Functional and Cooperative Interactions between the Homeodomain PDX1, Pbx, and Prep1 Factors on the Somatostatin Promoter*
- From the Laboratoire de Biologie Moléculaire et de Génie Génétique, Institut de Chimie, Batiment B6, Université de Liège, B-4000 Sart-Tilman, Belgium
Abstract
Expression of the somatostatin gene in endocrine pancreatic cells is controlled by several regulatorycis-elements located in the promoter region. Among these, the adjacent UE-A and TSEI elements, located from −113 to −85 relative to the transcription initiation site, function in combination and act as a pancreas-specific mini-enhancer. The TSEI element is recognized by the pancreatic homeodomain factor PDX1. In the present study, we show that the UE-A element binds a heterodimeric complex composed of a Pbx factor and the Prep1 protein, both belonging to the atypical three-amino acid loop extension homeodomain family. Recombinant Pbx1 and Prep1 proteins bind cooperatively to the UE-A site, whereas neither protein can bind this site alone. Transient transfection experiments reveal that both Pbx1 and Prep1 are required to generate a strong transcriptional activation from the UE-A element when this element is inserted close to the TATA box. In contrast, in the context of the intact somatostatin promoter or mini-enhancer, Pbx1 and Prep1 alone have no effect, but they produce a drastic activation when the pancreatic homeodomain factor PDX1 is also coexpressed. Thus, the activity of the somatostatin mini-enhancer is mediated by a cooperative interaction between the Pbx-Prep1 heterodimeric complex and the pancreatic factor PDX1.
Footnotes
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↵* This work was supported by Grant 1.5.076.98 from the National Foundation for Scientific Research (Belgium), Grant 95/00-103 from the Actions de Recherche concertée, and Grant P4-30 from the Poles d’Attraction Interuniversitaires.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ Supported by a fellowship from Ligue Contre le Cancer.
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↵§ Present address: Institut für Biologie I, Abt. Entwicklungsbiologie, Universität Freiburg, Hauptstrasse 1, 19104 Freiburg, Germany.
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↵¶ Chercheur Qualifié from National Foundation for Scientific Research. To whom correspondence should be addressed. Tel.: 32-4-366-33-74; Fax: 32-4-366-29-68; E-mail: Bpeers{at}ulg.ac.be.
- Abbreviations:
- EXD
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extradenticle
- EMSA
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electrophoretic mobility shift assay.
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- Received October 2, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
