The early macrophage response to pathogens requires dynamic regulation of the nuclear paraspeckle.

To ensure a robust immune response to pathogens without risking immunopathology, the kinetics and amplitude of inflammatory gene expression in macrophages need to be exquisitely well controlled. There is a growing appreciation for stress-responsive membraneless organelles (MLOs) regulating various steps of eukaryotic gene expression in response to extrinsic cues. Here, we implicate the nuclear paraspeckle, a highly ordered biomolecular condensate that nucleates on the Neat1 lncRNA, in tuning innate immune gene expression in murine macrophages. In response to a variety of innate agonists, macrophage paraspeckles rapidly aggregate (0.5 h poststimulation) and disaggregate (2 h poststimulation). Paraspeckle maintenance and aggregation require active transcription and MAPK signaling, whereas paraspeckle disaggregation requires degradation of Neat1 via the nuclear RNA exosome. In response to lipopolysaccharide treatment, Neat1 KO macrophages fail to properly express a large cohort of proinflammatory cytokines, chemokines, and antimicrobial mediators. Consequently, Neat1 KO macrophages cannot control replication of Salmonella enterica serovar Typhimurium or vesicular stomatitis virus. These findings highlight a prominent role for MLOs in orchestrating the macrophage response to pathogens and support a model whereby dynamic assembly and disassembly of paraspeckles reorganizes the nuclear landscape to enable inflammatory gene expression following innate stimuli.

The mitochondria‒paraspeckle axis regulates the survival of transplanted stem cells under oxidative stress conditions.

Rationale: Stem cell-based therapies have emerged as promising tools for tissue engineering and regenerative medicine, but their therapeutic efficacy is largely limited by the oxidative stress-induced loss of transplanted cells at injured tissue sites. To address this issue, we aimed to explore the underlying mechanism and protective strategy of ROS-induced MSC loss. Methods: Changes in TFAM (mitochondrial transcription factor A) signaling, mitochondrial function, DNA damage, apoptosis and senescence in MSCs under oxidative stress conditions were assessed using real-time PCR, western blotting and RNA sequencing, etc. The impact of TFAM or lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) knockdown or overexpression on mitochondrial function, DNA damage repair, apoptosis and senescence in MSCs was also analyzed. The effect of mitochondrion-targeted antioxidant (Mito-TEMPO) on the survival of transplanted MSCs was evaluated in a mouse model of renal ischemia/reperfusion (I/R) injury. Results: Mitochondrial ROS (mtROS) bursts caused defects in TFAM signaling and overall mitochondrial function, which further impaired NEAT1 expression and its mediated paraspeckle formation and DNA repair pathways in MSCs, thereby jointly promoting MSC senescence and death under oxidative stress. In contrast, targeted inhibition of the mtROS bursts is a sufficient strategy for attenuating early transplanted MSC loss at injured tissue sites, and coadministration of Mito-TEMPO improved the local retention of transplanted MSCs and reduced oxidative injury in ischemic kidneys. Conclusions: This study identified the critical role of the mitochondria‒paraspeckle axis in regulating cell survival and may provide insights into developing advanced stem cell therapies for tissue engineering and regenerative medicine.

Shell protein composition specified by the lncRNA NEAT1 domains dictates the formation of paraspeckles as distinct membraneless organelles.

Many membraneless organelles (MLOs) formed through phase separation play crucial roles in various cellular processes. Although these MLOs co-exist in cells, how they maintain their independence without coalescence or engulfment remains largely unknown. Here, we investigated the molecular mechanism by which paraspeckles with core-shell architecture scaffolded by NEAT1_2 long noncoding RNAs exist as distinct MLOs. We identified NEAT1 deletion mutants that assemble paraspeckles that are incorporated into nuclear speckles. Several paraspeckle proteins, including SFPQ, HNRNPF and BRG1, prevent this incorporation and thus contribute to the segregation of paraspeckles from nuclear speckles. Shell localization of these proteins in the paraspeckles, which is determined by NEAT1_2 long noncoding RNA domains, is required for this segregation process. Conversely, U2-related spliceosomal proteins are involved in internalizing the paraspeckles into nuclear speckles. This study shows that the paraspeckle shell composition dictates the independence of MLOs in the nucleus, providing insights into the importance of the shell in defining features and functions of MLOs.

[Leukemia-associated gene ASXL1 involved in paraspeckle formation].

