Damage-induced lncRNAs control the DNA damage response through interaction with DDRNAs at individual double-strand breaks

Pre-ribosomal RNA reorganizes DNA damage repair factors in nucleus during meiotic prophase and DNA damage response

In response to DNA double-strand breaks (DSBs), DNA damage repair factors are recruited to DNA lesions and form nuclear foci. However, the underlying molecular mechanism remains largely elusive. Here, by analyzing the localization of DSB repair factors in the XY body and DSB foci, we demonstrate that pre-ribosomal RNA (pre-rRNA) mediates the recruitment of DSB repair factors around DNA lesions. Pre-rRNA exists in the XY body, a DSB repair hub, during meiotic prophase, and colocalizes with DSB repair factors, such as MDC1, BRCA1 and TopBP1. Moreover, pre-rRNA-associated proteins and RNAs, such as ribosomal protein subunits, RNase MRP and snoRNAs, also localize in the XY body. Similar to those in the XY body, pre-rRNA and ribosomal proteins also localize at DSB foci and associate with DSB repair factors. RNA polymerase I inhibitor treatment that transiently suppresses transcription of rDNA but does not affect global protein translation abolishes foci formation of DSB repair factors as well as DSB repair. The FHA domain and PST repeats of MDC1 recognize pre-rRNA and mediate phase separation of DSB repair factors, which may be the molecular basis for the foci formation of DSB repair factors during DSB response.

Small Cajal body-associated RNA 2 (scaRNA2) regulates DNA repair pathway choice by inhibiting DNA-PK

Evidence that long non-coding RNAs (lncRNAs) participate in DNA repair is accumulating, however, whether they can control DNA repair pathway choice is unknown. Here we show that the small Cajal body-specific RNA 2 (scaRNA2) can promote HR by inhibiting DNA-dependent protein kinase (DNA-PK) and, thereby, NHEJ. By binding to the catalytic subunit of DNA-PK (DNA-PKcs), scaRNA2 weakens its interaction with the Ku70/80 subunits, as well as with the LINP1 lncRNA, thereby preventing catalytic activation of the enzyme. Inhibition of DNA-PK by scaRNA2 stimulates DNA end resection by the MRN/CtIP complex, activation of ATM at DNA lesions and subsequent repair by HR. ScaRNA2 is regulated in turn by WRAP53β, which binds this RNA, sequestering it away from DNA-PKcs and allowing NHEJ to proceed. These findings reveal that RNA-dependent control of DNA-PK catalytic activity is involved in regulating whether the cell utilizes NHEJ or HR.

Proper repair of DNA double-strand breaks is essential for genomic stability. Here, the authors report that a long non-coding RNA, scaRNA2, inhibits DNA-PK and thereby regulates the choice between error-prone NHEJ and error-free HR DNA repair.

Rational design of small-molecules to recognize G-quadruplexes of c-MYC promoter and telomere and the evaluation of their in vivo antitumor activity against breast cancer

DNA G4-structures from human c-MYC promoter and telomere are considered as important drug targets; however, the developing of small-molecule-based fluorescent binding ligands that are highly selective in targeting these G4-structures over other types of nucleic acids is challenging. We herein report a new approach of designing small molecules based on a non-selective thiazole orange scaffold to provide two-directional and multi-site interactions with flanking residues and loops of the G4-motif for better selectivity. The ligands are designed to establish multi-site interactions in the G4-binding pocket. This structural feature may render the molecules higher selectivity toward c-MYC G4s than other structures. The ligand–G4 interaction studied with ¹H NMR may suggest a stacking interaction with the terminal G-tetrad. Moreover, the intracellular co-localization study with BG4 and cellular competition experiments with BRACO-19 may suggest that the binding targets of the ligands in cells are most probably G4-structures. Furthermore, the ligands that either preferentially bind to c-MYC promoter or telomeric G4s are able to downregulate markedly the c-MYC and hTERT gene expression in MCF-7 cells, and induce senescence and DNA damage to cancer cells. The in vivo antitumor activity of the ligands in MCF-7 tumor-bearing mice is also demonstrated.

DNA damage response at telomeres boosts the transcription of SARS-CoV-2 receptor ACE2 during aging

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the coronavirus disease 2019 (COVID-19), known to be more common in the elderly, who also show more severe symptoms and are at higher risk of hospitalization and death. Here, we show that the expression of the angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 cell receptor, increases during aging in mouse and human lungs. ACE2 expression increases upon telomere shortening or dysfunction in both cultured mammalian cells and in vivo in mice. This increase is controlled at the transcriptional level, and Ace2 promoter activity is DNA damage response (DDR)-dependent. Both pharmacological global DDR inhibition of ATM kinase activity and selective telomeric DDR inhibition by the use of antisense oligonucleotides prevent Ace2 upregulation following telomere damage in cultured cells and in mice. We propose that during aging telomere dysfunction due to telomeric shortening or damage triggers DDR activation and this causes the upregulation of ACE2, the SARS-CoV-2 cell receptor, thus contributing to make the elderly more susceptible to the infection.

The various regulatory functions of long noncoding RNAs in apoptosis, cell cycle, and cellular senescence

Long noncoding RNAs (lncRNAs) are a group of noncoding cellular RNAs involved in significant biological phenomena such as differentiation, cell development, genomic imprinting, adjusting the enzymatic activity, regulating chromosome conformation, apoptosis, cell cycle, and cellular senescence. The misregulation of lncRNAs interrupting normal biological processes has been implicated in tumor formation and metastasis, resulting in cancer. Apoptosis and cell cycle, two main biological phenomena, are highly conserved and intimately coupled mechanisms. Hence, some cell cycle regulators can influence both programmed cell death and cell division. Apoptosis eliminates defective and unwanted cells, and the cell cycle enables cells to replicate themselves. The improper regulation of apoptosis and cell cycle contributes to numerous disorders such as neurodegenerative and autoimmune diseases, viral infection, anemia, and mainly cancer. Cellular senescence is a tumor-suppressing response initiated by environmental and internal stress factors. This phenomenon has recently attained more attention due to its therapeutic implications in the field of senotherapy. In this review, the regulatory roles of lncRNAs on apoptosis, cell cycle, and senescence will be discussed. First, the role of lncRNAs in mitochondrial dynamics and apoptosis is addressed. Next, the interaction between lncRNAs and caspases, pro/antiapoptotic proteins, and also EGFR/PI3K/PTEN/AKT/mTORC1 signaling pathway will be investigated. Furthermore, the effect of lncRNAs in the cell cycle is surveyed through interaction with cyclins, cdks, p21, and wnt/β-catenin/c-myc pathway. Finally, the function of essential lncRNAs in cellular senescence is mentioned.

