QGRS Mapper: a web-based server for predicting G-quadruplexes in nucleotide sequences

Selection of DNA aptamers against Chikungunya virus Envelope 2 Protein and their application in sandwich ELASA

Chikungunya fever, caused by Chikungunya virus (CHIKV) exhibits clinical features that mimic that of other arbovirus infections such as dengue. CHIKV Envelope 2 (E2) protein, an antigenic epitope of CHIKV, has been identified as an ideal marker for diagnostics. The current CHIKV antigen detection tests are largely based on antibodies but are beleaguered by issues such as sensitivity to high temperature, expensive and prone to batch-to-batch variations. Aptamers are suitable alternatives to antibodies as they are cheaper and have no batch-to-batch variations compared to antibodies. In this study, DNA aptamer selection against CHIKV E2 proteins was performed using two different randomized ssDNA libraries. Chik-2 (96-mer) and Chik-3 (76-mer) were isolated from these two libraries and were identified as the potential aptamers against CHIKV E2 protein. The binding affinity of Chik-2 and Chik-3 against CHIKV E2 protein was estimated at 177.5 ± 32.69 nM and 30.01 ± 3.60 nM, respectively. A sandwich ELASA was developed, and this assay showed a detection limit of 2.17 x 103 PFU/mL. The sensitivity and specificity of the assay were 80 % and 100 %, respectively. The assay showed no cross-reactivity with dengue-positive samples, demonstrating the enormous diagnostic potential of these aptamers for the detection of CHIKV.

Sandwich enzyme-linked aptamer-based assay for the detection of Trichomonas vaginalis

Trichomoniasis is the most prevalent curable, non-viral sexually transmitted infection (STI), with an estimated 156 million new infections in 2020. It can potentially result in adverse birth outcomes as well as infertility in men, whilst it also increases the risk of acquiring HIV and contracting other vaginal infections. It is mostly prevalent among women in low-income countries and especially in Africa and the Americas. This STI is caused by Trichomonas vaginalis (TV) and a robust, cost-effective, sensitive, specific and rapid diagnostic test is urgently required. We report the screening of 6 full-length and 4 truncated aptamers previously selected in our group for use in a microplate-based sandwich assay. The combination of dual aptamers comprising a short 14-mer truncated capture aptamer (termed A1_14mer) and a full-length non-truncated reporter aptamer (A6) was elucidated to be the optimum pair for a sensitive sandwich enzyme-linked aptamer assay (ELAA) for the detection of TV achieving a detection limit of 3.02 × 104 TV cells/mL. The results obtained with the A1_14mer-A6 ELAA correlate excellently with wet-mount microscopy for the detection of TV in clinical specimens, cervicovaginal lavages and vaginal swabs, highlighting the potential clinical application of this assay for cost-effective population screening and subsequent prevention of the onset of complications associated with undiagnosed and untreated TV.

Nucleic acid aptamers protect against lead (Pb(II)) toxicity

Lead (Pb(II)) is a pervasive heavy metal toxin with many well-established negative effects on human health. Lead toxicity arises from cumulative, repeated environmental exposures. Thus, prophylactic strategies to protect against the bioaccumulation of lead could reduce lead-associated human pathologies. Here we show that DNA and RNA aptamers protect C. elegans from toxic phenotypes caused by lead. Reproductive toxicity, as measured by brood size assays, is prevented by co-feeding of animals with DNA or RNA aptamers. Similarly, lead-induced neurotoxicity, measured by behavioral assays, are also normalized by aptamer feeding. Further, cultured human HEK293 and primary murine osteoblasts are protected from lead toxicity by transfection with DNA aptamers. The osteogenic development, which is decreased by lead exposure, is maintained by prior transfection of lead-binding DNA aptamers. Aptamers may be an effective strategy for the protection of human health in the face of increasing environmental toxicants.

RHPS4 Targeted the G-Quadruplex of the 1a Gene of Cucumber Mosaic Virus to Inhibit Viral Proliferation

Small molecules targeting G-quadruplexes (G4s) in viruses could inhibit viral proliferation. The 1a protein of cucumber mosaic virus (CMV) act as RNA-dependent RNA polymerase (RdRp) that plays a crucial role in regulating the replication of CMV. In this study, four putative G4 sequences (CMV PQS1-PQS4) in the genetic coding region of CMV 1a were identified, and three of them (PQS2, PQS3, and PQS4) were confirmed to fold into G4 structures. The G4-ligand, RHPS4, could bind to CMV PQS2 and PQS4 with a strong binding affinity and preferred to interact with the 3' terminal G-quartet surfaces of CMV PQS2, and 5' terminal of CMV PQS4. RHPS4 was also found to stabilize the CMV PQS2 and PQS4 G4s. Further studies revealed that RHPS4 exhibited an excellent anti-CMV activity. This study suggested that CMV PQS2 and PQS4 could be considered potential targets for screening viral inhibitors.

Apurinic/Apyrimidinic Endodeoxyribonuclease 1 modulates RNA G-quadruplex folding of miR-92b and controls its expression in cancer cells

In the last decade, several novel functions of the mammalian Apurinic/Apyrimidinic Endodeoxyribonuclease 1 (APE1) have been discovered, going far beyond its canonical function as DNA repair enzyme and unveiling its potential roles in cancer development. Indeed, it was shown to be involved in DNA G-quadruplex biology and RNA metabolism, most importantly in the miRNA maturation pathway and the decay of oxidized or abasic miRNAs during oxidative stress conditions. In recent years, several noncanonical pathways of miRNA biogenesis have emerged, with a specific focus on guanosine-rich precursors that can form RNA G-quadruplex (rG4) structures. Here, we show that several miRNA precursors, dysregulated upon APE1 depletion, contain an rG4 motif and that their corresponding target genes are up-regulated after APE1 depletion. We also demonstrate, both by in vitro assays and by using different cancer cell lines, that APE1 can modulate the folding of an rG4 structure contained in pre-miR-92b, with a mechanism strictly dependent on lysine residues present in its N-terminal disordered region. Furthermore, APE1 cellular depletion alters the maturation process of miR-92b, mainly affecting the shuttling between the nucleus and cytosol. Bioinformatic analysis of APE1-regulated rG4-containing miRNAs supports the relevance of our findings in cancer biology. Specifically, these miRNAs exhibit high prognostic significance in lung, cervical, and liver tumors, as suggested by their involvement in several cancer-related pathways.

Identification and detection of conserved G-quadruplex in monkeypox virus using conformation specific fluorogenic probe

Identifying distinct noncanonical structures in pathogenic genomes is crucial for developing new diagnostic tools. This study uncovers stable G-quadruplex (GQ) structures in conserved DNA sequences unique to the monkeypox virus (MPV). Furthermore, we developed a method for the detection of target GQ using a fluorogenic probe.

Remodeling Ca2+ dynamics by targeting a promising E-box containing G-quadruplex at ORAI1 promoter in triple-negative breast cancer

ORAI1 is an intrinsic component of store-operated calcium entry (SOCE) that strictly regulates Ca2+ influx in most non-excitable cells. ORAI1 is overexpressed in a wide variety of cancers, and its signal transduction has been associated with chemotherapy resistance. There is extensive proteomic interaction of ORAI1 with other channels and effectors, resulting in various altered phenotypes. However, the transcription regulation of ORAI1 is not well understood. We have found a putative G-quadruplex (G4) motif, ORAI1-Pu, in the upstream promoter region of the gene, having regulatory functions. High-resolution 3-D NMR structure elucidation suggests that ORAI1-Pu is a stable parallel-stranded G4, having a long 8-nt loop imparting dynamics without affecting the structural stability. The protruded loop further houses an E-box motif that provides a docking site for transcription factors like Zeb1. The G4 structure was also endogenously observed using Chromatin Immunoprecipitation (ChIP) with anti-G4 antibody (BG4) in the MDA-MB-231 cell line overexpressing ORAI1. Ligand-mediated stabilization suggested that the stabilized G4 represses transcription in cancer cell line MDA-MB-231. Downregulation of transcription further led to decreased Ca2+ entry by the SOCE pathway, as observed by live-cell Fura-2 Ca2+ imaging.

