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J Biol Chem ; 276(13): 9720-5, 2001 Mar 30.
Article in English | MEDLINE | ID: mdl-11134019

ABSTRACT

Octamer transcription factor-1 (Oct-1) is a member of the POU (Pit-1, Oct-1, unc-86) family of transcription factors and is involved in the transcriptional regulation of a variety of gene expressions related to cell cycle regulation, development, and hormonal signals. It has been shown that Oct-1 acts not only as a transcriptional activator but also as a transcriptional repressor for certain genes. The mechanism of the repressive function of Oct-1 has not been well understood. Here we demonstrate by using the glutathione S-transferase pull-down assays and coimmunoprecipitation assays that the POU domain of Oct-1 directly interacts with a silencing mediator for retinoid and thyroid hormone receptors (SMRT). The interaction surfaces are located in the C-terminal region of SMRT, which are different from previously described silencing domains I and II or receptor interacting domains I and II. In transient transfection assays in COS1 cells, overexpression of SMRT attenuated the augmentation of Oct-1 transcriptional activity by OBF-1/OCA-B, activator for Oct-1. In pull-down assays, increasing amounts of SMRT could compete the binding of OCA-B to Oct-1 POU domain. The activity of Oct-1 could be determined by a regulated balance between SMRT and OCA-B. Furthermore, cotransfected unliganded thyroid hormone receptor enhanced the transactivation by Oct-1, and addition of 3,3',5-tri-iodo-l-thyronine obliterated the stimulatory effects. Consequently, in the presence of cotransfected thyroid hormone receptor, the octamer response element acts as an element negatively regulated by 3,3',5-tri-iodo-l-thyronine. The results suggest that the transcriptional activity of Oct-1 can be modulated by interaction through its POU domain by a silencing mediator SMRT resulting in the cross-talk between Oct-1 and nuclear receptors.


Subject(s)
DNA-Binding Proteins/metabolism , Gene Expression Regulation , Repressor Proteins/metabolism , Transcription Factors/metabolism , Animals , Binding, Competitive , Blotting, Western , COS Cells , Cell Nucleus/metabolism , Down-Regulation , Electrophoresis, Polyacrylamide Gel , Glutathione Transferase/metabolism , Host Cell Factor C1 , Nuclear Receptor Co-Repressor 2 , Octamer Transcription Factor-1 , Plasmids/metabolism , Precipitin Tests , Protein Binding , Protein Biosynthesis , Protein Structure, Tertiary , Recombinant Proteins/metabolism , Response Elements , Trans-Activators/metabolism , Transcription, Genetic , Transcriptional Activation , Transfection , Triiodothyronine, Reverse/pharmacology , Up-Regulation
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