Somatic mutations in the ASXL1 gene are commonly observed in myeloid neoplasms. Pathogenic ASXL1 mutations induce the expression of C-terminally truncated mutant ASXL1 protein. We have shown that wild-type ASXL1 is a phase-separating protein involved in the formation of paraspeckles, one of the best known membraneless organelles (MLOs). Mutant ASXL1 lacks the intrinsically disordered region, which is important for phase separation and fails to support paraspeckle formation. Additionally, paraspeckles are disrupted in hematopoietic cells derived from ASXL1-MT knockin mice. The disruption of paraspeckles in hematopoietic cells results in a dysfunction of the hematopoietic reconstitution capacity. Therefore, this review presents our findings and summarizes the knowledge of phase separation and MLOs as a hot topic in cell biology.

The disordered C terminus of ALKBH5 promotes phase separation and paraspeckles assembly.

Paraspeckles (PS) are nuclear structures scaffolded by the long noncoding RNA NEAT1 and protein components such as NONO and SFPQ. We previously found that the upregulation of RNA N6-methyl-adenosine (m6A) demethylase ALKBH5 facilitates hypoxia-induced paraspeckle assembly through erasing m6A marks on NEAT1, thus stabilizing it. However, it remains unclear how these processes are spatiotemporally coordinated. Here we discover that ALKBH5 specifically binds to proteins in PS and forms phase-separated droplets that are incorporated into PS through its C-terminal intrinsically disordered region (cIDR). Upon exposure to hypoxia, rapid ALKBH5 condensation in PS induces m6A demethylation of NEAT1, which further facilitates PS formation before the upregulation of ALKBH5 expression. In cells expressing ALKBH5 lacking cIDR, PS fail to be formed in response to hypoxia, accompanied with insufficient m6A demethylation of NEAT1 and its destabilization. We also demonstrate that ALKBH5-cIDR is indispensable for hypoxia-induced effects such as cancer cell invasion. Therefore, our study has identified the role of ALKBH5 in phase separation as the molecular basis of the positive feedback loop for PS formation between ALKBH5 incorporation into PS and NEAT1 stabilization.

NEAT1_2 and DAZAP1, Paraspeckle Components, Interact with PXR to Negatively Regulate CYP3A4 Induction.

Human pregnane X receptor (PXR) is a major nuclear receptor that upregulates the expression of drug-metabolizing enzymes such as CYP3A4. In our recent study, it was revealed that PXR interacts with DAZ-associated protein 1 (DAZAP1), which is an essential component of the paraspeckle, a membraneless nuclear body, and the interaction was disassociated by rifampicin, a ligand of PXR. The purpose of this study was to clarify the roles of paraspeckles in PXR-mediated transcriptional regulation. Immunoprecipitation assays using PXR-overexpressing HepG2 (ShP51) cells revealed that PXR interacts with not only DAZAP1 but also NEAT1_2, a long noncoding RNA included in the paraspeckle, and that the interaction between PXR and NEAT1_2 was disassociated by rifampicin. These results suggest that PXR is trapped in paraspeckles and that the activation of PXR by its ligands facilitates its disassociation from paraspeckles. Induction of CYP3A4 by rifampicin was significantly enhanced by the knockdown of NEAT1_2 or DAZAP1 in ShP51 cells and their parental HepG2 cells. A luciferase assay using a plasmid containing the PXR response elements of CYP3A4 revealed that the increased CYP3A4 induction by siNEAT1_2 or siDAZAP1 was due to the increased transactivation by PXR. These results suggest that paraspeckles play a role in trapping nuclear PXR in the absence of the ligand to negatively regulate transactivation of its downstream gene. Collectively, this is the first study to demonstrate that the paraspeckle components NEAT1_2 and DAZAP1 negatively regulate CYP3A4 induction by PXR. SIGNIFICANCE STATEMENT: This study revealed that PXR interacts with paraspeckle components NEAT1_2 and DAZAP1 to suppress CYP3A4 induction by PXR, and the interaction is dissociated by PXR ligands. This finding provides a novel concept that paraspeckles formed by liquid-liquid phase separation potentially affect drug metabolism via negative regulation of PXR function.

Long non-coding RNA nuclear paraspeckle assembly transcript 1 downregulation protects lens epithelial cells from oxidative stress-induced apoptosis by regulating the microRNA-124-3p/death-associated protein kinase 1 axis in age-related cataract.