Species-specific variation in mitochondrial genome tandem repeat polymorphisms in hares (Lepus spp., Lagomorpha, Leporidae) provides insight into their evolution

The non-coding regions of the mitochondrial DNAs (mtDNAs) of hares, rabbits, and pikas (Lagomorpha) contain short (∼20 bp) and long (130-160 bp) tandem repeats, absent in related mammalian orders. In the presented study, we provide in-depth analysis for mountain hare (Lepus timidus) and brown hare (L. europaeus) mtDNA non-coding regions, together with a species- and population-level analysis of tandem repeat variation. Mountain hare short tandem repeats (SRs) as well as other analyzed hare species consist of two conserved 10 bp motifs, with only brown hares exhibiting a single, more variable motif. Long tandem repeats (LRs) also differ in sequence and copy number between species. Mountain hares have four to seven LRs, median value five, while brown hares exhibit five to nine LRs, median value six. Interestingly, introgressed mountain hare mtDNA in brown hares obtained an intermediate LR length distribution, with median copy number being the same as with conspecific brown hare mtDNA. In contrast, transfer of brown hare mtDNA into cultured mtDNA-less mountain hare cells maintained the original LR number, whereas the reciprocal transfer caused copy number instability, suggesting that cellular environment rather than the nuclear genomic background plays a role in the LR maintenance. Due to their dynamic nature and separation from other known conserved sequence elements on the non-coding region of hare mitochondrial genomes, the tandem repeat elements likely to represent signatures of ancient genetic rearrangements. clarifying the nature and dynamics of these rearrangements may shed light on the possible role of NCR repeated elements in mitochondria and in species evolution.

G-quadruplexes in an SVA retrotransposon cause aberrant TAF1 gene expression in X-linked dystonia parkinsonism

G-quadruplexes (G4s) are non-canonical nucleic acid structures that form in guanine (G)-rich genomic regions. X-linked dystonia parkinsonism (XDP) is an inherited neurodegenerative disease in which a SINE-VNTR-Alu (SVA) retrotransposon, characterised by amplification of a G-rich repeat, is inserted into the coding sequence of TAF1, a key partner of RNA polymerase II. XDP SVA alters TAF1 expression, but the cause of this outcome in XDP remains unknown. To assess whether G4s form in XDP SVA and affect TAF1 expression, we first characterised bioinformatically predicted XDP SVA G4s in vitro. We next showed that highly stable G4s can form and stop polymerase amplification at the SVA region from patient-derived fibroblasts and neural progenitor cells. Using chromatin immunoprecipitazion (ChIP) with an anti-G4 antibody coupled to sequencing or quantitative PCR, we showed that XDP SVA G4s are folded even when embedded in a chromatin context in patient-derived cells. Using the G4 ligands BRACO-19 and quarfloxin and total RNA-sequencing analysis, we showed that stabilisation of the XDP SVA G4s reduces TAF1 transcripts downstream and around the SVA, and increases upstream transcripts, while destabilisation using the G4 unfolder PhpC increases TAF1 transcripts. Our data indicate that G4 formation in the XDP SVA is a major cause of aberrant TAF1 expression, opening the way for the development of strategies to unfold G4s and potentially target the disease.

G-quadruplex structures in FGFR3 promoter negatively regulate its gene expression and DNA replication

FGFR3 activating mutations and abnormal expression are linked to tumor development. However, the current state of research on FGFR3 gene expression regulation is relatively insufficient. In this study, we have reported that the FGFR3 promoter's positive strand contains several G-tracts and most likely forms a G-quadruplex (G4) structure. Circular dichroism investigations revealed that oligonucleotides from this region exhibit G-quadruplex-like molar ellipticity. We further validated the G4 structure of the FGFR3 promoter using biochemical and cellular molecular biology techniques. The G-quadruplex mutation enhanced the transcriptional activity of the FGFR3 promoter and DNA replication, suggesting that the G4 structure inhibits its expression. Furthermore, we conducted a preliminary screen for helicases associated with FGFR3 expression and explored their regulatory effects on FGFR3 gene transcription. Subsequently, we investigated the effect of curcumin on the stability of the G4 structure of the FGFR3 promoter and its regulatory effect on FGFR3 expression.

G-Quadruplex Structures as Epigenetic Regulatory Elements in Priming of Defense Genes upon Short-Term Trichoderma atroviride Inoculation in Maize

Symbiosis establishment between Trichoderma atroviride and plant roots triggers the priming of defense responses, among other effects. Currently, there is no clear evidence regarding the molecular mechanisms that allow the plant to remain alert to future stimulus, either by pathogen attack or any other abiotic stress. Epigenetic modifications have emerged as a strategy to explain the increased defense response of plants in a priming state conferred by Trichoderma. Recently, various non-canonical structures of nucleic acids, especially G-quadruplex structures (G-quadruplexes or G4s), have been identified as potential targets during the establishment or maintenance of plant signals. In the present study, we developed a screening test for the identification of putative G4-forming sequences (PQSs) in previously identified Z. mays priming genes. Bioinformatic analysis revealed the presence of PQSs in the promoter region of five essential genes playing a critical role in priming in maize. Biophysical and spectroscopy studies showed the formation of G4s by these PQSs in vitro, and ChIP assays demonstrate their formation in vivo. Therefore, G4 formation could play a role as an epigenetic regulatory mechanism involved in the long-lasting primed state in maize plants.

An unbiased lncRNA dropout CRISPR-Cas9 screen reveals RP11-350G8.5 as a novel therapeutic target for multiple myeloma

ABSTRACT

Multiple myeloma (MM) is an incurable malignancy characterized by altered expression of coding and noncoding genes promoting tumor growth and drug resistance. Although the crucial role of long noncoding RNAs (lncRNAs) in MM is clearly established, the function of the noncoding RNAome, which might allow the design of novel therapeutics, is largely unknown. We performed an unbiased CRISPR-Cas9 loss-of-function screen of 671 lncRNAs in MM cells and their bortezomib (BZB)-resistant derivative. To rank functionally and clinically relevant candidates, we designed and used a bioinformatic prioritization pipeline combining functional data from cellular screens with prognostic and transcriptional data from patients with MM. With this approach, we unveiled and prioritized 8 onco-lncRNAs essential for MM cell fitness, associated with high expression and poor prognosis in patients with MM. The previously uncharacterized RP11-350G8.5 emerged as the most promising target, irrespective of BZB resistance. We (1) demonstrated the anti-tumoral effect obtained by RP11-350G8.5 inhibition in vitro and in vivo; (2) highlighted a modulation of the unfolded protein response and the induction of immunogenic cell death triggered by the RP11-350G8.5 knockout, via RNA sequencing and molecular studies; (3) characterized its cytoplasmic homing through RNA fluorescence in situ hybridization; and (4) predicted its 2-dimensional structure and identified 2 G-quadruplex and 3 hairpin-forming regions by biophysical assays, including thioflavin T, 1H nuclear magnetic resonance, and circular dichroism, to pave the way to the development of novel targeted therapeutics. Overall, we provided innovative insights about unexplored lncRNAs in MM and identified RP11-350G8.5 as an oncogenic target for treatment-naïve and BZB-resistant patients with MM.

