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LEDGF/p75 promotes transcriptional pausing through preventing SPT5 phosphorylation

ABSTRACT: The transcriptional progression is regulated by SPT5, which is involved in both promoter-proximal RNA polymerase II (Pol II) pausing and elongation, which serve as rate-limiting steps in metazoan. However, the mechanism for SPT5 coordinating these processes remains unclear. Here we report that the disordered sub-regions within SPT5 contain a prion-like domain (PLD) that is required for Pol II pausing, while the phosphorylation site-rich domain (PRD) is essential for transcript elongation. Mechanically, SPT5-PLD helps stabilize Pol II pausing by preventing SPT5-PRD phosphorylation mediated by the super elongation complex (SEC). SPT5-PLD also maintains Pol II pausing by recruiting a newly identified transcriptional pause regulator, PSIP1, which inhibits phosphorylation required for elongation. Additionally, SPT5-PLD prevents premature release of Pol II pausing through PSIP1’s IBD domain by counteracting SEC. Our results demonstrate that SPT5 possesses intrinsic characteristics that balance the transcriptional process by preventing premature pause release and promoting progression to elongation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE250380 | GEO | 2025/01/08

REPOSITORIES: GEO

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The pausing zone and control of RNA polymerase II elongation by Spt5: implications for the pause-release model

Project description:The pause-release model of transcription proposes that pol II pauses 40-100 bases from the start site resulting in a pile-up that is relieved by subsequent release into productive elongation. Pause release is facilitated by PTEFb phosphorylation of the pol II elongation factor, Spt5. We mapped paused polymerases by eNETseq and found frequent pausing in zones that extend ~0.3-3kb into genes, even when PTEFb is inhibited. The fraction of paused polymerases or “pausiness” declines gradually over several kb, and not abruptly as predicted for a discrete pause release event. Spt5 depletion extends pausing zones suggesting that it promotes maturation of elongation complexes to a low-pausing state. Expression of mutants after Spt5 depletion showed that phosphomimetic substitutions in the Spt5 CTR1 domain diminished pausing throughout genes. In contrast mutants that prevent phosphorylation of the Spt5 RNA-binding domain strengthened pausing. Thus distinct Spt5 phospho-isoforms set the balance between pausing and elongation.

2022-10-01 | GSE202749 | GEO

PAF1, a molecular regulator of promoter-proximal pausing by RNA Polymerase II

Project description:The control of promoter-proximal pausing and the release of RNA polymerase II (RNA Pol II) is a widely used mechanism for regulating gene expression in metazoans, especially for genes that respond to environmental and developmental cues. Here, we identify Pol II associated Factor 1 (PAF1) as a major regulator of promoter-proximal pausing. Knockdown of PAF1 leads to increased release of paused Pol II into gene bodies at thousands of genes. Genes with the highest levels of paused Pol II exhibit the largest redistribution of Pol II from the promoter-proximal region into the gene body in the absence of PAF1. PAF1 depletion results in increased nascent transcription and increased levels of phosphorylation of Pol II’s c-terminal domain on serine 2 (Ser2P). These changes can be explained by the recruitment of the Ser2P kinase Super Elongation Complex (SEC) effecting increased release of paused Pol II into productive elongation, thus establishing a novel function for PAF1 as a major regulator of pausing in metazoans. ChIP-seq of Pol II of different forms, SEC subunits, PAFc subunits and H2Bub in human cell lines targeted by PAF1 or scramble shRNA. ChIP-seq of total Pol II in HCT116 cells targeted by BRE1A or scramble shRNA. ChIP-seq of total Pol II in S2 cells targeted by Paf1 or LacZ RNAi. Total RNA-seq, nascent RNA-seq and GRO-seq in HCT116 cells targeted by PAF1 or scramble shRNA.

