Up- and downregulation of mature miR-1587 function by modulating its G-quadruplex structure and using small molecules

Single-cell RNA sequencing reveals heterogeneity and differential expression of the maternal-fetal interface during ICP and normal pregnancy

OBJECTIVE

Intrahepatic cholestasis of pregnancy (ICP) can cause adverse perinatal outcomes. Previous studies have demonstrated that the placenta of an ICP pregnancy differs in morphology and gene expression from the placenta of a normal pregnancy. To date, however, the genetic mechanism by which ICP affects the placenta is poorly understood. Therefore, the aim of this study was to investigate the differences in main cell types, gene signatures, cell ratio, and functional changes in the placenta between ICP and normal pregnancy.

METHODS

Single-cell RNA sequencing (scRNA-seq) technology was used to detect the gene expression of all cells at the placental maternal-fetal interface. Two individuals were analyzed - one with ICP and one without ICP. The classification of cell types was determined by a graph-based clustering algorithm. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using the R software phyper () function and DAVID website. The differentially expressed genes (DEGs) encoding transcription factors (TFs) were identified using getorf and DIAMOND software.

RESULTS

We identified 14 cell types and 22 distinct cell subtypes that showed unique functional properties. Additionally, we found differences in the proportions of fibroblasts 1, helper T (Th) cells, extravillous trophoblasts, and villous cytotrophoblasts, and we observed heterogeneity of gene expression between ICP and control placentas. Furthermore, we identified 263 DEGs that belonged to TF families, including zf-C2H2, HMGI/HMGY, and Homeobox. In addition, 28 imprinted genes were preferentially expressed in specific cell types, such as PEG3 and PEG10 in trophoblasts as well as DLK1 and DIO3 in fibroblasts.

CONCLUSIONS

Our results revealed the differences in cell-type ratios, gene expression, and functional changes between ICP and normal placentas, and heterogeneity was found among cell subgroups. Hence, the imbalance of various cell types affects placental activity to varying degrees, indicating the complexity of the cell networks that form the placental tissue system, and this alteration of placental function is associated with adverse events in the perinatal period.

RNA G-quadruplex in functional regulation of noncoding RNA: Challenges and emerging opportunities

G-quadruplexes (G4s) are stable, noncanonical structures formed in guanine (G)-rich sequences of DNA/RNA. G4 structures are reported to play a regulatory role in various cellular processes and, recently, a considerable number of studies have attributed new biological functions to these structures, especially in RNA. Noncoding RNA (ncRNA), which does not translate into a functional protein, is widely expressed and has been shown to play a key role in shaping cellular activity. There has been growing evidence of G4 formation in several ncRNA classes, and it has been identified as a key part for diverse biological functions and physio-pathological contexts in neurodegenerative diseases and cancer. This review discusses RNA G4s (rG4s) in ncRNA, focusing on the molecular mechanism underlying its function. This review also aims to highlight potential and emerging opportunities to identify and target the rG4s in ncRNA to understand its function and, ultimately, treat many diseases.

G-quadruplex in the TMV Genome Regulates Viral Proliferation and Acts as Antiviral Target of Photodynamic Therapy

Plant viruses seriously disrupt crop growth and development, and classic protein-targeted antiviral drugs could not provide complete protection against them. It is urgent to develop antiviral compounds with novel targets. Photodynamic therapy shows potential in controlling agricultural pests, but nonselective damage from reactive oxygen species (ROS) unexpectedly affects healthy tissues. A G-quadruplex (G4)-forming sequence in the tobacco mosaic virus (TMV) genome was identified to interfere the RNA replication in vitro, and affect the proliferation of TMV in tobacco. N-methyl mesoporphyrin IX stabilizing the G4 structure exhibited inhibition against viral proliferation, which was comparable to the inhibition effect of ribavirin. This indicated that G4 could work as an antiviral target. The large conjugate planes shared by G4 ligands and photosensitizers (PSs) remind us that the PSs could work as antiviral agents by targeting G4 in the genome of TMV. Chlorin e6 (Ce6) was identified to stabilize the G4 structure in the dark and selectively cleave the G4 sequence by producing ROS upon LED-light irradiation, leading to 92.2% inhibition against TMV in vivo, which is higher than that of commercial ningnanmycin. The inhibition of Ce6 was lost against the mutant variants lacking the G4-forming sequence. These findings indicated that the G-quadruplex in the TMV genome worked as an important structural element regulating viral proliferation, and could act as the antiviral target of photodynamic therapy.