Oxidative stress plays a significant role in cataract development. It causes the apoptosis of lens epithelial cells (LECs), resulting in lens opacification and accelerating cataract progression. Long non-coding RNAs (lncRNAs) and microRNAs have been linked to cataract development. Notably, lncRNA nuclear paraspeckle assembly transcript 1 (NEAT1) is involved in LEC apoptosis and cataract formation. However, the molecular mechanism by which NEAT1 causes age-related cataracts remains unknown. In this study, LECs (SRA01/04) were exposed to 200 µM H2O2 to generate an in vitro cataract model. The apoptosis and viability of cells were determined using flow cytometry and 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide assays, respectively. Additionally, western blotting and quantitative polymerase chain reaction were used to determine the miRNA and lncRNA expression levels. When LECs were treated with hydrogen peroxide, lncRNA NEAT1 expression levels were significantly upregulated, which contributed to LEC apoptosis. Notably, lncRNA NEAT1 suppressed the expression of miR-124-3p, a critical regulator of apoptosis, whereas NEAT1 inhibition increased miR-124-3p expression and alleviated apoptosis. However, this effect was reversed when miR1243p expression was inhibited. Additionally, the miR1243p mimic effectively inhibited the death-associated protein kinase 1 (DAPK1) expression and apoptosis of LECs, while the DAPK1 mimic reversed these effects. In conclusion, our findings indicate that the lncRNA NEAT1/miR-124-3p/DAPK1 signaling loop is involved in the regulation of LEC apoptosis induced by oxidative stress, which can be exploited to develop potential treatment strategies for age-related cataracts.

Confined environments induce polarized paraspeckle condensates.

Cancer cells experience confinement as they navigate the tumour microenvironment during metastasis. Recent studies have revealed that the nucleus can function as a 'ruler' for measuring physical confinement via membrane tension, allowing for compression-sensitive changes in migration. Cell nuclei contain many nuclear bodies that form when their components phase separate and condense within permissive local regions within the nucleus. However, how sub-nuclear organisation and phase separation changes with cell confinement and compression is largely unknown. Here we focus on paraspeckles, stress-responsive subnuclear bodies that form by phase separation around the long non-coding RNA NEAT1. As cells entered moderate confinement, a significant increase in paraspeckle number and size was observed compared to unconfined cells. Paraspeckle polarization bias towards the leading edge was also observed in confinement, correlating with regions of euchromatin. Increasing paraspeckle abundance resulted in increases in confined migration likelihood, speed, and directionality, as well as an enhancement of paraspeckle polarization towards the leading edge. This polarization of paraspeckle condensates may play a key role in regulating confined migration and invasion in cancer cells, and illustrates the utility of microchannel-based assays for identifying phenomena not observed on 2D or 3D bulk substrates.

Obstructive sleep apnoea is related to melanoma aggressiveness through paraspeckle protein-1 upregulation.

BACKGROUND: In patients with obstructive sleep apnoea (OSA), intermittent hypoxia induces overexpression of paraspeckle component (PSPC)1, a master modulator of transforming growth factor (TGF)-ß signalling, which promotes cell cancer progression through epithelial-mesenchymal transition (EMT) and acquisition of cancer stem cell (CSC)-like features. However, the persistence of intermittent hypoxia-induced effects on PSPC1, and their consequences in cancer patients are not known. To this effect, circulating PSPC1 levels were compared in patients with cutaneous melanoma with or without OSA, and their relationship with tumour aggressiveness along with the in vitro effects of soluble PSPC1 and intermittent hypoxia on melanoma cell aggressiveness mechanisms were assessed. METHODS: In 292 cutaneous melanoma patients, sleep studies and serum levels of PSPC1 and TGF-ß were evaluated. The effect of PSPC1 on expression of EMT and CSC transcription factors was assessed using melanoma cell lines with patient sera under both normoxia and intermittent hypoxia conditions. RESULTS: PSPC1 levels were higher in patients with moderate-severe OSA compared with mild OSA or non-OSA patients. Serum levels of PSPC1 were associated with several cutaneous melanoma clinical aggressiveness indicators. Both intermittent hypoxia exposures and serum from OSA patients upregulated TGF-ß expression and amplified the expression of transcription factors associated with EMT activation and acquisition of CSC characteristics. CONCLUSION: In cutaneous melanoma patients, OSA severity is associated with higher PSPC1 serum levels, which jointly with intermittent hypoxia would enhance the self-reprogramming capabilities of EMT and CSC feature acquisition of melanoma cells, promoting their intrinsic aggressiveness.