2015-08-13 | E-GEOD-70408 | biostudies-arrayexpress

Regulation of RNA polymerase II processivity by Spt5 is restricted to a narrow window in elongation

Project description:Spt5 is a highly conserved RNA polymerase II (Pol II)-associated pausing and elongation factor. However, its impact on global elongation and Pol II processivity in mammalian cells has not been clarified. Here, we show that depleting Spt5 in mouse embryonic fibroblasts (MEFs) does not cause global elongation defects or decreased elongation rates. Instead, in the absence of Spt5, a fraction of Pol II molecules are dislodged during elongation thus decreasing the number of Pol II complexes that complete the transcription cycle. Most strikingly, this decrease is restricted to a narrow window between 15-20 kb from the promoter, a distance which coincides with the stage where accelerating Pol II attains maximum elongation speed and processivity. Consequently, long genes show a greater dependency on Spt5 for optimal elongation efficiency and overall gene expression than short genes. We propose that an important role of Spt5 in mammalian elongation is to promote the processivity of those Pol II complexes that are transitioning towards maximum elongation speed 15-20 kb from the promoter.

2018-03-06 | GSE106313 | GEO

PAF1, a molecular regulator of promoter-proximal pausing by RNA Polymerase II

2015-08-13 | GSE70408 | GEO

A Cdk9-PP1 switch regulates the elongation-termination transition of RNA polymerase II

Project description:The end of the RNA polymerase II (Pol II) transcription cycle is strictly regulated to ensure proper mRNA maturation and prevent interference between neighboring genes. Pol II slowing downstream of the cleavage and polyadenylation signal (CPS) leads to recruitment of cleavage and polyadenylation factors and termination, but how this chain of events is initiated remains unclear. In a chemical-genetic screen we identified protein phosphatase 1 (PP1) isoforms as substrates of human positive transcription elongation factor b (P-TEFb), the cyclin-dependent kinase 9 (Cdk9)-cyclin T1 complex. Here we show that Cdk9 and PP1 govern phosphorylation of the conserved transcription factor Spt5 in the fission yeast Schizosaccharomyces pombe. Cdk9 phosphorylates both Spt5 and a negative regulatory site on the PP1 isoform Dis2. Sites phosphorylated by Cdk9 in the Spt5 carboxy-terminal domain (CTD) are dephosphorylated by Dis2 in vitro, and Cdk9 inhibition in vivo leads to rapid Spt5 dephosphorylation that is retarded by concurrent Dis2 inactivation. Chromatin immunoprecipitation and sequencing (ChIP-seq) analysis indicates that Spt5 is dephosphorylated as transcription complexes traverse the CPS, prior to or concomitant with Pol II pausing. A Dis2-inactivating mutation stabilizes Spt5 phosphorylation (pSpt5) on chromatin, promotes transcription beyond the normal termination zone detected by precision run-on transcription and sequencing (PRO-seq), and is suppressed by ablation of Cdk9 target sites in Spt5. These results support a model whereby the transition of Pol II from elongation to termination is regulated by opposing activities of Cdk9 and Dis2 towards their common substrate Spt5—a bistable switch analogous to a Cdk1-PP1 module that controls exit from mitosis.

2018-06-07 | GSE102590 | GEO

Acetylation on Histone H3 Lysine 9 Mediates a Switch from Transcription Initiation to Elongation

Project description:The transition from transcription initiation to elongation is a key regulatory step in gene expression, which requires RNA polymerase II (Pol II) to escape promoter proximal pausing on chromatin. While elongation factors promote pause release leading to transcription elongation, the role of epigenetic modifications during this critical transition step is poorly understood. Two histone marks on histone H3, lysine 4 trimethylation (H3K4me3) and lysine 9 acetylation (H3K9ac), co-localize on active gene promoters and are associated with active transcription. H3K4me3 can promote transcription initiation, yet the functional role of H3K9ac is much less understood. We hypothesized that H3K9ac may function downstream of transcription initiation by recruiting specific proteins important for the next step of transcription. Here, we describe a functional role for H3K9ac in promoting Pol II pause release by directly recruiting the super elongation complex (SEC) to chromatin. H3K9ac serves as a substrate for direct binding of the SEC, as does acetylation of histone H4 lysine 5 (H4K5ac), to a lesser extent. Furthermore, lysine 9 on histone H3 is necessary for maximal Pol II pause release through SEC action, and loss of H3K9ac increases the Pol II pausing index on a subset of genes in HeLa cells. At select gene promoters, loss of H3K9ac or depletion of the SEC reduces gene expression and increases paused Pol II occupancy. We therefore propose that an ordered histone code drives progression through the transcription cycle, providing new mechanistic insight that SEC recruitment to certain acetylated histones promotes the subsequent release of paused Pol II needed for transcription elongation.

