Tumor cell survival dependence on the DHX9 DExH-box helicase

Targeting DHX9 Triggers Tumor-Intrinsic Interferon Response and Replication Stress in Small Cell Lung Cancer

Activating innate immunity in cancer cells through cytoplasmic nucleic acid sensing pathways, a phenomenon known as "viral mimicry," has emerged as an effective strategy to convert immunologically "cold" tumors into "hot." Through a curated CRISPR-based screen of RNA helicases, we identified DExD/H-box helicase 9 (DHX9) as a potent repressor of double-stranded RNA (dsRNA) in small cell lung cancers (SCLC). Depletion of DHX9 induced accumulation of cytoplasmic dsRNA and triggered tumor-intrinsic innate immunity. Intriguingly, ablating DHX9 also induced aberrant accumulation of R-loops, which resulted in an increase of DNA damage-derived cytoplasmic DNA and replication stress in SCLCs. In vivo, DHX9 deletion promoted a decrease in tumor growth while inducing a more immunogenic tumor microenvironment, invigorating responsiveness to immune-checkpoint blockade. These findings suggest that DHX9 is a crucial repressor of tumor-intrinsic innate immunity and replication stress, representing a promising target for SCLC and other "cold" tumors in which genomic instability contributes to pathology.

SIGNIFICANCE

One promising strategy to trigger an immune response within tumors and enhance immunotherapy efficacy is by inducing endogenous "virus-mimetic" nucleic acid accumulation. Here, we identify DHX9 as a viral-mimicry-inducing factor involved in the suppression of double-stranded RNAs and R-loops and propose DHX9 as a novel target to enhance antitumor immunity. See related commentary by Chiappinelli, p. 389. This article is featured in Selected Articles from This Issue, p. 384.

The DNA/RNA helicase DHX9 orchestrates the KDM2B-mediated transcriptional regulation of YAP1 in Ewing sarcoma

Ewing sarcomas (ES) are aggressive paediatric tumours of bone and soft tissues. Resistance to chemotherapy and high propensity to metastasize remain the main causes of treatment failure. Thus, identifying novel targets for alternative therapeutic approaches is urgently needed. DNA/RNA helicases are emerging as crucial regulators of many cellular processes often deregulated in cancer. Among them, DHX9 is up-regulated in ES and collaborates with EWS-FLI1 in ES transformation. We report that DHX9 silencing profoundly impacts on the oncogenic properties of ES cells. Transcriptome profiling combined to bioinformatic analyses disclosed a gene signature commonly regulated by DHX9 and the Lysine Demethylase KDM2B, with the Hippo pathway regulator YAP1 as a prominent target. Mechanistically, we found that DHX9 enhances H3K9 chromatin demethylation by KDM2B and favours RNA Polymerase II recruitment, thus promoting YAP1 expression. Conversely, EWS-FLI1 binding to the promoter represses YAP1 expression. These findings identify the DHX9/KDM2B complex as a new druggable target to counteract ES malignancy.

Structural basis of RNA-induced autoregulation of the DExH-type RNA helicase maleless

RNA unwinding by DExH-type helicases underlies most RNA metabolism and function. It remains unresolved if and how the basic unwinding reaction of helicases is regulated by auxiliary domains. We explored the interplay between the RecA and auxiliary domains of the RNA helicase maleless (MLE) from Drosophila using structural and functional studies. We discovered that MLE exists in a dsRNA-bound open conformation and that the auxiliary dsRBD2 domain aligns the substrate RNA with the accessible helicase tunnel. In an ATP-dependent manner, dsRBD2 associates with the helicase module, leading to tunnel closure around ssRNA. Furthermore, our structures provide a rationale for blunt-ended dsRNA unwinding and 3'-5' translocation by MLE. Structure-based MLE mutations confirm the functional relevance of our model for RNA unwinding. Our findings contribute to our understanding of the fundamental mechanics of auxiliary domains in DExH helicase MLE, which serves as a model for its human ortholog and potential therapeutic target, DHX9/RHA.

Development of assays to support identification and characterization of modulators of DExH-box helicase DHX9

DHX9 is a DExH-box RNA helicase that utilizes hydrolysis of all four nucleotide triphosphates (NTPs) to power cycles of 3' to 5' directional movement to resolve and/or unwind double stranded RNA, DNA, and RNA/DNA hybrids, R-loops, triplex-DNA and G-quadraplexes. DHX9 activity is important for both viral amplification and maintaining genomic stability in cancer cells; therefore, it is a therapeutic target of interest for drug discovery efforts. Biochemical assays measuring ATP hydrolysis and oligonucleotide unwinding for DHX9 have been developed and characterized, and these assays can support high-throughput compound screening efforts under balanced conditions. Assay development efforts revealed DHX9 can use double stranded RNA with 18-mer poly(U) 3' overhangs and as well as significantly shorter overhangs at the 5' or 3' end as substrates. The enzymatic assays are augmented by a robust SPR assay for compound validation. A mechanism-derived inhibitor, GTPγS, was characterized as part of the validation of these assays and a crystal structure of GDP bound to cat DHX9 has been solved. In addition to enabling drug discovery efforts for DHX9, these assays may be extrapolated to other RNA helicases providing a valuable toolkit for this important target class.

Crystal structures of the DExH-box RNA helicase DHX9

DHX9 is a DExH-box RNA helicase with versatile functions in transcription, translation, RNA processing and regulation of DNA replication. DHX9 has recently emerged as a promising target for oncology, but to date no mammalian structures have been published. Here, crystal structures of human, dog and cat DHX9 bound to ADP are reported. The three mammalian DHX9 structures share identical structural folds. Additionally, the overall architecture and the individual domain structures of DHX9 are highly conserved with those of MLE, the Drosophila orthologue of DHX9 previously solved in complex with RNA and a transition-state analogue of ATP. Due to differences in the bound substrates and global domain orientations, the localized loop conformations and occupancy of dsRNA-binding domain 2 (dsRBD2) differ between the mammalian DHX9 and MLE structures. The combined effects of the structural changes considerably alter the RNA-binding channel, providing an opportunity to compare active and inactive states of the helicase. Finally, the mammalian DHX9 structures provide a potential tool for structure-based drug-design efforts.

