INTAC endonuclease and phosphatase modules differentially regulate transcription by RNA polymerase II

PP1/PNUTS phosphatase binds the restrictor complex and stimulates RNA Pol II transcription termination

The restrictor ZC3H4/WDR82 terminates antisense transcription from bidirectional promoters, but its mechanism is poorly understood. We report that ZC3H4/WDR82 immunoprecipitates with PP1 phosphatase and its nuclear targeting subunit, PP1 phosphatase nuclear targeting subunit (PNUTS), which binds to WDR82. AlphaFold predicts a complex of PP1/PNUTS with the restrictor where both PNUTS and ZC3H4 contact WDR82. A substrate trap, PP1H66K-PNUTS, comprising inactive PP1 fused to the PNUTS C terminus, antagonizes restrictor-mediated termination, whereas PP1WT-PNUTS has less of an effect, suggesting that phosphatase activity is required for termination. One PP1/PNUTS substrate implicated in termination by the restrictor is RNA polymerase II (RNA Pol II) CTD Ser5-P. PP1H66K-PNUTS induces Ser5-P hyperphosphorylation at 5' ends, presumably by inhibiting dephosphorylation. NET-seq analysis suggests that CTD Ser5 dephosphorylation would promote termination by increasing RNA Pol II pausing. Both inhibition of termination and CTD hyperphosphorylation require the WDR82 binding domain of PP1H66K-PNUTS, which mediates restrictor binding. In summary, the PP1/PNUTS phosphatase associated with the restrictor via WDR82 promotes efficient transcription termination.

Integrator loss leads to dsRNA formation that triggers the integrated stress response

Integrator (INT) is a metazoan-specific complex that targets promoter-proximally paused RNA polymerase II (RNAPII) for termination, preventing immature RNAPII from entering gene bodies and functionally attenuating transcription of stress-responsive genes. Mutations in INT subunits are associated with many human diseases, including cancer, ciliopathies, and neurodevelopmental disorders, but how reduced INT activity contributes to disease is unknown. Here, we demonstrate that the loss of INT-mediated termination in human cells triggers the integrated stress response (ISR). INT depletion causes upregulation of short genes such as the ISR transcription factor activating transcription factor 3 (ATF3). Further, immature RNAPII that escapes into genes upon INT depletion is prone to premature termination, generating incomplete pre-mRNAs with retained introns. Retroelements within retained introns form double-stranded RNA (dsRNA) that is recognized by protein kinase R (PKR), which drives ATF4 activation and prolonged ISR. Critically, patient cells with INT mutations exhibit dsRNA accumulation and ISR activation, thereby implicating chronic ISR in diseases caused by INT deficiency.

Integrator complex subunit 12 knockout overcomes a transcriptional block to HIV latency reversal

The latent HIV reservoir is a major barrier to HIV cure. Combining latency reversal agents (LRAs) with differing mechanisms of action such as AZD5582, a non-canonical NF-kB activator, and I-BET151, a bromodomain inhibitor is appealing toward inducing HIV-1 reactivation. However, even this LRA combination needs improvement as it is inefficient at activating proviruses in cells of people living with HIV (PLWH). We performed a CRISPR screen in conjunction with AZD5582 & I-BET151 and identified a member of the Integrator complex as a target to improve this LRA combination, specifically Integrator complex subunit 12 (INTS12). Integrator functions as a genome-wide attenuator of transcription that acts on elongation through its RNA cleavage and phosphatase modules. Knockout of INTS12 improved latency reactivation at the transcriptional level and is more specific to the HIV-1 provirus than AZD5582 & I-BET151 treatment alone. We found that INTS12 is present on chromatin at the promoter of HIV and therefore its effect on HIV may be direct. Additionally, we observed more RNAPII in the gene body of HIV only with the combination of INTS12 knockout with AZD5582 & I-BET151, indicating that INTS12 induces a transcriptional elongation block to viral reactivation. Moreover, knockout of INTS12 increased HIV-1 reactivation in CD4 T cells from virally suppressed PLWH ex vivo, and we detected viral RNA in the supernatant from CD4 T cells of all three virally suppressed PLWH tested upon INTS12 knockout, suggesting that INTS12 prevents full-length HIV RNA production in primary T cells. Finally, we found that INTS12 more generally limits the efficacy of a variety of LRAs with different mechanisms of action.

