Mediator MED18 subunit plays a negative role in transcription via the CDK/cyclin module.
The Mediator complex (Mediator) is conserved among eukaryotes and is comprised of head, middle, tail and CDK/cyclin modules. The head module has received the most attention because its interaction with RNA polymerase II (Pol II) and the general transcription factors TFIIH and TBP facilitates phosphorylation of the carboxy-terminal domain (CTD) of the largest subunit of Pol II. We studied the human head module subunit hMED18 to elucidate how Mediator is involved in both transcriptional activation and repression. siRNA-mediated hMED18 depletion augmented transcription, indicating that hMED18 functions in transcriptional repression. Treatment of cells with two histone deacetylase (HDAC) inhibitors, the HDAC inhibitor trichostatin A (TSA) and the SIRT inhibitor nicotinamide showed that this repression was not caused by those HDAC activities. A screen for hMED18-target genes showed that the promoters for cap RNA methyltransferase RNMT-activating mini protein (RAM/FAM103A1) and divalent metal transporter 1 (DMT1/SLC11A2) genes were bound by hMED18. Depletion of hMED18 showed hMED18 and the middle module subunit hMED1 were lost from the promoters of those genes, whereas the CDK/cyclin module subunit hCDK8 remained bound. This indicates a novel transcriptional repression mechanism of hMED18 mediated by hCDK8 and further a novel positive role of free CDK/cyclin module in transcriptional activation. [Correction added on 12 June 2014, after first online publication: SLC11A2 amended from SCL11A2.].
Laboratory of Gene Regulation, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.
Masayuki
M
Kumafuji
Hiroyasu
H
Umemura
Tadashi
T
Furumoto
Rikiya
R
Fukasawa
Aki
A
Tanaka
Yoshiaki
Y
Ohkuma
D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006367:HeLa Cells; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D009536:Niacinamide / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D000099236:Solute Carrier Family 11, Member 2
D027682:Cation Transport Proteins; D018844:Cyclin-Dependent Kinases; D016213:Cyclins; D056572:Histone Deacetylase Inhibitors; D006877:Hydroxamic Acids; D009536:Niacinamide; D021122:Protein Subunits; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D000099236:Solute Carrier Family 11, Member 2; C000594771:MED18 protein, human; C012589:trichostatin A; C569288:RAMAC protein, human