 attenuated glioma growth by arresting cell cycle in the G0/G1 phase. Moreover, VAMP8 contributed to temozolomide (TMZ) resistance by elevating the expression levels of autophagy proteins and the number of autophagosomes. Further inhibition of autophagy via siRNA-mediated knockdown of autophagy-related gene 5 (ATG5) or syntaxin 17 (STX17) reversed TMZ resistance in VAMP8-overexpressing cells, while silencing of VAMP8 impaired the autophagic flux and alleviated TMZ resistance in glioma cells.

CONCLUSION

Our findings identified VAMP8 as a novel oncogene by promoting cell proliferation and therapeutic resistance in glioma. Targeting VAMP8 may serve as a potential therapeutic regimen for the treatment of glioma.

MicroRNA-377 inhibited proliferation and invasion of human glioblastoma cells by directly targeting specificity protein 1

BACKGROUND

Increasing evidence has indicated that microRNAs (miRNAs) are strongly implicated in the initiation and progression of glioblastoma multiforme (GBM). Here, we identified a novel tumor suppressive miRNA, miR-377, and investigated its role and therapeutic effect for GBM.

METHODS

MiRNA global screening was performed on GBM patient samples and adjacent nontumor brain tissues. The expression of miR-377 was detected by real-time reverse-transcription PCR. The effects of miR-377 on GBM cell proliferation, cell cycle progression, invasion, and orthotopic tumorigenicity were investigated The therapeutic effect of miR-377 mimic was explored in a subcutaneous GBM model. Western blot and luciferase reporter assay were used to identify the direct and functional target of miR-377.

RESULTS

MiR-377 was markedly downregulated in human GBM tissues and cell lines. Overexpression of miR-377 dramatically inhibited cell growth both in culture and in orthotopic xenograft tumor models, blocked G1/S transition, and suppressed cell invasion in GBM cells. Importantly, introduction of miR-377 could strongly inhibit tumor growth in a subcutaneous GBM model. Subsequent investigation revealed that specificity protein 1 (Sp1) was a direct and functional target of miR-377 in GBM cells. Silencing of Sp1 recapitulated the antiproliferative and anti-invasive effects of miR-377, whereas restoring the Sp1 expression antagonized the tumor-suppressive function of miR-377. Finally, analysis of miR-377 and Sp1 levels in human GBM tissues revealed that miR-377 is inversely correlated with Sp1 expression.

CONCLUSION

These findings reveal that miR-377/Sp1 signaling that may be required for GBM development and may consequently serve as a therapeutic target for the treatment of GBM.

Systems biology of cisplatin resistance: past, present and future

The platinum derivative cis-diamminedichloroplatinum(II), best known as cisplatin, is currently employed for the clinical management of patients affected by testicular, ovarian, head and neck, colorectal, bladder and lung cancers. For a long time, the antineoplastic effects of cisplatin have been fully ascribed to its ability to generate unrepairable DNA lesions, hence inducing either a permanent proliferative arrest known as cellular senescence or the mitochondrial pathway of apoptosis. Accumulating evidence now suggests that the cytostatic and cytotoxic activity of cisplatin involves both a nuclear and a cytoplasmic component. Despite the unresolved issues regarding its mechanism of action, the administration of cisplatin is generally associated with high rates of clinical responses. However, in the vast majority of cases, malignant cells exposed to cisplatin activate a multipronged adaptive response that renders them less susceptible to the antiproliferative and cytotoxic effects of the drug, and eventually resume proliferation. Thus, a large fraction of cisplatin-treated patients is destined to experience therapeutic failure and tumor recurrence. Throughout the last four decades great efforts have been devoted to the characterization of the molecular mechanisms whereby neoplastic cells progressively lose their sensitivity to cisplatin. The advent of high-content and high-throughput screening technologies has accelerated the discovery of cell-intrinsic and cell-extrinsic pathways that may be targeted to prevent or reverse cisplatin resistance in cancer patients. Still, the multifactorial and redundant nature of this phenomenon poses a significant barrier against the identification of effective chemosensitization strategies. Here, we discuss recent systems biology studies aimed at deconvoluting the complex circuitries that underpin cisplatin resistance, and how their findings might drive the development of rational approaches to tackle this clinically relevant problem.