Integrator complex subunit 12 knockout overcomes a transcriptional block to HIV latency reversal

The latent HIV reservoir is a major barrier to HIV cure. Combining latency reversal agents (LRAs) with differing mechanisms of action such as AZD5582, a non-canonical NF-kB activator, and I-BET151, a bromodomain inhibitor is appealing towards inducing HIV-1 reactivation. However, even this LRA combination needs improvement as it is inefficient at activating proviruses in cells from people living with HIV (PLWH). We performed a CRISPR screen in conjunction with AZD5582 & I-BET151 and identified a member of the Integrator complex as a target to improve this LRA combination, specifically Integrator complex subunit 12 (INTS12). Integrator functions as a genome-wide attenuator of transcription that acts on elongation through its RNA cleavage and phosphatase modules. Knockout of INTS12 improved latency reactivation at the transcriptional level and is more specific to the HIV-1 provirus than AZD5582 & I-BET151 treatment alone. We found that INTS12 is present on chromatin at the promoter of HIV and therefore its effect on HIV may be direct. Additionally, we observed more RNAPII in the gene body of HIV only with the combination of INTS12 knockout with AZD5582 & I-BET151, indicating that INTS12 induces a transcriptional elongation block to viral reactivation. Moreover, knockout of INTS12 increased HIV-1 reactivation in CD4 T cells from virally suppressed PLWH ex vivo, and we detected viral RNA in the supernatant from CD4 T cells of all three virally suppressed PLWH tested upon INTS12 knockout suggesting that INTS12 prevents full-length HIV RNA production in primary T cells. Finally, we found that INTS12 more generally limits the efficacy of a variety of LRAs with different mechanisms of action.

Roles of H3K4 methylation in biology and disease

Epigenetic modifications, including posttranslational modifications of histones, are closely linked to transcriptional regulation. Trimethylated H3 lysine 4 (H3K4me3) is one of the most studied histone modifications owing to its enrichment at the start sites of transcription and its association with gene expression and processes determining cell fate, development, and disease. In this review, we focus on recent studies that have yielded insights into how levels and patterns of H3K4me3 are regulated, how H3K4me3 contributes to the regulation of specific phases of transcription such as RNA polymerase II initiation, pause-release, heterogeneity, and consistency. The conclusion from these studies is that H3K4me3 by itself regulates gene expression and its precise regulation is essential for normal development and preventing disease.

LEDGF/p75 promotes transcriptional pausing through preventing SPT5 phosphorylation

SPT5 exhibits versatile functions in RNA Pol II promoter proximal pausing, pause release, and elongation in metazoans. However, the mechanism underlying the functional switch of SPT5 during early elongation has not been fully understood. Here, we report that the phosphorylation site-rich domain (PRD)/CTR1 and the prion-like domain (PLD)/CTR2, which are situated adjacent to each other within the C-terminal repeat (CTR) in SPT5, play pivotal roles in Pol II pausing and elongation, respectively. Our study demonstrates that LEDGF/p75 is highly enriched at promoters, especially paused promoters, and prevents the phosphorylation of SPT5 PRD by the super elongation complex (SEC). Furthermore, deletion of LEDGF IBD leads to increased SEC occupancies and SPT5 PRD phosphorylation at promoters and also increased pause release. In sum, our study reveals that LEDGF and SEC function cooperatively on SPT5 distinct domains to ensure proper transcriptional transition from pausing to elongation.

