title: TG-interacting factor is required for the differentiation of preadipocytes.
abstract: 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 beta (TGF-beta)-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-beta signaling in preadipocytes by stabilizing the putative Smad transcriptional corepressor TGIF and regulates adipocyte differentiation.
authors.affiliation: Department of Cardiovascular Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Horie
authors.forename: Koh
authors.initials: K
authors.lastname: Ono
authors.forename: Minako
authors.initials: M
authors.lastname: Kinoshita
authors.forename: Hitoo
authors.initials: H
authors.lastname: Nishi
authors.forename: Kazuya
authors.initials: K
authors.lastname: Nagao
authors.forename: Teruhisa
authors.initials: T
authors.lastname: Kawamura
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Abe
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Wada
authors.forename: Akira
authors.initials: A
authors.lastname: Shimatsu
authors.forename: Toru
authors.initials: T
authors.lastname: Kita
authors.forename: Koji
authors.initials: K
authors.lastname: Hasegawa
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology*; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000502:physiology*; D017931:DNA Primers; D018398:Homeodomain Proteins / Q000502:physiology*; D051379:Mice; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D012097:Repressor Proteins / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D017931:DNA Primers; D018398:Homeodomain Proteins; D012097:Repressor Proteins; C490797:Tgif1 protein, mouse; D046988:Proteasome Endopeptidase Complex