DHX9-mediated pathway contributes to the malignant phenotype of myelodysplastic syndromes

DHX9 is a member of the DEAH (Asp-Glu-Ala-His) helicase family and regulates DNA replication and RNA processing. DHX9 dysfunction promotes tumorigenesis in several solid cancers. However, the role of DHX9 in MDS is still unknown. Here, we analyzed the expression of DHX9 and its clinical significance in 120 MDS patients and 42 non-MDS controls. Lentivirus-mediated DHX9-knockdown experiments were performed to investigate its biological function. We also performed cell functional assays, gene microarray, and pharmacological intervention to investigate the mechanistic involvement of DHX9. We found that overexpression of DHX9 is frequent in MDS and associated with poor survival and high risk of acute myeloid leukemia (AML) transformation. DHX9 is essential for the maintenance of malignant proliferation of leukemia cells, and DHX9 suppression increases cell apoptosis and causes hypersensitivity to chemotherapeutic agents. Besides, knockdown of DHX9 inactivates the PI3K-AKT and ATR-Chk1 signaling, promotes R-loop accumulation, and R-loop-mediated DNA damage.

The DNA/RNA helicase DHX9 contributes to the transcriptional program of the androgen receptor in prostate cancer

Background

Prostate cancer (PC) is the most commonly diagnosed male malignancy and an important cause of mortality. Androgen deprivation therapy is the first line treatment but, unfortunately, a large part of patients evolves to a castration-resistant stage, for which no effective cure is currently available. The DNA/RNA helicase DHX9 is emerging as an important regulator of cellular processes that are often deregulated in cancer.

Methods

To investigate whether DHX9 modulates PC cell transcriptome we performed RNA-sequencing analyses upon DHX9 silencing in the androgen-responsive cell line LNCaP. Bioinformatics and functional analyses were carried out to elucidate the mechanism of gene expression regulation by DHX9. Data from The Cancer Genome Atlas were mined to evaluate the potential role of DHX9 in PC.

Results

We found that up-regulation of DHX9 correlates with advanced stage and is associated with poor prognosis of PC patients. High-throughput RNA-sequencing analysis revealed that depletion of DHX9 in androgen-sensitive LNCaP cells affects expression of hundreds of genes, which significantly overlap with known targets of the Androgen Receptor (AR). Notably, AR binds to the DHX9 promoter and induces its expression, while Enzalutamide-mediated inhibition of AR activity represses DHX9 expression. Moreover, DHX9 interacts with AR in LNCaP cells and its depletion significantly reduced the recruitment of AR to the promoter region of target genes and the ability of AR to promote their expression in response to 5α-dihydrotestosterone. Consistently, silencing of DXH9 negatively affected androgen-induced PC cell proliferation and migration.

Conclusions

Collectively, our data uncover a new role of DHX9 in the control of the AR transcriptional program and establish the existence of an oncogenic DHX9/AR axis, which may represent a new druggable target to counteract PC progression.

The Emerging Roles and Clinical Potential of circSMARCA5 in Cancer

Circular RNAs (circRNAs) are a type of endogenous non-coding RNA and a critical epigenetic regulation way that have a closed-loop structure and are highly stable, conserved, and tissue-specific, and they play an important role in the development of many diseases, including tumors, neurological diseases, and cardiovascular diseases. CircSMARCA5 is a circRNA formed by its parental gene SMARCA5 via back splicing which is dysregulated in expression in a variety of tumors and is involved in tumor development with dual functions as an oncogene or tumor suppressor. It not only serves as a competing endogenous RNA (ceRNA) by binding to various miRNAs, but it also interacts with RNA binding protein (RBP), regulating downstream gene expression; it also aids in DNA damage repair by regulating the transcription and expression of its parental gene. This review systematically summarized the expression and characteristics, dual biological functions, and molecular regulatory mechanisms of circSMARCA5 involved in carcinogenesis and tumor progression as well as the potential applications in early diagnosis and gene targeting therapy in tumors.

Case Report: First Report of T-Cell Large Granular Lymphocytic Leukemia With NPL-DHX9 Gene Fusion Successfully Treated With Cladribine: Clinical Experience and Literature Review

Background

T-cell large granular lymphocytic leukemia (T-LGLL) is a rare lymphoproliferative disorder that starts in T cells and is usually indolent. Long-term use of immunosuppressants, combined with agranulocytosis, is a double-edged sword, as both can lead to serious infections, especially in patients with combined hematologic malignancies and immune defects.

Case Presentation

A 30-year-old female patient was admitted to the hospital because of agranulocytosis for five years, with chest tightness, fatigue, and fever for two days. Pathology and metagenomic next-generation sequencing (mNGS) detected Aspergillus. Although she received cyclosporine and methylprednisolone, the patient showed drug intolerance and progression with invasive pulmonary fungal infections. After a bone marrow aspiration biopsy and other related examinations, she was diagnosed with T-LGLL and invasive pulmonary aspergillosis (IPA). T-cell immunophenotype was CD45+CD3dim+CD5-CD4-CD8+CD7+CD57p+CD25-CD30-, TCRγδ+, transducer and activator of transcripton-3 (STAT3) Y640F mutation and fusion gene NPL-DHX9 rearrangement were confirmed, which has never been reported in hematological diseases. After voriconazole regimen adjustment during treatment based on therapeutic drug concentration monitoring (TDM) and improvement in lung infection, the patient finally treated with purine nucleoside analogues (PNA) cladribine as a single agent at 0.14 mg/kg/d for 5 days. Complete response was achieved after four-cycles cladribine treatment (WBC 2.1*109/L, HGB 117 g/L, PLT 196*109/L, ANC 1.6*109/L, and ALC 0.2*109/L).

Conclusions

To our knowledge, this is the first case of T-LGLL with a rare γδ type and fusion gene NPL-DHX9 rearrangement. The patient was successfully treated with cladribine, suggesting that this regimen could be a promising therapeutic strategy for patients with aggressive T-LGLL.

DHX9 contributes to the malignant phenotypes of colorectal cancer via activating NF-κB signaling pathway

Colorectal cancer (CRC) is the leading cause of cancer-related mortality worldwide, which makes it urgent to identify novel therapeutic targets for CRC treatment. In this study, DHX9 was filtered out as the prominent proliferation promoters of CRC by siRNA screening. Moreover, DHX9 was overexpressed in CRC cell lines, clinical CRC tissues and colitis-associated colorectal cancer (CAC) mouse model. The upregulation of DHX9 was positively correlated with poor prognosis in patients with CRC. Through gain- and loss-of function experiments, we found that DHX9 promoted CRC cell proliferation, colony formation, apoptosis resistance, migration and invasion in vitro. Furthermore, a xenograft mouse model and a hepatic metastasis mouse model were utilized to confirm that forced overexpression of DHX9 enhanced CRC outgrowth and metastasis in vivo, while DHX9 ablation produced the opposite effect. Mechanistically, from one aspect, DHX9 enhances p65 phosphorylation, promotes p65 nuclear translocation to facilitate NF-κB-mediated transcriptional activity. From another aspect, DHX9 interacts with p65 and RNA polymerase II (RNA Pol II) to enhance the downstream targets of NF-κB (e.g., Survivin, Snail) expression to potentiate the malignant phenotypes of CRC. Together, our results suggest that DHX9 may be a potential therapeutic target for prevention and treatment of CRC patients.

