title: X-box binding protein 1 is a novel key regulator of peroxisome proliferator-activated receptor γ2.
abstract: X-box binding protein 1 (XBP1), a transcription factor of the unfolded protein response, plays various roles in many biological processes. We examined its pro-adipogenic activity and target genes during adipogenic differentiation in wild-type and genetically modified 3T3-L1 cells. Signalling pathways that contribute to Xbp1 mRNA splicing, and the correlation of the transcriptionally active XBP1 isoform (XBP1s) level with body mass index and the level of peroxisome proliferator-activated receptor γ2 (PPARγ2) in human adipose tissues were also examined. The mRNA and nuclear protein expression levels of XBP1s increased immediately following hormonal induction of adipogenesis, reaching a peak at 6 h. Results from cDNA microarray and gene expression analyses using genetically modified cells indicated that PPARγ2 was a principal target of XBP1s. The XBP1s-specific binding motif, which is distinct from the CCAAT/enhancer-binding protein α binding site, was identified in the PPARγ2 promoter by site-directed mutagenesis. Fetal bovine serum, insulin, 3-isobutyl-1-methylxanthine and dexamethasone contributed independently to Xbp1 mRNA splicing. In human subcutaneous adipose tissues, the levels of both Xbp1s and Pparγ2 mRNA increased proportionally with body mass index, and there was a significant positive correlation between the two genes. These data suggest for the first time that positive regulation of PPARγ2 is a principal mechanism of XBP1s-mediated adipogenesis in 3T3-L1 cells.
authors.affiliation: Department of Biochemistry, College of Medicine, The Catholic University of Korea, Seoul, Korea.
authors.forename: Yoon Mi
authors.initials: YM
authors.lastname: Cho
authors.forename: Su-Nam
authors.initials: SN
authors.lastname: Kwak
authors.forename: Nam-Seok
authors.initials: NS
authors.lastname: Joo
authors.forename: Dae Hun
authors.initials: DH
authors.lastname: Kim
authors.forename: Ann-Hwee
authors.initials: AH
authors.lastname: Lee
authors.forename: Kyung-Soo
authors.initials: KS
authors.lastname: Kim
authors.forename: Jong Bae
authors.initials: JB
authors.lastname: Seo
authors.forename: Seong-Whan
authors.initials: SW
authors.lastname: Jeong
authors.forename: Oh-Joo
authors.initials: OJ
authors.lastname: Kwon
mesh_terms: D041721:3T3-L1 Cells; D050156:Adipogenesis; D000328:Adult; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015992:Body Mass Index; D004268:DNA-Binding Proteins / Q000502:physiology*; D005260:Female; D015870:Gene Expression; D006801:Humans; D051379:Mice; D008875:Middle Aged; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012326:RNA Splicing; D000071701:Regulatory Factor X Transcription Factors; D050151:Subcutaneous Fat; D014157:Transcription Factors / Q000502:physiology*; D015533:Transcriptional Activation; D000071717:X-Box Binding Protein 1; D055815:Young Adult
chemical_list: D004268:DNA-Binding Proteins; D047495:PPAR gamma; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse
keywords: PPARγ2; XBP1; adipogenesis; insulin; obesity