Telomere dysfunction in ageing and age-related diseases

Ageing organisms accumulate senescent cells that are thought to contribute to body dysfunction. Telomere shortening and damage are recognized causes of cellular senescence and ageing. Several human conditions associated with normal ageing are precipitated by accelerated telomere dysfunction. Here, we systematize a large body of evidence and propose a coherent perspective to recognize the broad contribution of telomeric dysfunction to human pathologies.

Crosstalk between Long Non Coding RNAs, microRNAs and DNA Damage Repair in Prostate Cancer: New Therapeutic Opportunities?

Simple Summary

Non-coding RNAs are a type of genetic material that doesn’t make protein, but performs diverse regulatory functions. In prostate cancer, most treatments target proteins, and resistance to such therapies is common, leading to disease progression. Targeting non-coding RNAs may provide alterative treatment options and potentially overcome drug resistance. Major types of non-coding RNAs include tiny ‘microRNAs’ and much longer ‘long non-coding RNAs’. Scientific studies have shown that these form a major part of the human genome, and play key roles in altering gene activity and determining the fate of cells. Importantly, in cancer, their activity is altered. Recent evidence suggests that microRNAs and long non-coding RNAs play important roles in controlling response to DNA damage. In this review, we explore how different types of non-coding RNA interact to control cell DNA damage responses, and how this knowledge may be used to design better prostate cancer treatments and tests.

Abstract

It is increasingly appreciated that transcripts derived from non-coding parts of the human genome, such as long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), are key regulators of biological processes both in normal physiology and disease. Their dysregulation during tumourigenesis has attracted significant interest in their exploitation as novel cancer therapeutics. Prostate cancer (PCa), as one of the most diagnosed malignancies and a leading cause of cancer-related death in men, continues to pose a major public health problem. In particular, survival of men with metastatic disease is very poor. Defects in DNA damage response (DDR) pathways culminate in genomic instability in PCa, which is associated with aggressive disease and poor patient outcome. Treatment options for metastatic PCa remain limited. Thus, researchers are increasingly targeting ncRNAs and DDR pathways to develop new biomarkers and therapeutics for PCa. Increasing evidence points to a widespread and biologically-relevant regulatory network of interactions between lncRNAs and miRNAs, with implications for major biological and pathological processes. This review summarises the current state of knowledge surrounding the roles of the lncRNA:miRNA interactions in PCa DDR, and their emerging potential as predictive and diagnostic biomarkers. We also discuss their therapeutic promise for the clinical management of PCa.

Long noncoding RNA and phase separation in cellular stress response

Stress response is important for sensing and adapting to environmental changes. Recently, RNA-protein condensates, which are a type of membrane-less organelle formed by liquid-liquid phase separation, have been proposed to regulate the stress response. Because RNA-protein condensates are formed through interactions between positively charged proteins and negatively charged RNAs, the ratio of proteins to RNAs is critical for phase-separated condensate formation. In particular, long noncoding RNAs (lncRNAs) can efficiently nucleate phase-separated RNA-protein condensates because of their secondary structure and long length. Therefore, increased attention has been paid to lncRNAs because of their potential role as a regulator of biological condensates by phase separation under stress response. In this review, we summarize the current research on the involvement of lncRNAs in the formation of RNA-protein condensates under stress response. We also demonstrate that lncRNA-driven phase separation provides a useful basis to understanding the response to several kinds of cellular stresses.

Transcription-Replication Coordination

Transcription and replication are the two most essential processes that a cell does with its DNA: they allow cells to express the genomic content that is required for their functions and to create a perfect copy of this genomic information to pass on to the daughter cells. Nevertheless, these two processes are in a constant ambivalent relationship. When transcription and replication occupy the same regions, there is the possibility of conflicts between transcription and replication as transcription can impair DNA replication progression leading to increased DNA damage. Nevertheless, DNA replication origins are preferentially located in open chromatin next to actively transcribed regions, meaning that the possibility of conflicts is potentially an accepted incident for cells. Data in the literature point both towards the existence or not of coordination between these two processes to avoid the danger of collisions. Several reviews have been published on transcription-replication conflicts, but we focus here on the most recent findings that relate to how these two processes are coordinated in eukaryotes, considering advantages and disadvantages from coordination, how likely conflicts are at any given time, and which are their potential hotspots in the genome.

LINC00885 promotes cervical cancer progression through sponging miR-3150b-3p and upregulating BAZ2A

Background

Cervical cancer (CC) is one of the most common malignancies affecting female worldwide. Long non-coding RNAs (lncRNAs) are increasingly indicated as crucial participants and promising therapeutic targets in human cancers. The main objective of this study was to explore the functions and mechanism of LINC00885 in CC.

Methods

RT-qPCR and western blot were used to detect RNA and protein levels. Functional and mechanism assays were respectively done for the analysis of cell behaviors and molecular interplays.

Results

Long intergenic non-coding RNA 885 (LINC00885) was discovered to be upregulated in CC tissues and cell lines through bioinformatics analysis and RT-qPCR. Overexpression of LINC00885 promoted proliferation and inhibited apoptosis, whereas its silence exerted opposite effects. The cytoplasmic localization of LINC00885 was ascertained and furthermore, LINC00885 competitively bound with miR-3150b-3p to upregulate BAZ2A expression in CC cells. Rescue assays confirmed that LINC00885 regulated CC proliferation and apoptosis through miR-3150b-3p/BAZ2A axis. Finally, we confirmed that LINC00885 aggravated tumor growth through animal experiments.

Conclusions

LINC00885 exerted oncogenic function in CC via regulating miR-3150b-3p/BAZ2A axis. These findings suggested LINC00885 might serve as a potential promising therapeutic target for CC patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13062-021-00314-6.

The roles of RNA helicases in DNA damage repair and tumorigenesis reveal precision therapeutic strategies

DEAD-box RNA helicases belong to a large group of RNA processing factors and play vital roles unwinding RNA helices and in ribosomal RNA biogenesis. Emerging evidence indicates that RNA helicases are associated with genome stability, yet the mechanisms behind this association remain poorly understood. In this study, we performed a comprehensive analysis of RNA helicases using multiplatform proteogenomic databases. Over 50% (28/49) of detected RNA helicases were highly expressed in multiple tumor tissues, and more than 60% (17/28) of tumor-associated members were directly involved in DNA damage repair (DDR). Analysis of repair dynamics revealed that these RNA helicases are engaged in an extensively broad range of DDR pathways. Among these factors is DDX21, which was prominently upregulated in colorectal cancer. The high expression of DDX21 gave rise to frequent chromosome exchange and increased genome fragmentation. Mechanistically, aberrantly high expression of DDX21 triggered inappropriate repair processes by delaying homologous recombination repair and increasing replication stress, leading to genome instability and tumorigenesis. Treatment with distinct chemotherapeutic drugs caused higher lethality to cancer cells with genome fragility induced by DDX21, providing a perspective for treatment of tumors with high DDX21 expression. This study revealed the role of RNA helicases in DNA damage and their associations with cancer, which could expand therapeutic strategies and improve precision treatments for cancer patients with high expression of RNA helicases.

