Dicer Complex Research Articles

Dicer-Mediated mTORC1 Signaling and Parathyroid Gland Integrity and Function.

Secondary hyperparathyroidism of CKD contributes significantly to patient morbidity and mortality. The underlining mechanisms of CKD-induced secondary hyperparathyroidism remain elusive. We previously demonstrated that PT-Dicer-/- mice, with parathyroid specific deletion of the miRNA processing enzyme Dicer and consequently miRNA maintain normal basal serum PTH levels but do not develop secondary hyperparathyroidism induced by CKD. Additionally, we showed that the parathyroid mTORC1 pathway is activated in CKD. We now explored the roles of Dicer/miRNA and mTORC1 in parathyroid development and function. We generated mice with parathyroid specific Dicer (PT-Dicer-/-), mTOR (PT-mTOR-/-) or tuberous sclerosis complex 1 (PT-Tsc1-/-) deficiency combined with YFP or tdTomato expression, to identify the parathyroids by fluorescent microscopy. CKD was induced by an adenine-rich high phosphate diet. Despite normal basal serum PTH levels, PT-Dicer-/- mice displayed apoptotic loss of intact parathyroid glands postnatally, and reduced mTOR activity. PT-mTOR-/- mice lacked intact parathyroid glands, yet maintained normal serum PTH levels, mirroring the phenotype of PT-Dicer-/- mice. Conversely, PT-Tsc1-/- mice with hyperactivated mTORC1, exhibited enlarged glands along with elevated basal serum PTH and calcium levels. Significantly, PT-Dicer-/-;Tsc1-/- double knockout mice, preserved intact parathyroid glands and reinstated CKD-induced secondary hyperparathyroidism. mTORC1 operates downstream of Dicer and miRNA in the parathyroid and is essential for maintaining postnatal parathyroid gland integrity throughout life and for the pathogenesis of CKD-induced secondary hyperparathyroidism.

Promiscuous splicing-derived hairpins are dominant substrates of tailing-mediated defense of miRNA biogenesis in mammals.

Canonical microRNA (miRNA) hairpins are processed by the RNase III enzymes Drosha and Dicer into ∼22 nt RNAs loaded into an Argonaute (Ago) effector. In addition, splicing generates numerous intronic hairpins that bypass Drosha (mirtrons) to yield mature miRNAs. Here, we identify hundreds of previously unannotated, splicing-derived hairpins in intermediate-length (∼50-100 nt) but not small (20-30 nt) RNA data. Since we originally defined mirtrons from small RNA duplexes, we term this larger set as structured splicing-derived RNAs (ssdRNAs). These associate with Dicer and/or Ago complexes, but generally accumulate modestly and are poorly conserved. We propose they contaminate the canonical miRNA pathway, which consequently requires defense against the siege of splicing-derived substrates. Accordingly, ssdRNAs/mirtrons comprise dominant hairpin substrates for 3' tailing by multiple terminal nucleotidyltransferases, notably TUT4/7 and TENT2. Overall, the rampant proliferation of young mammalian mirtrons/ssdRNAs, coupled with an inhibitory molecular defense, comprises a Red Queen's race of intragenomic conflict.

Evidence of A Negative Feedback Network Between TDP-43 and miRNAs Dependent on TDP-43 Nuclear Localization

TAR DNA-binding protein 43 (TDP-43) is a DNA/RNA-binding protein that is integral to RNA processing. Among these functions is a critical role in microRNA (miRNA) biogenesis through interactions with the DROSHA and DICER complexes. It has been previously shown that there is a general reduction in miRNA levels within the spinal cord and spinal motor neurons of amyotrophic lateral sclerosis (ALS) patients. In addition, the most common pathological feature of ALS is re-distribution of TDP-43 from the nucleus to the cytoplasm where it forms cytoplasmic inclusions. Among miRNAs dysregulated in ALS, several are known to regulate TDP-43 expression. In this study, we demonstrate that TDP-43 is in a regulatory negative feedback network with miR-181c-5p and miR-27b-3p that is dependent on its nuclear localization within HEK293T cells. Further, we show that cellular stress which induces a redistribution of TDP-43 from the nucleus to the cytoplasm correlates with the reduced production of miR-27b-3p and miR-181c-5p. This suggests that reduced nuclear TDP-43 disrupts a negative feedback network between itself and miRNAs. These findings provide a further understanding of altered miRNA biogenesis as a key pathogenic process in ALS.

