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Chen SF, Chao TC, Kim HJ, Tang HC, Khadka S, Li T, Lee DF, Murakami K, Boyer TG, Tsai KL. Structural basis of the human transcriptional Mediator complex modulated by its dissociable Kinase module. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.01.601608. [PMID: 39005267 PMCID: PMC11244988 DOI: 10.1101/2024.07.01.601608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/16/2024]
Abstract
The eukaryotic Mediator, comprising a large Core (cMED) and a dissociable CDK8 kinase module (CKM), regulates RNA Polymerase II (Pol II)-dependent transcription. cMED recruits Pol II and promotes pre-initiation complex (PIC) formation in a manner inhibited by the CKM, which is also implicated in post-initiation control of gene expression. Herein we report cryo-electron microscopy structures of the human complete Mediator and its CKM, which explains the basis for CKM inhibition of cMED-activated transcription. The CKM binds to cMED through an intrinsically disordered region (IDR) in MED13 and HEAT repeats in MED12. The CKM inhibits transcription by allocating its MED13 IDR to occlude binding of Pol II and MED26 to cMED and further obstructing cMED-PIC assembly through steric hindrance with TFIIH and the +1 nucleosome. Notably, MED12 binds to the cMED Hook, positioning CDK8 downstream of the transcription start site, which sheds new light on its stimulatory function in post-initiation events.
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Li T, Tang HC, Tsai KL. Unveiling the noncanonical activation mechanism of CDKs: insights from recent structural studies. Front Mol Biosci 2023; 10:1290631. [PMID: 38028546 PMCID: PMC10666765 DOI: 10.3389/fmolb.2023.1290631] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 10/27/2023] [Indexed: 12/01/2023] Open
Abstract
The Cyclin-dependent kinases (CDKs) play crucial roles in a range of essential cellular processes. While the classical two-step activation mechanism is generally applicable to cell cycle-related CDKs, both CDK7 and CDK8, involved in transcriptional regulation, adopt distinct mechanisms for kinase activation. In both cases, binding to their respective cyclin partners results in only partial activity, while their full activation requires the presence of an additional subunit. Recent structural studies of these two noncanonical kinases have provided unprecedented insights into their activation mechanisms, enabling us to understand how the third subunit coordinates the T-loop stabilization and enhances kinase activity. In this review, we summarize the structure and function of CDK7 and CDK8 within their respective functional complexes, while also describing their noncanonical activation mechanisms. These insights open new avenues for targeted drug discovery and potential therapeutic interventions in various diseases related to CDK7 and CDK8.
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Affiliation(s)
- Tao Li
- Department of Biochemistry and Molecular Biology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Hui-Chi Tang
- Department of Biochemistry and Molecular Biology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Kuang-Lei Tsai
- Department of Biochemistry and Molecular Biology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX, United States
- MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences, Houston, TX, United States
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Muralimanoharan S, Shamby R, Stansbury N, Schenken R, de la Pena Avalos B, Javanmardi S, Dray E, Sung P, Boyer TG. Aberrant R-loop-induced replication stress in MED12-mutant uterine fibroids. Sci Rep 2022; 12:6169. [PMID: 35418189 PMCID: PMC9008039 DOI: 10.1038/s41598-022-10188-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 03/31/2022] [Indexed: 11/09/2022] Open
Abstract
Uterine fibroid (UF) driver mutations in Mediator complex subunit 12 (MED12) trigger genomic instability and tumor development through unknown mechanisms. Herein, we show that MED12 mutations trigger aberrant R-loop-induced replication stress, suggesting a possible route to genomic instability and a novel therapeutic vulnerability in this dominant UF subclass. Immunohistochemical analyses of patient-matched tissue samples revealed that MED12 mutation-positive UFs, compared to MED12 mutation-negative UFs and myometrium, exhibited significantly higher levels of R-loops and activated markers of Ataxia Telangiectasia and Rad3-related (ATR) kinase-dependent replication stress signaling in situ. Single molecule DNA fiber analysis revealed that primary cells from MED12 mutation-positive UFs, compared to those from patient-matched MED12 mutation-negative UFs and myometrium, exhibited defects in replication fork dynamics, including reduced fork speeds, increased and decreased numbers of stalled and restarted forks, respectively, and increased asymmetrical bidirectional forks. Notably, these phenotypes were recapitulated and functionally linked in cultured uterine smooth muscle cells following chemical inhibition of Mediator-associated CDK8/19 kinase activity that is known to be disrupted by UF driver mutations in MED12. Thus, Mediator kinase inhibition triggered enhanced R-loop formation and replication stress leading to an S-phase cell cycle delay, phenotypes that were rescued by overexpression of the R-loop resolving enzyme RNaseH. Altogether, these findings reveal MED12-mutant UFs to be uniquely characterized by aberrant R-loop induced replication stress, suggesting a possible basis for genomic instability and new avenues for therapeutic intervention that involve the replication stress phenotype in this dominant UF subtype.
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Affiliation(s)
- Sribalasubashini Muralimanoharan
- Department of Molecular Medicine, UT Health San Antonio, STRF, 8210 Floyd Curl Drive, Mail Code 8257, San Antonio, TX, 78229-3900, USA
| | - Ross Shamby
- Department of Molecular Medicine, UT Health San Antonio, STRF, 8210 Floyd Curl Drive, Mail Code 8257, San Antonio, TX, 78229-3900, USA
| | - Nicholas Stansbury
- Department of Obstetrics and Gynecology, UT Health San Antonio, San Antonio, TX, USA
| | - Robert Schenken
- Department of Obstetrics and Gynecology, UT Health San Antonio, San Antonio, TX, USA
| | | | - Samin Javanmardi
- Department of Molecular Medicine, UT Health San Antonio, STRF, 8210 Floyd Curl Drive, Mail Code 8257, San Antonio, TX, 78229-3900, USA
| | - Eloise Dray
- Department of Biochemistry and Structural Biology, UT Health San Antonio, San Antonio, TX, USA
| | - Patrick Sung
- Department of Biochemistry and Structural Biology, UT Health San Antonio, San Antonio, TX, USA
| | - Thomas G Boyer
- Department of Molecular Medicine, UT Health San Antonio, STRF, 8210 Floyd Curl Drive, Mail Code 8257, San Antonio, TX, 78229-3900, USA.
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