J Korean Diabetes Assoc.  2003 Feb;27(1):26-38.

Effect of Gi-proteins on Insulin Binding, Internalization and Recycling of Insulin Receptor in Bovine Aorta Endothelial Cell

Affiliations
  • 1Catholic Research Center of Medical Science, Korea.
  • 2Department of Internal Medicine, School of Medicine, Catholic University, Korea.

Abstract

BACKGROUND: Guanine nucleotide binding proteins (G-proteins) play important roles in the hormonal actions of many signal transduction systems. Possible roles for the Gi-protein in insulin action have been suggested. It is reported that Gi-protein is associated with insulin actions to a greater extent than Gs-protein. There are at least three different subtypes of Gi-proteins (Gi(alpha1), Gi(alpha2), and Gi(alpha3)), however, it is not certain which subtypes are associated with insulin receptors and their action.
METHODS
To investigate the effects of Gi-proteins on insulin action, the Gi-proteins were overexpressed in cultured bovine aortic endothelial cells (BAEC), using the DNA-polylysine-adenovirus complex transfection method. After incubating for 24 hours, the BAEC were treated with 200 ng/mL insulin to evaluate the insulin binding, receptor internalization and recycling.
RESULTS
The following results were found : 1) The binding of specific insulin bindings to the insulin receptors of endothelial cells were time-dependent, reaching their maximal levels in all cells after 30 minutes. The maximal specific bindings of the control, Gi(alpha1), Gi(alpha2), and Gi(alpha3) were 0.58+/-0.1, 0.54+/-0.08, 0.54+/-0.1, 0.53+/-0.09%, respectively. 2) The internalization of 125I-insulin, into endothelial cells, was assessed by the acid washing dissociation method, and occurred rapidly. There was a significant difference in the internalized radioactivity of the 125I-insulin in the overexpressed Gi(alpha2) protein group compared to the two groups. 3) The recycling of the insulin receptors in the three types of Gi-protein showed no significant difference between the three group.
CONCLUSION
In conclusion, the Gi(alpha2) protein may be associated with internalization of the insulin-insulin receptor complex, and appears to be important in both the action of insulin and the intracellular processing of insulin receptors.

Keyword

G proteins; Insulin receptor; Adenovirus; Endothelial cell; Internalization; Recycling

MeSH Terms

Adenoviridae
Aorta*
Carrier Proteins
Endothelial Cells*
GTP-Binding Proteins
Guanine
Insulin*
Radioactivity
Receptor, Insulin*
Recycling*
Signal Transduction
Transfection
Carrier Proteins
GTP-Binding Proteins
Guanine
Insulin
Receptor, Insulin
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