Revealing light-induced structural shifts in G-quadruplex-porphyrin complexes: a pulsed dipolar EPR study

The binding of G-quadruplex structures (G4s) with photosensitizers is of considerable importance in medicinal chemistry and drug discovery due to their promising potential in photodynamic therapy applications. G4s can experience structural changes as a result of ligand interactions and light exposure. Understanding these modifications is essential to uncover the fundamental biological roles of the complexes and optimize their therapeutic potential. The structural diversity of G4s makes it challenging to study their complexes with ligands, necessitating the use of various complementary methods to fully understand these interactions. In this study, we introduce, for the first time, the application of laser-induced dipolar EPR as a method to characterize G-quadruplex DNA complexes containing photosensitizers and to investigate light-induced structural modifications in these systems. To demonstrate the feasibility of this approach, we studied complexes of the human telomeric G-quadruplex (HTel-22) with cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio) porphyrin tetra(p-toluenesulfonate) (TMPyP4). In addition to showcasing a new methodology, we also aimed to provide insights into the mechanisms underlying photoinduced HTel-22/TMPyP4 structural changes, thereby aiding in the advancement of approaches targeting G4s in photodynamic therapy. EPR revealed G-quadruplex unfolding and dimer formation upon light exposure. Our findings demonstrate the potential of EPR spectroscopy for examining G4 complexes with photosensitizers and contribute to a better understanding of G4s' interactions with ligands under light.

Application of G-quadruplex targets in gastrointestinal cancers: Advancements, challenges and prospects

Genomic instability and inflammation are considered to be two enabling characteristics that support cancer development and progression. G-quadruplex structure is a key element that contributes to genomic instability and inflammation. G-quadruplexes were once regarded as simply an obstacle that can block the transcription of oncogenes. A ligand targeting G-quadruplexes was found to have anticancer activity, making G-quadruplexes potential anticancer targets. However, further investigation has revealed that G-quadruplexes are widely distributed throughout the human genome and have many functions, such as regulating DNA replication, DNA repair, transcription, translation, epigenetics, and inflammatory response. G-quadruplexes play double regulatory roles in transcription and translation. In this review, we focus on G-quadruplexes as novel targets for the treatment of gastrointestinal cancers. We summarize the application basis of G-quadruplexes in gastrointestinal cancers, including their distribution sites, structural characteristics, and physiological functions. We describe the current status of applications for the treatment of esophageal cancer, pancreatic cancer, hepatocellular carcinoma, gastric cancer, colorectal cancer, and gastrointestinal stromal tumors, as well as the associated challenges. Finally, we review the prospective clinical applications of G-quadruplex targets, providing references for targeted treatment strategies in gastrointestinal cancers.

G-quadruplexes from non-coding RNAs

Non-coding RNAs (ncRNAs) are significant regulators of gene expression in a wide range of biological processes, such as transcription, RNA maturation, or translation. ncRNAs interplay with proteins or other RNAs through not only classical sequence-based mechanisms but also unique higher-order structures such as RNA G-quadruplexes (rG4s). rG4s are predictably formed in guanine-rich sequences and are closely related to various human diseases, such as tumors, neurodegenerative diseases, and infections. This review focuses on the vital role of rG4s in ncRNAs, particularly lncRNAs and miRNAs. We outline the dynamic balance between rG4s and RNA stem-loop/hairpin structures and the interplay between ncRNAs and interactors, thereby modulating gene expression and disease progression. A complete understanding of the biological regulatory role and mechanism of rG4s in ncRNAs affirms the critical importance of folding into the appropriate three-dimensional structure in maintaining or modulating the functions of ncRNAs. It makes them novel therapeutic targets for adjusting potential-G4-containing-ncRNAs-associated diseases.

G-quadruplex from precursor miR-1587 modulated its maturation and function

A certain proportion of pre-miRNAs, which contained potential G-quadruplex forming sequences, was found to act as a mediator to Dicer-mediated cleavage, and that the regulation of miRNA production and function may be achieved through the G-quadruplex structure. In this study, human precursor miR-1587 sequence was transfected after the incubation with different solution conditions (K⁺, TMPyP4, etc.). Firstly, the formation of G-quadruplex from precursor miR-1587 sequences was confirmed by CD and UV melting. The expression of miR-1587 level was then evaluated by Q-RT-PCR, and the results showed that the formation of G-quadruplex inhibited the miR-1587 maturation process, resulting in a reduced miR-1587 expression. Meanwhile the destabilization of G-quadruplex led to an increased miR-1587 expression by contrast. Then, the weakened inhibition of miR-1587 towards its target genes, such as TAGLN or NCOR1, was presented confirming by Q-RT-PCR and western blot. Molecular mechanism by dual-luciferase assays showed that the modulations of miR-1587 expression and function were due to the G-quadruplex structure transformation, but not the simple change of solution conditions. This study highlighted the importance of maintaining specific structures during miRNA biosynthesis and provided a way to alter the function of G-rich precursor miRNAs by modulating molecular conformation using ionic solutions or ligands.

