Insulin-induced gene 2 involvement in human adipocyte metabolism and body weight regulation.
BACKGROUND
Insulin-induced genes (INSIGs) encode proteins that block proteolytic activation of sterol regulatory element-binding proteins, transcription factors that regulate lipogenic enzymes, and adipocyte differentiation.


OBJECTIVE
Here, we analyzed the relative significance of INSIG1 and INSIG2 in human liver and adipocyte metabolism, and defined a novel, functional polymorphism in the promoter of INSIG2 associated with body mass index.


METHODS
Variations in gene expression of different human tissues, of hepatoma cells exposed to INSIG1 and INSIG2 gene silencing probes, and of differentiating 3T3-L1 adipocytes were determined by real-time quantitative PCR. The functional significance of a novel polymorphism in the promoter of INSIG2 was analyzed using in vitro methods and gene expression analysis of human adipose tissue, whereas the phenotype associated with this polymorphism was studied in two cohorts of middle-aged men.


RESULTS
Gene expression analysis of 17 human tissues demonstrated that INSIG1 is highly expressed in the liver, whereas INSIG2 is ubiquitously expressed. Gene silencing experiments confirmed that INSIG1, but not INSIG2, regulates the expression of sterol regulatory element-binding proteins target genes in human hepatoma cells. In contrast, adipocyte differentiation of 3T3-L1 cells was associated with a 13-fold increase in expression of INSIG2. Significant relationships between the INSIG2-102G/A polymorphism and body mass index were observed in two cohorts of middle-aged men (ANOVA P = 0.017 and 0.044, respectively). In vitro studies and analysis of allele-specific expression in human adipose tissue substantiated the functional significance of the INSIG2-102G/A polymorphism.


CONCLUSIONS
INSIG2 is involved in adipocyte metabolism and body weight regulation.
Krapivner
Sergey
S
Atherosclerosis Research Unit, Department of Medicine Solna, Karolinska University Hospital, Stockholm, Sweden.
Popov
Sergej
S
Chernogubova
Ekaterina
E
Hellénius
Mai-Lis
ML
Fisher
Rachel M
RM
Hamsten
Anders
A
van't Hooft
Ferdinand M
FM
D017667:Adipocytes / Q000378:metabolism*; D050156:Adipogenesis; D015992:Body Mass Index; D001835:Body Weight; D045744:Cell Line, Tumor; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008875:Middle Aged; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051780:Sterol Regulatory Element Binding Protein 1 / Q000502:physiology
C108626:INSIG1 protein, human; C467727:INSIG2 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; C497387:SREBF1 protein, human; D051780:Sterol Regulatory Element Binding Protein 1