Paraspeckles interact with SWI/SNF subunit ARID1B to regulate transcription and splicing.

Paraspeckles are subnuclear RNA-protein structures that are implicated in important processes including cellular stress response, differentiation, and cancer progression. However, it is unclear how paraspeckles impart their physiological effect at the molecular level. Through biochemical analyses, we show that paraspeckles interact with the SWI/SNF chromatin-remodeling complex. This is specifically mediated by the direct interaction of the long-non-coding RNA NEAT1 of the paraspeckles with ARID1B of the cBAF-type SWI/SNF complex. Strikingly, ARID1B depletion, in addition to resulting in loss of interaction with the SWI/SNF complex, decreases the binding of paraspeckle proteins to chromatin modifiers, transcription factors, and histones. Functionally, the loss of ARID1B and NEAT1 influences the transcription and the alternative splicing of a common set of genes. Our findings reveal that dynamic granules such as the paraspeckles may leverage the specificity of epigenetic modifiers to impart their regulatory effect, thus providing a molecular basis for their function.

Sublethal heat treatment enhances lactic acid uptake in macrophages via MCT1, leading to reduced paraspeckle formation and a subsequent decrease in macrophage pyroptosis.

Introduction: Heat ablation is one of the key modalities in treating liver cancer, yet the residual cancer tissues suffering sublethal heat treatment possess a potential for increased malignancy. This study conducts a comprehensive analysis of cellular dynamics, metabolic shifts, and macrophage polarization within the tumor microenvironment following sublethal heat treatment. Methods: We observed significant acidification in tumor cell supernatants, attributed to increased lactic acid production. The study focused on how this pH shift, crucial in tumor progression and resistance, influences macrophage polarization, especially towards the M2 phenotype known for tumor-promoting functions. We also examined the upregulation of MCT1 expression post sublethal heat treatment and its primary role in lactic acid transport. Results: Notably, the study found minimal disparity in MCT1 expression between hepatocellular carcinoma patients and healthy liver tissues, highlighting the complexity of cancer biology. The research further revealed an intricate relationship between lactic acid, MCT1, and the inhibition of macrophage pyroptosis, offering significant insights for therapeutic strategies targeting the tumor immune environment. Post sublethal heat treatment, a reduction in paraspeckle under lactic acid exposure was observed, indicating diverse cellular impacts. Additionally, PKM2 was identified as a key molecule in this context, with decreased levels after sublethal heat treatment in the presence of lactic acid. Discussion: Collectively, these findings illuminate the intertwined mechanisms of sublethal heat treatments, metabolic alterations, and immune modulation in the tumor milieu, providing a deeper understanding of the complex interplay in cancer biology and treatment.

Long non-coding RNA Neat1 and paraspeckle components are translational regulators in hypoxia.

Internal ribosome entry sites (IRESs) drive translation initiation during stress. In response to hypoxia, (lymph)angiogenic factors responsible for tissue revascularization in ischemic diseases are induced by the IRES-dependent mechanism. Here, we searched for IRES trans-acting factors (ITAFs) active in early hypoxia in mouse cardiomyocytes. Using knock-down and proteomics approaches, we show a link between a stressed-induced nuclear body, the paraspeckle, and IRES-dependent translation. Furthermore, smiFISH experiments demonstrate the recruitment of IRES-containing mRNA into paraspeckle during hypoxia. Our data reveal that the long non-coding RNA Neat1, an essential paraspeckle component, is a key translational regulator, active on IRESs of (lymph)angiogenic and cardioprotective factor mRNAs. In addition, paraspeckle proteins p54nrb and PSPC1 as well as nucleolin and RPS2, two p54nrb-interacting proteins identified by mass spectrometry, are ITAFs for IRES subgroups. Paraspeckle thus appears as a platform to recruit IRES-containing mRNAs and possibly host IRESome assembly. Polysome PCR array shows that Neat1 isoforms regulate IRES-dependent translation and, more widely, translation of mRNAs involved in stress response.

Nuclear paraspeckle assembly transcript 1 promotes the podocyte injury via targeting miR-23b-3p/B-cell lymphoma-2 interacting protein 3 like axis.