Long non-coding RNAs regulate the hallmarks of cancer in HPV-induced malignancies

High-risk human papillomavirus (HPV) is the most frequent sexually transmitted agent worldwide and is responsible for approximately 5% of human cancers. Identifying novel biomarkers and therapeutic targets for these malignancies requires a deeper understanding of the mechanisms involved in the progression of HPV-induced cancers. Long non-coding RNAs (lncRNAs) are crucial in the regulation of biological processes. Importantly, these molecules are key players in the progression of multiple malignancies and are able to regulate the development of the different hallmarks of cancer. This review highlights the action of lncRNAs in the regulation of cellular processes leading to the typical hallmarks of cancer. The regulation of lncRNAs by HPV oncogenes, their targets and also their mechanisms of action are also discussed, in the context of HPV-induced malignancies. Overall, accumulating data indicates that lncRNAs may have a significant potential to become useful tools for clinical practice as disease biomarkers or therapy targets.

Nutlin-Induced Apoptosis Is Specified by a Translation Program Regulated by PCBP2 and DHX30

Activation of p53 by the small molecule Nutlin can result in a combination of cell cycle arrest and apoptosis. The relative strength of these events is difficult to predict by classical gene expression analysis, leaving uncertainty as to the therapeutic benefits. In this study, we report a translational control mechanism shaping p53-dependent apoptosis. Using polysome profiling, we establish Nutlin-induced apoptosis to associate with the enhanced translation of mRNAs carrying multiple copies of an identified 3' UTR CG-rich motif mediating p53-dependent death (CGPD-motif). We identify PCBP2 and DHX30 as CGPD-motif interactors. We find that in cells undergoing persistent cell cycle arrest in response to Nutlin, CGPD-motif mRNAs are repressed by the PCBP2-dependent binding of DHX30 to the motif. Upon DHX30 depletion in these cells, the translation of CGPD-motif mRNAs increases, and the response to Nutlin shifts toward apoptosis. Instead, DHX30 inducible overexpression in SJSA1 cells leads to decreased translation of CGPD-motif mRNAs.

RNA Helicases as Shadow Modulators of Cell Cycle Progression

The progress of the cell cycle is directly regulated by modulation of cyclins and cyclin-dependent kinases. However, many proteins that control DNA replication, RNA transcription and the synthesis and degradation of proteins can manage the activity or levels of master cell cycle regulators. Among them, RNA helicases are key participants in RNA metabolism involved in the global or specific tuning of cell cycle regulators at the level of transcription and translation. Several RNA helicases have been recently evaluated as promising therapeutic targets, including eIF4A, DDX3 and DDX5. However, targeting RNA helicases can result in side effects due to the influence on the cell cycle. In this review, we discuss direct and indirect participation of RNA helicases in the regulation of the cell cycle in order to draw attention to downstream events that may occur after suppression or inhibition of RNA helicases.

Androgen receptor decreases renal cell carcinoma bone metastases via suppressing the osteolytic formation through altering a novel circEXOC7 regulatory axis

BACKGROUND

Clear cell renal cell carcinoma (ccRCC) has gender differences, with the androgen receptor (AR) linked positively with metastasis to the lung. Its linkage to ccRCC bone metastases (RBMs), however, remains unclear.

METHODS

In the current study, five human RCC and five RCC bone metastasis tissues were deeply sequenced using Arraystar human circRNA V2.0 microarray. We conducted gain-of-function screening in vitro and in vivo to elucidate the AR's role in the RBM. Loss/gain-of-function was also implemented to verify the roles of related non-coding RNAs and proteins.

RESULTS

We uncovered that RBM also has a gender difference showing higher AR expression may be linked to fewer RBMs, which might involve suppressing osteolytic formation. Mechanism dissection indicates that AR can decrease the circular RNA EXOC7 (circEXOC7), expression via enhancing transcription of DHX9, a regulatory protein in circRNA biogenesis. The circEXOC7 can sponge/suppress miR-149-3p resulting in suppressing the CSF1 expression by directly binding to the 3'UTR region of CSF1 mRNA. Results from clinical epidemiological surveys also found that AR has a positive correlation with miR-149-3p and a negative correlation with CSF1 in AR-positive ccRCC tissues. Preclinical studies with Balb/c nude mouse model also validated that targeting this newly verified AR/DHX9/circEXOC7/miR-149-3p/CSF1 signaling via altering circEXOC7 or AR could lead to suppressing the RBM progression.

CONCLUSIONS

These data showed that AR/DHX9/circEXOC7/miR-149-3p/CSF1 signaling acts as a valuable feature in the bone metastasis of renal cancer, which may benefit in suppressing the RBM progression.

A STING-related prognostic score predicts high-risk patients of colorectal cancer and provides insights into immunotherapy

Background

Targeted therapeutic strategies for advanced colorectal cancer (CRC) have been limited. STING is crucial to the antitumor immunotherapy, for it stimulates IFN signaling to mediate the crosstalk between innate and adaptive immune responses. Emerging evidence suggests that STING also contributes to the prognosis of CRC. However, prognostic models relating to STING have not yet been explored.

Methods

A total of 431 CRC samples from the TCGA database were analyzed to explore the prognostic value of STING-related genes. We trained prognostic models using the multivariate Cox regression. A STING-related prognostic score (SPS) was calculated as the gene expression multiplied by the corresponding coefficients of the final model. A backward stepAIC strategy was adopted to select the optimal model. A nomogram was used to personalize medical decisions for CRC.

Results

The expression level of STING was upregulated in the CMS1 subtype (P=0.036). Among STING-related genes, DHX9 (HR =0.72, P=0.01), IRF2 (HR =1.34, P=0.022), and POLR1D (HR =1.23, P=0.038) showed significant prognostic value. The SPS was proven to be an independent risk factor (training: HR =2.9, P=0.00013; validation: HR =3.02, P=0.01), and outperformed random classifiers in identifying high-risk CRC. The high SPS group was characterized by less genomic aberrations, upregulated IL6-JAK-STAT3 and IL2-STAT5 signaling pathways, increased expression of TIM-3, increased infiltration of regulatory T (Treg) cells and T helper 17 (Th17) cells, and decreased infiltration of M0 macrophages. Finally, the nomogram based on the SPS and clinical factors showed good performance in CRC.

