The human nuclear exosome targeting complex is loaded onto newly synthesized RNA to direct early ribonucleolysis

ZC3H4/Restrictor Exerts a Stranglehold on Pervasive Transcription

The regulation of transcription by RNA polymerase II (RNAPII) underpins all cellular processes and is perturbed in thousands of diseases. In humans, RNAPII transcribes ∼20000 protein-coding genes and engages in apparently futile non-coding transcription at thousands of other sites. Despite being so ubiquitous, this transcription is usually attenuated soon after initiation and the resulting products are immediately degraded by the nuclear exosome. We and others have recently described a new complex, "Restrictor", which appears to control such unproductive transcription. Underpinned by the RNA binding protein, ZC3H4, Restrictor curtails unproductive/pervasive transcription genome-wide. Here, we discuss these recent discoveries and speculate on some of the many unknowns regarding Restrictor function and mechanism.

RBM7 deficiency promotes breast cancer metastasis by coordinating MFGE8 splicing switch and NF-kB pathway

Aberrant alternative splicing is well-known to be closely associated with tumorigenesis of various cancers. However, the intricate mechanisms underlying breast cancer metastasis driven by deregulated splicing events remain largely unexplored. Here, we unveiled that RBM7 is decreased in lymph node and distant organ metastases of breast cancer as compared to primary lesions and low expression of RBM7 is correlated with the reduced disease-free survival of breast cancer patients. Breast cancer cells with RBM7 depletion exhibited an increased potential for lung metastasis compared to scramble control cells. The absence of RBM7 stimulated breast cancer cell migration, invasion, and angiogenesis. Mechanistically, RBM7 controlled the splicing switch of MFGE8, favoring the production of the predominant isoform of MFGE8, MFGE8-L. This resulted in the attenuation of STAT1 phosphorylation and alterations in cell adhesion molecules. MFGE8-L exerted an inhibitory effect on the migratory and invasive capability of breast cancer cells, while the truncated isoform MFGE8-S, which lack the second F5/8 type C domain had the opposite effect. In addition, RBM7 negatively regulates the NF-κB cascade and an NF-κB inhibitor could obstruct the increase in HUVEC tube formation caused by RBM7 silencing. Clinically, we noticed a positive correlation between RBM7 expression and MFGE8 exon7 inclusion in breast cancer tissues, providing new mechanistic insights for molecular-targeted therapy in combating breast cancer.

SnoRNAs: Exploring Their Implication in Human Diseases

Small nucleolar RNAs (snoRNAs) are earning increasing attention from research communities due to their critical role in the post-transcriptional modification of various RNAs. These snoRNAs, along with their associated proteins, are crucial in regulating the expression of a vast array of genes in different human diseases. Primarily, snoRNAs facilitate modifications such as 2'-O-methylation, N-4-acetylation, and pseudouridylation, which impact not only ribosomal RNA (rRNA) and their synthesis but also different RNAs. Functionally, snoRNAs bind with core proteins to form small nucleolar ribonucleoproteins (snoRNPs). These snoRNAs then direct the protein complex to specific sites on target RNA molecules where modifications are necessary for either standard cellular operations or the regulation of pathological mechanisms. At these targeted sites, the proteins coupled with snoRNPs perform the modification processes that are vital for controlling cellular functions. The unique characteristics of snoRNAs and their involvement in various non-metabolic and metabolic diseases highlight their potential as therapeutic targets. Moreover, the precise targeting capability of snoRNAs might be harnessed as a molecular tool to therapeutically address various disease conditions. This review delves into the role of snoRNAs in health and disease and explores the broad potential of these snoRNAs as therapeutic agents in human pathologies.

Selection on synonymous sites: the unwanted transcript hypothesis

Although translational selection to favour codons that match the most abundant tRNAs is not readily observed in humans, there is nonetheless selection in humans on synonymous mutations. We hypothesize that much of this synonymous site selection can be explained in terms of protection against unwanted RNAs - spurious transcripts, mis-spliced forms or RNAs derived from transposable elements or viruses. We propose not only that selection on synonymous sites functions to reduce the rate of creation of unwanted transcripts (for example, through selection on exonic splice enhancers and cryptic splice sites) but also that high-GC content (but low-CpG content), together with intron presence and position, is both particular to functional native mRNAs and used to recognize transcripts as native. In support of this hypothesis, transcription, nuclear export, liquid phase condensation and RNA degradation have all recently been shown to promote GC-rich transcripts and suppress AU/CpG-rich ones. With such 'traps' being set against AU/CpG-rich transcripts, the codon usage of native genes has, in turn, evolved to avoid such suppression. That parallel filters against AU/CpG-rich transcripts also affect the endosomal import of RNAs further supports the unwanted transcript hypothesis of synonymous site selection and explains the similar design rules that have enabled the successful use of transgenes and RNA vaccines.

Characterizing nascent transcription patterns of PROMPTs, eRNAs, and readthrough transcripts in the ENCODE4 deeply profiled cell lines

Arising as co-products of canonical gene expression, transcription-associated lincRNAs, such as promoter upstream transcripts (PROMPTs), enhancer RNAs (eRNAs), and readthrough (RT) transcripts, are often regarded as byproducts of transcription, although they may be important for the expression of nearby genes. We identified regions of nascent expression of these lincRNA in 16 human cell lines using Bru-seq techniques, and found distinctly regulated patterns of PROMPT, eRNA, and RT transcription using the diverse biochemical approaches in the ENCODE4 deeply profiled cell lines collection. Transcription of these lincRNAs was influenced by sequence-specific features and the local or 3D chromatin landscape. However, these sequence and chromatin features do not describe the full spectrum of lincRNA expression variability we identify, highlighting the complexity of their regulation. This may suggest that transcription-associated lincRNAs are not merely byproducts, but rather that the transcript itself, or the act of its transcription, is important for genomic function.

Nuclear RNA homeostasis promotes systems-level coordination of cell fate and senescence

Understanding cellular coordination remains a challenge despite knowledge of individual pathways. The RNA exosome, targeting a wide range of RNA substrates, is often downregulated in cellular senescence. Utilizing an auxin-inducible system, we observed that RNA exosome depletion in embryonic stem cells significantly affects the transcriptome and proteome, causing pluripotency loss and pre-senescence onset. Mechanistically, exosome depletion triggers acute nuclear RNA aggregation, disrupting nuclear RNA-protein equilibrium. This disturbance limits nuclear protein availability and hinders polymerase initiation and engagement, reducing gene transcription. Concurrently, it promptly disrupts nucleolar transcription, ribosomal processes, and nuclear exporting, resulting in a translational shutdown. Prolonged exosome depletion induces nuclear structural changes resembling senescent cells, including aberrant chromatin compaction, chromocenter disassembly, and intensified heterochromatic foci. These effects suggest that the dynamic turnover of nuclear RNA orchestrates crosstalk between essential processes to optimize cellular function. Disruptions in nuclear RNA homeostasis result in systemic functional decline, altering the cell state and promoting senescence.

