Biology subjects

Kumar, A.

Publications and source records attributed to Kumar, A..

At least 271 records · Page 15Linked to original sources

bioRxiv2024

The Soybean Cyst Nematode Effector Cysteine Protease 1 (CPR1) Targets a Mitochondrial Soybean Branched-Chain Amino Acid Aminotransferase (GmBCAT1) for Degradation

The soybean cyst nematode (SCN; Heterodera glycines) facilitates infection by secreting a repertoire of effector proteins into host cells to establish a permanent feeding site composed of a syncytium of root cells. Among the diverse proteins secreted by the nematode, we were specifically interested in identifying proteases to pursue our goal of engineering decoy substrates that elicit an immune response when cleaved by an SCN protease. We identified a cysteine protease that we named Cysteine Protease 1 (CPR1), which was predicted to be a secreted effector based on transcriptomic data obtained from SCN esophageal gland cells, presence of a signal peptide, and lack of transmembrane domains. CPR1 is conserved in all isolates of SCN sequenced to date, suggesting it is critical for virulence. Transient expression of CPR1 in Nicotiana benthamiana leaves suppressed cell death induced by a constitutively active nucleotide binding leucine-rich repeat protein, RPS5, indicating that CPR1 inhibits effector-triggered immunity. CPR1 localizes in part to the mitochondria when expressed in planta. Proximity-based labeling in transgenic soybean roots, co-immunoprecipitation, and cleavage assays identified a branched-chain amino acid aminotransferase from soybean (GmBCAT1) as a substrate of CPR1. Silencing of the CPR1 transcript in the nematode reduced penetration frequency in soybean roots while the expression of CPR1 in soybean roots enhanced susceptibility. Our data demonstrates that CPR1 is a conserved effector protease with a direct target in soybean roots, highlighting it as a promising candidate for decoy engineering.

plant biology↗

bioRxiv2024

Nonlinear compliance of NompC gating spring and its implication in mechanotransduction

Cytoskeleton-tethered mechanosensitive channels (MSCs) utilize compliant proteins or protein domains called gating springs to convert mechanical stimuli into electric signals, enabling sound and touch sensation and proprioception. The mechanical properties of these gating springs, however, remain elusive. Here, we explored the mechanical properties of the homotetrameric NompC complex containing long ankyrin-repeat domains (ARDs). We developed a toehold-mediated strand displacement approach to tether single membrane proteins, allowing us to exert force on them and precisely measure their absolute extension using optical tweezers. Our findings revealed that each ARD has a low stiffness of [~]0.7 pN/nm and begins to unfold stepwise at [~]7 pN, leading to nonlinear compliance. Our calculations indicate that this nonlinear compliance may help regulate NompCs sensitivity, dynamic range, and kinetics to detect mechanical stimuli. Overall, our research highlights the importance of a compliant and unfolding-refolding gating spring in facilitating a graded response of MSC ion transduction across a wide spectrum of mechanical stimuli.

biophysics↗

bioRxiv2024

Designing Cell-Type-Specific Promoter Sequences Using Conservative Model-Based Optimization

Gene therapies have the potential to treat disease by delivering therapeutic genetic cargo to disease-associated cells. One limitation to their widespread use is the lack of short regulatory sequences, or promoters, that differentially induce the expression of delivered genetic cargo in target cells, minimizing side effects in other cell types. Such cell-type-specific promoters are difficult to discover using existing methods, requiring either manual curation or access to large datasets of promoter-driven expression from both targeted and untargeted cells. Model-based optimization (MBO) has emerged as an effective method to design biological sequences in an automated manner, and has recently been used in promoter design methods. However, these methods have only been tested using large training datasets that are expensive to collect, and focus on designing promoters for markedly different cell types, overlooking the complexities associated with designing promoters for closely related cell types that share similar regulatory features. Therefore, we introduce a comprehensive framework for utilizing MBO to design promoters in a data-efficient manner, with an emphasis on discovering promoters for similar cell types. We use conservative objective models (COMs) for MBO and highlight practical considerations such as best practices for improving sequence diversity, getting estimates of model uncertainty, and choosing the optimal set of sequences for experimental validation. Using three relatively similar blood cancer cell lines (Jurkat, K562, and THP1), we show that our approach discovers many novel cell-type-specific promoters after experimentally validating the designed sequences. For K562 cells, in particular, we discover a promoter that has 75.85% higher cell-type-specificity than the best promoter from the initial dataset used to train our models.

