Year of publication 2020
Nucleolin Discriminates Drastically between Long-Loop and Short-Loop Quadruplexes.Biochemistry : 59 : 1261-1272 : DOI : 10.1021/acs.biochem.9b01094 Learn more
We investigate herein the interaction between nucleolin (NCL) and a set of G4 sequences derived from the CEB25 human minisatellite that adopt a parallel topology while differing in the length of the central loop (from nine nucleotides to one nucleotide). It is revealed that NCL strongly binds to long-loop (five to nine nucleotides) G4 while interacting weakly with the shorter variants (loop with fewer than three nucleotides). Photo-cross-linking experiments using 5-bromo-2′-deoxyuridine (BrU)-modified sequences further confirmed the loop-length dependency, thereby indicating that the WT-CEB25-L191 (nine-nucleotide loop) is the best G4 substrate. Quantitative proteomic analysis (LC-MS/MS) of the product(s) obtained by photo-cross-linking NCL to this sequence enabled the identification of one contact site corresponding to a 15-amino acid fragment located in helix α2 of RNA binding domain 2 (RBD2), which sheds light on the role of this structural element in G4-loop recognition. Then, the ability of a panel of benchmark G4 ligands to prevent the NCL-G4 interaction was explored. It was found that only the most potent ligand PhenDC3 can inhibit NCL binding, thereby suggesting that the terminal guanine quartet is also a strong determinant of G4 recognition, putatively through interaction with the RGG domain. This study describes the molecular mechanism by which NCL recognizes G4-containing long loops and leads to the proposal of a model implying a concerted action of RBD2 and RGG domains to achieve specific G4 recognition via a dual loop-quartet interaction.Fold up
A mechanism for the extension and unfolding of parallel telomeric G-quadruplexes by human telomerase at single-molecule resolutionbioRxiv : DOI : 10.1101/2020.02.26.965269 Learn more
Telomeric G-quadruplexes (G4) were long believed to form a protective structure at telomeres, preventing their extension by the ribonucleoprotein telomerase. Contrary to this belief, we have previously demonstrated that parallel-stranded conformations of telomeric G4 can be extended by human and ciliate telomerase. However, a mechanistic understanding of the interaction of telomerase with structured DNA remained elusive. Here, we use single-molecule fluorescence resonance energy transfer (smFRET) microscopy and bulk-phase enzymology to propose a mechanism for the resolution and extension of parallel G4 by telomerase. Binding is initiated by the RNA template of telomerase interacting with the G-quadruplex; nucleotide addition then proceeds to the end of the RNA template. It is only through the large conformational change of translocation following synthesis that the G-quadruplex structure is completely unfolded to a linear product. Surprisingly, parallel G4 stabilization with either small molecule ligands or by chemical modification does not always inhibit G4 unfolding and extension by telomerase. These data reveal that telomerase is a parallel G-quadruplex resolvase.Fold up
Harnessing intrinsic fluorescence for typing of secondary structures of DNAbioRxiv : DOI : 10.1101/2020.01.15.907501 Learn more
DNA is polymorphic since, despite its ubiquitous presence as a double-stranded helix, it is able to fold into a plethora of other secondary structures both in vitro and in cells. Despite the considerable advances that have been made in understanding this structural diversity, its high-throughput investigation still faces severe limitations. This mainly stems from the lack of suitable label-free methods, combining a fast and cheap experimental workflow with high information content. Here, we explore the use of intrinsic fluorescence emitted by nucleic acids for this scope. After a preliminary assessment of the suitability of this phenomenon for tracking the conformational changes of DNA, we examined the intrinsic steady-state emission spectra of an 89-membered set of synthetic oligonucleotides with reported conformation (G-quadruplexes, i-motifs, single- and double stranded DNA) by means of multivariate analysis. Specifically, principal component analysis of emission spectra resulted in successful clustering of oligonucleotides into three