Selective inhibition of CDK7 reveals high-confidence targets and new models for TFIIH function in transcription
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ABSTRACT: CDK7 associates with the 10-subunit TFIIH complex and regulates transcription by phosphorylating the C-terminal domain (CTD) of RNA polymerase II (RNAPII). Few additional CDK7 substrates are known. Here, using the covalent inhibitor SY-351 and quantitative phosphoproteomics, we identified CDK7 kinase substrates in human cells. Among hundreds of high-confidence targets, the vast majority are unique to CDK7 (i.e. distinct from other transcription-associated kinases), with a subset that suggest novel cellular functions. Transcription-associated factors were predominant CDK7 substrates, including SF3B1, U2AF2, and other splicing components. Accordingly, widespread and diverse splicing defects, such as alternative exon inclusion and intron retention, were characterized in CDK7-inhibited cells. Combined with biochemical assays, we establish that CDK7 directly activates other transcription-associated kinases CDK9, CDK12, and CDK13, invoking a “master regulator” role in transcription. We further demonstrate that TFIIH restricts CDK7 kinase function to the RNAPII CTD, whereas other substrates (e.g. SPT5, SF3B1) are phosphorylated by the 3-subunit CDK-activating kinase (CAK; CCNH, MAT1, CDK7). These results suggest new models for CDK7 function in transcription and implicate CAK dissociation from TFIIH as essential for kinase activation. This straightforward regulatory strategy ensures CDK7 activation is spatially and temporally linked to transcription, and may apply toward other transcription-associated kinases.
Project description:Cyclin dependent kinases activation and RNA polymerase II transcription are linked by the Cdk7 kinase that phosphorylates Cdks as a trimeric CAK complex, and serine 5 within the PolII C-terminal domain (CTD) as TFIIH bound CAK. However, the physiological importance of integrating these processes is not understood. Beside the Cdk7 ortholog Mcs6, fission yeast possesses a second CAK, Csk1. Both enzymes were proposed to act redundantly to activate Cdc2. Using an improved analogue sensitive Mcs6-as kinase, we show that Csk1 is not a relevant CAK for Cdc2. Further analyses revealed that Csk1 lacks a 20 amino acid sequence required for its budding yeast counterpart, Cak1, to bind Cdc2. Transcriptome profiling of the Mcs6-as mutant in the presence or absence of the budding yeast Cak1 kinase, in order to uncouple the CTD kinase and CAK activities of Mcs6, revealed an unanticipated role of the CAK branch in the transcriptional control of the cluster of genes implicated in ribosome biogenesis and cell growth. The analysis of a Cdc2 CAK site mutant confirmed these data. Our data show that the Cdk7 kinase modulates transcription through both its well-described RNA Polymerase II CTD kinase activity, but also through the Cdc2 activating kinase activity.
Project description:We report that inactivation of the fission yeast Cdk7 kinase affects gene expression through both its RNA Polymerase II CTD kinase activity and its Cdc2-activating kinase activity. The ribosome biogenesis cluster is specifically downregulated when Cdc2 T167 phosphorylation is abolished, which results is slow growth. We propose that Cdc2 activation by CAK defines the rate change point observed in mid G2 and that CAK therefore couples cell growth to cell division. Total RNA was isolated from two biological replicates for all conditions, and each biological replicate was hybridized in duplicate on Agilent arrays (dye-swap).
Project description:We combined cryo-EM, transcriptomics, and a clinically relevant inhibitor to define how the TFIIH-associated CDK7 kinase coordinately controls the cell cycle and RNA polymerase II (RNAPII) transcription. CDK7 inhibition rapidly blocked expression of constitutively active genes, whereas inducible genes were unaffected. Distinct sets of sequence-specific, DNA-binding transcription factors (TFs) regulate constitutive vs. inducible genes; accordingly, inducible TFs (e.g. HSF1) were refractory to CDK7 inhibition. By contrast, CDK7 was required to maintain activity of a core set of promoter-associated TFs that drive proliferative gene expression programs; these core TFs (n=78) are constitutively active in proliferating cells. Thus, a major biological function for CDK7 is regulation of TFs that drive cell proliferation, revealing an apparent universal mechanism by which CDK7 coordinates RNAPII transcription with cell cycle regulation.