synthetic biology↗

bioRxiv2024

Molecular principles of redox-coupled sodium pumping of the ancient Rnf machinery

The Rnf complex is the primary respiratory enzyme of several anaerobic prokaryotes that transfers electrons from ferredoxin to NAD+ and pumps sodium ions (Na+) across a membrane, powering ATP synthesis. Rnf is widespread in primordial organisms and the evolutionary predecessor of the Na+-pumping NADH-quinone oxidoreductase (Nqr)1. By running in reverse, Rnf reduces ferredoxin with NADH as reductant at the expense of the transmembrane electrochemical ion gradient and provides low potential electrons for nitrogenases as well as CO2 reductases. Yet, the molecular principles that couple the long-range electron transfer to the Na+ translocation across the membrane remain elusive. Here we resolve key functional states along the electron transfer pathway using redox-controlled cryo-electron microscopy (cryo-EM) that, in combination with biochemical functional assays and atomistic molecular simulations, provide key insight into the redox-driven Na+ pumping mechanism. We show that the reduction of the unique membrane-embedded [2Fe2S] cluster in the vestibule between the RnfA/E subunits electrostatically attracts the sodium ions, and in turn, triggers an inward/outward transition with alternating membrane access driving the Na+ pump and the reduction of NAD+. Our study unveils an ancient mechanism for redox-driven ion pumping, and provides key understanding of the fundamental principles governing energy conversion in biological systems.

biochemistry↗

bioRxiv2024

Myogenic dedifferentiation involves a p53-dependent reorganization of PLK4 localization during centrosome regeneration

Multinucleated skeletal muscle cells are stably withdrawn from the cell cycle in most vertebrates. Muscle dedifferentiation is however naturally occurring during limb regeneration in newts and can be artificially induced in mammalian myotubes. Dedifferentiation involves fragmentation of myofibers and myotubes into mononucleate cells which subsequently reenter the cell cycle, and give rise to proliferative progeny. Here we addressed the dynamics of centrosomes, which are key organelles for cell proliferation during myogenic differentiation and dedifferentiation. We show that, in contrast to their mammalian counterparts, newt muscle cells retain centrosomes during differentiation and demonstrate that regeneration of centrosomes in dedifferentiated mouse muscle cells depends on inhibition of the tumor suppressor p53. We also find that regulation of the subcellular localization of Polo-Like Kinase 4 rather than its expression level is a hallmark of myogenic differentiation and dedifferentiation, identifying a novel cellular process underlying the plasticity of the differentiated state.

developmental biology↗

bioRxiv2024

Latrophilin-2 mediates fluid shear stress mechanotransduction at endothelial junctions

Endothelial cell responses to fluid shear stress from blood flow are crucial for vascular development, function and disease. A complex of PECAM-1, VE-cadherin, VEGF receptors (VEGFRs) and PlexinD1 located at cell-cell junctions mediates many of these events. But available evidence suggests that another mechanosensor upstream of PECAM-1 initiates signaling. Hypothesizing that GPCR and G proteins may serve this role, we performed siRNA screening of G subunits and found that Gi2 and Gq/11 are required for activation of the junctional complex. We then developed a new activation assay, which showed that these G proteins are activated by flow. We next mapped the G residues required for activation and developed an affinity purification method that used this information to identify latrophilin-2 (Lphn-2/ADGRL2) as the upstream GPCR. Latrophilin-2 is required for all PECAM-1 downstream events tested. In both mice and zebrafish, latrophilin-2 is required for flow-dependent angiogenesis and artery remodeling. Furthermore, endothelial specific knockout demonstrates that latrophilin plays a role in flow-dependent artery remodeling. Human genetic data reveal a correlation between the latrophilin-2-encoding Adgrl2 gene and cardiovascular disease. Together, these results define a pathway that connects latrophilin-dependent G protein activation to subsequent endothelial signaling, vascular physiology and disease.