RAD18 mediates resistance to ionizing radiation in human glioma cells

Radioresistance remains a major challenge in the treatment of glioblastoma multiforme (GBM). RAD18 a central regulator of translesion DNA synthesis (TLS), has been shown to play an important role in regulating genomic stability and DNA damage response. In the present study, we investigate the relationship between RAD18 and resistance to ionizing radiation (IR) and examined the expression levels of RAD18 in primary and recurrent GBM specimens. Our results showed that RAD18 is an important mediator of the IR-induced resistance in GBM. The expression level of RAD18 in glioma cells correlates with their resistance to IR. Ectopic expression of RAD18 in RAD18-low A172 glioma cells confers significant resistance to IR treatment. Conversely, depletion of endogenous RAD18 in RAD18-high glioma cells sensitized these cells to IR treatment. Moreover, RAD18 overexpression confers resistance to IR-mediated apoptosis in RAD18-low A172 glioma cells, whereas cells deficient in RAD18 exhibit increased apoptosis induced by IR. Furthermore, knockdown of RAD18 in RAD18-high glioma cells disrupts HR-mediated repair, resulting in increased accumulation of DSB. In addition, clinical data indicated that RAD18 was significantly higher in recurrent GBM samples that were exposed to IR compared with the corresponding primary GBM samples. Collectively, our findings reveal that RAD18 may serve as a key mediator of the IR response and may function as a potential target for circumventing IR resistance in human GBM.

A distinct reactive oxygen species profile confers chemoresistance in glioma-propagating cells and associates with patient survival outcome

AIMS

We explore the role of an elevated O2(-):H2O2 ratio as a prosurvival signal in glioma-propagating cells (GPCs). We hypothesize that depleting this ratio sensitizes GPCs to apoptotic triggers.

RESULTS

We observed that an elevated O2(-):H2O2 ratio conferred enhanced resistance in GPCs, and depletion of this ratio by pharmacological and genetic methods sensitized cells to apoptotic triggers. We established the reactive oxygen species (ROS) Index as a quantitative measure of a normalized O2(-):H2O2 ratio and determined its utility in predicting chemosensitivity. Importantly, mice implanted with GPCs of a reduced ROS Index demonstrated extended survival. Analysis of tumor sections revealed effective targeting of complementarity determinant 133 (CD133)- and nestin-expressing neural precursors. Further, we established the Connectivity Map to interrogate a gene signature derived from a varied ROS Index for the patterns of association with individual patient gene expression in four clinical databases. We showed that patients with a reduced ROS Index demonstrate better survival. These data provide clinical evidence for the viability of our O2(-):H2O2-mediated chemosensitivity profiles.

INNOVATION AND CONCLUSION

Gliomas are notoriously recurrent and highly infiltrative, and have been shown to arise from stem-like cells. We implicate an elevated O2(-):H2O2 ratio as a prosurvival signal in GPC self-renewal and proliferation. The ROS Index provides quantification of O2(-):H2O2-mediated chemosensitivity, an advancement in a previously qualitative field. Intriguingly, glioma patients with a reduced ROS Index correlate with longer survival and the Proneural molecular classification, a feature frequently associated with tumors of better prognosis. These data emphasize the feasibility of manipulating the O2(-):H2O2 ratio as a therapeutic strategy.