BACKGROUND: Given the reported effects of nuclear paraspeckle assembly transcript 1 (NEAT1) on kidney injury, a study is worth formulating to investigate whether and how NEAT1 impacts podocytes. MATERIALS AND METHODS: A mouse podocyte injury model was established using the adriamycin (ADR)-induced mouse podocyte cell line (MPC5). The target relationships between NEAT1 and microRNA (miR)-23b-3p and between miR-23b-3p and Bcl-2 interacting protein 3 like (BNIP3L) were verified by dual-luciferase reporter assay and RNA immunoprecipitation assay. After ADR-induced MPC5 cells were transfected with NEAT1 overexpression plasmid (oe-NEAT1) or shNEAT1, the viability and apoptosis of MPC5 cells were evaluated by Cell Counting Kit-8 (CCK-8) assay and flow cytometry, respectively. The expressions of MPC5, miR-23b-3p, BNIP3L and the factors related to podocyte injury, apoptosis and epithelial-mesenchymal transition were determined using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot. RESULTS: NEAT1 was high-expressed in ADR-induced cell model. After transfection with oe-NEAT1, the expression of NEAT1, the levels of marker (Desmin) and apoptosis were promoted, while the viability and the levels of podocyte injury markers (WT1, Nephrin) were inhibited in ADR-induced cells. However, shNEAT1 generated the effects opposite to oe-NEAT1. Besides, miR-23b-3p competitively bound to NEAT1 and targeted BNIP3L. MiR-23b-3p inhibitor reversed the effect of shNEAT1, while its effect could be further offset by shBNIP3L. Furthermore, miR-23b-3p inhibitor affected mouse podocyte injury through downregulating Bcl-2 and E-cadherin levels and upregulating Cleaved-caspase-3, Bax, N-cadherin, Vimentin and Snail levels, but shBNIP3L did oppositely. CONCLUSION: NEAT1 promotes the podocyte injury via targeting miR-23b-3p/BNIP3L axis.

Paraspeckle subnuclear bodies depend on dynamic heterodimerisation of DBHS RNA-binding proteins via their structured domains.

RNA-binding proteins of the DBHS (Drosophila Behavior Human Splicing) family, NONO, SFPQ, and PSPC1 have numerous roles in genome stability and transcriptional and posttranscriptional regulation. Critical to DBHS activity is their recruitment to distinct subnuclear locations, for example, paraspeckle condensates, where DBHS proteins bind to the long noncoding RNA NEAT1 in the first essential step in paraspeckle formation. To carry out their diverse roles, DBHS proteins form homodimers and heterodimers, but how this dimerization influences DBHS localization and function is unknown. Here, we present an inducible GFP-NONO stable cell line and use it for live-cell 3D-structured illumination microscopy, revealing paraspeckles with dynamic, twisted elongated structures. Using siRNA knockdowns, we show these labeled paraspeckles consist of GFP-NONO/endogenous SFPQ dimers and that GFP-NONO localization to paraspeckles depends on endogenous SFPQ. Using purified proteins, we confirm that partner swapping between NONO and SFPQ occurs readily in vitro. Crystallographic analysis of the NONO-SFPQ heterodimer reveals conformational differences to the other DBHS dimer structures, which may contribute to partner preference, RNA specificity, and subnuclear localization. Thus overall, our study suggests heterodimer partner availability is crucial for NONO subnuclear distribution and helps explain the complexity of both DBHS protein and paraspeckle dynamics through imaging and structural approaches.

A Novel Gene Controls a New Structure: PiggyBac Transposable Element-Derived 1, Unique to Mammals, Controls Mammal-Specific Neuronal Paraspeckles.

Although new genes can arrive from modes other than duplication, few examples are well characterized. Given high expression in some human brain subregions and a putative link to psychological disorders [e.g., schizophrenia (SCZ)], suggestive of brain functionality, here we characterize piggyBac transposable element-derived 1 (PGBD1). PGBD1 is nonmonotreme mammal-specific and under purifying selection, consistent with functionality. The gene body of human PGBD1 retains much of the original DNA transposon but has additionally captured SCAN and KRAB domains. Despite gene body retention, PGBD1 has lost transposition abilities, thus transposase functionality is absent. PGBD1 no longer recognizes piggyBac transposon-like inverted repeats, nonetheless PGBD1 has DNA binding activity. Genome scale analysis identifies enrichment of binding sites in and around genes involved in neuronal development, with association with both histone activating and repressing marks. We focus on one of the repressed genes, the long noncoding RNA NEAT1, also dysregulated in SCZ, the core structural RNA of paraspeckles. DNA binding assays confirm specific binding of PGBD1 both in the NEAT1 promoter and in the gene body. Depletion of PGBD1 in neuronal progenitor cells (NPCs) results in increased NEAT1/paraspeckles and differentiation. We conclude that PGBD1 has evolved core regulatory functionality for the maintenance of NPCs. As paraspeckles are a mammal-specific structure, the results presented here show a rare example of the evolution of a novel gene coupled to the evolution of a contemporaneous new structure.