Nuclear mRNA decay: regulatory networks that control gene expression

Proper regulation of mRNA production in the nucleus is critical for the maintenance of cellular homoeostasis during adaptation to internal and environmental cues. Over the past 25 years, it has become clear that the nuclear machineries governing gene transcription, pre-mRNA processing, pre-mRNA and mRNA decay, and mRNA export to the cytoplasm are inextricably linked to control the quality and quantity of mRNAs available for translation. More recently, an ever-expanding diversity of new mechanisms by which nuclear RNA decay factors finely tune the expression of protein-encoding genes have been uncovered. Here, we review the current understanding of how mammalian cells shape their protein-encoding potential by regulating the decay of pre-mRNAs and mRNAs in the nucleus.

The role of non-protein-coding RNAs in ischemic acute kidney injury

Acute kidney injury (AKI) is a condition characterized by a rapid decline in kidney function within a span of 48 hours. It is influenced by various factors including inflammation, oxidative stress, excessive calcium levels within cells, activation of the renin-angiotensin system, and dysfunction in microcirculation. Ischemia-reperfusion injury (IRI) is recognized as a major cause of AKI; however, the precise mechanisms behind this process are not yet fully understood and effective treatments are still needed. To enhance the accuracy of diagnosing AKI during its early stages, the utilization of innovative markers is crucial. Numerous studies suggest that certain noncoding RNAs (ncRNAs), such as long noncoding RNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs), play a central role in regulating gene expression and protein synthesis. These ncRNAs are closely associated with the development and recovery of AKI and have been detected in both kidney tissue and bodily fluids. Furthermore, specific ncRNAs may serve as diagnostic markers and potential targets for therapeutic interventions in AKI. This review aims to summarize the functional roles and changes observed in noncoding RNAs during ischemic AKI, as well as explore their therapeutic potential.

Keep quiet: the HUSH complex in transcriptional silencing and disease

The human silencing hub (HUSH) complex is an epigenetic repressor complex whose role has emerged as an important guardian of genome integrity. It protects the genome from exogenous DNA invasion and regulates endogenous retroelements by recruiting histone methyltransferases catalyzing histone 3 lysine 9 trimethylation (H3K9me3) and additional proteins involved in chromatin compaction. In particular, its regulation of transcriptionally active LINE1 retroelements, by binding to and neutralizing LINE1 transcripts, has been well characterized. HUSH is required for mouse embryogenesis and is associated with disease, in particular cancer. Here we provide insights into the structural and biochemical features of the HUSH complex. Furthermore, we discuss the molecular mechanisms by which the HUSH complex is recruited to specific genomic regions and how it silences transcription. Finally, we discuss the role of HUSH complex members in mammalian development, antiretroviral immunity, and diseases such as cancer.

Nuclear RNA catabolism controls endogenous retroviruses, gene expression asymmetry, and dedifferentiation

Endogenous retroviruses (ERVs) are remnants of ancient parasitic infections and comprise sizable portions of most genomes. Although epigenetic mechanisms silence most ERVs by generating a repressive environment that prevents their expression (heterochromatin), little is known about mechanisms silencing ERVs residing in open regions of the genome (euchromatin). This is particularly important during embryonic development, where induction and repression of distinct classes of ERVs occur in short temporal windows. Here, we demonstrate that transcription-associated RNA degradation by the nuclear RNA exosome and Integrator is a regulatory mechanism that controls the productive transcription of most genes and many ERVs involved in preimplantation development. Disrupting nuclear RNA catabolism promotes dedifferentiation to a totipotent-like state characterized by defects in RNAPII elongation and decreased expression of long genes (gene-length asymmetry). Our results indicate that RNA catabolism is a core regulatory module of gene networks that safeguards RNAPII activity, ERV expression, cell identity, and developmental potency.

Noncoding snoRNA host genes are a distinct subclass of long noncoding RNAs

Mammalian genomes are pervasively transcribed into different noncoding (nc)RNA classes, each one with its own hallmarks and exceptions. Some of them are nested into each other, such as host genes for small nucleolar RNAs (snoRNAs), which were long believed to simply act as molecular containers strictly facilitating snoRNA biogenesis. However, recent findings show that noncoding snoRNA host genes (ncSNHGs) display features different from those of 'regular' long ncRNAs (lncRNAs) and, more importantly, they can exert independent and unrelated functions to those of the encoded snoRNAs. Here, we review and summarize past and recent evidence that ncSNHGs form a defined subclass among the plethora of lncRNAs, and discuss future research that can further elucidate their biological relevance.

PAPγ associates with PAXT nuclear exosome to control the abundance of PROMPT ncRNAs

Pervasive transcription of the human genome generates an abundance of RNAs that must be processed and degraded. The nuclear RNA exosome is the main RNA degradation machinery in the nucleus. However, nuclear exosome must be recruited to its substrates by targeting complexes, such as NEXT or PAXT. By proteomic analysis, we identify additional subunits of PAXT, including many orthologs of MTREC found in S. pombe. In particular, we show that polyA polymerase gamma (PAPγ) associates with PAXT. Genome-wide mapping of the binding sites of ZFC3H1, RBM27 and PAPγ shows that PAXT is recruited to the TSS of hundreds of genes. Loss of ZFC3H1 abolishes recruitment of PAXT subunits including PAPγ to TSSs and concomitantly increases the abundance of PROMPTs at the same sites. Moreover, PAPγ, as well as MTR4 and ZFC3H1, is implicated in the polyadenylation of PROMPTs. Our results thus provide key insights into the direct targeting of PROMPT ncRNAs by PAXT at their genomic sites.

Enhancer in cancer pathogenesis and treatment

Enhancers are essential cis-acting regulatory elements that determine cell identity and tumor progression. Enhancer function is dependent on the physical interaction between the enhancer and its target promoter inside its local chromatin environment. Enhancer reprogramming is an important mechanism in cancer pathogenesis and can be driven by both cis and trans factors. Super enhancers are acquired at oncogenes in numerous cancer types and represent potential targets for cancer treatment. BET and CDK inhibitors act through mechanisms of enhancer function and have shown promising results in therapy for various types of cancer. Genome editing is another way to reprogram enhancers in cancer treatment. The relationship between enhancers and cancer has been revised by several authors in the past few years, which mainly focuses on the mechanisms by which enhancers can impact cancer. Here, we emphasize SE's role in cancer pathogenesis and the new therapies involving epigenetic regulators (BETi and CDKi). We suggest that understanding mechanisms of activity would aid clinical success for these anti-cancer agents.