Catalytic-independent functions of the Integrator-PP2A complex (INTAC) confer sensitivity to BET inhibition

Chromatin and transcription regulators are critical to defining cell identity through shaping epigenetic and transcriptional landscapes, with their misregulation being closely linked to oncogenesis. Pharmacologically targeting these regulators, particularly the transcription-activating BET proteins, has emerged as a promising approach in cancer therapy, yet intrinsic or acquired resistance frequently occurs, with poorly understood mechanisms. Here, using genome-wide CRISPR screens, we find that BET inhibitor efficacy in mediating transcriptional silencing and growth inhibition depends on the auxiliary/arm/tail module of the Integrator-PP2A complex (INTAC), a global regulator of RNA polymerase II pause-release dynamics. This process bypasses a requirement for the catalytic activities of INTAC and instead leverages direct engagement of the auxiliary module with the RACK7/ZMYND8-KDM5C complex to remove histone H3K4 methylation. Targeted degradation of the COMPASS subunit WDR5 to attenuate H3K4 methylation restores sensitivity to BET inhibitors, highlighting how simultaneously targeting coordinated chromatin and transcription regulators can circumvent drug-resistant tumors.

Restrictor slows early transcription elongation to render RNA polymerase II susceptible to termination at non-coding RNA loci

The eukaryotic genome is broadly transcribed by RNA polymerase II (RNAPII) to produce protein-coding messenger RNAs (mRNAs) and a repertoire of non-coding RNAs (ncRNAs). Whereas RNAPII is very processive during mRNA transcription, it terminates rapidly during synthesis of many ncRNAs, particularly those that arise opportunistically from accessible chromatin at gene promoters or enhancers. The divergent fates of mRNA versus ncRNA species raise many questions about how RNAPII and associated machineries discriminate functional from spurious transcription. The Restrictor complex, comprised of the RNA binding protein ZC3H4 and RNAPII-interacting protein WDR82, has been implicated in restraining the expression of ncRNAs. However, the determinants of Restrictor targeting and the mechanism of transcription suppression remain unclear. Here, we investigate Restrictor using unbiased sequence screens, and rapid protein degradation followed by nascent RNA sequencing. We find that Restrictor promiscuously suppresses early elongation by RNAPII, but this activity is blocked at most mRNAs by the presence of a 5' splice site. Consequently, Restrictor is a critical determinant of transcription directionality at divergent promoters and prevents transcriptional interference. Finally, our data indicate that rather than directly terminating RNAPII, Restrictor acts by reducing the rate of transcription elongation, rendering RNAPII susceptible to early termination by other machineries.

Pause Patrol: Negative Elongation Factor's Role in Promoter-Proximal Pausing and Beyond

RNA polymerase (Pol) II is highly regulated to ensure appropriate gene expression. Early transcription elongation is associated with transient pausing of RNA Pol II in the promoter-proximal region. In multicellular organisms, this pausing is stabilized by the association of transcription elongation factors DRB-sensitivity inducing factor (DSIF) and Negative Elongation Factor (NELF). DSIF is a broadly conserved transcription elongation factor whereas NELF is mostly restricted to the metazoan lineage. Mounting evidence suggests that NELF association with RNA Pol II serves as checkpoint for either release into rapid and productive transcription elongation or premature termination at promoter-proximal pause sites. Here we summarize NELF's roles in promoter-proximal pausing, transcription termination, DNA repair, and signaling based on decades of cell biological, biochemical, and structural work and describe areas for future research.

The PNUTS phosphatase complex controls transcription pause release

Gene expression is regulated by controlling distinct steps of the transcriptional cycle, including initiation, pausing, elongation, and termination. Kinases phosphorylate RNA polymerase II (RNA Pol II) and associated factors to control transitions between these steps and to act as central gene regulatory nodes. Similarly, phosphatases that dephosphorylate these components are emerging as important regulators of transcription, although their roles remain less well understood. Here, we discover that the mouse PNUTS-PP1 phosphatase complex plays an essential role in controlling transcription pause release in addition to its previously described function in transcription termination. Transcription pause release by the PNUTS complex is essential for almost all RNA Pol II-dependent gene transcription, relies on its PP1 phosphatase subunit, and controls the phosphorylation of factors required for pause release and elongation. Together, these observations reveal an essential new role for a phosphatase complex in transcription pause release and show that the PNUTS complex is essential for RNA Pol II-dependent transcription.