DOT1L complex suppresses transcription from enhancer elements and ectopic RNAi in Caenorhabditis elegans.

Methylation of histone H3 on lysine 79 (H3K79) by DOT1L is associated with actively transcribed genes. Earlier, we described that DOT-1.1, the Caenorhabditis elegans homolog of mammalian DOT1L, cooperates with the chromatin-binding protein ZFP-1 (AF10 homolog) to negatively modulate transcription of highly and widely expressed target genes. Also, the reduction of ZFP-1 levels has consistently been associated with lower efficiency of RNA interference (RNAi) triggered by exogenous double-stranded RNA (dsRNA), but the reason for this is not clear. Here, we demonstrate that the DOT1L complex suppresses transcription originating from enhancer elements and antisense transcription, thus potentiating the expression of enhancer-regulated genes. We also show that worms lacking H3K79 methylation do not survive, and this lethality is suppressed by a loss of caspase-3 or Dicer complex components that initiate gene silencing response to exogenous dsRNA. Our results suggest that ectopic elevation of endogenous dsRNA directly or indirectly resulting from global misregulation of transcription in DOT1L complex mutants may engage the Dicer complex and, therefore, limit the efficiency of exogenous RNAi.

Evidence for Host Epigenetic Signatures Arising From Arbovirus Infections: A Systematic Review

Background: Arbovirus infections have steadily become a major pandemic threat. This study aimed at investigating the existence of host epigenetic markers arising from the principal arboviruses infections impacting on human health. We set to systematically review all published evidence describing any epigenetic modifications associated with infections from arboviruses, including, but not limited to, microRNAs, DNA methylation, and histone modifications.Methods: A comprehensive search was conducted using the electronic databases PubMed, Science Direct and Cochrane Library from inception to January 4th, 2018. We included reports describing original in vivo or in vitro studies investigating epigenetic changes related to arbovirus infections in either clinical subjects or human cell lines. Studies investigating epigenetic modifications related to the virus or the arthropod vector were excluded. A narrative synthesis of the findings was conducted, contextualizing comparative evidence from in vitro and in vivo studies.Results: A total of 853 unique references were identified and screened by two independent researchers. Thirty-two studies met the inclusion criteria and were reviewed. The evidence was centered mainly on microRNA and DNA methylation signatures implicated with secondary Dengue fever. Evidence for recent epidemic threats, such as the infections by Zika or Chikungunya viruses is still scant.Conclusions: Major epigenetic alterations found on arboviruses infections were miR-146, miR-30e and the Dicer complex. However, existing studies frequently tested distinct hypotheses resulting in a heterogeneity of methodological approaches. Whilst epigenetic signatures associated with arbovirus infections have been reported, existing studies have largely focused on a small number of diseases, particularly dengue. Validation of epigenetic signatures have an untapped potential, but concerted investigations are certainly required to deliver robust candidates of clinical utility for diagnosis, staging and prognosis of specific arboviral diseases.

Regulation of microRNA biogenesis and its crosstalk with other cellular pathways

MicroRNAs (miRNAs) are short non-coding RNAs that inhibit the expression of target genes by directly binding to their mRNAs. miRNAs are transcribed as precursor molecules, which are subsequently cleaved by the endoribonucleases Drosha and Dicer. Mature miRNAs are bound by a member of the Argonaute (AGO) protein family to form the RNA-induced silencing complex (RISC) in a process termed RISC loading. Advances in structural analyses of Drosha and Dicer complexes enabled elucidation of the mechanisms that drive these molecular machines. Transcription of miRNAs, their processing by Drosha and Dicer and RISC loading are key steps in miRNA biogenesis, and various additional factors facilitate, support or inhibit these processes. Recent work has revealed that regulatory factors not only coordinate individual miRNA processing steps but also connect miRNA biogenesis with other cellular processes. Protein phosphorylation, for example, links miRNA biogenesis to various signalling pathways, and such modifications are often associated with disease. Furthermore, not all miRNAs follow canonical processing routes, and many non-canonical miRNA biogenesis pathways have recently been characterized.

Technology of RNA Interference in Advanced Medicine.