Insights into the Molecular Structure, Stability, and Biological Significance of Non-Canonical DNA Forms, with a Focus on G-Quadruplexes and i-Motifs

This article provides a comprehensive examination of non-canonical DNA structures, particularly focusing on G-quadruplexes (G4s) and i-motifs. G-quadruplexes, four-stranded structures formed by guanine-rich sequences, are stabilized by Hoogsteen hydrogen bonds and monovalent cations like potassium. These structures exhibit diverse topologies and are implicated in critical genomic regions such as telomeres and promoter regions of oncogenes, playing significant roles in gene expression regulation, genome stability, and cellular aging. I-motifs, formed by cytosine-rich sequences under acidic conditions and stabilized by hemiprotonated cytosine-cytosine (C:C+) base pairs, also contribute to gene regulation despite being less prevalent than G4s. This review highlights the factors influencing the stability and dynamics of these structures, including sequence composition, ionic conditions, and environmental pH. Molecular dynamics simulations and high-resolution structural techniques have been pivotal in advancing our understanding of their folding and unfolding mechanisms. Additionally, the article discusses the therapeutic potential of small molecules designed to selectively bind and stabilize G4s and i-motifs, with promising implications for cancer treatment. Furthermore, the structural properties of these DNA forms are explored for applications in nanotechnology and molecular devices. Despite significant progress, challenges remain in observing these structures in vivo and fully elucidating their biological functions. The review underscores the importance of continued research to uncover new insights into the genomic roles of G4s and i-motifs and their potential applications in medicine and technology. This ongoing research promises exciting developments in both basic science and applied fields, emphasizing the relevance and future prospects of these intriguing DNA structures.

G-quadruplex is involved in the regulation of BmSGF1 expression in the Silkworm, Bombyx mori

Advanced DNA structures, such as the G-quadruplex (G4) and the i-motif, are widely but not randomly present in the genomes of many organisms. A G4 structure was identified in the promoter of the silk gland factor-1 gene (SGF1), which is the main regulatory gene for silk production in Bombyx mori. In this study, a BmSGF1 G4-/- homozygous mutant was generated with the G4 sequence knocked out. The promoter activity of BmSGF1 was lowered in the BmSGF1 G4-/- mutant. Pyridostatin (PDS) stabilized the G4 structure and increased the promoter activity of BmSGF1, whereas anti-sense oligonucleotide (ASO) complementary to the G4 sequence suppressed the promoter activity of BmSGF1. Compared with wild-type larvae, the deletion of the BmSGF1 G4 structure decreased both the expression of BmSGF1 and the fibroin heavy chain gene BmFib-H in the posterior silk gland and the weight of the cocoons. Overall, these results suggest that the promoter G4 structure of BmSGF1 participates in the transcription regulation of the BmSGF1 gene in the silkworm.

Human genomic DNA is widely interspersed with i-motif structures

DNA i-motif structures are formed in the nuclei of human cells and are believed to provide critical genomic regulation. While the existence, abundance, and distribution of i-motif structures in human cells has been demonstrated and studied by immunofluorescent staining, and more recently NMR and CUT&Tag, the abundance and distribution of such structures in human genomic DNA have remained unclear. Here we utilise high-affinity i-motif immunoprecipitation followed by sequencing to map i-motifs in the purified genomic DNA of human MCF7, U2OS and HEK293T cells. Validated by biolayer interferometry and circular dichroism spectroscopy, our approach aimed to identify DNA sequences capable of i-motif formation on a genome-wide scale, revealing that such sequences are widely distributed throughout the human genome and are common in genes upregulated in G0/G1 cell cycle phases. Our findings provide experimental evidence for the widespread formation of i-motif structures in human genomic DNA and a foundational resource for future studies of their genomic, structural, and molecular roles.

G-quadruplexes in long non-coding RNAs and their interactions with proteins

Long non-coding RNAs (lncRNAs) have emerged as crucial regulators of cellular processes, with their dysregulation linked to various disease states. Among the structural motifs in lncRNAs, RNA G-quadruplexes (rG4s) have gained increasing attention due to their diverse roles in cellular function and disease pathogenesis. This review provides an updated and comprehensive overview of rG4s in lncRNAs, elucidating their formation, interaction with proteins, and distinctive roles in cellular processes. We discuss current methodologies for experimentally probing RNA G4s, including the use of specific small molecules, biomolecular ligands and fluorescent probes. The commonly found RNA G4-interacting protein domains are summarised along with potential strategies for disrupting lncRNA G4-protein interactions from a therapeutic perspective.

Effective lowering of α-synuclein expression by targeting G-quadruplex structures within the SNCA gene

Alpha-synuclein, encoded by the SNCA gene, is a pivotal protein implicated in the pathogenesis of synucleinopathies, including Parkinson's disease. Current approaches for modulating alpha-synuclein levels involve antisense nucleotides, siRNAs, and small molecules targeting SNCA's 5'-UTR mRNA. Here, we propose a groundbreaking strategy targeting G-quadruplex structures to effectively modulate SNCA gene expression and lowering alpha-synuclein amount. Novel G-quadruplex sequences, identified on the SNCA gene's transcription starting site and 5'-UTR of SNCA mRNAs, were experimentally confirmed for their stability through biophysical assays and in vitro experiments on human genomic DNA. Biological validation in differentiated SH-SY5Y cells revealed that well-known G-quadruplex ligands remarkably stabilized these structures, inducing the modulation of SNCA mRNAs expression, and the effective decrease in alpha-synuclein amount. Besides, a novel peptide nucleic acid conjugate, designed to selectively disrupt of G-quadruplex within the SNCA gene promoter, caused a promising lowering of both SNCA mRNA and alpha-synuclein protein. Altogether our findings highlight G-quadruplexes' key role as intriguing biological targets in achieving a notable and successful reduction in alpha-synuclein expression, pointing to a novel approach against synucleinopathies.

Untargeted CUT&Tag and BG4 CUT&Tag are both enriched at G-quadruplexes and accessible chromatin

G-quadruplex DNA structures (G4s) form within single-stranded DNA in nucleosome-free chromatin. As G4s modulate gene expression and genomic stability, genome-wide mapping of G4s has generated strong research interest. Recently, the Cleavage Under Targets and Tagmentation (CUT&Tag) method was performed with the G4-specific BG4 antibody to target Tn5 transposase to G4s. While this method generated a novel high-resolution map of G4s, we unexpectedly observed a strong correlation between the genome-wide signal distribution of BG4 CUT&Tag and accessible chromatin. To examine whether untargeted Tn5 cutting at accessible chromatin contributes to BG4 CUT&Tag signal, we examined the genome-wide distribution of signal from untargeted (i.e. negative control) CUT&Tag datasets. We observed that untargeted CUT&Tag signal distribution was highly similar to both that of accessible chromatin and of BG4 CUT&Tag. We also observed that BG4 CUT&Tag signal increased at mapped G4s, but this increase was accompanied by a concomitant increase in untargeted CUT&Tag at the same loci. Consequently, enrichment of BG4 CUT&Tag over untargeted CUT&Tag was not increased at mapped G4s. These results imply that either the vast majority of accessible chromatin regions contain mappable G4s or that the presence of G4s within accessible chromatin cannot reliably be determined using BG4 CUT&Tag alone.

The RNA-binding protein PCBP1 modulates transcription by recruiting the G-quadruplex-specific helicase DHX9

PCBP1, polycytosine (poly(C)) binding protein 1, an RNA and single-stranded DNA (ssDNA) binding protein, binds poly(C) DNA tracts but it remains unclear whether its ability to bind ssDNA contributes to transcriptional regulation. Here, we report that PCBP1's DNA binding sites are enriched at transcription start sites and that by binding to promoter regions, PCBP1 regulates transcription in addition to splicing and translation. At PCBP1 target genes, we show that PCBP1 interacts with several RNA/DNA hybrid (R-loop) associated G-quadruplex resolving helicases. Furthermore, we find that PCBP1 interacts with RNA Helicase A (DHX9) to modulate transcription by regulating DHX9 accumulation and activity. PCBP1 depletion leads to defects in R-loop processing and dysregulation of transcription of PCBP1 target genes. PCBP1's high sequence specificity and interaction with helicases suggest that its mechanism in transcription involves guiding helicases to specific loci during transcription, thereby modulating their activity.