Comprehensive analysis to identify DNA damage response-related lncRNA pairs as a prognostic and therapeutic biomarker in gastric cancer

OBJECTIVE

Gastric cancer (GC) is the fifth most common malignancy and the fourth leading cause of cancer-related mortality worldwide. The identification of valuable predictive signatures to improve the prognosis of patients with GC is becoming a realistic prospect. DNA damage response-related long noncoding ribonucleic acids (drlncRNAs) play an important role in the development of cancers. However, their prognostic and therapeutic values remain sparse in gastric cancer (GC).

METHODS

We obtained the transcriptome data and clinical information from The Cancer Genome Atlas Stomach Adenocarcinoma (TCGA-STAD) cohort. Co-expression network analyses were performed to discover functional modules using the igaph package. Subsequently, lncRNA pairs were identified by bioinformation analysis, and prognostic pairs were determined by univariate analysis, respectively. In addition, we utilized least absolute shrinkage and selection operator (LASSO) cox regression analysis to construct the risk model based on lncRNA pairs. Then, we distinguished between the high- or low- risk groups from patients with GC based on the optimal model. Finally, we reevaluated the association between risk score and overall survival, tumor immune microenvironment, specific tumor-infiltrating immune cells related biomarkers, and the sensitivity of chemotherapeutic agents.

RESULTS

32 drlncRNA pairs were obtained, and a 17-drlncRNA pairs signature was constructed to predict the overall survival of patients with GC. The ROC was 0.797, 0.812 and 0.821 at 1, 2, 3 years, respectively. After reclassifying these patients into different risk-groups, we could differentiate between them based on negative overall survival outcome, specialized tumor immune infiltration status, higher expressed immune cell related biomarkers, and a lower chemotherapeutics sensitivity. Compared with previous models, our model showed better performance with a higher ROC value.

CONCLUSION

The prognostic and therapeutic signature established by novel lncRNA pairs could provide promising prediction value, and guide individual treatment strategies in the future.

Early recruitment of PARP-dependent m8A RNA methylation at DNA lesions is subsequently accompanied by active DNA demethylation

RNA methylation, especially 6-methyladenosine (m⁶A)-modified RNAs, plays a specific role in DNA damage response (DDR). Here, we also observe that RNA modified at 8-methyladenosine (m⁸A) is recruited to UVA-damaged chromatin immediately after microirradiation. Interestingly, the level of m⁸A RNA at genomic lesions was reduced after inhibition of histone deacetylases and DNA methyltransferases. It appears in later phases of DNA damage response, accompanied by active DNA demethylation. Also, PARP inhibitor (PARPi), Olaparib, prevented adenosine methylation at microirradiated chromatin. PARPi abrogated not only m⁶A and m⁸A RNA positivity at genomic lesions, but also XRCC1, the factor of base excision repair (BER), did not recognize lesions in DNA. To this effect, Olaparib enhanced the genome-wide level of γH2AX. This histone modification interacted with m⁸A RNAs to a similar extent as m⁸A RNAs with DNA. Pronounced interaction properties we did not observe for m⁶A RNAs and DNA; however, m⁶A RNA interacted with XRCC1 with the highest efficiency, especially in microirradiated cells. Together, we show that the recruitment of m⁶A RNA and m⁸A RNA to DNA lesions is PARP dependent. We suggest that modified RNAs likely play a role in the BER mechanism accompanied by active DNA demethylation. In this process, γH2AX stabilizes m⁶A/m⁸A-positive RNA-DNA hybrid loops via its interaction with m⁸A RNAs. R-loops could represent basic three-stranded structures recognized by PARP-dependent non-canonical m⁶A/m⁸A-mediated DNA repair pathway.

RNA polymerase II is recruited to DNA double-strand breaks for dilncRNA transcription in Drosophila

DNA double-strand breaks are among the most toxic lesions that can occur in a genome and their faithful repair is thus of great importance. Recent findings have uncovered local transcription that initiates at the break and forms a non-coding transcript, called damage-induced long non-coding RNA (dilncRNA), which helps to coordinate the DNA transactions necessary for repair. We provide nascent RNA sequencing-based evidence that RNA polymerase II transcribes the dilncRNA in Drosophila and that this is more efficient for DNA breaks in an intron-containing gene, consistent with the higher damage-induced siRNA levels downstream of an intron. The spliceosome thus stimulates recruitment of RNA polymerase II to the break, rather than merely promoting the annealing of sense and antisense RNA to form the siRNA precursor. In contrast, RNA polymerase III nascent RNA libraries did not contain reads corresponding to the cleaved loci and selective inhibition of RNA polymerase III did not reduce the yield of damage-induced siRNAs. Finally, the damage-induced siRNA density was unchanged downstream of a T8 sequence, which terminates RNA polymerase III transcription. We thus found no evidence for a participation of RNA polymerase III in dilncRNA transcription in cultured Drosophila cells.

Targeting DNA repair pathway in cancer: Mechanisms and clinical application

Over the last decades, the growing understanding on DNA damage response (DDR) pathways has broadened the therapeutic landscape in oncology. It is becoming increasingly clear that the genomic instability of cells resulted from deficient DNA damage response contributes to the occurrence of cancer. One the other hand, these defects could also be exploited as a therapeutic opportunity, which is preferentially more deleterious in tumor cells than in normal cells. An expanding repertoire of DDR-targeting agents has rapidly expanded to inhibitors of multiple members involved in DDR pathways, including PARP, ATM, ATR, CHK1, WEE1, and DNA-PK. In this review, we sought to summarize the complex network of DNA repair machinery in cancer cells and discuss the underlying mechanism for the application of DDR inhibitors in cancer. With the past preclinical evidence and ongoing clinical trials, we also provide an overview of the history and current landscape of DDR inhibitors in cancer treatment, with special focus on the combination of DDR-targeted therapies with other cancer treatment strategies.

