Overexpression of Inducible Cyclic AMP Early Repressor Inhibits Transactivation of Genes and Cell Proliferation in Pancreatic β Cells

Abstract

Transcriptional control mediated by the cyclic AMP-responsive element (CRE) represents an important mechanism of gene regulation. To test our hypothesis that increased inducible cyclic AMP early repressor (ICER) Iγ inhibits function of CRE-binding proteins and thus disrupts CRE-mediated transcription in pancreatic β cells, we generated transgenic mice with β-cell-directed expression of ICER Iγ, a powerful repressor that is greatly increased in diabetes. Three transgenic lines clearly show that increased ICER Iγ expression in β cells results in early severe diabetes. From birth islets were severely disorganized with a significantly increased proportion of α cells throughout the islet. Diabetes results from the combined effects of impaired insulin expression and a decreased number of β cells. The decrease in β cells appears to result from impaired proliferation rather than from increased apoptosis after birth. Cyclin A gene expression is impaired by the strong inhibition of ICER; the suppression of cyclin A results in a substantially decreased proliferation of β cells in the postnatal period. These results suggest that CRE and CRE-binding factors have an important role in pancreatic β-cell physiology not only directly by regulation of gene trans-activation but also indirectly by regulation of β-cell mass.

We thank Kinichiro Oda (Science University of Tokyo, Chiba, Japan) and Arata Takeuchi (Chiba University, Chiba, Japan) for providing the rat cyclin A promoter plasmid, Marina Schorpp-Kistner (Deutsches Krebsforschungszentrum, Heidelberg, Germany) for providing the mouse cyclin A promoter plasmid, and Joel. F. Habener (Massachusetts General Hospital, Howard Hughes Medical Institute, Boston, Mass.) for providing S4-CREM antibody. We thank Gordon C. Weir (Joslin Diabetes Center) and Shunsuke Ishii (Riken Tsukuba Institute, Japan) for critical reading of the manuscript and Hirofumi Noguchi and Rafael Nesher (Joslin Diabetes Center; Hebrew University Hadassah Medical Center, Jerusalem, Israel) for helpful discussions. We also thank Sarah Yasui and Shun Nawata for technical assistance, Haruyasu Kohda and Makio Fujioka for electron microscopy, Oogi Inada for frequent help with mouse care, Hiroshi Kanamori and Hidenori Arai for providing 7-day-old mouse pancreases, Chris Cahill for confocal microscopy, and Sonya Yokoff for fluorescent dual-color immunostaining.

This study was supported by in part by Grants-in-Aid for Scientific Research and for Creative Scientific Research (NP10NPO201) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and by grants from the Research for the Future Program from the Japan Society for the Promotion of Science (JSPS-RFTF97I00201), the Joslin NIH DERC Advanced Microscopy Core, and the Diabetes and Wellness Research Foundation. A.I. is the recipient of a fellowship and grant from the Yamanouchi Foundation 2002 and from the Manpei Suzuki Diabetes Foundation 2002.