RNA interference (RNAi) and related pathways involving small interfering RNAs (siRNAs), microRNAs (miRNAs), and PIWI-interacting RNAs (piRNAs) regulate processes such as antiviral defense, genome surveillance, heterochromatin formation, and gene expression in animals, plants, and fungi. Studies on RNAi have revealed a two-step mechanism: (i) Degradation of dsRNA into small interfering RNAs (siRNAs), 21 to 25 nucleotides long, by an RNase III-like activity. (ii) The siRNAs join an RNase complex, RISC (RNA-induced silencing complex), which acts on the mRNA and degrades it. Molecular structures of Dicer, Argonaute proteins, and RNA-bound complexes have offered insights into the underlying mechanisms of RNA-silencing pathways. Sequence specific gene silencing using small interfering RNA (siRNA) is now being evaluated as a novel therapeutic strategy. Recently, promising data have been obtained from clinical trials for the treatment of respiratory syncytial virus and age-related macular degeneration. The exact mechanism of the RNAi pathways is still unclear. Our review summarizes the RNAi pathways and the known functions of siRNAs, miRNAs, and piRNAs in lower and higher organisms (mostly focusing on mammals) and discusses the potential applications of RNAi.

Abstract 161: β-Arrestin-Biased Agonism of β-Adrenergic Receptor Regulates Dicer-mediated MicroRNA Maturation to Promote Cardioprotective Signaling

MicroRNAs (miRs) are small, non-coding RNAs that function to post-transcriptionally regulate gene expression. First transcribed as primary miR transcripts (pri-miRs), they are enzymatically processed by Drosha into premature miRs (pre-miRs) and further processed by Dicer into mature miRs. Initially discovered to desensitize β-adrenergic receptor (βAR) signaling, β-arrestins are now well-appreciated to modulate multiple effector pathways independent of G protein-mediated signaling, a concept known as biased signaling. Using the β-arrestin-biased βAR ligand carvedilol (Carv), we previously showed that β-arrestin1-biased β1AR cardioprotective signaling stimulates Drosha-mediated processing of a subset of miRs. Here, we investigate whether Carv could regulate Dicer-mediated miR maturation, thereby providing a novel mechanism for its cardioprotective effects. In mouse hearts, Carv indeed upregulates 3 mature miRs, but not their pre-miRs and pri-miRs, in a β-arrestin1/2-dependent manner. Interestingly, Carv-mediated activation of miR-466g and miR-532 is dependent on β2AR, while the activation of miR-674 by Carv is β1AR-dependent. Mechanistically, β-arrestins regulate maturation of 3 newly identified βAR/β-arrestin-responsive miRs (β-miRs) by associating with the Dicer complex as well as hnRNPK and dyskerin on 3 pre-miRs (Fig. A). Cardiac cell approaches uncover that β-miRs act as gatekeepers of cardiac cell function by repressing detrimental target genes (Fig. B). In conclusion, our findings indicate a novel role for βAR-mediated β-arrestin signaling activated by Carv in miR maturation, which may be linked, in part, to its protective mechanism.

Caenorhabditis elegans RIG-I Homolog Mediates Antiviral RNA Interference Downstream of Dicer-Dependent Biogenesis of Viral Small Interfering RNAs.

ABSTRACTDicer enzymes process virus-specific double-stranded RNA (dsRNA) into small interfering RNAs (siRNAs) to initiate specific antiviral defense by related RNA interference (RNAi) pathways in plants, insects, nematodes, and mammals. Antiviral RNAi in Caenorhabditis elegans requires Dicer-related helicase 1 (DRH-1), not found in plants and insects but highly homologous to mammalian retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), intracellular viral RNA sensors that trigger innate immunity against RNA virus infection. However, it remains unclear if DRH-1 acts analogously to initiate antiviral RNAi in C. elegans. Here, we performed a forward genetic screen to characterize antiviral RNAi in C. elegans. Using a mapping-by-sequencing strategy, we uncovered four loss-of-function alleles of drh-1, three of which caused mutations in the helicase and C-terminal domains conserved in RLRs. Deep sequencing of small RNAs revealed an abundant population of Dicer-dependent virus-derived small interfering RNAs (vsiRNAs) in drh-1 single and double mutant animals after infection with Orsay virus, a positive-strand RNA virus. These findings provide further genetic evidence for the antiviral function of DRH-1 and illustrate that DRH-1 is not essential for the sensing and Dicer-mediated processing of the viral dsRNA replicative intermediates. Interestingly, vsiRNAs produced by drh-1 mutants were mapped overwhelmingly to the terminal regions of the viral genomic RNAs, in contrast to random distribution of vsiRNA hot spots when DRH-1 is functional. As RIG-I translocates on long dsRNA and DRH-1 exists in a complex with Dicer, we propose that DRH-1 facilitates the biogenesis of vsiRNAs in nematodes by catalyzing translocation of the Dicer complex on the viral long dsRNA precursors.