molecular biology↗

bioRxiv2024

Multispectral live-cell imaging with uncompromised spatiotemporal resolution

Multispectral imaging is an established method to extend the number of colours usable in fluorescence imaging beyond the typical limit of three or four, but standard approaches are poorly suited to live-cell imaging. We introduce an approach for multispectral imaging in live cells, comprising an iterative spectral unmixing algorithm and eight channel camera-based image acquisition hardware. This enables the accurate unmixing of low signal-to-noise ratio datasets, typical of live-cell imaging, captured at video rates. We use this approach on a commercial spinning disk confocal microscope and a home-built oblique plane light sheet microscope to image 1-7 spectrally distinct fluorophore species simultaneously, using both fluorescent protein fusions and small-molecule dyes. We further use de novo designed protein-binding proteins (minibinders), labelled with organic fluorophores, and use these in combination with our multispectral imaging approach to study the endosomal trafficking of cell-surface receptors at endogenous levels.

biophysics↗

bioRxiv2024

Single-nucleus transcriptomic analysis reveals the regulatory circuitry of myofiber XBP1 during regenerative myogenesis

Endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) are activated in skeletal muscle in multiple conditions. However, the role of the UPR in the regulation of muscle regeneration remains less understood. We demonstrate that gene expression of various markers of the UPR is induced in both myogenic and non-myogenic cells in regenerating muscle. Genetic ablation of XBP1, a downstream target of the IRE1 arm of the UPR, in myofibers attenuates muscle regeneration in adult mice. Single nucleus RNA sequencing (snRNA-seq) analysis showed that deletion of XBP1 in myofibers perturbs proteolytic systems and mitochondrial function in myogenic cells. Trajectory analysis of snRNA-seq dataset showed that XBP1 regulates the abundance of satellite cells and the formation of new myofibers in regenerating muscle. In addition, ablation of XBP1 disrupts the composition of non-myogenic cells in injured muscle microenvironment. Collectively, our study suggests that myofiber XBP1 regulates muscle regeneration through both cell-autonomous and -non-autonomous mechanisms. HIGHLIGHTSO_LIThe UPR is activated in different cell types during muscle regeneration. C_LIO_LITargeted deletion of XBP1 impairs muscle regeneration in adult mice C_LIO_LIMyofiber XBP1 regulates satellite cell dynamics during regenerative myogenesis C_LIO_LIMyofiber XBP1 regulates abundance of non-myogenic cells in regenerating muscle C_LI

cell biology↗

bioRxiv2024

Snake venom-inspired novel peptides protect Caenorhabditis elegans against paraquat induced Parkinson's pathology

The in vivo protective mechanisms of two low molecular mass ([~]1.4 kDa) novel custom peptides (CPs) against paraquat (PT)-induced neurodegenerative dysfunction in the Caenorhabditis elegans model were deciphered. CPs prevent the PT binding to the nerve ring adjacent to the pharynx in C. elegans (N2 strain) by stable and high-affinity binding to the tyrosine-protein kinase receptor CAM-1, resulting in significant inhibition of PT-induced toxicity by reducing enhanced reactive oxygen species production, mitochondrial membrane depolarization, and chemosensory dysfunction. The CPs inhibited PT-induced dopaminergic (DAergic) neuron degeneration and alpha-synuclein aggregation, the hallmarks of Parkinsons Disease, in transgenic BZ555 and NL5901 strains of C. elegans. The transcriptomic, functional proteomics, and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analyses show that CPs prevented the increased expression of the genes involved in the skn-1 downstream pathway, thereby restoring PT-mediated oxidative stress, apoptosis, and neuronal damage in C. elegans. The CPs ability to repair PT-induced damage was demonstrated by a network of gene expression profiles illustrating the molecular relationships between the regulatory proteins. Further, CPs (10 mg/kg, parental route) did not show toxicity or induce inflammatory mediators in the mouse model.