Enhancer RNAs: mechanisms in transcriptional regulation and functions in diseases

In recent years, increasingly more non-coding RNAs have been detected with the development of high-throughput sequencing technology, including microRNAs (miRNAs), long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), small nucleolar RNAs (snoRNAs), and piwi-interacting RNA (piRNAs). The discovery of enhancer RNAs (eRNAs) in 2010 has further broadened the range of non-coding RNAs revealed. eRNAs are non-coding RNA molecules produced by the transcription of DNA cis-acting elements, enhancer fragments. Recent studies revealed that the transcription of eRNAs may be a biological marker responding to enhancer activity that can participate in the regulation of coding gene transcription. In this review, we discussed the biological characteristics of eRNAs, their functions in transcriptional regulation, the regulation factors of eRNAs production, and the research progress of eRNAs in different diseases. Video Abstract.

EvIPqPCR, Target Circulating Tumorous Extracellular Vesicles for Detection of Pancreatic Cancer

Pancreatic cancer patients predominantly present with advanced disease at diagnosis, contributing to its high mortality. A noninvasive, fast screening method to detect this disease is an unmet need. Tumor-derived extracellular vesicles (tdEVs) bearing information from parental cells have emerged as a promising cancer diagnostic biomarker. However, most tdEV-based assays have impractical sample volumes and time-consuming, complex, and costly techniques. To overcome these limitations, we developed a novel diagnostic method for pancreatic cancer screening. Our approach utilizes the mitochondrial DNA to nuclear DNA ratio of EVs as a collective cell-specific characteristic. We introduce EvIPqPCR, a fast method that combines immunoprecipitation (IP) and qPCR quantification to detect tumor-derived EVs directly from serum. Importantly, our method employs DNA isolation-free and duplexing probes for qPCR, saving at least 3 h. This technique has the potential to serve as a translational assay for cancer screening with a weak correlation to prognosis biomarkers and sufficient discriminatory power among healthy controls, pancreatitis, and pancreatic cancer cases.

The life and times of a tRNA

The study of eukaryotic tRNA processing has given rise to an explosion of new information and insights in the last several years. We now have unprecedented knowledge of each step in the tRNA processing pathway, revealing unexpected twists in biochemical pathways, multiple new connections with regulatory pathways, and numerous biological effects of defects in processing steps that have profound consequences throughout eukaryotes, leading to growth phenotypes in the yeast Saccharomyces cerevisiae and to neurological and other disorders in humans. This review highlights seminal new results within the pathways that comprise the life of a tRNA, from its birth after transcription until its death by decay. We focus on new findings and revelations in each step of the pathway including the end-processing and splicing steps, many of the numerous modifications throughout the main body and anticodon loop of tRNA that are so crucial for tRNA function, the intricate tRNA trafficking pathways, and the quality control decay pathways, as well as the biogenesis and biology of tRNA-derived fragments. We also describe the many interactions of these pathways with signaling and other pathways in the cell.

ARS2 instructs early transcription termination-coupled RNA decay by recruiting ZC3H4 to nascent transcripts

The RNA-binding ARS2 protein is centrally involved in both early RNA polymerase II (RNAPII) transcription termination and transcript decay. Despite its essential nature, the mechanisms by which ARS2 enacts these functions have remained unclear. Here, we show that a conserved basic domain of ARS2 binds a corresponding acidic-rich, short linear motif (SLiM) in the transcription restriction factor ZC3H4. This interaction recruits ZC3H4 to chromatin to elicit RNAPII termination, independent of other early termination pathways defined by the cleavage and polyadenylation (CPA) and Integrator (INT) complexes. We find that ZC3H4, in turn, forms a direct connection to the nuclear exosome targeting (NEXT) complex, hereby facilitating rapid degradation of the nascent RNA. Hence, ARS2 instructs the coupled transcription termination and degradation of the transcript onto which it is bound. This contrasts with ARS2 function at CPA-instructed termination sites where the protein exclusively partakes in RNA suppression via post-transcriptional decay.

A ZTF-7/RPS-2 complex mediates the cold-warm response in C. elegans

Temperature greatly affects numerous biological processes in all organisms. How multicellular organisms respond to and are impacted by hypothermic stress remains elusive. Here, we found that cold-warm stimuli induced depletion of the RNA exosome complex in the nucleoli but enriched it in the nucleoplasm. To further understand the function and mechanism of cold-warm stimuli, we conducted forward genetic screening and identified ZTF-7, which is required for RNA exosome depletion from nucleoli upon transient cold-warm exposure in C. elegans. ZTF-7 is a putative ortholog of human ZNF277 that may contribute to language impairments. Immunoprecipitation followed by mass spectrometry (IP-MS) found that ZTF-7 interacted with RPS-2, which is a ribosomal protein of the small subunit and participates in pre-rRNA processing. A partial depletion of RPS-2 and other proteins of the small ribosomal subunit blocked the cold-warm stimuli-induced reduction of exosome subunits from the nucleoli. These results established a novel mechanism by which C. elegans responds to environmental cold-warm exposure.

Temporal-iCLIP captures co-transcriptional RNA-protein interactions

Dynamic RNA-protein interactions govern the co-transcriptional packaging of RNA polymerase II (RNAPII)-derived transcripts. Yet, our current understanding of this process in vivo primarily stems from steady state analysis. To remedy this, we here conduct temporal-iCLIP (tiCLIP), combining RNAPII transcriptional synchronisation with UV cross-linking of RNA-protein complexes at serial timepoints. We apply tiCLIP to the RNA export adaptor, ALYREF; a component of the Nuclear Exosome Targeting (NEXT) complex, RBM7; and the nuclear cap binding complex (CBC). Regardless of function, all tested factors interact with nascent RNA as it exits RNAPII. Moreover, we demonstrate that the two transesterification steps of pre-mRNA splicing temporally separate ALYREF and RBM7 binding to splicing intermediates, and that exon-exon junction density drives RNA 5'end binding of ALYREF. Finally, we identify underappreciated steps in snoRNA 3'end processing performed by RBM7. Altogether, our data provide a temporal view of RNA-protein interactions during the early phases of transcription.