LINC02532 Contributes to Radiosensitivity in Clear Cell Renal Cell Carcinoma through the miR-654-5p/YY1 Axis

Background: Studies have shown that long non-coding RNAs (lncRNAs) play essential roles in tumor progression and can affect the response to radiotherapy, including in clear cell renal cell carcinoma (ccRCC). LINC02532 has been found to be upregulated in ccRCC. However, not much is known about this lncRNA. Hence, this study aimed to investigate the role of LINC02532 in ccRCC, especially in terms of radioresistance. Methods: Quantitative real-time PCR was used to detect the expression of LINC02532, miR-654-5p, and YY1 in ccRCC cells. Protein levels of YY1, cleaved PARP, and cleaved-Caspase-3 were detected by Western blotting. Cell survival fractions, viability, and apoptosis were determined by clonogenic survival assays, CCK-8 assays, and flow cytometry, respectively. The interplay among LINC02532, miR-654-5p, and YY1 was detected by chromatin immunoprecipitation and dual-luciferase reporter assays. In addition, in vivo xenograft models were established to investigate the effect of LINC02532 on ccRCC radioresistance in 10 nude mice. Results: LINC02532 was highly expressed in ccRCC cells and was upregulated in the cells after irradiation. Moreover, LINC02532 knockdown enhanced cell radiosensitivity both in vitro and in vivo. Furthermore, YY1 activated LINC02532 in ccRCC cells, and LINC02532 acted as a competing endogenous RNA that sponged miR-654-5p to regulate YY1 expression. Rescue experiments indicated that miR-654-5p overexpression or YY1 inhibition recovered ccRCC cell functions that had been previously impaired by LINC02532 overexpression. Conclusions: Our results revealed a positive feedback loop of LINC02532/miR-654-5p/YY1 in regulating the radiosensitivity of ccRCC, suggesting that LINC02532 might be a potential target for ccRCC radiotherapy. This study could serve as a foundation for further research on the role of LINC02532 in ccRCC and other cancers.

Long non-coding RNAs: novel regulators of cellular physiology and function

Long non-coding RNAs were once considered as “junk” RNA produced by aberrant DNA transcription. They are now understood to play central roles in diverse cellular processes from proliferation and migration to differentiation, senescence and DNA damage control. LncRNAs are classed as transcripts longer than 200 nucleotides that do not encode a peptide. They are relevant to many physiological and pathophysiological processes through their control of fundamental molecular functions. This review summarises the recent progress in lncRNA research and highlights the far-reaching physiological relevance of lncRNAs. The main areas of lncRNA research encompassing their characterisation, classification and mechanisms of action will be discussed. In particular, the regulation of gene expression and chromatin landscape through lncRNA control of proteins, DNA and other RNAs will be introduced. This will be exemplified with a selected number of lncRNAs that have been described in numerous physiological contexts and that should be largely representative of the tens-of-thousands of mammalian lncRNAs. To some extent, these lncRNAs have inspired the current thinking on the central dogmas of epigenetics, RNA and DNA mechanisms.

Phospho-Ku70 induced by DNA damage interacts with RNA Pol II and promotes the formation of phospho-53BP1 foci to ensure optimal cNHEJ

Canonical non-homologous end-joining (cNHEJ) is the prominent mammalian DNA double-strand breaks (DSBs) repair pathway operative throughout the cell cycle. Phosphorylation of Ku70 at ser27-ser33 (pKu70) is induced by DNA DSBs and has been shown to regulate cNHEJ activity, but the underlying mechanism remained unknown. Here, we established that following DNA damage induction, Ku70 moves from nucleoli to the sites of damage, and once linked to DNA, it is phosphorylated. Notably, the novel emanating functions of pKu70 are evidenced through the recruitment of RNA Pol II and concomitant formation of phospho-53BP1 foci. Phosphorylation is also a prerequisite for the dynamic release of Ku70 from the repair complex through neddylation-dependent ubiquitylation. Although the non-phosphorylable ala-Ku70 form does not compromise the formation of the NHEJ core complex per se, cells expressing this form displayed constitutive and stress-inducible chromosomal instability. Consistently, upon targeted induction of DSBs by the I-SceI meganuclease into an intrachromosomal reporter substrate, cells expressing pKu70, rather than ala-Ku70, are protected against the joining of distal DNA ends. Collectively, our results underpin the essential role of pKu70 in the orchestration of DNA repair execution in living cells and substantiated the way it paves the maintenance of genome stability.

Integration of DNA damage responses with dynamic spatial genome organization

The maintenance of genome stability and cellular homeostasis depends on the temporal and spatial coordination of successive events constituting the classical DNA damage response (DDR). Recent findings suggest close integration and coordination of DDR signaling with specific cellular processes. The mechanisms underlying such coordination remain unclear. We review emerging crosstalk between DNA repair factors, chromatin remodeling, replication, transcription, spatial genome organization, cytoskeletal forces, and liquid-liquid phase separation (LLPS) in mediating DNA repair. We present an overarching DNA repair framework within which these dynamic processes intersect in nuclear space over time. Collectively, this interplay ensures the efficient assembly of DNA repair proteins onto shifting genome structures to preserve genome stability and cell survival.

Home and Away: The Role of Non-Coding RNA in Intracellular and Intercellular DNA Damage Response

Non-coding RNA (ncRNA) has recently emerged as a vital component of the DNA damage response (DDR), which was previously believed to be solely regulated by proteins. Many species of ncRNA can directly or indirectly influence DDR and enhance DNA repair, particularly in response to double-strand DNA breaks, which may hold therapeutic potential in the context of cancer. These include long non-coding RNA (lncRNA), microRNA, damage-induced lncRNA, DNA damage response small RNA, and DNA:RNA hybrid structures, which can be categorised as cis or trans based on the location of their synthesis relative to DNA damage sites. Mechanisms of RNA-dependent DDR include the recruitment or scaffolding of repair factors at DNA break sites, the regulation of repair factor expression, and the stabilisation of repair intermediates. DDR can also be communicated intercellularly via exosomes, leading to bystander responses in healthy neighbour cells to generate a population-wide response to damage. Many microRNA species have been directly implicated in the propagation of bystander DNA damage, autophagy, and radioresistance, which may prove significant for enhancing cancer treatment via radiotherapy. Here, we review recent developments centred around ncRNA and their contributions to intracellular and intercellular DDR mechanisms.

HOTAIR beyond repression: In protein degradation, inflammation, DNA damage response, and cell signaling

Long noncoding RNAs (lncRNAs) are pervasively transcribed from the mammalian genome as transcripts that are usually >200 nucleotides long. LncRNAs generally do not encode proteins but are involved in a variety of physiological processes, principally as epigenetic regulators. HOX transcript antisense intergenic RNA (HOTAIR) is a well-characterized lncRNA that has been implicated in several cancers and in various other diseases. HOTAIR is a repressor lncRNA and regulates various repressive chromatin modifications. However, recent studies have revealed additional functions of HOTAIR in regulation of protein degradation, microRNA (miRNA) sponging, NF-κB activation, inflammation, immune signaling, and DNA damage response. Herein, we have summarized the diverse functions and modes of action of HOTAIR in protein degradation, inflammation, DNA repair, and diseases, beyond its established functions in gene silencing.