neuroscience↗

bioRxiv2024

Pathobiology of the autophagy-lysosomal pathway in the Huntington's disease brain

Accumulated levels of mutant huntingtin protein (mHTT) and its fragments are considered contributors to the pathogenesis of Huntingtons disease (HD). Although lowering mHTT by stimulating autophagy has been considered a possible therapeutic strategy, the role and competence of autophagy-lysosomal pathway (ALP) during HD progression in the human disease remains largely unknown. Here, we used multiplex confocal and ultrastructural immunocytochemical analyses of ALP functional markers in relation to mHTT aggresome pathology in striatum and the less affected cortex of HD brains staged from HD2 to HD4 by Vonsattel neuropathological criteria compared to controls. Immunolabeling revealed the localization of HTT/mHTT in ALP vesicular compartments labeled by autophagy-related adaptor proteins p62/SQSTM1 and ubiquitin, and cathepsin D (CTSD) as well as HTT-positive inclusions. Although comparatively normal at HD2, neurons at later HD stages exhibited progressive enlargement and clustering of CTSD-immunoreactive autolysosomes/lysosomes and, ultrastructurally, autophagic vacuole/lipofuscin granules accumulated progressively, more prominently in striatum than cortex. These changes were accompanied by rises in levels of HTT/mHTT and p62/SQSTM1, particularly their fragments, in striatum but not in the cortex, and by increases of LAMP1 and LAMP2 RNA and LAMP1 protein. Importantly, no blockage in autophagosome formation and autophagosome-lysosome fusion was detected, thus pinpointing autophagy substrate clearance deficits as a basis for autophagic flux declines. The findings collectively suggest that upregulated lysosomal biogenesis and preserved proteolysis maintain autophagic clearance in early-stage HD, but failure at advanced stages contributes to progressive HTT build-up and potential neurotoxicity. These findings support the prospect that ALP stimulation applied at early disease stages, when clearance machinery is fully competent, may have therapeutic benefits in HD patients.

pathology↗

bioRxiv2024

Lipidomics and colistin resistance in non-human isolates of Acinetobacter seifertii

Acinetobacter baumannii is most well known for its role as a human pathogen and as a member of the Acinetobacter calcoaceticus-baumannii (ACB) complex. However, lesser characterised members of the ACB complex, have also been implicated in hospital-acquired infections. Once mainly considered opportunistic pathogens, many A. baumannii and non-baumannii strains are being isolated from agricultural, water and food sources. The surveillance and tracking of Acinetobacter spp. have been recently suggested to be part of the One Health consortium, to understand and prevent the spread of antimicrobial resistance. Here, we isolated four Acinetobacter strains from tank milk in Bogor, Indonesia and using ANI and dDDH techniques have identified them as Acinetobacter seifertii. MLST methods assigned these A. seifertii strains to a novel Sequence Types (ST), highlighting the diversity not only within the ACB complex but also in non-human Acinetobacter spp. These four A. seifertii strains are colistin-resistant and while they do not harbour any known mechanism of colistin resistance, they do share amino acid substitutions in regulatory proteins, AdeS, PmrAB, H-NS, and the membrane associated proteins, LpxACD, MlaD, PldA, LpsB and EptA that may contribute to this phenotype. Furthermore, down-regulation of the RND efflux pump AdeAB, may also be a key factor in colistin resistance in these non-human A. seifertii strains. Lipidomics revealed an acyl-homoserine lactone (AHL) molecule, and lyso-phosphatidylethanolamine (lyso-PE) in significant abundance compared to colistin-sensitive A. baumannii ATCC17978 revealing lipidomic differences between species. Finally, these four tank milk A. seifertii strains are avirulent in an insect model of virulence. It is possible that A. seifertii strains are intrinsically resistant to colistin and require further study. By investigating these less understood Acinetobacter spp. from non-human sources, our study supports the One Health approach to combatting antibiotic resistance.