G-Quadruplexes Regulate miRNA Biogenesis in Live Zebrafish Embryos

RNA guanine quadruplexes (G4s) regulate RNA functions, metabolism, and processing. G4s formed within precursors of microRNAs (pre-miRNAs) may impair pre-miRNAs maturation by Dicer, thus repressing mature miRNA biogenesis. As miRNAs are essential for proper embryonic development, we studied the role of G4s on miRNA biogenesis in vivo during zebrafish embryogenesis. We performed a computational analysis on zebrafish pre-miRNAs to find putative G4 forming sequences (PQSs). The precursor of the miRNA 150 (pre-miR-150) was found to contain an evolutionarily conserved PQS formed by three G-tetrads and able to fold in vitro as G4. MiR-150 controls the expression of myb, which shows a well-defined knock-down phenotype in zebrafish developing embryos. We microinjected zebrafish embryos with in vitro transcribed pre-miR-150 synthesized using either GTP (G-pre-miR-150) or 7-Deaza-GTP, a GTP analogue unable to form G4s (7DG-pre-miR-150). Compared to embryos injected with G-pre-miR-150, embryos injected with 7DG-pre-miR-150 showed higher levels of miRNA 150 (miR-150) and lower levels of myb mRNA and stronger phenotypes associated with myb knock-down. The incubation of pre-miR-150 prior to the injection with the G4 stabilizing ligand pyridostatin (PDS) reverted gene expression variations and rescued the phenotypes related to myb knock-down. Overall, results suggest that the G4 formed in pre-miR-150 functions in vivo as a conserved regulatory structure competing with the stem-loop structure necessary for miRNA biogenesis.

miR-107 is involved in the regulation of NEDD9-mediated invasion and metastasis in breast cancer

Background

As a metastasis-related protein, NEDD9 has been reported in breast cancer (BC) metastasis research. However, there are few studies on the upstream regulators of NEDD9, especially involving the potential role of miRNAs. The purpose of this study was to explain whether miR-107 potentially regulates NEDD9, which may lead to invasion and metastasis of BC.

Methods

MCF-7 and MDA-MB-231 cells were transduced with lentiviruses to construct stably transduced cells with miR-107 overexpression, miR-107 silencing or empty vectors. A luciferase reporter assay was performed to verify the binding of miR-107 and NEDD9. The scratch test and Transwell assay were used to measure cell migration and invasion ability, respectively. For the study of metastasis in vivo, we injected MDA-MB-231 cells into the fat pad of nude mice to develop an orthotopic breast cancer model.

Results

We found that NEDD9 expression correlates with the prognosis of BC patients. In BC cell lines, NEDD9 was positively correlated with cell migration ability. Further research revealed that miR-107 inhibited NEDD9 expression by targeting the 3′-untranslated region of NEDD9. Overexpression of miR-107 suppressed the expression of NEDD9, thereby inhibiting the invasion, migration and proliferation of BC cells, but interference with miR-107 promoted the expression of NEDD9 as well as invasion, migration and proliferation. In an in vivo model, overexpression of miR-107 decreased the expression of NEDD9 and inhibited tumour growth, invasion and metastasis; however, these effects were reversed by inhibiting miR-107.

Conclusions

These findings indicated the potential role of miR-107 in regulating NEDD9 in the invasion, migration and proliferation of BC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09603-3.

Ligands as Stabilizers of G-Quadruplexes in Non-Coding RNAs

The non-coding RNAs (ncRNA) are RNA transcripts with different sizes, structures and biological functions that do not encode functional proteins. RNA G-quadruplexes (rG4s) have been found in small and long ncRNAs. The existence of an equilibrium between rG4 and stem-loop structures in ncRNAs and its effect on biological processes remains unexplored. For example, deviation from the stem-loop leads to deregulated mature miRNA levels, demonstrating that miRNA biogenesis can be modulated by ions or small molecules. In light of this, we report several examples of rG4s in certain types of ncRNAs, and the implications of G4 stabilization using small molecules, also known as G4 ligands, in the regulation of gene expression, miRNA biogenesis, and miRNA-mRNA interactions. Until now, different G4 ligands scaffolds were synthesized for these targets. The regulatory role of the above-mentioned rG4s in ncRNAs can be used as novel therapeutic approaches for adjusting miRNA levels.