An update on post-transcriptional regulation of retrotransposons

Retrotransposons, including LINE-1, Alu, SVA, and endogenous retroviruses, are one of the major constituents of human genomic repetitive sequences. Through the process of retrotransposition, some of them occasionally insert into new genomic locations by a copy-paste mechanism involving RNA intermediates. Irrespective of de novo genomic insertions, retrotransposon expression can lead to DNA double-strand breaks and stimulate cellular innate immunity through endogenous patterns. As a result, retrotransposons are tightly regulated by multi-layered regulatory processes to prevent the dangerous effects of their expression. In recent years, significant progress was made in revealing how retrotransposon biology intertwines with general post-transcriptional RNA metabolism. Here, I summarize current knowledge on the involvement of post-transcriptional factors in the biology of retrotransposons, focusing on LINE-1. I emphasize general RNA metabolisms such as methylation of adenine (m⁶ A), RNA 3'-end polyadenylation and uridylation, RNA decay and translation regulation. I discuss the effects of retrotransposon RNP sequestration in cytoplasmic bodies and autophagy. Finally, I summarize how innate immunity restricts retrotransposons and how retrotransposons make use of cellular enzymes, including the DNA repair machinery, to complete their replication cycles.

Maturation of small nucleolar RNAs: from production to function

Small Nucleolar RNAs (snoRNAs) are an abundant group of non-coding RNAs with well-defined roles in ribosomal RNA processing, folding and chemical modification. Besides their classic roles in ribosome biogenesis, snoRNAs are also implicated in several other cellular activities including regulation of splicing, transcription, RNA editing, cellular trafficking, and miRNA-like functions. Mature snoRNAs must undergo a series of processing steps tightly regulated by transiently associating factors and coordinated with other cellular processes including transcription and splicing. In addition to their mature forms, snoRNAs can contribute to gene expression regulation through their derivatives and degradation products. Here, we review the current knowledge on mechanisms of snoRNA maturation, including the different pathways of processing, and the regulatory mechanisms that control snoRNA levels and complex assembly. We also discuss the significance of studying snoRNA maturation, highlight the gaps in the current knowledge and suggest directions for future research in this area.

C-terminal determinants for RNA binding motif 7 protein stability and RNA recognition

The 7SK ribonucleoprotein (RNP) is a critical regulator of eukaryotic transcription. Recently, RNA binding motif 7 (RBM7) containing an RNA recognition motif (RRM) was reported to associate with 7SK RNA and core 7SK RNP protein components in response to DNA damage. However, little is known about the mode of RBM7-7SK RNA recognition. Here, we found that RRM constructs containing extended C-termini have increased solubility compared to a minimal RRM construct, although these constructs aggregate in a temperature and concentration-dependent manner. Using solution NMR dynamics experiments, we identified additional structural features observed previously in crystal but not in solution structures. To identify potential RBM7-7SK RNA binding sites, we analyzed deposited data from in cellulo crosslinking experiments and found that RBM7 primarily crosslinks to the distal region of 7SK stem-loop 3 (SL3). Electrophoretic mobility shift assays and NMR chemical shift perturbation experiments showed weak binding to 7SK SL3 constructs in vitro. Together, these results provide new insights into RBM7 RRM folding and recognition of 7SK RNA.

Structural analysis of Red1 as a conserved scaffold of the RNA-targeting MTREC/PAXT complex

To eliminate specific or aberrant transcripts, eukaryotes use nuclear RNA-targeting complexes that deliver them to the exosome for degradation. S. pombe MTREC, and its human counterpart PAXT, are key players in this mechanism but inner workings of these complexes are not understood in sufficient detail. Here, we present an NMR structure of an MTREC scaffold protein Red1 helix-turn-helix domain bound to the Iss10 N-terminus and show this interaction is required for proper cellular growth and meiotic mRNA degradation. We also report a crystal structure of a Red1-Ars2 complex explaining mutually exclusive interactions of hARS2 with various ED/EGEI/L motif-possessing RNA regulators, including hZFC3H1 of PAXT, hFLASH or hNCBP3. Finally, we show that both Red1 and hZFC3H1 homo-dimerize via their coiled-coil regions indicating that MTREC and PAXT likely function as dimers. Our results, combining structures of three Red1 interfaces with in vivo studies, provide mechanistic insights into conserved features of MTREC/PAXT architecture.

MPP6 stimulates both RRP6 and DIS3 to degrade a specified subset of MTR4-sensitive substrates in the human nucleus

Recent in vitro reconstitution analyses have proven that the physical interaction between the exosome core and MTR4 helicase, which promotes the exosome activity, is maintained by either MPP6 or RRP6. However, knowledge regarding the function of MPP6 with respect to in vivo exosome activity remains scarce. Here, we demonstrate a facilitative function of MPP6 that composes a specific part of MTR4-dependent substrate decay by the human exosome. Using RNA polymerase II-transcribed poly(A)+ substrate accumulation as an indicator of a perturbed exosome, we found functional redundancy between RRP6 and MPP6 in the decay of these poly(A)+ transcripts. MTR4 binding to the exosome core via MPP6 was essential for MPP6 to exert its redundancy with RRP6. However, at least for the decay of our identified exosome substrates, MTR4 recruitment by MPP6 was not functionally equivalent to recruitment by RRP6. Genome-wide classification of substrates based on their sensitivity to each exosome component revealed that MPP6 deals with a specific range of substrates and highlights the importance of MTR4 for their decay. Considering recent findings of competitive binding to the exosome between auxiliary complexes, our results suggest that the MPP6-incorporated MTR4-exosome complex is one of the multiple alternative complexes rather than the prevailing one.

Computational identification of signals predictive for nuclear RNA exosome degradation pathway targeting

The RNA exosome degrades transcripts in the nucleoplasm of mammalian cells. Its substrate specificity is mediated by two adaptors: the ‘nuclear exosome targeting (NEXT)’ complex and the ‘poly(A) exosome targeting (PAXT)’ connection. Previous studies have revealed some DNA/RNA elements that differ between the two pathways, but how informative these features are for distinguishing pathway targeting, or whether additional genomic features that are informative for such classifications exist, is unknown. Here, we leverage the wealth of available genomic data and develop machine learning models that predict exosome targets and subsequently rank the features the models use by their predictive power. As expected, features around transcript end sites were most predictive; specifically, the lack of canonical 3′ end processing was highly predictive of NEXT targets. Other associated features, such as promoter-proximal G/C content and 5′ splice sites, were informative, but only for distinguishing NEXT and not PAXT targets. Finally, we discovered predictive features not previously associated with exosome targeting, in particular RNA helicase DDX3X binding sites. Overall, our results demonstrate that nucleoplasmic exosome targeting is to a large degree predictable, and our approach can assess the predictive power of previously known and new features in an unbiased way.