corresponding conformational groups, albeit without discrimination between single- and double-stranded structures. Linear discriminant analysis of the same training set was exploited for the assessment of new sequences, allowing the evaluation of their G4-forming propensity. Our method does not require any labelling agent or dye, avoiding the related intrinsic bias, and can be utilized to screen novel sequences of interest in a high-throughput and cost-effective manner. In addition, we observed that left-handed (Z-) G4 structures were systematically more fluorescent than most other G4 structures, almost reaching the quantum yield of 5′-d[(G3T)3G3]-3′ (G3T), the most fluorescent G4 structure reported to date. This property is likely to arise from the similar base-stacking geometry in both types of structures.Fold up
Year of publication 2019
Low retinal toxicity of intravitreal carboplatin associated with good retinal tumor control in transgenic murine retinoblastoma.Clinical & experimental ophthalmology : DOI : 10.1111/ceo.13711 Learn more
Retinoblastoma is a rare intraocular malignancy in children. Current treatments have many adverse effects. New therapeutic approaches like intravitreal injections of chemotherapies are currently being developed but their toxicities need to be evaluated on animal models. This study compares the efficacy and toxicity of intravitreal melphalan, topotecan and carboplatin, alone or in combination (sequential administration), in the LHBetaTag retinoblastoma mice. Mice were divided into 9 groups: control, carboplatin 1.5 and 4μg, melphalan 0.1 and 1μg, topotecan 0.1 and 1μg, carboplatin 4μg/ topotecan 0.1μg and melphalan 1μg/ topotecan 0.1μg. The follow‐up was performed using fundus imaging and optical coherence tomography combined with histopathological analysis. Absence of tumor and presence of calcified tumors were the criteria for therapeutic response assessment. Ocular complications were assessed after 4 weekly injections. Retinal toxicity was defined by the decrease of retinal thickness and of the number of retinal layers. Topotecan was inactive on retinal tumors. Melphalan (1μg) led to a complete tumor control in 91.7% of eyes. Carboplatin strongly decreased the tumor burden (85.7‐93.8% of eyes without retinal tumor). The intravitreal injection itself led to ocular complications (25% of media opacities and 45.7% of retinal detachment). Only melphalan at 1μg showed a strong retinal toxicity. The two combinations showed a good efficacy in reducing the number of eyes with retinal tumors with a reduced retinal toxicity. This preclinical study suggests that intravitreal injection of carboplatin has a low toxicity and could be evaluated in clinical practice to treat patients suffering from retinoblastoma.
Retinoblastoma is a rare intraocular malignancy in children. Current treatments have many adverse effects. New therapeutic approaches like intravitreal injections of chemotherapies are currently being developed but their toxicities need to be evaluated on animal models. This study compares the efficacy and toxicity of intravitreal melphalan, topotecan and carboplatin, alone or in combination (sequential administration), in the LHBetaTag retinoblastoma mice.
Mice were divided into 9 groups: control, carboplatin 1.5 and 4μg, melphalan 0.1 and 1μg, topotecan 0.1 and 1μg, carboplatin 4μg/ topotecan 0.1μg and melphalan 1μg/ topotecan 0.1μg. The follow‐up was performed using fundus imaging and optical coherence tomography combined with histopathological analysis. Absence of tumor and presence of calcified tumors were the criteria for therapeutic response assessment. Ocular complications were assessed after 4 weekly injections. Retinal toxicity was defined by the decrease of retinal thickness and of the number of retinal layers.
Topotecan was inactive on retinal tumors. Melphalan (1μg) led to a complete tumor control in 91.7% of eyes. Carboplatin strongly decreased the tumor burden (85.7‐93.8% of eyes without retinal tumor). The intravitreal injection itself led to ocular complications (25% of media opacities and 45.7% of retinal detachment). Only melphalan at 1μg showed a strong retinal toxicity. The two combinations showed a good efficacy in reducing the number of eyes with retinal tumors with a reduced retinal toxicity.