In Vitro Selection and Characterization of a Light-up DNA Aptamer for Thiazole Orange

A new DNA aptamer that binds to the target Thiazole Orange-biotin (TO1-biotin) was isolated after nine rounds of in vitro selection. The selection was performed on streptavidin-coated beads with the target bound to the surface and with free dye in solution in higher selection rounds to select for slower off-rate binding. Using next-generation sequencing (NGS), the libraries after the 4th and 9th rounds of selection were sequenced to identify enriched sequences. Several sequence families emerged, showing superior fluorescence enhancement and high affinity for the target compared to the other families obtained by NGS analysis. These sequence families were further studied to understand the binding interactions better. Primary sequence and secondary structure analysis tools were used to identify a hypothetical three-tiered G-quadruplex motif for these families. This indicates that the TO1-biotin DNA aptamer identified here uses a similar ligand-binding topology to the original Mango RNA aptamer.

Viral hijacking of hnRNPH1 unveils a G-quadruplex-driven mechanism of stress control

Viral genomes are enriched with G-quadruplexes (G4s), non-canonical structures formed in DNA or RNA upon assembly of four guanine stretches into stacked quartets. Because of their critical roles, G4s are potential antiviral targets, yet their function remains largely unknown. Here, we characterize the formation and functions of a conserved G4 within the polymerase coding region of orthoflaviviruses of the Flaviviridae family. Using yellow fever virus, we determine that this G4 promotes viral replication and suppresses host stress responses via interactions with hnRNPH1, a host nuclear protein involved in RNA processing. G4 binding to hnRNPH1 causes its cytoplasmic retention with subsequent impacts on G4-containing tRNA fragments (tiRNAs) involved in stress-mediated reductions in translation. As a result, these host stress responses and associated antiviral effects are impaired. These data reveal that the interplay between hnRNPH1 and both host and viral G4 targets controls the integrated stress response and viral replication.

Topical application of a CCL22-binding aptamer suppresses contact allergy

Allergic contact dermatitis is a prevalent occupational disease with limited therapeutic options. The chemokine CCL22, a ligand of the chemokine receptor CCR4, directs the migration of immune cells. Here, it is shown that genetic deficiency of CCL22 effectively ameliorated allergic reactions in contact hypersensitivity (CHS), a commonly used mouse model of allergic contact dermatitis. For the pharmacological inhibition of CCL22, DNA aptamers specific for murine CCL22 were generated by the systematic evolution of ligands by exponential enrichment (SELEX). Nine CCL22-binding aptamers were initially selected and functionally tested in vitro. The 29-nt DNA aptamer AJ102.29m profoundly inhibited CCL22-dependent T cell migration and did not elicit undesired Toll-like receptor-dependent immune activation. AJ102.29m efficiently ameliorated CHS in vivo after systemic application. Moreover, CHS-associated allergic symptoms were also reduced following topical application of the aptamer on the skin. Microscopic analysis of skin treated with AJ102.29m ex vivo demonstrated that the aptamer could penetrate into the epidermis and dermis. The finding that epicutaneous application of the aptamer AJ102.29m in a cream was as effective in suppressing the allergic reaction as intraperitoneal injection paves the way for therapeutic use of aptamers beyond the current routes of systemic administration.

Mapping the structural landscape of the yeast Ty3 retrotransposon RNA genome

Long terminal repeat (LTR)-retrotransposons are significant contributors to the evolution and diversity of eukaryotic genomes. Their RNA genomes (gRNA) serve as a template for protein synthesis and reverse transcription to a DNA copy, which can integrate into the host genome. Here, we used the SHAPE-MaP strategy to explore Ty3 retrotransposon gRNA structure in yeast and under cell-free conditions. Our study reveals the structural dynamics of Ty3 gRNA and the well-folded core, formed independently of the cellular environment. Based on the detailed map of Ty3 gRNA structure, we characterized the structural context of cis-acting sequences involved in reverse transcription and frameshifting. We also identified a novel functional sequence as a potential initiator for Ty3 gRNA dimerization. Our data indicate that the dimer is maintained by direct interaction between short palindromic sequences at the 5' ends of the two Ty3 gRNAs, resembling the model characteristic for other retroelements like HIV-1 and Ty1. This work points out a range of cell-dependent and -independent Ty3 gRNA structural changes that provide a solid background for studies on RNA structure-function relationships important for retroelement biology.

IGF2BP1-Mediated Regulation of CCN1 Expression by Specific Binding to G-Quadruplex Structure in Its 3'UTR

The intricate regulation of gene expression is fundamental to the biological complexity of higher organisms, and is primarily governed by transcriptional and post-transcriptional mechanisms. The 3'-untranslated region (3'UTR) of mRNA is rich in cis-regulatory elements like G-quadruplexes (G4s), and plays a crucial role in post-transcriptional regulation. G4s have emerged as significant gene regulators, impacting mRNA stability, translation, and localization. In this study, we investigate the role of a robust parallel G4 structure situated within the 3'UTR of CCN1 mRNA in post-transcriptional regulation. This G4 structure is proximal to the stop codon of human CCN1, and evolutionarily conserved. We elucidated its interaction with the insulin-like growth factor 2 binding protein 1 (IGF2BP1), a noncanonical RNA N6-methyladenosine (m6A) modification reader, revealing a novel interplay between RNA modifications and G-quadruplex structures. Knockdown experiments and mutagenesis studies demonstrate that IGF2BP1 binds specifically to the G4 structure, modulating CCN1 mRNA stability. Additionally, we unveil the role of IGF2BP1's RNA recognition motifs in G4 recognition, highlighting this enthalpically driven interaction. Our findings offer fresh perspectives on the complex mechanisms of post-transcriptional gene regulation mediated by G4 RNA secondary structures.

Japanese encephalitis virus NS5 protein interacts with nucleolin to enhance the virus replication

Japanese encephalitis virus (JEV) is an arthropod-borne, plus-strand flavivirus causing viral encephalitis in humans with a high case fatality rate. The JEV non-structural protein 5 (NS5) with the RNA-dependent RNA polymerase activity interacts with the viral and host proteins to constitute the replication complex. We have identified the multifunctional protein Nucleolin (NCL) as one of the several NS5-interacting host proteins. We demonstrate the interaction and colocalization of JEV NS5 with NCL in the virus-infected HeLa cells. The siRNA-mediated knockdown of NCL indicated that it was required for efficient viral replication. Importantly, JEV grew to higher titers in cells over-expressing exogenous NCL, demonstrating its pro-viral role. We demonstrated that NS5 interacted with the RRM and GAR domains of NCL. We show that the NCL-binding aptamer AS1411 containing the G-quadruplex (GQ) structure and the GQ ligand BRACO-19 caused significant inhibition of JEV replication. The antiviral effect of AS1411 and BRACO-19 could be overcome in HeLa cells by the overexpression of exogenous NCL. We demonstrated that the synthetic RNAs derived from the 3'-NCR of JEV genomic RNA containing the GQ sequence could bind NCL in vitro. The replication complex binding to the 3'-NCR is required for the viral RNA synthesis. It is likely that NCL present in the replication complex destabilizes the GQ structures in the genomic RNA, thus facilitating the movement of the replication complex resulting in efficient virus replication.IMPORTANCEJapanese encephalitis virus (JEV) is endemic in most parts of South-East Asia and the Western Pacific region, causing epidemics of encephalitis with a high case fatality rate. While a tissue culture-derived JEV vaccine is available, no antiviral therapy exists. The JEV NS5 protein has RNA-dependent RNA polymerase activity. Together with several host and viral proteins, it constitutes the replication complex necessary for virus replication. Understanding the interaction of NS5 with the host proteins could help design novel antivirals. We identified Nucleolin (NCL) as a crucial host protein interactor of JEV NS5 having a pro-viral role in virus replication. The NS5-interacting NCL binds to the G-quadruplex (GQ) structure sequence in the 3'-NCR of JEV RNA. This may smoothen the movement of the replication complex along the genomic RNA, thereby facilitating the virus replication. This study is the first report on how NCL, a host protein, helps in JEV replication through GQ-binding.