Redundant pathways for removal of defective RNA polymerase II complexes at a promoter-proximal pause checkpoint

The biological purpose of Integrator and RNA polymerase II (RNAPII) promoter-proximal pausing remains uncertain. Here, we show that loss of INTS6 in human cells results in increased interaction of RNAPII with proteins that can mediate its dissociation from the DNA template, including the CRL3ARMC5 E3 ligase, which ubiquitylates CTD serine5-phosphorylated RPB1 for degradation. ARMC5-dependent RNAPII ubiquitylation is activated by defects in factors acting at the promoter-proximal pause, including Integrator, DSIF, and capping enzyme. This ARMC5 checkpoint normally curtails a sizeable fraction of RNAPII transcription, and ARMC5 knockout cells produce more uncapped transcripts. When both the Integrator and CRL3ARMC5 turnover mechanisms are compromised, cell growth ceases and RNAPII with high pausing propensity disperses from the promoter-proximal pause site into the gene body. These data support a model in which CRL3ARMC5 functions alongside Integrator in a checkpoint mechanism that removes faulty RNAPII complexes at promoter-proximal pause sites to safeguard transcription integrity.

The phosphatase PP1 sustains global transcription by promoting RNA polymerase II pause release

RNA polymerase II progression from initiation to elongation is driven in part by a cascade of protein kinases acting on the core transcription machinery. Conversely, the corresponding phosphatases, notably PP2A and PP1-the most abundant serine-threonine phosphatases in cells-are thought to mainly impede polymerase progression, respectively restraining pause release at promoters and elongation at terminators. Here, we reveal an unexpected role of PP1, within the phosphatase 1 nuclear targeting subunit (PNUTS)-PP1 complex, in sustaining global transcriptional activation in human cells. Acute disruption of PNUTS-PP1 leads to severe defects in the release of paused polymerase and subsequent downregulation for the majority of transcribed genes. PNUTS-PP1 promotes pause release by dephosphorylating multiple substrates, including the 7SK small nuclear ribonucleoprotein particle (snRNP) subunit MEPCE, a known pausing regulator. PNUTS-PP1 exhibits antagonistic functions compared with Integrator-PP2A (INTAC) phosphatase, which generally inhibits pause release. Our research thus highlights opposing roles of PP1 and PP2A in modulating genome-wide transcriptional pausing and gene expression.

CRL3ARMC5 ubiquitin ligase and Integrator phosphatase form parallel mechanisms to control early stages of RNA Pol II transcription

Control of RNA polymerase II (RNA Pol II) through ubiquitylation is essential for the DNA-damage response. Here, we reveal a distinct ubiquitylation pathway in human cells, mediated by CRL3ARMC5, that targets excessive and defective RNA Pol II molecules at the initial stages of the transcription cycle. Upon ARMC5 loss, RNA Pol II accumulates in the free pool and in the promoter-proximal zone but is not permitted into elongation. We identify Integrator subunit 8 (INTS8) as a gatekeeper preventing the release of excess RNA Pol II molecules into gene bodies. Combined loss of ARMC5 and INTS8 has detrimental effects on cell growth and results in the uncontrolled release of excessive RNA Pol II complexes into early elongation, many of which are transcriptionally incompetent and fail to reach the ends of genes. These findings uncover CRL3ARMC5 and Integrator as two distinct pathways acting in parallel to monitor the quantity and quality of transcription complexes before they are licensed into elongation.

DNA-directed termination of mammalian RNA polymerase II

The best-studied mechanism of eukaryotic RNA polymerase II (RNAPII) transcriptional termination involves polyadenylation site-directed cleavage of the nascent RNA. The RNAPII-associated cleavage product is then degraded by XRN2, dislodging RNAPII from the DNA template. In contrast, prokaryotic RNAP and eukaryotic RNAPIII often terminate directly at T-tracts in the coding DNA strand. Here, we demonstrate a similar and omnipresent capability for mammalian RNAPII. Importantly, this termination mechanism does not require upstream RNA cleavage. Accordingly, T-tract-dependent termination can take place when XRN2 cannot be engaged. We show that T-tracts can terminate snRNA transcription independently of RNA cleavage by the Integrator complex. Importantly, we found genome-wide termination at T-tracts in promoter-proximal regions but not within protein-coding gene bodies. XRN2-dependent termination dominates downstream from protein-coding genes, but the T-tract process is sometimes used. Overall, we demonstrate global DNA-directed attrition of RNAPII transcription, suggesting that RNAPs retain the potential to terminate over T-rich sequences throughout evolution.