This preclinical study suggests that intravitreal injection of carboplatin has a low toxicity and could be evaluated in clinical practice to treat patients suffering from retinoblastoma.
Deciphering the mechanism of inhibition of SERCA1a by sarcolipin using molecular simulationsbioRxiv : DOI : 10.1101/2019.12.17.879825 Learn more
SERCA1a is an ATPase calcium pump that transports Ca2+ from the cytoplasm to the sarco/endoplasmic reticulum lumen. Sarcolipin (SLN), a transmembrane peptide, regulates the activity of SERCA1a by decreasing its Ca2+ transport rate, but its mechanism of action is still not well understood. To decipher this mechanism, we have performed normal modes analysis in the all-atom model, with the SERCA1a-SLN complex or the isolated SERCA1a embedded in an explicit membrane. The comparison of the results allowed us to provide an explanation for the action of SLN that is in good agreement with experimental observations. In our analyses, the presence of SLN locally perturbs the TM6 transmembrane helix and as a consequence modifies the position of D800, one of the key metal-chelating residues. Additionally, it reduces the flexibility of the gating residues, V304 and E309 in TM4, at the entrance of the Ca2+ binding sites, which would decrease the affinity for Ca2+. Unexpectedly, SLN has also an effect on the ATP binding site more than 35 r A away, due to the straightening of TM5, a long helix considered as the spine of the protein. The straightening of TM5 modifies the structure of the P-N linker that sits above it, and which comprises the 351DKTG354 conserved motif, resulting in an increase of the distance between ATP and the phosphorylation site. As a consequence, the turn-over rate could be affected. All this gives SERCA1a the propensity to go toward a Ca2+-deprived E2-like state in the presence of SLN and toward a Ca2+ high-affinity E1-like state in the absence of SLN, although the SERCA1a-SLN complex was crystallized in an E1-like state. In addition to a general mechanism of inhibition of SERCA1a regulatory peptides, this study also provides an insight in the conformational transition between the E2 and E1 states.Fold up
DNA junction ligands trigger DNA damage and are synthetic lethal with DNA repair inhibitors in cancer cellsJournal of the American Chemical Society : 142 : 424-435 : DOI : 10.1021/jacs.9b11150 Learn more
Translocation of DNA and RNA polymerases along their duplex substrates results in DNA supercoiling. This torsional stress promotes the formation of plectonemic structures, including three-way DNA junction (TWJ), which can block DNA transactions and lead to DNA damage. While cells have evolved multiple mechanisms to prevent the accumulation of such structures, stabilizing TWJ through ad hoc ligands offer an opportunity to trigger DNA damage in cells with high level of transcription and replication, such as cancer cells. Here, we develop a series of azacryptand-based TWJ ligands, we thoroughly characterize their TWJ-interacting properties in vitro and demonstrate their capacity to trigger DNA damage in rapidly dividing human cancer cells. We also demonstrate that TWJ ligands are amenable to chemically induced synthetic lethality strategies upon association with inhibitors of DNA repair, thus paving the way towards innovative drug combinations to fight cancers.Fold up
The level of activity of the alternative lengthening of telomeres correlates with patient age in IDH-mutant ATRX-loss-of-expression anaplastic astrocytomas.Acta neuropathologica communications : 7 : 175 : DOI : 10.1186/s40478-019-0833-0 Learn more
All cancer cells need to maintain functional telomeres to sustain continuous cell division and proliferation. In human diffuse gliomas, functional telomeres are maintained due either to reactivation of telomerase expression, the main pathway in most cancer types, or to activation of a mechanism called the alternative lengthening of telomeres (ALT). The presence of IDH1/2 mutations (IDH-mutant) together with loss of ATRX expression (ATRX-lost) are frequently associated with ALT in diffuse gliomas. However, detection of ALT, and a fortiori its quantification, are rarely, if ever, measured in neuropathology laboratories. We measured the level of ALT activity using the previously described quantitative “C-circle” assay and analyzed it in a well characterized