Structural insights into i-motif DNA structures in sequences from the insulin-linked polymorphic region

The insulin-linked polymorphic region is a variable number of tandem repeats region of DNA in the promoter of the insulin gene that regulates transcription of insulin. This region is known to form the alternative DNA structures, i-motifs and G-quadruplexes. Individuals have different sequence variants of tandem repeats and although previous work investigated the effects of some variants on G-quadruplex formation, there is not a clear picture of the relationship between the sequence diversity, the DNA structures formed, and the functional effects on insulin gene expression. Here we show that different sequence variants of the insulin linked polymorphic region form different DNA structures in vitro. Additionally, reporter genes in cellulo indicate that insulin expression may change depending on which DNA structures form. We report the crystal structure and dynamics of an intramolecular i-motif, which reveal sequences within the loop regions forming additional stabilising interactions that are critical to formation of stable i-motif structures. The outcomes of this work reveal the detail in formation of stable i-motif DNA structures, with potential for rational based drug design for compounds to target i-motif DNA.

RNA tertiary structure and conformational dynamics revealed by BASH MaP

The functional effects of an RNA can arise from complex three-dimensional folds known as tertiary structures. However, predicting the tertiary structure of an RNA and whether an RNA adopts distinct tertiary conformations remains challenging. To address this, we developed BASH MaP, a single-molecule dimethyl sulfate (DMS) footprinting method and DAGGER, a computational pipeline, to identify alternative tertiary structures adopted by different molecules of RNA. BASH MaP utilizes potassium borohydride to reveal the chemical accessibility of the N7 position of guanosine, a key mediator of tertiary structures. We used BASH MaP to identify diverse conformational states and dynamics of RNA G-quadruplexes, an important RNA tertiary motif, in vitro and in cells. BASH MaP and DAGGER analysis of the fluorogenic aptamer Spinach reveals that it adopts alternative tertiary conformations which determine its fluorescence states. BASH MaP thus provides an approach for structural analysis of RNA by revealing previously undetectable tertiary structures.

A Branched SELEX Approach Identifies RNA Aptamers That Bind Distinct HIV-1 Capsid Structural Components

The HIV-1 capsid protein (CA) assumes distinct structural forms during replication, each presenting unique, solvent-accessible surfaces that facilitate multifaceted functions and host factor interactions. However, functional contributions of individual CA structures remain unclear, as evaluation of CA presents several technical challenges. To address this knowledge gap, we identified CA-targeting aptamers with different structural specificities, which emerged through a branched SELEX approach using an aptamer library previously selected to bind the CA hexamer lattice. Subsets were either highly specific for the CA lattice or bound both the CA lattice and CA hexamer. We then evaluated four representatives to reveal aptamer regions required for binding, highlighting interesting structural features and challenges in aptamer structure determination. Further, we demonstrate binding to biologically relevant CA structural forms and aptamer-mediated affinity purification of CA from cell lysates without virus or host modification, supporting the development of structural form-specific aptamers as exciting new tools for the study of CA.

A label-free G-quadruplex aptamer/gold nanoparticle-based colorimetric biosensor for rapid detection of bovine viral diarrhea virus genotype 1

Bovine viral diarrhea virus (BVDV) is the cause of bovine viral diarrhea disease, one of the most economically important livestock diseases worldwide. The majority of BVD disease control programs rely on the detection and then elimination of persistent infection (PI) cattle, as the continuing source of disease. The main purpose of this study was to design and develop an accurate G-quadruplex-based aptasensor for rapid and simple detection of BVDV-1. In this work, we utilized in silico techniques to design a G-quadruplex aptamer specific for the detection of BVDV-1. Also, the rationally designed aptamer was validated experimentally and was used for developing a colorimetric biosensor based on an aptamer-gold nanoparticle system. Firstly, a pool of G-quadruplex forming ssDNA sequences was constructed. Then, based on the stability score in secondary and tertiary structures and molecular docking score, an aptamer (Apt31) was selected. In the experimental part, gold nanoparticles (AuNPs) with an average particle size of 31.7 nm were synthesized and electrostatically linked with the Apt31. The colorimetric test showed that salt-induced color change of AuNPs from red to purple-blue occurs only in the presence of BVDV-Apt31 complex, after 20 min. These results approved the specificity of Apt31 for BVDV. Furthermore, our biosensor could detect the virus at as low as 0.27 copies/ml, which is an acceptable value in comparison to the qPCR method. The specificity of the aptasensor was confirmed through cross-reactivity testing, while its selectivity was confirmed through plasma testing. The sample analysis showed 90% precision and 94% accuracy. It was concluded that the biosensor was adequately sensitive and specific for the detection of BVDV in plasma samples and could be used as a simple and rapid method on the farm.

A highly specific aptamer for the SARS-CoV-2 spike protein from the authentic strain

DNA aptamers are oligonucleotides that specifically bind to target molecules, similar to how antibodies bind to antigens. We identified an aptamer named MEZ that is highly specific to the receptor-binding domain, RBD, of the SARS-CoV-2 spike protein from the Wuhan-Hu-1 strain. The SELEX procedure was utilized to enrich the initial 31-mer oligonucleotide library with the target aptamer. The aptamer identification was performed using the novel protocol based on nanopore sequencing developed in this study. The MEZ aptamer was chemically synthesized and tested for binding with the SARS-CoV-2 RBD of the spike protein from different strains. The Kd is 6.5 nM for the complex with the RBD from the Wuhan-Hu-1 strain, which is comparable with known aptamers; the advantage is that the MEZ aptamer is smaller than known analogs. The proposed aptamer is highly selective for the RBD protein from the Wuhan-Hu-1 strain and does not form complexes with the RBD from Beta, Delta and Omicron strains. Experimental and theoretical studies together revealed the molecular mechanism of aptamer binding. The aptamer occupies the same binding site as ACE2 when bound to the RBD. The 3'-end of the MEZ aptamer is important for complex formation and is responsible for the discrimination of the RBD protein from a specific strain. The 5'-end is responsible for the formation of a loop in the 3D structure of the aptamer, which is important for proper binding.

Characterization of G-quadruplexes in the Helicobacter pylori genome and assessment of therapeutic potential of G4 ligands

Helicobacter pylori, a leading human pathogen associated with duodenal ulcer and gastric cancer, presents a significant threat to human health due to increasing antibiotic resistance rates. This study investigates G-quadruplexes (G4s), which are non-canonical secondary structures form in G-rich regions within the H. pylori genome. Extensive research on G4s in eukaryotes has revealed their role in epigenetically regulating cellular processes like gene transcription, DNA replication, and oncogene expression. However, understanding of G4-mediated gene regulation in other organisms, especially bacterial pathogens, remains limited. Although G4 motifs have been extensively studied in a few bacterial species such as Mycobacterium, Streptococci, and Helicobacter, research on G4 motifs in other bacterial species is still sparse. Like in other organisms such as archaea, mammals, and viruses, G4s in H. pylori display a non-random distribution primarily situated within open reading frames of various protein-coding genes. The occurrence of G4s in functional regions of the genome and their conservation across different species indicates that their placement is not random, suggesting an evolutionary pressure to maintain these sequences at specific genomic sites. Moreover, G-quadruplexes show enrichment in specific gene classes, suggesting their potential involvement in regulating the expression of genes related to cell wall/membrane/envelope biogenesis, amino acid transport, and metabolism. This indicates a probable regulatory role for G4s in controlling the expression of genes essential for H. pylori survival and virulence. Biophysical techniques such as Circular Dichroism spectroscopy and Nuclear Magnetic Resonance were used to characterize G4 motifs within selected H. pylori genes. The study revealed that G-quadruplex ligand inhibited the growth of H. pylori, with minimal inhibitory concentrations in the low micromolar range. This suggests that targeting G4 structures could offer a promising approach for developing novel anti-H. pylori drugs.

