Insulin activates CCAAT/enhancer binding proteins and proinflammatory gene expression through the phosphatidylinositol 3-kinase pathway in vascular smooth muscle cells.
Phosphatidylinositol 3-kinase (PI3K) is a key molecule mediating signals of insulin in vascular smooth muscle cells (VSMCs). To examine the effect of chronic activation of PI3K on the gene expression of VSMCs, membrane-targeted p110CAAX, a catalytic subunit of PI3K, was overexpressed in rat VSMCs by adenovirus-mediated gene transfer. Similar to insulin's effects, cells overexpressing p110CAAX exhibited a 10- to 15-fold increase in monocyte chemoattractant protein-1 (MCP-1) mRNA expression as compared with the control cells. Electrophoretic mobility shift assay analysis showed that the overexpression of p110CAAX activated neither the NF-kappaB binding nor the activator protein (AP-1) binding activities. We found that two CCAAT/enhancer binding protein (C/EBP) binding sites located between 2.6 and 3.6 kb upstream of the MCP-1 gene were responsible for the induction by p110CAAX. The overexpression of C/EBP-beta and C/EBP-delta but not C/EBP-alpha caused 6- to 8-fold induction of MCP-1 promoter activity. Consistently, the overexpression of p110CAAX as well as insulin induced mRNA expression and nuclear expression of C/EBP-beta and C/EBP-delta in VSMCs. These results clearly indicate that the activation of PI3K induced proinflammatory gene expression through activating C/EBP-beta and C/EBP-delta but not NF-kappaB, which may explain the proinflammatory effect of insulin in the insulin-resistant state.
Sekine
Osamu
O
Division of Endocrinology and Metabolism, Department of Medicine, Shiga University of Medical Science, Seta, Otsu, Shiga 520-2192, Japan.
Nishio
Yoshihiko
Y
Egawa
Katsuya
K
Nakamura
Takaaki
T
Maegawa
Hiroshi
H
Kashiwagi
Atsunori
A
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism*; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D020134:Catalytic Domain; D002460:Cell Line; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D008297:Male; D008957:Models, Genetic; D009130:Muscle, Smooth / Q000166:cytology*; D016297:Mutagenesis, Site-Directed; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013552:Swine; D014157:Transcription Factors
D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; C497254:Cebpd protein, rat; D018932:Chemokine CCL2; D004791:Enzyme Inhibitors; D007328:Insulin; D012333:RNA, Messenger; D014157:Transcription Factors; D051743:CCAAT-Enhancer-Binding Protein-delta; D019869:Phosphatidylinositol 3-Kinases