2017-07-11 | GSE99998 | GEO

Elongation/termination factor exchange mediated by PP1 phosphatase orchestrates trancription termination

Project description:Termination of RNA polymerase II (Pol II) transcription is a key step, that is important for 3’end formation of functional mRNA, mRNA release and Pol II recycling. Even so, this underlying termination mechanism is not yet understood. Here, we demonstrate that the conserved and essential termination factor Seb1 interacts with Pol II near the end of the RNA exit channel and the Rpb4/7 stalk. Furthermore, the Seb1 interaction surface with Pol II largely overlaps with that of the elongation factor Spt5. Notably, Seb1 co-transcriptional recruitment is dependent on Spt5 de-phosphorylation by the conserved PP1 phosphatase Dis2, which also de-phosphorylates threonine 4 within the Pol II heptad repeated C-terminal domain. We propose that Dis2 orchestrates the transition from elongation to termination phase during the transcription cycle by mediating elongation to termination factor exchange and de-phosphorylation of Pol II C-terminal domain.

2018-12-26 | GSE111326 | GEO

Transcription Pausing Regulates Mouse Embryonic Stem Cell Differentiation [GRO-seq]

Project description:The pluripotency of embryonic stem cells (ESCs) relies on appropriate responsiveness to developmental cues. Promoter-proximal pausing of RNA polymerase II (Pol II) has been suggested to play a role in keeping genes poised for future activation. To identify the role of Pol II pausing in regulating ESC pluripotency, we have generated mouse ESCs carrying a mutation in the pause-inducing factor SPT5. Consistent with previous in vitro studies showing the pausing deficiency of this mutant SPT5, our genomic analysis reveals genome-wide reduction of paused Pol II in mutant mESCs. Furthermore, we find that genes differentially regulated by mutant SPT5 correlates with distinct chromatin states. Functionally, this pausing-deficient SPT5 disrupts ESC differentiation without affecting self-renewal. Thus, our study uncovers an important role of Pol II pausing in regulating ESC differentiation and also suggests that Pol II pausing can both positively and negatively influence transcription depending on the local chromatin environment.

2017-12-08 | GSE99747 | GEO

Transcription Pausing Regulates Mouse Embryonic Stem Cell Differentiation [ATAC-seq]

2017-12-08 | GSE99746 | GEO

Distinct Cdk9-phosphatase switches act on elongation factor Spt5 at the beginning and end of the RNA polymerase II transcription cycle

Project description:The Pol II transcription cycle is ordered by CDKs and phosphatases. In fission yeast, Cdk9 phosphorylates carboxy-terminal repeats (CTRs) of Spt5 while inhibiting PP1 during elongation. Transcription past the cleavage and polyadenylation signal (CPS) coincides with PP1-dependent Spt5 dephosphorylation and leads to Pol II pausing with phosphorylated CTD-Ser2 (pSer2). Here we show this switch is conserved in humans: Cdk9 inhibition decreases phosphorylation of both PP1g and Spt5-Thr806 (pThr806), and induces pSer2 upstream of the CPS, whereas PP1 depletion increases pThr806. Moreover, in unperturbed cells, pThr806 is diminished in 3’-paused complexes where pSer2 is maximal. Cdk9 also phosphorylates Spt5 on Ser666, a PP1-refractory site between conserved KOW4 and KOW5 motifs; pSer666 increases upon promoter-proximal pause release and, in contrast to pThr806, persists beyond the CPS. We identify PP4—another target of inhibitory phosphorylation by Cdk9—as a pSer666 phosphatase. PP4 and PP1g are enriched at 5’ and 3’ ends of genes, respectively, consistent with pSer666 and pThr806 distributions. Therefore, distinct Cdk9-phosphatase switches operate on Spt5 at different steps in transcription.

2020-08-04 | GSE138548 | GEO

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