PRMT5-mediated arginine methylation of FXR1 is essential for RNA binding in cancer cells

Emerging evidence indicates that arginine methylation promotes the stability of arginine-glycine-rich (RGG) motif-containing RNA-binding proteins (RBPs) and regulates gene expression. Here, we report that post-translational modification of FXR1 enhances the binding with mRNAs and is involved in cancer cell growth and proliferation. Independent point mutations in arginine residues of FXR1's nuclear export signal (R386 and R388) and RGG (R453, R455 and R459) domains prevent it from binding to RNAs that form G-quadruplex (G4) RNA structures. Disruption of G4-RNA structures by lithium chloride failed to bind with FXR1, indicating its preference for G4-RNA structure containing mRNAs. Furthermore, loss-of-function of PRMT5 inhibited FXR1 methylation both in vivo and in vitro, affecting FXR1 protein stability, inhibiting RNA-binding activity and cancer cell growth and proliferation. Finally, the enhanced crosslinking and immunoprecipitation (eCLIP) analyses reveal that FXR1 binds with the G4-enriched mRNA targets such as AHNAK, MAP1B, AHNAK2, HUWE1, DYNC1H1 and UBR4 and controls its mRNA expression in cancer cells. Our findings suggest that PRMT5-mediated FXR1 methylation is required for RNA/G4-RNA binding, which promotes gene expression in cancer cells. Thus, FXR1's structural characteristics and affinity for RNAs preferentially G4 regions provide new insights into the molecular mechanism of FXR1 in oral cancer cells.

Deciphering the cis-regulatory landscape of natural yeast Transcript Leaders

Protein synthesis is a vital process that is highly regulated at the initiation step of translation. Eukaryotic 5' transcript leaders (TLs) contain a variety of cis-regulatory features that influence translation and mRNA stability. However, the relative influences of these features in natural TLs are poorly characterized. To address this, we used massively parallel reporter assays (MPRAs) to quantify RNA levels, ribosome loading, and protein levels from 11,027 natural yeast TLs in vivo and systematically compared the relative impacts of their sequence features on gene expression. We found that yeast TLs influence gene expression over two orders of magnitude. While a leaky scanning model using Kozak contexts and uAUGs explained half of the variance in expression across transcript leaders, the addition of other features explained ~70% of gene expression variation. Our analyses detected key cis-acting sequence features, quantified their effects in vivo, and compared their roles to motifs reported from an in vitro study of ribosome recruitment. In addition, our work quantitated the effects of alternative transcription start site usage on gene expression in yeast. Thus, our study provides new quantitative insights into the roles of TL cis-acting sequences in regulating gene expression.

Identification of a conserved G-quadruplex within the E165R of African swine fever virus (ASFV) as a potential antiviral target

Identification of a conserved G-quadruplex in E165R of ASFVAfrican swine fever virus (ASFV) is a double-stranded DNA arbovirus with high transmissibility and mortality rates. It has caused immense economic losses to the global pig industry. Currently, no effective vaccines or medications are to combat ASFV infection. G-quadruplex (G4) structures have attracted increasing interest because of their regulatory role in vital biological processes. In this study, we identified a conserved G-rich sequence within the E165R gene of ASFV. Subsequently, using various methods, we verified that this sequence could fold into a parallel G4. In addition, the G4-stabilizers pyridostatin and 5,10,15,20-tetrakis-(N-methyl-4-pyridyl) porphin (TMPyP4) can bind and stabilize this G4 structure, thereby inhibiting E165R gene expression, and the inhibitory effect is associated with G4 formation. Moreover, the G4 ligand pyridostatin substantially impeded ASFV proliferation in Vero cells by reducing gene copy number and viral protein expression. These compelling findings suggest that G4 structures may represent a promising and novel antiviral target against ASFV.

CGG repeats in the human FMR1 gene regulate mRNA localization and cellular stress in developing neurons

The human genome has many short tandem repeats, yet the normal functions of these repeats are unclear. The 5' untranslated region (UTR) of the fragile X messenger ribonucleoprotein 1 (FMR1) gene contains polymorphic CGG repeats, the length of which has differing effects on FMR1 expression and human health, including the neurodevelopmental disorder fragile X syndrome. We deleted the CGG repeats in the FMR1 gene (0CGG) in human stem cells and examined the effects on differentiated neurons. 0CGG neurons have altered subcellular localization of FMR1 mRNA and protein, and differential expression of cellular stress proteins compared with neurons with normal repeats (31CGG). In addition, 0CGG neurons have altered responses to glucocorticoid receptor (GR) activation, including FMR1 mRNA localization, GR chaperone HSP90α expression, GR localization, and cellular stress protein levels. Therefore, the CGG repeats in the FMR1 gene are important for the homeostatic responses of neurons to stress signals.

The Rise of Bacterial G-Quadruplexes in Current Antimicrobial Discovery

Antimicrobial resistance (AMR) is a silent critical issue that poses several challenges to health systems. While the discovery of novel antibiotics is currently stalled and prevalently focused on chemical variations of the scaffolds of available drugs, novel targets and innovative strategies are urgently needed to face this global threat. In this context, bacterial G-quadruplexes (G4s) are emerging as timely and profitable targets for the design and development of antimicrobial agents. Indeed, they are expressed in regulatory regions of bacterial genomes, and their modulation has been observed to provide antimicrobial effects with translational perspectives in the context of AMR. In this work, we review the current knowledge of bacterial G4s as well as their modulation by small molecules, including tools and techniques suitable for these investigations. Finally, we critically analyze the needs and future directions in the field, with a focus on the development of small molecules as bacterial G4s modulators endowed with remarkable drug-likeness.

Novel and Recurrent Copy Number Variants in ABCA4-Associated Retinopathy

ABCA4 is the most frequently mutated gene leading to inherited retinal disease (IRD) with over 2200 pathogenic variants reported to date. Of these, ~1% are copy number variants (CNVs) involving the deletion or duplication of genomic regions, typically >50 nucleotides in length. An in-depth assessment of the current literature based on the public database LOVD, regarding the presence of known CNVs and structural variants in ABCA4, and additional sequencing analysis of ABCA4 using single-molecule Molecular Inversion Probes (smMIPs) for 148 probands highlighted recurrent and novel CNVs associated with ABCA4-associated retinopathies. An analysis of the coverage depth in the sequencing data led to the identification of eleven deletions (six novel and five recurrent), three duplications (one novel and two recurrent) and one complex CNV. Of particular interest was the identification of a complex defect, i.e., a 15.3 kb duplicated segment encompassing exon 31 through intron 41 that was inserted at the junction of a downstream 2.7 kb deletion encompassing intron 44 through intron 47. In addition, we identified a 7.0 kb tandem duplication of intron 1 in three cases. The identification of CNVs in ABCA4 can provide patients and their families with a genetic diagnosis whilst expanding our understanding of the complexity of diseases caused by ABCA4 variants.

Y chromosome damage underlies testicular abnormalities in ATR-X syndrome

ATR-X (alpha thalassemia, mental retardation, X-linked) syndrome features genital and testicular abnormalities including atypical genitalia and small testes with few seminiferous tubules. Our mouse model recapitulated the testicular defects when Atrx was deleted in Sertoli cells (ScAtrxKO) which displayed G2/M arrest and apoptosis. Here, we investigated the mechanisms underlying these defects. In control mice, Sertoli cells contain a single novel "GATA4 PML nuclear body (NB)" that contained the transcription factor GATA4, ATRX, DAXX, HP1α, and PH3 and co-localized with the Y chromosome short arm (Yp). ScAtrxKO mice contain single giant GATA4 PML-NBs with frequent DNA double-strand breaks (DSBs) in G2/M-arrested apoptotic Sertoli cells. HP1α and PH3 were absent from giant GATA4 PML-NBs indicating a failure in heterochromatin formation and chromosome condensation. Our data suggest that ATRX protects a Yp region from DNA damage, thereby preventing Sertoli cell death. We discuss Y chromosome damage/decondensation as a mechanism for testicular failure.

