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In the field of molecular biology, a corepressor is a substance that inhibits the expression of genes. In prokaryotes, corepressors are small molecules whereas in eukaryotes, corepressors are proteins. A corepressor does not directly bind to DNA, but instead indirectly regulates gene expression by binding to repressors.

A corepressor downregulates (or represses) the expression of genes by binding to and activating a repressor transcription factor. The repressor in turn binds to a gene promoter (a sequence of DNA adjacent to the regulated gene), thereby blocking transcription of that gene.

Function

Prokaryotes

In prokaryotes, the term corepressor is used to denote the activating ligand of a repressor protein. For example, the E. coli tryptophan repressor (TrpR) is only able to bind to DNA and repress transcription of the trp operon when its corepressor tryptophan is bound to it. TrpR in the absence of tryptophan is known as an aporepressor and is inactive in repressing gene transcription.^[1] Trp operon encodes enzymes responsible for the synthesis of tryptophan. Hence TrpR provides a negative feedback mechanism that regulates the biosynthesis of tryptophan.

In short tryptophan acts as a corepressor for its own biosynthesis.^[2]

Eukaryotes

In eukaryotes, a corepressor is a protein that binds to transcription factors.^[3] In the absence of corepressors and in the presence of coactivators, transcription factors upregulate gene expression. Coactivators and corepressors compete for the same binding sites on transcription factors. A second mechanism by which corepressors may repress transcriptional initiation when bound to transcription factor/DNA complexes is by recruiting histone deacetylases which catalyze the removal of acetyl groups from lysine residues. This increases the positive charge on histones which strengthens the electrostatic attraction between the positively charged histones and negatively charged DNA, making the DNA less accessible for transcription.^[4]^[5]

In humans several dozen to several hundred corepressors are known, depending on the level of confidence with which the characterisation of a protein as a corepressors can be made.^[6]

References

^ Evans PD, Jaseja M, Jeeves M, Hyde EI (December 1996). "NMR studies of the Escherichia coli Trp repressor.trpRs operator complex". Eur. J. Biochem. 242 (3): 567–75. doi:10.1111/j.1432-1033.1996.0567r.x. PMID 9022683.
^ Foster JB, Slonczewski J (2010). Microbiology: An Evolving Science (Second ed.). New York: W. W. Norton & Company. ISBN 0-393-93447-0.
^ Jenster G (August 1998). "Coactivators and corepressors as mediators of nuclear receptor function: an update". Mol. Cell. Endocrinol. 143 (1-2): 1–7. doi:10.1016/S0303-7207(98)00145-2. PMID 9806345.
^ Lazar MA (2003). "Nuclear receptor corepressors". Nucl Recept Signal 1: e001. doi:10.1621/nrs.01001. PMC 1402229. PMID 16604174.
^ Goodson M, Jonas BA, Privalsky MA (2005). "Corepressors: custom tailoring and alterations while you wait". Nucl Recept Signal 3 (Oct 21): e003. doi:10.1621/nrs.03003. PMC 1402215. PMID 16604171.
^ Schaefer U, Schmeier S, Bajic VB (January 2011). "TcoF-DB: dragon database for human transcription co-factors and transcription factor interacting proteins". Nucleic Acids Res. 39 (Database issue): D106–10. doi:10.1093/nar/gkq945. PMC 3013796. PMID 20965969.

External links

Co-Repressor Proteins at the US National Library of Medicine Medical Subject Headings (MeSH)

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3. 急性前骨髄球性白血病の分子生物学 molecular biology of acute promyelocytic leukemia
4. プロゲステロン受容体モジュレーター（PRM）の薬理学および作用機序 pharmacology and mechanism of action of progesterone receptor modulators prms
5. 前立腺肥大症の疫学および病因 epidemiology and pathogenesis of benign prostatic hyperplasia

English Journal

RECEPTOR TYROSYNE KINASE EPHA2 IS A DIRECT TARGET-GENE OF HIC1 (HYPERMETHYLATED IN CANCER 1).

Foveau B, Boulay G, Pinte S, Van Rechem C, Rood BR, Leprince D.SourceIBL CNRS UMR8161, France;
The Journal of biological chemistry.J Biol Chem.2012 Jan 3. [Epub ahead of print]
The tumor suppressor gene Hypermethylated in Cancer 1 (HIC1), which encodes a transcriptional repressor, is epigenetically silenced in many human tumors. Here, we show that ectopic expression of HIC1 in the highly malignant MDA-MB-231 breast cancer cell line severely impairs cell proliferation, migr
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Structural basis of coactivation of liver receptor homolog-1 by β-catenin.

Yumoto F, Nguyen P, Sablin EP, Baxter JD, Webb P, Fletterick RJ.SourceDepartment of Biochemistry and Biophysics, University of California San Francisco, 600 16th Street, San Francisco, CA 94158.
Proceedings of the National Academy of Sciences of the United States of America.Proc Natl Acad Sci U S A.2012 Jan 3;109(1):143-8. Epub 2011 Dec 20.
We report the three-dimensional structure of a β-catenin armadillo repeat in complex with the liver receptor homolog-1 (LRH-1) ligand binding domain at 2.8 Å resolution as the first structure of β-catenin in complex with any nuclear receptor. The surface of β-catenin that binds LRH-1 partly ov
PMID 22187462

Japanese Journal

Acquisition of the Ability To Assimilate Mannitol by Saccharomyces cerevisiae through Dysfunction of the General Corepressor Tup1-Cyc8.

Applied and environmental microbiology 81(1), 9-16, 2015-01-01
NAID 120005530974

Production of pyruvate from mannitol by mannitol-assimilating pyruvate decarboxylase-negative Saccharomyces cerevisiae.

Bioengineered 6(6), 347-350, 2015
NAID 120005743650

Molecular Mechanisms of the Antileukemia Activities of Retinoid and Arsenic

Journal of Pharmacological Sciences 126(3), 179-185, 2014
NAID 130004699218

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