Conclusions

SPS is an independent risk factor that could identify high-risk CRC. While ICBs may benefit patients of the CMS1 subtype, for the CMS2, CMS3, and CMS4 subtypes in the high SPS group, STING agonists and immunotherapies targeting the Th17 axis may be beneficial. Finally, the SPS-based nomogram could help advance personalized medical decisions for CRC.

The multifaceted functions of RNA helicases in the adaptive cellular response to hypoxia: From mechanisms to therapeutics

Hypoxia is a hallmark of cancer. Hypoxia-inducible factor (HIF), a master player for sensing and adapting to hypoxia, profoundly influences genome instability, tumor progression and metastasis, metabolic reprogramming, and resistance to chemotherapies and radiotherapies. High levels and activity of HIF result in poor clinical outcomes in cancer patients. Thus, HIFs provide ideal therapeutic targets for cancers. However, HIF biology is sophisticated, and currently available HIF inhibitors have limited clinical utility owing to their low efficacy or side effects. RNA helicases, which are master players in cellular RNA metabolism, are usually highly expressed in tumors to meet the increased oncoprotein biosynthesis demand. Intriguingly, recent findings provide convincing evidence that RNA helicases are crucial for the adaptive cellular response to hypoxia via a mutual regulation with HIFs. More importantly, some RNA helicase inhibitors may suppress HIF signaling by blocking the translation of HIF-responsive genes. Therefore, RNA helicase inhibitors may work synergistically with HIF inhibitors in cancer to improve treatment efficacy. In this review, we discuss current knowledge of how cells sense and adapt to hypoxia through HIFs. However, our primary focus is on the multiple functions of RNA helicases in the adaptive response to hypoxia. We also highlight how these hypoxia-related RNA helicases can be exploited for anti-cancer therapeutics.

The Current View on the Helicase Activity of RNA Helicase A and Its Role in Gene Expression

RNA helicase A (RHA) is a DExH-box helicase that plays regulatory roles in a variety of cellular processes, including transcription, translation, RNA splicing, editing, transport, and processing, microRNA genesis and maintenance of genomic stability. It is involved in virus replication, oncogenesis, and innate immune response. RHA can unwind nucleic acid duplex by nucleoside triphosphate hydrolysis. The insight into the molecular mechanism of helicase activity is fundamental to understanding the role of RHA in the cell. Herein, we reviewed the current advances on the helicase activity of RHA and its relevance to gene expression, particularly, to the genesis of circular RNA.

The enigmatic helicase DHX9 and its association with the hallmarks of cancer

Much interest has been expended lately in characterizing the association between DExH-Box helicase 9 (DHX9) dysregulation and malignant development, however, the enigmatic nature of DHX9 has caused conflict as to whether it regularly functions as an oncogene or tumor suppressor. The impact of DHX9 on malignancy appears to be cell-type specific, dependent upon the availability of binding partners and activation of inter-connected signaling pathways. Realization of DHX9's pivotal role in the development of several hallmarks of cancer has boosted the enzyme's potential as a cancer biomarker and therapeutic target, opening up novel avenues for exploring DHX9 in precision medicine applications. Our review discusses the ascribed functions of DHX9 in cancer, explores its enigmatic nature and potential as an antineoplastic target.

Circular RNAs in cancer: limitations in functional studies and diagnostic potential

Circular RNAs (circRNAs) are a large class of noncoding RNAs, generated from a process called back-splicing, that possess critical regulatory functions in many cellular events. A large body of literature has reported various circRNA functions and their underlying mechanisms, including sponging miRNA, exerting transcriptional and translational regulation, interacting with proteins, and translating into peptides and proteins. CircRNA dysregulation has been implicated in many cancers, including lung, breast, liver, gastric, colorectal, and ovarian cancer. They are detectable in bodily fluids and relatively stable, making them potential cancer biomarker candidates. Furthermore, targeting circRNA expression levels is a potential therapeutic approach for treating cancers. In this review, we describe the functional mechanisms of circRNAs and discuss limitations of current mechanism studies. Following this, we outline the potential of circRNAs to be effective biomarkers in various cancers and present circRNA-based therapeutic approaches. Finally, we discuss challenges in using circRNAs as diagnostic and therapeutic tools and propose future research directions.

Diagnostic and prognostic value of MCM3 and its interacting proteins in hepatocellular carcinoma

Aberrant DNA replication is one of the driving forces behind oncogenesis. Furthermore, minichromosome maintenance complex component 3 (MCM3) serves an essential role in DNA replication. Therefore, in the present study, the diagnostic and prognostic value of MCM3 and its interacting proteins in hepatocellular carcinoma (HCC) were investigated. By utilizing The Cancer Genome Atlas (TCGA) database, global MCM3 mRNA levels were assessed in HCC and normal liver tissues. Its effects were further analyzed by reverse transcription-quantitative PCR (RT-qPCR), western blotting and immunohistochemistry in 78 paired HCC and adjacent tissues. Functional and pathway enrichment analyses were performed using the Search Tool for the Retrieval of Interacting Genes database. The expression levels of proteins that interact with MCM3 were also analyzed using the TCGA database and RT-qPCR. Finally, algorithms combining receiver operating characteristic (ROC) curves were constructed using binary logistic regression using the TCGA results. Increased MCM3 mRNA expression with high α-fetoprotein levels and advanced Edmondson-Steiner grade were found to be characteristic of HCC. Survival analysis revealed that high MCM3 expression was associated with poor outcomes in patients with HCC. In addition, MCM3 protein expression was associated with increased tumor invasion in HCC tissues. MCM3 and its interacting proteins were found to be primarily involved in DNA replication, cell cycle and a number of binding processes. Algorithms combining ROCs of MCM3 and its interacting proteins were found to have improved HCC diagnosis ability compared with MCM3 and other individual diagnostic markers. In conclusion, MCM3 appears to be a promising diagnostic biomarker for HCC. Additionally, the present study provides a basis for the multi-gene diagnosis of HCC using MCM3.

Splicing Regulator p54nrb /Non-POU Domain-Containing Octamer-Binding Protein Enhances Carcinogenesis Through Oncogenic Isoform Switch of MYC Box-Dependent Interacting Protein 1 in Hepatocellular Carcinoma

BACKGROUND AND AIMS

Alternative splicing (AS) is a key step that increases the diversity and complexity of the cancer transcriptome. Recent evidence has highlighted that AS has an increasingly crucial role in cancer. Nonetheless, the mechanisms underlying AS and its dysregulation in hepatocellular carcinoma (HCC) remain elusive. Here, we report that the expression of RNA-binding protein p54^nrb /non-POU domain-containing octamer-binding protein (NONO) is frequently increased in patients with HCC and is associated with poor outcomes.

