Investigation of intracellular pathways of stimulus-secretion signaling in vivo is possible by transgenic expression of agents known to influence specific biochemical interactions in the cells. The objective of the present study was to establish an experimental model for analyzing signal transduction mechanisms in pancreatic beta-cells in vivo, by expressing the cholera toxin A1 subunit under control of the insulin promoter, intending a constant activation of the Gs-protein, and thereby constant generation of cAMP. Surprisingly, the transgenic mice demonstrated mild hyperglycemia and hypoinsulinemia in vivo, and diminished glucose-induced insulin release from the in vitro perfused pancreas, whereas the pancreatic insulin content was normal. These observations suggest a deficiency in either the insulin release mechanisms or glucose recognition. Although the translated cholera toxin A1 subunit was biologically active, there was no increase in the islet content of cAMP. We conclude that the observed phenotype in the cholera toxin transgenic mice may be caused by a deleterious effect of the transgene itself on beta-cell function, or that counter regulatory mechanisms may compensate for the transgene-induced changes in intracellular enzymatic pathways.
Bibliographical noteFunding Information:
L. Wogenseni s supportedb y a postdoctoralf ellow-ship from the Juvenile Diabetes Foundation International, New York, USA (Grant no. 391221)a nd the Danish Medical ResearchF oundation.This study was furthermore supported by NIH grants DK41801, HD29764 (N. Sarvetnick),D K01410 (G.M. Grodsky), DK38325 (R.P. Robertson) and GM32355 (J.G. Sut-cliffe). We are grateful to Marijo Gallina and Glen Davis for their invaluableh elp with testing mice for presenceo f the transgene.W e are indebted to drs. T.F. Walseth and M.B. Armstrong, Dept. of Pharmacology, University of Minnesota, Minneapolis, Minnesota, for their contributionst o the ribosylatione x-periments.W e thank dr. Chris Nygart for critical com-mentso n the manuscript.M anuscript# 7899-NP.
- Cholera toxin
- Cyclic AMP
- Insulin release