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Journal of Lipid Research, Vol. 49, 1224-1234, June 2008
Copyright © 2008 by American Society for Biochemistry and Molecular Biology





* Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan
Division of Translational Research, Clinical Research Institute, Kyoto Medical Center, Kyoto, Japan
This study was supported in part by grants (T.K., K.H., K.O.) from the Ministry of Education, Culture, Science, Sports, and Technology of Japan.
Published, JLR Papers in Press, February 28, 2008.
1 To whom correspondence should be addressed. e-mail: kohono{at}kuhp.kyoto-u.ac.jp
The accumulation of visceral adipose tissue is closely associated with insulin resistance and metabolic syndrome. Therefore, it is important to identify genes that are required for adipocyte differentiation. To identify genes that are required for the differentiation of 3T3-L1 preadipocytes into mature adipocytes, we used retrovirus insertion-mediated random mutagenesis to generate 3T3-L1 cell lines that lose their ability to differentiate into mature adipocytes. One of the genes identified was TG-interacting factor (TGIF), a DNA binding homeodomain protein that has been demonstrated to suppress Smad-mediated activation of transforming growth factor β (TGF-β)-regulated transcription. In the TGIF-disrupted clone of 3T3-L1 preadipocytes, the rate of differentiation into mature adipocytes was clearly reduced compared with that in the wild-type clone. Suppression of TGIF by lentivirus-mediated RNAi also inhibited the differentiation of 3T3-L1 cells. Insulin specifically increased the abundance of TGIF protein, primarily by enhancing its stability. In addition, insulin caused the rapid accumulation of TGIF in the nuclei. Forced expression of exogenous TGIF repressed both endogenous and overexpressed Smad2/3-mediated promoter activity in 3T3-L1. These findings suggest that insulin specifically antagonizes TGF-β signaling in preadipocytes by stabilizing the putative Smad transcriptional corepressor TGIF and regulates adipocyte differentiation.
Supplementary key words adipocyte signal transduction transforming growth factor β
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