A toolkit for the identification of NEAT1_2/paraspeckle modulators.

Paraspeckles are ribonucleoprotein granules assembled by NEAT1_2 lncRNA, an isoform of Nuclear Paraspeckle Assembly Transcript 1 (NEAT1). Dysregulation of NEAT1_2/paraspeckles has been linked to multiple human diseases making them an attractive drug target. However currently NEAT1_2/paraspeckle-focused translational research and drug discovery are hindered by a limited toolkit. To fill this gap, we developed and validated a set of tools for the identification of NEAT1_2 binders and modulators comprised of biochemical and cell-based assays. The NEAT1_2 triple helix stability element was utilized as the target in the biochemical assays, and the cellular assay ('ParaQuant') was based on high-content imaging of NEAT1_2 in fixed cells. As a proof of principle, these assays were used to screen a 1,200-compound FDA-approved drug library and a 170-compound kinase inhibitor library and to confirm the screening hits. The assays are simple to establish, use only commercially-available reagents and are scalable for higher throughput. In particular, ParaQuant is a cost-efficient assay suitable for any cells growing in adherent culture and amenable to multiplexing. Using ParaQuant, we identified dual PI3K/mTOR inhibitors as potent negative modulators of paraspeckles. The tools we describe herein should boost paraspeckle studies and help guide the search, validation and optimization of NEAT1_2/paraspeckle-targeted small molecules.

AATF/Che-1 localizes to paraspeckles and suppresses R-loops accumulation and interferon activation in Multiple Myeloma.

Several kinds of stress promote the formation of three-stranded RNA:DNA hybrids called R-loops. Insufficient clearance of these structures promotes genomic instability and DNA damage, which ultimately contribute to the establishment of cancer phenotypes. Paraspeckle assemblies participate in R-loop resolution and preserve genome stability, however, the main determinants of this mechanism are still unknown. This study finds that in Multiple Myeloma (MM), AATF/Che-1 (Che-1), an RNA-binding protein fundamental to transcription regulation, interacts with paraspeckles via the lncRNA NEAT1_2 (NEAT1) and directly localizes on R-loops. We systematically show that depletion of Che-1 produces a marked accumulation of RNA:DNA hybrids. We provide evidence that such failure to resolve R-loops causes sustained activation of a systemic inflammatory response characterized by an interferon (IFN) gene expression signature. Furthermore, elevated levels of R-loops and of mRNA for paraspeckle genes in patient cells are linearly correlated with Multiple Myeloma progression. Moreover, increased interferon gene expression signature in patients is associated with markedly poor prognosis. Taken together, our study indicates that Che-1/NEAT1 cooperation prevents excessive inflammatory signaling in Multiple Myeloma by facilitating the clearance of R-loops. Further studies on different cancer types are needed to test if this mechanism is ubiquitously conserved and fundamental for cell homeostasis.

DNA damage-induced paraspeckle formation enhances DNA repair and tumor radioresistance by recruiting ribosomal protein P0.

Paraspeckles are mammal-specific membraneless nuclear bodies that participate in various biological processes. NONO, a central paraspeckle component, has been shown to play pivotal roles in DNA double-strand breaks (DSB) repair, whereas its underlying mechanism needs to be further disclosed. Here, using co-immunoprecipitation and mass spectrum, we identified ribosomal protein P0 (RPLP0) as a DSB-induced NONO-binding protein; RPLP0 binds to the RRM1 and RRM2 domains of NONO. Similar to NONO, RPLP0 enhances non-homologous end joining-mediated DSB repair, which was ascribed to a ribosome-independent manner. Interestingly, paraspeckles were induced as early as 15 min after irradiation; it further recruited nuclear RPLP0 to enhance its interaction with NONO. Radiation-induced NONO/RPLP0 complex subsequently anchored at the damaged DNA and increased the autophosphorylation of DNA-PK at Thr2609, thereby enhancing DSB repair. Consistently, in vivo and in vitro experiments showed that depletion of NONO sensitizes tumor cells to radiation. For patients with locally advanced rectal cancer, NONO expression was remarkably increased in tumor tissues and correlated with a poor response to radiochemotherapy. Our findings suggest a pivotal role of radiation-induced paraspeckles in DNA repair and tumor radioresistance, and provide a new insight into the ribosome-independent function of ribosomal proteins.

