title: MED25 is distinct from TRAP220/MED1 in cooperating with CBP for retinoid receptor activation.
abstract: We isolated MED25, which associates with retinoic acid (RA)-bound retinoic acid receptor (RAR) through the C-terminal nuclear hormone receptor (NR) box/LxxLL motif, and increases RAR/RXR-mediated transcription. When tethered to a promoter, MED25 showed intrinsic transcriptional activity in its PTOV domain, which is likely accomplished by direct association with CBP. Reporter assays using dominant negatives of MED25 demonstrated the importance of the N-terminal Mediator-binding and C-terminal domains in CBP and RAR/RXR binding, which affect MED25 activity. Downregulation of MED25 specifically reduced RAR but not thyroid hormone receptor (TR) activity. Stimulation of RAR by MED25 was correlated with enhanced RA cytotoxicity in vivo. Chromatin immunoprecipitation (ChIP) assays revealed the RA-dependent recruitment of MED25 to the RARbeta2 promoter. Recruitment of CBP and TRAP220 was diminished by the overexpression of a MED25 NR box deletion mutant, and by treatment with MED25 siRNA. Time-course ChIP assays indicated that CBP, together with RAR and MED25, is recruited early, whereas TRAP220 is recruited later to the promoter. Our data suggest that MED25, in cooperation with CBP and Mediators through its distinct domains, imposes a selective advantage on RAR/RXR activation.
authors.affiliation: Department of Bioscience and Biotechnology, Institute of Bioscience, Sejong University, Seoul, Korea.
authors.forename: Hye-Kyung
authors.initials: HK
authors.lastname: Lee
authors.forename: Ui-Hyun
authors.initials: UH
authors.lastname: Park
authors.forename: Eun-Joo
authors.initials: EJ
authors.lastname: Kim
authors.forename: Soo-Jong
authors.initials: SJ
authors.lastname: Um
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D003345:Corticosterone; D006801:Humans; D056892:Mediator Complex; D056913:Mediator Complex Subunit 1; D051379:Mice; D034622:RNA Interference; D034741:RNA, Small Interfering; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014212:Tretinoin / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; C538855:MED1 protein, human; C483045:MED25 protein, human; C538856:Med1 protein, mouse; D056892:Mediator Complex; D056913:Mediator Complex Subunit 1; D034741:RNA, Small Interfering; D018168:Receptors, Retinoic Acid; D015534:Trans-Activators; D014157:Transcription Factors; C082925:retinoic acid receptor beta; D014212:Tretinoin; D003345:Corticosterone