TRBP ensures efficient Dicer processing of precursor microRNA in RNA-crowded environments.

The RNA-binding protein TRBP is a central component of the Dicer complex. Despite a decade of biochemical and structural studies, the essential functionality of TRBP in microRNA (miRNA) biogenesis remains unknown. Here we show that TRBP is an integral cofactor for time-efficient Dicer processing in RNA-crowded environments. We competed for Dicer processing of pre-miRNA with a large amount of cellular RNA species and found that Dicer-TRBP, but not Dicer alone, remains resilient. To apprehend the mechanism of this substrate selectivity, we use single-molecule fluorescence. The real-time observation reveals that TRBP acts as a gatekeeper, precluding Dicer from engaging with pre-miRNA-like substrates. TRBP acquires the selectivity using the PAZ domain of Dicer, whereas Dicer moderates the RNA-binding affinity of TRBP for fast turnover. This coordinated action between TRBP and Dicer accomplishes an efficient way of discarding pre-miRNA-like substrates.

Abstract 310: Beta-adrenergic Receptor/beta-arrestin-mediated MicroRNA Maturation Confers Cardiac Cell Survival

MicroRNAs (miRs) are small, non-coding RNAs that function to post-transcriptionally regulate gene expression. First transcribed as primary miR transcripts (pri-miRs), they are enzymatically processed in the nucleus by Drosha into hairpin-shaped premature miRs (pre-miRs) and further processed in the cytoplasm by Dicer into mature miRs. MiRs regulate cellular processes upon activation by various signals such as those stimulated by beta-adrenergic receptors (betaARs). Initially discovered to desensitize betaAR signaling, beta-arrestins are now appreciated to regulate diverse effector pathways independent of G protein-mediated second messenger accumulation, a concept known as biased signaling. Using the beta-arrestin-biased betaAR ligand carvedilol (Carv), we test whether Carv could modulate Dicer-mediated miR maturation, thereby providing a novel mechanism for its cardioprotective effects. In mouse hearts, Carv indeed upregulates 3 mature miRs, but not their pre-miRs and pri-miRs, in beta-arrestin1/2- and GPCR kinase 5/6-dependent manners. Interestingly, Carv-mediated activation of miR-466g and miR-532-5p is dependent on beta2AR while the activation of miR-674-5p by Carv is beta1AR-dependent. Mechanistically, beta-arrestins regulate miR maturation by associating with components of Dicer complex on these three pre-miRs (Figure A). Loss-of-function studies in cardiac cells show that miR-466g and miR-532-5p act as gatekeepers of cardiac endothelial cell survival (Figure B). Our findings indicate a novel role for betaAR-mediated beta-arrestin signaling activated by Carv in miR maturation, which may be linked, in part, to its cell survival mechanism.

Role of human GRP75 in miRNA mediated regulation of dengue virus replication

In recent times, RNAi has emerged as an important defence system that regulates replication of pathogens in host cells. Many RNAi related host factors especially the host miRNAs play important roles in all intrinsic cellular functions, including viral infection. We have been working on identification of mammalian host factors involved in Dengue virus infection. In the present study, we identified Glucose Regulated Protein 75kDa (GRP75), as a host factor that is associated with dicer complex, in particular with HADHA (trifunctional enzyme subunit alpha, mitochondrial), an auxiliary component of dicer complex. Knockdown of GRP75 by respective siRNAs in Huh-7 cells resulted in the accumulation of dengue viral genomic RNA suggesting a role of GRP75 in regulating dengue virus replication in human cell lines. To elucidate the mode of action of GRP75, we over expressed the protein in Huh-7 cells and analysed the host miRNAs processing. The results revealed that, GRP75 is involved in processing of host miRNA, hsa-mir-126, that down regulates dengue virus replication. These findings suggest a regulatory role of human miRNA pathway especially GRP75 protein and hsa-mir-126 in dengue virus replication. These results thus provide insights into the role of miRNAs and RNAi machinery in dengue life cycle.