Species-specific formation of paraspeckles in intestinal epithelium revealed by characterization of NEAT1 in naked mole-rat.

Paraspeckles are mammalian-specific nuclear bodies built on the long noncoding RNA NEAT1_2 The molecular mechanisms of paraspeckle formation have been mainly studied using human or mouse cells, and it is not known if the same molecular components are involved in the formation of paraspeckles in other mammalian species. We thus investigated the expression pattern of NEAT1_2 in naked mole-rats (nNEAT1_2), which exhibit extreme longevity and lower susceptibility to cancer. In the intestine, nNEAT1_2 is widely expressed along the entire intestinal epithelium, which is different from the expression of mNeat1_2 that is restricted to the cells of the distal tip in mice. Notably, the expression of FUS, a FET family RNA binding protein, essential for the formation of paraspeckles both in humans and mice, was absent in the distal part of the intestinal epithelium in naked mole-rats. Instead, mRNAs of other FET family proteins EWSR1 and TAF15 were expressed in the distal region. Exogenous expression of these proteins in Fus-deficient murine embryonic fibroblast cells rescued the formation of paraspeckles. These observations suggest that nNEAT1_2 recruits a different set of RNA binding proteins in a cell type-specific manner during the formation of paraspeckles in different organisms.

mTOR regulates aerobic glycolysis through NEAT1 and nuclear paraspeckle-mediated mechanism in hepatocellular carcinoma.

Background: Hepatocellular Carcinoma (HCC) is a major form of liver cancer and a leading cause of cancer-related death worldwide. New insights into HCC pathobiology and mechanism of drug actions are urgently needed to improve patient outcomes. HCC undergoes metabolic reprogramming of glucose metabolism from respiration to aerobic glycolysis, a phenomenon known as the 'Warburg Effect' that supports rapid cancer cell growth, survival, and invasion. mTOR is known to promote Warburg Effect, but the underlying mechanism(s) remains poorly defined. The aim of this study is to understand the mechanism(s) and significance of mTOR regulation of aerobic glycolysis in HCC. Methods: We profiled mTORC1-dependent long non-coding RNAs (lncRNAs) by RNA-seq of HCC cells treated with rapamycin. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays were used to explore the transcriptional regulation of NEAT1 by mTORC1. [U-13C]-glucose labeling and metabolomic analysis, extracellular acidification Rate (ECAR) by Seahorse XF Analyzer, and glucose uptake assay were used to investigate the role of mTOR-NEAT1-NONO signaling in the regulation of aerobic glycolysis. RNA immunoprecipitation (RIP) and NONO-binding motif scanning were performed to identify the regulatory mechanism of pre-mRNA splicing by mTOR-NEAT1. Myristoylated AKT1 (mAKT1)/NRASV12-driven HCC model developed by hydrodynamic transfection (HDT) was employed to explore the significance of mTOR-NEAT1 signaling in HCC tumorigenesis and mTOR-targeted therapy. Results: mTOR regulates lncRNA transcriptome in HCC and that NEAT1 is a major mTOR transcriptional target. Interestingly, although both NEAT1_1 and NEAT1_2 are down-regulated in HCC, only NEAT1_2 is significantly correlated with poor overall survival of HCC patients. NEAT1_2 is the organizer of nuclear paraspeckles that sequester the RNA-binding proteins NONO and SFPQ. We show that upon oncogenic activation, mTORC1 suppresses NEAT1_2 expression and paraspeckle biogenesis, liberating NONO/SFPQ, which in turn, binds to U5 within the spliceosome, stimulating mRNA splicing and expression of key glycolytic enzymes. This series of actions lead to enhanced glucose transport, aerobic glycolytic flux, lactate production, and HCC growth both in vitro and in vivo. Furthermore, the paraspeckle-mediated mechanism is important for the anticancer action of US FDA-approved drugs rapamycin/temsirolimus. Conclusions: These findings reveal a molecular mechanism by which mTOR promotes the 'Warburg Effect', which is important for the metabolism and development of HCC, and anticancer response of mTOR-targeted therapy.