Glucose-regulated Glucagon Secretion Requires Insulin Receptor Expression in Pancreatic α-Cells
The insulin receptor (IR) and its signaling appear to be essential for insulin secretion from pancreatic β-cells. However, much less is known about the role of the IR in α-cells. To assess the role of the IR in glucagon and insulin secretion, we engineered adeno-viruses for high efficiency small i...
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Published in | The Journal of biological chemistry Vol. 280; no. 39; p. 33487 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
American Society for Biochemistry and Molecular Biology
30.09.2005
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Online Access | Get full text |
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Summary: | The insulin receptor (IR) and its signaling appear to be essential for insulin secretion from pancreatic β-cells. However,
much less is known about the role of the IR in α-cells. To assess the role of the IR in glucagon and insulin secretion, we
engineered adeno-viruses for high efficiency small interference RNA (siRNA)-IR expression in isolated mouse pancreatic islets
and lentiviruses for siRNA-IR expression in pancreatic α- and β-cell lines (α-TC6 and MIN6) with specific, long term stable
IR knockdown. Western blot analysis showed that these strategies resulted in 60-80% reduction of IR protein in islets and
α- and β-cell lines. Cell growth was reduced by 35-50% in α-TC and MIN6 cells stably expressing siRNA-IR, respectively. Importantly,
glucagon secretion, in response to glucose (25 to 2.8 m m ), was completely abolished in islets expressing siRNA-IR, whereas secretion increased 1.7-fold in islets expressing control
siRNA. In contrast, there was no difference in glucose-stimulated insulin secretion when comparing siRNA-IR and siRNA control,
with both groups showing a 1.7-fold increase. Islet glucagon and insulin content were also unaffected by IR knockdown. To
further explore the role of the IR, siRNA-IR was stably expressed in pancreatic cell lines, which dramatically suppressed
glucose-regulated glucagon secretion in α-TC6 cells (3.4-fold) but did not affect GSIS in MIN6 cells. Defects in siRNA-IR-expressing
α-cells were associated with an alteration in the activity of Akt and p70 S6K where insulin-induced phosphorylation of protein kinase B/AKt was greatly reduced while p70 S6K activation was enhanced, suggesting that the related pathways play important roles in α cell function. This study provides
direct evidence that appropriate expression of the IR in α-cells is required for glucose-dependent glucagon secretion. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.M506276200 |