microbiology↗

bioRxiv2024

Use of Stem Cell-Derived Cardiomyocyte and Nasal Epithelium Models to Establish a Multi-Tissue Model Platform to Validate Repurposed Drugs Against SARS-CoV-2 Infection

The novel coronavirus disease (COVID-19) and any future coronavirus outbreaks will require more affordable, effective and safe treatment options to complement current ones such as Paxlovid. Drug repurposing can be a promising approach if we are able to find a rapid, robust and reliable way to down-select and screen candidates using in silico and in vitro approaches. With repurposed drugs, ex vivo models could offer a rigorous route to human clinical trials with less time invested into nonclinical animal (in vivo) studies. We have previously shown the value of commercially available ex vivo/3D airway and alveolar tissue models, and this paper takes this further by developing and validating human nasal epithelial model and embryonic stem cells derived cardiomyocyte model. Five shortlisted candidates (fluvoxamine, everolimus, pyrimethamine, aprepitant and sirolimus) were successfully compared with three control drugs (remdesivir, molnupiravir, nirmatrelvir) when tested against key variants of the SARS-CoV-2 virus including Delta and Omicron, and we were able to reconfirm our earlier finding that fluvoxamine can induce antiviral efficacy in combination with other drugs. Scalability of this high-throughput screening approach has been demonstrated using a liquid handling robotic platform for future Disease-X outbreaks.

microbiology↗

bioRxiv2024

Targeted Degradation of CDK9 Potently Disrupts the MYC Transcriptional Network

Cyclin-dependent kinase 9 (CDK9) coordinates signaling events that regulate RNA polymerase II (Pol II) pause-release states. It is an important co-factor for transcription factors, such as MYC, that drive aberrant cell proliferation when their expression is deregulated. CDK9 modulation offers an approach for attenuating dysregulation in such transcriptional programs. As a result, numerous drug development campaigns to inhibit CDK9 kinase activity have been pursued. More recently, targeted degradation has emerged as an attractive approach. However, comprehensive evaluation of degradation versus inhibition is still critically needed to assess the biological contexts in which degradation might offer superior therapeutic benefits. We validated that CDK9 inhibition triggers a compensatory mechanism that dampens its effect on MYC expression and found that this feedback mechanism was absent when the kinase is degraded. Importantly, CDK9 degradation is more effective than its inhibition for disrupting MYC transcriptional regulatory circuitry likely through the abrogation of both enzymatic and scaffolding functions of CDK9. Highlights- KI-CDK9d-32 is a highly potent and selective CDK9 degrader. - KI-CDK9d-32 leads to rapid downregulation of MYC protein and mRNA transcripts levels. - KI-CDK9d-32 represses canonical MYC pathways and leads to a destabilization of nucleolar homeostasis. - Multidrug resistance ABCB1 gene emerged as the strongest resistance marker for the CDK9 PROTAC degrader.

cancer biology↗

bioRxiv2024

MicroRNA hsa-miR-203a-3p promotes H1N1 and NDV Virus Replication by suppressing the IFNA signaling.

MicroRNAs (miRNAs) are small non-coding molecules that act as essential post-transcriptional regulators in various biological processes. Many studies suggest that miRNAs may modulate the hosts immune response during virus infections. We analyzed publicly available transcriptomics data involving infection with different RNA viruses and selected the most prominent candidate, miR-203a-3p. miR-203a-3p is upregulated during H7N1, HCV, and HIV+HPV infections. Interestingly, pathway analysis of microRNA-targeted genes shows that miR-203a-3p targets the type-I interferon pathway. In this study, we report that the expression of miR-203a-3p is elevated in response to polyinosinic-polycytidylic acid [poly(I:C)] transfection and infection with RNA viruses like Newcastle Disease Virus (NDV) and H1N1 influenza virus. We found that overexpression of miR-203-3p promotes the replication of H1N1 virus by suppressing the hosts type-I interferons and interferon-stimulated genes. In addition, miR-203a-3p overexpression reduced the expression of ISGs, and is attributed to the binding of miR-203a-3p to 3 UTRs of Janus-activated kinase 1 (JAK1), STAT1, SOCS3, and multiple IFNA transcripts, as shown by luciferase and Ago-2 pulldown assays. Altogether, these findings strongly suggest that miR-203a-3p acts as a pro-viral molecule during H1N1 and NDV infection by targeting the hosts IFN signaling pathways.

