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N-CoR interacts directly with the DNA sequence ATNNTNCTC
Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.ORCID iD: 0000-0003-3927-4394
(English)Manuscript (preprint) (Other academic)
Abstract [en]

N-CoR (nuclear receptor corepressor) and SMRT (silencing mediator of thyroid and retinoid hormone receptors) are large proteins which are constituent parts of numerous multicomponent repressor complexes. They function by recruiting repressors to the sites of DNA-bound transcription factors, thereby modifying chromatin condensation to restrict access for general transcription factors to a regulated gene. Both N-CoR and SMRT contain two highly conserved SANT (SWI3, ADA2, N-CoR, TFIIIB) domains which, by homology, have been suggested to confer DNA-binding properties. To date however, there have been no data published that support a DNA-binding function for N-CoR (or SMRT). To investigate if N-CoR is capable of binding to DNA, we used stably transfected S2 cells expressing FLAGtagged N-CoR We then allowed N-CoR to interact with double stranded degenerated oligonucleotides. Our results showed that oligonucleotides were retained by N-CoR, and that these contained the consensus sequence ATNNTNCTC.

National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-84853OAI: diva2:562546
Available from: 2012-10-25 Created: 2012-10-25 Last updated: 2013-10-23Bibliographically approved
In thesis
1. Nuclear receptor corepressor N-CoR: role in transcriptional repression
Open this publication in new window or tab >>Nuclear receptor corepressor N-CoR: role in transcriptional repression
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The human body consists of a multitude of cells of varying appearance and function. With a few exceptions they are genetically identical, and the key to their divergence lies in their different specific patterns of gene expression. Gene expression may be regulated at the level of transcription, in two opposing directions; either activation or repression. Gene transcription is controlled by transcription factors, which bind to regulatory DNA sequences, and direct gene expression in concert with auxiliary proteins. Among these the nuclear receptor corepressor N-CoR holds a central position. It serves as a docking unit between many different DNA-bound transcription factors, such as nuclear receptors, and large complexes of repressor proteins. Many repressor complexes of distinct compositions have been shown to contain N-CoR.

N-CoR plays a vital part in normal fetal development, and its involvement has been implicated in several pathological conditions. It has been shown to interact with unliganded nuclear receptors via CoRNR-box motifs in the C-terminal half of the protein. We have identified an NR-box motif, typical of coactivators, in the N-terminal part of N-CoR, which we have shown to be capable of interacting with the nuclear receptors RARα and TRß both in vitro and in vivo. A mutated NR-box motif did not interact accordingly. We discovered that the NR-box motif found in N-CoR displayed a ligand-dependent interaction with TRß in GST pulldown experiments, and that the immediate NR-box environment in N-CoR resembles NRbox environments in the coactivator CBP. We investigated a possible role for theN-CoR NRbox motif in regulation of the TSHß gene from a negative TR response element found in its promoter. In transient transfectiqns of GH3 cells, we found that both TRß3 and N-CoR are necessary for ligand-induced repression from this response element to occur. Mutating the NR-box abolished the repressive potential of N-CoR. The results were corroborated by results from transient transfections of HEK293/T cells, where siRNA-targeted degradation of endogenous N-CoR mRNA annihilated the ligand-induced repression, and where wild type mouse N-CoR but not mutated N-CoR restored the repression. In vitro binding assays also showed that TR, bound to its negative response element in the TSHß gene promoter, displayed an obligate ligand dependence in its interaction with N-CoR.

In several different leukemias N-CoR holds a key role. Abberant transcription factors bind stronger toN-CoR than their normal counterparts, leading to constitutive repression of key genes in hematopoiesis. Retinoid signaling, mediated by RARs plays a central part in differentiation of myeloid cells. We therefore investigated the extent of N-CoR expression in the myeloid cell line THP-1 during differentiation. Analyses both at mRNA- and at protein level showed that N-CoR expression was down-regulated as the myeloid cells differentiated. Exploring the effects of this on genes controlled by retinoic acid, we found in transient transfections of THP-1 cells that N-CoR modulated the expression level both at basal and at ligand-activated level. Several reports by others have also emphasized the importance of relative levels of different coregulatory proteins for determining the amplitude of the transcriptional response.

N-CoR binds both to transcription factors and to repressor complexes, but so far no report has been published regarding its possible DNA-binding capacity, anticipated by analysis of its amino acid sequence. Employing the selected and amplified binding sites (SAAB) assay we showed that N-CoR bound to DNA. Sequence determination resulted in the identification of a DNA sequence, ATNNTNCTC, which binds specifically toN-CoR. This finding adds another variable in the spectrum of N-CoR interactions.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2004. 72 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 869
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-24064 (URN)3623 (Local ID)91-7373-846-8 (ISBN)3623 (Archive number)3623 (OAI)
Public defence
2004-07-01, Berzelius-salen, Hälsouniversitetet, Linköping, 09:00 (Swedish)
Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2014-06-13Bibliographically approved

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