Single-molecule pull-down for investigating protein–nucleic acid interactions

The genome and transcriptome are constantly modified by proteins in the cell. Recent advances in single-molecule techniques allow for high spatial and temporal observations of these interactions between proteins and nucleic acids. However, due to the difficulty of obtaining functional protein complexes, it remains challenging to study the interactions between macromolecular protein complexes and nucleic acids. Here, we combined single-molecule fluorescence with various protein complex pull-down techniques to determine the function and stoichiometry of ribonucleoprotein complexes. Through the use of three examples of protein complexes from eukaryotic cells (Drosha, Dicer, and TUT4 protein complexes), we provide step-by-step guidance for using novel single-molecule techniques. Our single-molecule methods provide sub-second and nanometer resolution and can be applied to other nucleoprotein complexes that are essential for cellular processes.

Association of HADHA with human RNA silencing machinery

In RNA silencing, small RNAs produced by dicer mediate target repression guided by RNA induced silencing complex (RISC). To effectively mediate this response, one or more proteins are employed at each stage. In the present study, we investigated HADHA, a new component in the human RNA silencing machinery. Immunoprecipitation analysis revealed that, HADHA associates with dicer complex and immunohistochemical studies confirmed its co localization with Dicer in the cytoplasm. Further, over expression of HADHA resulted in higher abundance levels of mature miRNA against a reduction in respective precursor levels and vice versa in HADHA knocked down cells. These findings suggest an auxiliary role for HADHA in miRNA biogenesis and help in better understanding of molecular mechanisms underlying RNAi pathway in mammals.

A New Tool for in vivo Manipulation of Brain microRNA Levels: The Work of Smalheiser et al. (2014)

A New Tool for in vivo Manipulation of Brain microRNA Levels: The Work of Smalheiser et al. (2014)

Interplay between steroid signalling and microRNAs: implications for hormone-dependent cancers.

Hormones are key drivers of cancer development. To date, interest has largely been focussed on the classical model of hormonal gene regulation, but there is increasing evidence for a role of hormone signalling pathways in post-translational regulation of gene expression. In particular, a complex and dynamic network of bi-directional interactions with microRNAs (miRs) at all stages of biogenesis and during target gene repression is emerging. miRs, which act mainly by negatively regulating gene expression through association with 3'-UTRs of mRNA species, are increasingly understood to be important in development, normal physiology and pathogenesis. Given recent demonstrations of altered miR profiles in a diverse range of cancers, their ability to function as oncogenes or tumour suppressors, and hormonal regulation of miRs, understanding mechanisms by which miRs are generated and regulated is vitally important. miRs are transcribed by RNA polymerase II and then processed in the nucleus by the Drosha-containing Microprocessor complex and in the cytoplasm by Dicer, before mature miRs are incorporated into the RNA-induced silencing complex. It is increasingly evident that multiple cellular signalling pathways converge upon the miR biogenesis cascade, adding further layers of regulatory complexity to modulate miR maturation. This review summarises recent advances in identification of novel components and regulators of the Microprocessor and Dicer complexes, with particular emphasis on the role of hormone signalling pathways in regulating their activity. Understanding hormone regulation of miR production and how this is perturbed in cancer are critical for the development of miR-based therapeutics and biomarkers.

A MicroRNA Processing Defect in Smokers' Macrophages Is Linked to SUMOylation of the Endonuclease DICER

Despite the fact that alveolar macrophages play an important role in smoking-related disease, little is known about what regulates their pathophysiologic phenotype. Evaluating smoker macrophages, we found significant down-regulation of multiple microRNAs (miRNAs). This work investigates the hypothesis that cigarette smoke alters mature miRNA expression in lung macrophages by inhibiting processing of primary miRNA transcripts. Studies on smoker alveolar macrophages showed a defect in miRNA maturation. Studies on the miRNA biogenesis machinery led us to focus on the cytosolic RNA endonuclease, DICER. DICER cleaves the stem-loop structure from pre-miRNAs, allowing them to dissociate into their mature 20-22-nucleotide single-stranded form. DICER activity assays confirmed impaired DICER activity following cigarette smoke exposure. Further protein studies demonstrated a decreased expression of the native 217-kDa form of DICER and an accumulation of high molecular weight forms with cigarette smoke exposure. This molecular mass shift was shown to contain SUMO moieties and could be blocked by silencing RNA directed at the primary SUMOylating ligase, Ubc9. In determining the cigarette smoke components responsible for changes in DICER, we found that N-acetylcysteine, an antioxidant and anti-aldehyde, protected DICER protein and activity from cigarette smoke extract. This massive down-regulation of miRNAs (driven in part by alterations in DICER) may be an important regulator of the disease-promoting macrophage phenotype found in the lungs of smokers.

