title: Snail, a transcriptional regulator, represses adiponectin expression by directly binding to an E-box motif in the promoter.
abstract: OBJECTIVE
  Adiponectin is a hormone that modulates many metabolic processes and is exclusively expressed in adipose tissue. However, complete understanding of the factors that regulate adiponectin expression is lacking. The following were investigated: (1) functional analysis of the human adiponectin promoter, (2) putative adiponectin repressor sequence activity in 3T3-L1 adipocytes using promoter mutagenesis, (3) whether Snail, an E-box binding transcription factor, binds this repressor sequence, (4) if Snail regulates adiponectin expression in 3T3-L1 pre-adipocytes.
  
  
  METHODS
  To further understand how adiponectin expression is regulated, we isolated the human adiponectin promoter and analyzed its activity after serial deletions.
  
  
  RESULTS
  We found a negative cis-regulatory element located in the adiponectin proximal promoter sequence (-174 to -152 bp), which contained an E-box site (CAACTG). The DNA binding activity of this putative negative regulatory factor was found to be sequence-specific and the binding activity is decreased during adipocyte differentiation time-dependently. Affinity chromatography identified the zinc-finger transcription factor Snail (SNAI1) as the putative negative regulatory factor. Chromatin immunoprecipitation assay and electrophoretic mobility shift assay confirmed that Snail binds to this negative cis-regulatory element in pre-adipocytes, exclusively. Inhibition of Snail expression using small interfering RNA techniques increased adiponectin expression in 3T3-L1 adipocytes, while overexpression of Snail reduced adiponectin expression. Furthermore, we observed an inverse relation between the expression of Snail and the expression of CCAAT-enhancer-binding protein alpha and peroxisome proliferator-activated receptor gamma, which are transcription factors that regulate adipogenesis.
  
  
  CONCLUSIONS
  Snail is a novel regulator of adiponectin expression and probably has a role in regulating adipogenesis.
authors.affiliation: Division of Endocrinology and Metabolism, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea.
authors.forename: Young Mi
authors.initials: YM
authors.lastname: Park
authors.forename: Yong-ho
authors.initials: YH
authors.lastname: Lee
authors.forename: Soo Hyun
authors.initials: SH
authors.lastname: Kim
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Lee
authors.forename: Kyung-Sup
authors.initials: KS
authors.lastname: Kim
authors.forename: Darren R
authors.initials: DR
authors.lastname: Williams
authors.forename: Hyun Chul
authors.initials: HC
authors.lastname: Lee
mesh_terms: D041721:3T3-L1 Cells; D052242:Adiponectin / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D015153:Blotting, Western; D047369:Chromatin Immunoprecipitation; D017931:DNA Primers; D024202:Electrophoretic Mobility Shift Assay; D020868:Gene Silencing; D006801:Humans; D051379:Mice; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D052242:Adiponectin; D017931:DNA Primers; C000604407:SNAI1 protein, human; C000604429:Snai1 protein, mouse; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors