The MODY1 Gene for Hepatocyte Nuclear Factor 4α and a Feedback Loop Control COUP-TFII Expression in Pancreatic Beta Cells

Abstract

Pancreatic islet beta cell differentiation and function are dependent upon a group of transcription factors that maintain the expression of key genes and suppress others. Knockout mice with the heterozygous deletion of the gene for chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) or the complete disruption of the gene for hepatocyte nuclear factor 4α (HNF4α) in pancreatic beta cells have similar insulin secretion defects, leading us to hypothesize that there is transcriptional cross talk between these two nuclear receptors. Here, we demonstrate specific HNF4α activation of a reporter plasmid containing the COUP-TFII gene promoter region in transfected pancreatic beta cells. The stable association of the endogenous HNF4α with a region of the COUP-TFII gene promoter that contains a direct repeat 1 (DR-1) binding site was revealed by chromatin immunoprecipitation. Mutation experiments showed that this DR-1 site is essential for HNF4α transactivation of COUP-TFII. The dominant negative suppression of HNF4α function decreased endogenous COUP-TFII expression, and the specific inactivation of COUP-TFII by small interfering RNA caused HNF4α mRNA levels in 832/13 INS-1 cells to decrease. This positive regulation of HNF4α by COUP-TFII was confirmed by the adenovirus-mediated overexpression of human COUP-TFII (hCOUP-TFII), which increased HNF4α mRNA levels in 832/13 INS-1 cells and in mouse pancreatic islets. Finally, hCOUP-TFII overexpression showed that there is direct COUP-TFII autorepression, as COUP-TFII occupies the proximal DR-1 binding site of its own gene in vivo. Therefore, COUP-TFII may contribute to the control of insulin secretion through the complex HNF4α/maturity-onset diabetes of the young 1 (MODY1) transcription factor network operating in beta cells.

ACKNOWLEDGMENTS

This work was supported by grants from Nestlé France 2007; from the Programme National de Recherches sur le Diabète-INSERM/ARD (grant no. PNRD-A06064KS); from the Agence Nationale pour la Recherche (ANR 2005 Cardiovasculaire, Obésité et Diabète grant no. ANR-05-PCOD-088-01); from Bonus Qualité Recherche, Université Paris 5; from the Swiss National Science Foundation (grant no. 32-66907.01 to C.B.W.); and from ADA (grant no. 7-04-RA-106 to D.K.S.). A.P. is the recipient of a doctoral fellowship from the Ministère de l'Enseignement Supérieur et de la Recherche and from Fondation pour la Recherche Médicale.

We are grateful to C. Newgard for the 832/13 INS-1 cell line and to F. Petit for the gift of some of the COUP-TFII promoter constructs. We thank all the INSERM, U649, team for their expertise in adenovirus preparation. We thank P. Bossard for critical reading of the manuscript, and T. Becker for helpful discussion of the siRNA experiments. We thank K. Kaestner and J. Ferrer for helpful discussions.