Identifying G-Quadruplex-DNA-Disrupting Small Molecules

The quest for small molecules that strongly bind to G-quadruplex-DNA (G4), so-called G4 ligands, has invigorated the G4 research field from its very inception. Massive efforts have been invested to discover or rationally design G4 ligands, evaluate their G4-interacting properties in vitro through a series of now widely accepted and routinely implemented assays, and use them as innovative chemical biology tools to interrogate cellular networks that might involve G4s. In sharp contrast, only uncoordinated efforts aimed at developing small molecules that destabilize G4s have been invested to date, even though it is now recognized that such molecular tools would have tremendous application in neurobiology as many genetic and age-related diseases are caused by an overrepresentation of G4s. Herein, we report on our efforts to develop in vitro assays to reliably identify molecules able to destabilize G4s. This workflow comprises the newly designed G4-unfold assay, adapted from the G4-helicase assay implemented with Pif1, as well as a series of biophysical and biochemical techniques classically used to study G4/ligand interactions (CD, UV-vis, PAGE, and FRET-melting), and a qPCR stop assay, adapted from a Taq-based protocol recently used to identify G4s in the genomic DNA of Schizosaccharomyces pombe. This unique, multipronged approach leads to the characterization of a phenylpyrrolocytosine (PhpC)-based G-clamp analog as a prototype of G4-disrupting small molecule whose properties are validated through many different and complementary in vitro evaluations.

Quadruplex Ligands in Cancer Therapy

Nucleic acids can adopt alternative secondary conformations including four-stranded structures known as quadruplexes. To date, quadruplexes have been demonstrated to exist both in human chromatin DNA and RNA. In particular, quadruplexes are found in guanine-rich sequences constituting G-quadruplexes, and in cytosine-rich sequences forming i-Motifs as a counterpart. Quadruplexes are associated with key biological processes ranging from transcription and translation of several oncogenes and tumor suppressors to telomeres maintenance and genome instability. In this context, quadruplexes have prompted investigations on their possible role in cancer biology and the evaluation of small-molecule ligands as potential therapeutic agents. This review aims to provide an updated close-up view of the literature on quadruplex ligands in cancer therapy, by grouping together ligands for DNA and RNA G-quadruplexes and DNA i-Motifs.

m6A demethylase ALKBH5 suppresses proliferation and migration of enteric neural crest cells by regulating TAGLN in Hirschsprung's disease

OBJECTIVES

This study aims to investigate the role of demethylase ALKBH5 mediated demethylation of TAGLN mRNA in the occurrence of Hirschsprung's disease (HSCR), and to clarify how ALKBH5 reduces the m⁶A level of TAGLN mRNA and inhibits its degradation, thereby inhibiting the proliferation and migration of neural crest cells, and potentially contributing to the occurrence of HSCR.

MATERIAL AND METHODS

Quantitative real-time PCR (qRT-PCR) and Western-Blot (WB) were conducted to test the expression level of ALKBH5 and TAGLN genes. Cell function assays were adopted to detect cell phenotypes. The qRT-PCR and methylated RNA immunoprecipitation (MeRIP-qPCR) were used to test the regulation of TAGLN by ALKBH5.

RESULTS

1. Compared with control intestinal tissue, the expression level of TAGLN and ALKBH5 in the aganglionic intestinal tissue of HSCR is increased. 2. The MeRIP-PCR and dualluciferase report confirmed that ALKBH5 could bind to m⁶A sites of TAGLN mRNA and reduce the m⁶A level of TAGLN mRNA. 3. In vitro cell experiments confirmed that overexpression of ALKBH5 can inhibit the degradation of TAGLN mRNA, increase the expression of TAGLN, thereby inhibiting cell proliferation and migration. 4. A zebrafish model of ALKBH5 overexpression was constructed. Studies have shown that ALKBH5 could inhibit the proliferation and migration of zebrafish enteric neurons.

CONCLUSIONS

ALKBH5 could demethylate TAGLN mRNA and up-regulate TAGLN expression, leading to the inhibition of proliferation and migration of enteric neural crest cells and contributing to the occurrence of HSCR.