immunology↗

bioRxiv2024

Probing the Molecular Interactions of A22 with Prokaryotic Actin MreB and Eukaryotic Actin: A Computational and Experimental Study

Actin is a major cytoskeletal system that mediates the intricate organization of macromolecules within cells. The bacterial cytoskeletal protein MreB is a prokaryotic actin-like protein governing cell shape and intracellular organization in many rod-shaped bacteria including pathogens. MreB stands as a target for antibiotic development, and compounds like A22 and its analogue, MP265, are identified as potent inhibitors of MreB. The bacterial actin MreB shares structural homology with eukaryotic actin, despite lacking sequence similarity. It is currently not clear whether small molecules that inhibit MreB can act on the eukaryotic actin due to their structural similarity. In this study, we investigate the molecular interactions between A22 and both MreB and eukaryotic actin through molecular dynamics approach. Employing MD simulations and free energy calculations with an all-atom model, we unveil robust A22-MreB interaction and substantial binding affinity with eukaryotic actin. Experimental assays reveal A22s toxicity to eukaryotic cells, including yeast and human glioblastoma cells. Microscopy analysis demonstrates profound effects of A22 on actin organization in human glioblastoma cells. Overall, this integrative computational and experimental study advances our understanding of A22s mode of action and highlights its potential as a versatile tool for probing actin dynamics and as a candidate for therapeutic intervention in pathological conditions like cancer.

biophysics↗

bioRxiv2024

Real-time visualization reveals Mycobacterium tuberculosis ESAT-6 disrupts phagosome via fibril-mediated vesiculation

Mycobacterium tuberculosis (Mtb) evades host defense by hijacking and rupturing the phagosome, enabling it to escape to the host cytosol for its survival. ESAT-6, a secreted virulence protein of Mtb, is known to be critical for phagosome rupture. However, the mechanism of ESAT-6-mediated disruption of the phagosomal membrane remains unknown. Using in vitro reconstitution and numerical simulations, we discover that ESAT-6 polymerization remodels and vesiculates phagosomal membrane. In contrast to the pore formation triggered by a bilayer-spanning conformation, we find that the binding of ESAT-6 to the phagosomal membrane is shallow. Such shallow insertion leads to membrane shape transition leading to tubular and bud-like deformations on the membrane in a concentration-dependent manner, facilitated by the reduction in membrane tension and compressibility modulus. Strikingly, our observations suggest that ESAT-6 polymerizes in bulk and on the membrane, both in vitro and in macrophage. Numerical simulations demonstrate that growing fibrils generate both radial and tangential forces causing local remodeling and shape transition of the membrane. Using micropipette aspiration, we quantitatively show that ESAT-6 bound tensed membrane undergoes local changes in membrane curvature and lipid phase separation, also facilitated by the direct contact of the bacteria inside the phagosome. Nonetheless, the vesiculation of the buds is primarily driven by the forces exerted by the polymerization of ESAT-6. Such ESAT-6 mediated vesiculation induces apoptosis and host cell death in a concentration and time-dependent manner that promotes infection. Overall, the findings provide mechanistic insights into the long-standing question of phagosome disruption by Mtb for its escape.

biophysics↗

bioRxiv2024

Advancing Tolerogenic Immunotherapy: A Multi-Epitope Vaccine Design Targeting the CYP2D6 Autoantigen in Autoimmune Hepatitis Through Immuno-Informatics