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.

Cytoplasmic binding partners of the Integrator endonuclease INTS11 and its paralog CPSF73 are required for their nuclear function

INTS11 and CPSF73 are metal-dependent endonucleases for Integrator and pre-mRNA 3'-end processing, respectively. Here, we show that the INTS11 binding partner BRAT1/CG7044, a factor important for neuronal fitness, stabilizes INTS11 in the cytoplasm and is required for Integrator function in the nucleus. Loss of BRAT1 in neural organoids leads to transcriptomic disruption and precocious expression of neurogenesis-driving transcription factors. The structures of the human INTS9-INTS11-BRAT1 and Drosophila dIntS11-CG7044 complexes reveal that the conserved C terminus of BRAT1/CG7044 is captured in the active site of INTS11, with a cysteine residue directly coordinating the metal ions. Inspired by these observations, we find that UBE3D is a binding partner for CPSF73, and UBE3D likely also uses a conserved cysteine residue to directly coordinate the active site metal ions. Our studies have revealed binding partners for INTS11 and CPSF73 that behave like cytoplasmic chaperones with a conserved impact on the nuclear functions of these enzymes.

Assembly mechanism of Integrator's RNA cleavage module

The modular Integrator complex is a transcription regulator that is essential for embryonic development. It attenuates coding gene expression via premature transcription termination and performs 3'-processing of non-coding RNAs. For both activities, Integrator requires endonuclease activity that is harbored by an RNA cleavage module consisting of INTS4-9-11. How correct assembly of Integrator modules is achieved remains unknown. Here, we show that BRAT1 and WDR73 are critical biogenesis factors for the human cleavage module. They maintain INTS9-11 inactive during maturation by physically blocking the endonuclease active site and prevent premature INTS4 association. Furthermore, BRAT1 facilitates import of INTS9-11 into the nucleus, where it is joined by INTS4. Final BRAT1 release requires locking of the mature cleavage module conformation by inositol hexaphosphate (IP6). Our data explain several neurodevelopmental disorders caused by BRAT1, WDR73, and INTS11 mutations as Integrator assembly defects and reveal that IP6 is an essential co-factor for cleavage module maturation.

Transcription directionality is licensed by Integrator at active human promoters

A universal characteristic of eukaryotic transcription is that the promoter recruits RNA polymerase II (RNAPII) to produce both precursor mRNAs (pre-mRNAs) and short unstable promoter upstream transcripts (PROMPTs) toward the opposite direction. However, how the transcription machinery selects the correct direction to produce pre-mRNAs is largely unknown. Here, through multiple acute auxin-inducible degradation systems, we show that rapid depletion of an RNAPII-binding protein complex, Integrator, results in robust PROMPT accumulation throughout the genome. Interestingly, the accumulation of PROMPTs is compensated by the reduction of pre-mRNA transcripts in actively transcribed genes. Consistently, Integrator depletion alters the distribution of polymerase between the sense and antisense directions, which is marked by increased RNAPII-carboxy-terminal domain Tyr1 phosphorylation at PROMPT regions and a reduced Ser2 phosphorylation level at transcription start sites. Mechanistically, the endonuclease activity of Integrator is critical to suppress PROMPT production. Furthermore, our data indicate that the presence of U1 binding sites on nascent transcripts could counteract the cleavage activity of Integrator. In this process, the absence of robust U1 signal at most PROMPTs allows Integrator to suppress the antisense transcription and shift the transcriptional balance in favor of the sense direction.

