Pax-6 and Cdx-2/3 Interact to Activate Glucagon Gene Expression on the G1 Control Element*
- From the ‡Diabetes Unit, Centre Médical Universitaire, 1211 Genève 4, Switzerland and the¶Laboratoire de Differentiation Cellulaire et Moléculaire, CNRS EP56, Institut Pasteur, 59019 Lille Cedex, France
Abstract
The promoter element G1, critical for α-cell-specific expression of the glucagon gene, contains two AT-rich sequences important for transcriptional activity. Pax-6, a paired homeodomain protein previously shown to be required for normal α-cell development and to interact with the enhancer element G3 of the glucagon gene, binds as a monomer to the distal AT-rich site of G1. However, although the paired domain of Pax-6 is sufficient for interaction with the G3 element, the paired domain and the homeodomain are required for high affinity binding to G1. In addition to monomer formation, Pax-6 interacts with Cdx-2/3, a caudal-related homeodomain protein binding to the proximal AT-rich site, to form a heterodimer on G1. Both proteins are capable of directly interacting in the absence of DNA. In BHK-21 cells, Pax-6 activates glucagon gene transcription both through G3 and G1, and heterodimerization with Cdx-2/3 on G1 leads to more than additive transcriptional activation. In glucagon-producing cells, both G1 and G3 are critical for basal transcription, and the Pax-6 and Cdx-2/3 binding sites are required for activation. We conclude that Pax-6 is not only critical for α-cell development but also for glucagon gene transcription by its independent interaction with the two DNA control elements, G1 and G3.
Footnotes
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↵* This work was supported by the Swiss National Fund, the Institute for Human Genetics and Biochemistry, the Berger Foundation, the Carlos and Elsie de Reuters Foundation, and the Horten Foundation.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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↵§ To whom correspondence should be addressed. Tel.: 41-22-702-55-67; Fax: 41-22-702-55-43; E-mail: Laser{at}cmu.unige.ch.
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↵2 B. Ritz-Laser, manuscript in preparation.
- Abbreviations:
- bp
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base pair(s)
- CAT
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chloramphenicol acetyltransferase
- EMSA
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electrophoretic mobility shift assay
- GST
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glutathione S-transferase.
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- Received March 6, 1998.
- Revision received October 12, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