Project description:We combined cryo-EM, transcriptomics, and a clinically relevant inhibitor to define how the TFIIH-associated CDK7 kinase coordinately controls the cell cycle and RNA polymerase II (RNAPII) transcription. CDK7 inhibition rapidly blocked expression of constitutively active genes, whereas inducible genes were unaffected. Distinct sets of sequence-specific, DNA-binding transcription factors (TFs) regulate constitutive vs. inducible genes; accordingly, inducible TFs (e.g. HSF1) were refractory to CDK7 inhibition. By contrast, CDK7 was required to maintain activity of a core set of promoter-associated TFs that drive proliferative gene expression programs; these core TFs (n=78) are constitutively active in proliferating cells. Thus, a major biological function for CDK7 is regulation of TFs that drive cell proliferation, revealing an apparent universal mechanism by which CDK7 coordinates RNAPII transcription with cell cycle regulation.
Project description:Mediator is an essential, broadly utilized eukaryotic transcriptional co-activator. How and what it communicates from activators to RNA polymerase II remains an open question. Here we performed genome-wide location profiling of yeast Mediator subunits. Mediator is not found at core promoters but rather occupies the upstream activating sequence (UAS), upstream of the pre-initiation complex. In the absence of Kin28/CDK7 kinase activity, or in cells where the CTD is mutated to replace Ser5 with alanines, however, Mediator accumulates at core promoters together with RNAPII. We propose that Mediator is quickly released from promoters upon Ser5 phosphorylation by Kin28/CDK7, which also allows for RNAPII to escape from the promoter. We took a systematic approach to examine the genome-wide distribution (using ChIP-chip) of the various Mediator subunits. Mediator occupancy was also assayed in mutants for most of the CTD kinases and in strains where some CTD serines had been replaced by alanines. Mediator ChIPs were performed with Myc-tagged subunits, except in some preliminary experiments where polyclonal antibodies were used. Most ChIPs (in Cy5) were hybridyzed against a control ChIP sample from an isogenic non-tagged strain (in Cy3). In some of the preliminary experiments, non immunoprecipitated DNA (input) was used as the control. In addition to Mediator ChIPs, the project includes TFIIB and RNAPII (Rpb3) ChIP-chip datasets. All ChIP-chip experiments were done in duplicates except for the preliminary experiments that were done in monoplicat for the most part. Each microarray was normalized using the Lima Loess and replicates were combined using a weighted average method as previously described (Pokholok et al., 2005).
Project description:CDK7 is a component of the general transcription factor IIH, which regulates RNAPII initiation and elongation.THZ2, a new molecular inhibitor, can completely inhibit the phosphorylation of the established intracellular CDK7 substrate RNAPII CTD at Ser-2, -5 and -7 through irreversible covalent binding to CDK7. Gene expression profiling was then performed to investigate the THZ2-induced transcription effect, and search the subset of sensitive genes in these 2 osteosarcoma cell lines.
Project description:During transcription initiation, the TFIIH-kinase Kin28/Cdk7 marks RNA polymerase II (Pol II) by phosphorylating the C-terminal domain (CTD) of its largest subunit. Here we describe a structure-guided chemical approach to covalently and specifically inactivate Kin28 kinase activity in vivo. This method of irreversible inactivation recapitulates both the lethal phenotype and the key molecular signatures that result from genetically disrupting Kin28 function in vivo. Inactivating Kin28 impacts promoter release to differing degrees and reveals a “checkpoint” during the transition to productive elongation. While promoter-proximal pausing is not observed in budding yeast, inhibition of Kin28 attenuates elongation-licensing signals, resulting in Pol II accumulation at the +2 nucleosome and reduced transition to productive elongation. Furthermore, upon inhibition, global stabilization of mRNA masks different degrees of reduction in nascent transcription. This study resolves long-standing controversies on the role of Kin28 in transcription and provides a rational approach to irreversibly inhibit other kinases in vivo.
Project description:During transcription initiation, the TFIIH-kinase Kin28/Cdk7 marks RNA polymerase II (Pol II) by phosphorylating the C-terminal domain (CTD) of its largest subunit. Here we describe a structure-guided chemical approach to covalently and specifically inactivate Kin28 kinase activity in vivo. This method of irreversible inactivation recapitulates both the lethal phenotype and the key molecular signatures that result from genetically disrupting Kin28 function in vivo. Inactivating Kin28 impacts promoter release to differing degrees and reveals a “checkpoint” during the transition to productive elongation. While promoter-proximal pausing is not observed in budding yeast, inhibition of Kin28 attenuates elongation-licensing signals, resulting in Pol II accumulation at the +2 nucleosome and reduced transition to productive elongation. Furthermore, upon inhibition, global stabilization of mRNA masks different degrees of reduction in nascent transcription. This study resolves long-standing controversies on the role of Kin28 in transcription and provides a rational approach to irreversibly inhibit other kinases in vivo.