Juvenile autoimmune hepatitis (JAIH) is a rare autoimmune disorder affecting children, characterized by the immune systems misguided attack on liver cells, primarily targeting the CYP2D6 autoantigen. This repeated attack leads to hepatic inflammation, fibrosis, and eventual liver failure. Current therapeutic strategies predominantly rely on immunosuppressive agents or whole B cell depletion antibodies, which render patients susceptible to infections and cancers. Hence, there is an urgent need for antigen-specific therapies to mitigate the severity of autoimmune hepatitis. Tolerogenic antigens represent a promising avenue in immunotherapy, capable of dampening autoimmunity. Here, we present a novel computationally designed multi-epitope tolerogenic vaccine tailored to target CYP2D6, aimed at inducing tolerogenic dendritic cells (DCs) and halting autoimmune progression in JAIH patients. To validate our approach, we have developed a similar vaccine for testing in mouse models of JAIH. The selected tolerogenic epitopes exhibit antigenicity without allergenicity or toxicity, and specifically induce IL-10 production (restricted to CD4+ T cell epitopes). In our vaccine design, tolerogenic poly-epitopes are linked with Toll-like receptor (TLR)-4-agonist, the 50S ribosomal unit, and IL-10, effectively programming DCs towards a tolerogenic state. Molecular docking and dynamic simulations have confirmed strong binding affinities and stable complexes between the vaccine structures, TLR4 and IL-10 receptor alpha (IL-10RA), indicating their potential for in vivo DC interaction and programming. Consequently, this innovative vaccine approach demands further exploration through wet lab experiments to assess its tolerogenicity, safety, and efficacy, thereby laying the groundwork for potential application in clinical settings.

immunology↗

bioRxiv2024

p53 restores the silencing of activated L1 Transposons

Long Interspersed Nuclear Element 1 (LINE1/L1) retrotransposons, comprising around 17% of the human genome, typically remain quiescent in healthy somatic cells but become activated in various cancer types. Our recent investigation reveals that p53 silences L1 transposons in human somatic cells, potentially constituting a tumor suppressive pathway. In this study, we demonstrate that p53 silences both L1mRNA-gDNA (cis L1 R-loops) and L1mRNA-cDNA hybrids (trans L1 R-loops) formed during retrotransposition. The activation of L1 transposons by HDAC inhibitors (HDACi) led to accumulation of these cis and trans L1 R-loops in p53-/- cells, which were mitigated by treatment with a reverse transcriptase inhibitor. Furthermore, p53 established re-silencing of hyperactivated L1 transposons induced by HDACi. The p53-mediated restoration of silencing was accompanied by recruiting histone repressive marks specifically H3K9me3 and H3K27me3 and inhibiting the deposition of H3K4me3 and H3K9ac marks at the L1 promoter. This study elucidates a novel role of p53 in regulating the formation of RNA-DNA hybrids, a pivotal intermediate component of retrotransposition, and initiating the suppression of hyperactivated L1 elements. These findings underscore the significance of p53 in preserving genome stability through the regulation of L1-derived R-loops. In BriefThe role of L1 transposon derived L1mRNA-cDNA hybrids; an intermediate product formed during retrotransposition, in DNA damage and inflammation is not clear. Paul et al. reveals that p53 prevents L1cDNA derived RNA-DNA hybrids to control DNA damage and activation of inflammatory genes. The findings also elucidate the role of p53 in initiating the repression of hyperactivated transposons by facilitating the recruitment of epigenetic repressive marks and preventing the deposition of activating marks at L1-5UTR. HighlightsO_LIp53 loss facilitates accumulation of both cis (L1mRNA-gDNA) and trans (L1mRNA-cDNA) forms of L1 R-loops. C_LIO_LIThe youngest, actively retrotransposing full-length L1s contribute to the formation of trans (L1mRNA-cDNA) R-loops. C_LIO_LIp53 aids immediate L1 re-silencing by restoring deposition of epigenetic repressive and inhibition of activating marks. C_LIO_LIReverse transcriptase inhibitor prevents L1 mediated DNA damage. C_LI Subject Categories: L1/LINE1, p53, Retrotransposons, RNA-DNA hybrids, Cis R loops, Trans R-loop, L1/LINE1 Graphical O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=123 SRC="FIGDIR/small/589154v3_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@1e37111org.highwire.dtl.DTLVardef@11430c8org.highwire.dtl.DTLVardef@8e9c0corg.highwire.dtl.DTLVardef@a6e98d_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