APPROACH AND RESULTS

Knockdown of NONO significantly abolished liver cancer cell proliferation, migration, and tumor formation. RNA-sequencing revealed that NONO regulates MYC box-dependent interacting protein 1 (or bridging integrator 1 [BIN1]; also known as amphiphysin 2 3P9) exon 12a splicing. In the normal liver, BIN1 generates a short isoform (BIN1-S) that acts as a tumor suppressor by inhibiting the binding of c-Myc to target gene promoters. In HCC, NONO is highly up-regulated and produces a long isoform (BIN1-L, which contains exon 12a) instead of BIN1-S. High levels of BIN1-L promote carcinogenesis by binding with the protein polo-like kinase 1 to enhance its stability through the prevention of ubiquitin/proteasome-dependent cullin 3 degradation. Further analysis revealed that NONO promotes BIN1 exon 12a inclusion through interaction with DExH-box helicase 9 (DHX9) and splicing factor proline and glutamine-rich (SFPQ). Notably, frequent coexpression of DHX9-NONO-SFPQ is observed in patients with HCC.

CONCLUSIONS

Taken together, our findings identify the DHX9-NONO-SFPQ complex as a key regulator manipulating the oncogenic splicing switch of BIN1 and as a candidate therapeutic target in liver cancer.

SPOP attenuates migration and invasion of choriocarcinoma cells by promoting DHX9 degradation

Speckle-type POZ protein (SPOP), a novel cancer- associated protein, was previously reported to function as a tumor suppressor or promoter in different malignant tumors. This research aims to investigate the biological functions and underlying molecular mechanisms of SPOP in choriocarcinoma. Our analysis of patient tissues and cell lines showed significantly decreased SPOP expression and highly expressed Nuclear DNA helicase II and RNA helicase A (DHX9), both of them are mainly located into the nucleus. Induction or depletion of endogenous SPOP with a lentivirus-based system correspondingly suppressed or promoted migration and invasion of choriocarcinoma cells. Mechanistically, we found that SPOP bound to DHX9 and induced the ubiquitination and degradation of DHX9 by recognizing a typical SPOP-binding motif in DHX9. SPOP-DHX9 interaction was demonstrated to play a critical role in regulating migration and invasion abilities of choriocarcinoma cells, the promotion of mobility ability in knocking down SPOP was partly counteracted by transfection with siRNA against DHX9. Taken together, our results suggest that SPOP suppresses migration and invasion of choriocarcinoma by promoting the ubiquitination and subsequent degradation of DHX9, which identifies the SPOP-DHX9 interaction may serve as a potential therapeutic target against choriocarcinoma.

NLRP6 inflammasome

NOD-like receptor family pyrin domain containing 6 (NLRP6) is a novel NLR family member, that shows high expression in the intestine and liver (in contrast to NLRP3 in myeloid cells), to regulate inflammation and host defense against microbes. NLRP6 is reported to involved in inflammasome activation, regulation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling, antiviral interferon (IFN) signaling, mucus secretion, and antimicrobial peptide (AMP) production. Here, we discuss the recent findings as well as debates regarding: how NLRP6 is induced ("signal I″) and activated ("signal II"); its roles in intestinal cells and immune cells; how NLRP6 and NLRP9 coordinate to regulate the anti-viral immune response in the intestine; potential targeting of NLRP6 in human diseases.

The mRNA encoding the JUND tumor suppressor detains nuclear RNA-binding proteins to assemble polysomes that are unaffected by mTOR

One long-standing knowledge gap is the role of nuclear proteins in mRNA translation. Nuclear RNA helicase A (DHX9/RHA) is necessary for the translation of the mRNAs of JUND (JunD proto-oncogene AP-1 transcription factor subunit) and HIV-1 genes, and nuclear cap-binding protein 1 (NCBP1)/CBP80 is a component of HIV-1 polysomes. The protein kinase mTOR activates canonical messenger ribonucleoproteins by post-translationally down-regulating the eIF4E inhibitory protein 4E-BP1. We posited here that NCBP1 and DHX9/RHA (RHA) support a translation pathway of JUND RNA that is independent of mTOR. We present evidence from reciprocal immunoprecipitation experiments indicating that NCBP1 and RHA both are components of messenger ribonucleoproteins in several cell types. Moreover, tandem affinity and RT-quantitative PCR results revealed that JUND mRNA is a component of a previously unknown ribonucleoprotein complex. Results from the tandem IP indicated that another component of the JUND-containing ribonucleoprotein complex is NCBP3, a recently identified ortholog of NCBP2/CBP20. We also found that NCBP1, NCBP3, and RHA, but not NCBP2, are components of JUND-containing polysomes. Mutational analysis uncovered two dsRNA-binding domains of RHA that are necessary to tether JUND-NCBP1/NCBP3 to polysomes. We also found that JUND translation is unaffected by inhibition of mTOR, unless RHA was down-regulated by siRNA. These findings uncover a noncanonical cap-binding complex consisting of NCBP1/NCBP3 and RHA substitutes for the eukaryotic translation initiation factors 4E and 4G and activates mTOR-independent translation of the mRNA encoding the tumor suppressor JUND.

Oxaliplatin-Induced DHX9 Phosphorylation Promotes Oncogenic Circular RNA CCDC66 Expression and Development of Chemoresistance

Circular RNA (circRNA), generated through backsplicing in which the downstream splice donor joins the upstream splice acceptor, is a novel class of RNA molecules. Our previous study found that a novel oncogenic circRNA—consisting exon 8–10 of CCDC66—is aberrantly expressed in colorectal cancer (CRC) tissues and cells. The failure of treatment for colorectal cancer is typically associated with recurrent and chemoresistant cancerous tissues. In this study, we aimed to investigate the role(s) of circCCDC66 during the development of chemoresistance. We discovered that the expression level of circCCDC66 is elevated in colorectal cancer cells with resistance to oxaliplatin. Knockdown of circCCDC66 caused the downregulation of a subset of genes which are regulated by circCCDC66-associated miRNAs and related to the modulation of apoptosis and the cell cycle, suppressing cell survival, promoting oxaliplatin-induced apoptosis and, thus, hindering the development of oxaliplatin-resistance (OxR). The induction of circCCDC66 was dependent on the time-course and dose of oxaliplatin treatment. Our analyses revealed that DHX9 harbors two phosphorylation sites of phosphatidylinositol 3-kinase-related kinases (PI3KKs) close to substrate-binding domains. Blockage of phosphorylation by either PI3KK inhibitors or nonphosphorable mutants of DHX9 decreased the oxaliplatin-induced circCCDC66 expression and the ability to develop chemoresistant cells. Taken together, we demonstrated and linked the functional role of DHX9 phosphorylation to oncogenic circCCDC66 expression during the development of resistance to oxaliplatin, providing a mechanistic insight for the development of therapeutic strategies to recurring/chemoresistant colorectal cancer.