Inducible and reversible inhibition of miRNA-mediated gene repression in vivo

Although virtually all gene networks are predicted to be controlled by miRNAs, the contribution of this important layer of gene regulation to tissue homeostasis in adult animals remains unclear. Gain and loss-of-function experiments have provided key insights into the specific function of individual miRNAs, but effective genetic tools to study the functional consequences of global inhibition of miRNA activity in vivo are lacking. Here we report the generation and characterization of a genetically engineered mouse strain in which miRNA-mediated gene repression can be reversibly inhibited without affecting miRNA biogenesis or abundance. We demonstrate the usefulness of this strategy by investigating the consequences of acute inhibition of miRNA function in adult animals. We find that different tissues and organs respond differently to global loss of miRNA function. While miRNA-mediated gene repression is essential for the homeostasis of the heart and the skeletal muscle, it is largely dispensable in the majority of other organs. Even in tissues where it is not required for homeostasis, such as the intestine and hematopoietic system, miRNA activity can become essential during regeneration following acute injury. These data support a model where many metazoan tissues primarily rely on miRNA function to respond to potentially pathogenic events.

Transcription-coupled DNA double-strand break repair

The genomic DNA is constantly under attack by cellular and/or environmental factors. Fortunately, the cell is armed to safeguard its genome by various mechanisms such as nucleotide excision, base excision, mismatch and DNA double-strand break repairs. While these processes maintain the integrity of the genome throughout, DNA repair occurs preferentially faster at the transcriptionally active genes. Such transcription-coupled repair phenomenon plays important roles to maintain active genome integrity, failure of which would interfere with transcription, leading to an altered gene expression (and hence cellular pathologies/diseases). Among the various DNA damages, DNA double-strand breaks are quite toxic to the cells. If DNA double-strand break occurs at the active gene, it would interfere with transcription/gene expression, thus threatening cellular viability. Such DNA double-strand breaks are found to be repaired faster at the active gene in comparison to its inactive state or the inactive gene, thus supporting the existence of a new phenomenon of transcription-coupled DNA double-strand break repair. Here, we describe the advances of this repair process.

DNA Polymerase θ: A Cancer Drug Target with Reverse Transcriptase Activity

The emergence of precision medicine from the development of Poly (ADP-ribose) polymerase (PARP) inhibitors that preferentially kill cells defective in homologous recombination has sparked wide interest in identifying and characterizing additional DNA repair enzymes that are synthetic lethal with HR factors. DNA polymerase theta (Polθ) is a validated anti-cancer drug target that is synthetic lethal with HR factors and other DNA repair proteins and confers cellular resistance to various genotoxic cancer therapies. Since its initial characterization as a helicase-polymerase fusion protein in 2003, many exciting and unexpected activities of Polθ in microhomology-mediated end-joining (MMEJ) and translesion synthesis (TLS) have been discovered. Here, we provide a short review of Polθ's DNA repair activities and its potential as a drug target and highlight a recent report that reveals Polθ as a naturally occurring reverse transcriptase (RT) in mammalian cells.

Dealing with transcription-blocking DNA damage: Repair mechanisms, RNA polymerase II processing and human disorders

Transcription-blocking DNA lesions (TBLs) in genomic DNA are triggered by a wide variety of DNA-damaging agents. Such lesions cause stalling of elongating RNA polymerase II (RNA Pol II) enzymes and fully block transcription when unresolved. The toxic impact of DNA damage on transcription progression is commonly referred to as transcription stress. In response to RNA Pol II stalling, cells activate and employ transcription-coupled repair (TCR) machineries to repair cytotoxic TBLs and resume transcription. Increasing evidence indicates that the modification and processing of stalled RNA Pol II is an integral component of the cellular response to and the repair of TBLs. If TCR pathways fail, the prolonged stalling of RNA Pol II will impede global replication and transcription as well as block the access of other DNA repair pathways that may act upon the TBL. Consequently, such prolonged stalling will trigger profound genome instability and devastating clinical features. In this review, we will discuss the mechanisms by which various types of TBLs are repaired by distinct TCR pathways and how RNA Pol II processing is regulated during these processes. We will also discuss the clinical consequences of transcription stress and genotype-phenotype correlations of related TCR-deficiency disorders.

Oxidative Stress Induces Telomere Dysfunction and Shortening in Human Oocytes of Advanced Age Donors

Research from the past decades provided strong evidence that in humans the pool of oocytes starts to decline already before the birth of a female individual, and from menarche to menopause the oocyte is exposed to different environmental stimuli. Since more and more women of the 21st century in developed countries wish to postpone the first pregnancy to their thirties, higher rates of miscarriage and chromosomal non-disjunction might occur. In oocytes of advanced maternal age, meaning above 35 years of age, characteristics such as chromosomal instabilities/abnormalities, spindle defects, decreased mitochondrial function and telomere shortening become more prevalent than in younger counterparts. Telomere attrition belongs to the so-called “hallmarks of aging” which are also relevant for the female germ-line cells. In oocytes, telomeres shorten with advancing maternal age due to the effects of reactive oxygen species and not upon replicative senescence, similar to how it is common in dividing cells.

Role of mammalian long non-coding RNAs in normal and neuro oncological disorders

Long non-coding RNAs (lncRNAs) are expressed at lower levels than protein-coding genes but have a crucial role in gene regulation. LncRNA is distinct, they are being transcribed using RNA polymerase II, and their functionality depends on subcellular localization. Depending on their niche, they specifically interact with DNA, RNA, and proteins and modify chromatin function, regulate transcription at various stages, forms nuclear condensation bodies and nucleolar organization. lncRNAs may also change the stability and translation of cytoplasmic mRNAs and hamper signaling pathways. Thus, lncRNAs affect the physio-pathological states and lead to the development of various disorders, immune responses, and cancer. To date, ~40% of lncRNAs have been reported in the nervous system (NS) and are involved in the early development/differentiation of the NS to synaptogenesis. LncRNA expression patterns in the most common adult and pediatric tumor suggest them as potential biomarkers and provide a rationale for targeting them pharmaceutically. Here, we discuss the mechanisms of lncRNA synthesis, localization, and functions in transcriptional, post-transcriptional, and other forms of gene regulation, methods of lncRNA identification, and their potential therapeutic applications in neuro oncological disorders as explained by molecular mechanisms in other malignant disorders.