What's NEXT for the exosome?

Two recent studies by Gerlach et al. (2022) and Puno and Lima (2022) provide new structural and functional insight into the assembly of the nuclear exosome targeting complex (NEXT) and how it may target specific classes of RNA for degradation.

Structural basis for RNA surveillance by the human nuclear exosome targeting (NEXT) complex

RNA quality control relies on co-factors and adaptors to identify and prepare substrates for degradation by ribonucleases such as the 3' to 5' ribonucleolytic RNA exosome. Here, we determined cryogenic electron microscopy structures of human nuclear exosome targeting (NEXT) complexes bound to RNA that reveal mechanistic insights to substrate recognition and early steps that precede RNA handover to the exosome. The structures illuminate ZCCHC8 as a scaffold, mediating homodimerization while embracing the MTR4 helicase and flexibly anchoring RBM7 to the helicase core. All three subunits collaborate to bind the RNA, with RBM7 and ZCCHC8 surveying sequences upstream of the 3' end to facilitate RNA capture by MTR4. ZCCHC8 obscures MTR4 surfaces important for RNA binding and extrusion as well as MPP6-dependent recruitment and docking onto the RNA exosome core, interactions that contribute to RNA surveillance by coordinating RNA capture, translocation, and extrusion from the helicase to the exosome for decay.

Anomalous HIV-1 RNA, How Cap-Methylation Segregates Viral Transcripts by Form and Function

The acquisition of m7G-cap-binding proteins is now recognized as a major variable driving the form and function of host RNAs. This manuscript compares the 5'-cap-RNA binding proteins that engage HIV-1 precursor RNAs, host mRNAs, small nuclear (sn)- and small nucleolar (sno) RNAs and sort into disparate RNA-fate pathways. Before completion of the transcription cycle, the transcription start site of nascent class II RNAs is appended to a non-templated guanosine that is methylated (m7G-cap) and bound by hetero-dimeric CBP80-CBP20 cap binding complex (CBC). The CBC is a nexus for the co-transcriptional processing of precursor RNAs to mRNAs and the snRNA and snoRNA of spliceosomal and ribosomal ribonucleoproteins (RNPs). Just as sn/sno-RNAs experience hyper-methylation of m7G-cap to trimethylguanosine (TMG)-cap, so do select HIV RNAs and an emerging cohort of mRNAs. TMG-cap is blocked from Watson:Crick base pairing and disqualified from participating in secondary structure. The HIV TMG-cap has been shown to license select viral transcripts for specialized cap-dependent translation initiation without eIF4E that is dependent upon CBP80/NCBP3. The exceptional activity of HIV precursor RNAs secures their access to maturation pathways of sn/snoRNAs, canonical and non-canonical host mRNAs in proper stoichiometry to execute the retroviral replication cycle.

Structure and regulation of the nuclear exosome targeting complex guides RNA substrates to the exosome

In mammalian cells, spurious transcription results in a vast repertoire of unproductive non-coding RNAs, whose deleterious accumulation is prevented by rapid decay. The nuclear exosome targeting (NEXT) complex plays a central role in directing non-functional transcripts to exosome-mediated degradation, but the structural and molecular mechanisms remain enigmatic. Here, we elucidated the architecture of the human NEXT complex, showing that it exists as a dimer of MTR4-ZCCHC8-RBM7 heterotrimers. Dimerization preconfigures the major MTR4-binding region of ZCCHC8 and arranges the two MTR4 helicases opposite to each other, with each protomer able to function on many types of RNAs. In the inactive state of the complex, the 3′ end of an RNA substrate is enclosed in the MTR4 helicase channel by a ZCCHC8 C-terminal gatekeeping domain. The architecture of a NEXT-exosome assembly points to the molecular and regulatory mechanisms with which the NEXT complex guides RNA substrates to the exosome.

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NEXT homodimerizes through two intertwined ZCCHC8 subunits

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ZCCHC8 binds MTR4 with both constitutive and regulatory interactions

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Stable MTR4 arch interactions orient the two helicases in opposite directions

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Regulatory interactions at the MTR4 helicase domain guide RNA to the exosome

Inflammatory Immune-Associated eRNA: Mechanisms, Functions and Therapeutic Prospects

The rapid development of multiple high-throughput sequencing technologies has made it possible to explore the critical roles and mechanisms of functional enhancers and enhancer RNAs (eRNAs). The inflammatory immune response, as a fundamental pathological process in infectious diseases, cancers and immune disorders, coordinates the balance between the internal and external environment of the organism. It has been shown that both active enhancers and intranuclear eRNAs are preferentially expressed over inflammation-related genes in response to inflammatory stimuli, suggesting that enhancer transcription events and their products influence the expression and function of inflammatory genes. Therefore, in this review, we summarize and discuss the relevant inflammatory roles and regulatory mechanisms of eRNAs in inflammatory immune cells, non-inflammatory immune cells, inflammatory immune diseases and tumors, and explore the potential therapeutic effects of enhancer inhibitors affecting eRNA production for diseases with inflammatory immune responses.

Enhancer RNA Transcription Is Essential for a Novel CSF1 Enhancer in Triple-Negative Breast Cancer

Enhancers are critical regulatory elements in the genome that help orchestrate spatiotemporal patterns of gene expression during development and normal physiology. In cancer, enhancers are often rewired by various genetic and epigenetic mechanisms for the activation of oncogenes that lead to initiation and progression. A key feature of active enhancers is the production of non-coding RNA molecules called enhancer RNAs, whose functions remain unknown but can be used to specify active enhancers de novo. Using a combination of eRNA transcription and chromatin modifications, we have identified a novel enhancer located 30 kb upstream of Colony Stimulating Factor 1 (CSF1). Notably, CSF1 is implicated in the progression of breast cancer, is overexpressed in triple-negative breast cancer (TNBC) cell lines, and its enhancer is primarily active in TNBC patient tumors. Genomic deletion of the enhancer (via CRISPR/Cas9) enabled us to validate this regulatory element as a bona fide enhancer of CSF1 and subsequent cell-based assays revealed profound effects on cancer cell proliferation, colony formation, and migration. Epigenetic silencing of the enhancer via CRISPR-interference assays (dCas9-KRAB) coupled to RNA-sequencing, enabled unbiased identification of additional target genes, such as RSAD2, that are predictive of clinical outcome. Additionally, we repurposed the RNA-guided RNA-targeting CRISPR-Cas13 machinery to specifically degrade the eRNAs transcripts produced at this enhancer to determine the consequences on CSF1 mRNA expression, suggesting a post-transcriptional role for these non-coding transcripts. Finally, we test our eRNA-dependent model of CSF1 enhancer function and demonstrate that our results are extensible to other forms of cancer. Collectively, this work describes a novel enhancer that is active in the TNBC subtype, which is associated with cellular growth, and requires eRNA transcripts for proper enhancer function. These results demonstrate the significant impact of enhancers in cancer biology and highlight their potential as tractable targets for therapeutic intervention.