DNA sensors, crucial receptors to resist pathogens, are deregulated in colorectal cancer and associated with initiation and progression of the disease

Background: DNA sensors are innate immune receptors that detect intracellular endogenous or exogenous DNA. They are critical to trigger immune response against DNA viral and intracellular bacterial infection, and are involved in inflammatory diseases and tumorigenesis. Recent accumulating evidences indicated that DNA sensors are also crucial for controlling the development of colorectal cancer (CRC). However, a systematic study on the expression profile of DNA sensors in CRC and their clinical significance are still lacking.

Methods: We investigated the expression profile of DNA sensors in CRC and their clinical significance by taking advantage of clinical CRC samples, mouse AOM/DSS treatment model, and Oncomine ® bioinformatics platform.

Results: Our study identified that the expression of DNA sensors, including AIM2, DAI, as well as inflammasome molecules ASC/IL-18, TLR9 and adaptor MyD88, and DDX60 decreased in human CRC, whereas the expression of DHX9, DHX36, and DDX41 significantly increased. Among them, the expression of AIM2/ASC/IL-18, MyD88, DAI, DHX36, and DDX60 were associated with cancer stages. In addition, we also performed correlation analysis between DNA sensors and their main signaling molecules to explore the possible mechanisms. The results showed that there were positive correlations between AIM2 and ASC/IL-18, DHX9 and MAVS, and TLR9 and MyD88 expression. In addition, the gene expression patterns of some DNA sensors were confirmed by Western-blot analysis.

Conclusions: Our study revealed that the expression of multiple DNA sensors was deregulated in CRC and might be involved in tumor development. More importantly, the study identified that, among all these DNA sensors, AIM2, DAI, and DDX60 could be potentially critical for diagnosis, prognosis, and therapy of CRC and deserve further investigation.

Hsa_Circ_0001206 is downregulated and inhibits cell proliferation, migration and invasion in prostate cancer

Our study is to explore the expression profiles and potential functions of circRNAs in prostate cancer (PCa). A total of 95 circRNAs and 830 mRNAs were screened to be significantly differentially expressed in PCa tissues by microarrays. Co-expression and competitive endogenous RNA (ceRNA) network were constructed to reveal the potential regulatory mechanisms of circRNAs. Three circRNAs, hsa_circ_0001206, hsa_circ_0001633, and hsa_circ_0009061 were validated to be down-regulated in PCa by quantitative real-time PCR (qRT-PCR) and hsa_circ_0001206 as well as hsa_circ_0009061 was significantly associated with clinical features of PCa patients. Meanwhile, Receiver Operating Characteristic (ROC) curves showed their good diagnostic value as biomarkers for PCa. The down-regulation of hsa_circ_001206 was partly because of the regulation of DExH-Box Helicase 9 (DHX9). Moreover, overexpression of hsa_circ_0001206 inhibited PCa cell proliferation, migration, and invasion in vitro and prevented tumor growth in vivo. Dual-luciferase reporter assays showed hsa_circ_0001206 could directly bind to miR-1285-5p. The expression of Smad4, a well-known suppressive gene in PCa, can be increased by overexpression of hsa_circ_0001206 and this effect could be partly reversed by co-transfection of miR-1285-5p mimic. The study revealed expression profiles and potential functions of circRNAs and demonstrated hsa_circ_0001206 played a suppressive role in the pathogenesis of PCa.

A DHX9-lncRNA-MDM2 interaction regulates cell invasion and angiogenesis of cervical cancer

Cervical cancer (CC) is the third most common carcinoma and the fourth leading cause of cancer-associated mortality in women. Here, we report that MDM2-DHX9 interaction mediates CC motility and angiogenesis in a long noncoding RNA-dependent fashion. A long noncoding RNA, named lnc-CCDST, is significantly downregulated in CC tissues, and binds to pro-oncogenic DHX9. DHX9 is upregulated in CC tissue, and promotes CC cell motility and angiogenesis. The lnc-CCDST and DHX9 interaction promotes DHX9 degradation through the ubiquitin proteasome pathway. Furthermore, DHX9 bound to E3 ubiquitin ligase MDM2, and this interaction is enhanced by lnc-CCDST. Thus, lnc-CCDST promotes DHX9 degradation by serving as a scaffold to facilitate the formation of MDM2 and DHX9 complexes. Moreover, HPV oncogenes E6 and E7 abolish the expression of lnc-CCDST resulting in the increase of DHX9. Our results have revealed a novel mechanism by which high-risk HPVs promote motility and angiogenesis of CC by inhibiting expression of lnc-CCDST to disrupt MDM2 and DHX9 interaction, and DHX9 degradation, and identified a potential therapeutic target for CC.

Bidirectional regulation of adenosine-to-inosine (A-to-I) RNA editing by DEAH box helicase 9 (DHX9) in cancer

Adenosine-to-inosine (A-to-I) RNA editing entails the enzymatic deamination of adenosines to inosines by adenosine deaminases acting on RNA (ADARs). Dysregulated A-to-I editing has been implicated in various diseases, including cancers. However, the precise factors governing the A-to-I editing and their physiopathological implications remain as a long-standing question. Herein, we unravel that DEAH box helicase 9 (DHX9), at least partially dependent of its helicase activity, functions as a bidirectional regulator of A-to-I editing in cancer cells. Intriguingly, the ADAR substrate specificity determines the opposing effects of DHX9 on editing as DHX9 silencing preferentially represses editing of ADAR1-specific substrates, whereas augments ADAR2-specific substrate editing. Analysis of 11 cancer types from The Cancer Genome Atlas (TCGA) reveals a striking overexpression of DHX9 in tumors. Further, tumorigenicity studies demonstrate a helicase-dependent oncogenic role of DHX9 in cancer development. In sum, DHX9 constitutes a bidirectional regulatory mode in A-to-I editing, which is in part responsible for the dysregulated editome profile in cancer.

