Diabetes & Metabolism Journal

Original Articles

Effect of Gi-proteins on Insulin Binding, Internalization and Recycling of Insulin Receptor in Bovine Aorta Endothelial Cell.: Hyuk Ho Kwon, Hyun Shik Son, Jung Min Lee, Seung Hyun Ko, Ok Ki Hong, Sung Dae Moon, Sang Ah Chang, Kun Ho Yoon, Bong Yun Cha, Kwang Woo Lee, Ho Young Son, Sung Koo Kang; Korean Diabetes J. 2003;27(1):26-38. Published online February 1, 2003

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Abstract PDF: 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.

The Role of Akt-1/PKBalpha on Insulin Action in 3T3-L1 Adipocyte.: Jung Min Lee, Hyun Shik Son, Hyuk Sang Kwon, Seung Ki Kwack, Seung Hyun Ko, Sang Ah Chang, Kun Ho Yoon, Bong Yun Cha, Kwang Woo Lee, Ho Young Son, Sung Koo Kang, Prem Sharma; Korean Diabetes J. 2002;26(4):274-285. Published online August 1, 2002

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Abstract PDF: BACKGROUND
S: Akt/PKB as a serine/threonine kinase is stimulated by insulin and other growth factors. And insulin stimulates glucose uptake by promoting the translocation of glucose transporter 4 (GLUT4) to the cell membrane. But, it is not clear that Akt/PKB, a downstream target of PI 3-kinase, is involved in glucose uptake pathway. In this study, we investigated the role of Akt/PKB, especially Akt-1, on insulin action in 3T3-L1 adipocyte. METHODS: We made recombinant Ad5.Akt-1 vector by the insertion of Akt-1 gene to adenoviral vector. And then, we overexpressed Akt-1 proteins(wild type and kinase inactive type) in 3T3-L1 adipocytes by using a adenoviral transfection method. We observed the changes of glucose uptake, glycogen synthesis, activities of mitogen-activated protein kinase (MAPK, also called extracellular signal-regulated kinase), p70 ribosomal s6 protein kinase (p70s6k), and glycogen synthase kinase 3 (GSK3) according to Akt-1 activity and insulin treatment. RESULTS: First, overexpression of Akt-1 did not affect to glucose uptake, whether insulin stimulates or not. Second, overexpression of Akt-1 did not affect the phosphorylation of p44/42-MAPK, either. Third, the glycogen synthesis was increased by overexpression of Akt-1. CONCLUSION: Akt-1 activation is necessary for glycogen synthesis, but is not essential for glucose transport in 3T3-L1 adipocytes.

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