Commuting to Work: Nucleolar Long Non-Coding RNA Control Ribosome Biogenesis from Near and Far

Gene expression is an essential process for cellular growth, proliferation, and differentiation. The transcription of protein-coding genes and non-coding loci depends on RNA polymerases. Interestingly, numerous loci encode long non-coding (lnc)RNA transcripts that are transcribed by RNA polymerase II (RNAPII) and fine-tune the RNA metabolism. The nucleolus is a prime example of how different lncRNA species concomitantly regulate gene expression by facilitating the production and processing of ribosomal (r)RNA for ribosome biogenesis. Here, we summarise the current findings on how RNAPII influences nucleolar structure and function. We describe how RNAPII-dependent lncRNA can both promote nucleolar integrity and inhibit ribosomal (r)RNA synthesis by modulating the availability of rRNA synthesis factors in trans. Surprisingly, some lncRNA transcripts can directly originate from nucleolar loci and function in cis. The nucleolar intergenic spacer (IGS), for example, encodes nucleolar transcripts that counteract spurious rRNA synthesis in unperturbed cells. In response to DNA damage, RNAPII-dependent lncRNA originates directly at broken ribosomal (r)DNA loci and is processed into small ncRNA, possibly to modulate DNA repair. Thus, lncRNA-mediated regulation of nucleolar biology occurs by several modes of action and is more direct than anticipated, pointing to an intimate crosstalk of RNA metabolic events.

The multi-functionality of UHRF1: epigenome maintenance and preservation of genome integrity

During S phase, the cooperation between the macromolecular complexes regulating DNA synthesis, epigenetic information maintenance and DNA repair is advantageous for cells, as they can rapidly detect DNA damage and initiate the DNA damage response (DDR). UHRF1 is a fundamental epigenetic regulator; its ability to coordinate DNA methylation and histone code is unique across proteomes of different species. Recently, UHRF1’s role in DNA damage repair has been explored and recognized to be as important as its role in maintaining the epigenome. UHRF1 is a sensor for interstrand crosslinks and a determinant for the switch towards homologous recombination in the repair of double-strand breaks; its loss results in enhanced sensitivity to DNA damage. These functions are finely regulated by specific post-translational modifications and are mediated by the SRA domain, which binds to damaged DNA, and the RING domain. Here, we review recent studies on the role of UHRF1 in DDR focusing on how it recognizes DNA damage and cooperates with other proteins in its repair. We then discuss how UHRF1’s epigenetic abilities in reading and writing histone modifications, or its interactions with ncRNAs, could interlace with its role in DDR.

Non-homologous end-joining at challenged replication forks: an RNA connection?

Defective DNA replication, known as 'replication stress', is a source of DNA damage, a hallmark of numerous human diseases, including cancer, developmental defect, neurological disorders, and premature aging. Recent work indicates that non-homologous end-joining (NHEJ) is unexpectedly active during DNA replication to repair replication-born DNA lesions and to safeguard replication fork integrity. However, erroneous NHEJ events are deleterious to genome stability. RNAs are novel regulators of NHEJ activity through their ability to modulate the assembly of repair complexes in trans. At DNA damage sites, RNAs and DNA-embedded ribonucleotides modulate repair efficiency and fidelity. We discuss here how RNAs and associated proteins, including RNA binding proteins, may regulate NHEJ to sustain genome stability during DNA replication.

RNAi and Ino80 complex control rate limiting translocation step that moves rDNA to eroding telomeres

The discovery of HAATIrDNA, a telomerase-negative survival mode in which canonical telomeres are replaced with ribosomal DNA (rDNA) repeats that acquire chromosome end-protection capability, raised crucial questions as to how rDNA tracts 'jump' to eroding chromosome ends. Here, we show that HAATIrDNA formation is initiated and limited by a single translocation that juxtaposes rDNA from Chromosome (Chr) III onto subtelomeric elements (STE) on Chr I or II; this rare reaction requires RNAi and the Ino80 nucleosome remodeling complex (Ino80C), thus defining an unforeseen relationship between these two machineries. The unique STE-rDNA junction created by this initial translocation is efficiently copied to the remaining STE chromosome ends, independently of RNAi or Ino80C. Intriguingly, both RNAi and Ino80C machineries contain a component that plays dual roles in HAATI subtype choice. Dcr1 of the RNAi pathway and Iec1 of Ino80C both promote HAATIrDNA formation as part of their respective canonical machineries, but both also inhibit formation of the exceedingly rare HAATISTE (where STE sequences mobilize throughout the genome and assume chromosome end protection capacity) in non-canonical, pathway-independent manners. This work provides a glimpse into a previously unrecognized crosstalk between RNAi and Ino80C in controlling unusual translocation reactions that establish telomere-free linear chromosome ends.

DNA-RNA hybrids at DSBs interfere with repair by homologous recombination

DNA double-strand breaks (DSBs) are the most harmful DNA lesions and their repair is crucial for cell viability and genome integrity. The readout of DSB repair may depend on whether DSBs occur at transcribed versus non-transcribed regions. Some studies have postulated that DNA-RNA hybrids form at DSBs to promote recombinational repair, but others have challenged this notion. To directly assess whether hybrids formed at DSBs promote or interfere with the recombinational repair, we have used plasmid and chromosomal-based systems for the analysis of DSB-induced recombination in Saccharomyces cerevisiae. We show that, as expected, DNA-RNA hybrid formation is stimulated at DSBs. In addition, mutations that promote DNA-RNA hybrid accumulation, such as hpr1∆ and rnh1∆ rnh201∆, cause high levels of plasmid loss when DNA breaks are induced at sites that are transcribed. Importantly, we show that high levels or unresolved DNA-RNA hybrids at the breaks interfere with their repair by homologous recombination. This interference is observed for both plasmid and chromosomal recombination and is independent of whether the DSB is generated by endonucleolytic cleavage or by DNA replication. These data support a model in which DNA-RNA hybrids form fortuitously at DNA breaks during transcription and need to be removed to allow recombinational repair, rather than playing a positive role.

Non-coding RNAs in chromatin folding and nuclear organization

One of the most intriguing questions facing modern biology concerns how the genome directs the construction of cells, tissues, and whole organisms. It is tempting to suggest that the part of the genome that does not encode proteins contains architectural plans. We are still far from understanding how these plans work at the level of building tissues and the body as a whole. However, the results of recent studies demonstrate that at the cellular level, special non-coding RNAs serve as scaffolds for the construction of various intracellular structures. The term "architectural RNAs" was proposed to designate this subset of non-coding RNAs. In this review, we discuss the role of architectural RNAs in the construction of the cell nucleus and maintenance of the three-dimensional organization of the genome.

The evolving complexity of DNA damage foci: RNA, condensates and chromatin in DNA double-strand break repair

Formation of biomolecular condensates is increasingly recognized as a mechanism employed by cells to deal with stress and to optimize enzymatic reactions. Recent studies have characterized several DNA repair foci as phase-separated condensates, behaving like liquid droplets. Concomitantly, the apparent importance of long non-coding RNAs and RNA-binding proteins for the repair of double-strand breaks has raised many questions about their exact contribution to the repair process. Here we discuss how RNA molecules can participate in condensate formation and how RNA-binding proteins can act as molecular scaffolds. We furthermore summarize our current knowledge about how properties of condensates can influence the choice of repair pathway (homologous recombination or non-homologous end joining) and identify the open questions in this field of emerging importance.