The Host DHX9 DExH-Box Helicase Is Recruited to Chikungunya Virus Replication Complexes for Optimal Genomic RNA Translation

Beyond their role in cellular RNA metabolism, DExD/H-box RNA helicases are hijacked by various RNA viruses in order to assist replication of the viral genome. Here, we identify the DExH-box RNA helicase 9 (DHX9) as a binding partner of chikungunya virus (CHIKV) nsP3 mainly interacting with the C-terminal hypervariable domain. We show that during early CHIKV infection, DHX9 is recruited to the plasma membrane, where it associates with replication complexes. At a later stage of infection, DHX9 is, however, degraded through a proteasome-dependent mechanism. Using silencing experiments, we demonstrate that while DHX9 negatively controls viral RNA synthesis, it is also required for optimal mature nonstructural protein translation. Altogether, this study identifies DHX9 as a novel cofactor for CHIKV replication in human cells that differently regulates the various steps of CHIKV life cycle and may therefore mediate a switch in RNA usage from translation to replication during the earliest steps of CHIKV replication.IMPORTANCE The reemergence of chikungunya virus (CHIKV), an alphavirus that is transmitted to humans by Aedes mosquitoes, is a serious global health threat. In the absence of effective antiviral drugs, CHIKV infection has a significant impact on human health, with chronic arthritis being one of the most serious complications. The molecular understanding of host-virus interactions is a prerequisite to the development of targeted therapeutics capable to interrupt viral replication and transmission. Here, we identify the host cell DHX9 DExH-Box helicase as an essential cofactor for early CHIKV genome translation. We demonstrate that CHIKV nsP3 protein acts as a key factor for DHX9 recruitment to replication complexes. Finally, we establish that DHX9 behaves as a switch that regulates the progression of the viral cycle from translation to genome replication. This study might therefore have a significant impact on the development of antiviral strategies.

Deregulation of Circular RNAs in Cancer From the Perspectives of Aberrant Biogenesis, Transport and Removal

CircRNAs (circular RNAs) are a class of RNAs generated from circularization with multiple novel functions. Recent studies have revealed the aberrant expression and aberrant functions of circRNAs in various tumors; thus, circRNAs have been recognized as promising cancer biomarkers. However, the underlying mechanisms behind their aberrant expression and functions remain unclear. In this review, we discuss at length the cancer-specific deregulation of circRNAs and the potential underlying aberrant events in circRNA biogenesis, localization and removal in cancer cells.

Circular RNA cSMARCA5 inhibits growth and metastasis in hepatocellular carcinoma

BACKGROUND & AIMS

In recent years, circular RNAs (circRNAs) have been shown to have critical regulatory roles in cancer biology. However, the contributions of circRNAs to hepatocellular carcinoma (HCC) remain largely unknown.

METHODS

cSMARCA5 (a circRNA derived from exons 15 and 16 of the SMARCA5 gene, hsa_circ_0001445) was identified by RNA-sequencing and validated by quantitative reverse transcription PCR. The role of cSMARCA5 in HCC progression was assessed both in vitro and in vivo. circRNAs in vivo precipitation, luciferase reporter assay, biotin-coupled microRNA capture and fluorescence in situ hybridization were conducted to evaluate the interaction between cSMARCA5 and miR-17-3p/miR-181b-5p.

RESULTS

The expression of cSMARCA5 was lower in HCC tissues, because of the regulation of DExH-Box Helicase 9, an abundant nuclear RNA helicase. The downregulation of cSMARCA5 in HCC was significantly correlated with aggressive characteristics and served as an independent risk factor for overall survival and recurrence-free survival in patients with HCC after hepatectomy. Our in vivo and in vitro data indicated that cSMARCA5 inhibits the proliferation and migration of HCC cells. Mechanistically, we found that cSMARCA5 could promote the expression of TIMP3, a well-known tumor suppressor, by sponging miR-17-3p and miR-181b-5p.

CONCLUSION

These results reveal an important role of cSMARCA5 in the growth and metastasis of HCC and provide a fresh perspective on circRNAs in HCC progression.

LAY SUMMARY

Herein, we studied the role of cSMARCA5, a circular RNA, in hepatocellular carcinoma. Our in vitro and in vivo data showed that cSMARCA5 inhibits the growth and migration of hepatocellular carcinoma cells, making it a potential therapeutic target.

Dependence of p53-deficient cells on the DHX9 DExH-box helicase

DHX9 is a DExH-box helicase family member with key regulatory roles in a broad range of cellular processes. It participates at multiple levels of gene regulation, including DNA replication, transcription, translation, RNA transport, and microRNA processing. It has been implicated in tumorigenesis and recent evidence suggests that it may be a promising chemotherapeutic target. Previous studies have determined that DHX9 suppression elicits an apoptotic or senescence response by activating p53 signaling. Here, we show that DHX9 inhibition can also have deleterious effects in cells lacking functional p53. Loss of DHX9 led to increased cell death in p53-deficient mouse lymphomas and HCT116 human colon cancer cells, and G0/G1 cell cycle arrest in p53-deficient mouse embryonic fibroblasts. Analysis of mRNA levels for p53 transcriptional targets showed that a subset of p53 targets in the p53-null lymphomas and HCT116 cells were activated despite the absence of functional p53. This implies an alternative pathway of DHX9-mediated activation of cell death and cell cycle arrest in p53-deficient cells and supports the feasibility of targeting DHX9 in p53-deficient tumors.

Minichromosome maintenance protein 2 and 3 promote osteosarcoma progression via DHX9 and predict poor patient prognosis

A label free quantitative proteomic approach (SWATH™ experiment) was performed to identify tumor-associated nuclear proteins that are differentially expressed between osteosarcoma cells and osteoblast cells. By functional screening, minichromosome maintenance protein 2 (MCM2) and minichromosome maintenance protein 3 (MCM3) were found to be related to osteosarcoma cell growth. Here, we show that knockdown of MCM2 or MCM3 inhibits osteosarcoma growth in vitro and in vivo. In co-immunoprecipitation and co-localization experiments, MCM2 and MCM3 were found to interact with DExH-box helicase 9 (DHX9) in osteosarcoma cells. A rescue study showed that the decreased growth of osteosarcoma cells by MCM2 or MCM3 knockdown was reversed by DHX9 overexpression, indicating that MCM2 and MCM3 activity was DHX9-dependent. In addition, the depletion of DHX9 hindered osteosarcoma cell proliferation. Notably, MCM2 and MCM3 expression levels were positively correlated with the DHX9 expression level in tumor samples and were associated with a poor prognosis in patients with osteosarcoma. Taken together, these results suggest that the MCM2/MCM3–DHX9 axis has an important role in osteosarcoma progression.

