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Type: Journal article
Title: Transcriptional regulation of the distal promoter of the rat pyruvate carboxylase gene by hepatocyte nuclear factor 3β/Foxa2 and upstream stimulatory factors in insulinoma cells
Other Titles: Transcriptional regulation of the distal promoter of the rat pyruvate carboxylase gene by hepatocyte nuclear factor 3beta/Foxa2 and upstream stimulatory factors in insulinoma cells
Author: Boonsaen, T.
Rojvirat, P.
Surinya, K.
Wallace, J.
Jitrapakdee, S.
Citation: Biochemical Journal, 2007; 405 Part 2(2):359-367
Publisher: Portland Press
Issue Date: 2007
ISSN: 0264-6021
Statement of
Thirajit Boonsaen, Pinnara Rojvirat, Kathy H. Surinya, John C. Wallace and Sarawut Jitrapakdee
Abstract: PC (pyruvate carboxylase) plays a crucial role in intermediary metabolism including glucose-induced insulin secretion in pancreatic islets. In the present study, we identified two regions of the 1.2 kb distal promoter, the -803/-795 site and the -408/-403 E-box upstream of the transcription start site, as the important cis-acting elements for transcriptional activation of the luciferase reporter gene. Site-directed mutagenesis of either one of these sites in the context of this 1.2 kb promoter fragment, followed by transient transfections in the insulinoma cell line, INS-1, abolished reporter activity by approx. 50%. However, disruption of either the -803/-795 or the -408/-403 site did not affect reporter gene activity in NIH 3T3 cells, suggesting that this promoter fragment is subjected to cell-specific regulation. The nuclear proteins that bound to these -803/-795 and -408/-403 sites were identified by gel retardation assays as HNF3b (hepatocyte nuclear factor 3b)/Foxa2 (forkhead/winged helix transcription factor box2) and USFs (upstream stimulatory factors), USF1 and USF2, respectively. Chromatin immunoprecipitation assays using antisera against HNF3b/Foxa2, USF1 and USF2 demonstrated that endogenous HNF3b/Foxa2 binds to the -803/-795 Foxa2 site, and USF1 and USF2 bind to the -408/-403 E-box respectively in vivo, consistent with the gel retardation assay results. Although there are weak binding sites located at regions -904 and -572 for PDX1 (pancreatic duodenal homeobox-1), a transcription factor that controls expression of b-cell-specific genes, it did not appear to regulate PC expression in INS-1 cells in the context of the 1.2 kb promoter fragment. The results presented here show that Foxa2 and USFs regulate the distal promoter of the rat PC gene in a cell-specific manner.
Description: Copyright © The Authors. Journal compilation © 2007 Biochemical Society
RMID: 0020072477
DOI: 10.1042/BJ20070276
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Appears in Collections:Molecular and Biomedical Science publications

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