Cooperative activity of cdk8 and GCN5L within Mediator directs tandem phosphoacetylation of histone H3.
The human Mediator complex is generally required for expression of protein-coding genes. Here, we show that the GCN5L acetyltransferase stably associates with Mediator together with the TRRAP polypeptide. Yet, contrary to expectations, TRRAP/GCN5L does not associate with the transcriptionally active core Mediator but rather with Mediator that contains the cdk8 subcomplex. Consequently, this derivative 'T/G-Mediator' complex does not directly activate transcription in a reconstituted human transcription system. However, within T/G-Mediator, cdk8 phosphorylates serine-10 on histone H3, which in turn stimulates H3K14 acetylation by GCN5L within the complex. Tandem phosphoacetylation of H3 correlates with transcriptional activation, and ChIP assays demonstrate co-occupancy of T/G-Mediator components at several activated genes in vivo. Moreover, cdk8 knockdown causes substantial reduction of global H3 phosphoacetylation, suggesting that T/G-Mediator is a major regulator of this H3 mark. Cooperative H3 modification provides a mechanistic basis for GCN5L association with cdk8-Mediator and also identifies a biochemical means by which cdk8 can indirectly activate gene expression. Indeed our results suggest that T/G-Mediator directs early events-such as modification of chromatin templates-in transcriptional activation.
Meyer
Krista D
KD
Department of Chemistry and Biochemistry, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA.
Donner
Aaron J
AJ
Knuesel
Matthew T
MT
York
Autumn G
AG
Espinosa
Joaquín M
JM
Taatjes
Dylan J
DJ
D000107:Acetylation; D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D051548:Histone Acetyltransferases / Q000737:chemistry / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D006801:Humans; D056913:Mediator Complex Subunit 1; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D012694:Serine / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism; D015533:Transcriptional Activation; D000099224:p300-CBP-Associated Factor
D048868:Adaptor Proteins, Signal Transducing; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases; D051548:Histone Acetyltransferases; D006657:Histones; D056913:Mediator Complex Subunit 1; D009687:Nuclear Proteins; D012694:Serine; D014157:Transcription Factors; C538855:MED1 protein, human; C113829:transformation-transcription domain-associated protein; C501179:KAT2A protein, human; D000099224:p300-CBP-Associated Factor; C095686:CDK8 protein, human