cohort of 104 IDH-mutant and ATRX-lost adult diffuse gliomas. We report that in IDH-mutant ATRX-lost anaplastic astrocytomas, the intensity of ALT was inversely correlated with age (p < 0.001), the younger the patient, the higher the intensity of ALT. Strikingly, glioblastomas having progressed from anaplastic astrocytomas did not exhibit this correlation. ALT activity level in the tumor did not depend on telomere length in healthy tissue cells from the same patient. In summary, we have uncovered the existence, in anaplastic astrocytomas but not in glioblastomas with the same IDH and ATRX mutations, of a correlation between patient age and the level of activity of ALT, a telomerase-independent pathway of telomere maintenance.Fold up
TGF-β-induced fibrotic stress increases G-quadruplex formation in human fibroblasts.FEBS letters : 593 : 3149-3161 : DOI : 10.1002/1873-3468.13658 Learn more
Scar formation after wound healing is a major medical problem. A better understanding of the dynamic nuclear architecture of the genome during wound healing could provide insights into the underlying pathophysiology and enable novel therapeutic strategies. Here, we demonstrate that TGF-β- induced fibrotic stress increases formation of the dynamic secondary DNA structures called G-quadruplexes in skin fibroblasts, which is coincident with increased expression of collagen 1. This G-quadruplex formation is attenuated by a small molecule inhibitor of intracellular Ca influx and an anti-fibrotic compound. In addition, we identify G-quadruplex-forming sequences in the promoter region of COL1A1, which encodes collagen 1, and confirm their ability to form G-quadruplex structures under physiologically relevant conditions. Our findings reveal a link between G-quadruplexes and scar formation that may lead to novel therapeutic interventions.Fold up
Highly active G-quadruplex/hemin DNAzyme for sensitive colorimetric determination of lead(II)Microchimica Acta : 186 : 786 : DOI : 10.1007/s00604-019-3950-3 Learn more
A UV-vis, CD, and differential pulse voltammetric study was performed on the deactivation of the activity of parallel G-quadruplex/hemin DNAzymes (G4 DNAzymes) by Pb(II). The G4 DNAzyme carries a d[TC] sequence at its 3extasciiacutex end and is stabilized by potassium(I). On addition of Pb(II), the K(I) ions in the parallel G4 are replaced by Pb(II) to keep the parallel topology. Intruded Pb(II) decrease the affinity between the topology and hemin, this leads to a decrease of DNAzyme activity for catalyzing the oxidation of 2,2extasciiacutex-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) by hydrogen peroxide to form a green dye with an absorption maximum at 420 nm. The assay does not use any amplification, and has a linear response in the 0.01 to 10 muM Pb(II) concentration range and a 7.1 nM limit of detection. The method was successfully applied to the analysis of spiked water samples.Fold up
Proper chromosome alignment depends on BRCA2 phosphorylation by PLK1bioRxiv : Preprint : DOI : 10.1101/265934 Learn more
The BRCA2 tumor suppressor protein is involved in the maintenance of genome integrity through its role in homologous recombination in S/G2 phases of the cell cycle. A much less established function of BRCA2 takes place in mitosis where it interacts with the SAC component BUBR1 and is involved in cytokinesis by interaction with midbody components. Also in mitosis, BRCA2 is phosphorylated by the cell cycle regulator Polo-like kinase 1 (PLK1), so we asked whether this phosphorylation would have a role in the control of mitosis. Here we combined biophysical, biochemical and cell biology approaches to characterize the phenotype of BRCA2 variants that alter PLK1 phosphorylation. We identified T207 in BRCA2 as a bona fide docking site for PLK1. The 3D structure of the BRCA2 peptide bound to PLK1 Polo-box domain exhibits all the characteristics of an optimal and specific phosphopeptide-PLK1 interface. We show that this interaction is required for the phosphorylation of BUBR1 and pBUBR1 binding to the phosphatase PP2A-B56α, both critical for the establishment of proper kinetochore-microtubules attachments. Precluding T207 binding to PLK1 as observed in BRCA2 missense variants identified in breast cancer results in reduced phosphorylation of BUBR1 at PLK1-dependent sites and decreases the interaction of BUBR1 with the phosphatase PP2A-B56α. This leads to unaligned chromosomes, faulty chromosome segregation and aneuploidy. We thus reveal a direct mitotic role of BRCA2 in the alignment of chromosomes, distinct from its DNA repair function, with important consequences on chromosome stability. These findings may explain in part the aneuploidy observed in BRCA2-deficient tumors.Fold up
