| Abstract: |
It is well documented that unliganded thyroid hormone receptor (TR) functions as a transcriptional repressor of specific cellular target genes by acting in concert with a corepressor complex harboring histone deacetylase (HDAC) activity. To fully explore the cofactors that interact with the transcriptionally repressive form of TR, we biochemically isolated a multiprotein complex that assembles on a TR·retinoid X receptor (RXR) heterodimer in HeLa nuclear extracts and identified its polypeptide components by mass spectrometry. A subset of TR·RXR-associated polypeptides included NCoR, SMRT, TBL1, and HDAC3, which represent the core components of a previously described NCoR/SMRT corepressor complex. We also identified several polypeptides that constitute a DNA-dependent protein kinase (DNA-PK) enzyme complex, a regulator of DNA repair, recombination, and transcription. These polypeptides included the catalytic subunit DNA-PKcs, the regulatory subunits Ku70 and Ku86, and the poly(ADP-ribose) polymerase 1. Density gradient fractionation and immunoprecipitation analyses provided evidence for the existence of a high molecular weight TR·RXR·corepressor holocomplex containing both NCoR/SMRT and DNA-PK complexes. Chromatin immunoprecipitation studies confirmed that unliganded TR·RXR recruits both complexes to the triiodothyronine-responsive region of growth hormone gene in vivo. Interestingly, DNA-PKcs, a member of the phosphatidylinositol 3-kinase family, was found to phosphorylate HDAC3 when the purified TR·RXR· corepressor holocomplex was incubated with ATP. This phosphorylation was accompanied by a significant enhancement of the HDAC activity of this complex. Collectively, our results indicated that DNA-PK promotes the establishment of a repressive chromatin at a TR target promoter by enhancing the HDAC activity of the receptor-bound NCoR/SMRT corepressor complex. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc. |
| Notes: |
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- "Cited By (since 1996): 17"
- "Export Date: 17 November 2011"
- "CODEN: JBCHA"
- "Molecular Sequence Numbers: GENBANK: AAH37545, AAI12128, AAK00301, AAW34364, BAA92618, CAA59230, CAA73319, CAG46550, JH0148, NP_001395, NP_003874, NP_005336, NP_006302, NP_006303, NP_008835, Q15652, XP_078933, XP_088468;"
- "Source: Scopus"
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