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Diabetologia
Published in: Diabetologia 6/2003

01-06-2003 | Article

Ectopic expression of the beta-cell specific transcription factor Pdx1 inhibits glucagon gene transcription

Authors: B. Ritz-Laser, PhD, B. R. Gauthier, A. Estreicher, A. Mamin, T. Brun, F. Ris, P. Salmon, P. A. Halban, D. Trono, J. Philippe

Published in: Diabetologia | Issue 6/2003

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Abstract

Aims/hypothesis

The transcription factor Pdx1 is required for the development and differentiation of all pancreatic cells. Beta-cell specific inactivation of Pdx1 in developing or adult mice leads to an increase in glucagon-expressing cells, suggesting that absence of Pdx1could favour glucagon gene expression by a default mechanism.

Method

We investigated the inhibitory role of Pdx1 on glucagon gene expression in vitro. The glucagonoma cell line InR1G9 was transduced with a Pdx1-encoding lentiviral vector and insulin and glucagon mRNA levels were analysed by northern blot and real-time PCR. To understand the mechanism by which Pdx1 inhibits glucagon gene expression, we studied its effect on glucagon promoter activity in non-islet cells using transient transfections and gel-shift analysis.

Results

In glucagonoma cells transduced with a Pdx1-encoding lentiviral vector, insulin gene expression was induced while glucagon mRNA levels were reduced by 50 to 60%. In the heterologous cell line BHK-21, Pdx1 inhibited by 60 to 80% the activation of the α-cell specific element G1 conferred by Pax-6 and/or Cdx-2/3. Although Pdx1 could bind three AT-rich motifs within G1, two of which are binding sites for Pax-6 and Cdx-2/3, the affinity of Pdx1 for G1 was much lower as compared to Pax-6. In addition, Pdx1 inhibited Pax-6 mediated activation through G3, to which Pdx1 was unable to bind. Moreover, a mutation impairing DNA binding of Pdx1 had no effect on its inhibition on Cdx-2/3. Since Pdx1 interacts directly with Pax-6 and Cdx-2/3 forming heterodimers, we suggest that Pdx1 inhibits glucagon gene transcription through protein to protein interactions with Pax-6 and Cdx-2/3.

Conclusion/interpretation

Cell-specific expression of the glucagon gene can only occur when Pdx1 expression extinguishes from the early α cell precursor.
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Metadata
Title
Ectopic expression of the beta-cell specific transcription factor Pdx1 inhibits glucagon gene transcription
Authors
B. Ritz-Laser, PhD
B. R. Gauthier
A. Estreicher
A. Mamin
T. Brun
F. Ris
P. Salmon
P. A. Halban
D. Trono
J. Philippe
Publication date
01-06-2003
Publisher
Springer-Verlag
Published in
Diabetologia / Issue 6/2003
Print ISSN: 0012-186X
Electronic ISSN: 1432-0428
DOI
https://doi.org/10.1007/s00125-003-1115-7

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