Maintaining HNF6 expression prevents AdHNF3beta-mediated decrease in hepatic levels of Glut-2 and glycogen.
The hepatocyte nuclear factor 3 (HNF-3) proteins are members of the Forkhead Box (Fox) family of transcription factors that play important roles in regulating expression of genes involved in cellular proliferation, differentiation, and metabolic homeostasis. In previous studies we increased liver expression of HNF-3beta by using either transgenic mice (transthyretin HNF-3beta) or recombinant adenovirus infection (AdHNF3beta), and observed diminished hepatic levels of glycogen, and glucose transporter 2 (Glut-2), as well as the HNF-6, HNF-3, HNF-1alpha, HNF-4alpha, and C/EBPalpha transcription factors. We conducted the present study to determine whether maintaining HNF-6 protein expression during AdHNF3beta infection prevents reduction of hepatic levels of glycogen and the earlier-mentioned genes. Here, we show that AdHNF3beta- and AdHNF6-infected mouse liver displayed increased hepatic levels of glycogen, Glut-2, HNF-3gamma, HNF-1alpha, and HNF-4alpha at 2 and 3 days postinfection (PI). Furthermore, restoration of hepatic glycogen levels after AdHNF3beta and AdHNF6 coinfection was associated with increased Glut-2 expression. AdHNF6 infection alone caused a 2-fold increase in hepatic Glut-2 levels, suggesting that HNF 6 stimulates in vivo transcription of the Glut-2 gene. DNA binding assays showed that only recombinant HNF-6 protein, but not the HNF-3 proteins, binds to the mouse -185 to -144 bp Glut-2 promoter sequences. Cotransfection assays in human hepatoma (HepG2) cells with either HNF-3 or HNF-6 expression vectors show that only HNF-6 provided significant transcriptional activation of the Glut-2 promoter. In conclusion, these studies show that the hepatic Glut-2 promoter is a direct target for HNF-6 transcriptional activation.
Tan
Yongjun
Y
Department of Molecular Genetics, College of Medicine, University of Illinois at Chicago, Chicago, IL 60607-7170, USA.
Adami
Guy
G
Costa
Robert H
RH
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics / Q000494:pharmacology*; D018014:Gene Transfer Techniques; D005822:Genetic Vectors; D051273:Glucose Transporter Type 2; D006003:Glycogen / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051542:Hepatocyte Nuclear Factor 3-beta; D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008815:Mice, Inbred Strains; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000494:pharmacology* / Q000502:physiology; D014157:Transcription Factors
D004268:DNA-Binding Proteins; C496503:Foxa2 protein, mouse; D051273:Glucose Transporter Type 2; D051559:Hepatocyte Nuclear Factor 6; D018398:Homeodomain Proteins; D009004:Monosaccharide Transport Proteins; D009687:Nuclear Proteins; C496606:Onecut1 protein, mouse; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D051542:Hepatocyte Nuclear Factor 3-beta; D006003:Glycogen