A Non-Coding RNA Network Involved in KSHV Tumorigenesis

Regulatory pathways involving non-coding RNAs (ncRNAs), such as microRNAs (miRNAs) and long non-coding RNAs (lncRNA), have gained great relevance due to their role in the control of gene expression modulation. Using RNA sequencing of KSHV Bac36 transfected mouse endothelial cells (mECK36) and tumors, we have analyzed the host and viral transcriptome to uncover the role lncRNA-miRNA-mRNA driven networks in KSHV tumorigenesis. The integration of the differentially expressed ncRNAs, with an exhaustive computational analysis of their experimentally supported targets, led us to dissect complex networks integrated by the cancer-related lncRNAs Malat1, Neat1, H19, Meg3, and their associated miRNA-target pairs. These networks would modulate pathways related to KSHV pathogenesis, such as viral carcinogenesis, p53 signaling, RNA surveillance, and cell cycle control. Finally, the ncRNA-mRNA analysis allowed us to develop signatures that can be used to an appropriate identification of druggable gene or networks defining relevant AIDS-KS therapeutic targets.

Recruitment of KMT2C/MLL3 to DNA Damage Sites Mediates DNA Damage Responses and Regulates PARP Inhibitor Sensitivity in Cancer

When recruited to promoters, histone 3 lysine 4 (H3K4) methyltransferases KMT2 (KMT2A-D) activate transcription by opening chromatin through H3K4 methylation. Here, we report that KMT2 mutations occur frequently in non-small cell lung cancer (NSCLC) and are associated with high mutation loads and poor survival. KMT2C regulated DNA damage responses (DDR) through direct recruitment to DNA damage sites by Ago2 and small noncoding DNA damage response RNA, where it mediates H3K4 methylation, chromatin relaxation, secondary recruitment of DDR factors, and amplification of DDR signals along chromatin. Furthermore, by disrupting homologous recombination (HR)-mediated DNA repair, KMT2C/D mutations sensitized NSCLC to Poly(ADP-ribose) polymerase inhibitors (PARPi), whose efficacy is unclear in NSCLC due to low BRCA1/2 mutation rates. These results demonstrate a novel, transcription-independent role of KMT2C in DDR and identify high-frequency KMT2C/D mutations as much-needed biomarkers for PARPi therapies in NSCLC and other cancers with infrequent BRCA1/2 mutations. SIGNIFICANCE: This study uncovers a critical role for KMT2C in DDR via direct recruitment to DNA damage sites, identifying high-frequency KMT2C/D mutations as biomarkers for response to PARP inhibition in cancer.

The Ultimate (Mis)match: When DNA Meets RNA

RNA-containing structures, including ribonucleotide insertions, DNA:RNA hybrids and R-loops, have recently emerged as critical players in the maintenance of genome integrity. Strikingly, different enzymatic activities classically involved in genome maintenance contribute to their generation, their processing into genotoxic or repair intermediates, or their removal. Here we review how this substrate promiscuity can account for the detrimental and beneficial impacts of RNA insertions during genome metabolism. We summarize how in vivo and in vitro experiments support the contribution of DNA polymerases and homologous recombination proteins in the formation of RNA-containing structures, and we discuss the role of DNA repair enzymes in their removal. The diversity of pathways that are thus affected by RNA insertions likely reflects the ancestral function of RNA molecules in genome maintenance and transmission.

Senataxin Ortholog Sen1 Limits DNA:RNA Hybrid Accumulation at DNA Double-Strand Breaks to Control End Resection and Repair Fidelity

An important but still enigmatic function of DNA:RNA hybrids is their role in DNA double-strand break (DSB) repair. Here, we show that Sen1, the budding yeast ortholog of the human helicase Senataxin, is recruited at an HO endonuclease-induced DSB and limits the local accumulation of DNA:RNA hybrids. In the absence of Sen1, hybrid accumulation proximal to the DSB promotes increased binding of the Ku70-80 (KU) complex at the break site, mutagenic non-homologous end joining (NHEJ), micro-homology-mediated end joining (MMEJ), and chromosome translocations. We also show that homology-directed recombination (HDR) by gene conversion is mostly proficient in sen1 mutants after single DSB. However, in the absence of Sen1, DNA:RNA hybrids, Mre11, and Dna2 initiate resection through a non-canonical mechanism. We propose that this resection mechanism through local DNA:RNA hybrids acts as a backup to prime HDR when canonical pathways are altered, but at the expense of genome integrity.

RNA transcripts stimulate homologous recombination by forming DR-loops

Homologous recombination (HR) repairs DNA double-strand breaks (DSBs) in the S and G2 phases of the cell cycle1-3. Several HR proteins are preferentially recruited to DSBs at transcriptionally active loci4-10, but how transcription promotes HR is poorly understood. Here we develop an assay to assess the effect of local transcription on HR. Using this assay, we find that transcription stimulates HR to a substantial extent. Tethering RNA transcripts to the vicinity of DSBs recapitulates the effects of local transcription, which suggests that transcription enhances HR through RNA transcripts. Tethered RNA transcripts stimulate HR in a sequence- and orientation-dependent manner, indicating that they function by forming DNA-RNA hybrids. In contrast to most HR proteins, RAD51-associated protein 1 (RAD51AP1) only promotes HR when local transcription is active. RAD51AP1 drives the formation of R-loops in vitro and is required for tethered RNAs to stimulate HR in cells. Notably, RAD51AP1 is necessary for the DSB-induced formation of DNA-RNA hybrids in donor DNA, linking R-loops to D-loops. In vitro, RAD51AP1-generated R-loops enhance the RAD51-mediated formation of D-loops locally and give rise to intermediates that we term 'DR-loops', which contain both DNA-DNA and DNA-RNA hybrids and favour RAD51 function. Thus, at DSBs in transcribed regions, RAD51AP1 promotes the invasion of RNA transcripts into donor DNA, and stimulates HR through the formation of DR-loops.

Untangling the crosstalk between BRCA1 and R-loops during DNA repair

R-loops are RNA:DNA hybrids assembled during biological processes but are also linked to genetic instability when formed out of their natural context. Emerging evidence suggests that the repair of DNA double-strand breaks requires the formation of a transient R-loop, which eventually must be removed to guarantee a correct repair process. The multifaceted BRCA1 protein has been shown to be recruited at this specific break-induced R-loop, and it facilitates mechanisms in order to regulate R-loop removal. In this review, we discuss the different potential roles of BRCA1 in R-loop homeostasis during DNA repair and how these processes ensure faithful DSB repair.