Transcriptional alterations in glioma result primarily from DNA methylation-independent mechanisms.Genome research : 29 : 1605-1621 : DOI : 10.1101/gr.249219.119 Learn more
In cancer cells, aberrant DNA methylation is commonly associated with transcriptional alterations, including silencing of tumor suppressor genes. However, multiple epigenetic mechanisms, including polycomb repressive marks, contribute to gene deregulation in cancer. To dissect the relative contribution of DNA methylation-dependent and -independent mechanisms to transcriptional alterations at CpG island/promoter-associated genes in cancer, we studied 70 samples of adult glioma, a widespread type of brain tumor, classified according to their isocitrate dehydrogenase (IDH1) mutation status. We found that most transcriptional alterations in tumor samples were DNA methylation-independent. Instead, altered histone H3 trimethylation at lysine 27 (H3K27me3) was the predominant molecular defect at deregulated genes. Our results also suggest that the presence of a bivalent chromatin signature at CpG island promoters in stem cells predisposes not only to hypermethylation, as widely documented, but more generally to all types of transcriptional alterations in transformed cells. In addition, the gene expression strength in healthy brain cells influences the choice between DNA methylation- and H3K27me3-associated silencing in glioma. Highly expressed genes were more likely to be repressed by H3K27me3 than by DNA methylation. Our findings support a model in which altered H3K27me3 dynamics, more specifically defects in the interplay between polycomb protein complexes and the brain-specific transcriptional machinery, is the main cause of transcriptional alteration in glioma cells. Our study provides the first comprehensive description of epigenetic changes in glioma and their relative contribution to transcriptional changes. It may be useful for the design of drugs targeting cancer-related epigenetic defects.Fold up
Sneaking Out for Happy Hour: Yeast-Based Approaches to Explore and Modulate Immune Response and Immune EvasionGenes : 10 : 667-689 : DOI : 10.3390/genes10090667 Learn more
Many pathogens (virus, bacteria, fungi, or parasites) have developed a wide variety of mechanisms to evade their host immune system. The budding yeast Saccharomyces cerevisiae has successfully been used to decipher some of these immune evasion strategies. This includes the cis-acting mechanism that limits the expression of the oncogenic Epstein–Barr virus (EBV)-encoded EBNA1 and thus of antigenic peptides derived from this essential but highly antigenic viral protein. Studies based on budding yeast have also revealed the molecular bases of epigenetic switching or recombination underlying the silencing of all except one members of extended families of genes that encode closely related and highly antigenic surface proteins. This mechanism is exploited by several parasites (that include pathogens such as Plasmodium, Trypanosoma, Candida, or Pneumocystis) to alternate their surface antigens, thereby evading the immune system. Yeast can itself be a pathogen, and pathogenic fungi such as Candida albicans, which is phylogenetically very close to S. cerevisiae, have developed stealthiness strategies that include changes in their cell wall composition, or epitope-masking, to control production or exposure of highly antigenic but essential polysaccharides in their cell wall. Finally, due to the high antigenicity of its cell wall, yeast has been opportunistically exploited to create adjuvants and vectors for vaccination.Fold up
First molecular electronic hyperpolarizability of series of π-conjugated oxazole dyes in solution: an experimental and theoretical studyRSC Adv. : 9 : 26476-26482 : DOI : 10.1039/C9RA05246A Learn more