Trans-activation Response (TAR) RNA-binding Protein 2 Is a Novel Modulator of Transient Receptor Potential Canonical 4 (TRPC4) Protein

TRPC4 proteins function as Ca(2+) conducting, non-selective cation channels in endothelial, smooth muscle, and neuronal cells. To further characterize the roles of TRPC4 in vivo, detailed information about the molecular composition of native channel complexes and their association with cellular signaling networks is needed. Therefore, a mouse brain cDNA library was searched for novel TRPC4-interacting proteins using a modified yeast two-hybrid assay. This screen identified Trans-activation Response RNA-binding protein 2 (Tarpb2), a protein that recruits the Dicer complex to Ago2 for microRNA processing and gene silencing. Tarbp2 was found to bind to the C terminus of TRPC4 and TRPC5 and to modulate agonist-dependent TRPC4-induced Ca(2+) entry. A stretch of basic residues within the Tarbp2 protein is required for these actions. Tarbp2 binding to and modulation of TRPC4 occurs in the presence of endogenously expressed Dicer but is no longer detectable when the Dicer cDNA is overexpressed. Dicer activity in crude cell lysates is increased in the presence of Ca(2+), most probably by Ca(2+)-dependent proteolytic activation of Dicer. Apparently, Tarbp2 binding to TRPC4 promotes changes of cytosolic Ca(2+) and, thereby, leads to a dynamic regulation of Dicer activity, essentially at low endogenous Dicer concentrations.

Deep Sequencing Insights in Therapeutic shRNA Processing and siRNA Target Cleavage Precision

TT-034 (PF-05095808) is a recombinant adeno-associated virus serotype 8 (AAV8) agent expressing three short hairpin RNA (shRNA) pro-drugs that target the hepatitis C virus (HCV) RNA genome. The cytosolic enzyme Dicer cleaves each shRNA into multiple, potentially active small interfering RNA (siRNA) drugs. Using next-generation sequencing (NGS) to identify and characterize active shRNAs maturation products, we observed that each TT-034–encoded shRNA could be processed into as many as 95 separate siRNA strands. Few of these appeared active as determined by Sanger 5′ RNA Ligase-Mediated Rapid Amplification of cDNA Ends (5-RACE) and through synthetic shRNA and siRNA analogue studies. Moreover, NGS scrutiny applied on 5-RACE products (RACE-seq) suggested that synthetic siRNAs could direct cleavage in not one, but up to five separate positions on targeted RNA, in a sequence-dependent manner. These data support an on-target mechanism of action for TT-034 without cytotoxicity and question the accepted precision of substrate processing by the key RNA interference (RNAi) enzymes Dicer and siRNA-induced silencing complex (siRISC).

DNA-Damage-Induced Nuclear Export of Precursor MicroRNAs Is Regulated by the ATM-AKT Pathway

Expression of microRNAs (miRNAs) involves transcription of miRNA genes and maturation of the primary transcripts. Recent studies have shown that posttranscriptional processing of primary and precursor miRNAs is induced after DNA damage through regulatory RNA-binding proteins in the Drosha and Dicer complexes, such as DDX5 and KSRP. However, little is known about the regulation of nuclear export of pre-miRNAs in the DNA-damage response, a critical step in miRNA maturation. Here, we show that nuclear export of pre-miRNAs is accelerated after DNA damage in an ATM-dependent manner. The ATM-activated AKT kinase phosphorylates Nup153, a key component of the nucleopore, leading to enhanced interaction between Nup153 and Exportin-5 (XPO5) and increased nuclear export of pre-miRNAs. These findings define an important role of DNA-damage signaling in miRNA transport and maturation.