Chromatin modifier HUSH co-operates with RNA decay factor NEXT to restrict transposable element expression

Transposable elements (TEs) are widespread genetic parasites known to be kept under tight transcriptional control. Here, we describe a functional connection between the mouse-orthologous “nuclear exosome targeting” (NEXT) and “human silencing hub” (HUSH) complexes, involved in nuclear RNA decay and the epigenetic silencing of TEs, respectively. Knocking out the NEXT component ZCCHC8 in embryonic stem cells results in elevated TE RNA levels. We identify a physical interaction between ZCCHC8 and the MPP8 protein of HUSH and establish that HUSH recruits NEXT to chromatin at MPP8-bound TE loci. However, while NEXT and HUSH both dampen TE RNA expression, their activities predominantly affect shorter non-polyadenylated and full-length polyadenylated transcripts, respectively. Indeed, our data suggest that the repressive action of HUSH promotes a condition favoring NEXT RNA decay activity. In this way, transcriptional and post-transcriptional machineries synergize to suppress the genotoxic potential of TE RNAs.

Garland et al. report a physical and functional connection between the NEXT complex, involved in RNA decay, and the HUSH complex, involved in chromatin regulation. Together, NEXT and HUSH cooperate to control transposable element (TE) RNA expression in embryonic stem cells, suppressing pA⁻ and pA⁺ transcripts, respectively.

Catalytic activities, molecular connections, and biological functions of plant RNA exosome complexes

RNA exosome complexes provide the main 3'-5'-exoribonuclease activities in eukaryotic cells and contribute to the maturation and degradation of virtually all types of RNA. RNA exosomes consist of a conserved core complex that associates with exoribonucleases and with multimeric cofactors that recruit the enzyme to its RNA targets. Despite an overall high level of structural and functional conservation, the enzymatic activities and compositions of exosome complexes and their cofactor modules differ among eukaryotes. This review highlights unique features of plant exosome complexes, such as the phosphorolytic activity of the core complex, and discusses the exosome cofactors that operate in plants and are dedicated to the maturation of ribosomal RNA, the elimination of spurious, misprocessed, and superfluous transcripts, or the removal of mRNAs cleaved by the RNA-induced silencing complex and other mRNAs prone to undergo silencing.

Rapid factor depletion highlights intricacies of nucleoplasmic RNA degradation

Turnover of nucleoplasmic transcripts by the mammalian multi-subunit RNA exosome is mediated by two adaptors: the Nuclear EXosome Targeting (NEXT) complex and the Poly(A) tail eXosome Targeting (PAXT) connection. Functional analyses of NEXT and PAXT have largely utilized long-term factor depletion strategies, facilitating the appearance of indirect phenotypes. Here, we rapidly deplete NEXT, PAXT and core exosome components, uncovering the direct consequences of their acute losses. Generally, proteome changes are sparse and largely dominated by co-depletion of other exosome and adaptor subunits, reflecting possible subcomplex compositions. While parallel high-resolution 3′ end sequencing of newly synthesized RNA confirms previously established factor specificities, it concomitantly demonstrates an inflation of long-term depletion datasets by secondary effects. Most strikingly, a general intron degradation phenotype, observed in long-term NEXT depletion samples, is undetectable upon short-term depletion, which instead emphasizes NEXT targeting of snoRNA-hosting introns. Further analysis of these introns uncovers an unusual mode of core exosome-independent RNA decay. Our study highlights the accumulation of RNAs as an indirect result of long-term decay factor depletion, which we speculate is, at least partly, due to the exhaustion of alternative RNA decay pathways.

β-Sheet Richness of the Circulating Tumor-Derived Extracellular Vesicles for Noninvasive Pancreatic Cancer Screening

Tumor-derived extracellular vesicles (EVs) are under intensive study for their potential as noninvasive diagnosis biomarkers. Most EV-based cancer diagnostic assays trace supernumerary of a single cancer-associated marker or marker signatures. These types of biomarker assays are either subtype-specific or vulnerable to be masked by high background signals. In this study, we introduce using the β-sheet richness (BR) of the tumor-derived EVs as an effective way to discriminate EVs originating from malignant and nonmalignant cells, where EV contents are evaluated as a collective attribute rather than single factors. Circular dichroism, Fourier transform infrared spectroscopy, fluorescence staining assays, and a de novo workflow combining proteomics, bioinformatics, and protein folding simulations were employed to validate the collective attribute at both cellular and EV levels. Based on the BR of the tumorous EVs, we integrated immunoprecipitation and fluorescence labeling targeting the circulating tumor-derived EVs in serum and developed the process into a clinical assay, named EvIPThT. The assay can distinguish patients with and without malignant disease in a pilot cohort, with weak correlations to prognosis biomarkers, suggesting the potential for a cancer screening panel with existing prognostic biomarkers to improve overall performance.

Nuclear RNA Exosome and Pervasive Transcription: Dual Sculptors of Genome Function

The genome is pervasively transcribed across various species, yielding numerous non-coding RNAs. As a counterbalance for pervasive transcription, various organisms have a nuclear RNA exosome complex, whose structure is well conserved between yeast and mammalian cells. The RNA exosome not only regulates the processing of stable RNA species, such as rRNAs, tRNAs, small nucleolar RNAs, and small nuclear RNAs, but also plays a central role in RNA surveillance by degrading many unstable RNAs and misprocessed pre-mRNAs. In addition, associated cofactors of RNA exosome direct the exosome to distinct classes of RNA substrates, suggesting divergent and/or multi-layer control of RNA quality in the cell. While the RNA exosome is essential for cell viability and influences various cellular processes, mutations and alterations in the RNA exosome components are linked to the collection of rare diseases and various diseases including cancer, respectively. The present review summarizes the relationships between pervasive transcription and RNA exosome, including evolutionary crosstalk, mechanisms of RNA exosome-mediated RNA surveillance, and physiopathological effects of perturbation of RNA exosome.