In this work, we report the experimental and theoretical first molecular electronic hyperpolarizability (βHRS) of eleven π-conjugated oxazoles compounds in toluene medium. The Hyper-Rayleigh Scattering (HRS) technique allowed the determination of the experimental dynamic βHRS values, by exciting the compounds with a picosecond pulse trains from a Q-switched and mode-locked Nd:YAG laser tuned at 1064 nm. Theoretical predictions based on time-dependent density functional theory level using the Gaussian 09 program package were performed with three different functionals (B3LYP, CAM-B3LYP, and M06-2X), to calculate both static and dynamic theoretical βHRS values. Good accordance was found between the experimental and theoretical values, in particular for the CAM-B3LYP and M06-2X functionals.Fold up
Monitoring DNA–Ligand Interactions in Living Human Cells Using NMR SpectroscopyJournal of the Americal Chemical Society : 141 : 13281-13285 : DOI : 10.1021/jacs.9b03031 Learn more
Studies on DNA–ligand interactions in the cellular environment are problematic due to the lack of suitable biophysical tools. To address this need, we developed an in-cell NMR-based approach for monitoring DNA–ligand interactions inside the nuclei of living human cells. Our method relies on the acquisition of NMR data from cells electroporated with preformed DNA–ligand complexes. The impact of the intracellular environment on the integrity of the complexes is assessed based on in-cell NMR signals from unbound and ligand-bound forms of a given DNA target. This technique was tested on complexes of two model DNA fragments and four ligands, namely, a representative DNA minor-groove binder (netropsin) and ligands binding DNA base-pairing defects (naphthalenophanes). In the latter case, we demonstrate that two of the three in vitro-validated ligands retain their ability to form stable interactions with their model target DNA in cellulo, whereas the third one loses this ability due to off-target interactions with genomic DNA and cellular metabolites. Collectively, our data suggest that direct evaluation of the behavior of drug-like molecules in the intracellular environment provides important insights into the development of DNA-binding ligands with desirable biological activity and minimal side effects resulting from off-target binding.Fold up
Identification of optimal fluorescent probes for G-quadruplex nucleic acids through systematic exploration of mono- and distyryl dye librariesBeilstein Journal of Organic Chemistry : 15 : 1872–1889 : DOI : 10.3762/bjoc.15.183 Learn more
A library of 52 distyryl and 9 mono-styryl cationic dyes was synthesized and investigated with respect to their optical properties, propensity to aggregation in aqueous medium, and capacity to serve as fluorescence “light-up” probes for G-quadruplex (G4) DNA and RNA structures. Among the 61 compounds, 57 dyes showed preferential enhancement of fluorescence intensity in the presence of one or another G4-DNA or RNA structure, while no dye displayed preferential response to double-stranded DNA or single-stranded RNA analytes employed at equivalent nucleotide concentration. Thus, preferential fluorimetric response towards G4 structures appears to be a common feature of mono- and distyryl dyes, including long-known mono-styryl dyes used as mitochondrial probes or protein stains. However, the magnitude of the G4-induced “light-up” effect varies drastically, as a function of both the molecular structure of the dyes and the nature or topology of G4 analytes. Although our results do not allow to formulate comprehensive structure–properties relationships, we identified several structural motifs, such as indole- or pyrrole-substituted distyryl dyes, as well as simple mono-stryryl dyes such as DASPMI [2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide] or its 4-isomer, as optimal fluorescent light-up probes characterized by high fluorimetric response (I/I0 of up to 550-fold), excellent selectivity with respect to double-stranded DNA or single-stranded RNA controls, high quantum yield in the presence of G4 analytes (up to 0.32), large Stokes shift (up to 150 nm) and, in certain cases, structural selectivity with respect to one or another G4 folding topology. These dyes can be considered as promising G4-responsive sensors for in vitro or imaging applications. As a possible application, we implemented a simple two-dye fluorimetric assay allowing rapid topological classification of G4-DNA structures.Fold up