Gene Silencing of Phogrin Unveils Its Essential Role in Glucose-Responsive Pancreatic β-Cell Growth
- Seiji Torii1,
- Naoya Saito1,
- Ayumi Kawano1,
- Ni Hou1,
- Kohjiro Ueki2,
- Rohit N. Kulkarni3 and
- Toshiyuki Takeuchi1
- 1Secretion Biology Lab, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma, Japan
- 2Department of Metabolic Diseases, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan
- 3Research Division, Joslin Diabetes Center and Department of Medicine, Harvard Medical School, Boston, Massachusetts
- Corresponding author: Toshiyuki Takeuchi, tstake{at}showa.gunma-u.ac.jp
Abstract
OBJECTIVE—Phogrin and IA-2, autoantigens in insulin-dependent diabetes, have been shown to be involved in insulin secretion in pancreatic β-cells; however, implications at a molecular level are confusing from experiment to experiment. We analyzed biological functions of phogrin in β-cells by an RNA interference technique.
RESEARCH DESIGN AND METHODS—Adenovirus-mediated expression of short hairpin RNA specific for phogrin (shPhogrin) was conducted using cultured β-cell lines and mouse islets. Both glucose-stimulated insulin secretion and cell proliferation rate were determined in the phogrin-knockdown cells. Furthermore, protein expression was profiled in these cells. To see the binding partner of phogrin in β-cells, coimmunoprecipitation analysis was carried out.
RESULTS—Adenoviral expression of shPhogrin efficiently decreased its endogenous expression in pancreatic β-cells. Silencing of phogrin in β-cells abrogated the glucose-mediated mitogenic effect, which was accompanied by a reduction in the level of insulin receptor substrate 2 (IRS2) protein, without any changes in insulin secretion. Phogrin formed a complex with insulin receptor at the plasma membrane, and their interaction was promoted by high-glucose stimulation that in turn led to stabilization of IRS2 protein. Corroboratively, phogrin knockdown had no additional effect on the proliferation of β-cell line derived from the insulin receptor–knockout mouse.
CONCLUSIONS—Phogrin is involved in β-cell growth via regulating stability of IRS2 protein by the molecular interaction with insulin receptor. We propose that phogrin and IA-2 function as an essential regulator of autocrine insulin action in pancreatic β-cells.
Footnotes
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Published ahead of print at http://diabetes.diabetesjournals.org on 10 December 2008.
S.T. and N.S. contributed equally to this work.
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- Accepted December 5, 2008.
- Received May 1, 2008.
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