Biological relevance and therapeutic potential of G-quadruplex structures in the human noncoding transcriptome

Noncoding RNAs are functional transcripts that are not translated into proteins. They represent the largest portion of the human transcriptome and have been shown to regulate gene expression networks in both physiological and pathological cell conditions. Research in this field has made remarkable progress in the comprehension of how aberrations in noncoding RNA drive relevant disease-associated phenotypes; however, the biological role and mechanism of action of several noncoding RNAs still need full understanding. Besides fulfilling its function through sequence-based mechanisms, RNA can form complex secondary and tertiary structures which allow non-canonical interactions with proteins and/or other nucleic acids. In this context, the presence of G-quadruplexes in microRNAs and long noncoding RNAs is increasingly being reported. This evidence suggests a role for RNA G-quadruplexes in controlling microRNA biogenesis and mediating noncoding RNA interaction with biological partners, thus ultimately regulating gene expression. Here, we review the state of the art of G-quadruplexes in the noncoding transcriptome, with their structural and functional characterization. In light of the existence and further possible development of G-quadruplex binders that modulate G-quadruplex conformation and protein interactions, we also discuss the therapeutic potential of G-quadruplexes as targets to interfere with disease-associated noncoding RNAs.

The role of RNA G-quadruplexes in human diseases and therapeutic strategies

G-quadruplexes (GQs) are four-stranded secondary structures formed by G-rich nucleic acid sequence(s). DNA GQs are present abundantly in the genome and affect a wide range of processes associated with DNA. Recent studies show that RNA GQs are present in different transcripts, including coding and noncoding areas of mRNA, telomeric RNA as well as in other premature and mature noncoding RNAs. When present at specific locations within the RNAs, GQs play important roles in key biological functions, including the regulation of gene expression and telomere homeostasis. RNA GQs regulate pre-mRNA processing, such as splicing and polyadenylation. Evidently, among other processes, RNA GQs also control mRNA translation, miRNA and piRNA biogenesis, and RNA localization. The regulatory mechanisms controlled by RNA GQs mainly involve binding to RNA binding protein that modulate GQ conformation or serve as an entity in recruiting additional protein regulators to act as a block element to the processing machinery. Here we provide an overview of the ever-increasing number of discoveries revealing the role of RNA GQs in biology and their relevance in human diseases and therapeutics. This article is categorized under: RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA in Disease and Development > RNA in Disease.

Normal expression of KCNJ11 is maintained by the G-quadruplex

MicroRNAs affect various pathological pathways by binding to multiple target mRNAs. Recently, it was reported that eukaryotic RNA G-quadruplexes were enriched in mRNA 3'-UTR, where microRNAs can also bind. To determine the roles of the G-quadruplex within mRNA 3'-UTR in microRNA binding sites, a bioinformatics approach was utilized to identify candidate microRNA target mRNAs with potential G-quadruplex formation. Circular dichroism spectrometry demonstrated the formation of RNA G-quadruplexes in vitro in candidate G-rich sequences. Mutated guanosines that are critical for G-quadruplex formation significantly decreased luciferase activities. Moreover, a G-quadruplex ligand TMPyP4 was used to destabilize the KCNJ11 RNA G-quadruplex in cardiomyocytes, resulting in binding of the microRNA to mRNA and subsequent suppression of KCNJ11 expression. In conclusion, our study showed that the G-quadruplex structure affects microRNA binding to its target mRNA. Thus, our study reveals a novel mechanism for G-quadruplex-dependent regulation of microRNA-mRNA interaction, which is essential to maintain normal gene expression.

Promise of G-Quadruplex Structure Binding Ligands as Epigenetic Modifiers with Anti-Cancer Effects

Evidences from more than three decades of work support the function of non-duplex DNA structures called G-quadruplex (G4) in important processes like transcription and replication. In addition, G4 structures have been studied in connection with DNA base modifications and chromatin/nucleosome arrangements. Recent work, interestingly, shows promise of G4 structures, through interaction with G4 structure-interacting proteins, in epigenetics-in both DNA and histone modification. Epigenetic changes are found to be intricately associated with initiation as well as progression of cancer. Multiple oncogenes have been reported to harbor the G4 structure at regulatory regions. In this context, G4 structure-binding ligands attain significance as molecules with potential to modify the epigenetic state of chromatin. Here, using examples from recent studies we discuss the emerging role of G4 structures in epigenetic modifications and, therefore, the promise of G4 structure-binding ligands in epigenetic therapy.