Heterogeneity among enhancer RNAs: origins, consequences and perspectives

Enhancer RNAs (eRNAs) are non-coding RNAs transcribed from distal cis-regulatory elements (i.e. enhancers), which are stereotyped as short, rarely spliced and unstable. In fact, a non-negligible fraction of eRNAs seems to be longer, spliced and more stable, and their cognate enhancers are epigenomically and functionally distinguishable from typical enhancers. In this review, we first summarized the genomic and molecular origins underlying the observed heterogeneity among eRNAs. Then, we discussed how their heterogeneous properties (e.g. stability) affect the modes of interaction with their regulatory partners, from promiscuous cis-interactions to specific trans-interactions. Finally, we highlighted the existence of a seemingly continuous spectrum of eRNA properties and its implications in the genomic origins of non-coding RNA genes from an evolutionary perspective.

DNA-guided photoactivatable probe-based chemical proteomics reveals the reader protein of mRNA methylation

Chemical modification on mRNA can recruit specific binding proteins (readers/partners) to determine post-transcriptional gene regulation. However, the identification of the reader is extremely limited owing to the rather weak and highly dynamic non-covalent interactions between mRNA modification and reader, and therefore the sensitive and robust approaches are desirable. Here, we report a DNA-guided photoactivatable-based chemical proteomic approach for profiling the readers of mRNA methylation. By use of N⁶-methyladenosine (m⁶A), we illustrated that this method can be successfully utilized for labelling and enriching the readers of mRNA modification, as well as for the discovery of new partners. Thus we applied this strategy to a new modification 2'-O-methyladenosine. As a result, DDX1 was identified and verified as a potential binding protein. Our study therefore provides a powerful chemical proteomics tool for identifying the binding factors of mRNA modification and reveals the underlying function of mRNA modification.

Combined bioscaffold with stem cells and exosomes can improve traumatic brain injury

The intricacy of the brain, along with the existence of blood brain barrier (BBB) does complicate the delivery of effective therapeutics through simple intravascular injection. Hence, an effective delivery mechanism of therapeutics in the event of either traumatic brain injury (TBI) or other brain injuries is needed. Stem cells can promote regeneration and repair injury. The usage of biomaterials and exosomes in transporting stem cells to target lesion sites has been suggested as a potential option. The combination of biomaterials with modified exosomes can help in transporting stem cells to injury sites, whiles also increasing their survival and promoting effective treatment. Herein, we review the current researches pertinent to biological scaffolds and exosomes in repairing TBI and present the current progress and new direction in the clinical setting. We begin with the role of bioscaffold in treating neuronal conditions, the effect of exosomes in injury, and conclude with the improvement of TBI via the employment of combined exosomes, bioscaffold and stem cells.

ARS2/SRRT: at the nexus of RNA polymerase II transcription, transcript maturation and quality control

ARS2/SRRT is an essential eukaryotic protein that has emerged as a critical factor in the sorting of functional from non-functional RNA polymerase II (Pol II) transcripts. Through its interaction with the Cap Binding Complex (CBC), it associates with the cap of newly made RNAs and acts as a hub for competitive exchanges of protein factors that ultimately determine the fate of the associated RNA. The central position of the protein within the nuclear gene expression machinery likely explains why its depletion causes a broad range of phenotypes, yet an exact function of the protein remains elusive. Here, we consider the literature on ARS2/SRRT with the attempt to garner the threads into a unifying working model for ARS2/SRRT function at the nexus of Pol II transcription, transcript maturation and quality control.

A Two-Layered Targeting Mechanism Underlies Nuclear RNA Sorting by the Human Exosome

Degradation of transcripts in human nuclei is primarily facilitated by the RNA exosome. To obtain substrate specificity, the exosome is aided by adaptors; in the nucleoplasm, those adaptors are the nuclear exosome-targeting (NEXT) complex and the poly(A) (pA) exosome-targeting (PAXT) connection. How these adaptors guide exosome targeting remains enigmatic. Employing high-resolution 3' end sequencing, we demonstrate that NEXT substrates arise from heterogenous and predominantly pA^- 3' ends often covering kilobase-wide genomic regions. In contrast, PAXT targets harbor well-defined pA⁺ 3' ends defined by canonical pA site use. Irrespective of this clear division, NEXT and PAXT act redundantly in two ways: (1) regional redundancy, where the majority of exosome-targeted transcription units produce NEXT- and PAXT-sensitive RNA isoforms, and (2) isoform redundancy, where the PAXT connection ensures fail-safe decay of post-transcriptionally polyadenylated NEXT targets. In conjunction, this provides a two-layered targeting mechanism for efficient nuclear sorting of the human transcriptome.

Regulation of human telomerase RNA biogenesis and localization

Maintenance of telomeres is essential for genome integrity and replicative capacity in eukaryotic cells. Telomerase, the ribonucleoprotein complex that catalyses telomere synthesis is minimally composed of a reverse transcriptase and an RNA component. The sequence and structural domains of human telomerase RNA (hTR) have been extensively characterized, while the regulation of hTR transcription, maturation, and localization, is not fully understood. Here, we provide an up-to-date review of hTR, with an emphasis on current breakthroughs uncovering the mechanisms of hTR maturation and localization.

Effects of codon usage on gene expression are promoter context dependent

Codon usage bias is a universal feature of all genomes. Although codon usage has been shown to regulate mRNA and protein levels by influencing mRNA decay and transcription in eukaryotes, little or no genome-wide correlations between codon usage and mRNA levels are detected in mammalian cells, raising doubt on the significance of codon usage effect on gene expression. Here we show that gene-specific regulation reduces the genome-wide codon usage and mRNA correlations: Constitutively expressed genes exhibit much higher genome-wide correlations than differentially expressed genes from fungi to human cells. Using Drosophila S2 cells as a model system, we showed that the effect of codon usage on mRNA expression level is promoter-dependent. Regions downstream of the core promoters of differentially expressed genes can repress the codon usage effects on mRNA expression. An element in the Hsp70 promoter was identified to be necessary and sufficient for this inhibitory effect. The promoter-dependent codon usage effects on mRNA levels are regulated at the transcriptional level through modulation of histone modifications, nucleosome densities and premature termination. Together, our results demonstrate that promoters play a major role in determining whether codon usage influences gene expression and further establish the transcription-dependent codon usage effects on gene expression.

Mtr4 RNA helicase structures and interactions

Mtr4 is a Ski2-like RNA helicase that plays a central role in RNA surveillance and degradation pathways as an activator of the RNA exosome. Multiple crystallographic and cryo-EM studies over the past 10 years have revealed important insight into the Mtr4 structure and interactions with protein and nucleic acid binding partners. These structures place Mtr4 at the center of a dynamic process that recruits RNA substrates and presents them to the exosome. In this review, we summarize the available Mtr4 structures and highlight gaps in our current understanding.

