Silencing mediator for retinoid and thyroid hormone receptors interacts with octamer transcription factor-1 and acts as a transcriptional repressor.
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.
Kakizawa
T
T
Department of Aging Medicine and Geriatrics, Shinshu University School of Medicine, Matsumoto 390-8621, Japan.
Miyamoto
T
T
Ichikawa
K
K
Takeda
T
T
Suzuki
S
S
Mori
J
J
Kumagai
M
M
Yamashita
K
K
Hashizume
K
K
D000818:Animals; D001667:Binding, Competitive; D015153:Blotting, Western; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D005786:Gene Expression Regulation; D005982:Glutathione Transferase / Q000378:metabolism; D051863:Host Cell Factor C1; D056985:Nuclear Receptor Co-Repressor 2; D050811:Octamer Transcription Factor-1; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D020218:Response Elements; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D014285:Triiodothyronine, Reverse / Q000494:pharmacology; D015854:Up-Regulation
D004268:DNA-Binding Proteins; D051863:Host Cell Factor C1; D056985:Nuclear Receptor Co-Repressor 2; D050811:Octamer Transcription Factor-1; D011994:Recombinant Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D014285:Triiodothyronine, Reverse; D005982:Glutathione Transferase