Pathogenic SNPs Affect Both RNA and DNA G-Quadruplexes' Responses to Ligands

Single nucleotide polymorphisms (SNPs) are common genetic variations that are present in over 1% of the population and can significantly modify the structures of both DNA and RNA. G-quadruplex structures (G4) are formed by the superposition of tetrads of guanines. To date, the impact of SNPs on both G4 ligands' binding efficacies and specificities has not been investigated. Here, using a bioinformatically predicted G4 and SNPs found in the α-synuclein gene as a proof-of-concept, it was demonstrated that SNPs can modulate both DNA and RNA G4s' responses to ligands. Specifically, six widely recognized ligands (Phen-DC3, PDS, 360A, RHPS4, BRACO19, and TMPyP4) were shown to differentially affect both the structure and the polymerase stalling of the different SNPs. This work highlights the importance of choosing the appropriate G4 ligand when dealing with an SNP identified in a G-rich gene.

eIF4A controls translation of estrogen receptor alpha and is a therapeutic target in advanced breast cancer

The majority of human breast cancers are dependent on hormone-stimulated estrogen receptor alpha (ER) and are sensitive to its inhibition. Treatment resistance arises in most advanced cancers due to genetic alterations that promote ligand independent activation of ER itself or ER target genes. Whereas re-targeting of the ER ligand binding domain (LBD) with newer ER antagonists can work in some cases, these drugs are largely ineffective in many genetic backgrounds including ER fusions that lose the LBD or in cancers that hyperactivate ER targets. By identifying the mechanism of ER translation, we herein present an alternative strategy to target ER and difficult to treat ER variants. We find that ER translation is cap-independent and mTOR inhibitor insensitive, but dependent on 5' UTR elements and sensitive to pharmacologic inhibition of the translation initiation factor eIF4A, an mRNA helicase. EIF4A inhibition rapidly reduces expression of ER and short-lived targets of ER such as cyclin D1 and other components of the cyclin D-CDK complex in breast cancer cells. These effects translate into suppression of growth of a variety of ligand-independent breast cancer models including those driven by ER fusion proteins that lack the ligand binding site. The efficacy of eIF4A inhibition is enhanced when it is combined with fulvestrant-an ER degrader. Concomitant inhibition of ER synthesis and induction of its degradation causes synergistic and durable inhibition of ER expression and tumor growth. The clinical importance of these findings is confirmed by results of an early clinical trial (NCT04092673) of the selective eIF4A inhibitor zotatifin in patients with estrogen receptor positive metastatic breast cancer. Multiple clinical responses have been observed on combination therapy including durable regressions. These data suggest that eIF4A inhibition could be a useful new strategy for treating advanced ER+ breast cancer.

DDX5 inhibits hyaline cartilage fibrosis and degradation in osteoarthritis via alternative splicing and G-quadruplex unwinding

Hyaline cartilage fibrosis is typically considered an end-stage pathology of osteoarthritis (OA), which results in changes to the extracellular matrix. However, the mechanism behind this is largely unclear. Here, we found that the RNA helicase DDX5 was dramatically downregulated during the progression of OA. DDX5 deficiency increased fibrosis phenotype by upregulating COL1 expression and downregulating COL2 expression. In addition, loss of DDX5 aggravated cartilage degradation by inducing the production of cartilage-degrading enzymes. Chondrocyte-specific deletion of Ddx5 led to more severe cartilage lesions in the mouse OA model. Mechanistically, weakened DDX5 resulted in abundance of the Fn1-AS-WT and Plod2-AS-WT transcripts, which promoted expression of fibrosis-related genes (Col1, Acta2) and extracellular matrix degradation genes (Mmp13, Nos2 and so on), respectively. Additionally, loss of DDX5 prevented the unfolding Col2 promoter G-quadruplex, thereby reducing COL2 production. Together, our data suggest that strategies aimed at the upregulation of DDX5 hold significant potential for the treatment of cartilage fibrosis and degradation in OA.

Investigating G-quadruplex structures in RPGR gene: Implications for understanding X-linked retinal degeneration

Aims

This pilot study investigates the potential pathogenic role of G-quadruplex (G4) structures in RPGR-associated retinal degeneration, starting from a case of suspected X-linked form affected family. We hypothesize that the stabilization of these structures might alter DNA replication and transcription, inducing genetic instability and influencing gene expression.

Main methods

We conducted whole genome amplification experiments and next-generation sequencing to detect the blockade of polymerase activity by G4 structures. Our specific focus was the RPGR gene, which hosts a high concentration of predicted G4-forming motifs and is implicated in most X-linked retinal degeneration cases. To understand the potential interference of G4 structures, we applied computational and 3D molecular modeling to visualize interferences in DNA replication and transcription regulation.

Key findings

Our data confirmed the obstruction of DNA polymerase enzymes by G4 structures, particularly when stabilized by the compound pyridostatin. This obstruction was evident in the reduced amplification of RPGR gene regions and a shift in the start/end sites of putative G4 motifs. Moreover, the modeling indicated a potential disruption of critical promoter elements and RNA polymerase binding, which could drastically alter gene expression.

Significance

Our findings suggest that G4 formation in the RPGR gene could lead to genetic instability and affect the expression of RPGR, contributing to retinal dystrophy. Moreover, this study underscores the broader implications of G4 structures in other genetic disorders. Improved understanding of G4 structures could reveal novel therapeutic targets to combat genetic disorders, promoting the advancement of personalized medicine and precision health.

DNA G-Quadruplex in NRP1 Promoter Facilitates SARS-CoV-2 Infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection continues to raise concerns worldwide. Numerous host factors involved in SARS-CoV-2 infection have been identified, but the regulatory mechanisms of these host factor remain unclear. Here, we report the role of G-quadruplexes (G4s) located in the host factor promoter region in SARS-CoV-2 infection. Using bioinformatics, biochemical, and biological assays, we provide evidence for the presence of G4 structures in the promoter regions of SARS-CoV-2 host factors NRP1. Specifically, we focus on two representative G4s in the NRP1 promoter and highlight its importance in SARS-CoV-2 pathogenesis. The presence of the G4 structure greatly increases NRP1 expression, facilitating SARS-CoV-2 entry into cells. Utilizing published single-cell RNA sequencing data obtained from simulated SARS-CoV-2 infection in human bronchial epithelial cells (HBECs), we found that ciliated cells with high levels of NRP1 are prominently targeted by the virus during infection. Furthermore, our study identifies E2F1 act as a transcription factor that binds to G4s. These findings uncover a previously unknown mechanism underlying SARS-CoV-2 infection and suggest that targeting G4 structures could be a potential strategy for COVID-19 prevention and treatment.

Basic protein- and peptide-induced stabilization of long-loop DNA G-guadruplexes

The human genome contains many G-quadruplex-forming sequences, including sequences containing long single-stranded loops that are believed to be unfavorable for G-quadruplex formation. The intracellular environment of biological cells is crowded with proteins with charged surfaces. Understanding the effects of protein-rich environments is important for understanding the formation of G-quadruplexes in an intracellular environment. In this study, we investigated the structural stability of DNA G-quadruplexes in the presence of several types of globular proteins (lysozyme, cytochrome c, bovine serum albumin, myoglobin, histone proteins, and serum proteins), unstructured polypeptides (protamine and poly-l-lysine), and oligopeptides (RGG/RG-domain peptides and short repeated peptides). Thermal melting studies of G-quadruplex-forming oligonucleotides derived from the human telomeric repeat sequence revealed that environments containing high concentrations of proteins and peptides differently affected the G-quadruplex stability according to their loop lengths. We found that weak electrostatic interactions of G-quadruplex loops with basic proteins and peptides improved the stability of long-loop G-quadruplexes and the interactions were strengthened under crowded conditions simulated by dextran. The comparison of the effects of different types of proteins and peptides indicated that excluded volume interactions and structural flexibility of both DNA and polypeptide chains influenced the efficiency of their interactions. This study provides insights into long-loop G-quadruplex stability in a crowded intracellular environment and the recognition of G-quadruplexes by arginine-rich domains of G-quadruplex-binding proteins.