The biology of DHX9 and its potential as a therapeutic target

DHX9 is member of the DExD/H-box family of helicases with a “DEIH” sequence at its eponymous DExH-box motif. Initially purified from human and bovine cells and identified as a homologue of the Drosophila Maleless (MLE) protein, it is an NTP-dependent helicase consisting of a conserved helicase core domain, two double-stranded RNA-binding domains at the N-terminus, and a nuclear transport domain and a single-stranded DNA-binding RGG-box at the C-terminus. With an ability to unwind DNA and RNA duplexes, as well as more complex nucleic acid structures, DHX9 appears to play a central role in many cellular processes. Its functions include regulation of DNA replication, transcription, translation, microRNA biogenesis, RNA processing and transport, and maintenance of genomic stability. Because of its central role in gene regulation and RNA metabolism, there are growing implications for DHX9 in human diseases and their treatment. This review will provide an overview of the structure, biochemistry, and biology of DHX9, its role in cancer and other human diseases, and the possibility of targeting DHX9 in chemotherapy.

Targeting RNA helicases in cancer: The translation trap

Cancer cells are reliant on the cellular translational machinery for both global elevation of protein synthesis and the translation of specific mRNAs that promote tumor cell survival. Targeting translational control in cancer is therefore increasingly recognized as a promising therapeutic strategy. In this regard, DEAD/H box RNA helicases are a very interesting group of proteins, with several family members regulating mRNA translation in cancer cells. In this review, we delineate the mechanisms by which DEAD/H box proteins modulate oncogenic translation and how inhibition of these RNA helicases can be exploited for anti-cancer therapeutics.

Emerging cancer-specific therapeutic aptamers

PURPOSE OF REVIEW

We will describe recently discovered smart aptamers with tumor specificity, with an emphasis on targeted delivery of novel therapeutic molecules, cancer-specific biomarkers, and immunotherapy.

RECENT FINDINGS

The development of cancer-specific aptamers has facilitated targeted delivery of potent therapeutic molecules to cancer cells without harming nontumoral cells. This specificity also makes it possible to discover novel cancer biomarkers. Furthermore, alternative immune-checkpoint blockade aptamers have been developed for combinational immunotherapy.

SUMMARY

Aptamers selected against cancer cells show cancer specificity, which has great potential for targeting. First, functionalizing targeted aptamers with therapeutic molecule payloads (e.g., small activating RNAs, antimitotic drugs, therapeutic antibodies, and peptides) facilitates successful delivery into cancer cells. This approach greatly improves the therapeutic index by minimizing side-effects in nontumoral cells. Second, cancer-specific proteins have been identified as cancer biomarkers through in-vitro and in-vivo selection, aptamer pull-down assays, and mass spectrometry. These newly discovered biomarkers improve therapeutic intervention and diagnostic specificity. In addition, the development of alternative immune-checkpoint blockade aptamers is suggested for use in combinational immunotherapeutic with current immune blockade regimens, to reduce the resistance and exhaustion of T cells in clinical trials. VIDEO ABSTRACT: http://links.lww.com/COON/A21.

Suppression of Transposable Elements in Leukemic Stem Cells

Genomic transposable elements (TEs) comprise nearly half of the human genome. The expression of TEs is considered potentially hazardous, as it can lead to insertional mutagenesis and genomic instability. However, recent studies have revealed that TEs are involved in immune-mediated cell clearance. Hypomethylating agents can increase the expression of TEs in cancer cells, inducing ‘viral mimicry’, causing interferon signalling and cancer cell killing. To investigate the role of TEs in the pathogenesis of acute myeloid leukaemia (AML), we studied TE expression in several cell fractions of AML while tracking its development (pre-leukemic haematopoietic stem cells, leukemic stem cells [LSCs], and leukemic blasts). LSCs, which are resistant to chemotherapy and serve as reservoirs for relapse, showed significant suppression of TEs and interferon pathways. Similarly, high-risk cases of myelodysplastic syndrome (MDS) showed far greater suppression of TEs than low-risk cases. We propose TE suppression as a mechanism for immune escape in AML and MDS. Repression of TEs co-occurred with the upregulation of several genes known to modulate TE expression, such as RNA helicases and autophagy genes. Thus, we have identified potential pathways that can be targeted to activate cancer immunogenicity via TEs in AML and MDS.

RNA helicase DHX9 may be a therapeutic target in lung cancer and inhibited by enoxacin

RNA helicase DHX9 is a member of human RNA enzymes. Previous studies have reported that DHX9 is highly expressed in various types of malignant tumor. However, its role in the progression of lung cancer remains to be fully clarified. The present study aims to investigate the oncogenic role of DHX9 in serum, tissues and lung cancer cell lines in vitro. We used RNA interference to downregulate DHX9 expression in A549 cells using a small interfering RNA lentiviral vector. Subsequently, enoxacin was used to inhibit cell proliferation, and this effect was detected using MTT. The results showed that DHX9 was overexpressed in the serum and tissues of lung cancer, especially in small cell lung cancer. Though enoxacin suppressed the proliferation of NSCLC cells, the inhibition effect was diminished when DHX9 was knocked down. In conclusion, the present study provided evidence suggesting that DHX9 was overexpressed in lung cancer and may contribute to the growth of lung cancer, and enoxacin may inhibit the proliferation based on DHX9. Thus DHX9 may be used as a diagnostic marker and a potential therapeutic target for the treatment of NSCLC.

DHX9/RHA Binding to the PBS-Segment of the Genomic RNA during HIV-1 Assembly Bolsters Virion Infectivity

Cellular RNA-binding proteins incorporated into virions during human immunodeficiency virus type 1 (HIV-1) assembly promote the replication efficiency of progeny virions. Despite its critical role in bolstering virion infectivity, the molecular basis for the incorporation of DHX9/RNA helicase A (RHA) to virions remains unclear. Here, cell-based experiments demonstrate that the truncation of segments of the HIV-1 5'-untranslated region (5'-UTR) distinct from the core encapsidation sequence eliminated virion incorporation of RHA, indicating that RHA recruitment is mediated by specific interactions with the HIV-1 5'-UTR. In agreement with biological data, isothermal titration calorimetry determined that the dimer conformation of the 5'-UTR binds one RHA molecule per RNA strand, and the interaction is independent of nucleocapsid protein binding. NMR spectra employing a deuterium-labeling approach enabled resolution of the dimeric 5'-UTR in complex with the RHA N-terminal domain. The structure of the large molecular mass complex was dependent on RHA binding to a double-stranded region of the primer binding site (PBS)-segment of the 5'-UTR. A single A-to-C substitution was sufficient to disrupt biophysical conformation and attenuate virion infectivity in cell-based assays. Taken together, our studies demonstrate the structural basis for HIV-1 genomic RNA to recruit beneficial cellular cofactor to virions. The support of progeny virion infectivity by RHA is attributable to structure-dependent binding at the PBS-segment of the HIV-1 5'-UTR during virus assembly.