Enhancing tumor cell response to chemotherapy through nanoparticle-mediated codelivery of siRNA and cisplatin prodrug

Cisplatin and other DNA-damaging chemotherapeutics are widely used to treat a broad spectrum of malignancies. However, their application is limited by both intrinsic and acquired chemoresistance. Most mutations that result from DNA damage are the consequence of error-prone translesion DNA synthesis, which could be responsible for the acquired resistance against DNA-damaging agents. Recent studies have shown that the suppression of crucial gene products (e.g., REV1, REV3L) involved in the error-prone translesion DNA synthesis pathway can sensitize intrinsically resistant tumors to chemotherapy and reduce the frequency of acquired drug resistance of relapsed tumors. In this context, combining conventional DNA-damaging chemotherapy with siRNA-based therapeutics represents a promising strategy for treating patients with malignancies. To this end, we developed a versatile nanoparticle (NP) platform to deliver a cisplatin prodrug and REV1/REV3L-specific siRNAs simultaneously to the same tumor cells. NPs are formulated through self-assembly of a biodegradable poly(lactide-coglycolide)-b-poly(ethylene glycol) diblock copolymer and a self-synthesized cationic lipid. We demonstrated the potency of the siRNA-containing NPs to knock down target genes efficiently both in vitro and in vivo. The therapeutic efficacy of NPs containing both cisplatin prodrug and REV1/REV3L-specific siRNAs was further investigated in vitro and in vivo. Quantitative real-time PCR results showed that the NPs exhibited a significant and sustained suppression of both genes in tumors for up to 3 d after a single dose. Administering these NPs revealed a synergistic effect on tumor inhibition in a human Lymph Node Carcinoma of the Prostate xenograft mouse model that was strikingly more effective than platinum monotherapy.

REV1 and DNA polymerase zeta in DNA interstrand crosslink repair

DNA interstrand crosslinks (ICLs) are covalent linkages between two strands of DNA, and their presence interferes with essential metabolic processes such as transcription and replication. These lesions are extremely toxic, and their repair is essential for genome stability and cell survival. In this review, we will discuss how the removal of ICLs requires interplay between multiple genome maintenance pathways and can occur in the absence of replication (replication-independent ICL repair) or during S phase (replication-coupled ICL repair), the latter being the predominant pathway used in mammalian cells. It is now well recognized that translesion DNA synthesis (TLS), especially through the activities of REV1 and DNA polymerase zeta (Polζ), is necessary for both ICL repair pathways operating throughout the cell cycle. Recent studies suggest that the convergence of two replication forks upon an ICL initiates a cascade of events including unhooking of the lesion through the actions of structure-specific endonucleases, thereby creating a DNA double-stranded break (DSB). TLS across the unhooked lesion is necessary for restoring the sister chromatid before homologous recombination repair. Biochemical and genetic studies implicate REV1 and Polζ as being essential for performing lesion bypass across the unhooked crosslink, and this step appears to be important for subsequent events to repair the intermediate DSB. The potential role of Fanconi anemia pathway in the regulation of REV1 and Polζ-dependent TLS and the involvement of additional polymerases, including DNA polymerases kappa, nu, and theta, in the repair of ICLs is also discussed in this review.

RAD52 variants predict platinum resistance and prognosis of cervical cancer

RAD52 is an important but not well characterized homologous recombination repair gene that can bind to single-stranded DNA ends and mediate the DNA-DNA interaction necessary for the annealing of complementary DNA strands. To evaluate the role of RAD52 variants in the response of tumor cells to platinum agents, we investigated their associations with platinum resistance and prognosis in cervical cancer patients. We enrolled 154 patients with cervical squamous cell carcinoma, who had radical surgery between 2008 and 2009, and genotyped three potentially functional RAD52 variants by the SNaPshot assay. We tested in vitro platinum resistance and RAD52 expression by using the MTT and immunohistochemistry methods, respectively. In 144 cases who had genotyping data, we found that both the rs1051669 variant and RAD52 protein expression were significantly associated with carboplatin resistance (P = 0.024 and 0.028, respectively) and rs10774474 with nedaplatin resistance (P = 0.018). The rs1051669 variant was significantly associated with RAD52 protein expression (adjusted OR = 4.7, 95% CI = 1.4-16.1, P = 0.013). When these three RAD52 variants were combined, progression-free survival was lower in patients who carried at least one (≥1) variant allele compared to those without any of the variant alleles (P = 0.047). Therefore, both RAD52 variants and protein expression can predict platinum resistance, and RAD52 variants appeared to predict prognosis in cervical cancer patients. Large studies are warranted to validate these findings.