Essential role of insulin receptor substrate 1 (IRS-1) and IRS-2 in adipocyte differentiation.
To investigate the role of insulin receptor substrate 1 (IRS-1) and IRS-2, the two ubiquitously expressed IRS proteins, in adipocyte differentiation, we established embryonic fibroblast cells with four different genotypes, i.e., wild-type, IRS-1 deficient (IRS-1(-/-)), IRS-2 deficient (IRS-2(-/-)), and IRS-1 IRS-2 double deficient (IRS-1(-/-) IRS-2(-/-)), from mouse embryos of the corresponding genotypes. The abilities of IRS-1(-/-) cells and IRS-2(-/-) cells to differentiate into adipocytes are approximately 60 and 15%, respectively, lower than that of wild-type cells, at day 8 after induction and, surprisingly, IRS-1(-/-) IRS-2(-/-) cells have no ability to differentiate into adipocytes. The expression of CCAAT/enhancer binding protein alpha (C/EBPalpha) and peroxisome proliferator-activated receptor gamma (PPARgamma) is severely decreased in IRS-1(-/-) IRS-2(-/-) cells at both the mRNA and the protein level, and the mRNAs of lipoprotein lipase and adipocyte fatty acid binding protein are severely decreased in IRS-1(-/-) IRS-2(-/-) cells. Phosphatidylinositol 3-kinase (PI 3-kinase) activity that increases during adipocyte differentiation is almost completely abolished in IRS-1(-/-) IRS-2(-/-) cells. Treatment of wild-type cells with a PI 3-kinase inhibitor, LY294002, markedly decreases the expression of C/EBPalpha and PPARgamma, a result which is associated with a complete block of adipocyte differentiation. Moreover, histologic analysis of IRS-1(-/-) IRS-2(-/-) double-knockout mice 8 h after birth reveals severe reduction in white adipose tissue mass. Our results suggest that IRS-1 and IRS-2 play a crucial role in the upregulation of the C/EBPalpha and PPARgamma expression and adipocyte differentiation.
Miki
H
H
Department of Internal Medicine, Graduate School of Medicine, University of Tokyo, Tokyo 113-8655, Japan.
Yamauchi
T
T
Suzuki
R
R
Komeda
K
K
Tsuchida
A
A
Kubota
N
N
Terauchi
Y
Y
Kamon
J
J
Kaburagi
Y
Y
Matsui
J
J
Akanuma
Y
Y
Nagai
R
R
Kimura
S
S
Tobe
K
K
Kadowaki
T
T
D017667:Adipocytes / Q000166:cytology* / Q000502:physiology*; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D018345:Mice, Knockout; D010750:Phosphoproteins / Q000502:physiology*
D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D010750:Phosphoproteins