Nucleic Acid Aptamers Protect Against Lead (Pb(II)) Toxicity

Lead (Pb(II)) is a pervasive heavy metal toxin with many well-established negative effects on human health. Lead toxicity arises from cumulative, repeated environmental exposures. Thus, prophylactic strategies to protect against the bioaccumulation of lead could reduce lead-associated human pathologies. Here we show that DNA and RNA aptamers protect C. elegans from toxic phenotypes caused by lead. Reproductive toxicity, as measured by brood size assays, is prevented by co-feeding of animals with DNA or RNA aptamers. Similarly, lead-induced behavioral anomalies are also normalized by aptamer feeding. Further, cultured human HEK293 and primary murine osteoblasts are protected from lead toxicity by transfection with DNA aptamers. The osteogenic development, which is decreased by lead exposure, is maintained by prior transfection of lead-binding DNA aptamers. Aptamers may be an effective strategy for the protection of human health in the face of increasing environmental toxicants.

The transcription of the main gene associated with Treacher-Collins syndrome (TCOF1) is regulated by G-quadruplexes and cellular nucleic acid binding protein (CNBP)

Treacle ribosome biogenesis factor 1 (TCOF1) is responsible for about 80% of mandibular dysostosis (MD) cases. We have formerly identified a correlation between TCOF1 and CNBP (CCHC-type zinc finger nucleic acid binding protein) expression in human mesenchymal cells. Given the established role of CNBP in gene regulation during rostral development, we explored the potential for CNBP to modulate TCOF1 transcription. Computational analysis for CNBP binding sites (CNBP-BSs) in the TCOF1 promoter revealed several putative binding sites, two of which (Hs791 and Hs2160) overlap with putative G-quadruplex (G4) sequences (PQSs). We validated the folding of these PQSs measuring circular dichroism and fluorescence of appropriate synthetic oligonucleotides. In vitro studies confirmed binding of purified CNBP to the target PQSs (both folded as G4 and unfolded) with Kd values in the nM range. ChIP assays conducted in HeLa cells chromatin detected the CNBP binding to TCOF1 promoter. Transient transfections of HEK293 cells revealed that Hs2160 cloned upstream SV40 promoter increased transcription of downstream firefly luciferase reporter gene. We also detected a CNBP-BS and PQS (Dr2393) in the zebrafish TCOF1 orthologue promoter (nolc1). Disrupting this G4 in zebrafish embryos by microinjecting DNA antisense oligonucleotides complementary to Dr2393 reduced the transcription of nolc1 and recapitulated the craniofacial anomalies characteristic of Treacher Collins Syndrome. Both cnbp overexpression and Morpholino-mediated knockdown in zebrafish induced nolc1 transcription. These results suggest that CNBP modulates the transcriptional expression of TCOF1 through a mechanism involving G-quadruplex folding/unfolding, and that this regulation is active in vertebrates as distantly related as bony fish and humans. These findings may have implications for understanding and treating MD.

Prediction of DNA i-motifs via machine learning

i-Motifs (iMs), are secondary structures formed in cytosine-rich DNA sequences and are involved in multiple functions in the genome. Although putative iM forming sequences are widely distributed in the human genome, the folding status and strength of putative iMs vary dramatically. Much previous research on iM has focused on assessing the iM folding properties using biophysical experiments. However, there are no dedicated computational tools for predicting the folding status and strength of iM structures. Here, we introduce a machine learning pipeline, iM-Seeker, to predict both folding status and structural stability of DNA iMs. The programme iM-Seeker incorporates a Balanced Random Forest classifier trained on genome-wide iMab antibody-based CUT&Tag sequencing data to predict the folding status and an Extreme Gradient Boosting regressor to estimate the folding strength according to both literature biophysical data and our in-house biophysical experiments. iM-Seeker predicts DNA iM folding status with a classification accuracy of 81% and estimates the folding strength with coefficient of determination (R2) of 0.642 on the test set. Model interpretation confirms that the nucleotide composition of the C-rich sequence significantly affects iM stability, with a positive correlation with sequences containing cytosine and thymine and a negative correlation with guanine and adenine.

Guide for phenotype-specific profiling of DNA G-quadruplex-regulated genes

DNA G-quadruplex (G4) is a non-canonical four-stranded secondary structure that has been shown to play a role in epigenetic modulation of gene expression. Here, we present a primer on phenotype-specific profiling of DNA G-quadruplex-regulated genes. We provide guidance on in silico exploration of G4-related genes and phenotypes, and in vitro and in vivo validation of the relationship between G4 and phenotype. We describe commonly utilized techniques and detail critical steps involved in determining the phenotype-specific G4-regulated genes for subsequent investigations.

Virtual screening and site-directed mutagenesis-derived aptamers for precise Salmonella typhimurium prediction: emphasizing OmpD targeting and G-quadruplex stability

The efficient detection of the foodborne pathogen Salmonella typhimurium has historically been hampered by the constraints of traditional methods, characterized by protracted culture periods and intricate DNA extraction processes for PCR. To address this, our research innovatively focuses on the crucial and relatively uncharted virulence factor, the Outer Membrane Protein D (OmpD) in Salmonella typhimurium. By harmoniously integrating the power of virtual screening and site-directed mutagenesis, we unveiled aptamers exhibiting marked specificity for OmpD. Among these, aptamer 7ZQS stands out with its heightened binding affinity. Capitalizing on this foundation, we further engineered a repertoire of mutant aptamers, wherein APT6 distinguished itself, reflecting unmatched stability and specificity. Our rigorous validation, underpinned by cutting-edge bioinformatics tools, amplifies the prowess of APT6 in discerning and binding OmpD across an array of Salmonella typhimurium strains. This study illuminates a transformative approach to the prompt and accurate detection of Salmonella typhimurium, potentially redefining boundaries in applied analytical chemistry and bolstering diagnostic precision across diverse research and clinical domains.Communicated by Ramaswamy H. Sarma.

Nucleolin-RNA interaction modulates rotavirus replication

Rotavirus infection is a leading cause of gastroenteritis in children worldwide; the genome of this virus is composed of 11 segments of dsRNA packed in a triple-layered protein capsid. Here, we investigated the role of nucleolin, a protein with diverse RNA-binding domains, in rotavirus infection. Knocking down the expression of nucleolin in MA104 cells by RNA interference resulted in a remarkable 6.3-fold increase in the production of infectious rhesus rotavirus (RRV) progeny, accompanied by an elevated synthesis of viral mRNA and genome copies. Further analysis unveiled an interaction between rotavirus segment 10 (S10) and nucleolin, potentially mediated by G-quadruplex domains on the viral genome. To determine whether the nucleolin-RNA interaction regulates RRV replication, MA104 cells were transfected with AGRO100, a compound that forms G4 structures and selectively inhibits nucleolin-RNA interactions by blocking the RNA-binding domains. Under these conditions, viral production increased by 1.5-fold, indicating the inhibitory role of nucleolin on the yield of infectious viral particles. Furthermore, G4 sequences were identified in all 11 RRV dsRNA segments, and transfection of oligonucleotides representing G4 sequences in RRV S10 induced a significant increase in viral production. These findings show that rotavirus replication is negatively regulated by nucleolin through the direct interaction with the viral RNAs by sequences forming G4 structures.IMPORTANCEViruses rely on cellular proteins to carry out their replicative cycle. In the case of rotavirus, the involvement of cellular RNA-binding proteins during the replicative cycle is a poorly studied field. In this work, we demonstrate for the first time the interaction between nucleolin and viral RNA of rotavirus RRV. Nucleolin is a cellular protein that has a role in the metabolism of ribosomal rRNA and ribosome biogenesis, which seems to have regulatory effects on the quantity of viral particles and viral RNA copies of rotavirus RRV. Our study adds a new component to the current model of rotavirus replication, where cellular proteins can have a negative regulation on rotavirus replication.