Transcriptionally active enhancers in human cancer cells

The growth of human cancer cells is driven by aberrant enhancer and gene transcription activity. Here, we use transient transcriptome sequencing (TT-seq) to map thousands of transcriptionally active putative enhancers in fourteen human cancer cell lines covering seven types of cancer. These enhancers were associated with cell type-specific gene expression, enriched for genetic variants that predispose to cancer, and included functionally verified enhancers. Enhancer-promoter (E-P) pairing by correlation of transcription activity revealed ~ 40,000 putative E-P pairs, which were depleted for housekeeping genes and enriched for transcription factors, cancer-associated genes, and 3D conformational proximity. The cell type specificity and transcription activity of target genes increased with the number of paired putative enhancers. Our results represent a rich resource for future studies of gene regulation by enhancers and their role in driving cancerous cell growth.

Long Non-Coding RNAs, the Dark Matter: An Emerging Regulatory Component in Plants

Long non-coding RNAs (lncRNAs) are pervasive transcripts of longer than 200 nucleotides and indiscernible coding potential. lncRNAs are implicated as key regulatory molecules in various fundamental biological processes at transcriptional, post-transcriptional, and epigenetic levels. Advances in computational and experimental approaches have identified numerous lncRNAs in plants. lncRNAs have been found to act as prime mediators in plant growth, development, and tolerance to stresses. This review summarizes the current research status of lncRNAs in planta, their classification based on genomic context, their mechanism of action, and specific bioinformatics tools and resources for their identification and characterization. Our overarching goal is to summarize recent progress on understanding the regulatory role of lncRNAs in plant developmental processes such as flowering time, reproductive growth, and abiotic stresses. We also review the role of lncRNA in nutrient stress and the ability to improve biotic stress tolerance in plants. Given the pivotal role of lncRNAs in various biological processes, their functional characterization in agriculturally essential crop plants is crucial for bridging the gap between phenotype and genotype.

Post-transcriptional control of cellular differentiation by the RNA exosome complex

Given the complexity of intracellular RNA ensembles and vast phenotypic remodeling intrinsic to cellular differentiation, it is instructive to consider the role of RNA regulatory machinery in controlling differentiation. Dynamic post-transcriptional regulation of protein-coding and non-coding transcripts is vital for establishing and maintaining proteomes that enable or oppose differentiation. By contrast to extensively studied transcriptional mechanisms governing differentiation, many questions remain unanswered regarding the involvement of post-transcriptional mechanisms. Through its catalytic activity to selectively process or degrade RNAs, the RNA exosome complex dictates the levels of RNAs comprising multiple RNA classes, thereby regulating chromatin structure, gene expression and differentiation. Although the RNA exosome would be expected to control diverse biological processes, studies to elucidate its biological functions and how it integrates into, or functions in parallel with, cell type-specific transcriptional mechanisms are in their infancy. Mechanistic analyses have demonstrated that the RNA exosome confers expression of a differentiation regulatory receptor tyrosine kinase, downregulates the telomerase RNA component TERC, confers genomic stability and promotes DNA repair, which have considerable physiological and pathological implications. In this review, we address how a broadly operational RNA regulatory complex interfaces with cell type-specific machinery to control cellular differentiation.

Out or decay: fate determination of nuclear RNAs

In eukaryotes, RNAs newly synthesized by RNA polymerase II (RNAPII) undergo several processing steps prior to transport to the cytoplasm. It has long been known that RNAs with defects in processing or export are removed in the nucleus. Recent studies revealed that RNAs without apparent defects are also subjected to nuclear degradation, indicating that nuclear RNA fate is determined in a more complex and dynamic way than previously thought. Nuclear RNA sorting directly determines the quality and quantity of RNA pools for future translation and thus is of significant importance. In this essay, we will summarize recent studies on this topic, mainly focusing on findings in mammalian system, and discuss about important remaining questions and possible biological relevance for nuclear RNA fate determination.

Oncogenic action of the exosome cofactor RBM7 by stabilization of CDK1 mRNA in breast cancer

RNA exosome can target the specific RNAs for their processing/degradation by distinct exosome cofactors. As a key component in exosome cofactors, RNA binding motif protein 7 (RBM7) shows the binding specificity for uridine-rich sequences in mRNAs via its RNA recognition motifs. However, the specific function of RBM7 in human breast cancer remains unclear. In vitro, experiments revealed that knockdown of RBM7 dramatically inhibited breast cancer cell proliferation, while inducing G1 cell cycle arrest; the opposite was true when RBM7 was overexpressed. Meanwhile, experiments in vivo confirmed the oncogenic function of RBM7 in breast cancer. RNA sequencing and the following pathway analysis found that cyclin-dependent kinase1 (CDK1) was one of the main gene regulated by RBM7. Overexpression of RBM7 increased CDK1 expression, while RBM7 knockdown decreased it. RIP assays additionally found that RBM7 bound directly to CDK1 mRNA. It was also showed that RBM7 could directly bind to the AU-rich elements (AREs) in 3'-UTR of CDK1 mRNA, which contributed to the stability of CDK1 mRNA by lengthening its half-life. More importantly, the oncogenic activity reduced by knockdown of RBM7 could be rescued by overexpression of CDK1 both in vitro and in vivo, but mutant CDK1 failed. All the evidences implied RBM7 promoted breast cancer cell proliferation by stabilizing CDK1 mRNA via binding to AREs in its 3'-UTR. As we knew, it was the first attempt to connect the RNA exosome to the tumor development, providing new insights into the mechanisms of RNA exosome-linked diseases.

The RNA exosome shapes the expression of key protein-coding genes

The ribonucleolytic exosome complex is central for nuclear RNA degradation, primarily targeting non-coding RNAs. Still, the nuclear exosome could have protein-coding (pc) gene-specific regulatory activities. By depleting an exosome core component, or components of exosome adaptor complexes, we identify ∼2900 transcription start sites (TSSs) from within pc genes that produce exosome-sensitive transcripts. At least 1000 of these overlap with annotated mRNA TSSs and a considerable portion of their transcripts share the annotated mRNA 3′ end. We identify two types of pc-genes, both employing a single, annotated TSS across cells, but the first type primarily produces full-length, exosome-sensitive transcripts, whereas the second primarily produces prematurely terminated transcripts. Genes within the former type often belong to immediate early response transcription factors, while genes within the latter are likely transcribed as a consequence of their proximity to upstream TSSs on the opposite strand. Conversely, when genes have multiple active TSSs, alternative TSSs that produce exosome-sensitive transcripts typically do not contribute substantially to overall gene expression, and most such transcripts are prematurely terminated. Our results display a complex landscape of sense transcription within pc-genes and imply a direct role for nuclear RNA turnover in the regulation of a subset of pc-genes.