Structural basis of the Integrator complex assembly and association with transcription factors

Integrator is a multi-subunit protein complex responsible for premature transcription termination of coding and non-coding RNAs. This is achieved via two enzymatic activities, RNA endonuclease and protein phosphatase, acting on the promoter-proximally paused RNA polymerase Ⅱ (RNAPⅡ). Yet, it remains unclear how Integrator assembly and recruitment are regulated and what the functions of many of its core subunits are. Here, we report the structures of two human Integrator sub-complexes: INTS10/13/14/15 and INTS5/8/10/15, and an integrative model of the fully assembled Integrator bound to the RNAPⅡ paused elongating complex (PEC). An in silico protein-protein interaction screen of over 1,500 human transcription factors (TFs) identified ZNF655 as a direct interacting partner of INTS13 within the fully assembled Integrator. We propose a model wherein INTS13 acts as a platform for the recruitment of TFs that could modulate the stability of the Integrator's association at specific loci and regulate transcription attenuation of the target genes.

Basis of gene-specific transcription regulation by the Integrator complex

The Integrator complex attenuates gene expression via the premature termination of RNA polymerase II (RNAP2) at promoter-proximal pausing sites. It is required for stimulus response, cell differentiation, and neurodevelopment, but how gene-specific and adaptive regulation by Integrator is achieved remains unclear. Here, we identify two sites on human Integrator subunits 13/14 that serve as binding hubs for sequence-specific transcription factors (TFs) and other transcription effector complexes. When Integrator is attached to paused RNAP2, these hubs are positioned upstream of the transcription bubble, consistent with simultaneous TF-promoter tethering. The TFs co-localize with Integrator genome-wide, increase Integrator abundance on target genes, and co-regulate responsive transcriptional programs. For instance, sensory cilia formation induced by glucose starvation depends on Integrator-TF contacts. Our data suggest TF-mediated promoter recruitment of Integrator as a widespread mechanism for targeted transcription regulation.

Human promoter directionality is determined by transcriptional initiation and the opposing activities of INTS11 and CDK9

RNA polymerase II (RNAPII) transcription initiates bidirectionally at many human protein-coding genes. Sense transcription usually dominates and leads to messenger RNA production, whereas antisense transcription rapidly terminates. The basis for this directionality is not fully understood. Here, we show that sense transcriptional initiation is more efficient than in the antisense direction, which establishes initial promoter directionality. After transcription begins, the opposing functions of the endonucleolytic subunit of Integrator, INTS11, and cyclin-dependent kinase 9 (CDK9) maintain directionality. Specifically, INTS11 terminates antisense transcription, whereas sense transcription is protected from INTS11-dependent attenuation by CDK9 activity. Strikingly, INTS11 attenuates transcription in both directions upon CDK9 inhibition, and the engineered recruitment of CDK9 desensitises transcription to INTS11. Therefore, the preferential initiation of sense transcription and the opposing activities of CDK9 and INTS11 explain mammalian promoter directionality.

A CPF-like phosphatase module links transcription termination to chromatin silencing

The interconnections between co-transcriptional regulation, chromatin environment, and transcriptional output remain poorly understood. Here, we investigate the mechanism underlying RNA 3' processing-mediated Polycomb silencing of Arabidopsis FLOWERING LOCUS C (FLC). We show a requirement for ANTHESIS PROMOTING FACTOR 1 (APRF1), a homolog of yeast Swd2 and human WDR82, known to regulate RNA polymerase II (RNA Pol II) during transcription termination. APRF1 interacts with TYPE ONE SERINE/THREONINE PROTEIN PHOSPHATASE 4 (TOPP4) (yeast Glc7/human PP1) and LUMINIDEPENDENS (LD), the latter showing structural features found in Ref2/PNUTS, all components of the yeast and human phosphatase module of the CPF 3' end-processing machinery. LD has been shown to co-associate in vivo with the histone H3 K4 demethylase FLOWERING LOCUS D (FLD). This work shows how the APRF1/LD-mediated polyadenylation/termination process influences subsequent rounds of transcription by changing the local chromatin environment at FLC.

Integrator-mediated clustering of poised RNA polymerase II synchronizes histone transcription

Numerous components of the transcription machinery, including RNA polymerase II (Pol II), accumulate in regions of high local concentration known as clusters, which are thought to facilitate transcription. Using the histone locus of Drosophila nurse cells as a model, we find that Pol II forms long-lived, transcriptionally poised clusters distinct from liquid droplets, which contain unbound and paused Pol II. Depletion of the Integrator complex endonuclease module, but not its phosphatase module or Pol II pausing factors disperses these Pol II clusters. Consequently, histone transcription fails to reach peak levels during S-phase and aberrantly continues throughout the cell cycle. We propose that Pol II clustering is a regulatory step occurring near promoters that limits rapid gene activation to defined times.

