Effects of glucose and insulin on rat apolipoprotein A-I gene expression.
We have examined the regulation of apolipoprotein A-I (apoA-I) gene expression in response to glucose and insulin. In Hep G2 cells, endogenous apoA-I mRNA was suppressed by one-half or induced 2-fold following 48 h of exposure to high concentrations of glucose (22.4 mM) or insulin (100 microunits/ml), respectively, compared with control. Transcriptional activity of the rat apoA-I promoter (-474 to -7) in Hep G2 cells paralleled endogenous mRNA expression, and this activity was dependent on the dose of glucose or insulin. Deletional analysis showed that a 50-base pair fragment spanning -425 to -376 of the promoter mediated the effects of both insulin and glucose. Within this DNA fragment there is a motif (-411 to -404) that is homologous to a previously identified insulin response core element (IRCE). Mutation of this motif abolished not only the induction of the promoter by insulin but also abrogated its suppression by glucose. Electrophoretic mobility shift assay analysis of nuclear extracts from Hep G2 cells revealed IRCE binding activity that formed a duplex with radiolabeled probe. The IRCE binding activity correlated with insulin induction of apoA-I expression. In summary, our data show that glucose decreases and insulin increases apoA-I promoter activity. This effect appears to be mediated by a single cis-acting element.
Endocrine Research Group, Departments of Medicine and Medical Biochemistry, the Faculty of Medicine, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
K
K
Murao
Y
Y
Wada
T
T
Nakamura
A H
AH
Taylor
A D
AD
Mooradian
N C
NC
Wong
D000818:Animals; D016632:Apolipoprotein A-I / Q000096:biosynthesis / Q000235:genetics*; D005632:Fructose / Q000008:administration & dosage / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism; D006946:Hyperinsulinism / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D014407:Tumor Cells, Cultured
D016632:Apolipoprotein A-I; D007328:Insulin; D012333:RNA, Messenger; D005632:Fructose; D005947:Glucose