Disruption of a ∼23-24 nucleotide small RNA pathway elevates DNA damage responses in Tetrahymena thermophila

Endogenous RNA interference (RNAi) pathways regulate a wide range of cellular processes in diverse eukaryotes, yet in the ciliated eukaryote, Tetrahymena thermophila, the cellular purpose of RNAi pathways that generate ∼23–24 nucleotide (nt) small (s)RNAs has remained unknown. Here, we investigated the phenotypic and gene expression impacts on vegetatively growing cells when genes involved in ∼23–24 nt sRNA biogenesis are disrupted. We observed slower proliferation and increased expression of genes involved in DNA metabolism and chromosome organization and maintenance in sRNA biogenesis mutants RSP1Δ, RDN2Δ, and RDF2Δ. In addition, RSP1Δ and RDN2Δ cells frequently exhibited enlarged chromatin extrusion bodies, which are nonnuclear, DNA-containing structures that may be akin to mammalian micronuclei. Expression of homologous recombination factor Rad51 was specifically elevated in RSP1Δ and RDN2Δ strains, with Rad51 and double-stranded DNA break marker γ-H2A.X localized to discrete macronuclear foci. In addition, an increase in Rad51 and γ-H2A.X foci was also found in knockouts of TWI8, a macronucleus-localized PIWI protein. Together, our findings suggest that an evolutionarily conserved role for RNAi pathways in maintaining genome integrity may be extended even to the early branching eukaryotic lineage that gave rise to Tetrahymena thermophila.

Molecular Mechanisms of Specific Cellular DNA Damage Response and Repair Induced by the Mixed Radiation Field During Boron Neutron Capture Therapy

The impact of a mixed neutron-gamma beam on the activation of DNA damage response (DDR) proteins and non-coding RNAs (ncRNAs) is poorly understood. Ionizing radiation is characterized by its biological effectiveness and is related to linear energy transfer (LET). Neutron-gamma mixed beam used in boron neutron capture therapy (BNCT) can induce another type of DNA damage such as clustered DNA or multiple damaged sites, as indicated for high LET particles, such as alpha particles, carbon ions, and protons. We speculate that after exposure to a mixed radiation field, the repair capacity might reduce, leading to unrepaired complex DNA damage for a long period and may promote genome instability and cell death. This review will focus on the poorly studied impact of neutron-gamma mixed beams with an emphasis on DNA damage and molecular mechanisms of repair. In case of BNCT, it is not clear which repair pathway is involved, and recent experimental work will be presented. Further understanding of BNCT-induced DDR mechanisms may lead to improved therapeutic efficiency against different tumors.

Alternative Splicing of Human Telomerase Reverse Transcriptase (hTERT) and Its Implications in Physiological and Pathological Processes

Alternative splicing (AS) of human telomerase catalytic subunit (hTERT, human telomerase reverse transcriptase) pre-mRNA strongly regulates telomerase activity. Several proteins can regulate AS in a cell type-specific manner and determine the functions of cells. In addition to being involved in telomerase activity regulation, AS provides cells with different splice variants that may have alternative biological activities. The modulation of telomerase activity through the induction of hTERT AS is involved in the development of different cancer types and embryos, and the differentiation of stem cells. Regulatory T cells may suppress the proliferation of target human and murine T and B lymphocytes and NK cells in a contact-independent manner involving activation of TERT AS. This review focuses on the mechanism of regulation of hTERT pre-mRNA AS and the involvement of splice variants in physiological and pathological processes.

New Faces of old Friends: Emerging new Roles of RNA-Binding Proteins in the DNA Double-Strand Break Response

DNA double-strand breaks (DSBs) are highly cytotoxic DNA lesions. To protect genomic stability and ensure cell homeostasis, cells mount a complex signaling-based response that not only coordinates the repair of the broken DNA strand but also activates cell cycle checkpoints and, if necessary, induces cell death. The last decade has seen a flurry of studies that have identified RNA-binding proteins (RBPs) as novel regulators of the DSB response. While many of these RBPs have well-characterized roles in gene expression, it is becoming increasingly clear that they also have non-canonical functions in the DSB response that go well beyond transcription, splicing and mRNA processing. Here, we review the current understanding of how RBPs are integrated into the cellular response to DSBs and describe how these proteins directly participate in signal transduction, amplification and repair at damaged chromatin. In addition, we discuss the implications of an RBP-mediated DSB response for genome instability and age-associated diseases such as cancer and neurodegeneration.

FUS-dependent liquid-liquid phase separation is important for DNA repair initiation

RNA-binding proteins (RBPs) are emerging as important effectors of the cellular DNA damage response (DDR). The RBP FUS is implicated in RNA metabolism and DNA repair, and it undergoes reversible liquid-liquid phase separation (LLPS) in vitro. Here, we demonstrate that FUS-dependent LLPS is necessary for the initiation of the DDR. Using laser microirradiation in FUS-knockout cells, we show that FUS is required for the recruitment to DNA damage sites of the DDR factors KU80, NBS1, and 53BP1 and of SFPQ, another RBP implicated in the DDR. The relocation of KU80, NBS1, and SFPQ is similarly impaired by LLPS inhibitors, or LLPS-deficient FUS variants. We also show that LLPS is necessary for efficient γH2AX foci formation. Finally, using superresolution structured illumination microscopy, we demonstrate that the absence of FUS impairs the proper arrangement of γH2AX nanofoci into higher-order clusters. These findings demonstrate the early requirement for FUS-dependent LLPS in the activation of the DDR and the proper assembly of DSB repair complexes.

Chromatin-associated MRN complex protects highly transcribing genes from genomic instability

MRN-MDC1 plays a central role in the DNA damage response (DDR) and repair. Using proteomics of isolated chromatin fragments, we identified DDR factors, such as MDC1, among those highly associating with a genomic locus upon transcriptional activation. Purification of MDC1 in the absence of exogenous DNA damage revealed interactions with factors involved in gene expression and RNA processing, in addition to DDR factors. ChIP-seq showed that MRN subunits, MRE11 and NBS1, colocalized throughout the genome, notably at TSSs and bodies of actively transcribing genes, which was dependent on the RNAPII transcriptional complex rather than transcription per se. Depletion of MRN increased RNAPII abundance at MRE11/NBS1-bound genes. Prolonged MRE11 or NBS1 depletion induced single-nucleotide polymorphisms across actively transcribing MRN target genes. These data suggest that association of MRN with the transcriptional machinery constitutively scans active genes for transcription-induced DNA damage to preserve the integrity of the coding genome.

The Emerging Role of RNA Modifications in DNA Double-Strand Break Repair

The correct repair of DNA double-strand breaks is essential for maintaining the stability of the genome, thus ensuring the survival and fitness of any living organism. Indeed, the repair of these lesions is a complicated affair, in which several pathways compete for the DNA ends in a complex balance. Thus, the fine-tuning of the DNA double-strand break repair pathway choice relies on the different regulatory layers that respond to environmental cues. Among those different tiers of regulation, RNA modifications have just emerged as a promising field.