One Sentence Summary

Using the Drosophila histone locus as a model, we show that clustered RNA polymerase II is poised for synchronous activation.

IntS6 and the Integrator phosphatase module tune the efficiency of select premature transcription termination events

The metazoan-specific Integrator complex catalyzes 3' end processing of small nuclear RNAs (snRNAs) and premature termination that attenuates the transcription of many protein-coding genes. Integrator has RNA endonuclease and protein phosphatase activities, but it remains unclear if both are required for complex function. Here, we show IntS6 (Integrator subunit 6) over-expression blocks Integrator function at a subset of Drosophila protein-coding genes, although having no effect on snRNAs or attenuation of other loci. Over-expressed IntS6 titrates protein phosphatase 2A (PP2A) subunits, thereby only affecting gene loci where phosphatase activity is necessary for Integrator function. IntS6 functions analogous to a PP2A regulatory B subunit as over-expression of canonical B subunits, which do not bind Integrator, is also sufficient to inhibit Integrator activity. These results show that the phosphatase module is critical at only a subset of Integrator-regulated genes and point to PP2A recruitment as a tunable step that modulates transcription termination efficiency.

Protocol for rapidly inducing genome-wide RNA Pol II hyperphosphorylation by selectively disrupting INTAC phosphatase activity

While several inhibitors targeting RNA polymerase II (Pol II) kinases have been applied for inhibiting RNA Pol II phosphorylation, there are few approaches for inducing RNA Pol II hyperphosphorylation. Here, we present a protocol for constructing the INTS8 degradation tag (dTAG) system combined with ectopic expression of N-terminally truncated INTS8 (INTS8-ΔN) in DLD-1 cells. We describe steps for INTS8-dTAG cell line construction, validation of knockin and degradation, and INTS8-ΔN rescue. We then detail validation of RNA Pol II phosphorylation upregulation. For complete details on the use and execution of this protocol, please refer to Hu et al. (2023).1.

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.

Transcriptional elongation control in developmental gene expression, aging, and disease

The elongation stage of transcription by RNA polymerase II (RNA Pol II) is central to the regulation of gene expression in response to developmental and environmental cues in metazoan. Dysregulated transcriptional elongation has been associated with developmental defects as well as disease and aging processes. Decades of genetic and biochemical studies have painstakingly identified and characterized an ensemble of factors that regulate RNA Pol II elongation. This review summarizes recent findings taking advantage of genetic engineering techniques that probe functions of elongation factors in vivo. We propose a revised model of elongation control in this accelerating field by reconciling contradictory results from the earlier biochemical evidence and the recent in vivo studies. We discuss how elongation factors regulate promoter-proximal RNA Pol II pause release, transcriptional elongation rate and processivity, RNA Pol II stability and RNA processing, and how perturbation of these processes is associated with developmental disorders, neurodegenerative disease, cancer, and aging.

R-loop-dependent promoter-proximal termination ensures genome stability

The proper regulation of transcription is essential for maintaining genome integrity and executing other downstream cellular functions1,2. Here we identify a stable association between the genome-stability regulator sensor of single-stranded DNA (SOSS)3 and the transcription regulator Integrator-PP2A (INTAC)4-6. Through SSB1-mediated recognition of single-stranded DNA, SOSS-INTAC stimulates promoter-proximal termination of transcription and attenuates R-loops associated with paused RNA polymerase II to prevent R-loop-induced genome instability. SOSS-INTAC-dependent attenuation of R-loops is enhanced by the ability of SSB1 to form liquid-like condensates. Deletion of NABP2 (encoding SSB1) or introduction of cancer-associated mutations into its intrinsically disordered region leads to a pervasive accumulation of R-loops, highlighting a genome surveillance function of SOSS-INTAC that enables timely termination of transcription at promoters to constrain R-loop accumulation and ensure genome stability.